LASER(abbreviation from the initial letters of English. Light Amplification by Stimulated Emission of Radiation - amplification of light by stimulated emission; syn. optical quantum generator) is a technical device that emits electromagnetic radiation focused in the form of a beam in the range from infrared to ultraviolet, which has high energy and biological effects. L. were created in 1955 by N. G. Basov, A. M. Prokhorov (USSR) and Ch. Townes (USA), who were awarded the 1964 Nobel Prize for this invention.
The main parts of a laser are the working fluid, or active medium, the pump lamp, and the mirror resonator (Fig. 1). Laser radiation can be continuous or pulsed. Semiconductor lasers can operate in both modes. As a result of a strong light flash from the pump lamp, electrons of the active substance move from calm state excited. Acting on each other, they create an avalanche of light photons. Reflecting from the resonant screens, these photons, breaking through the translucent mirror screen, emerge as a narrow monochromatic beam of high energy light.
The working fluid of a glass can be solid (crystals of artificial ruby with the addition of chromium, some tungsten and molybdenum salts, various types of glass with an admixture of neodymium and some other elements, etc.), liquid (pyridine, benzene, toluene, bromonaphthalene, nitrobenzene etc.), gas (a mixture of helium and neon, helium and cadmium vapor, argon, krypton, carbon dioxide, etc.).
To transfer the atoms of the working fluid to an excited state, you can use light radiation, a flow of electrons, a flow radioactive particles, chem. reaction.
If we imagine the active medium as an artificial ruby crystal with an admixture of chromium, the parallel ends of which are designed in the form of a mirror with internal reflection and one of them is translucent, and illuminate this crystal powerful flash pump lamp, then as a result of such powerful illumination or, as is commonly called, optical pumping, a larger number of chromium atoms will go into an excited state.
Returning to the ground state, the chromium atom spontaneously emits a photon, which collides with the excited chromium atom, knocking out another photon. These photons, in turn meeting with other excited chromium atoms, again knock out photons, and this process increases like an avalanche. The flow of photons, repeatedly reflected from the mirror ends, increases until the radiation energy density reaches a limiting value sufficient to overcome the translucent mirror, and breaks out in the form of a pulse of monochromatic coherent (strictly directed) radiation, the wavelength of which is 694 .3 nm and pulse duration 0.5-1.0 ms with energy from fractions to hundreds of joules.
The energy of a light flare can be estimated using the following example: the total spectrum energy density on the solar surface is 10 4 W/cm 2 , and a focused beam from a light with a power of 1 MW creates a radiation intensity at the focus of up to 10 13 W/cm 2 .
Monochromaticity, coherence, small beam divergence angle, and the possibility of optical focusing make it possible to obtain a high energy concentration.
A focused laser beam can be directed over an area of several microns. This achieves a colossal concentration of energy and creates an extremely high temperature in the irradiated object. Laser radiation melts steel and diamond and destroys any material.
Laser devices and their areas of application
The special properties of laser radiation - high directivity, coherence and monochromaticity - open up practically great opportunities for its use in various fields of science, technology and medicine.
For honey Various lasers are used for purposes, the radiation power of which is determined by the objectives of surgical or therapeutic treatment. Depending on the intensity of irradiation and the characteristics of its interaction with different tissues, the effects of coagulation, extirpation, stimulation and regeneration are achieved. In surgery, oncology and ophthalmic practice, lasers with a power of tens of watts are used, and to obtain stimulating and anti-inflammatory effects, lasers with a power of tens of milliwatts are used.
With the help of L. it is possible to simultaneously transmit a huge number of telephone conversations, communicate both on earth and in space, and locate celestial bodies.
The small divergence of the laser beam allows them to be used in surveying practice, the construction of large engineering structures, for landing aircraft, and in mechanical engineering. Gas lasers are used to obtain three-dimensional images (holography). Various types of laser rangefinders are widely used in geodetic practice. L. are used in meteorology, to control pollution environment, in measuring and computing technology, instrument making, for dimensional processing of microelectronic circuits, initiation of chemical reactions, etc.
In laser technology, both solid-state and gas lasers of pulsed and continuous action are used. For cutting, drilling and welding of various high-strength materials - steels, alloys, diamonds, watch stones - laser systems are produced on carbon dioxide (LUND-100, TILU-1, Impulse), on nitrogen (Signal-3), on ruby (LUCH- 1M, K-ZM, LUCH-1 P, SU-1), on neodymium glass (Kvant-9, Korund-1, SLS-10, Kizil), etc. Most laser technology processes use the thermal effect of light caused by its absorption processed material. To increase the radiation flux density and localize the treatment zone, optical systems are used. The features of laser technology are the following: high radiation energy density in the processing zone, which gives the necessary thermal effect in a short time; locality of the influencing radiation, due to the possibility of its focusing, and light beams of extremely small diameter; small thermally affected zone provided by short-term exposure to radiation; the ability to conduct the process in any transparent environment, through technological windows. cameras, etc.
The radiation power of lasers used for control and measuring instruments of guidance and communication systems is low, on the order of 1-80 mW. For experimental studies (measuring the flow rates of liquids, studying crystals, etc.), powerful lasers are used that generate radiation in a pulsed mode with a peak power from kilowatts to hectowatts and a pulse duration of 10 -9 -10 -4 seconds. For processing materials (cutting, welding, piercing holes, etc.), various lasers with output power from 1 to 1000 watts or more are used.
Laser devices significantly increase labor efficiency. Thus, laser cutting provides significant savings in raw materials, instant punching of holes in any materials facilitates the work of the driller, the laser method of manufacturing microcircuits improves the quality of products, etc. It can be argued that laser has become one of the most common devices used for scientific, technical and medical applications. . goals.
The mechanism of action of a laser beam on biological tissue is based on the fact that the energy of the light beam sharply increases the temperature in a small area of the body. The temperature in the irradiated area, according to J. P. Minton, can rise to 394°, and therefore the pathologically changed area instantly burns and evaporates. The thermal effect on surrounding tissues extends over a very short distance, since the width of the direct monochromatic focused radiation beam is equal to
0.01 mm. Under the influence of laser radiation, not only the coagulation of living tissue proteins occurs, but also its explosive destruction from the action of a kind of shock wave. This shock wave is formed as a result of the fact that at high temperatures, tissue fluid instantly turns into a gaseous state. Features biol, actions depend on the wavelength, pulse duration, power, energy of laser radiation, as well as on the structure and properties of the irradiated tissues. What matters is the color (pigmentation), thickness, density, degree of tissue filling with blood, their physiol, condition and the presence of patol, changes in them. The greater the power of laser radiation, the deeper it penetrates and the stronger its effect.
In experimental studies, the effect of light radiation of various ranges on cells, tissues and organs (skin, muscles, bones, internal organs, etc.) was studied. the results differ from thermal and radiation effects. After direct impact laser radiation on tissues and organs, limited lesions of varying area and depth appear in them, depending on the nature of the tissue or organ. When gistol, studying tissues and organs exposed to L., three zones of morphol changes can be identified in them: the zone of superficial coagulation necrosis; area of hemorrhage and swelling; zone of dystrophic and necrobiotic changes in the cell.
Lasers in medicine
The development of pulsed lasers, as well as continuous lasers, capable of generating light radiation with a high energy density, created the conditions for the widespread use of lasers in medicine. By the end of the 70s. 20th century Laser irradiation began to be used for diagnosis and treatment in various fields of medicine - surgery (including traumatology, cardiovascular, abdominal surgery, neurosurgery, etc.) > oncology, ophthalmology, dentistry. It should be emphasized that the founder of modern methods of laser eye microsurgery is the Soviet ophthalmologist, academician of the USSR Academy of Medical Sciences M. M. Krasnov. There have been prospects for the practical use of L. in therapy, physiotherapy, etc. Spectrochemical and molecular studies of biological objects are already closely related to the development of laser emission spectroscopy, absorption and fluorescence spectrophotometry using frequency-tunable L., laser Raman spectroscopy. These methods, along with increasing the sensitivity and accuracy of measurements, reduce the time of analysis, which has provided a sharp expansion in the scope of research for the diagnosis of occupational diseases, monitoring the use of medications, in the field of forensic medicine, etc. In combination with fiber optics, laser spectroscopy methods can be used for X-raying the chest cavity, examining blood vessels, photographing internal organs in order to study their functions, functions and detect tumors.
Study and identification of large molecules (DNA, RNA, etc.) and viruses, immunol, research, study of kinetics and biol, activity of microorganisms, microcirculation in blood vessels, measurement of flow rates of biol, liquids - the main areas of application of laser Rayleigh and Doppler spectrometry methods, highly sensitive express methods that allow measurements to be made at extremely low concentrations of the particles under study. With the help of L., a microspectral analysis of tissues is performed, guided by the nature of the substance that has evaporated under the influence of radiation.
Dosimetry of laser radiation
In connection with fluctuations in the power of the active body of L., especially gas (for example, helium-neon), during their operation, as well as according to safety requirements, dosimetric monitoring is systematically carried out using special dosimeters calibrated against standard reference power meters, in particular type IMO-2, and certified by the state metrological service. Dosimetry allows you to determine effective therapeutic doses and power density, which determines biol, the effectiveness of laser radiation.
Lasers in surgery
The first area of application of L. in medicine was surgery.
Indications
The ability of the L. beam to dissect tissue made it possible to introduce it into surgical practice. The bactericidal effect and coagulating properties of the “laser scalpel” served as the basis for its use in operations on gastrointestinal tract. tract, parenchymal organs, during neurosurgical operations, in patients suffering from increased bleeding (hemophilia, radiation sickness, etc.).
Helium-neon and carbon dioxide lasers are successfully used for certain surgical diseases and injuries: infected, long-term non-healing wounds and ulcers, burns, obliterating endarteritis, deforming arthrosis, fractures, autotransplantation of skin onto burn surfaces, abscesses and phlegmon of soft tissues, etc. Laser machines “Scalpel” and “Pulsar” are designed for cutting bones and soft tissues. It has been established that L. radiation stimulates regeneration processes, changing the duration of the phases of the wound process. For example, after opening ulcers and treating the walls of L. cavities, the healing time of wounds is significantly reduced compared to other methods of treatment due to the reduction of infection of the wound surface, accelerating the cleansing of the wound from purulent-necrotic masses and the formation of granulations and epithelization. Gistol, and cytol, studies have shown an increase in reparative processes due to an increase in the synthesis of RNA and DNA in the cytoplasm of fibroblasts and the glycogen content in the cytoplasm of neutrophil leukocytes and macrophages, a decrease in the number of microorganisms and the number of microbial associations in wound discharge, a decrease in biol, the activity of pathogenic staphylococcus.
Methodology
The lesion (wound, ulcer, burn surface, etc.) is conventionally divided into fields. Each field is irradiated daily or every 1-2 days with low-power lasers (10-20 mW) for 5-10 minutes. The course of treatment is 15-25 sessions. If necessary, after 25-30 days you can repeat the course; usually they are not repeated more than 3 times.
The use of lasers in surgery (from additional materials)
Experimental studies to study the influence of laser radiation on biological objects began in 1963-1964. in the USSR, USA, France and some other countries. The properties of laser radiation were identified, which determined the possibility of using it in clinical medicine. The laser beam causes obliteration of blood and lymphatic vessels, thus preventing the dissemination of malignant tumor cells and causing a hemostatic effect. The thermal effect of laser radiation on tissues located near the operation area is minimal, but sufficient to ensure asepticity of the wound surface. Laser wounds heal faster than wounds caused by a scalpel or electric knife. The laser does not affect the operation of bioelectric potential sensors. In addition, laser radiation causes a photodynamic effect - the destruction of previously photosensitized tissues, and excimer lasers, used, for example, in oncology, cause the effect of photodecomposition (tissue destruction). Radiation from low-energy lasers has a stimulating effect on tissue, and therefore is used to treat trophic ulcers.
The properties of different types of lasers are determined by the wavelength of the light. Thus, a carbon dioxide laser with a wavelength of 10.6 microns has the property of dissecting biological tissues and, to a lesser extent, coagulating them; a laser operating on yttrium aluminum garnet with neodymium (YAG laser) with a shorter wavelength (1.06 microns) - the ability to destroy and coagulate tissue, and its ability to dissect tissue is relatively small.
To date, several dozen types of laser systems operating in different ranges are used in clinical medicine. electromagnetic spectrum(from infrared to ultraviolet). Carbon dioxide lasers, argon lasers, YAG lasers, etc. are mass-produced abroad for use in surgery; helium-veon and semiconductor lasers are produced for therapeutic purposes. In the USSR, carbon dioxide lasers of the "Yatagan" type are commercially produced for use in ophthalmology, lasers "Scalpel-1", "Romashka-1" (color Fig. 13), "Romashka-2" for use in surgery, helium-neon lasers of the type L G-75 and Yagoda for therapeutic purposes, semiconductor lasers are being prepared for industrial production.
In the mid-60s. Soviet surgeons B. M. Khromov, N. F. Gamaleya, S. D. Pletnev were among the first to use lasers for the treatment of benign and malignant tumors of the skin and visible mucous membranes. The development of laser surgery in the USSR is associated with the creation in 1969-1972. serial samples of Soviet carbon dioxide lasers. In 1973-1974 A. I. Golovnya and A. A. Vishnevsky (junior) et al. published data on the successful use of carbon dioxide laser for surgery on the Vater nipple and for skin grafting purposes. In 1974, A.D. Arapov et al. reported the first operations for correction of valvular pulmonary artery stenosis performed using laser radiation.
In 1973-1975 employees of the laboratory of laser surgery (currently, the Scientific Research Institute of Laser Surgery M3 USSR) under the leadership of prof. O.K. Skobelkina carried out fundamental experimental research on the use of carbon dioxide laser in abdominal, skin-plastic and purulent surgery, and since 1975 they began to introduce them into clinical practice. Currently, experience in using lasers in medicine has already been accumulated and specialists in laser surgery have been trained; tens of thousands of operations using laser radiation have been performed in medical institutions. At the USSR Research Institute of Laser Surgery M3, new directions are being developed for the use of laser technology, for example, in endoscopic surgical interventions, in cardiac surgery and angiology, in microsurgical operations, for photodynamic therapy, and reflexology.
Laser surgery of the esophagus, stomach and intestines. Operations on organs of the gastrointestinal tract. tract, carried out using conventional cutting instruments, are accompanied by bleeding, the formation of intraorgan microhematomas along the line of dissection of the wall of a hollow organ, as well as infection of tissues with the contents of hollow organs along the line of cut. The use of a laser scalpel made it possible to avoid this. The operation is performed on a “dry” sterile field. In cancer patients, the risk of malignant tumor cells spreading through the blood and lymphatic vessels beyond the surgical wound is simultaneously reduced. Necrobiotic changes near the laser incision are minimal, in contrast to damage caused by traditional cutting instruments and electric knives. Therefore, laser wounds heal with minimal inflammatory reaction. The unique properties of the laser scalpel have given rise to numerous attempts to use it in abdominal surgery. However, these attempts did not give the expected effect, since tissue dissection was carried out with approximate visual focusing and free movement of the light spot of the laser beam along the intended cut line. At the same time, it was not always possible to perform a bloodless section of tissues, especially richly vascularized ones, such as the tissues of the stomach and intestinal walls. Cutting blood vessels with a diameter greater than 1 mm with a laser causes profuse bleeding; the spilled blood shields the laser radiation, quickly reduces the speed of dissection, as a result of which the laser loses the properties of a scalpel. In addition, there is a risk of accidental damage to underlying tissues and organs, as well as overheating of tissue structures.
The works of Soviet scientists O.K. Skobelkin, E.I. Brekhov, B.N. Malyshev, V.A. Salyuk (1973) showed that temporary cessation of blood circulation along the line of organ dissection makes it possible to make maximum use of the positive properties of the carbon dioxide laser, significantly reducing the area coagulation necrosis, increase the cutting speed, achieve “biological welding” of the dissected tissue layers using low-power laser radiation (15-25 W). The latter is especially important in abdominal surgery. The light adhesion formed during the incision due to surface coagulation of tissue holds the layers of the dissected wall of the stomach or intestine at the same level, which creates optimal conditions for performing the most labor-intensive and critical stage of the operation - the formation of an anastomosis. The use of a laser scalpel for operations on hollow organs became possible after the development of a set of special laser surgical instruments and stitching devices (color fig. 1, 2). Numerous experiments and clinical experience in the use of lasers in abdominal surgery have made it possible to formulate the basic requirements for instruments. They must have the ability to create local compression and ensure bleeding of organs along the line of tissue dissection; protect surrounding tissues and organs from direct and reflected rays; in size and shape must be adapted to perform one or another surgical technique, especially in hard-to-reach areas; promote accelerated tissue dissection without increasing the power of laser radiation due to the presence of a constant interval between the tissues and the light guide cone; ensure high-quality biological welding of tissues.
Currently in abdominal surgery wide use received mechanical stitching devices (see). They reduce the time of operations, allow aseptic and high-quality dissection and connection of the walls of hollow organs, however, the mechanical suture line often bleeds, and the high scraper ridge requires careful peritonization. Laser stitching devices are more advanced, for example, the unified NZhKA-60. They also use the principle of dosed local tissue compression: first, the wall of the hollow organ is sutured with metal staples, and then cut between two rows of applied staples using a laser. Unlike a conventional mechanical suture, the laser suture line is sterile, mechanically and biologically sealed, and does not bleed; thin film coagulation necrosis along the cut line prevents the penetration of microorganisms into the tissues; the scraper ridge is low and easily submerged by serous-muscular sutures.
The laser surgical suturing device UPO-16 is original; its design differs in many respects from the known mechanical suturing devices. The peculiarity of its design is that it allows, at the moment of compression of the fabric, to also stretch it due to a special fixing frame. This makes it possible to more than double the speed of tissue dissection without increasing the radiation power. The UPO-16 device is used for resection of the stomach, small and large intestine, as well as for cutting out a tube from the greater curvature of the stomach during esophageal plastic surgery.
The creation of laser instruments and stitching devices made it possible to develop methods for proximal and distal resection of the stomach, total gastrectomy, various options for plastic surgery of the esophagus with fragments of the stomach and colon, and surgical interventions on the colon (flowers, table, art. 432, Fig. 6-8). The collective experience of health care institutions using these methods, based on large material(2 thousand surgical interventions), allows us to come to the conclusion that operations using lasers, unlike traditional ones, are accompanied by 2-4 times fewer complications and 1.5-3 times less mortality. In addition, when using laser technology, more favorable long-term results of surgical treatment are observed.
In surgical interventions on extrahepatic bile ducts, lasers have an undeniable advantage over other cutting instruments. Complete sterility and perfect hemostasis in the area of tissue dissection greatly facilitate the surgeon’s work and help improve the quality of the operation and improve treatment results. To perform operations on the extrahepatic bile ducts, special laser instruments have been created, which make it possible to successfully perform various types of choledochotomy with the application of biliodigestive anastomoses, papillosphincterotomy and papillosphincteroplasty. The operations are practically bloodless and atraumatic, which ensures a high level of technical performance.
