Lasers as a therapeutic tool have been used in medicine since 1961, but there are only a few papers on Dosimetry1. Considering the question how to measure the effective dose for a given medical procedure it is not sufficient to monitor the laser output precisely as a source of electromagnetic radiation but in addition one has to take into account the optical and thermal properties of human tissue as a target for the impinging laser radiation as well as the biological reaction of living tissue. Fig. 1 shows a sketch of the spectral behaviour of human skin. In the UV, the penetration depth turns out to be nearly zero, the maximum is at 780-800 urn and in the mid JR at 10 m the penetration depth becomes shallow again. The penetration depth for most tissue varies from jm in the Uv and mid JR to about one centimeter in the visible red and near JR region. The differentpenetration depth and the different interaction times from picoseconds to minutes give rise to the various effects of laser tissue interaction2. This is quite different from the situation for ionizing radiation.

The iiin reason to use lasers for cutting tissue is the instant generation of a coagulated zone along the incision walls . This zone acts baertota however if it becone-s too thi it leads to undesired scar forxrtion durir the healing process. The thickness of the coagulated zone is strongly dependent on the details of the cutting rrecbanisrn that itself is determined by the laser and material pararreters. We studied the influence of laser penetration depth intensity and focal geoirtry as well as physical tissue properties on the resultir laser incisions . We iide our investigations on a ndel substance in as well as on freshly excis animal dermis . Laser pulses of 250 p. s duration and 4 Hz repetition rate were eniployed . We corrared incisions made with an laser at 2 . 94 imi to incisions from a laser. We studiI cutting for various focusing conditions . We found that often hydrodynaxnic instabilities developed within the crater and also learned how they can be avoided . The extensions of thermal damage zones depend much stronger on focusing geometry arid intensity than on the optical penetration depth of the cutting beam. Tissue material is eated liquefied and partially ejected during laser cutting. We show that the deree of thermal damage originates from the aimunt of hot material that is not ejected out of the crater of incision. Further we that tissue material is elastically displaced during laser cutting and recoils after cuttir back to exactly its initial position. In soft materials usually the incisions close at the upper end of the hole alnxst instantaneously after termination of the laser pulse . The vacancies left behind are filled with hot water vapor that condenses upon cooling leading to a strong suction process . Thus material from the surface can be pulled into the depth of the incision without being biologically deactivated. 1.

Approximate algebraic expressions describing the thresbold fluen ces and depths per pulse are proposed to the laser tissue ablation. Comparison with various experiments sbows that this description holds for homogeneously absorbing soft tissues. I .

Pulsed C:02 1ser emission cn be effectively used for cuttinq driilinq and evaoratino o+ biotissues with low water contentS

To explore the possibility of extracting cataracts percutaneously we have carried out in-vitro studies on ablation of cataractous human eye lenses using a TE-C02 laser of pulse duration 135 nsec FWHM. The threshold flue2ce of ablation is found to be about 5 J/cm and the ablation yield about 0. 5 mg/Jcm which slowly tends to decrease with the laser fluence. Temporal evolution of the ablation shows a sharp spike of about 1 psec FWHM followed by a long ejection pulse of about 30 jjsec FWHM. Compared to the commonly used XeCl excimer laser for phaco-ablation a TE-C02 laser results in a more efficient ablation on an energy basis and does not invol ye the risk of carcinogenesis or cataracts. Thermal damage in the remainder tissue can be comparable at shorter pulse durations of the TE-C02 laser to that of the XeCl excimer laser. 1.

In order to determine the interaction between laser light and biological tissues quantitatively the physical parameters of the biological objects have to be related to the parameters of the laser light. The degree and extent of the effect depend on the one hand on the properties of the tissue which are determined by the structure water content and blood circulation and on the other hand on the geometry of the laser beam and the wavelength. Depending on the duration of the laser irradiation on tissue and on the laser irradiance in surface or volume interaction three types of tissue interactions can be distinguished: photochemical effects photothermal effects and photoionizing effects. With extremely long interaction times and low power densities photo chemical transformation occurs by absorption of light with no primary heating of the tissue. With decreasing interaction time and higher power density the transition to photothermally induced effects begins. The early and main surgical applications for lasers are based on the conversion of laser light into heat. This thermal effect is broadly applied in surgery for tissue removal and tissue coagulation with the sealing of vessels and lymphatics as well as for tissue7weldig. When exceeding a power density of 10 W/cm nonlinear effects result. The high irradiance generates strong electric fields which lead to a dissociation or ionization of the material involved. Thus laser light is converted into kinetic energy. From

The generation of mechanical stresses and sound pulses in water solutions due to the absorbtion of diferent type lasers'' radiation is considered. Optoacoustical concentrator of sound pulses is discussed. I .

