Tissue optical properties are determined by an interpretation of pressure transients generated by irradiation with pulsed laser light. These pressure signals are detected using piezoelectric transducers. The signals are influenced by numerous processes during generation, propagation and detection. To study each process in particular, specific experiments were performed using biological tissue in vitro as well as different substances with various absorption and scattering properties. Especially acoustical diffraction effects cause a strong distortion of the shape and spatial oscillations in the amplitude of the transients. These phenomenons were investigated experimentally and verified theoretically.

The knowledge of laser tissue interaction, the light propagation in tissue and thus its optical properties are of fundamental importance for both laser treatment and diagnostics. We use the method of pulsed photothermal radiometry (PPTR) to evaluate optical or thermal properties of tissue-like phantoms. Because its a non-destructive and non-contact technique its a promising tool for tissue optics in vivo. As phantoms we used gelatine of known optical properties with ink added as absorber. Once the thermal features are known, one can determine the optical properties of the sample and vice versa. PPTR investigations of absorption coefficients were compared to other methods such as time resolved stress detection and optical transmission measurements. PPTR is a suitable tool to perform spectroscopy under conditions of high pressure and/or temperature and can therefore be used to investigate the ablation process.

Although the light distribution during Holmium laser ablation of biological tissue is dominated by absorption like in homogeneous optically uniform media, indications exist that light scattering and thermal lensing also have considerable influence on the light distribution in tissue. These mechanisms influence the ablation threshold and the lateral extent of thermally altered tissue. With a fast temperature measurement technique we are able to measure the spatial beam profile before and after traversing a water layer or a tissue sample of defined thickness. the experiments were done with a free running Ho:YAG laser. The radiation was delivered through a single mode fiber in order to receive a well defined and reproducible laser beam. First results show a broadening of the laser beam after penetration of the sample relative to the incident beam, indicating light scattering and thermal lensing.

Changes of coefficients of scattering ((mu) _s), absorption ((mu) _a) and average cosine of scattering (g) depending on shear rate of moving whole blood are described. The most interesting result is observed nonlinear dependence between absorption coefficient and shear rate of moving blood with maximum of (mu) _a at 135 s^-1 which is close connected with erythrocytes orientation and deformation in the cuvette. Phenomenon takes place for 488 and 587 nm within blood layer thickness form 100 to 200 micrometers . Theoretical analysis for angular dependence of coefficient of absorption whole blood from erythrocyte orientation and is presented.

Reduction of oxyhemoglobin concentration during laser irradiation of whole blood with the photosensitizer has been investigated in vitro in real time. Described method of optical investigation of whole blood in vitro could be considered as a good model for fast evaluation of 'dose- responsible' dependence for different kind of oxygen dependent photosensitizers.

Changes. of coefficients of scattering (ts), absorption (j.ta) and average cosine of scattering (g: depending on shear rate of moving whole blood are described. The most interesting result is observed nonlinear dependence between absorption coefficient and shear rate of moving blood with maximum of .ta at 1 35 s' which is close connected with erythrocytes orientation and deformation in the cuvette. Phenomenon takes place for 488 and 587 nm within blood layer thickness from 100 to 200 m. Theoretical analysis for angular dependence of coefficient of absorption whole blood from erythrocyte orientation and is presente4.

A Monte Carlo model has been developed to simulate the fluence distribution in a fully cylindrical geometry, when a finite linear light source is placed on the axis of a hollow organ during PDT treatment. Height and radius of the cavity, scattering and absorption coefficients, anisotropy factor (g), refractive index of medium and cavity are required as input by the MC code. Data obtained from this model were subsequently compared with experimental results using a tissue simulating phantom. An aqueous solution of Intralipid-10 percent and black ink were used to simulate optical properties. A helium-neon laser, coupled to a cylindrical diffuser was employed as light source. A good agreement between the MC simulations and experimental measurements was found.

In the previous paper we have proposed a new mathematical model for local thermal coagulation due to laser light absorption and the corresponding necrosis growth. The classic bioheat equation does not hold on small spacial scales on which the fraction of undamaged tissue varies substantially. Therefore we use the free boundary approach regarding the region of partially damaged tissue as an infinitely thin layer. In order to complete the free boundary approach certain conditions should be imposed on the temperature distribution at this interface. Previously we have assumed that the coagulation occurs when the temperature at the necrosis interface exceeds a certain threshold value. This approximation, however can lead to a wrong prediction for treatment of long duration. In the present work we generalize this model which no longer considers the interface temperature fixed and is based on the relation between the interface velocity and the boundary values of temperature distribution. It is shown that this model describes adequately the necrosis growth also in the treatment course of long duration.