The use of a laser scalpel during cholecystectomy is no less effective. With favorable topographic-anatomical relationships, when a focused laser beam can be freely applied to all parts of the gallbladder, it is removed using the effect of photohydraulic preparation, which eliminates the slightest injury to the hepatic parenchyma. At the same time, bleeding and bile leakage from the small ducts of the bladder bed are completely stopped. Therefore, further suturing is not required. In the absence of conditions for free manipulation of the laser beam in the depths of the wound, cholecystectomy is performed in the usual way, and stopping parenchymal bleeding and bile leakage in the operation area is carried out with a defocused beam of laser radiation. IN in this case the laser also eliminates the application of hemostatic sutures on the bed of the gallbladder, which, injuring nearby vessels and bile ducts, lead to their focal necrosis.
In emergency surgery of the biliary tract, a laser scalpel can be indispensable. It is used in some cases to remove the gallbladder, and in some cases - as a highly effective means of stopping bleeding. In cases where the gallbladder is practically irremovable and its demucosation is required, which when performed acutely is associated with the risk of bleeding, it is advisable to evaporate the mucous membrane with defocused laser radiation. Complete removal of the mucous membrane with complete hemostasis and sterilization of the wound surface ensure a smooth postoperative course. The use of laser technology opens up new opportunities for improving the quality of treatment of patients with diseases of the biliary system; the frequency of surgical interventions for which has now increased significantly.
The use of lasers in surgery of parenchymal abdominal organs. Features of the anatomical structure of parenchymal organs with their branched vascular system determine the difficulties of surgical intervention and the severity of the postoperative period. Therefore, the search for the most effective means and methods of stopping bleeding, bile leakage and enzyme leakage during surgical interventions on parenchymal organs is still underway. Many methods and means have been proposed to stop bleeding from the liver tissue, which, unfortunately, do not satisfy surgeons.
Since 1976, the possibilities and prospects of using various types of lasers in operations on parenchymal organs have been studied. Not only were the results of the effects of lasers on the parenchyma studied, but also methods of surgical interventions on the liver, pancreas and spleen were developed.
When choosing a method of surgical intervention on the liver, it is necessary to simultaneously solve such problems as temporarily stopping blood flow in the part of the organ being removed, stopping bleeding from large vessels and bile leakage from the ducts after resection of the organ, stopping parenchymal bleeding.
To bleed the part of the liver to be removed in an experiment, a special hepatoclamp was developed. Unlike previously proposed similar instruments, it provides complete uniform compression of the organ. In this case, the liver parenchyma is not damaged, and the blood flow in its distal part stops. A special fixing device allows you to hold the hepatoclamp at the edge of the non-removable part of the liver after cutting off the area to be removed. This, in turn, allows free manipulation not only on large vessels and ducts, but also on the parenchyma of the organ.
When choosing methods for treating large vessels and ducts of the liver, it is necessary to take into account that carbon dioxide lasers and YAG lasers will be used to stop parenchymal bleeding from small vessels and bile leakage from small ducts. For suturing large vessels and ducts, it is advisable to use a stapler, which ensures a complete stop of bleeding from them using tantalum staples; You can clip them with special clamps. As the results of the study showed, the staples are firmly held on the vascular duct bundles both before and after treatment of the wound surface of the organ with a laser beam. At the border of the remaining and removed parts of the liver, hepatoclamps are applied and fixed, which compresses the parenchyma and at the same time large vessels and ducts. The liver capsule is cut with a surgical scalpel, and the vessels and ducts are sutured with a stapler. The part of the liver to be removed is cut off with a scalpel along the edge of the staples. To completely stop bleeding and bile leakage, the liver parenchyma is treated with a defocused beam of a carbon dioxide laser or YAG laser. Stopping parenchymal bleeding from liver wounds using an YAG laser occurs 3 times faster than using a carbon dioxide laser.
Surgery on the pancreas has its own characteristics. As is known, this organ is very sensitive to any surgical trauma, therefore rough manipulations of the pancreas often contribute to the development of postoperative pancreatitis. A special clamp has been developed that allows resection of the pancreatic parenchyma with a laser beam without destroying the pancreatic parenchyma. A laser clamp with a slot in the center is applied to the part to be removed. Along the guide slot, the gland tissue is crossed with a focused beam of a carbon dioxide laser. In this case, the parenchyma of the organ and the pancreatic duct, as a rule, are completely hermetically sealed, which avoids additional trauma when sutures are applied to seal the organ stump.
A study of the hemostatic effect of various types of lasers for injuries of the spleen showed that bleeding from small wounds can be stopped with both a carbon dioxide laser and an YAG laser, and stopping bleeding from large wounds is possible only with the help of YAG laser radiation.
The use of lasers in lung and pleural surgery. A carbon dioxide laser beam is used for thoracotomy (to intersect the intercostal muscles and pleura), due to which blood loss at this stage does not exceed 100 ml. Using compression clamps, atypical small lung resections are performed after suturing the lung tissue with U0-40 or U0-60 devices. Dissection of the resected part of the lung with a focused laser beam and subsequent treatment of the pulmonary parenchyma with a defocused beam makes it possible to obtain reliable hemostasis and aerostasis. When performing anatomical resections of the lungs, the main bronchus is sutured with a U0-40 or U0-60 device and crossed with a focused beam of a carbon dioxide laser. As a result, sterilization and sealing of the bronchial stump is achieved. The wound surface of the lung tissue is treated with a defocused beam for the purpose of hemostasis and aerostasis. When using a laser, surgical blood loss is reduced by 30-40%, postoperative blood loss by 2-3 times.
In the surgical treatment of pleural empyema, the opening of the empyema cavity and manipulations in it are performed with a focused beam of a carbon dioxide laser; final hemostasis and sterilization of the empyema cavity is carried out with a defocused beam. As a result, the duration of the intervention is reduced by 1V2 times, and blood loss is reduced by 2-4 times.
The use of lasers in heart surgery. For the treatment of supraventricular arrhythmias of the heart, an A and G laser is used, with the help of which the His bundle or abnormal conduction pathways of the heart are crossed. The laser beam is delivered intracardially during thoracotomy and cardiotomy or intravasally using a flexible light guide placed in a special vascular probe.
Recently, promising studies on laser revascularization of the myocardium for coronary heart disease have been started in the USSR and the USA. Laser revascularization in combination with coronary artery bypass grafting is performed on a stopped heart, and laser-only intervention is performed on a beating heart. With short pulses of a powerful carbon dioxide laser, 40-70 through channels are made in the wall of the left ventricle. The epicardial part of the canals is thrombosed by pressing a tampon for several minutes. The intramural part of the canals serves to supply the ischemic myocardium with blood coming from the lumen of the ventricle. Subsequently, a network of microcapillaries is formed around the channels, improving myocardial nutrition.
Use of laser in skin plastic surgery. A focused beam of a carbon dioxide laser is used for radical excision of small benign and malignant tumors within healthy tissue. Larger formations (fibromas, atheromas, papillomas, pigmented nevi, skin cancer and melanoma, skin metastases of malignant tumors, as well as tattoos) are destroyed by exposure to a defocused laser beam (color fig. 12-15). Healing of small wounds in such cases occurs under the scab. Large wound surfaces are covered with skin autograft. The advantages of laser surgery are good hemostasis, sterility of the wound surface and high radicality of the intervention. For inoperable, especially disintegrating, malignant skin tumors, a laser is used to evaporate and destroy the tumor, which allows for surface sterilization, stopping bleeding and eliminating unpleasant odors.
Good results, especially in cosmetic terms, are achieved using an argon laser in the treatment of vascular tumors and tattoo removal. Laser radiation is used to prepare the recipient site and harvest (take) a skin graft. The recipient site for trophic ulcers is sterilized and refreshed using a focused and defocused laser beam; for wounds after deep burns, necrectomy is performed with a defocused beam. To take a full-thickness skin flap as a graft, the effect of laser photohydraulic preparation of biological tissues, developed at the M3 Laser Surgery Research Institute of the USSR, is used. To do this, an isotonic saline solution or 0.25-0.5% novocaine solution is injected into the subcutaneous tissue. Using a focused beam of a carbon dioxide laser, the graft is separated from the underlying tissues due to cavitation of the previously introduced liquid, the edges appear under the influence of high temperature at the point of laser impact. As a result, hematomas are not formed and the sterility of the graft is achieved, which contributes to its better engraftment (color. Fig. 9-11). According to extensive clinical material, the survival rate of an autograft taken using a laser generally reaches 96.5%, and in maxillofacial surgery - 100%.
Laser surgery of purulent soft tissue diseases. The use of a laser in this area has made it possible to achieve a reduction in treatment time by 1.5-2 times, as well as savings in medications and dressings. For a relatively small purulent focus (abscess, carbuncle), it is radically excised with a focused beam of a carbon dioxide laser and a primary suture is applied. On open parts body, it is more expedient to evaporate the lesion with a defocused beam and heal the wound under the scab, which gives a completely satisfactory cosmetic effect. Large abscesses, including post-injection abscesses, as well as purulent mastitis, are opened mechanically. After removing the contents of the abscess, the walls of the cavity are treated alternately with a focused and defocused laser beam in order to evaporate necrotic tissue, sterilization and hemostasis (color. Fig. 3-5). After laser treatment, purulent wounds, including postoperative wounds, are sutured; in this case, active and fractional aspiration of their contents and rinsing of the cavity are necessary. According to bacteriological research, as a result of the use of laser radiation, the number of microbial bodies in 1 g of wound tissue in all patients is below the critical level (104-101). To stimulate the healing of purulent wounds, it is advisable to use low-energy lasers.
For third-degree thermal burns, necrectomy is performed with a focused beam of a carbon dioxide laser, thereby achieving hemostasis and sterilization of the wound. Blood loss when using a laser is reduced by 3-5 times, and the loss of protein with exudate is also reduced. The intervention ends with autoplasty using a skin flap prepared by laser photohydraulic preparation of biological tissues. This method reduces mortality and improves functional and cosmetic results.
When performing interventions on the anorectal area, for example, for the surgical treatment of hemorrhoids, a carbon dioxide laser is often used. It is typical that wound healing after cutting off a hemorrhoidal node occurs with less severe pain than after a conventional operation, the sphincter apparatus begins to function earlier, and anal strictures develop less frequently. Excision of pararectal fistulas and anal fissures with a carbon dioxide laser beam makes it possible to achieve complete sterility of the wound, and therefore it heals well after suturing tightly. The use of a laser is effective for radical excision of epithelial coccygeal fistulas.
Application of lasers in urology and gynecology. Carbon dioxide lasers are used for circumcision, removal of benign and malignant tumors of the penis, and the outer part of the urethra. With a defocused laser beam, small tumors of the bladder are evaporated using transabdominal access; with a focused beam, the bladder wall is resected for larger tumors, thereby achieving good hemostasis and increasing the radicality of the intervention. Intraurethral tumors and strictures, as well as bladder tumors, are removed and recanalized using an argon or YAG laser, the energy of which is supplied to the surgical site using fiber optics through rigid or flexible retrocystoscopes.
Carbon dioxide lasers are used to treat benign and malignant tumors of the external genitalia, for vaginal plastic surgery and transvaginal amputation of the uterus. Laser conization of the cervix has gained recognition in the treatment of erosions, precancerous diseases, cancer of the cervix and cervical canal. Using a carbon dioxide laser, resection of the uterine appendages, uterine amputation, and myomectomy are performed. Special interest present reconstructive operations using microsurgical techniques in the treatment of female infertility. The laser is used to dissect adhesions, resect obstructed areas of the fallopian tubes, and create artificial openings in the distal part of the fallopian tube or in its intramural part.
Laser endoscopic surgery is used to treat diseases of the larynx, pharynx, trachea, bronchi, esophagus, stomach, intestines, urethra and bladder. Where access to the tumor is possible only with the help of rigid endoscopic systems, a carbon dioxide laser connected to an operating microscope is used. The beam of this laser makes it possible to evaporate or destroy a tumor or to recanalize the lumen of a tubular organ walled off by a tumor or stricture. The impact on pathological formations located in tubular organs and accessible for inspection only with the help of flexible endoscopic equipment is carried out by an argon or YAG laser, the energy of which is supplied through quartz fiber optics.
Endoscopic methods of laser surgery are most widely used for coagulation of blood vessels in acute bleeding from gastric and duodenal ulcers. Recently, laser radiation has been used for radical treatment of stage I gastric cancer, rectal and colon cancer, as well as for recanalization of the lumen of the esophagus or rectum obstructed by a tumor, which avoids the imposition of a permanent gastrostomy or colostomy.
Laser microsurgery. Laser microsurgical interventions are performed using a carbon dioxide laser connected to an operating microscope equipped with a micromanipulator. This method is used to evaporate or destroy small tumors of the oral cavity, pharynx, larynx, vocal cords, trachea, bronchi, during operations on the middle ear, for the treatment of diseases of the cervix, for reconstructive interventions on the fallopian tubes. Using an operating microscope with a micromanipulator, a thin laser beam (diameter 0.1 - 0.15 mm) is directed precisely at the object being operated on, which allows precision interventions without damaging healthy tissue. Laser microsurgery has two more advantages: hemostasis is carried out simultaneously with the removal of the pathological formation; The laser manipulator is 30-40 cm away from the object being operated on, so the surgical field is clearly visible, whereas during conventional operations it is blocked by instruments. Recently, the energy of lasers operating on carbon dioxide, argon and yttrium aluminum garnet with neodymium has been used to anastomose small blood vessels, tendons and nerves.
Laser angioplasty. Currently, the possibility of restoring the patency of medium-sized arteries using radiation from carbon dioxide, argon lasers and YAG lasers is being studied. Due to the thermal component of the laser beam, it is possible to destroy or evaporate blood clots and atherosclerotic plaques. However, when using these lasers, the wall of the blood vessel itself is often damaged, which leads to bleeding or the formation of a blood clot in the area affected by the laser. No less effective and safer is the use of radiation from excimer lasers, the energy of which causes destruction of the pathological formation due to photo chemical reaction, not accompanied by fever and inflammatory reaction. The widespread introduction of laser angioplasty into clinical practice is hampered by the limited number of excimer lasers and special very complex catheters with channels for illumination, supply of laser energy and removal of tissue decay products.
Laser photo dynamic therapy. It is known that certain derivatives of hematoporphyrins are more actively absorbed by the cells of malignant tumors and remain in them longer than in normal cells. Photodynamic therapy of tumors of the skin and visible mucous membranes, as well as tumors of the trachea, bronchi, esophagus, stomach, intestines, and bladder is based on this effect. A malignant tumor, previously photosensitized by the introduction of hematoporphyrin, is irradiated with a laser in the red or blue-green band of the spectrum. As a result of this effect, tumor cells are destroyed, while nearby normal cells that were also exposed to radiation remain unchanged.
Lasers in oncology
In 1963-1965 Experiments on animals were carried out in the USSR and CETA, showing that L. radiation can destroy transplantable tumors. In 1969, at the Institute of Oncology Problems of the Academy of Sciences of the Ukrainian SSR (Kiev), the first department of laser therapy oncology was opened, equipped with a special installation, with the help of which patients with skin tumors were treated (Fig. 2). Subsequently, attempts were made to spread laser therapy for tumors and other localizations.
Indications
L. is used in the treatment of benign and malignant skin tumors, as well as some precancerous conditions of the female genital organs. Effects on deep-lying tumors usually require exposing them, since laser radiation is significantly attenuated when passing through tissue. Due to more intense absorption of light, pigmented tumors - melanomas, hemangiomas, pigmented nevi, etc. - are more easily amenable to laser therapy than non-pigmented ones (Fig. 3). Methods are being developed for using L. for the treatment of tumors of other organs (larynx, genitals, mammary gland, etc.).
Contraindication for L.'s use are tumors located near the eyes (due to the risk of damage to the organ of vision).
Methodology
There are two methods of using L.: irradiation of the tumor for the purpose of necrotization and its excision. When carrying out treatment in order to cause tumor necrosis, the following is carried out: 1) treatment of the object with small doses of radiation, iodine, which destroys the tumor area, and the rest of it gradually becomes necrotic; 2) irradiation with high doses (from 300 to 800 J/cm2); 3) multiple irradiation, which results in total death of the tumor. When treated with the necrotization method, irradiation of skin tumors begins from the periphery, gradually moving towards the center, usually capturing a border strip of normal tissue 1.0-1.5 cm wide. It is necessary to irradiate the entire mass of the tumor, since non-irradiated areas are a source of regrowth. The amount of radiation energy is determined by the type of laser (pulsed or continuous), the spectral region and other radiation parameters, as well as the characteristics of the tumor (pigmentation, size, density, etc.). When treating non-pigmented tumors, colored compounds can be injected into them to enhance radiation absorption and tumor destruction. Due to tissue necrosis, a black or dark gray crust forms at the site of the skin tumor, the edges disappear after 2-6 weeks. (Fig. 4).
When excising a tumor using a laser, a good hemostatic and aseptic effect is achieved. The method is under development.
Outcomes
L. any tumor accessible to radiation can be destroyed. In this case, there are no side effects, in particular in the hematopoietic system, which makes it possible to treat elderly patients, weakened patients and young children. In pigmented tumors, only tumor cells are selectively destroyed, which ensures a gentle effect and cosmetically favorable results. The radiation can be precisely focused and, therefore, the intervention can be strictly localized. The hemostatic effect of laser radiation makes it possible to limit blood loss). Successful results in the treatment of skin cancer, according to 5-year observations, were noted in 97% of cases (Fig. 5).
Complications: charring
tissues when dissected.
Lasers in ophthalmology
Traditional pulsed unmodulated lasers (usually ruby) were used until the 70s. for cauterization on the fundus, for example, for the purpose of forming a chorioretinal adhesive in the treatment and prevention of retinal detachment, for small tumors, etc. At this stage, the scope of their application was approximately the same as that of photocoagulators using conventional (non-monochromatic, incoherent) a ray of light.
In the 70s In ophthalmology, new types of lasers were successfully used (color Fig. 1 and 2): gas lasers of constant action, modulated lasers with “giant” pulses (“cold” lasers), dye-based lasers, and a number of others. This significantly expanded the area of wedge application on the eye - it became possible to actively intervene on the inner membranes of the eye without opening its cavity.
The following areas wedge, laser ophthalmology are of great practical importance.
1. It is known that vascular diseases of the fundus of the eye are coming (and in a number of countries have already come) to first place among the causes of incurable blindness. Among them, diabetic retinopathy is widespread; it develops in almost all patients with diabetes with a disease duration of 17-20 years.
Patients usually lose vision as a result of repeated intraocular hemorrhages from newly formed pathologically altered vessels. Using a laser beam ( best results give gas, for example, argon, L. of constant action) both changed vessels with areas of extravasation and zones of newly formed vessels, especially susceptible to rupture, undergo coagulation. A successful result that lasts for a number of years is observed in approximately 50% of patients. Usually, unaffected areas of the retina that do not have primary function are coagulated (panretinal coagulation).
2. Thrombosis of retinal vessels (especially veins) also became available for direct treatment. exposure only using L. Laser coagulation helps to activate blood circulation and oxygenation in the retina, reduce or eliminate trophic edema of the retina, which cannot be treated. exposure usually ends with severe irreversible changes (color. Fig. 7-9).
3. Retinal degeneration, especially in the transudation stage, in some cases can be successfully treated with laser therapy, which is practically the only way of active intervention in this pathol process.
4. Focal inflammatory processes in the fundus, periphlebitis, limited manifestations of angiomatosis in some cases are also successfully cured with laser therapy.
5. Secondary cataracts and membranes in the area of the pupil, tumors and cysts of the iris, thanks to the use of L., became the object of non-surgical treatment for the first time (color. Fig. 4-6).
