The narrowing of the spectral linewidth and the increasing of the peak intensity characteristic of laser action was observed in emission spectra of dye-infused biological tissues. The fresh tissue was infused with a solution of Rhodamine 640 perchlorate in ethanol and then excited with frequency-doubled Q-switched Nd:YAG laser pulses. The sharp spectral peaks of laser action in tissues may find applications in detection of superficial disease.

Non-contact fiber guided IR-tissue treatment under water requires the formation of a water vapor channel at the fiber tip to bridge the water layer between the fiber and the tissue surface and to allow transmission of the radiation. The formation of the channel, however, consumes most of the initial pulse energy which strongly restricts the ablation efficiency. The goal of this study was to determine optimum laser parameters which guarantee a high ablation efficiency and a high cutting precision. A multi-wavelength-laser system was realized by simultaneously guiding erbium and holmium laser radiation via a single ZrF₄ fiber. Both lasers were operated in free-running mode at pulse durations adjustable between 100 microsecond(s) and 1 ms. Pressure measurements and video flash photography were performed to study the channel formation process as a function of laser wavelength, pulse duration and delay time between laser pulses at different wavelengths. The tissue response of human meniscus after laser impact was histologically investigated. The efficiency of erbium laser tissue ablation under water increases from 25% up to 80% by using a multi-wavelength system emitting 2.1 micrometers and 2.79 micrometers radiation. This is achieved when a 200 microsecond(s) long holmium laser pulse of low energy is used to open a water vapor channel through which the ablating erbium laser radiation can be transmitted. The induced thermal tissue damage is essentially determined by the holmium laser parameters and the delay time between both pulses. The combination of erbium and holmium laser radiation offers the surgeon the possibility for efficient and precise cutting of tissue under water. Moreover, it represents an universal medical instrument for cutting and/or coagulation just by changing the laser parameters without changing the instrument.

Laser thermokeratoplasty (LTK) is a minimally invasive method to correct hyperopia and astigmatism. The alteration in refractive power of the eye is achieved by thermally induced shrinkage of stromal collagen in the corneal periphery with a mid-IR laser system ((lambda) equals 1.4 - 2.5 micrometers ) and thereby mechanically increasing the central corneal curvature. In order to evaluate the best choice of laser parameters and exposure geometry a mechanical model of the cornea, which is highly dependent on the material parameters of the corneal tissue, is to be developed. For this reason uniaxial tensile tests were performed on specimens of porcine cornea to determine their nonlinear stress-strain relations and their viscoelastic behavior. Laser induced stress has been measured while corneal stripes were being exposed to a pulsed Cr:Tm:Ho:YAG laser ((lambda) equals 2.12 micrometers ) system. The stresses observed correlated just beyond the threshold qualitatively well with the number of applied pulses. For larger pulse energies the stress stabilized after a few pulses, which means further laser application could neither increase nor decrease the level of stress. After the end of the last laser pulse the specimens relaxed within several minutes down to a level of residual stress, which is probably to be held responsible for the refractive change in LTK.

Efficient and well controlled laser drilling of the zona pellucida of mouse eggs has been demonstrated recently using a 1.48 micrometers laser diode. The zona pellucida openings (5 - 10 micrometers ) can be obtained within the culture dish in an either tangential or more poleward irradiation in respect to the spherical egg structure. Zone drilling is achieved at a laser power of 47 mW and typical irradiation times of 8 - 20 ms for mouse oocytes. Cultured mouse embryos evidence strongly modified hatching behavior when drilled. No increase of the outer diameter of the zona pellucida and no thinning are induced prior to hatching in the lased group, in contrast to the control non-drilled group. Drilled embryos hatches one day earlier than control non-drilled embryos. Obviously no mechanical constraint is induced on the zona pellucida during the initial development of the drilled blastocysts before hatching and hatching is facilitated.

A Q-switched alexandrite laser (180 ns at 755 nm) was used to irradiate samples of agar embedded with red, black and green tattoo dyes. The acoustic waves generated in the samples were detected using a PVDF membrane hydrophone and compared to theoretical expectations. The laser pulses were found to generate acoustic waves in the black and green samples but not in the red pigment. Pressures of up to 1.4 MPa were produced with irradiances of up to 96 MWcm^-2 which is comparable to the irradiances used to clear pigment embedded in skin. The pressure gradient generated across pigment particles was approximately 1.09 X 10¹⁰ Pam^-1 giving a pressure difference of 1.09 +/- 0.17 MPa over a particle with mean diameter 100 micrometers . This is not sufficient to permanently damage skin which has a tensile strength of 7.4 MPa.

