Laser radiation in medicine is a forced or stimulated wave of the optical range with a length from 10 nm to 1000 microns (1 micron = 1000 nm).

Laser radiation has:
- coherence - the coordinated flow of several wave processes one frequency;
- monochromatic - one wavelength;
- polarization - orderliness of the orientation of the tension vector electromagnetic field waves in a plane perpendicular to its propagation.

Physical and physiological effects laser radiation

Laser radiation (LR) has photobiological activity. Biophysical and biochemical reactions of tissues to laser radiation are different and depend on the range, wavelength and photon energy of the radiation:

IR radiation (1000 µm - 760 nm, photon energy 1-1.5 EV) penetrates to a depth of 40-70 mm, causing oscillatory processes- thermal effect;
- visible radiation(760-400 nm, photon energy 2.0-3.1 EV) penetrates to a depth of 0.5-25 mm, causes dissociation of molecules and activation of photochemical reactions;
- UV radiation (300-100 nm, photon energy 3.2-12.4 EV) penetrates to a depth of 0.1-0.2 mm, causes dissociation and ionization of molecules - a photochemical effect.

The physiological effect of low-intensity laser radiation (LILR) is realized through the nervous and humoral pathways:

Changes in tissues, biophysical and chemical processes;
- changes in metabolic processes;
- change in metabolism (bioactivation);
- morphological and functional changes in nervous tissue;
- stimulation of the cardiovascular system;
- stimulation of microcirculation;
- increasing the biological activity of cellular and tissue elements of the skin, activates intracellular processes in muscles, redox processes, and the formation of myofibrils;
- increases the body's resistance.

High intensity laser radiation (10.6 and 9.6 µm) causes:

Thermal tissue burn;
- coagulation of biological tissues;
- charring, combustion, evaporation.

Therapeutic effect of low-intensity laser (LILI)

Anti-inflammatory, reducing tissue swelling;
- analgesic;
- stimulation of reparative processes;
- reflexogenic effect - stimulation of physiological functions;
- generalized effect - stimulation of the immune response.

Therapeutic effect of high-intensity laser radiation

Antiseptic effect, formation of a coagulation film, protective barrier against toxic agents;
- cutting fabrics (laser scalpel);
- welding of metal prostheses, orthodontic devices.

LILI indications

Acute and chronic inflammatory processes;
- soft tissue injury;
- burns and frostbite;
- skin diseases;
- peripheral diseases nervous system;
- diseases of the musculoskeletal system;
- cardiovascular diseases;
- respiratory diseases;
- diseases gastrointestinal tract;
- diseases of the genitourinary system;
- diseases of the ear, nose and throat;
- disorders of the immune status.

Indications for laser radiation in dentistry

Diseases of the oral mucosa;
- periodontal diseases;
- non-carious lesions of hard dental tissues and caries;
- pulpitis, periodontitis;
- inflammatory process and trauma of the maxillofacial area;
- TMJ diseases;
- facial pain.

Contraindications

Tumors are benign and malignant;
- pregnancy up to 3 months;
- thyrotoxicosis, type 1 diabetes, blood diseases, insufficiency of respiratory, kidney, liver, and circulatory function;
- feverish conditions;
- mental illness;
- presence of an implanted pacemaker;
- convulsive conditions;
- individual intolerance factor.

Equipment

Lasers are a technical device that emits radiation in a narrow optical range. Modern lasers are classified:

By active substance (source of induced radiation) - solid-state, liquid, gas and semiconductor;
- by wavelength and radiation - infrared, visible and ultraviolet;
- according to radiation intensity - low-intensity and high-intensity;
- according to the radiation generation mode - pulsed and continuous.

The devices are equipped with emitting heads and specialized attachments - dental, mirror, acupuncture, magnetic, etc., ensuring the effectiveness of the treatment. The combined use of laser radiation and a constant magnetic field enhances the therapeutic effect. Mainly three types of laser therapeutic equipment are commercially produced:

1) based on helium-neon lasers operating in continuous radiation mode with a wavelength of 0.63 microns and an output power of 1-200 mW:

ULF-01, “Yagoda”
- AFL-1, AFL-2
- SHUTTLE-1
- ALTM-01
- FALM-1
- "Platan-M1"
- "Atoll"
- ALOC-1 - laser blood irradiation device

2) based on semiconductor lasers operating in a continuous mode of generating radiation with a wavelength of 0.67-1.3 microns and an output power of 1-50 mW:

ALTP-1, ALTP-2
- "Izel"
- "Mazik"
- "Vita"
- "Bell"