Preventive measures against damage from laser beams
Protective and gig. measures to prevent the adverse effects of radiation from radiation and other associated factors should include activities of a collective nature: organizational, engineering and technical. planning, sanitary and hygienic, and also provide personal protective equipment.
It is mandatory to assess the main unfavorable factors and features of the propagation of laser radiation (both direct and reflected) before starting to operate a laser installation. Instrumental measurements (in extreme cases, by calculation) determine the probable directions and areas in which radiation levels that are dangerous to the body (exceed the maximum permissible limit) are possible.
To ensure safe working conditions, in addition to strict adherence to collective measures, it is recommended to use personal protective equipment - goggles, shields, masks with spectral selective transparency, and special protective clothing. An example of domestic protective glasses against laser radiation in the spectral region with a wavelength of 0.63-1.5 microns are glasses made of blue-green glass SZS-22, which provide eye protection from ruby and neodymium radiation. When working with powerful lasers. Protective shields and masks are more effective; gloves made of suede or leather are put on your hands. Wearing aprons and robes is recommended various colors. The choice of protective equipment must be made individually in each specific case by qualified specialists.
Medical supervision of those working with lasers. Work related to the maintenance of laser systems is included in the list of works with hazardous working conditions, and workers are subject to preliminary and periodic (once a year) medical examinations. The examination requires the participation of an ophthalmologist, therapist, and neurologist. When examining the organ of vision, a slit lamp is used.
In addition to the medical examination, a wedge and a blood test are performed to determine hemoglobin, red blood cells, reticulocytes, platelets, leukocytes and ROE.
Bibliography: Aleksandrov M. T. Application of lasers in experimental and clinical dentistry, Med. abstract. journal, sec. 12 - Dentistry, No. 1, p. 7, 1978, bibliogr.; Gamaleya N. F. Lasers in experiment and clinic, M., 1972, bibliogr.; Kavetsky R. E. et al. Lasers in biology and medicine, Kyiv, 1969; K o r y t n y D. L. Laser therapy and its application in dentistry, Alma-Ata, 1979; Krasnov M. M. Laser microsurgery of the eye, Vestn, ophthalm., No. 1, p. 3, 1973, bibliogr.; Lazarev I. R. Lasers in oncology, Kyiv, 1977, bibliogr.; Osipov G.I. and Pyatin M.M. Damage to the eye by a laser beam, Vestn, ophthalm., No. 1, p. 50, 1978; P l e t n e in S. D. et al. Gas lasers in experimental and clinical oncology, M., 1978; P r o-khonchukov A. A. Achievements of quantum electronics in experimental and clinical dentistry, Dentistry, v. 56, no. 5, p. 21, 1977, bibliogr.; Semenov A.I. The influence of laser radiation on the body and preventive measures, Gig. labor and prof. zabolev., No. 8, p. 1, 1976; Means and methods of quantum electronics in medicine, ed. R.I. Utyamy-sheva, p. 254, Saratov, 1976; Khromov B. M. Lasers in experimental surgery, L., 1973, bibliogr.; Khromov B.M. and others. Laser therapy of surgical diseases, Vestn, hir., No. 2, p. 31, 1979; L'Esperance F. A. Ocular photocoagulation, a stereoscopic atlas, St Louis, 1975; Laser applications in medicine and biology, ed. by M. L. Wolbarsht, v< i -з? N. Y.- L., 1971-1977, bibliogr.
The use of lasers in surgery- Arapov A.D. et al. The first experience of using a laser beam in cardiac surgery, Eksperim. hir., No. 4, p. 10, 1974; Vishnevsky A. A., Mitkova G. V. and Khariton A. S. Optical quantum generators of continuous action in plastic surgery, Surgery, No. 9, p. 118, 1974; Gamaleya N. F. Lasers in experiment and clinic, M., 1972; G o l o vnya A. I. Reconstructive and repeated operations on the nipple of Vater using a laser beam, in the book: Issues. compensation in surgery, ed. A. A. Vishnevsky and others, p. 98, M., 1973; Lasers in clinical medicine, ed. S. D. Pletneva, p. 153, 169, M., 1981; Pletnev S. D., Abdurazakov M. III. and Karpenko O. M. Application of lasers in oncological practice, Surgery, JV& 2, p. 48, 1977; Khromov B. M. Lasers in experimental surgery, L., 1973; Chernousov A.F., D o mrachev S.A. and Abdullaev A.G. Application of laser in surgery of the esophagus and stomach, Surgery, No. 3, p. 21, 1983, bibliogr.
V. A. Polyakov; V. I. Belkevich (tech.), N. F. Gamaleya (onc.), M. M. Krasnov (ph.), Yu. P. Paltsev (gig.), A. A. Prokhonchukov (ostomy), V. I. Struchkov (sir.), O. K. Skobelkin (sir.), E. I. Brekhov (sir.), G. D. Litvin (sir.), V. I. Korepanov (sir.).
Send your good work in the knowledge base is simple. Use the form below
Students, graduate students, young scientists who use the knowledge base in their studies and work will be very grateful to you.
Posted on http://www.allbest.ru/
Introduction
1. Lasers and their use in medicine
2. Use of high-intensity laser radiation in surgery (general principles)
3. Light breakdown
Conclusion
List of used literature
Introduction
Lasers or optical quantum generators are modern sources coherent radiation, which have a number of unique properties. The creation of lasers was one of the most remarkable achievements of physics in the second half of the 20th century, which led to revolutionary changes in many areas of science and technology. To date, a large number of lasers with different characteristics have been created - gas, solid-state, semiconductor, emitting light in various optical ranges. Lasers can operate in pulsed and continuous modes. The radiation power of lasers can vary from fractions of a milliwatt to 10 12 -10 13 W (in pulsed mode). Lasers are widely used in military equipment, materials processing technology, medicine, optical navigation, communication and location systems, in precision interference experiments, in chemistry, just in everyday life, etc.
One of the most important properties of laser radiation is its extremely high degree of monochromaticity, which is unattainable in the radiation of non-laser sources. This and all other unique properties of laser radiation arise as a result of the coordinated, cooperative emission of light quanta by many atoms of the working substance.
To understand the principle of laser operation, you need to more carefully study the processes of absorption and emission of light quanta by atoms. An atom can be in different energy states with energies E 1, E 2, etc. In Bohr's theory, these states are called stable. In fact, a stable state, in which an atom can remain indefinitely in the absence of external disturbances, is only the state with the lowest energy. This condition is called basic. All other states are unstable. An excited atom can remain in these states only for a very short time, about 10 - 8 s, after which it spontaneously goes into one of the lower states, emitting a quantum of light, the frequency of which can be determined from Bohr's second postulate. Radiation emitted during the spontaneous transition of an atom from one state to another is called spontaneous. An atom can remain at some energy levels for a much longer time, on the order of 10 - 3 s. Such levels are called metastable.
The transition of an atom to a higher energy state can occur through resonant absorption of a photon, the energy of which is equal to the difference between the energies of the atom in the final and initial states.
Transitions between atomic energy levels do not necessarily involve the absorption or emission of photons. An atom can gain or give up some of its energy and move into another quantum state as a result of interactions with other atoms or collisions with electrons. Such transitions are called non-radiative.
In 1916, A. Einstein predicted that the transition of an electron in an atom from an upper energy level to a lower one can occur under the influence of an external electromagnetic field, the frequency of which is equal to the natural frequency of the transition. The resulting radiation is called forced or induced. Stimulated emission has an amazing property. It differs sharply from spontaneous emission. As a result of the interaction of an excited atom with a photon, the atom emits another photon of the same frequency, propagating in the same direction. On the tongue wave theory this means that the atom emits an electromagnetic wave whose frequency, phase, polarization and direction of propagation are exactly the same as the original wave. As a result of the stimulated emission of photons, the amplitude of the wave propagating in the medium increases. From point of view quantum theory, as a result of the interaction of an excited atom with a photon, the frequency of which is equal to the transition frequency, two completely identical twin photons appear.
It is stimulated radiation that is the physical basis for the operation of lasers.
1 . Lasers and their use in medicine
Despite the common nature of light and radio waves, for many years optics and radio electronics developed independently, independently of each other. It seemed that the light sources - excited particles and radio wave generators - had little in common. Only in the middle of the 20th century did work appear on the creation of molecular amplifiers and radio wave generators, which marked the beginning of a new independent field of physics - quantum electronics.
Quantum electronics studies methods for amplifying and generating electromagnetic oscillations using stimulated emission of quantum systems. Advances in this area of knowledge are found by everyone greater application in science and technology. Let's get acquainted with some of the phenomena underlying quantum electronics and the operation of optical quantum generators - lasers.
Lasers are light sources that operate on the basis of the process of forced (stimulated, induced) emission of photons by excited atoms or molecules under the influence of radiation photons having the same frequency. A distinctive feature of this process is that the photon produced during stimulated emission is identical in frequency, phase, direction and polarization to the external photon that caused it. This determines the unique properties of quantum generators: high coherence of radiation in space and time, high monochromaticity, narrow directivity of the radiation beam, huge concentration of power flow and the ability to focus into very small volumes. Lasers are created on the basis of various active media: gaseous, liquid or solid. They can produce radiation in a very wide range of wavelengths - from 100 nm (ultraviolet light) to 1.2 microns (infrared radiation) - and can operate in both continuous and pulsed modes.
The laser consists of three fundamentally important components: an emitter, a pump system and a power source, the operation of which is ensured with the help of special auxiliary devices.
The emitter is designed to convert pump energy (transfer the helium-neon mixture 3 into an active state) into laser radiation and contains an optical resonator, which is generally a system of carefully manufactured reflective, refractive and focusing elements, in the internal space of which a certain type of electromagnetic waves is excited and maintained fluctuations in the optical range. The optical resonator must have minimal losses in the working part of the spectrum, high precision in the manufacture of components and their mutual installation.
The creation of lasers turned out to be possible as a result of the implementation of three fundamental physical ideas: stimulated emission, the creation of a thermodynamically nonequilibrium inverse population of atomic energy levels, and the use of positive feedback.
Excited molecules (atoms) are capable of emitting luminescence photons. Such radiation is a spontaneous process. It is random and chaotic in time, frequency (there may be transitions between different levels), direction of propagation and polarization. Another radiation - forced or induced - occurs when a photon interacts with an excited molecule if the photon energy is equal to the difference in the corresponding energy levels. With forced (induced) emission, the number of transitions performed per second depends on the number of photons entering the substance during the same time, i.e., on the intensity of light, as well as on the number of excited molecules. In other words, the higher the population of the corresponding excited energy states, the higher the number of forced transitions.
Induced radiation is identical to incident radiation in all respects, including in phase, so we can talk about coherent amplification of an electromagnetic wave, which is used as the first fundamental idea in the principles of laser generation.
The second idea, implemented when creating lasers, is to create thermodynamically nonequilibrium systems in which, contrary to Boltzmann's law, there are more particles at a higher level than at a lower one. The state of the medium in which for at least two energy levels it turns out that the number of particles with higher energy exceeds the number of particles with lower energy is called a state with inverted population of levels, and the medium is called active. It is the active medium in which photons interact with excited atoms, causing their forced transitions to a lower level with the emission of quanta of induced (stimulated) radiation, that is the working substance of the laser. A state with an inverse population of levels is formally obtained from the Boltzmann distribution for T< О К, поэтому иногда называется состоянием с "отрицательной" температурой. По мере распространения света в активной среде интенсивность его возрастает, имеет место явление, обратное поглощению, т. е. усиление света. Это означает, что в законе Бугера kX < 0, поэтому инверсная населенность соответствует среде с negative indicator absorption.
A population inversion state can be created by selecting particles with lower energy or by specially exciting the particles, for example, with light or an electrical discharge. By itself, a state of negative temperature does not exist for a long time.
The third idea used in the principles of laser generation originated in radiophysics and is the use of positive feedback. During its implementation, part of the generated stimulated emission remains inside the working substance and causes stimulated emission by more and more excited atoms. To implement such a process, the active medium is placed in an optical resonator, usually consisting of two mirrors, selected so that the radiation arising in it repeatedly passes through the active medium, turning it into a generator of coherent stimulated radiation.
The first such generator in the microwave range (maser) was designed independently in 1955 by Soviet scientists N.G. Bason and A.M. Prokhorov and American - C. Townes and others. Since the operation of this device was based on stimulated emission of ammonia molecules, the generator was called molecular.
In 1960, the first quantum generator in the visible range of radiation was created - a laser with a ruby crystal as a working substance (active medium). In the same year, the helium-neon gas laser was created. The huge variety of currently created lasers can be classified according to the type of working substance: gas, liquid, semiconductor and solid-state lasers are distinguished. Depending on the type of laser, the energy to create a population inversion is supplied in different ways: excitation with very intense light - “optical pumping”, electric gas discharge, and in semiconductor lasers - electric current. Based on the nature of their glow, lasers are divided into pulsed and continuous.
Let's consider the operating principle of a solid-state ruby laser. Ruby is a crystal of aluminum oxide Al 2 0 3 containing approximately 0.05% chromium ions Cr 3 + as an impurity. Excitation of chromium ions is carried out by optical pumping using high-power pulsed light sources. One of the designs uses a tubular reflector with an elliptical cross-section. Inside the reflector there is a direct xenon flash lamp and a ruby rod located along lines passing through the foci of the ellipse (Fig. 1). The inner surface of the aluminum reflector is highly polished or silver plated. The main property of an elliptical reflector is that the light coming out of one of its focus (xenon lamp) and reflected from the walls enters the other focus of the reflector (ruby rod).
The ruby laser operates according to a three-level scheme (Fig. 2 a). As a result of optical pumping, chromium ions move from the ground level 1 to the short-lived excited state 3. Then a non-radiative transition occurs to the long-lived (metastable) state 2, from which the probability of a spontaneous radiative transition is relatively small. Therefore, the accumulation of excited ions in state 2 occurs and an inverse population is created between levels 1 and 2. Under normal conditions, the transition from the 2nd to the 1st level occurs spontaneously and is accompanied by luminescence with a wavelength of 694.3 nm. The laser cavity has two mirrors (see Fig. 1), one of which has a reflection coefficient R of the intensity of the light reflected and incident on the mirror), the other mirror is translucent and transmits part of the radiation incident on it (R< 100 %). Кванты люминесценции в зависимости от направления их движения либо вылетают из боковой поверхности рубинового стержня и теряются, либо, многократно отражаясь от зеркал, сами вызывают вынужденные переходы. Таким образом, пучок, перпендикулярный зеркалам, будет иметь наибольшее развитие и выходит наружу через полупрозрачное зеркало. Такой лазер работает в импульсном режиме. лазер пробой медицинское биологическое
Along with the ruby laser operating according to a three-level scheme, four-level laser schemes based on ions of rare earth elements (neodymium, samarium, etc.) embedded in a crystalline or glass matrix have become widespread (Fig. 24, b). In such cases, a population inversion is created between two excited levels: the long-lived level 2 and the short-lived level 2."
A very common gas laser is the helium-neon laser, which is excited by an electrical discharge. The active medium in it is a mixture of helium and neon in a ratio of 10:1 and a pressure of about 150 Pa. Neon atoms are emitting, helium atoms play a supporting role. In Fig. 24, c shows the energy levels of helium and neon atoms. Generation occurs during the transition between levels 3 and 2 of neon. In order to create an inverse population between them, it is necessary to populate level 3 and empty level 2. The population of level 3 occurs with the help of helium atoms. During an electrical discharge, electron impact excites helium atoms into a long-lived state (with a lifetime of about 10 3 s). The energy of this state is very close to the energy of level 3 of neon, therefore, when an excited helium atom collides with an unexcited neon atom, energy is transferred, as a result of which level 3 of neon is populated. For pure neon, the lifetime at this level is short and the atoms move to levels 1 or 2, and the Boltzmann distribution is realized. Depletion of level 2 of neon occurs mainly due to the spontaneous transition of its atoms to the ground state upon collisions with the walls of the discharge tube. This ensures a stationary inverse population of levels 2 and 3 of neon.
The main structural element of a helium-neon laser (Fig. 3) is a gas-discharge tube with a diameter of about 7 mm. Electrodes are built into the tube to create a gas discharge and excite helium. At the ends of the tube at the Brewster angle there are windows, due to which the radiation is plane-polarized. Plane-parallel resonator mirrors are mounted outside the tube, one of them is translucent (reflection coefficient R< 100 %). Таким образом, пучок вынужденного излучения выходит наружу через полупрозрачное зеркало. Это лазер непрерывного действия.
The resonator mirrors are made with multilayer coatings, and due to interference, the required reflection coefficient is created for a given wavelength. The most commonly used lasers are helium-neon lasers, which emit red light with a wavelength of 632.8 nm. The power of such lasers is low, it does not exceed 100 mW.
The use of lasers is based on the properties of their radiation: high monochromaticity (~ 0.01 nm), sufficiently high power, beam narrowness and coherence.
The narrowness of the light beam and its low divergence made it possible to use lasers to measure the distance between the Earth and the Moon (the resulting accuracy is about tens of centimeters), the rotation speed of Venus and Mercury, etc.
Their use in holography is based on the coherence of laser radiation. Gastroscopes have been developed based on a helium-neon laser using fiber optics, which make it possible to holographically form a three-dimensional image of the internal cavity of the stomach.
The monochromatic nature of laser radiation is very convenient for exciting Raman spectra of atoms and molecules.
Lasers are widely used in surgery, dentistry, ophthalmology, dermatology, and oncology. The biological effects of laser radiation depend on both the properties of the biological material and the properties of the laser radiation.
All lasers used in medicine are conventionally divided into 2 types: low-intensity (intensity does not exceed 10 W/cm2, most often about 0.1 W/cm2) - therapeutic and high-intensity - surgical. The intensity of the most powerful lasers can reach 10 14 W/cm 2; in medicine, lasers with an intensity of 10 2 - 10 6 W/cm 2 are usually used.
Low-intensity lasers are those that do not cause a noticeable destructive effect on tissue directly during irradiation. In the visible and ultraviolet regions of the spectrum, their effects are caused by photochemical reactions and do not differ from the effects caused by monochromatic light received from conventional, incoherent sources. In these cases, lasers are simply convenient monochromatic light sources that provide precise localization and dosage of exposure. Examples include the use of helium-neon laser light for the treatment of trophic ulcers, coronary heart disease, etc., as well as krypton and other lasers for photochemical damage to tumors in photodynamic therapy.
Qualitatively new phenomena are observed when using visible or ultraviolet radiation from high-intensity lasers. In laboratory photochemical experiments with conventional light sources, as well as in nature under the influence of sunlight, single-photon absorption usually occurs. This is stated in the second law of photochemistry, formulated by Stark and Einstein: each molecule participating in a chemical reaction under the influence of light absorbs one quantum of radiation, which causes the reaction. The single-photon nature of absorption, described by the second law, is fulfilled because at ordinary light intensities it is practically impossible for two photons to simultaneously enter a molecule in the ground state. If such an event were to take place, the expression would take the form:
2hv = E t - E k ,
which would mean the summation of the energy of two photons for the transition of a molecule from the energy state E k to a state with energy E g. There is also no absorption of photons by electronically excited molecules, since their lifetime is short, and the irradiation intensities usually used are low. Therefore, the concentration of electronically excited molecules is low, and their absorption of another photon is extremely unlikely.