The effects of 2.12 micrometers Cr:Tm:Ho:YAG laser pulses delivered in isotonic saline solution via an optical fiber system on fresh porcine femur patellar groove cartilage were studied in vitro. Various irradiation geometry, corresponding to angles of 0 - 90 degree(s) of the delivering fiber with respect to the cartilage surface, have been investigated. A laser pulse energies of 1.0 J with a pulse duration of 250 microsecond(s) (FWHM) was used. The dynamics of the induced transient vapor bubbles and the ablation process were monitored by time resolved flash videography techniques. Acoustic transients of up to 200 bars induced by bubble collapses were measured by a calibrated piezoelectric needle probe hydrophone. Histological assessment of the irradiated cartilage samples was performed using azan and Safranin-O stains. The extent of the area of altered cartilage cells is larger than the zone of tissue matrix damage. The predominant mechanism of tissue damage is thermal rather than acousto-mechanical. Cartilage treatment at an angle of incidence of 30 degree(s) reduces significantly the overall damage as compared to 60 degree(s) or 90 degree(s) irradiation.

The ablation of joint cartilage by Holmium laser radiation is followed by the creation of an unexpected large avital cell area below of the irradiated spot. To examine the reasons for the tissue destruction the effect of shockwaves as well as the temporal development of temperature due to the laser absorption was investigated. The temperature raise was observed by an infrared-camera. The creation of cell destroying temperatures below the irradiated area is explained by the absorption of the Holmium laser light and the spread out of heat from the absorption area, whereby the effects due to shockwave seem to be neglible. To reduce the development of high temperatures a method is presented that allows a local coding of the irradiated area.

The starting mechanisms of laser induced bubble formation at the submerged fiber tip was investigated by pressure measurements and fast flash light videography. The radiation of a free running or Q-switched Ho:Tm:YAG-laser operating at a wavelength of (lambda) equals 2.1 micrometers was delivered via a fiber into a water filled cuvette. The spatial intensity distribution at the distal end of the fiber was investigated with a thermal image method. It was shown that the beam profile exhibits hot spots which result in an inhomogeneous temperature distribution of the water volume underneath the fiber tip. It was found that at high laser intensities (3 MW/cm²) micro bubbles can appear already at the very beginning of the laser pulse at average water temperatures below the boiling temperature. Corresponding to each sub-ablative laser spike a bipolar thermo-elastic pressure signal was recorded. We came to the opinion that the lowering of pressure by the negative component of the bipolar pressure transients leads to initiation of bubbles by cavitation at high laser intensities. When the laser intensity was reduced from 1 to 0.5 MW/cm² a fast increase of the bubble formation temperature was found. At laser intensities less than 0.5 MW/cm² bubble formation takes place at temperatures near the critical temperature of water.

Short laser pulses transmitted through optical fibers are an important tool for minimally invasive surgery. In the regime of temperature and stress confinement these pulses are capable of producing combined mechanical and thermal effects in absorbing media, which are initiated by the formation of micro cavities. Pulses with a duration of 6 ns created by an optical parametrical oscillator (OPO) were guided via a quartz fiber into an aqueous dye solution. The absorption coefficient of the solution could be varied between 24 cm^-1 and 900 cm^-1 by tuning the wavelength of the OPO. The micro bubble dynamics were observed with time-resolved imaging. Stress transients were measured with piezoelectric detectors. At high absorption the formation of micro bubbles can be seen clearly outside the optically heated zone in front of the fiber tip. At low absorption bubbles are formed in the optically heated zone at temperatures below the boiling point. These observations together with the occurrence of bipolar stress signals support the assumption that thermoelastic stress waves with negative components arising from the limited geometric extension of the stress source are responsible for the generation of the bubbles. Far from the fiber tip this edge effect leads to diffraction of the wave. The hypothesis is further verified by theoretical calculations. In non-contact applications of infrared laser pulses where the radiation has to be transmitted through an absorbing water layer to the tissue this effect might be an efficient starting mechanism for the generation of a transparent vapor channel. When the fiber tip is in direct contact to the tissue the tensile stresses may help to initiate ablation due to fracture of the tissue material.