Physical model of a biological tissue for comparison with earlier created mathematical model of a biological tissue and researches of distribution photosensitizer in a depth was created and investigated. Mathematical model is based on granulated representation of optical medium. The model of a biological tissue was created on the basis of enough thin layers of a special material. For fluorescence excitation laser sources with a various wavelength were used. For investigation of scattering and fluorescent signal laser- fiber spectrum-analyzer LESA-5 was applied. Water solution of aluminum phthalocyanine and oil solution of zinc phthalocyanine were used for receiving of fluorescent signal. Created samples have certain absorbing and fluorescent properties. Scattering properties of samples are close to scattering properties of real human skin. By virtue of layered structure the model permits to simulate as a biological tissue without photosensitizer accumulation in it, as tissue with photosensitizer accumulation with certain distribution in a depth. Dependence of fields distribution on a surface was investigated at change of parameters of a model. Essential changes of distribution on a surface depending on the characteristics of model was revealed. The space and angular characteristics was investigated also. The investigations with physical model correspond to predicted results of theoretical model.

The skin response was studied for different radiant exposure of short and long laser pulses and reaction to multipulse action using Er-glass laser radiation. Lesion ranging from a mild erytherma to tissue coagulation were produced on porcine skin. Radiant exposure producing 50 percent probability of a particular grade of lesion were established. A dependence of ED50 of minimum erythema versus number of pulses and beam cross section were studied. Histological investigation of the damage zone was made for qualitative study of injured skin. The dose-response relationship for producing different grades of burns were determined for energy densities of single laser pulse within the range 0.5-35 J/cm² and pulse duration 100 ns and 3 ms. The single pulse dose in a chain of repetitive pulses producing minimum erythema were determined for 2ⁿ(n equals 1-6) pulses. The minimum reaction of skin on laser irradiance were studied for different beam diameter. The reaction of skin in mostly considered as local super heating. The data obtained are adequate to update safety standards for cutaneous injury within these ranges of radiant exposure and beam spotsize.

The data bank contains optical, ordinary biochemical and biophysical information on 120 venous blood samples of donors, healthy persons, patients with high pathology, 60 tissue samples. The optical parameters include diffuse reflection R((lambda) ) and transmission T((lambda) ) coefficients for optically thick layers, the absorption K((lambda) ) and extinction (epsilon) ((lambda) ) spectra, oxygenation degree CO2, parameter p determined by sizes and shapes of cells and their aggregates, refractive index of a disperse phase relative to surrounding media, and cooperative effects at high relative concentration. The peculiarities in absorption K((lambda) spectra are connected with different pathologies. It is shown from K((lambda) ) that the grade of pathology connected with the concentration of hemoglobin and mithohondrion together with oxygenation degree of blood and tissues, with the pathological hemoglobin's forms and its decomposition products of different levels. Parameter p is an important diagnostic parameter. We consider that it is necessary to include the oxygenation degree and erythrocyte's aggregation parameter to extend the range of common diagnostic parameters of blood by the first rota.

Experimental laser thrombosis is induced in rat mesenteric microvessels. Temperature increase within irradiated microvessels was calculated on the basis of relatively simple heat transfer model and appeared to be near 50 degrees C above the initial value. This temperature increase decay practically to initial level during the period between two subsequent laser impulses. It is stated that the zone of endothelium thermal damage is less than thrombus length along the vessel wall.

The Nd:YAG/KTP laser offers to the surgeon two wavelengths that can be used to coagulate and vaporize. Our objective was to investigate the combined effect of both wavelengths and to determine the irradiation parameters allowing the largest lesion volume. Chicken breast was irradiated ex vivo. 1064 nm and 532 nm Nd:YAG/KTP laser irradiations were performed sequentially at different combinations with variable fluence and compared to isofluent single wavelengths 40 W irradiation. Although the mean total lesion volume showed no difference between the different wavelengths combinations a significant enhancement of the maximum lesion depth was found under combined irradiation in the 20W/20W conditions. Dual wavelengths irradiation with the Nd:YAG/KTP laser thus induces a specific denaturation process which is more directional and results in an increased total lesion depth. This may represent a ne approach to increase the depth of coagulation necrosis and thus the total lesion volume, thereby improving long term results.

Background and objectives: the aim of this study was to examine the pattern of healing in rat calvarial defects prepared with the erbium-YAG laser, using the 'guided tissue regeneration' technique. Materials and method: PTFE membranes were placed over lased skull defects, and the skin wounds sutured. Rats were killed humanely at intervals after surgery, and the skulls processed for paraffin wax histology. A further group of mature rats were also killed humanely and the calvariae removed. Slots were prepared using the erbium-YAG laser and immediately examined under the environmental scanning electron microscope (ESEM) in hydrated conditions, which avoided drying artifacts. Results: An amorphous, mineral-rich carbon layer surrounds the lased bone defect, which in the in vivo experiments was seen as a basophilic zone which was resistant to resorption.