However, if the light intensity is increased, two-photon absorption becomes possible. For example, irradiation of DNA solutions with high-intensity pulsed laser radiation with a wavelength of about 266 nm led to ionization of DNA molecules similar to that caused by y-radiation. Exposure to low-intensity ultraviolet radiation did not cause ionization. It was established that irradiation of aqueous solutions of nucleic acids or their bases with picosecond (pulse duration 30 ps) or nanosecond (10 ns) pulses with intensities above 10 6 W/cm 2 led to electronic transitions resulting in the ionization of molecules. With picosecond pulses (Fig. 4, a), the population of high electronic levels occurred according to the scheme (S 0 -> S1 -> S n), and with hv hv nanosecond pulses (Fig. 4, b) - according to the scheme (S 0 -> S1 -> T g -> T p). In both cases, the molecules received energy exceeding the ionization energy.
The absorption band of DNA is located in the ultraviolet region of the spectrum at< 315 нм, видимый свет нуклеиновые кислоты совсем не поглощают. Однако воздействие высокоинтенсивным лазерным излучением около 532 нм переводит ДНК в электронно-возбужденное состояние за счет суммирования энергии двух фотонов (рис. 5).
The absorption of any radiation leads to the release of a certain amount of energy in the form of heat, which is dissipated from the excited molecules into the surrounding space. Infrared radiation is absorbed mainly by water and causes mainly thermal effects. Therefore, the radiation of high-intensity infrared lasers causes a noticeable immediate thermal effect on tissue. The thermal effect of laser radiation in medicine is mainly understood as evaporation (cutting) and coagulation of biological tissues. This applies to various lasers with intensities from 1 to 10 7 W/cm 2 and with irradiation durations from milliseconds to several seconds. These include, for example, a gas C 0 2 laser (with a wavelength of 10.6 μm), Nd:YAG laser (1.064 μm) and others. Nd:YAG laser is the most widely used solid-state four-level laser. Generation is carried out on transitions of neodymium ions (Nd 3+) introduced into Y 3 Al 5 0 12 yttrium aluminum garnet (YAG) crystals.
Along with heating the tissue, some of the heat is removed due to thermal conductivity and blood flow. At temperatures below 40 °C, irreversible damage is not observed. At a temperature of 60 °C, protein denaturation, tissue coagulation and necrosis begin. At 100-150 °C dehydration and charring are caused, and at temperatures above 300 °C the tissue evaporates.
When radiation comes from a high-intensity focused laser, the amount of heat generated is large, creating a temperature gradient in the tissue. At the point where the beam hits, the tissue evaporates, and charring and coagulation occurs in the adjacent areas (Fig. 6). Photoevaporation is a method of layer-by-layer removal or cutting of tissue. As a result of coagulation, the blood vessels are sealed and bleeding stops. Thus, a focused beam of a continuous C 0 2 laser () with a power of about 2 * 10 3 W/cm 2 is used as a surgical scalpel for cutting biological tissues.
If you reduce the duration of exposure (10-10 s) and increase the intensity (above 10 6 W/cm 2), then the sizes of the charring and coagulation zones become negligible. This process is called photoablation (photoremoval) and is used to remove tissue layer by layer. Photoablation occurs at energy densities of 0.01-100 J/cm 2 .
With a further increase in intensity (10 W/cm and higher), another process is possible - “optical breakdown”. This phenomenon is that due to the very high electric field strength of laser radiation (comparable to the strength of intra-atomic electric fields), matter ionizes, plasma is formed and mechanical shock waves are generated. Optical breakdown does not require the absorption of light quanta by a substance in the usual sense; it is observed in transparent media, for example, in air.
2. Application of high-intensity laser radiation in surgery (general principles)
The main method of treating surgical diseases is operations involving the dissection of biological tissues. The impact of highly concentrated light energy on biological tissue leads to its strong heating, followed by evaporation of interstitial and intracellular fluid, compaction and coagulation of tissue structures. At low exposures, the surface layers of biological tissue are destroyed. With increasing exposure, the depth and volume of destruction increase.
Surgical lasers are either continuous or pulsed, depending on the type of active medium. Conventionally, they can be divided into three groups according to power level:
coagulating: 1-5 W;
evaporating and shallow cutting: 5-20 W;
deep cutting: 20-100 W.
Of course, this division is largely arbitrary, since the radiation wavelength and operating mode greatly influence the requirements for the output power of a surgical laser
When using high-power laser radiation, a very rapid increase in tissue temperature occurs at the point of contact of the laser beam with the biological tissue. This leads to the effect of reversible denaturation of the protein (40-53 °C), a further increase in temperature (55-63 °C) leads to irreversible destruction of protein structures. An increase in temperature from 63 to 100 °C leads to coagulation, and from 100 °C or more to evaporation and carbonization of biological tissue.
The operation, performed using a non-contact method, provides a pronounced hemostatic effect. The impact is carried out practically bloodless or with minimal blood loss, which simplifies its implementation and is accompanied by minor trauma to surrounding tissues.
The depth of penetration of laser radiation into tissue depends on the exposure time and the degree of tissue hydration. The higher the hydrophilicity, the smaller the penetration depth, and vice versa, the less less degree tissue hydration, the deeper the radiation penetrates. With pulsed laser radiation, biological tissue is not heated to the required depth as a result of significant surface absorption, and therefore evaporation does not occur, but only coagulation takes place. With prolonged exposure after charring, the tissue absorption parameters change and evaporation begins.
Laser surgery uses high-intensity laser radiation (HILI), which is obtained using CO 2, EnYAG laser and argon laser.
Laser surgical instruments have high precision and accuracy in producing destructive effects on the operated organs and tissues. This is relevant and sometimes is always the missing link in key stages operations, especially operations performed on tissues and organs with intense blood supply, in order to cause coagulation of the destruction front and avoid hemorrhage. Also, the use of a laser scalpel ensures absolute sterility of the operation. Here we can cite the medical complexes “Scalpel-1”, “Kalina”, “Razbor”, “Lancet-1” - CO and laser models designed for surgical operations in various areas of medical practice. Laser surgical devices are a universal cutting tool and can be used at key stages of surgical interventions. Indications for the use of laser radiation during surgery are: the need to perform operations on organs that are abundantly supplied with blood, when complete hemostasis is required, and its implementation by conventional methods is accompanied by large blood loss; the need to sterilize purulent wounds and prevent possible microbial contamination of clean surgical wounds (this circumstance is extremely important in regions with a tropical climate); the need for precision surgical techniques; surgical interventions in patients with blood clotting disorders.
There are no universal laser treatment modes for various tissues. Therefore, the selection of optimal parameters and modes of exposure is carried out by the surgeon independently, based on the basic methods of using laser surgical units in medical practice. For surgical treatment, these techniques were developed by employees of the Russian State scientific center laser medicine and MMA named after. THEM. Sechenov, Tver Medical Academy based on a generalization of clinical experience in various fields of medicine: in surgical dentistry and maxillofacial surgery, abdominal surgery, lung and pleural surgery, plastic surgery, cosmetology, purulent surgery, burn surgery, anorectal surgery, gynecology, urology , otolaryngology.
The nature of the interaction of laser radiation with biological tissue depends on the power density of the laser radiation and the interaction time. The speed of cutting tissue with a laser beam at different stages of the operation is selected by the surgeon experimentally, depending on the type of tissue and the desired quality of the cut with the selected laser radiation parameters. Slowing the cutting speed can lead to increased tissue carbonation and the formation of a deep coagulation zone. In the superpulse mode and especially in the pulse-periodic mode, carbonization and necrosis associated with overheating of surrounding tissues are practically eliminated at any speed of the laser beam. Let us present the main characteristics of the devices used in medical practice. The radiation wavelength is 10.6 microns. Output radiation power (adjustable) - 0.1-50 W. Power in the "medipulse" mode - 50 W. The power density of laser irradiation is limited from above by a conditional value of 50-150 W/cm 2 for pulsed lasers and a value of 10 W/cm 2 for continuous lasers. Diameter of laser beam on fabric (switchable) - 200; 300; 500 microns. Guidance of the main radiation by a diode laser beam - 2 mW, 635 nm. Radiation modes (switchable) - continuous, pulse-periodic, medipulse. Radiation exposure time (adjustable) - 0.1-25 min. The duration of the radiation pulse in the pulse-periodic mode (adjustable) is 0.05-1.0 s. The duration of the pause between pulses is 0.05-1.0 s. Remote control panel. Turning the radiation on and off - foot pedal. Removal of combustion products - smoke evacuation system. The radius of the operating space is up to 1200 mm. The cooling system is autonomous, air-liquid type. Placement in the operating room is floor or tabletop. Power supply ( alternating current) - 220 V, 50 Hz, 600 W. Overall dimensions and weight vary. As you can see, the main difference between a laser for surgery and others is medical lasers is the high radiation power, especially in the pulse. This is necessary so that during the pulse the tissue substance has time to absorb radiation, heat up and evaporate into the surrounding environment. air space. Basically, all surgical lasers operate in the mid-infrared region of the optical range.
JIM-10, a laser surgical device "Lasermed" - the latest achievement in the field of laser technology, is suitable for carrying out operations in a mobile version. Built on the basis of semiconductor lasers emitting at a wavelength of 1.06 microns, the device is highly reliable, small in size and weight. Output radiation power - 0-7(10) W, packaged dimensions 470 x 350 x 120 mm, weight no more than 8 kg. This device is designed in the form of a suitcase, which, if necessary, can be transformed into a working position.
Also among the products of other domestic manufacturers, the following surgical complexes can be mentioned: ALOD-OBALKOM "Surgeon" (near-IR surgical laser device with adjustable radiation power). There are 5 modifications available, differing in the maximum laser radiation power - 6 W, 9 W, 12 W, 15 W, 30 W. Used for PT therapy (coagulation, removal of tumors, tissue cutting), installations based on carbon dioxide, YAG-neodymium (general surgery) and argon (ophthalmology) lasers of the company, as well as many others based on both gas, solid-state and semiconductor active avg.
There are many foreign and domestic analogues, the principles of use of which are similar to those stated above.
3. Light breakdown
Light breakdown (optical breakdown, optical discharge, laser spark), the transition of a substance as a result of intense ionization to the plasma state under the influence of electromagnetic fields of optical frequencies. Light breakdown was first observed in 1963 when radiation from a high-power pulsed ruby crystal laser operating in the Q-switched mode was focused in air. When a light breakdown occurs, a spark appears at the focus of the lens, the effect is perceived by the observer as a bright flash, accompanied by strong sound. For the breakdown of gases at optical frequencies, huge electric fields of the order of 106-107 V/cm are required, which corresponds to the intensity of the light flux in the laser beam = 109-1011 W/cm 2 (for comparison, microwave breakdown of atmospheric air occurs at a field strength = 104 V/cm). There are two possible mechanisms: Light breakdown of a gas under the influence of intense light radiation. The first of them does not differ in nature from the breakdown of gases in fields of not very high frequencies (this also includes the microwave range). The first seed electrons, which appear for one reason or another in the field, first gain energy by absorbing photons in collisions with gas atoms. This process is the opposite of the bremsstrahlung emission of quanta during electron neutron scattering. excited atoms. Having accumulated energy sufficient for ionization, the electron ionizes the atom, and instead of one, two slow electrons appear, and the process repeats. This is how an avalanche develops (see AVALANCHE DISCHARGE). IN strong fields This process occurs quite quickly and a breakdown breaks out in the gas. The second mechanism for the occurrence of light breakdown, characteristic specifically for optical frequencies, is of a purely quantum nature. Electrons can be torn away from atoms as a result of the multiquantum photoelectric effect, i.e., with the simultaneous absorption of several photons at once. A single-quantum photoelectric effect in the case of frequencies in the visible range is impossible, since the ionization potentials of atoms are several times higher than the energy of the quantum. So, for example, the photon energy of a ruby laser is 1.78 eV, and the ionization potential of argon is 15.8 eV, i.e., 9 photons are required to remove an electron. Typically, multiphoton processes are unlikely, but their speed increases sharply with increasing photon number density, and at those high intensities at which Light Breakdown is observed, their probability reaches a significant value. In dense gases, at pressures on the order of atmospheric pressure and higher, avalanche ionization always occurs; multiphoton processes here are only the cause of the appearance of the first electrons. In rarefied gases and in fields of picosecond pulses, when electrons fly out of the field action area without having had time to experience many collisions, the avalanche does not develop and Light breakdown is possible only due to the direct ejection of electrons from atoms under the influence of light. This is only possible with very strong light fields >107 V/cm. At high pressures, light breakdown is observed in much weaker fields. The entire mechanism of Light Breakdown is complex and diverse.
Basic light quantities
Light breakdown is also observed in condensed media when powerful laser radiation propagates through it and can cause destruction of materials and optical parts of laser devices.
The use of a semiconductor laser opens up new possibilities in the quality and timing of treatment. This high-tech surgical instrument and apparatus can be used for prevention and wound management in the postoperative period. This becomes possible through the use of physiotherapeutic properties of infrared laser radiation, which has a pronounced anti-inflammatory effect, bacteriostatic and bactericidal effect, and has a stimulating effect on tissue immunity and regeneration processes. It is also worth mentioning the possibility of using a diode laser to whiten teeth by 3-4 shades in one visit. However, the most common areas of laser application are surgery and periodontics.
The results obtained when working with a laser give reason to assert: a diode laser is an almost indispensable doctor’s assistant in everyday work, which is confirmed by positive reviews from patients. In their opinion, the use of this type of treatment is justified and comfortable. The operation is bloodless, quick, and the postoperative stage is easier to bear.
Objectively, a decrease in healing time by 2 times is observed, less painful sensations during and after operations, allowing you to do without anesthetics, faster regeneration, absence of edema - it is not surprising that an increasing number of patients prefer laser manipulation. But that's not all - the developed technique for managing patients with periodontal disease allows us to reduce the number and delay flap operations. Encouraging results have also been obtained in endodontics - treatment of canals with laser light seems very promising.
Areas of use. Diode lasers perfectly dissect, disinfect, coagulate and reconstruct soft tissues, making it possible to successfully perform the following manipulations:
* Gum correction during pre-prosthetic preparation makes it easier to work with materials. The bloodless field gives direct access to surfaces covered by the mucous membrane.
* Frenuloplasty - short frenulums of the tongue are eliminated and upper lip, plastic surgery of the oral vestibule. In most cases, complete removal of the frenulum is successful. During the healing process, minimal swelling is observed - significantly less than wounds from intervention with a scalpel.
* Treatment of periodontal pockets for gingivitis and initial periodontitis. After a course of radiation, a quick and good result is achieved. It has also been noted that hard dental deposits are easier to remove after exposure to laser radiation.
* Gingivoplasty. Gingival hyperplasia resulting from orthodontic treatment and mechanical irritation is becoming increasingly common. It is known that stimulation of mucous tissues leads to pathological coating of the tooth. The tissue response is permanent and usually requires removal of excess tissue. Laser surgery is an effective method of removing excess tissue, restoring the normal appearance of the mucosa.
* Treatment of aphthous ulcers and herpes hyperesthesia. The physiotherapeutic capabilities of the diode laser are used. Laser energy in the form of an unfocused beam, directed at the surface of these lesions, affects the nerve endings (with hyperesthesia). More difficult cases require light surface contact.
* Cosmetic reconstruction of the mucous membrane. This manipulation is a perfect aesthetic treatment method. Lasers make it possible to remove tissue layer by layer. The absence of bleeding allows these operations to be performed with greater accuracy. Gum tissue is easily evaporated, leaving clear edges. The parameters of the width, length of the incisions and height of the gingival contours are easily achievable.
* Periodontal treatment. In this situation, the most successful is an integrated approach combining surgery and physical therapy. There are treatment programs that lead to long-term remission if the patient follows oral hygiene recommendations. At the first visit, the acute process is stopped, then the pathological pockets are sanitized, and, if necessary, surgical manipulations are performed using additional bone materials. Next, the patient undergoes a maintenance course of laser therapy. The treatment period takes on average 14 days.
* Endodontic treatment. The traditional use of laser in endodontics is the evaporation of pulp residues and disinfection of canals. Special endodontic tips allow you to work directly in the open canal up to the apex. Using a laser, tissue remains are ablated, bacteria are destroyed, and the canal walls are glazed. If there is a fistula, the laser beam passes through the fistula channel towards the source of inflammation. At the same time, the spread of infection is stopped for some time and the symptoms are suppressed, but relapse is obvious if the root canal is not fully processed.
* Whitening. One should not ignore the fact that this is one of the most popular aesthetic procedures among patients. With the help of a diode laser, a significant whitening effect can be achieved in just one visit. The procedure itself is extremely simple and consists of activating a pre-applied whitening gel with laser radiation.
Advantages. In surgical dentistry and periodontology, the advantages of a laser are determined by factors such as accuracy and ease of access to the surgical field. At the same time, there is no bleeding during the operation, which allows the surgical field to remain dry, and this naturally provides a better overview - as a result, the operation time is reduced. Additionally, it is worth noting that during the operation the vessels are coagulated, thereby minimizing postoperative swelling.
Also, due to the anti-inflammatory and bacteriostatic effects of laser radiation, the risk of complications is reduced. Wound healing occurs faster compared to traditional techniques.
With laser conservative treatment of gingivitis and periodontitis with pocket depths up to 5 mm, there is no bleeding or inflammation; in some cases, bone tissue regeneration is observed, which is confirmed by x-ray studies.
When carrying out bleaching, in addition to the short procedure time (about 1 hour), a significant advantage is the minimal manifestation of hypersensitivity after the bleaching procedure.
Domestic developments. As you can see, there are many advantages of using diode lasers. There is truth and one serious drawback inherent in all innovative developments in all areas of human knowledge - high price. Indeed, the cost of such devices, especially those produced by well-known Western brands, is significant. Fortunately, there are also Russian developments in this area, and this is a rather rare case (when it comes to high-tech developments) when “Russian” does not mean “worst”. Since Soviet times, domestic developments in the field of laser technologies are not only not inferior to Western analogues, but often surpass them - many prototypes of modern laser systems were developed in our country.
There is also a domestic semiconductor dental laser - this is the Lamy S device (a joint development of the Denta-Rus Medical Center and the Opttekhnika Research and Production Center), which some Western companies have already become interested in, because among other things, its indisputable advantage is the fact that the cost of the laser is 3 times lower compared to imported analogues.
The device uses semiconductor laser crystals operating from low-voltage low-power (350 W) power sources, rather than gas-discharge tubes that require a special high-voltage power source. This design allows you to solve several problems at once - the absence of high voltage is a certain guarantee of safety for the doctor and the patient, there are no harmful electromagnetic fields, and no special cooling is required.
But let’s return to the low price of the device - this allows you to recoup your financial investments much faster and start making a profit. Agree, in addition to improving the quality of patient care, this is also very important in a commercial setting.
Among other features of the Lamy devices, it makes sense to note the following - they do not require special conditions and special maintenance, are small in size and easily transported within the clinic, and are reliable and stable parameters. Service is organized in such a way that if a malfunction occurs, the doctor receives another device during repairs.