3) based on semiconductor lasers operating in a pulsed mode generating radiation with a wavelength of 0.8-0.9 microns, pulse power 2-15 W:

- "Pattern", "Pattern-2K"
- "Lazurit-ZM"
- "Luzar-MP"
- "Nega"
- "Azor-2K"
- "Effect"

Devices for magnetic laser therapy:

- "Mlada"
- AMLT-01
- "Svetoch-1"
- "Azure"
- "Erga"
- MILTA - magnetic infrared

Technology and methodology of laser radiation

Exposure to radiation is carried out on the lesion or organ, segmental-metameric zone (cutaneously), biologically active point. In the treatment of deep caries and pulpitis biological method irradiation is carried out in the area of ​​the bottom of the carious cavity and the neck of the tooth; periodontitis - a light guide is inserted into the root canal, previously mechanically and medicinally treated, and advanced to the apex of the tooth root.

The laser irradiation technique is stable, stable-scanning or scanning, contact or remote.

Dosing

Responses to LI depend on dosing parameters:

Wavelength;
- methodology;
- operating mode - continuous or pulsed;
- intensity, power density (PM): low-intensity LR - soft (1-2 mW) is used to influence reflexogenic zones; medium (2-30 mW) and hard (30-500 mW) - on the area of ​​the pathological focus;
- time of exposure to one field - 1-5 minutes, total time no more than 15 minutes. daily or every other day;
- a course of treatment of 3-10 procedures, repeated after 1-2 months.

Safety precautions

The eyes of the doctor and the patient are protected with glasses SZS-22, SZO-33;
- you cannot look at the radiation source;
- the walls of the office should be matte;
- press the “start” button after installing the emitter on the pathological focus.

IN modern medicine Many achievements of science and technology are used. They help in the timely diagnosis of diseases and contribute to their successful therapy. Doctors actively use the capabilities of laser radiation in their work. Depending on the wavelength, it can have different effects on body tissues. Therefore, scientists have invented many medical multifunctional devices that are widely used in clinical practice. Let's discuss the use of lasers and radiation in medicine in a little more detail.

Laser medicine is developing in three main areas: surgery, therapy and diagnostics. The effect of laser radiation on tissue is determined by the radiation range, wavelength and photon energy of the emitter. In general, all types of laser effects in medicine on the body can be divided into two groups

Low-intensity laser radiation;
- high-intensity laser radiation.

How does low-intensity laser radiation affect the body?

Exposure to such a laser can cause changes in biophysical and chemical processes in the tissues of the body. Also, such therapy leads to changes in metabolism (metabolic processes) and its bioactivation. The effect of low-intensity laser causes morphological and functional changes in nerve tissue.

This effect also stimulates the cardiovascular system and microcirculation.
Another low-intensity laser increases the biological activity of cellular and tissue elements of the skin, leading to the activation of intracellular processes in the muscles. Its use allows you to start redox processes.
Among other things, this method of influence has a positive effect on the overall stability of the body.

What therapeutic effect is achieved by using low-intensity laser radiation?

This method of therapy helps eliminate inflammation, reduce swelling, eliminate pain and activate regeneration processes. In addition, it stimulates physiological functions and immune response.

In what cases can doctors use low-intensity laser radiation?

This method of exposure is indicated for patients with acute and chronic inflammatory processes of various localizations, soft tissue injuries, burns, frostbite and skin ailments. It makes sense to use it for ailments of the peripheral nervous system, diseases of the musculoskeletal system and for many diseases of the heart and blood vessels.

Low-intensity laser radiation is also used in the treatment of the respiratory system, digestive tract, genitourinary system, ENT diseases and disorders of the immune status.

This method of therapy is widely used in dentistry: for the correction of diseases of the mucous membranes oral cavity, periodontal diseases and TMJ (temporomandibular joint).

In addition, this laser treats non-carious lesions that have arisen in the hard tissues of teeth, caries, pulpitis and periodontitis, facial pain, inflammatory lesions and injuries of the maxillofacial area.

Application of high-intensity laser radiation in medicine

High-intensity laser radiation is most often used in surgery, and in various areas. After all, the influence of high-intensity laser radiation helps to cut tissue (acts like a laser scalpel). Sometimes it is used to achieve an antiseptic effect, to form a coagulation film and to form a protective barrier from aggressive influences. In addition, such a laser can be used for welding metal prostheses and various orthodontic devices.

How does high-intensity laser radiation affect the body?

This method of exposure causes thermal burns of tissues or leads to their coagulation. It causes evaporation, combustion or charring of the affected areas.