Medicine, arid surry in prticu1r, ha'vE rather visib1e and fixed objects and tasks On the hc1e they incILId diagnosis of thE? patological process, division of the tissues, control of tissue mtabo1ism. Each component of mdica1 practice contains in different aspects these general basic Itments EvEn now Iasr technology gives physicians thee opportunity to gain some benefit, in recognizing and measuring living obJects, modulation of metabol ism coagulation and vapor-ation of tissue water

The aim of this paper is to show relationship first, between light parameters and biostimulation (metabolism regulation effect), and second, between physiological conditions of cells at the moment of irradiation and stimulation effects magnitude. These studies have been performed on cellular level, and as a model, a culture of procaryotic cells Escherichia coil WP2 was used. As a criterion for the division rate of E. coil WP2 cells was measured. There is no grounds to believe the existence of a single universal biostimula tion mechanism active on molecular, cellular, and organism levels. On the other hand, undoubtedly there are many connections between mechanisms of light stimulation on different levels. For example, as concerning light stimulation on organism level (i.e., low-power laser therapy), there exist dependences of therapeutic effects on parameters of light (fluence, intensity) (see reviews: Karu, 1990 a, b). As far as mechanism of biostimulation is concerned, we will show in this paper that the stimulation effects are connected with certain chromophores (primary photoacceptors) in a cell.

Biostimulation is discussed from the platform of signal processing. A comprehensive evaluation of the data presented in more than 5000 reports shows that laser radiation has no qualitative properties differing from those of monochromatic noncoherent radiation of the same wavelength and the same environmental parameters. A possible genotoxic action ofvery narrow band radiation is discussed and a triple blind experiment procedure is proposed to investigate this possibility. 1. HISTORICAL

This field report presents and analyzes results on 1 cases of rnusculoskeletal disorders of equine athletes treated either with a Soft Laser 632 device (Worldwide Lasers International Geneva) or with an Omega Biotherapy infrared multiprobe multiwavelength device (Omega Labs London). It proposes a codification of low power laser forms of treatment onthefield and suggests modalities of such treatment(s). The therapeutic effects of low power laser beams as well as their postulated modes of action are discussed. Further a new technique utilizing a low power laser device (Technosynthese AG Zurich) for the accurate rnesurement of the height of ponies and horses is described. After testing in over 500 equines the apparatus and the technique were found accurate with an error factor not exceeding 1. 2 mm (1/20 inch) whereas the ancient ''standard stick'' method was found to produce a constant significant error in all animals measured. MATERIALS AND METHODS Soft Laser 632R device: Portable 25 mW heliumneon laser device emitting a visible red band of 632. 8 nm either through a ''window'' or through an optic fiber probe. Omega Biotherapy device: Portable 50 mW infrared laser device with two probes and a multiprobe emitting four wavelength laser bands. Pony_MetreR: Portable heliumneon device with two incorporated nivels and sliding through a rotating ''head'' placed at the top of a tripod that can move on either the vertical (x) or horizontal y) axis. RESULTS

The results of the investigations of light propagation in the human hard tooth t issues are represented. It is shown that apart from light scattering the novel effect of waveuide light propagat ion from the enamel surface to the tooth cavity is taken place. The trajectories of light flows are the same that the direct ions of enamel prisms and dent inal tubules orientat ions. Anomal optical properties of the tooth are shown to be explained by the waveguide-scattering media model which is developed in this paper.

Using spectral fluorescence analysis the distribution of HpD and Photosun - II has been studied in mice with spontaneous adenocarcinoma of the breast. As a preliminary step the comparative morphological analysis of spontaneous adenocarcinoma has been carried out. It has been shown that photosensitizer distribution nature depends on tumor morphology. The tumor fluorescence contrast has been observed only after HpD administration while Photosun-Il has been found in high blood concentration 24 hours after i. v. administration. 1.