Conclusion
The main instruments that the surgeon uses for tissue dissection are a scalpel and scissors, i.e. cutting instruments. However, wounds and cuts made with a scalpel and scissors are accompanied by bleeding, requiring the use of special hemostasis measures. In addition, when in contact with tissue, cutting instruments can spread microflora and malignant tumor cells along the cut line. In this regard, for a long time, surgeons have dreamed of having at their disposal an instrument that would make a bloodless cut, while simultaneously destroying pathogenic microflora and tumor cells in the surgical wound. Interventions on a “dry surgical field” are ideal for surgeons of any profile.
Attempts to create an “ideal” scalpel date back to the end of the last century, when the so-called electric knife, operating using high-frequency currents, was designed. This device, in more advanced versions, is currently used quite widely by surgeons of various specialties. However, as experience has accumulated, the negative aspects of “electrosurgery” have been identified, the main one of which is too large a zone of thermal tissue burn in the area of the incision. It is known that the wider the burn area, the worse the surgical wound heals. In addition, when using an electric knife, it becomes necessary to include the patient’s body in an electrical circuit. Electrosurgical devices negatively affect the operation of electronic devices and devices for monitoring the body's vital functions during surgery. Cryosurgical machines also cause significant tissue damage, impairing the healing process. The speed of tissue dissection with a cryoscalpel is very low. In fact, this does not involve dissection, but tissue destruction. A significant burn area is also observed when using a plasma scalpel. If we take into account that the laser beam has pronounced hemostatic properties, as well as the ability to seal the bronchioles, bile ducts and pancreatic ducts, then the use of laser technology in surgery becomes extremely promising. Briefly listed some of the advantages of using lasers in surgery relate primarily to carbon dioxide lasers (C 0 2 lasers). In addition to them, lasers that operate on other principles and on other working substances are used in medicine. These lasers have fundamentally different qualities when affecting biological tissues and are used for relatively narrow indications, in particular in cardiovascular surgery, oncology, for the treatment of surgical diseases of the skin and visible mucous membranes, etc.
WITHlist of used literature
1. A.N. Remizov "Medical and biological physics".
2. O.K. Skobelkin "Lasers in surgery, edited by professor."
3. S.D. Pletnev "Lasers in clinical medicine" edited.
Posted on Allbest.ru
...Similar documents
The main directions and goals of the medical and biological use of lasers. Measures for protection against laser radiation. Penetration of laser radiation into biological tissues, their pathogenetic mechanisms of interaction. The mechanism of laser biostimulation.
abstract, added 01/24/2011
The concept and purpose of a laser, the principle of operation and structure of the laser beam, the nature of its interaction with tissue. Features of the practical use of lasers in dentistry, assessment of the main advantages and disadvantages this method dental treatment.
abstract, added 05/14/2011
General concept of quantum electronics. History of development and principle of laser design, properties of laser radiation. Low-intensity and high-intensity lasers: properties, effect on biological tissues. Application of laser technologies in medicine.
abstract, added 05/28/2015
Laser radiation process. Research in the field of lasers in the X-ray wavelength range. Medical application of CO2 lasers and argon and krypton ion lasers. Generation of laser radiation. Coefficient useful action lasers of various types.
abstract, added 01/17/2009
Physical basis of the use of laser technology in medicine. Types of lasers, operating principles. The mechanism of interaction of laser radiation with biological tissues. Promising laser methods in medicine and biology. Serially produced medical laser equipment.
abstract, added 08/30/2009
The concept of laser radiation. The mechanism of laser action on tissue. Its use in surgery for cutting tissue, stopping bleeding, removing pathologies and welding biological tissues; dentistry, dermatology, cosmetology, treatment of retinal diseases.
presentation, added 10/04/2015
Laser diagnostic methods. Optical quantum generators. The main directions and goals of the medical and biological use of lasers. Angiography. Diagnostic capabilities of holography. Thermography. Laser medical installation for radiation therapy.
abstract, added 02/12/2005
Physical nature and therapeutic effects ultrasound. The main directions of its medical and biological applications. Danger and side effects ultrasound examination. The essence of echocardiography. Making a diagnosis of diseases of internal organs.
presentation, added 02/10/2016
Application ionizing radiation in medicine. Technology of medical procedures. Installations for external radiation therapy. Application of isotopes in medicine. Means of protection against ionizing radiation. The process of obtaining and using radionuclides.
presentation, added 02/21/2016
Familiarization with the history of the discovery and properties of lasers; examples of use in medicine. Consideration of the structure of the eye and its functions. Diseases of the organs of vision and methods of their diagnosis. Study of modern methods of vision correction using lasers.
In medicine, laser systems have found their application in the form of a laser scalpel. Its use for surgical operations is determined by the following properties:
It makes a relatively bloodless cut, since simultaneously with tissue dissection, it coagulates the edges of the wound by “sealing” not too large blood vessels;
The laser scalpel is distinguished by its constant cutting properties. Contact with a hard object (for example, bone) does not disable the scalpel. For a mechanical scalpel, such a situation would be fatal;
The laser beam, due to its transparency, allows the surgeon to see the operated area. The blade of an ordinary scalpel, as well as the blade of an electric knife, always to some extent blocks the working field from the surgeon;
The laser beam cuts the tissue at a distance without exerting any mechanical effect on the tissue;
The laser scalpel ensures absolute sterility, because only radiation interacts with the tissue;
The laser beam acts strictly locally, tissue evaporation occurs only at the focal point. Adjacent areas of tissue are damaged significantly less than when using a mechanical scalpel;
Clinical practice has shown that a wound caused by a laser scalpel hardly hurts and heals faster.
The practical use of lasers in surgery began in the USSR in 1966 at the A.V. Vishnevsky Institute. The laser scalpel was used in operations on the internal organs of the thoracic and abdominal cavities. Currently, laser beams are used to perform skin plastic surgery, operations of the esophagus, stomach, intestines, kidneys, liver, spleen and other organs. It is very tempting to perform operations using a laser on organs containing a large number of blood vessels, for example, on the heart and liver.
Characteristics of some types of lasers.
Currently, there is a huge variety of lasers, differing in active media, powers, operating modes and other characteristics. There is no need to describe them all. Therefore, here is a brief description of lasers that fairly fully represent the characteristics of the main types of lasers (operating mode, pumping methods, etc.)
Ruby laser. First quantum generator The source of light was the ruby laser, created in 1960.
The working substance is ruby, which is a crystal of aluminum oxide Al 2 O 3 (corundum), into which chromium oxide Cr 2 Oz is introduced as an impurity during growth. The red color of ruby is due to the positive ion Cr +3. In the Al 2 O 3 crystal lattice, the Cr +3 ion replaces the Al +3 ion. As a result, two absorption bands appear in the crystal: one in the green, the other in the blue part of the spectrum. The density of the red color of a ruby depends on the concentration of Cr +3 ions: the higher the concentration, the thicker the red color. In dark red ruby, the concentration of Cr +3 ions reaches 1%.
Along with the blue and green absorption bands, there are two narrow energy levels E 1 and E 1 ', upon transition from which to the main level light is emitted with wavelengths of 694.3 and 692.8 nm. The line width is approximately 0.4 nm at room temperatures. The probability of forced transitions for the 694.3 nm line is greater than for the 692.8 nm line. Therefore, it is easier to work with the 694.3 nm line. However, it is also possible to generate 692.8 nm lines if you use special mirrors that have a large reflection coefficient for radiation l = 692.8 nm and a small one for l = 694.3 nm.
When ruby is irradiated with white light, the blue and green parts of the spectrum are absorbed, and the red part is reflected. The ruby laser uses optical pumping with a xenon lamp, which produces high-intensity flashes of light when a current pulse passes through it, heating the gas to several thousand Kelvin. Continuous pumping is impossible because the lamp cannot withstand continuous operation at such a high temperature. The resulting radiation is close in its characteristics to the radiation of a completely black body. The radiation is absorbed by Cr + ions, which as a result move to energy levels in the region of absorption bands. However, from these levels, Cr +3 ions very quickly, as a result of a nonradiative transition, move to the levels E 1, E 1 '. In this case, excess energy is transferred to the lattice, i.e., it is converted into the energy of lattice vibrations or, in other words, into the energy of photons. Levels E 1, E 1 ’ are metastable. The lifetime at level E 1 is 4.3 ms. During the pump pulse, excited atoms accumulate at the E 1 and E 1 ' levels, creating a significant inverse population relative to the E 0 level (this is the level of unexcited atoms).
The ruby crystal is grown in the form of a round cylinder. For lasers, crystals of the following sizes are usually used: length L = 5 cm, diameter d = 1 cm. A xenon lamp and a ruby crystal are placed in an elliptical cavity with a highly reflective inner surface. To ensure that all the xenon lamp radiation reaches the ruby, the ruby crystal and the lamp, which also has the shape of a round cylinder, are placed at the foci of the elliptical section of the cavity parallel to its generatrices. Thanks to this, radiation with a density almost equal to the radiation density at the pump source is directed at the ruby.
One of the ends of the ruby crystal is cut so that complete reflection and return of the beam is ensured from the edges of the cut. This cut replaces one of the laser mirrors. The second end of the ruby crystal is cut at Brewster's angle. It ensures that the beam exits the ruby crystal without reflecting with appropriate linear polarization. The second resonator mirror is placed in the path of this beam. Thus, the radiation from a ruby laser is linearly polarized.
Helium-neon laser. The active medium is a gaseous mixture of helium and neon. Generation occurs due to transitions between energy levels of neon, and helium plays the role of an intermediary through which energy is transferred to neon atoms to create population inversion.
Neon, in principle, can generate laser studies as a result of more than 130 different transitions. However, the most intense lines are at wavelengths of 632.8 nm, 1.15 and 3.39 µm. The wave of 632.8 nm is in the visible part of the spectrum, and the waves of 1.15 and 3.39 microns are in the infrared.
When current is passed through a helium-neon mixture of gases by electron impact, helium atoms are excited to the 2 3 S and 2 2 S states, which are metastable, since the transition to the ground state from them is prohibited by quantum mechanical selection rules. When a current passes, atoms accumulate at these levels. When an excited helium atom collides with an unexcited neon atom, the excitation energy goes to the latter. This transition occurs very efficiently due to the good coincidence of the energies of the corresponding levels. As a result, an inverse population is formed at the 3S and 2S levels of neon relative to the 2P and 3P levels, leading to the possibility of generating laser radiation. The laser can operate in continuous mode. The radiation of a helium-neon laser is linearly polarized. Typically, the pressure of helium in the chamber is 332 Pa, and neon - 66 Pa. The constant voltage on the tube is about 4 kV. One of the mirrors has a reflection coefficient of the order of 0.999, and the second, through which the laser radiation exits, is about 0.990. Multilayer dielectrics are used as mirrors, since lower reflection coefficients do not ensure that the lasing threshold is reached.
Gas lasers. They are perhaps the most widely used type of laser today and are arguably superior to even ruby lasers in this regard. Most of the research performed is also devoted to gas lasers. Among the different types gas lasers it is always possible to find one that will satisfy almost any requirement for a laser, with the exception of very high power in the visible region of the spectrum in pulsed mode. High powers are needed for many experiments when studying the nonlinear optical properties of materials. At present, high powers have not been obtained in gas lasers for the simple reason that the density of atoms in them is not high enough. However, for almost all other purposes, a specific type of gas laser can be found that will be superior to both optically pumped solid-state lasers and semiconductor lasers. Much effort has been devoted to making these lasers competitive with gas lasers, and some success has been achieved in a number of cases, but it has always been on the edge of possibility, while gas lasers show no signs of waning in popularity.
The peculiarities of gas lasers are often due to the fact that they, as a rule, are sources of atomic or molecular spectra. Therefore, the wavelengths of the transitions are precisely known. They are determined by atomic structure and are usually independent of environmental conditions. The stability of the lasing wavelength under certain efforts can be significantly improved compared to the stability of spontaneous emission. There are now lasers with monochromaticity better than any other device. With an appropriate choice of the active medium, lasing can be achieved in any part of the spectrum, from the ultraviolet (~2OOO A) to the far infrared region (~0.4 mm), partially covering the microwave region.
There is also no reason to doubt that in the future it will be possible to create lasers for the vacuum ultraviolet region of the spectrum. The rarefaction of the working gas ensures the optical homogeneity of the medium with a low refractive index, which allows the use of simple mathematical theory to describe the structure of the resonator modes and provides confidence that the properties of the output signal are close to theoretical ones. Although the efficiency of converting electrical energy into stimulated emission energy in a gas laser cannot be as high as in a semiconductor laser, due to the simplicity of controlling the discharge, a gas laser turns out to be the most convenient for most purposes to operate as one of the laboratory instruments. When it comes to high continuous power (as opposed to pulsed power), the nature of gas lasers allows them to outperform all other types of lasers in this regard.
C0 2 -laser with a closed volume. Carbon dioxide molecules, like other molecules, have a striped spectrum due to the presence of vibrational and rotational energy levels. The transition used in the CO 2 laser produces radiation with a wavelength of 10.6 microns, i.e., it lies in the infrared region of the spectrum. Using vibrational levels, it is possible to slightly vary the radiation frequency in the range from approximately 9.2 to 10.8 μm. Energy is transferred to CO 2 molecules from nitrogen molecules N 2, which themselves are excited by electron impact when current passes through the mixture.
The excited state of the nitrogen molecule N2 is metastable and is located at a distance of 2318 cm -1 from the ground level, which is very close to the energy level (001) of the CO2 molecule. Due to the metastability of the excited state of N2, the number of excited atoms accumulates during the passage of current. When N 2 collides with CO 2, a resonant transfer of excitation energy from N 2 to CO 2 occurs. As a result, population inversion occurs between the levels (001), (100), (020) of CO 2 molecules. Usually, to reduce the population of level (100), which has a long lifetime, which impairs generation upon transition to this level, helium is added. Under typical conditions, the gas mixture in the laser consists of helium (1330 Pa), nitrogen (133 Pa) and carbon dioxide (133 Pa).
When a CO 2 laser operates, CO 2 molecules disintegrate into CO and O, due to which the active medium is weakened. Next, CO decomposes into C and O, and carbon is deposited on the electrodes and walls of the tube. All this worsens the operation of the CO 2 laser. To overcome the harmful effects of these factors, water vapor is added to the closed system, which stimulates the reaction
CO + O ® CO 2 .
Platinum electrodes are used, the material of which is a catalyst for this reaction. To increase the supply of active medium, the resonator is connected to additional containers containing CO 2, N 2, He, which are added in the required quantity to the cavity volume to maintain optimal laser operating conditions. Such a closed CO 2 laser is able to operate for many thousands of hours.
Flow CO 2 -laser. An important modification is a flow-through CO 2 laser, in which a mixture of gases CO 2 , N 2 , He is continuously pumped through the resonator. Such a laser can generate continuous coherent radiation with a power of over 50 W per meter of the length of its active medium.
Neodymium laser. The name may be misleading. The laser body is not neodymium metal, but ordinary glass with an admixture of neodymium. Ions of neodymium atoms are randomly distributed among silicon and oxygen atoms. Pumping is done with lightning lamps. The lamps produce radiation within the wavelength range from 0.5 to 0.9 microns. A wide band of excited states appears. Atoms make non-radiative transitions to the upper laser level. Each transition produces a different energy, which is converted into vibrational energy of the entire “lattice” of atoms.
Laser radiation, i.e. transition to the empty lower level, has a wavelength of 1.06 µm.
T-laser. In many practical applications, an important role is played by a CO 2 laser, in which the working mixture is under atmospheric pressure and excited by a transverse electric field (T laser). Since the electrodes are located parallel to the axis of the resonator, to obtain large values of the electric field strength in the resonator, relatively small potential differences between the electrodes are required, which makes it possible to operate in a pulsed mode at atmospheric pressure, when the concentration of CO 2 in the resonator is high. Consequently, it is possible to obtain high power, usually reaching 10 MW or more in one radiation pulse with a duration of less than 1 μs. The pulse repetition rate in such lasers is usually several pulses per minute.
Gas dynamic lasers. A mixture of CO 2 and N 2 heated to a high temperature (1000-2000 K) flows at high speed through an expanding nozzle and is greatly cooled. The upper and lower energy levels are thermally insulated at different rates, resulting in the formation of an inverse population. Consequently, by forming an optical resonator at the exit from the nozzle, it is possible to generate laser radiation due to this inverse population. Lasers operating on this principle are called gas-dynamic. They make it possible to obtain very high radiation powers in continuous mode.
Dye lasers. Dyes are very complex molecules that have highly vibrational energy levels. Energy levels in the spectrum band are located almost continuously. Due to intramolecular interaction, the molecule very quickly (in times of the order of 10 -11 -10 -12 s) passes non-radiatively to the lower energy level of each band. Therefore, after the molecules are excited, after a very short period of time, all excited molecules will concentrate at the lower level of the E 1 band. They then have the ability to make a radiative transition to any of the energy levels of the lower band. Thus, radiation of almost any frequency is possible in the interval corresponding to the width of the zero band. This means that if dye molecules are taken as an active substance to generate laser radiation, then depending on the resonator settings, an almost continuous tuning of the frequency of the generated laser radiation can be obtained. Therefore, dye lasers with tunable generation frequencies are being created. Dye lasers are pumped by gas-discharge lamps or by radiation from other lasers.
The selection of generation frequencies is achieved by creating a generation threshold only for a narrow frequency range. For example, the positions of the prism and mirror are selected so that only rays with a certain wavelength return to the medium after reflection from the mirror due to dispersion and different angles of refraction. Laser generation is provided only for such wavelengths. By rotating the prism, it is possible to continuously adjust the frequency of the dye laser radiation. Lasing was carried out with many dyes, which made it possible to obtain laser radiation not only in the entire optical range, but also in a significant part of the infrared and ultraviolet regions of the spectrum.
Semiconductor lasers. The main example of the operation of semiconductor lasers is the magnetic-optical storage device (MO).
Operating principles of MO storage.
The MO drive is built on a combination of magnetic and optical principles of information storage. Information is written using a laser beam and a magnetic field, and read using only a laser.
During the recording process on an MO disk, a laser beam heats certain points on the disks, and under the influence of temperature, the resistance to polarity change for a heated point drops sharply, which allows the magnetic field to change the polarity of the point. After heating is completed, the resistance increases again. The polarity of the heated point remains in accordance with the magnetic field applied to it at the moment of heating.
Today's available MO drives use two cycles to record information: an erase cycle and a write cycle. During the erase process, the magnetic field has the same polarity, corresponding to binary zeros. The laser beam sequentially heats the entire erased area and thus writes a sequence of zeros to the disk. During the write cycle, the polarity of the magnetic field is reversed, which corresponds to a binary one. In this cycle, the laser beam is turned on only in those areas that should contain binary ones, leaving areas with binary zeros unchanged.
In the process of reading from a MO disk, the Kerr effect is used, which consists in changing the plane of polarization of the reflected laser beam, depending on the direction of the magnetic field of the reflecting element. The reflective element in this case is a point on the disk surface magnetized during recording, corresponding to one bit of stored information. When reading, a laser beam of low intensity is used, which does not lead to heating of the readable area, so the stored information is not destroyed during reading.
This method, unlike the usual one used in optical discs, does not deform the surface of the disc and allows repeated recording without additional equipment. This method also has an advantage over traditional magnetic recording in terms of reliability. Since remagnetization of disk sections is possible only under the influence of high temperature, the probability of accidental magnetization reversal is very low, in contrast to traditional magnetic recording, the loss of which can be caused by random magnetic fields.