For an interpretation of pressure signals detected by piezoelectric PVDF-foils several parameters are of importance. These are for example pressure pulse duration and rise times, active area of the film and specifications concerning the high-frequency technique of the experimental setup. Using an input-resistance of 1 M(Omega) at the storage-oscilloscope leads to reflections of the signal which superimpose each other when reflected a second time at the foil. This might cause an apparent increase of the amplitude. The utilization of a longer cable allows a separation of each reflected pulse, but it causes the problem, that the cable's input- impedance approaches its characteristic impedance of 50 (Omega) . This will lead to a time derived signal as well as using 50 (Omega) as input-resistance at the scope. Therefore a direct measurement of short pressure transients requires a very short cable and an input-resistance of 1 M(Omega) . Otherwise the measured signal allows no proportional relation between pressure transient and measured voltage signal. In the latter case a frequency-dependent correction of the signal becomes necessary. This has been developed in this paper by means of Fast Fourier Transform algorithm. After correction in the frequency-domain the signal is transformed back into the time-domain.

The homogeneous and inhomogeneous model media, human aorta tissue were investigated under irradiation of Q-switched Nd-YAG laser and XeCl excimer laser. Temporal course of acoustic pressure with resolution of 3 - 5 ns, the efficiency of ablation, the distribution of ejected droplets over sizes were studied for laser fluencies 0.1 - 15 J/cm2. Pressure course depends on laser fluence and at high fluencies the tensile phase vanishes completely due to recoil pressure of ejected products. The amplitude of the compression wave is proportional to the laser fluence and may be as high as 80 MPa. The efficiency of ablation rise up considerably with laser fluence rise over the threshold. This is connected with the large droplets ejection and streaming from irradiation surface. Droplets with sizes about 1 mm were detected. The efficiency of ablation both for homogeneously and heterogeneously absorbing media is determined by volume density of laser energy. It is two orders higher for the medium, containing absorbing particles rather than for homogeneously absorbing medium. Detection of acoustic wave with high temporal resolution possesses to investigate the laser ablation process in detail. No cold photomechanical damage spallation by the powerful rarefaction wave formed upon the reflection of the laser-induced compression wave at the biotissue-air interface is observed in the course of laser ablation. The higher ablation efficiency for heterogeneously absorbing medium is determined by local overheating of microareas with increased absorption.

Selective photothermolysis with pulsed lasers is presumably the most successful therapy for port wine stain birthmarks (flammeus nevi). Selectivity is obtained by using an optical wavelength corresponding to high absorption in blood together with small absorption in tissue. Further on, the pulse length is selected to be long enough to allow heat to diffuse into the vessel wall, but simultaneously short enough to prevent thermal damage to perivascular tissues. The optimal wavelength and pulse length are therefore dependent on vessel diameter, vessel wall thickness and depth in dermis. The present work, that is based on analytical mathematical modeling, demonstrates that in the case of a 0.45 ms long pulse at 585 nm wavelength vessels of diameter in the range of 40 - 60 micrometers require minimum optical fluence. Smaller vessels require higher fluence because the amount of heat needed to heat the wall then becomes a substantial fraction of the absorbed optical energy, and larger vessels require higher dose because the attenuation of light is blood prevents the blood in central part of the lumen to participate in the heating process. Further on, it is shown that the commonly used dose in the range of 6 - 7 J/cm² is expected to inflict vessel rupture rather than thermolysis is superficially located vessels. The present analysis might serve to draw guide lines for a protocol where the optical energy, wavelength and pulse length are optimized with respect to vessel diameter and depth.

The model of human calculi fragmentation process by laser radiation is proposed. It is shown, that under the conditions typical for laser lithotripsy, plasma can not be considered as the effective transformer of laser radiation energy into shock waves. It is considered that the human calculi has a multi-layer structure. In this structure the organic layers are separated by layers of nonorganic matter. Organic matter is supposed to have high absorption, while nonorganic matter--low absorption and high scattering. The basic geometry is presented. It was shown that the ablation process can be treated as consisting of three phases. The first stage is the pure heating of organic matter. The second one is the decomposition of organic matter leading to gas and pyrocarbon formation. Due to this process the absorption coefficient of laser radiation increases dramatically, and this leads to the sharp temperature growth, so (third stage) the conditions for plasma flash can be reached.