Advantages and fields of application for modern medical laser systems with fiber optic cables optical diagnostics of the irradiated zone and beam parameters optimized for concrete type of operation are considered.

Lasers for medical applications can be classified into five interaction groups (Table 1): - photochemical interaction - thermal interaction/coagulation - cutting / vaporisation - photoablation - electromechanical interaction / disruption Each interaction mechanism has typical interaction times and power levels. Typical laser systems are established within each field. Tissue coagulation is done on the time scale of 0.01 - 10 seconds with continuouswave (cw) lasers. Depending on the penetration depth needed a laser in the green, near infrared or for infrased region in used. For 10.6 jm (CO2 -laser) the penetration depth is so small, that even medium intensities effect vaporisation (Fig. 1).

1. Central Clinical Hospital No 1, the USSR Ministry of Communications, Moscow 2. II Surgery Department, Central Institute for Advanced Medical Training, Moscow 3. Central Clinical Hospital No 4, the USSR Ministry of Communications, Moscow 4. Central Clinical Hospital of the RSFSR Ministry of Health, Moscow 5. General Physics Institute of the USSR Academy of Sciences, Moscow Progress in biliferous system surgery is to a considerable extent associated with realization of endosurgery methods on gallbladder and main biliary tracts. Radical alterations in the treatment tactics and the up-date developments of this trend put forward new technical and methodical tasks. The problem of safe disintegration of gallstones.is one of them. Introduction into clinical practice of endoscopic draining operations on the distal section of hepaticocholedoch eliminating such complications as wedging into it of the stone remains and recurrent lithogenesis, inevitably puts forward the problem of lithotripsy which is often of top priority as determining the radical effect of endosurgical interference.

Stornatologic service is most popular of all kinds of medical aid, since up to 90% of people suffer from caries, parodontosis holds the second place after such a widespread disease as cardiovascular pathology. The treatment of the tooth hard tissue, intervention into pulp and parodontium using conventional methods are accompanied with painfulness and unpleasant sensation. A lack of efficient methods of anesthesia and pulp devitalization, a high percentage of complica tions after pulpitis treatment made it necessary to search for new methods of treatment which exclude these negative aspects. Application of laser radiation may be one of the ways in resolving this problem. Such attempts have been made repeatedly with the development of laser technology.'3 However, not all of them turned out to be successful. The greatest difficulties occurred on surgical intervention into hard tooth tissue. The best results have been so far attained when using pulsed CO2 laser operated at the wavelength A =1O.61um. For instance, at pulse width 1O1us and frequency 10-20 Hz, the tooth channel drilling was efficient at energy density in pulse P . 10 JIcm2. 4'5 The electron-microscopic investigations have proved the tooth microstructure to be preserved for this laser operation mode. The traces of graphitization were observed only in the vicinity of the lateral walls of the channel.

Argon - dye photocoagulator for the microsurgery of the interior structure of the eye is deseribed. The technical specifications are given. Some technical parameters of the argon laser tube are described.

Continual C°2 - and CO- lasers are widely used in surgery for cutting of tissue, stopping of bloodflow by means of vascular coagulation and tissue evaporation. Recently laser units have been made for microsurgery in which laser radiation is directed to an object with the help a of a surgery microscope manipulator. However such a design does not permit to irradiate an object from different angles. A surgent, therefore, has to turn welded blood vessels for example for nearly 360 degrees which is not always possible. The aim of our work was to create a laser instrument without a rigid link with a surgery microscope. A new instrument would enable a surgent to manipulate it as nearly freely as an ordinary surgical instrument. Mirror laser beam transmitting systems which are used now considerably limit a space mobility of existing laser surgical instruments.

A flexible laser-scalpel founded on hollow metallic waveguides have been developed. The laser-scalpel demonstrated high transmissi on on bends and twists. We have proposed a model of crater formation by continuous laser radiation, that allows to optimize the choice of the laser-scalpel focusing elements.