The scope of application of MO disks is determined by its high performance in terms of reliability, volume and turnover. An MO disk is necessary for tasks that require large disk space. These are tasks such as image and sound processing. However, the low speed of data access does not make it possible to use MO disks for tasks with critical system reactivity. Therefore, the use of MO disks in such tasks comes down to storing temporary or backup information on them. A very beneficial use for MO disks is for backing up hard drives or databases. Unlike tape drives traditionally used for these purposes, storing backup information on MO disks significantly increases the speed of data recovery after a failure. This is explained by the fact that MO disks are random access devices, which allows you to recover only the data that has failed. In addition, with this recovery method there is no need to completely stop the system until the data is completely restored. These advantages, combined with high reliability of information storage, make the use of MO disks for backup profitable, although more expensive compared to tape drives.
The use of MO disks is also advisable when working with large volumes of private information. Easy replacement of disks allows you to use them only during work, without worrying about protecting your computer during non-working hours; data can be stored in a separate, protected place. This same property makes MO disks indispensable in situations where it is necessary to transport large volumes from place to place, for example from work to home and back.
The main prospects for the development of MO disks are primarily related to increasing the speed of data recording. The slow speed is determined primarily by the two-pass recording algorithm. In this algorithm, zeros and ones are written in different passes due to the fact that the magnetic field that sets the direction of polarization of specific points on the disk cannot change its direction quickly enough.
The most realistic alternative to two-pass recording is a technology based on changing phase state. Such a system has already been implemented by some manufacturing companies. There are several other developments in this direction related to polymer dyes and modulations of the magnetic field and laser radiation power.
Phase change technology is based on the ability of a substance to change from a crystalline state to an amorphous one. It is enough to illuminate a certain point on the surface of the disk with a laser beam of a certain power, and the substance at this point will go into amorphous state. In this case, the reflectivity of the disk at this point changes. Writing information occurs much faster, but at the same time the surface of the disk is deformed, which limits the number of rewrite cycles.
Technology is currently being developed that allows the polarity of a magnetic field to be reversed in just a few nanoseconds. This will allow the magnetic field to change synchronously with the arrival of data for recording. There is also a technology based on modulation of laser radiation. In this technology, the drive operates in three modes: low-intensity read mode, medium-intensity write mode and high-intensity write mode. Modulating the laser beam intensity requires more complex structure disk and supplementing the drive mechanism with an initializing magnet installed in front of the bias magnet and having the opposite polarity. In the simplest case, the disk has two working layers - initializing and recording. The initializing layer is made of such a material that the initializing magnet can change its polarity without additional laser exposure.
Of course, MO disks are promising and rapidly developing devices that can solve emerging problems with large volumes of information. But their further development depends not only on the technology of recording on them, but also on progress in the field of other storage media. And unless a more efficient way to store information is invented, MO disks may take a dominant role.
The use of lasers in medicine is fundamentally different from other numerous areas of technological application of lasers. Laser medical technologies are distinguished by their humanistic orientation. If a health problem is acute enough for the person himself or his loved one, then medical problems become immeasurably more important than any other problems.
Laser medical technologies are distinguished by their versatility, complexity, and diversity. Laser medicine includes the effect of laser radiation on various parts of the body: skin, bones, muscles, fatty tissues, tendons, internal organs, eyes, dental tissues, etc. Moreover, each of them, in turn, has a complex structure. So in a tooth you can separately examine the enamel, dentin, and pulp. In the skin - the stratum corneum, epidermis, dermis. All these fabrics have their own properties, like optical ( spectral characteristics, reflection coefficient, radiation penetration depth) and thermophysical (thermal conductivity, thermal diffusivity, heat capacity), different from the properties of other biological tissues. Therefore, the nature of the effect of laser radiation on them also differs. Accordingly, in each case it is necessary to select individual parameters of the irradiation mode: wavelength, duration of exposure, power, pulse repetition rate, etc. The strong difference in the properties of biological tissues makes specific effects possible, for example, percutaneous effects on pathological tissues (irradiation of subcutaneous tissues without significant damage to the skin).
Each fabric, due to its biological nature heterogeneous, has a complex microstructure. Soft tissues contain a significant amount of water. Bones contain various minerals. The consequence of this is the fact that the effect of radiation on tissue, especially destructive, surgical, for different tissues and wavelengths of radiation differs not only quantitatively, but also qualitatively. This means that there are several completely different mechanisms for removing biological tissue: thermal and low-energy coagulation followed by resorption, explosive mechanisms, “cold” ablation.
Interestingly, to carry out a therapeutic effect on a specific part of the body, laser exposure can be directed to a completely different object. Laser therapy is indicative here, when irradiation of blood, special points or projections of organs on the human skin (Zakharyin-Ged zones), foot or palm, or spinal area has an effect on internal organs very remote from the area of influence, and on the entire body as a whole.
In addition, since the body is a single whole, the effect of the effect continues for a very long time after its end. After laser surgery, the body's reaction continues for days, weeks and even months.
This complexity and complexity of laser medicine makes it very interesting for the research and development of new technologies.
Why has laser radiation found such widespread use in medicine? The main features of laser radiation as applied to laser medicine are:
- -directivity, monochromaticity, coherence, which determine the possibility of energy localization,
- - wide spectral range of existing lasers (this is especially important in the case when absorption is resonant in nature),
- - the ability to widely control the duration of exposure (existing lasers provide duration of exposure from the femtosecond range to continuous exposure),
- - the ability to smoothly change the intensity of exposure over a wide range,
- - the possibility of changing the frequency characteristics of the influence,
- - wide possibilities for optical process control, including the possibility of organizing feedback,
- - a wide range of mechanisms of action: thermal, photochemical, purely biophysical, chemical,
- - ease of radiation delivery,
- - the possibility of contactless exposure, which ensures sterility,
- - the possibility of performing bloodless operations associated with the thermal and, therefore, coagulation effect of radiation.
Thus, the laser appears to be an extremely precise, versatile and easy-to-use tool and has great potential for future medical applications.
Laser operating principle
The principle diagram of the operation of any laser emitter can be presented as follows (Fig. 1).
Rice. 1.
The structure of each of them includes a cylindrical rod with a working substance, at the ends of which there are mirrors, one of which has low permeability. In the immediate vicinity of the cylinder with the working substance there is a flash lamp, which can be parallel to the rod or serpentinely surround it. It is known that in heated bodies, for example in an incandescent lamp, spontaneous radiation occurs, in which each atom of the substance emits in its own way, and thus there are fluxes of light waves randomly directed relative to each other. A laser emitter uses so-called stimulated emission, which differs from spontaneous emission and occurs when an excited atom is attacked by a light quantum. The photon emitted in this case is over all electromagnetic characteristics absolutely identical to the primary one that attacked the excited atom. As a result, two photons appear with the same wavelength, frequency, amplitude, direction of propagation and polarization. It is easy to imagine that in the active medium there is a process of an avalanche-like increase in the number of photons, copying the primary “seed” photon in all parameters and forming a unidirectional light flux. The working substance acts as such an active medium in the laser emitter, and the excitation of its atoms (laser pumping) occurs due to the energy of the flash lamp. Streams of photons, the direction of propagation of which is perpendicular to the plane of the mirrors, reflected from their surface, repeatedly pass through the working substance back and forth, causing more and more new avalanche-like chain reactions. Since one of the mirrors is partially transparent, some of the resulting photons exit in the form of a visible laser beam.
Thus, a distinctive feature of laser radiation is monochromaticity, coherence and high polarization of electromagnetic waves in the light flux. Monochromaticity is characterized by the presence in the spectrum of a photon source of predominantly one wavelength; coherence is the synchronization in time and space of monochromatic light waves. High polarization is a natural change in the direction and magnitude of the radiation vector in a plane perpendicular to the light beam. That is, photons in a laser light flux have not only constant wavelengths, frequencies and amplitudes, but also the same direction of propagation and polarization. While ordinary light consists of randomly scattering heterogeneous particles. To put it into perspective, the difference between the light emitted by a laser and an ordinary incandescent lamp is the same as the difference between the sound of a tuning fork and the noise of the street.
Application of lasers in dentistry
In dentistry, laser radiation has firmly occupied a fairly large niche. At the department orthopedic dentistry BSMU is conducting work to study the possibilities of using laser radiation, which covers both the physiotherapeutic and surgical aspects of the action of the laser on the organs and tissues of the maxillofacial area, and issues of the technological use of lasers at the stages of manufacturing and repair of prostheses and devices.
Light has been used to treat a variety of diseases for centuries. The ancient Greeks and Romans often “took the sun” as medicine. And the list of diseases that were supposed to be treated with light was quite large.
The real dawn of phototherapy came in the 19th century - with the invention of electric lamps, new possibilities appeared. At the end of the 19th century, they tried to treat smallpox and measles with red light by placing the patient in a special chamber with red emitters. Also, various “color baths” (that is, light of different colors) have been successfully used to treat mental illness. Moreover, the leading position in the field of phototherapy by the beginning of the twentieth century was occupied by the Russian Empire.
In the early sixties, the first laser medical devices appeared. Today, laser technologies are used for almost any disease.
1. Physical basis for the use of laser technology in medicine
1.1 Laser operating principle
Lasers are based on the phenomenon of stimulated emission, the existence of which was postulated by A. Einstein in 1916. In quantum systems with discrete energy levels, there are three types of transitions between energy states: induced transitions, spontaneous transitions and non-radiative relaxation transitions. The properties of stimulated emission determine the coherence of radiation and gain in quantum electronics. Spontaneous emission causes the presence of noise, serves as a seed impetus in the process of amplification and excitation of vibrations, and, together with non-radiative relaxation transitions, plays an important role in obtaining and maintaining a thermodynamically nonequilibrium radiating state.
During induced transitions, a quantum system can be transferred from one energy state to another, both by absorbing the energy of an electromagnetic field (transition from a lower energy level to an upper one) and by emitting electromagnetic energy (transition from an upper level to a lower one).
Light propagates in the form of an electromagnetic wave, while the energy during emission and absorption is concentrated in light quanta, while during the interaction of electromagnetic radiation with matter, as was shown by Einstein in 1917, along with absorption and spontaneous emission stimulated emission occurs, which forms the basis for the development of lasers.
Amplification of electromagnetic waves due to stimulated emission or initiation of self-excited oscillations of electromagnetic radiation in the centimeter wave range and thereby creating a device called maser(microwave amplification by stimulated emission of radiation), was implemented in 1954. Following a proposal (1958) to extend this amplification principle to significantly shorter light waves, the first laser(light amplification by stimulated emission of radiation).
A laser is a light source with which coherent electromagnetic radiation can be produced, which is known to us from radio engineering and microwave technology, as well as in the short-wave, especially infrared and visible, regions of the spectrum.
1.2 Types of lasers
Existing types Lasers can be classified according to several criteria. First of all, according to the state of aggregation of the active medium: gas, liquid, solid. Each of these large classes is divided into smaller ones: according to the characteristic features of the active medium, type of pumping, method of creating inversion, etc. For example, among solid-state lasers, a broad class of semiconductor lasers is quite clearly distinguished, in which injection pumping is most widely used. Gas lasers include atomic, ion and molecular lasers. A special place among all other lasers is occupied by the free electron laser, whose operation is based on the classical effect of light generation by relativistic charged particles in a vacuum.
1.3 Characteristics of laser radiation
Laser radiation differs from radiation from conventional light sources in the following characteristics:
High spectral energy density;
Monochromatic;
High temporal and spatial coherence;
High stability of laser radiation intensity in stationary mode;
The ability to generate very short light pulses.
These special properties of laser radiation provide it with a wide variety of applications. They are determined mainly by the process of generating radiation due to stimulated emission, which is fundamentally different from conventional light sources.
The main characteristics of a laser are: wavelength, power and operating mode, which can be continuous or pulsed.
Lasers are widely used in medical practice and primarily in surgery, oncology, ophthalmology, dermatology, dentistry and other fields. The mechanism of interaction of laser radiation with a biological object has not yet been fully studied, but it can be noted that either thermal effects or resonant interactions with tissue cells occur.
Laser treatment is safe and is very important for people with allergies to medications.
2. Mechanism of interaction of laser radiation with biological tissues
2.1 Types of interaction
An important property of laser radiation for surgery is the ability to coagulate blood-saturated (vascularized) biological tissue.
Mostly, coagulation occurs due to the absorption of laser radiation by the blood, its strong heating to the point of boiling and the formation of blood clots. Thus, the absorbing target during coagulation can be hemoglobin or the water component of the blood. This means that radiation from lasers in the orange-green spectrum (KTP laser, copper vapor) and infrared lasers (neodymium, holmium, erbium in glass, CO2 laser) will effectively coagulate biological tissue.
However, with very high absorption in biological tissue, such as, for example, an erbium garnet laser with a wavelength of 2.94 microns, laser radiation is absorbed at a depth of 5 - 10 microns and may not even reach the target - the capillary.
Surgical lasers are divided into two large groups: ablative(from Latin ablatio - “taking away”; in medicine - surgical removal, amputation) and non-ablative lasers. Ablative lasers are closer to the scalpel. Non-oblation lasers operate on a different principle: after treating an object, for example, a wart, papillomas or hemangiomas, with such a laser, this object remains in place, but after some time a series of biological effects take place in it and it dies. In practice, it looks like this: the neoplasm mummifies, dries out and falls off.
Continuous CO2 lasers are used in surgery. The principle is based on thermal effects. The advantages of laser surgery are that it is non-contact, practically bloodless, sterile, local, provides smooth healing of the dissected tissue, and hence good cosmetic results.
In oncology, it was noticed that a laser beam has a destructive effect on tumor cells. The destruction mechanism is based on the thermal effect, due to which a temperature difference arises between the surface and internal parts object, leading to strong dynamic effects and destruction of tumor cells.
Today, such a direction as photodynamic therapy is also very promising. Many articles appear on the clinical application of this method. Its essence is that a special substance is introduced into the patient’s body - photosensitizer. This substance is selectively accumulated by a cancerous tumor. After irradiating the tumor with a special laser, a series of photochemical reactions occur, releasing oxygen, which kills cancer cells.
One of the ways to influence the body with laser radiation is intravenous laser blood irradiation(ILBI), which is currently successfully used in cardiology, pulmonology, endocrinology, gastroenterology, gynecology, urology, anesthesiology, dermatology and other areas of medicine. Deep scientific study of the issue and predictability of results contribute to the use of ILBI both independently and in combination with other treatment methods.
For ILBI, laser radiation in the red region of the spectrum is usually used
(0.63 microns) with a power of 1.5-2 mW. Treatment is carried out daily or every other day; per course from 3 to 10 sessions. The exposure time for most diseases is 15-20 minutes per session for adults and 5-7 minutes for children. Intravenous laser therapy can be performed in almost any hospital or clinic. The advantage of outpatient laser therapy is that it reduces the possibility of developing a hospital-acquired infection; it creates a good psycho-emotional background, allowing the patient to remain functional for a long time while undergoing procedures and receiving full treatment.
In ophthalmology, lasers are used for both treatment and diagnosis. Using a laser, the retina of the eye is welded and the vessels of the ocular choroid are welded. Argon lasers emitting in the blue-green region of the spectrum are used for microsurgery to treat glaucoma. Excimer lasers have long been successfully used for vision correction.
In dermatology, many severe and chronic skin diseases are treated with laser radiation, and tattoos are also removed. When irradiated with a laser, the regenerative process is activated and the exchange of cellular elements is activated.
The basic principle of using lasers in cosmetology is that light affects only the object or substance that absorbs it. In the skin, light is absorbed by special substances - chromophores. Each chromophore absorbs in a certain range of wavelengths, for example, for the orange and green spectrum it is hemoglobin in the blood, for the red spectrum it is melanin in the hair, and for the infrared spectrum it is cellular water.
When radiation is absorbed, the energy of the laser beam is converted into heat in the area of the skin that contains the chromophore. With sufficient laser beam power, this leads to thermal destruction of the target. Thus, with the help of a laser it is possible to selectively target, for example, hair roots, pigment spots and other skin defects.
However, due to heat transfer, neighboring areas also heat up, even if they contain few light-absorbing chromophores. The processes of heat absorption and transfer depend on the physical properties of the target, its depth and size. Therefore, in laser cosmetology it is important to carefully select not only the wavelength, but also the energy and duration of laser pulses.
In dentistry, laser radiation is the most effective physiotherapeutic treatment for periodontal disease and diseases of the oral mucosa.
A laser beam is used instead of acupuncture. The advantage of using a laser beam is that there is no contact with a biological object, and, therefore, the process is sterile and painless with great efficiency.
Light guide instruments and catheters for laser surgery are designed to deliver powerful laser radiation to the site of surgery during open, endoscopic and laparoscopic operations in urology, gynecology, gastroenterology, general surgery, arthroscopy, dermatology. Allows cutting, excision, ablation, vaporization and coagulation of tissues during surgical operations in contact with biological tissue or in a non-contact mode of use (when the end of the fiber is removed from the biological tissue). The radiation can be output either from the end of the fiber or through a window on the side surface of the fiber. Can be used in both air (gas) and water (liquid) environments. On special order, for ease of use, catheters are equipped with an easily removable handle - a light guide holder.
In diagnostics, lasers are used to detect various inhomogeneities (tumors, hematomas) and measure the parameters of a living organism. The basics of diagnostic operations come down to passing a laser beam through the patient’s body (or one of his organs) and a diagnosis is made based on the spectrum or amplitude of the transmitted or reflected radiation. There are known methods for detecting cancerous tumors in oncology, hematomas in traumatology, as well as for measuring blood parameters (almost any, from blood pressure to sugar and oxygen content).
2.2 Features of laser interaction at various radiation parameters
For surgical purposes, the laser beam must be powerful enough to heat biological tissue above 50 - 70 ° C, which leads to its coagulation, cutting or evaporation. Therefore, in laser surgery, when talking about the laser radiation power of a particular device, they use numbers indicating units, tens and hundreds of Watts.
Surgical lasers are either continuous or pulsed, depending on the type of active medium. Conventionally, they can be divided into three groups according to power level.
1. Coagulating: 1 - 5 W.
2. Evaporating and shallow cutting: 5 - 20 W.
3. Deep cutting: 20 - 100 W.
Each type of laser is primarily characterized by the wavelength of the radiation. The wavelength determines the degree of absorption of laser radiation by biological tissue, and, therefore, the depth of penetration and the degree of heating of both the surgical area and the surrounding tissue.
Considering that water is contained in almost all types of biological tissue, we can say that for surgery it is preferable to use a type of laser whose radiation has an absorption coefficient in water of more than 10 cm-1 or, what is the same, the penetration depth of which does not exceed 1 mm.
Other important characteristics of surgical lasers,
determining their use in medicine:
radiation power;
continuous or pulse mode of operation;
the ability to coagulate blood-saturated biological tissue;
possibility of transmitting radiation via optical fiber.
When biological tissue is exposed to laser radiation, it first heats up and then evaporates. To effectively cut biological tissue, you need rapid evaporation at the cut site on the one hand, and minimal concomitant heating of the surrounding tissues on the other hand.
At the same average radiation power, a short pulse heats tissue faster than continuous radiation, and the spread of heat to surrounding tissue is minimal. But, if the pulses have a low repetition rate (less than 5 Hz), then it is difficult to make a continuous cut; it is more like a perforation. Therefore, the laser should preferably have a pulsed operating mode with a pulse repetition rate greater than 10 Hz, and the pulse duration should be as short as possible to obtain high peak power.