The temperature of a soft tissue model was measured during laser irradiation. A diode laser with a continuous wave output power of up to 10 W and a wavelength of 990 nm was used to heat and ablate samples of agar gel doped with haemoglobin. The internal temperature of the tissue was measured at depths of 2 - 5 mm below the surface using a thermocouple. The temperature at the surface was measured remotely using an infra-red sensor (over an area 1.4 mm in diameter at the center of the interaction). This method of measurement provides an inexpensive alternative to thermal imaging cameras. Temperature changes in time during the interaction both at the tissue surface and as a function of tissue depth are presented. At the onset of tissue surface rupturing and subsequent tissue ablation the temperature at a depth of 2 mm was found to be 75 +/- 6 degree(s)C. At this time a temperature of 60 +/- 2 degree(s)C, high enough to cause tissue coagulation, had been reached to a depth of 3 mm. After 10 s of continuous tissue ablation, the temperature at a depth of 3.5 mm and beyond had not reached coagulation temperature. The surface temperature rose steadily during irradiation and reached a temperature of 100 degree(s)C at the time of rupturing of the tissue surface. During the subsequent tissue ablation the measured temperature increased rapidly, reaching a maximum of 250 +/- 30 degree(s)C within a further 10 s.

Successful laserinduced tumor therapy requires the knowledge of optical properties of tissue as well as of the thermal ones (specific heat capacity, thermal conductivity, thermal diffusivity). Therefore, a comprehensive review of one of those values, the specific heat capacity c_p, of different human and animal tissues is given measured calorimetrically by us or collected from the literature. A Differential Scanning Calorimeter was used to determine the in vitro specific heat capacities of various healthy and tumorous human tissues. The influence of freezing in liquid nitrogen and of thermal coagulation on the specific heat capacity was investigated.

The principle of laser induced selective photothermolysis is to induced thermal damage to specific targets in such a manner that the temperature of the surrounding tissue is maintained below the threshold for thermal damage. The selectivity is obtained by selection of a proper wavelength and pulse duration. The technique is presently being used in the clinic for removal of port-wine stains. The presence of melanin in the epidermal layer can represent a limitation to the selectivity. Melanin absorption drops off significantly with increasing wavelength, but is significant in the entire wavelength region where the blood absorption is high. Treatment of port-wine stain in patients with high skin pigmentation may therefore give overheating of the epidermis, resulting in epidermal necrosis. Melanosomal heating is dependent on the energy and duration of the laser pulse. The heating mechanism for time scales less than typically 1 microsecond(s) corresponds to a transient local heating of the individual melanosomes. For larger time scales, heat diffusion out of the melanosomes become of increased importance, and the temperature distribution will reach a local steady state condition after typically 10 microsecond(s) . For even longer pulse duration, heat diffusing from neighboring melanosomes becomes important, and the temperature rise in a time scale from 100 - 500 microsecond(s) is dominated by this mechanism. The epidermal heating during the typical 450 microsecond(s) pulse used for therapy is thus dependent on the average epidermal melanin content rather than on the absorption coefficient of the individual melanosomes. This study will present in vivo measurements of the epidermal melanin absorption of human skin when exposed to short laser pulses (< 0.1 microsecond(s) ) from a Q-switched ruby laser and with long laser pulses (approximately 500 microsecond(s) ) from a free-running ruby laser or a long pulse length flashlamp pumped dye laser. The epidermal melanin absorption coefficient of human skin of various pigmentation and races will be presented.