Perspectives to develop a new line of compact simple-to-use reliable and low-cost high- power laser devices on the base of activated glass fibers will discuss. They may find wide applications in multipurpose diagnostic therapeutic and surgical complexes also as in a lot of special medical devices. . 1.

This research is dedicated to spectral analysis methods of i&raction of high enerciy laser radiation with biological objects like humain vessel affected by atheroscie rosis (investigated immediately after its surgical removal) and gallstones of diffe rent kinds. In our work ie used laser sources jithA3fl8 nm (Eximer laser Xe-Cl), A532 nm andlO64 nm ( YAG:Nd3).

In this paper we investigated the spectral-luminescence characteristics of human intracavital organs. We observed the specimens of lung and stomach malignant tumors directly after ektomy and tumors of larinx and stomach in vivo. In our investigations we proposed the existance of difference between luminescence characteristics of normal and malignant tissues.

Cervicoocipital headache observed in 112 patient were treated, half of them with acupuncture, and other 50% with He-e laser (con tinuous emission- lo mW, 633nm: IEC). With this treatment was also combined an exercise program ne cesary for the mobilisation of functionaly blocked vertebral segment.

It is shown under in-vitro conditions that lasers can be used percutaneously to occlude the fallopian tube ostium by coagulation necrosis for female sterilization. The maximum depth of coagulation obtained without charring is about 3 mm with the Nd:YAG laser radiation at 6.5 W of power and 50 sec. interaction time and about 1 m m with the cw-C °2 laser radiation at 1 W and 20 sec. In general the surface of the coagulated tubal tissue gets carbonized at much lower powers of the C °2 laser than that of the Nd:YAG laser. Although use of a sapphire cold contact probe with the Nd:YAG laser delivery fibre makes the operation snore convenient but it is found to be very lossy for the laser radiation. Recanalization of the laser occluded fallopian tubes can be done using laser induced vapourization. Threshold fluence for vapourization of the coa gulated tubal tissue is found to be about 2 K]/cm2 for the CO2 laser and 27 KJ/cm2 for the Nd:Y A C laser and these values are found to increase on increasing the interaction time. At 4W of power, the cw-C °2 laser beam focussed to a spot diameter of about 300 jm was satisfactorily used to recanalize the occluded fallopian tubes.

Surgeon's hand, guiding a light ray, Laser, instead of holding a common lancet, for dissecting delicately tissues with simultaneous haemostasis on small vessels, represents one of the most interesting expressions of modern technology applied to surgery. The use of Laser in surgery dates back to 25 years ago. Its medical applications, however, are a little more recent. The word Laser comes from "Light Amplification by Stimulated Emission of Radiation". It • is known that any material, which has been stimulated, emits energy of excitation through the so called spontaneous Energy. This means irradiation of "quanta" of electro-magnetic energy untidily in space and time (so called "incoherent Emission"). A Laser source, conversely, emits "coherent" electro-magnetic radiations (so called "stimulated Emission") , whose characteristics consist in: monochromaticity,directional ity, coherence and brilliance.

Fine structural alteratious produced iediate1y after irradiation with either XeC1 excimer or Nd:Y.AG laser have been studied in rat liver samples processed histochemically for glucose-6-phosphatase (GP) activity, a marker enzyme for the endoplasmic reticulum (ER) of hepatocytes. General vesiculation of ER along with moderate inactivation of GP was apparent following excimer lazing which contrasted with better structural but poorer enzymatic preservation of ER in the hepatocytes irradiated with Nd:YAG laser. c'i the basis of this and our recent study. (A. Nevorotin, M. Kul 1 . 1989. Arch. Pathol . v. 51, N 7, pp. 63'TO ) a conclus ion is drawn on a potential surgical advantage of excimer laser over its Nd:YAG counterpart due presumably to lesser extent of cellular and macromolecular damage implicative in the process of healing of laser-inflicted lesions. A mechanism of ER vesiculation is considered in the iignt of probable dynamic impact transferred to the ER membranes by excimer irradiation by analogy with other nign energy mechanical forces (e.g. nign gravitation or ultrasonication) known to interfere with membrane structural organization.