When high intensity laser light is used

This method of influencing the body is widely used when performing a variety of surgical interventions in the field of urology, gynecology, ophthalmology, otolaryngology, orthopedics, neurosurgery, etc.

At the same time, laser surgery has a lot of advantages:

Virtually bloodless operations;
- maximum asepticity (sterility);
- minimum postoperative complications;
- minimum impact on neighboring tissues;
- short postoperative period;
- high precision;
- reducing the likelihood of scar formation.

Laser diagnostics

This diagnostic method is progressive and evolving. It allows you to identify many serious diseases at an early stage of development. There is evidence that laser diagnostics helps in identifying cancer of the skin, bone tissue and internal organs. It is used in ophthalmology to detect cataracts and determine its stage. In addition, this research method is practiced by hematologists - in order to study qualitative and quantitative changes blood cells.

The laser effectively determines the boundaries of healthy and pathological tissues; it can be used in combination with endoscopic equipment.

Use of radiation in other medicine

Doctors widely use different kinds radiation in therapy, diagnosis and prevention different states. To learn about the use of radiation, simply follow the links of interest:

X-rays in medicine
- radio waves
- thermal and ionizing rays
- ultraviolet radiation in medicine
- infrared radiation in medicine

Word LASER (Light Amplification by the Stimulated Emission) is translated from English as Amplifying Light by Stimulating Radiation. The very action of the laser was described by Einstein back in 1917, but the first working laser was built only 43 years later by Theodor Maiman, who worked at Hugres Aircraft. To produce millisecond pulses of laser radiation, he used an artificial ruby ​​crystal as an active medium. The wavelength of that laser was 694 nm. After some time, a laser with a wavelength of 1060 nm was tried, which is the near-IR region of the spectrum. The active medium in this laser was glass rods doped with neodymium.

But practical application At that time there was no laser. Leading physicists looked for its purpose in various fields of human activity. First experimental experiments with lasers in medicine were not entirely successful. Laser radiation at those waves was quite poorly absorbed; it was not yet possible to accurately control the power. However, in the 60s, the red ruby ​​laser showed good results in ophthalmology.

History of the use of lasers in medicine

In 1964, the argon ion laser was developed and tested. It was a continuous wave laser with a blue-green spectrum and a wavelength of 488 nm. This is a gas laser and it was easier to control its power. Hemoglobin absorbed its radiation well. Later a short time Laser systems based on argon lasers began to appear, which helped in the treatment of retinal diseases.

In the same year 64, the Bell Laboratory developed a laser based on yttrium aluminum garnet doped with neodymium () and. CO2 is a gas laser whose radiation is continuous, with a wavelength of 1060 nm. Water absorbs its radiation very well. And since soft fabrics In humans, they mainly consist of water, then the CO2 laser has become a good alternative to a conventional scalpel. By using this laser to cut tissue, blood loss is minimized. In the 70s, carbon dioxide lasers found widespread use in institutional hospitals in the United States. Scope of application at that time for laser scalpels: gynecology and otolaryngology.

1969 was the year the first pulsed dye laser was developed, and already in 1975 the first excimer laser. Since that time, the laser began to be actively used and introduced into various areas activities.

Lasers began to become widespread in medicine in the 80s in hospitals and clinics in the United States. For the most part, carbon dioxide and argon lasers were used at that time and they were used in surgery and ophthalmology. One of the disadvantages of lasers of that time is that they had constant continuous radiation, which excluded the possibility of more precise work, which led to thermal damage to the tissue around the treated area. The successful use of laser technologies at that time required enormous work experience.

The next step in the development of laser technologies for medicine was the invention of the pulsed laser. This laser made it possible to act exclusively on the problem area, without damaging surrounding tissue. And in the 80s the first ones appeared. This marked the beginning of the use of lasers in cosmetology. Such laser systems could remove capillary hemangiomas and birthmarks. A little later, capable lasers appeared. These were Q-switched lasers (Q-switched lser).

In the early 90s, scanning technologies were developed and introduced. The accuracy of laser processing was now computer controlled and it became possible to carry out laser skin resurfacing (), which significantly increased the popularity of and.

Today, the scope of lasers in medicine is very wide. These are surgery, ophthalmology, dentistry, neurosurgery, cosmetology, urology, gynecology, cardiology, etc. You can imagine that once a laser was only a good alternative to a scalpel, but today it can be used to remove cancer cells and perform very precise operations on various organs, diagnose serious illnesses in the earliest stages, such as cancer. Now laser technologies in medicine are moving towards the development of combined treatment methods, when, along with laser therapy Physiotherapy, medications, and ultrasound are used. For example, in the treatment of purulent diseases, a set of measures has been developed, which includes laser treatment, the use of antioxidants and various biologically active materials.