Visible reflectance spectra of human skin might serve as a valuable tool for determining blood volume and pigmentation. They can therefore be used to evaluate the response to various skin treatments such as, e.g., port-wine stain therapy. A fiber-optic system is preferable for clinical evaluation of the therapeutic response due to its higher flexibility. Diffuse reflectance spectra obtained using a fiber system are compared with the corresponding spectra from an integrating sphere system. The results show that the most accurate reflectance spectra are obtained using the integrating sphere set-up. The aperture should then be much larger than the optical penetration depth of the skin. The system will then collect all the reflected light from superficial and deeper layers, and this enables a qualitative comparison between the wavelengths. However, the size and localization of many dermal lesions limit its use. In these cases the fiber-optic system is preferable. Light with an optical penetration depth shorter than the distance between the excitation and collecting fibers is, however, favorized. Normal dermis has typically a penetration depth of 600 micrometers and 2000 micrometers for, respectively, green/yellow and red light. Consequently, the collection efficiency of a typical fiber-optic system with a distance of 100 - 200 micrometers between the emitting and collecting fibers, will be higher in the green/yellow than in the red part of the spectrum. It is, however, important to remember that the relevant parameter is the change in reflectance at each particular wavelength, rather than comparison between the wavelengths. When such a comparison is required, the spectra collected by the fiber-optic system can be calibrated. The more accurate integrating sphere system is maybe preferable in a research laboratory environment, whereas the more flexible fiber-optic system is the most applicable for use in the clinic.

Optical parameters such as total and diaphragm transmission and diffuse reflection have been investigated by in vitro set up for whole blood. Original construction cuvette allows change thickness of a layer inside without removing of content. Changes of the blood concentration have been created by dilution of centrifuged blood. Hematocrit, hemoglobin and oxyhemoglobin concentration have been measured simultaneously by independent methods. According to the received data the coefficients of scattering and absorption and the average cosine of scattering are calculated for whole blood by the Monte-Carlo simulations. The curve of light penetration into whole blood is created for the following wavelengths: 488, 587, 633, 675, 820, 860 nm.

Laser-induced thrombosis is one of the most adequate methods of studying of thrombus formation in mesenteric vessels. The in vivo simulation of different conditions of thrombi growth and the developed phenomenological theory of these processes confirm the concept of platelet activation time in treatment of the thrombi phenomenon.

Main point in this study was the investigation of the gaseous and low-boiling substances produced in the laser plume during cw CO₂ laser and XeCl laser irradiation of tissue by gas chromatography (GC)/mass spectrometry. The characteristic emitted amounts of chemicals were determined quantitatively using porcine muscular tissue. The produced components were used to determine the character of the chemical reaction conditions inside the interaction zone. It was found that the temperature, and the water content of the tissue are the main parameter determining kind and amount of the emitted substances. The relative intensity of the GC peak of benzene corresponds to a high temperature inside the interaction area while a relative strong methylbutanal peak is connected with a lower temperature which favors Maillard type reaction products. The water content of the tissue determines the extent of oxidation processes during laser tissue interaction. For that reason the moisture in the tissue is the most important parameter to reduce the emission of harmful chemicals in the laser plume. The same methods of investigation are applicable to characterize the interaction of a controlled and an uncontrolled rf electrosurgery device with tissue. The results obtained with model tissue are in agreement with the situation characteristic in laser surgery.

The specific possibilities of the time-resolved fluorescence spectroscopy have been used to determine in on-line measurements the reactive species arising in the reaction zone during laser tissue interaction. The measured radicals, ions and excited atoms are the basic components for the formation of stable harmful chemicals observed in laser plume and therefore the best parameters for the optimization of the laser tissue interaction process. A water aerosol spray system that reduces the emission of the harmful components in the laser plume is described. The effectiveness of this arrangement depends strongly on the water concentration in the interaction zone. The determination of C₂, CH and CN radicals which lead to the formation of harmful substances and the OH and O species which characterize the water content of the tissue by laser spectroscopic measurements gives the possibility to optimize the interaction process.

Chlorine atoms were detected by laser spectroscopic methods in the laser smoke produced during the cutting and evaporation of tissue for medical purposes. A sensitive ion mobility drift sensor, optimized for the selective detection of hydrocarbon chlorides was used for further investigation of the laser smoke. Different chlorine containing substances were detected. The hazard potential of these substances to the medical staff and patients was estimated.

For the investigation of laser plume for the existence of HPV DNA fragments, which possibly occur during laser treatment of virus infected tissue, human papillomas and condylomas were treated in vitro with the CO₂-laser. For the sampling of the laser plume a new method for the trapping of the material was developed by use of water-soluble gelatine filters. These samples were analyzed with the polymerase chain reaction (PCR) technique, which was optimized in regard of the gelatine filters and the specific primers. Positive PCR results for HPV DNA fragments up to the size of a complete oncogene were obtained and are discussed regarding infectiousity.