A total of 14 patients who had failed all conventional modalities for cancer of the vulva vagina and perianal area were treated with photodynamic therapy PDT. The affinity of porphyrins to neopJ. astic tissue enables treatment to be concentrated at the tumor site. An Aurora FL Argon pumped dye laser (Cooper LaserSonics Inc. USA) was used to pump dicyanomethylene dye as an activating source for a red light at a wavelength of 630 nm. The combination of a tumor localizing photosensitizer and photoactivating red light produces a photo chemical reaction that is destructive to the cancerous lesion. The treatment time varied between 10-30 minutes. Vulvar sites ranged from 9-38 cm2. Delivered light doses were from 50-125 J/cm2 and power density from 50 to 75 mW/cm2. A complete response was obtained in 80 of the sites treated as evidenced by negative biopsies taken at 3 months post treatment. Adverse reactions to PDT included a transient cutaneous photosensitivity due to retention of the photosensitizers in the skin. This reaction usually persisted from 45-60 days. 1.

Laser Doppler velocimetry (LDV) and back scattering nephelometry techniques are used to study the dynamic properties of blood. These are determined significantly by the properties and the behavior of the erythrocytes in shear flow and are particularly manifested by the shapes of the velocity and of the concentration profiles of the directional streaming of blood in thin capillaries. These profiles are known to differ from those of simple homogeneous fluids. The potentialities of LDV are discussed to obtain the velocity profiles for the flow of the whole blood and of the erythrocytes suspensions at different hematocrites through horizontally positioned thin glass capillaries from 100 to 400 im in diameter. Possible artifacts are demonstrated inherent to LDV measurements of the velocity profiles due to the multiple scattering of laser light unavoidable in such thick layers of blood. Significant difference is experimentally obtained between the Brownian diffusion coefficient of the erythrocytes in suspension at the state of rest and their shear diffusion coefficient in the Couette flow. 1.

It is known, that the application of chromium ions for the effective sensitized luminescence of rare-earth ions in crystals with garnet structure has allowed to solve a number of problems in physics and technology of solid-state lasers. So, for example, the efficiency of pulsed neodymium lasers has been increased 2-3 times . and effective lasing on both erbium2 (=2.79 pin) and golmium (A,=2.088 pin) transitions with low probability was obtained. The possibility of sensitization has a principle character for erbium and golmium ions due to rather low pump efficiency into its absorption bands. It should be mentioned that the interest to 2-pam and 3-pin lasers especially increased whn5 the possibility of their medical application was demonstrated

Overview of the development in crystalline infrared fibers and is made for the practical use of the last results in applications of the cables based on these fibers. 1. INTRC)DUCTIOL Flexible cables for IR laser power delivery can be based on fluoride or chalcogenide glass fibers on crystalline fibers. The properties of crystalline fibers and hollow waveguides which are more suitable for power delivery of erbium CO- and C02-lasers are discussed from the point of view of their application in medicine. 2. CHOICE OF STARTING CRYSIALL The proper choice of starting crystals is based on the estimation of their minimum of intrinsic optical losses (Fig. 1) along with their fitness to fiber fabrication and a set of other substantial physical parameters (Table 1). Looking for non-fragile non-toxic and non-hygroscopic material we have to find the AgHal and A12O3 as the best candidates for crystalline fibers. Arid we have to note that the value of absorption in the purest samples is much higher than intrinsic level due to the presence of absorbing impurities. Hence the technology of more pure crystals needs in further development. The lowest absorption at 10. 6 im for AgHal were measured by laser calorimetry for the samples of crystals of solid solutions O. 25AgCl : O. 75AgBr (KRS-13) and O. 5OAgC1 : O. 5OAgBr - 6-1O cm (26 dB/m). 3. TECHNOLOGY OF FIBER FABRICATIQL There are some known

A great variety of new chemical compounds, potential photosensitizers, require testing their photodynamic activity ( PDA ) and tumor localizing capacity. Comparative analysis of phthalocyanines according to qiven criteria seems to be urgent, phthalocyanines being most prospective photosensitizers for photodynamic therapy ( PDT ) of malignant tumors ( 1, 2 ). The absence of scientificly based correlations between the compound chemical structure and its photodynamic activity puts forward the task of initial screening estimation of photosensitizing and tumor localizing properties of chemical compounds.