Laser technology and medicine must go hand in hand into the future. Even today latest developments in laser medicine they help in removing cancerous tumors, are used in body correction in cosmetology and vision correction in ophthalmology. Minimally invasive surgery, when very complex operations are performed using a laser.

Additional Information:

INTRODUCTION

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, with for a long time surgeons 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 was designed, operating using high-frequency currents. This device, in more advanced versions, is currently used quite widely by surgeons. 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 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 (CO 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.

LASERS AND THEIR APPLICATION IN MEDICINE

Despite general nature 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 amplification and generation techniques electromagnetic vibrations 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 unique properties 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 (convert a helium-neon mixture 3 into active state) into laser radiation and contains an optical resonator, which is general case a system of carefully manufactured reflecting, refractive and focusing elements, in the internal space of which a certain type of electromagnetic oscillations of the optical range is excited and maintained. The optical resonator must have minimal losses in the working part of the spectrum, high accuracy manufacturing of units 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 phase, so we can talk about coherent amplification 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 them forced transitions to a lower level with the emission of quanta of induced (stimulated) radiation, which 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 сред интенсивность его возрастает, имеет место явление, обратное поглощению, т. е. усиление света. Это означает, что в законе Бугера kX < 0, поэтому population inversion corresponds to the environment with negative indicator absorption.

A population inversion state can be created by selecting particles with lower energy or by specially exciting particles, for example with light or 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 in 1955 independently by Soviet scientists N. G. Basoi and A. M. Prokhorov and American scientists - C. Townes and others. Since the operation of this device was based on stimulated emission ammonia molecules, the generator was called molecular.

In 1960 the first quantum generator visible range of radiation - 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 the population inversion is reported different ways: excitation by very intense light - "optical pumping", by electric gas discharge, in semiconductor lasers - electric shock. 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 pulsed light sources high power. 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). Inner surface aluminum reflector is well 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 greatest development and comes out through a translucent mirror. This laser operates in pulsed mode.

Along with a ruby ​​laser operating according to a three-level scheme, wide use obtained four-level laser circuits using ions of rare earth elements (neodymium, samarium, etc.) embedded in a crystalline or glass matrix (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, in shown energy levels 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. In case of electrical discharge electronic shock Helium atoms are excited 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.

Main structural element 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 gas discharge and excitation of 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 continuous action.

The resonator mirrors are made with multilayer coatings, and due to interference, the necessary reflection coefficient is created for given length waves. 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 allow holographic formation three-dimensional image the inner 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 when irradiating 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, culminating 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, visible light nucleic acids They don't absorb at all. However, exposure to high-intensity laser radiation around 532 nm transforms DNA into an electronically excited state due to the summation of the energy of two photons (Fig. 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 CO 2 gas 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, part 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 CO 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 above), 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 forces are generated. shock waves. 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.

laser eye medicine vision

Lasers used in medicine

From a practical point of view, especially for use in medicine, lasers are classified according to the type of active material, the method of power supply, the wavelength and power of the generated radiation.

The active medium can be a gas, liquid or solid. The forms of the active medium can also be different. Most often, gas lasers use glass or metal cylinders filled with one or more gases. The situation is approximately the same with liquid active media, although rectangular cuvettes made of glass or quartz are often found. Liquid lasers are lasers in which the active medium is solutions of certain organic dye compounds in a liquid solvent (water, ethyl or methyl alcohol, etc.).

In gas lasers, the active medium is various gases, their mixtures or metal pairs. These lasers are divided into gas-discharge, gas-dynamic and chemical. In gas-discharge lasers, excitation is carried out by an electric discharge in a gas, in gas-dynamic lasers it is used fast cooling upon expansion of preheated gas mixture, and in chemical - the active medium is excited due to the energy released when chemical reactions environmental components. The spectral range of gas lasers is much wider than that of all other types of lasers. It covers the region from 150 nm to 600 µm.

These lasers have high stability of radiation parameters compared to other types of lasers.

Solid state lasers have an active medium in the form of a cylindrical or rectangular rod. Such a rod is most often a special synthetic crystal, for example ruby, alexandrite, garnet or glass with impurities of the corresponding element, for example erbium, holmium, neodymium. The first working laser worked on a ruby ​​crystal.