Two laser systems emitting at 2 and 3 micrometers have been developed for application in the biomedical field, such as photoablation and microsurgery. The design involved the evaluation of active materials, the optimization of pumping chamber and the analysis of different configurations of the resonant cavity. Holmium, Thulium and Erbium active ions in the YAG host have been considered. A complete characterization of the laser behavior has been carried out for the most interesting combinations of components. The Erbium laser has been also operated in Q-switch regime. The achieved results are comparable with the state of the art performances on the international market.

Porcine liver was irradiated with a medical CO₂-laser. The generated particles were sampled with glass fiber filters and a clean-up procedure specific for polycyclic aromatic hydrocarbons (PAH) was carried out. Separation and detection was done by gas chromatography/mass spectrometry. This clean-up procedure was controlled by fluorinated Internal Standards. Rather low amounts of PAH and their guide substance Benzo[a]pyrene were found. Compared to its threshold limit value no potential risk for the medical staff seems to be given.

We report on investigations of laser ablation of larger particles which may be in the minority but are known to be the main carrier of possibly infectious materia. We determined the dynamics of the ablated material by means of short-time exposure video recording with a Schlieren-Optik device. In addition, ablated particles were collected on microscopical slides and examined visually. The region of interest was imaged on a CCD-camera and transferred to a image processing system to get information about the size distribution and the morphology of the particulate matter. For the experiments we irradiated both soft and hard tissues and tissue modelling substances with pulsed and, for comparison, with continuous wave lasers. The particle velocities and the morphology of the ablated matter, either of irregular or special form, depend strongly on the laser type and laser parameters, respectively the treated material. In case of spherical aerosols we quantitatively determined the particle size distributions, for irregular shaped particles (mostly fibrous) only qualitative statements can be made.

Laser-tissue interaction may generate by energy absorption a complex mixture of gaseous, volatile, semi-volatile and particular substances. At the time about 150 different components are known from IR-laser interaction with different organ tissues like liver, fat, muscle and skin. The laser-tissue interaction process thereby is dominated by heating processes, which is confirmed by the similarity of formed chemical products in comparison with conventional cooking processes for food preparation. With the identified chemical substances and relative amounts in backmind a walk along the think path of risk assessment with special reference to pyrolysis products is given. The main way of intake of pyrolysis products is the inhalative one, which results from the fine aerosols formed and the high spreading energy out of the irradiated source. The liberated amounts of irritative chemicals as (unsaturated) aldehydes, heterocycles of bad odor and possibly cancerogenic acting substances relates to some (mu) g/g of laser vaporized tissue. With regard to this exposure level in a hypothetic one cubic meter volume the occupational limit settings are far away. Even indoor air exposure levels are in nearly all cases underwent, for the content of bad smelling substances forces an effective ventilation. Up to now no laser typical chemical substance could be identified, which was not elsewhere known by frying or baking processes of meat, food or familiar. Starting with the GRAS concept of 1957 the process of risk assessment by modified food products and new ingredients is still improofing. The same process of risk assessment is governing the laser pyrolysis products of mammalian tissues. By use of sufficient suction around the laser tissue source the odor problems as well as the toxicological problems could be solved.

Cutting and vaporization of biological tissue, performing surgical procedures are always connected with the generation of pyrolysis products due to heat increase caused by laser radiation, direct thermal heating or radiofrequency- (RF-) current application. This paper presents quantitative and qualitative results on the produced pyrolysis products considering latest device developments. Volatile organic compounds were adsorbed using a multisorbent sampler and evaluated with a gas chromatography system coupled with a FTIR spectrometer. The calibration of the system together with geometrical considerations of the adsorption allows for a quantitative determination of some toxicological relevant substances. For a quantitative statement, a standardized application of optical and electrical energy is requested. Therefore, in vitro investigations were performed Nd:YAG laser radiation and radiofrequency current in monopolar and bipolar technique were used for simulation of cutting in open surgery. We used a 600 micrometers bare fiber, a monopolar and a bipolar needle electrode with similar geometric shape for tissue incisions. The depth and speed of cutting was standardized for all experiments. The cutting parameters for laser and RF application were chosen in such a way that the quality and the depth of the coagulation zone are comparable for all applications.