In practice, the optimal power output for surgery ranges from 15 to 60 W depending on the laser wavelength and application.
3. Promising laser methods in medicine and biology
The development of laser medicine follows three main branches: laser surgery, laser therapy and laser diagnostics. The unique properties of the laser beam make it possible to perform previously impossible operations using new effective and minimally invasive methods.
There is growing interest in non-drug treatments, including physical therapy. Situations often arise when it is necessary to carry out not one physical procedure, but several, and then the patient has to move from one cabin to another, dress and undress several times, which creates additional problems and loss of time.
The variety of therapeutic methods requires the use of lasers with different radiation parameters. For these purposes, various emitting heads are used, which contain one or more lasers and electronic device pairing control signals from the base unit with the laser.
The emitting heads are divided into universal ones, allowing them to be used both externally (using mirror and magnetic attachments) and intracavity using special optical attachments; matrix ones, having a large radiation area and applied superficially, as well as specialized ones. Various optical attachments allow radiation to be delivered to the desired area of influence.
The block principle allows the use of a wide range of laser and LED heads with different spectral, spatiotemporal and energy characteristics, which, in turn, raises the quality new level treatment effectiveness due to the combined implementation of various laser therapy techniques. The effectiveness of treatment is determined primarily effective methods and the equipment that ensures their implementation. Modern techniques require the ability to select various exposure parameters (radiation mode, wavelength, power) over a wide range. A laser therapy device (ALT) must provide these parameters, their reliable control and display, and at the same time be simple and convenient to operate.
4. Lasers used in medical technology
4.1 CO2 lasers
CO2 laser, i.e. A laser whose emitting component of the active medium is carbon dioxide CO2 occupies a special place among the variety of existing lasers. This unique laser is distinguished primarily by the fact that it is characterized by both high energy output and high efficiency. In continuous mode, enormous powers were obtained - several tens of kilowatts, pulsed power reached a level of several gigawatts, pulse energy is measured in kilojoules. The efficiency of a CO2 laser (about 30%) exceeds the efficiency of all lasers. The repetition rate in a pulse-periodic mode can be several kilohertz. The CO2 laser radiation wavelengths are in the range of 9-10 microns (IR range) and fall within the atmospheric transparency window. Therefore, CO2 laser radiation is convenient for intense exposure to matter. In addition, the CO2 laser radiation wavelength range includes the resonant absorption frequencies of many molecules.
Figure 1 shows the lower vibrational levels of the ground electronic state along with a symbolic representation of the vibrational mode of the CO2 molecule.
Figure 20 - Lower levels of the CO2 molecule
Laser pumping cycle of a CO2 laser in inpatient conditions as follows. Glow discharge plasma electrons excite nitrogen molecules, which transfer excitation energy to the asymmetrical stretching vibration of CO2 molecules, which has a long lifetime and is the upper laser level. The lower laser level is usually the first excited level of the symmetric stretching vibration, which is strongly coupled by the Fermi resonance to the bending vibration and therefore quickly relaxes along with this vibration in collisions with helium. It is obvious that the same relaxation channel is effective in the case when the lower laser level is the second excited level of the deformation mode. Thus, a CO2 laser is a laser using a mixture of carbon dioxide, nitrogen and helium, where CO2 provides radiation, N2 pumps the upper level, and He depletes the lower level.
CO2 lasers of medium power (tens - hundreds of watts) are designed separately in the form of relatively long tubes with a longitudinal discharge and longitudinal pumping of gas. A typical design of such a laser is shown in Figure 2. Here 1 - discharge tube, 2 - ring electrodes, 3 - slow renewal of the medium, 4 - discharge plasma, 5 - external tube, 6 - cooling running water, 7,8 - resonator.
Figure 20 - Diagram of a CO2 laser with diffusion cooling
Longitudinal pumping serves to remove dissociation products of the gas mixture in the discharge. Cooling of the working gas in such systems occurs due to diffusion onto the externally cooled wall of the discharge tube. The thermal conductivity of the wall material is essential. From this point of view, it is advisable to use pipes made of corundum (Al2O3) or beryllium (BeO) ceramics.
The electrodes are made ring-shaped, so as not to block the path to radiation. Joule heat is carried away by thermal conduction to the walls of the tube, i.e. Diffusion cooling is used. A solid mirror is made of metal, a translucent one is made of NaCl, KCl, ZnSe, AsGa.
An alternative to diffusion cooling is convection cooling. The working gas is blown through the discharge region at high speed, and Joule heat is removed by the discharge. The use of fast pumping makes it possible to increase the density of energy release and energy removal.
The CO2 laser is used in medicine almost exclusively as an “optical scalpel” for cutting and vaporization in all surgical operations. The cutting effect of a focused laser beam is based on the explosive evaporation of intra- and extracellular water in the focusing area, due to which the structure of the material is destroyed. The destruction of the tissue leads to the characteristic shape of the wound edges. In a narrowly limited interaction region, the temperature of 100 °C is exceeded only when dehydration (evaporative cooling) is achieved. Further increases in temperature result in material being removed by charring or evaporation of the tissue. Directly in the marginal zones, due to generally poor thermal conductivity, a thin necrotic thickening with a thickness of 30-40 microns is formed. At a distance of 300-600 microns, tissue damage no longer occurs. In the coagulation zone, blood vessels with a diameter of up to 0.5-1 mm spontaneously close.
Surgical devices based on CO2 lasers are currently offered in a fairly wide range. Guidance of the laser beam in most cases is carried out using a system of articulated mirrors (manipulator), ending with an instrument with built-in focusing optics, which the surgeon manipulates in the operated area.
4.2 Helium-neon lasers
IN helium-neon laser The working substance is neutral neon atoms. Excitation is carried out by electrical discharge. It is difficult to create an inversion in continuous mode in pure neon. This difficulty, which is quite general in many cases, is overcome by introducing an additional gas into the discharge - helium, which acts as a donor of excitation energy. The energies of the first two excited metastable levels of helium (Figure 3) quite accurately coincide with the energies of the 3s and 2s levels of neon. Therefore, the conditions for resonant excitation transfer according to the scheme are well realized
Figure 20 - He-Ne laser level diagram
At correctly selected pressures of neon and helium, satisfying the condition
it is possible to achieve a population of one or both of the 3s and 2s levels of neon that is significantly higher than that in the case of pure neon, and to obtain a population inversion.
Depletion of the lower laser levels occurs in collisional processes, including collisions with the walls of the gas-discharge tube.
Excitation of helium (and neon) atoms occurs in a low-current glow discharge (Figure 4). In continuous-wave lasers on neutral atoms or molecules, weakly ionized plasma of the positive column of a glow discharge is most often used to create the active medium. The current density of the glow discharge is 100-200 mA/cm2. The strength of the longitudinal electric field is such that the number of electrons and ions appearing in a single segment of the discharge gap compensates for the loss of charged particles during their diffusion to the walls of the gas-discharge tube. Then the positive column of the discharge is stationary and homogeneous. The electron temperature is determined by the product of the gas pressure and the inner diameter of the tube. At low temperatures the electron temperature is high, at high temperatures it is low. The constancy of the value determines the conditions for the similarity of the discharges. At a constant density of the number of electrons, the conditions and parameters of the discharges will remain unchanged if the product is constant. The density of the number of electrons in the weakly ionized plasma of the positive column is proportional to the current density.
For a helium-neon laser, the optimal values of , as well as the partial composition of the gas mixture, are somewhat different for different spectral lasing regions.
In the region of 0.63 µm, the most intense of the lines in the series, the line (0.63282 µm), corresponds to the optimal Tor mm.
Figure 20 - Design diagram of a He-Ne laser
Characteristic values The radiation power of helium-neon lasers should be considered tens of milliwatts in the regions of 0.63 and 1.15 microns and hundreds in the region of 3.39 microns. The service life of lasers is limited by processes in the discharge and is calculated in years. Over time, the gas composition changes in the discharge. Due to the sorption of atoms in the walls and electrodes, a “hardening” process occurs, the pressure drops, and the ratio of the partial pressures of He and Ne changes.
The greatest short-term stability, simplicity and reliability of the helium-neon laser design is achieved by installing cavity mirrors inside the discharge tube. However, with this arrangement, the mirrors relatively quickly fail due to bombardment by charged particles of the discharge plasma. Therefore, the most widely used design is in which the gas-discharge tube is placed inside the resonator (Figure 5), and its ends are equipped with windows located at the Brewster angle to the optical axis, thereby ensuring linear polarization of the radiation. This arrangement has a number of advantages - the adjustment of the resonator mirrors is simplified, the service life of the gas-discharge tube and mirrors is increased, their replacement is easier, it becomes possible to control the resonator and use a dispersive resonator, mode separation, etc.
Figure 20 - He-Ne laser cavity
Switching between lasing bands (Figure 6) in a tunable helium-neon laser is usually achieved by introducing a prism, and a diffraction grating is usually used to finely tune the lasing line.
Figure 20 - Using a Leathrow prism
4.3 YAG lasers
The trivalent neodymium ion easily activates many matrices. Of these, the most promising were crystals yttrium aluminum garnet Y3Al5O12 (YAG) and glass. Pumping transfers Nd3+ ions from the ground state 4I9/2 to several relatively narrow stripes, playing the role of the top level. These bands are formed by a series of overlapping excited states, and their positions and widths vary slightly from matrix to matrix. From the pump bands there is a rapid transfer of excitation energy to the metastable level 4F3/2 (Figure 7).
Figure 20 - Energy levels of trivalent rare earth ions
The closer the absorption bands are to the 4F3/2 level, the higher the lasing efficiency. The advantage of YAG crystals is the presence of an intense red absorption line.
The crystal growth technology is based on the Czochralski method, when YAG and an additive are melted in an iridium crucible at a temperature of about 2000 °C, followed by the separation of part of the melt from the crucible using a seed. The temperature of the seed is slightly lower than the temperature of the melt, and when drawn out, the melt gradually crystallizes on the surface of the seed. The crystallographic orientation of the crystallized melt reproduces the orientation of the seed. The crystal is grown in an inert environment (argon or nitrogen) at normal pressure with a small addition of oxygen (1-2%). Once the crystal reaches the desired length, it is slowly cooled to prevent destruction due to thermal stress. The growth process takes from 4 to 6 weeks and is computer controlled.
Neodymium lasers operate in a wide range of lasing modes, from continuous to essentially pulsed with durations reaching femtoseconds. The latter is achieved by mode locking in a wide gain line, characteristic of laser glasses.
When creating neodymium, as well as ruby, lasers, all the characteristic methods for controlling the parameters of laser radiation developed by quantum electronics were implemented. In addition to the so-called free generation, which continues throughout almost the entire lifetime of the pump pulse, the modes of switched (switched) Q factor and synchronization (self-synchronization) of modes have become widespread.
In the free generation mode, the duration of the radiation pulses is 0.1...10 ms, the radiation energy in power amplification circuits is about 10 ps when used for Q-switching of electro-optical devices. Further shortening of the lasing pulses is achieved by using bleachable filters for both Q-switching (0.1...10 ps) and mode locking (1...10 ps).
When biological tissue is exposed to intense radiation from an Nd-YAG laser, sufficiently deep necrosis (coagulation focus) is formed. The effect of tissue removal and thus the cutting effect is negligible compared to the effect of a CO2 laser. Therefore, the Nd-YAG laser is used primarily for coagulation of bleeding and for necrotizing pathologically changed areas of tissue in almost all areas of surgery. Since radiation transmission is also possible through flexible optical cables, prospects for using Nd-YAG lasers in body cavities open up.
4.4 Semiconductor lasers
Semiconductor lasers emit coherent radiation in the UV, visible or IR ranges (0.32...32 µm); Semiconductor crystals are used as the active medium.
Currently, over 40 different semiconductor materials suitable for lasers are known. Pumping of the active medium can be carried out by electron beams or optical radiation (0.32...16 µm), in the p-n junction of a semiconductor material by electric current from an applied external voltage (injection of charge carriers, 0.57...32 µm).
Injection lasers differ from all other types of lasers in the following characteristics:
High power efficiency (above 10%);
Simplicity of excitation (direct conversion of electrical energy into coherent radiation - both in continuous and pulsed operating modes);
Possibility of direct modulation by electric current up to 1010 Hz;
Extremely small in size (length less than 0.5 mm; width no more than 0.4 mm; height no more than 0.1 mm);
Low pump voltage;
Mechanical reliability;
Long service life (up to 107 hours).
4.5 Excimer lasers
Excimer lasers, representing new class laser systems open up the UV range for quantum electronics. It is convenient to explain the operating principle of excimer lasers using the example of a xenon (nm) laser. The ground state of the Xe2 molecule is unstable. An unexcited gas consists mainly of atoms. Population of the upper laser state, i.e. the creation of excited stability of a molecule occurs under the action of a beam of fast electrons in a complex sequence of collisional processes. Among these processes, ionization and excitation of xenon by electrons play a significant role.
Excimers of noble gas halides (noble gas monohalides) are of great interest, mainly because, in contrast to the case of noble gas dimers, the corresponding lasers operate not only with electron beam, but also with gas-discharge excitation. The mechanism of formation of the upper terms of laser transitions in these excimers is largely unclear. Qualitative considerations indicate a greater ease of their formation compared to the case of noble gas dimers. There is a deep analogy between excited molecules composed of atoms of alkali material and halogen. An inert gas atom in an excited electronic state is similar to an alkali metal and halogen atom. An inert gas atom in an excited electronic state is similar to the alkali metal atom that follows it on the periodic table. This atom is easily ionized because the binding energy of the excited electron is low. Due to the high affinity of the halogen electron, this electron is easily detached and, when the corresponding atoms collide, willingly jumps to a new orbit that unites the atoms, thereby carrying out the so-called harpoon reaction.
Most common following types excimer lasers: Ar2 (126.5 nm), Kr2 (145.4 nm), Xe2 (172.5 nm), ArF (192 nm), KrCl (222.0 nm), KrF (249.0 nm), XeCl (308.0 nm), XeF (352.0 nm).
4.6 Dye lasers
Distinctive feature dye lasers is the ability to work in a wide range of wavelengths from near-IR to near-UV, smooth tuning of the lasing wavelength in a range of several tens of nanometers wide with monochromaticity reaching 1-1.5 MHz. Dye lasers operate in continuous, pulsed and pulse-periodic modes. The energy of radiation pulses reaches hundreds of joules, the continuous generation power reaches tens of watts, the repetition rate is hundreds of hertz, and the efficiency is tens of percent (with laser pumping). In the pulsed mode, the generation duration is determined by the duration of the pump pulses. In mode locking mode, picosecond and sub-picosecond duration ranges are achieved.
The properties of dye lasers are determined by the properties of their working substance, organic dyes. Dyes It is customary to call complex organic compounds with a branched system of complex chemical bonds that have intense absorption bands in the visible and near-UV regions of the spectrum. Colored organic compounds contain saturated chromophore groups type NO2, N=N, =CO, responsible for coloring. The presence of so-called auxochrome groups type NH3, OH gives the compound coloring properties.
4.7 Argon lasers
Argon laser refers to a type of gas-discharge lasers that generate at transitions between ion levels mainly in the blue-green part of the visible and near ultraviolet regions of the spectrum.
This laser typically emits at wavelengths of 0.488 µm and 0.515 µm, as well as ultraviolet wavelengths of 0.3511 µm and 0.3638 µm.
The power can reach 150 W (industrial samples 2 h 10 W, service life within 100 hours). The design diagram of an argon laser with direct current excitation is shown in Figure 8.
Figure 20 - Argon laser design diagram
1 - laser output windows; 2 - cathode; 3 - water cooling channel; 4 - gas discharge tube (capillary); 5 - magnets; 6 - anode; 7 - bypass gas pipe; 8 - fixed mirror; 9 - translucent mirror
The gas discharge is created in a thin gas-discharge tube (4), 5 mm in diameter, in a capillary, which is cooled by a liquid. The operating gas pressure is within tens of Pa. Magnets (5) create a magnetic field to “press” the discharge from the walls of the gas-discharge tube, which prevents the discharge from touching its walls. This measure makes it possible to increase the output power of laser radiation by reducing the relaxation rate of excited ions, which occurs as a result of collision with the walls of the tube.
The bypass channel (7) is designed to equalize the pressure along the length of the gas-discharge tube (4) and ensure free circulation of gas. In the absence of such a channel, gas accumulates in the anode part of the tube after the arc discharge is turned on, which can lead to its extinguishing. The mechanism of what was said is as follows. Under the influence of an electric field applied between the cathode (2) and anode (6), electrons rush to the anode 6, increasing the gas pressure at the anode. This requires equalizing the gas pressure in the gas discharge tube to ensure the normal flow of the process, which is carried out by means of a bypass tube (7).
To ionize neutral argon atoms, it is necessary to pass a current with a density of up to several thousand amperes per hour through the gas. square centimeter. Therefore, effective cooling of the gas-discharge tube is necessary.
The main areas of application of argon lasers: photochemistry, heat treatment, medicine. The argon laser, due to its high selectivity towards autogenous chromophores, is used in ophthalmology and dermatology.
5. Serially produced laser equipment
Therapists use low-power helium-neon lasers emitting in the visible region of the electromagnetic spectrum (λ=0.63 microns). One of the physiotherapeutic installations is a laser installation UFL-1, intended for the treatment of acute and chronic diseases of the maxillofacial area; can be used for the treatment of long-term non-healing ulcers and wounds, as well as in traumatology, gynecology, surgery (postoperative period). The biological activity of the red beam of a helium-neon laser is used (radiation power
20 mW, radiation intensity on the surface of the object is 50-150 mW/cm2).
There is evidence that these lasers are used to treat venous diseases (trophic ulcers). The course of treatment consists of 20-25 ten-minute sessions of irradiation of the trophic ulcer with a low-power helium-neon laser and, as a rule, ends with its complete healing. A similar effect is observed when treating non-healing traumatic and post-burn wounds with laser. The long-term effects of laser therapy for trophic ulcers and non-healing wounds were tested on a large number of cured patients over a period of two to seven years. During these periods, ulcers and wounds no longer opened in 97% of former patients, and only 3% experienced relapses of the disease.
Light puncture is used to treat various diseases of the nervous and vascular system, relieve pain due to radiculitis, regulate blood pressure, etc. Laser is mastering more and more new medical professions. Laser treats the brain. This is facilitated by the activity of the visible spectrum of low-intensity helium-neon lasers. The laser beam, as it turns out, can relieve pain, soothe and relax muscles, and accelerate tissue regeneration. Many drugs with similar properties are usually prescribed to patients who have suffered a traumatic brain injury, which gives extremely confusing symptoms. The laser beam combines the effect of all necessary drugs. This was confirmed by specialists from the Central Research Institute of Reflexology of the USSR Ministry of Health and the Research Institute of Neurosurgery named after. K N. Burdenko AMS USSR.
Research into the possibilities of treating benign and malignant tumors with a laser beam is being conducted by the Moscow Research Oncological Institute named after. P.A. Herzen", Leningrad Institute oncology named after N.N. Petrov and other oncology centers.