The dynamics of light scattering and internal force in cartilage in vitro are studied in the course of laser shaping. In experiments were used the samples of human cartilage which were collected from patients who underwent nasal septum stirgely. We found that the dynamic of scattered light intensity depends on heating rate and on the temperature of the sample. The sign of the derivative of the scattered light intensity changes when phase transition is occur. The stress force changes during laser heating and relax after action to much less value than it was before laser treatment. Histological investigation allow us to correlate the dynamics of optical and mechanical properties of cartilage with stable and nondestructive reshaping regimes.

The dependence of the fluence at the threshold of laser- induced optical breakdown on the laser pulse duration has been investigated experimentally and theoretically for human cornea, human enamel, and bovine brain tissue. For the experiments in the range from 100 fs to 200 ps, we used a femtosecond dye laser system and a picosecond Nd:YLF laser system. We observed a significant decrease of the fluence at the threshold when reducing the pulse duration. The measured dependence on the pulse duration is in good agrement with our model.

Detection of the laser-induced stress wave generated in tissue by irradiation with a short laser pulse is a method for direct measurement of the absorbed energy distribution. In this study we tried to optimize this technique in order to avoid distortion of the stress wave during its propagation from the irradiated volume to the detector. Stress waves are formed by short pulsed irradiation of an absorbing dye solution and of tissue samples with a Q- switched Nd:YAG laser at 532 nm. An optical transducer based on pressure-induced reflectivity changes of a glass-water interface detects the stress wave in front of the irradiated sample surface. It is shown theoretically and experimentally that this kind of detector, where the active area is a small spot close to the irradiated surface, minimizes signal distortion due to acoustic diffraction. The absorption coefficients of the dye solutions could be derived with high accuracy from the slopes of the recorded stress waves. Measurements in layered samples and in liver tissue demonstrated that apart form the optical constants also some information about the structure of the samples can be derived from the stress signals. The optical detector is sensitive enough to registrate pressure amplitudes in the range of 1 bar. This makes it possible to use it for in-vivo applications.

The application of focused picosecond laser pulses in stereotactic neurosurgery requires the knowledge of ablation efficiency and quality in consideration of clinical practice. In neurosurgical operations the laser beam must be guided through a thin endoscopic probe, which can be inserted into the human brain and is equipped with a rinsing/aspiration system. Thus, the laser ablation must be performed within a surrounding of rinsing liquid. We performed in vitro ablation experiments with a two-stage picosecond Nd:YLF laser system at 1053 nm to investigate the effects of liquid media on the ablation efficiency and quality. Ablations of fresh bovine tissue within a surrounding of distilled water and physiological saline, respectively, showed a nearly linear dependency of ablation depth on applied energy. The tissue residuals. The diameters of single ablation fragments were measured to be less than 50 micrometers . Following these results and taking into account the absorption of physiological saline, we designed the focusing optics as well as the aspiration channels inside the stereotactic laser probe. We also present the working principle and main system parameters of the stereotactic laser probe and describe the assigned operating strategy.

The ablation of soft tissue with free-running infrared lasers of low intensity is a thermal evaporation process. Nevertheless, the influence of the temperature dependent optical absorption is not yet understood. A detailed model of the photoablation process has been developed which was solved by the finite element method. Ablation rates and thermal damages are calculated and compared with experimental values. It has been shown, that the influence of the temperature dependent absorption coefficient cannot be neglected.

Laser spectroscopic methods have been used for on-line investigations of laser tissue interaction processes concerning the production of toxic and carcinogenic substances in the laser plume during cutting and evaporation of tissue in laser surgery. Laser spectroscopic investigations demonstrated that the original tissue molecules were split into basic metastable compounds under the high temperature conditions in the reaction zone. The produced radicals are one source for the formation of the chemical s produced during the laser tissue interaction process. The formation of the harmful substances can be influenced by the surrounding gas atmosphere. These substances can be reduced significantly by the addition of an oxygen donor e.g. water, into the reaction zone.

The characteristic gaseous and highly volatile organics emitted during laser tissue interaction were investigated in order to understand and to classify fundamental chemical processes as well as to influence the produced substances. The amount of oxygen available and the temperature efficient inside the reaction zone are the most important parameters, determining type and amount of the emitted chemicals. Summarizing the results, generally, it is possible to state that the emission of toxic and cancerogenic substances during laser tissue interaction is favored if high temperatures arise inside the reaction area, if dried or carbonized tissue is irradiated, or if inert gases are used. A high oxygen content available in the reaction area, realized, e.g. by addition of a water aerosol, lowers the production of harmful chemicals.