The aim is the assessment of potential health hazards of patients and medical staff which may be caused by inhalation of the vapors and aerosols produced. In vitro investigations have been carried out to study the process of laser- and rf-surgery induced vaporization of various tissue types to identify the large variety of pyrolytic substances, to calibrate the analytical equipment and to determine typical amounts of selected substances during the treatment. The organic compounds include acetate esters, aldehydes, nitriles, aromatics and ketones and have been analyzed by spectroscopic and gas chromatography techniques. Distribution studies of VOCs and aerosols in operating rooms revealed that concentrations of VOCs such as toluene, pyrrole, aldehyde are measured which are well below of any threshold limit values by some orders of magnitude. But in case of aerosols 5 minutes of tissue vaporization leads to concentrations for 30 min. which are similar to limit values for inert dust. But plume aerosols consists of complex mixtures of condensed pyrolysis products which will be investigated further by biomonitoring tests.

Information on pyrolysis products such as particle size distribution, concentration of plume aerosols and volatile organic compounds produced by laser treatment is required to evaluate the potential health hazards during treatment of biological tissue. In-vitro measurements and `in vivo' collection of samples were carried out for comparison. The concentration of pyrolysis products were determined for ENT and gynecological surgical laser treatments using a Nd:YAG laser and CO₂ laser. In consideration of the ventilation systems, room volume and suction efficiency the concentration of volatile organic compounds were measured by means of a multisorbent sampler and a gas chromatography system coupled with a FTIR spectrometer.

Fluence rate was measured in normal and cancerous (glioma) human brain samples using a multichannel detector. Detector consisted of 8 isotrope fiber probes positioned around the central irradiating probe. Detecting probes were displaced one from other at a step 0.5 mm along the central irradiating fiber. Bare ends of detecting fibers were coupled with photodiode array. He-Ne (633 nm) or Nd:YAG (1064 nm) lasers were coupled with irradiating probe. Fluence rate was measured in each of 8 points in the depth range 5 mm. Measured mean penetration depths of 633 nm light were 0.70 mm, 0.50 mm and 0.40 mm for white matter, grey matter and glioma, respectively. For Nd:YAG laser, penetration depth was about 2.3 mm for normal tissue and glioma. Multichannel computerized detector allows to provide a small invasive real-time measurements of fluence rate in different tissues.

As a consequence of the needs to solve expensive simulations that include time dependent partial differential equations solutions in short time intervals, laser/tissue interaction modelling has a high, implicit and natural computational demand. Another kind of demand that must be considered is for graphical representation and exploratory analysis of the results. For the first problem, we have used the simulation case of light generation on a semiconductor laser, to derive a novel scheme to solve the computational problem using parallel computers. The solution gets high efficiency and scales well in a message-passing parallel architecture. For graphical demands and in order to make the modelling task easier and less expensive, we have developed a library of functions that can be used to build high quality graphical interfaces.

Different types of porcine tissue were irradiated with a surgical CO₂ laser. The generated aerosols were sampled on glass fiber filters and incubated with human peripheral blood cells. Afterwards, these exposed cells were subjected to the comet assay. The single cell gel electrophoresis or comet assay represents a powerful technique for the detection of DNA strand breaks in eukaryotic cells. In short, the electrophoretic mobility of DNA fragments is proportional to the quantity of DNA damage caused by the genotoxic agent in question. By investigating porcine tissue laser pyrolysis products, it is demonstrated that the comet assay is an appropriate tool to assess the genotoxic capacity of even a heterogeneously composed class of substances with unknown modes of action and interaction.

The number of sparks per time window between a scalpel electrode and tissue is a measure of the electrosurgical cutting ability with a strong dependency on the electrical power dissipation. This parameter used as controlled variable in an appropriate circuit allows controlling electrosurgical treatments with best cutting quality at any kind of tissue. It is presented the effect of this control unit with regard to therapeutic aspects and smoke emission. Histological investigations of porcine muscular tissue reveal drastically reduced boiled zones and zones of oedema formation at controlled cuts in comparison to common uncontrolled treatments. A further comparison of the harmful components in the electrosurgical smoke shows the great advantage of the new system.