Semiconductors are also a type of solid-state active material. IN Lately Due to its small size and cost-effectiveness, the semiconductor industry is developing very rapidly. Therefore, semiconductor lasers are classified as a separate group.

So, according to the type of active material, they distinguish following types lasers:

Gas;

Liquid;

On a solid body (solid-state);

Semiconductor.

The type of active material determines the wavelength of the radiation generated. Different chemical elements in different matrices make it possible to identify more than 6,000 types of lasers today. They generate radiation from the region of the so-called vacuum ultraviolet (157 nm), including the visible region (385-760 nm), to the far infrared (> 300 µm) range. Increasingly, the concept of "laser", initially given to visible area spectrum, is also transferred to other regions of the spectrum.

Table 1 - lasers used in medicine.

Laser type	Physical state of the active substance	Wavelength, nm	Emission range
			Infrared
YAG:Er YSGG:Er YAG:Ho YAG:Nd	Solid	2940 2790 2140 1064/1320	Infrared
Semiconductor, such as gallium arsenide	Solid (semiconductor)		From visible to infrared
Ruby	Solid
Helium-neon (He-Ne)			Green, bright red, infrared
On dyes	Liquid	350-950 (tunable)	Ultraviolet - infrared
On a steam of gold
On copper vapor			Green yellow
Argon			Blue, green
Excimer: ArF KrF XeCI XeF			Ultraviolet

For example, for radiation of shorter wavelengths than infrared, the concept of “X-ray lasers” is used, and for radiation of longer wavelengths than ultraviolet, the concept of “lasers generating millimeter waves” is used.

Gas lasers use gas or a mixture of gases in a tube. Most gas lasers use a mixture of helium and neon (HeNe), with a primary output signal of 632.8 nm (nm = 10~9 m) visible red. This laser was first developed in 1961 and became the forerunner of a whole family of gas lasers. All gas lasers are quite similar in design and properties.

For example, a CO2 gas laser emits a wavelength of 10.6 microns in the far infrared region of the spectrum. Argon and krypton gas lasers operate at multiple frequencies, emitting predominantly in the visible part of the spectrum. The main wavelengths of argon laser radiation are 488 and 514 nm.

Solid-state lasers use laser material distributed in a solid matrix. One example is the neodymium (Kyo) laser. The term YAG is an abbreviation for the crystal -- yttrium aluminum garnet -- which serves as a carrier for neodymium ions. This laser emits infrared ray with a wavelength of 1.064 µm. Auxiliary devices, which can be either internal or external to the resonator, can be used to convert the output beam into the visible or ultraviolet range. Various crystals with different concentrations of activator ions can be used as laser media: erbium (Er3+), holmium (Ho3+), thulium (Tm3+).

From this classification, we will select the lasers that are most suitable and safe for medical use. To the more famous gas lasers used in dentistry include CO2 lasers, He-Ne lasers (helium-neon lasers). Gas excimer and argon lasers are also of interest. Of the solid-state lasers, the most popular in medicine is the YAG:Er laser, which has erbium active centers in the crystal. More and more people are turning to YAG:Ho lasers (with holmium centers). Used for diagnostic and therapeutic use large group both gas and semiconductor lasers. Currently, more than 200 types of semiconductor materials are used as active media in laser production.

Table 2 - characteristics of various lasers.

Lasers can be classified by type of power supply and mode of operation. Here, devices of continuous or pulse action are distinguished. A continuous wave laser produces radiation whose output power is measured in watts or milliwatts.

At the same time, the degree energy impact on biological tissue is characterized by:

Power density is the ratio of the radiation power to the cross-sectional area of ​​the laser beam p = P/s].

Units of measurement in laser medicine - [W/cm 2 ], [mW/cm 2 ];

Radiation dose P, equal to the ratio of the product of radiation power [P and irradiation time to the cross-sectional area of ​​the laser beam. Expressed in [W * s/cm2];

Energy [E= Рt] is the product of power and time. Units of measurement are [J], i.e. [W s].

In terms of radiant power (continuous or average) medical lasers are divided into:

Low power lasers: from 1 to 5 mW;

Medium power lasers: from 6 to 500 mW;

High power lasers (high intensity): more than 500 mW. Lasers of low and medium power belong to the group of so-called biostimulating lasers (low-intensity). Biostimulating lasers are finding increasing therapeutic and diagnostic use in experimental and clinical medicine.

From the point of view of operating mode, lasers are divided into:

Continuous radiation mode (wave gas lasers);

Mixed radiation mode (solid-state and semiconductor lasers);

Q-switched mode (possible for all types of lasers).