Different tissue samples have been irradiated with surgical XeCl- and CO₂-lasers. The generated laser plume was sampled and analyzed concerning medium and low volatile organic compounds. Differences in the composition of the pyrolysis products in dependance of tissues and lasers are presented. Quantification of aromatic hydrocarbons was carried out. It is obvious that the ratios between the single aromatic hydrocarbons gave hints at the temperatures of the laser tissue interaction process. Some aromatic hydrocarbons were typical high temperature products like phenylacetylene, whereas toluene could be found at lower temperatures with comparable high concentration. Two special classes of compounds, presumed by Curie point pyrolysis of proteins and not yet verified by synthesis, were identified in the aerosol of the CO₂-laser. Probably five different amino acids might be the precursors of these compounds whereas by Curie point pyrolysis only three amino acids were reported as precursors. The particular debris which was sampled separately on glass fiber filters was extracted with different solvents. Several compounds absorbed at the particles could be identified and will be discussed. In the polar acetone extract some of main compounds remained unknown. A special clean-up procedure for polycyclic aromatic hydrocarbons (PAH) was carried out. Qualitative and quantitative results of the PAH analysis are presented. The results are compared with the results of other working groups.

Actual occupational infections of medical staff is dominated by HBV, HIV and HCV-infections by dermal blood inoculation like needle injuries. What amount of these blood borne infections was possibly done via the aerosol pathway is unknown today. Looking at the laser generated aerodynamic particle sizes and the particle size of human pathogen viruses as circulating or cell fixed units shows common transmission abilities to the human respiratory system. In cell tissue monolayer model systems and contaminated serum systems with virus infections this mechanics were demonstrated as viable. For safety evaluation, the lifetime, spreading behavior and infection potential by viruses and bacterias of contaminated human laser aerosol must be further characterized.

Formation of laser plume by laser-tissue interaction means an inhomogeneous, pluriphasic and dynamic multicomponent system of biological material and induced modifications. While IR_laser applications often simulate processes of thermal food preservation, UV-lasers favor formation of aromatic organic compounds as VOC. Along with traces of PAH, nitriles and O-/N-containing heterocyclic compounds two classes of dialkyldiketopyrroli(di)nes are special formed VOC as laser solvents. Inhalable particles or partially dried and modified biomass contain - along with infectious particles - a lot of temperature degradation products. Ames tests and Comet-assays gave hint to some mutagenic activities present in laser smoke.

The final results of the German part of the joint project STILMED 'Safety Technology in Laser Medicine' are available and being prepared for publication. The question is raised, if parts of these results may be subject to international standards. An overview is given for the structure and procedure of national, European and international standardization. Existing standards are considered concerning their relationship to STILMED, which dealt with the chemical, particulate and microbiological composition and possible hazards of laser plume, as well as protection means, like plume evacuators, including the development of nozzles and instruments with integrated evacuation channels, and face masks. Results of basic research and experiences with medical treatment modalities are not matter for standardization. On the other hand, plume evacuators and their technical data should be submitted to standards, which define test procedures for their performance and safety. Also, surgical face masks, for which no international standards exists, could be well suited for standardization, although the multitude of application conditions would make it an excessive task. At least, products that claim 'for laser use' or 'laserproof' or similar should fulfill standardized requirements, and the respective wording needs protection by standard definition.

The better understanding of generation of by-products during laser application allows a rough risk assessment, which in turn results in a number of recommendations and guidelines. The main attention is directed to smoke evacuation systems in connection with sufficient room ventilation, both being obligatory for any invasive laser therapy. Minimal requirements and optimal use of such units are discussed and practical examples are presented. The important role of personal protection measures is pointed out. These measures are not new and more or less practiced in the past. However, they have been justified now in detail by the comprehensive investigations during the STILMED project.

Not long ago there were not acceptable Laser Safety Standard in Russia, that stood in the way of the further development of laser medicine and laser equipment market in Russia. Not a certain document inherited by Russia from USSR was corresponded to international standards. For example, the Russia State Standards No 12.1 .040-83, 12.1.031—81, 12.4.026-76 only enumerate an unhealthly factors of environment, not giving the way of safety. The using of the Russia Ministery of Public Health Sanitary Standard No 2392—81 was a dangerously for life. It was sadly to admit that Russia State Laser Safety Standards were not exactly what's needed for public health and for environmental protection.

The response of tissue to laser radiation spans the gauntlet from biostimulation at irradiance levels of mW to the violent disruptions of tissue with short pulses that have MW peak irradiances. The end result of laser interaction with tissue is governed by energy Deposition that depends upon laser parameters and tissue properties. In concept, PDT requires a laser wavelength that matches an absorption peak of the photosensitizer and a penetration depth to reach all of the targeted tissue. Dosimetry will depend upon the needed fluence rate 4(z) of the light at the targeted depth. Given the optical properties of the tissue, various methods of solving the transport equation can be used to calculate fluence rate [W1m2] as a function of depth. Since most wavelengths of interest for PDT are in the red and near IR, scattering dominates absorption; and the fluence rate just below the surface of tissue can be much larger than the irradiance, EO [W/m2].