In this case, different types of lasers are used: CO2 laser in continuous radiation mode (λ = 10.6 µm, power 100 W), helium-neon laser with continuous radiation mode (λ = 0.63 µm, power 30 mW), helium-cadmium laser laser operating in continuous radiation mode (λ = 0.44 μm, power 40 mW), pulsed nitrogen laser (λ = 0.34 μm, pulse power 1.5 kW, average radiation power 10 mW).
Three methods of influencing laser radiation on tumors (benign and malignant) have been developed and are used:
a) Laser irradiation - irradiation of a tumor with a defocused laser beam, leading to the death of cancer cells and loss of the ability to reproduce.
b) Laser coagulation - destruction of the tumor with a moderately focused beam.
c) Laser surgery - excision of the tumor along with adjacent tissues with a focused laser beam. Laser systems developed:
"Yakhroma"- power up to 2.5 W at the output of the light guide at a wavelength of 630 nm, exposure time from 50 to 750 sec; pulsed with a repetition rate of 104 pulses/sec.; on 2 lasers - pulsed dye laser and copper vapor laser "LGI-202". "Spectromed"- power 4 W with continuous generation mode, wavelength 620-690 nm, exposure time from 1 to 9999 sec using the device "Expo"; on two lasers - continuous dye laser "Amethyst" and argon laser "Inversion" for photodynamic therapy of malignant tumors (a modern method of selective exposure to cancer cells of the body).
The method is based on the difference in the absorption of laser radiation by cells that differ in their parameters. The doctor injects photosensitizing (the body acquires a specific increased sensitivity to foreign substances) medicine into the area of accumulation of pathological cells. Laser radiation striking body tissue is selectively absorbed by cancer cells containing the drug, destroying them, allowing the destruction of cancer cells without harming surrounding tissue.
Laser device ATKUS-10(JSC "Semiconductor Devices"), shown in Figure 9, allows you to influence neoplasms with laser radiation with two different wavelengths 661 and 810 nm. The device is intended for use in a wide range of medical institutions, as well as for solving various scientific and technical problems as a source of powerful laser radiation. When using the device, there are no significant destructive lesions of the skin and soft tissues. Removal of tumors with a surgical laser reduces the number of relapses and complications, shortens wound healing time, allows for a one-stage procedure and provides a good cosmetic effect.
Figure 20 - Laser device ATKUS-10
Semiconductor laser diodes are used as emitters. Transport optical fiber with a diameter of 600 microns is used.
LLC NPF "Techkon" has developed a laser therapy device " Alpha 1M"(Figure 10). As reported on the manufacturer's website, the installation is effective in the treatment of arthrosis, neurodermatitis, eczema, stomatitis, trophic ulcers, postoperative wounds, etc. The combination of two emitters - continuous and pulsed - provides great opportunities for therapeutic and research work. The built-in photometer allows you to set and control the irradiation power. Discrete time setting and smooth setting of the frequency of irradiation pulses are convenient for operating the device. Simplicity of control allows the use of the device by nursing staff.
Figure 20 - Laser therapeutic device "Alpha 1M"
Specifications devices are shown in Table 1.
Table 7 - Technical characteristics of the laser therapeutic device "Alpha 1M"
In the early 70s, academician M.M. Krasnov and his colleagues from the 2nd Moscow Medical Institute made efforts to cure glaucoma (occurs due to impaired outflow of intraocular fluid and, as a result, increased intraocular pressure) using a laser. Treatment of glaucoma was carried out with appropriate laser installations, created jointly with physicists.
Laser ophthalmic unit "Scimitar" doesn't have foreign analogues. Designed for surgical operations of the anterior part of the eye. Allows you to treat glaucoma and cataracts without compromising the integrity of the outer membranes of the eye. The installation uses a pulsed ruby laser. The radiation energy contained in a series of several light pulses ranges from 0.1 to 0.2 J. The duration of an individual pulse is from 5 to 70 ns, the interval between pulses is from 15 to 20 μs. The diameter of the laser spot is from 0.3 to 0.5 mm. Laser machine "Yatagan 4" with a pulse duration of 10-7 s., with a radiation wavelength of 1.08 microns and a spot diameter of 50 microns. With such irradiation of the eye, it is not the thermal, but the photochemical and even mechanical action of the laser beam (the appearance of a shock wave) that becomes decisive. The essence of the method is that a laser “shot” of a certain power is directed into the corner of the anterior chamber of the eye and forms a microscopic “channel” for the outflow of fluid and thereby restores the drainage properties of the iris, creating a normal outflow of intraocular fluid. In this case, the laser beam passes freely through the transparent cornea and “explodes” on the surface of the iris. In this case, it is not burning, which leads to inflammatory processes in the iris and rapid elimination of the duct, but punching a hole. The procedure takes approximately 10 to 15 minutes. Usually 15-20 holes (ducts) are punched for the outflow of intraocular fluid.
At the Leningrad Clinic of Eye Diseases of the Military Medical Academy, a group of specialists led by Doctor of Medical Sciences Professor V.V. Volkov used their method of treating dystrophic diseases of the retina and cornea using a low-power laser LG-75, operating in continuous mode. With this treatment, low-power radiation equal to 25 mW acts on the retina of the eye. Moreover, the radiation is scattered. The duration of one irradiation session does not exceed 10 minutes. In 10-15 sessions with intervals between them of one to five days, doctors successfully cure keratitis, inflammation of the cornea and other inflammatory diseases. Treatment regimens were obtained empirically.
In 1983, American ophthalmologist S. Trockel expressed the idea of the possibility of using an ultraviolet excimer laser to correct myopia. In our country, research in this direction was carried out at the Moscow Research Institute of Eye Microsurgery under the leadership of Professor S.N. Fedorov and A. Semenov.
To carry out such operations jointly by the MNTK "Eye Microsurgery" and the Institute general physics a laser installation was created under the leadership of academician A. M. Prokhorov "Profile 500" with a unique optical system that has no analogues in the world. When exposed to the cornea, the possibility of burns is completely eliminated, since heating of the tissue does not exceed 4-8°C. The duration of the operation is 20-70 seconds, depending on the degree of myopia. Since 1993, “Profile 500” has been successfully used in Japan, in Tokyo and Osaka, at the Irkutsk Interregional Laser Center.
Helium-neon laser ophthalmic apparatus MACDEL-08(JSC MAKDEL-Technologies), shown in Figure 11, has a digital control system, a power meter, a fiber-optic radiation supply, and sets of optical and magnetic attachments. The laser device operates from an alternating current network with a frequency of 50 Hz with a rated voltage of 220 V ± 10%. Allows you to set the session time (laser radiation) in the range from 1 to 9999 seconds with an error of no more than 10%. It has a digital display that allows you to initially set the time and control the time until the end of the procedure. If necessary, the session can be terminated early. The device provides frequency modulation of laser radiation from 1 to 5 Hz in steps of 1 Hz, in addition, there is a continuous radiation mode when the frequency is set to 0 Hz.
Figure 20 - Laser ophthalmological device MAKDEL-08
Infrared laser machine MACDEL-09 intended for the correction of accommodative-refractive vision impairment. Treatment consists of performing 10-12 procedures for 3-5 minutes. The results of therapy last for 4-6 months. If accommodation indicators decrease, it is necessary to repeat the course. The process of improving objective vision indicators extends for 30-40 days after the procedures. The average values of the positive part of the relative accommodation steadily increase by 2.6 diopters. and reach the level normal indicators. The maximum increase in reserve is 4.0 diopters, the minimum is 1.0 diopters. Rheocyclographic studies show a steady increase in the volume of circulating blood in the vessels of the ciliary body. The device allows you to set the laser session time from 1 to 9 minutes. The digital display on the control unit allows you to make the initial time setting, as well as control the time until the end of the session. If necessary, the session can be terminated early. At the end of the treatment session, the device emits an audible warning signal. The center-to-center distance regulation system allows you to set the distance between the centers of the channels from 56 to 68 mm. Setting the required center-to-center distance can be done using a ruler on the executive unit, or according to the image of reference LEDs.
Argon laser models ARGUS from Aesculap Meditek (Germany) for ophthalmology, used for photocoagulation of the retina. More than 500 argon lasers are used in Germany alone, all of which operate safely and reliably. ARGUS has convenient controls and is compatible with common models of slit lamps from Zeiss and Haag-Streit. ARGUS is optimally prepared for operation together with an Nd:YAG laser in one workplace.
Although ARGUS is designed as a single unit, the instrument stand and laser unit can be placed next to each other or in different locations and rooms, thanks to a connecting cable up to 10 meters long. The height-adjustable instrument stand provides maximum freedom for the patient and the doctor. Even if the patient is sitting in a wheelchair, treating him is not difficult.
To protect the eyes, ARGUS integrates a controlled low-noise filter for the doctor. The filter is inserted into the laser beam when the foot switch is pressed, i.e. only immediately before the laser flash is fired. Photocells and microprocessors control its correct position. Optimal illumination of the coagulation zone is provided by a special device for guiding the laser beam. The pneumatic micromanipulator allows precise positioning of the beam with one hand.
Technical characteristics of the device:
Laser Type Continuous Argon Ion Laser for Ophthalmic BeO Ceramic Tube
Power on cornea:
on the cornea: 50 mW - 3000 mW for all lines, 50 mW - 1500 mW for 514 nm
with a power supply with limited current consumption:
on the cornea: 50 mW - 2500 mW for all lines, 50 mW - 1000 mW for 514 nm
Argon pilot beam for all lines or 514 nm, maximum 1 mW
Pulse duration 0.02 - 2.0 sec, adjustable in 25 steps or smoothly
Pulse sequence 0.1 - 2.5 sec., with intervals adjustable in 24 steps
Starting a pulse with a foot switch; in pulse sequence mode, the desired series of flashes is activated by pressing the foot switch;
the function is interrupted when the pedal is released
Beam supply via light guide, fiber dia. 50 µm, 4.5 m long, both ends with SMA connector
Remote control options available:
remote control 1: manual adjustment using handwheel;
remote control 2: setting the contact pads of the film keyboard.
General signs: electroluminescent display, power display in digital and analog form, digital display of all other setting parameters, display of operating status (e.g. service recommendations) in clear text
Microprocessor control, control over power, protective filter for the doctor and shutters in 10 millisecond mode
Cooling
air: integrated low-noise fans
water: flow rate from 1 to 4 l/min, at a pressure from 2 to 4 bar and a temperature not higher than 24 °C
Mains power is available in three different units to choose from:
AC current, single-phase with neutral wire 230 V, 32 A, 50/60 Hz
AC current, single-phase with maximum current consumption limited to 25 A
three-phase current, three phases and neutral wire, 400 V, 16 A, 50/60 Hz
Recording of results: printing treatment parameters using an optional printer
Dimensions
device: 95cm x 37cm x 62cm (W x D x H)
table: 93cm x 40cm (W x D)
table height: 70 - 90 cm
"Laser Scalpel" found application in diseases of the digestive system (O.K. Skobelkin), skin plastic surgery and diseases of the biliary tract (A.A. Vishnevsky), in cardiac surgery (A.D. Arapov) and many other areas of surgery.
In surgery, CO2 lasers are used, emitting in the invisible infrared region of the electromagnetic spectrum, which imposes certain conditions during surgery, especially in the internal organs of a person. Due to the invisibility of the laser beam and the difficulty of manipulating it (the surgeon’s hand does not have feedback and does not feel the moment and depth of the dissection), clamps and pointers are used to ensure the accuracy of the cut.
The first attempts to use lasers in surgery were not always successful; nearby organs were injured and the beam burned through tissue. In addition, if handled carelessly, the laser beam could be dangerous for the doctor. But despite these difficulties, laser surgery has progressed. So, in the early 70s, under the leadership of academician B. Petrovsky, Professor Skobelkin, Doctor Brekhov and engineer A. Ivanov began creating a laser scalpel "Scalpel 1"(Figure 12).
Figure 20 - Laser surgical unit “Scalpel-1”
The laser surgical unit “Scalpel 1” is used for operations on the gastrointestinal tract, for stopping bleeding from acute ulcers of the gastrointestinal tract, for skin plastic surgeries, for the treatment of purulent wounds, and for gynecological operations. A continuous-emitting CO2 laser with a power output from the light guide of 20 W was used. The diameter of the laser spot is from 1 to 20 microns.
A diagram of the mechanism of action of CO2 laser light on tissue is presented in Figure 13.
Figure 20 - Diagram of the mechanism of action of CO2 laser light on tissue
Using a laser scalpel, operations are carried out contactlessly, CO2 laser light has antiseptic and antiblastic effects, and a dense coagulation film is formed, which ensures effective hemostasis (the lumens of arterial vessels up to 0.5 mm and venous vessels up to 1 mm in diameter are welded and do not require ligation ligatures), creates a barrier against infectious (including viruses) and toxic agents, while providing highly effective ablastics, stimulates post-traumatic tissue regeneration and prevents scarring (see diagram).
"Lasermed" (Design department instrumentation) is built on the basis of semiconductor lasers emitting at a wavelength of 1.06 microns. The device is characterized by high reliability, small overall dimensions and weight. Radiation is delivered to biological tissue through a laser unit or using a light guide. The main radiation is directed by pilot illumination of a semiconductor laser. Laser hazard class 4 according to GOST R 50723-94, electrical safety class I with protection type B according to GOST R 50267.0-92.
Laser surgical device "Lancet-1"(Figure 14) is a CO2 laser model designed for surgical operations in various areas of medical practice.
Figure 20 - Laser surgical device “Lancet-1”
The device is horizontal in design, portable, has original packaging in the form of a case, and meets the most modern requirements for surgical laser systems both in terms of its technical capabilities and in ensuring optimal working conditions for the surgeon, ease of control and design.
The technical characteristics of the device are given in Table 2.
Table 7 - Technical characteristics of the laser surgical device "Lancet-1"
Radiation wavelength, microns |
|
Output radiation power (adjustable), W |
|
Power in Medipulse mode, W |
|
Diameter of laser beam on tissue (switchable), microns |
|
Guiding the main radiation with a diode laser beam |
2 mW, 635 nm |
Radiation modes (switchable) |
continuous, pulse-periodic, Medipulse |
Radiation exposure time (adjustable), min |
|
Duration of radiation pulse in pulse-periodic mode (adjustable), s |
|
Pause duration between pulses, s |
|
Remote Control |
remote |
Turning on radiation |
foot pedal |
Removal of combustion products |
smoke evacuation system |
Radius of operating space, mm |
|
Cooling system |
autonomous, air-liquid type |
Placement in the operating room |
desktop |
Power supply (AC) |
220 V, 50 Hz, |
Overall dimensions, mm |
|
Weight, kg |
6. Medical laser equipment developed by KBAS
Universal optical attachment ( NOU) to lasers like LGN-111, LG-75-1(Figure 15) is designed to focus laser radiation into the light guide and change the spot diameter when external irradiation.
Figure 20 - Universal optical attachment (OU)
The attachment is used in the treatment of a number of diseases associated with circulatory disorders by inserting a light guide into a vein and irradiating the blood, as well as in the treatment of dermatological and rheumatic diseases. The attachment is easy to use, easily mounted on the laser body, and quickly adjusted to the operating mode. During external irradiation, the spot diameter is changed by moving the condenser lens.
Technical characteristics of the LEU are given in Table 3.
Table 7 - Technical characteristics of LEU
Physiotherapeutic unit "Sprut-1"(Figure 16) is intended for the treatment of a number of diseases in various fields of medicine: traumatology, dermatology, dentistry, orthopedics, reflexology, neuralgia.
Figure 20 - Laser physiotherapy unit “Sprut-1”
Treatment with the Sprut-1 installation ensures the absence of allergic reactions, painlessness and asepticity, and also leads to a significant reduction in treatment time and savings in medicines.
The operating principle is based on the use of the stimulating effect of laser radiation energy with a wavelength of 0.63 microns.
The installation consists of an emitter, the position of which is smoothly adjustable relative to the horizontal plane, a power supply with a counter for the number of starts and a counter for the total operating time of the installation.
The emitter and power supply are mounted on a lightweight mobile stand.
Technical characteristics of the Sprut-1 installation are given in Table 4.
Table 7 - Technical characteristics of the physiotherapeutic installation “Sprut-1”
Laser ophthalmic therapy unit "Lota"(Figure 17) is used in the treatment of erosions and ulcers of a trophic nature, after injuries, burns, keratitis and keratoconjunctivitis, postoperative keratopathies, as well as to accelerate the process of graft engraftment during corneal transplantation.
Figure 20 - Laser ophthalmological therapeutic unit “Lota”
Technical characteristics of the installation are given in Table 5.
Table 7 - Technical characteristics of the “Lota” laser system
Radiation wavelength, microns |
|
Radiation power density in the irradiation plane, W/cm2 |
no more than 5x105 |
Radiation power at the installation output, mW |
|
The nature of power regulation in the specified range |
|
Power consumption, VA |
no more than 15 |
Mean time between failures, hour |
not less than 5000 |
Average resource |
not less than 20000 |
Weight, kg |
Medical laser machine "Almitsin"(Figure 18) is used in therapy, dentistry, phthisiology, pulmonology, dermatology, surgery, gynecology, proctology and urology. Treatment methods: bactericidal effect, stimulation of microcirculation at the source of damage, normalization of immune and biochemical processes, improvement of regeneration, increase in the effectiveness of drug therapy.
Figure 20 - Medical laser device “Almitsin”
Technical characteristics of the installation are given in Table 6.
Table 7 - Technical characteristics of the medical laser system "Almitsin"
Spectral range |
close to UV |
Design |
|
Beam output |
light guide |
Light guide diameter, µm |
|
Light guide length, m |
|
Supply voltage at frequency 50 Hz, V |
|
Energy consumption, W |
no more than 200 |
Control |
automatic |
Irradiation time, min |
no more than 3 |
Dimensions of each block, mm |
|
no more than 40 kg |
Fiber optic "Ariadne-10"(Figure 19) is proposed to replace the low-mobility and inertial mirror-articulated radiation transmission mechanism for surgical installations (Scalpel-1 type) using CO2 lasers.
The main elements of the attachment are: radiation input device and general surgery light guide.
Figure 20 - Fiber optic attachment “Ariadna-10”
The light guide of the attachment works in conjunction with a smoke exhaust device, which makes it possible to simultaneously remove the products of radiation interaction with biological tissues from the surgical space while performing surgical operations.
Thanks to the flexibility of the light guide, the possibilities of using laser surgical systems using CO2 lasers are significantly expanded.
Technical characteristics of the installation are given in Table 7.
Table 7 - Technical characteristics of the fiber optic attachment "Ariadna-10"
The attachment diagram is shown in Figure 20.
Figure 20 - Diagram of the fiber optic attachment “Ariadna-10”
List of sources used
1. Zakharov V.P., Shakhmatov E.V. Laser technology: textbook. allowance. - Samara: Samar Publishing House. state aerospace University, 2006. - 278 p.
2. Handbook of laser technology. Per. from German. M., Energoatomizdat, 1991. - 544 p.
3. Zhukov B.N., Lysov N.A., Bakutsky V.N., Anisimov V.I. Lectures on laser medicine: Textbook. - Samara: Media, 1993. - 52 p.
4. Use of the laser surgical unit “Scalpel-1” for the treatment of dental diseases. - M.: Ministry of Health of the USSR, 1986. - 4 p.
5. Kanyukov V.N., Teregulov N.G., Vinyarsky V.F., Osipov V.V. Development of scientific and technical solutions in medicine: Textbook. - Orenburg: OSU, 2000. - 255 p.