The extent of tumor necrosis can be determined by the knowledge of the penetration depth of the light through tissue. So, we must determine the effective penetration depth `(delta) ' during treatment, depth at which the incident light intensity is reduced to 36.6%. Light transmission measurements through tissues is the experimental model usually used as a reference method to estimate the value of (delta) . In order to achieve subsequently on line and in situ light dosimetry during PDT, light backscattering has been studied in different concentrations of blue ink and intralipid-20%. All parameters which would influence the value of the back-attenuation coefficient (Sigma) <sub>ba</sub> have been reviewed separately. The results of transmission and backscattering measurements are compared. A correlation function `R' between (Sigma) _eff and (Sigma) _ba can be deduced, the knowledge of R allows us to determine the effective light penetration depth in tissue through backscattering measurement.

Fluence rates were measured in vivo at a piglet bladder wall during whole bladder wall (WBW) light irradiation at 458, 488, 514, 532, and 630 nm wavelengths. Bladder optical properties, the absorption-, scattering-, and anisotropy coefficient, were determined in vitro at these wavelengths using a double integrating sphere set-up. Monte Carlo (MC) computer simulations for WBW photodynamic therapy (PDT) were performed in a spherical geometry representing the bladder. The in vivo measured fluence multiplication factor ((beta) ) decreases from approximately equals 5 at 630 nm to approximately equals 1.5 at 458 nm. The simulated (beta) values, using the in vitro optical properties and non-absorbing (saline) bladder contents, are consistently larger with a minimum at 514/532 nm and a maximum at 458 and 630 nm. Simulations with slightly light absorbing bladder contents show that the inevitable urine in the cavity can at least partly be responsible for the lower in vivo values. Whereas the MC simulations use an in vitro absorption coefficient, the in vivo observed phenomenon might be attributed to additional light absorption by hemoglobin in the bladder tissue. Thus, WBW-PDT with red light is technically more advantageous than with green or blue light as this gives the strongest integrating sphere effect.

The optical properties of different types of tissue were measured in the wavelength range 330 - 1100 nm. The measurements were carried out in native as well as in coagulated tissues. We used the double integrating sphere technique to provide reflection and transmission measurements and a special homogenizing technique to prepare the tissue. The optical properties were evaluated using an inverse Monte-Carlo simulation, considering the geometry of the experimental set-up. All tissues show characteristic absorption bands at 420 nm and 550 nm, related to the strong absorption of hemoglobin. After coagulation the scattering increases drastically while absorption remains nearly unchanged. The anisotropy factor g increases with increasing wavelength and drops down slightly after coagulation.

Determination of laser light distribution in tissues is an important aspect of any laser treatment of living tissues. It is especially essential for clinical laser procedures where profile of light distribution changes during irradiation and requires adjustments of laser conditions. Time- resolved stress detection (TRSD) technique is developed for the monitoring of light distribution in laser irradiated biological tissues, and for the measurement of tissue optical properties. The z-axial profile of a transient stress generated in tissue under confined stress conditions of irradiation corresponds to z-axial distribution of absorbed laser energy in the irradiated volume. The shapes and amplitudes of stress transients induced in layered biological tissues carry information about absorption and scattering properties in each tissue layer. TRSD technique does not require any special preparations, such as tissue slicing, to determine differences in optical properties of layered tissue. The temporal profile of the acoustic signal formed by laser heating can be detected from tissue front or rear surfaces. These two options provide necessary flexibility for an investigator to measure various tissues in vivo. We present time-resolved measurements of acoustic transients induced in heterogeneous phantom tissues by nanosecond laser pulses. Results indicate a capability of TRSD technique to resolve differently absorbing tissue layers with 10 micrometers resolution. Sensitivity of this technique, its advantages and limitations are discussed. Capability of this technique to measure optical properties in layered tissues is defined by a combination of three factors: absorption coefficient, depth of certain layer and its thickness. Thickness of tissue layers with different optical properties can be measured with about 1-micrometers precision. Monte-Carlo simulations of light propagation in layered tissues yielded a good agreement with experimental results.

Novel light distributors for interstitial and esophageal photodynamic therapy are presented. A cylindrical light diffuser has been developed mainly for medical applications like interstitial photodynamic therapy, treatment of the bronchi and arterisclerosis. It can be made with a diameter as small as 1 mm or even less. For interstitial therapy, it can be introduced via a hypodermic needle. The main property of this light diffuser is the homogeneity of the light intensity emitted along its whole length which can be 100 mm or more, as well as its excellent radial homogeneity (360 degree(s)) and flexibility. Furthermore, its optical properties are hardly dependent on wavelength used for treatment (500 - 700 nm). Light distributors for esophageal treatment with homogeneity better than +/- 10% have been built and successfully used clinically. A measuring optical fiber allows the control of the dosimetry during the irradiation. Some other properties like the photosensitizer uptake in the tissue or the photobleaching can also be measured in situ and in real time during the treatment.

Optical fiber probes with isotropic response for direct measurement of fluence rate in tissue were studied. Two methods of probe fabrication were considered: in the first one, the isotropic spheres were fabricated by melting the fiber tips and then coated there with a layer of scattering material, in the second one, the spheres were fabricated from solid scattering material (milk glass). The core diameter of the quartz fiber was 120 micrometers ; maximum diameter of the probes was 420 micrometers . Anisotropy was determined as a standard deviation of light distribution at the isotropic fiber end. The second fiber end was coupled with different light sources: He-Ne, Ga-As lasers, or 200-W lamp. Melted probes had high anisotropy; it was necessary to cover the sphere by 4 or 5 layers to reduce the anisotropy less than 10%. Increase of isotropic response using a multi-layer covering was achieved at the expense of total transmission decrease (less than 1%). Melting technology deals with low reproduction and repetition of isotropic response. Anisotropy of glued probes was from 4.5% to 7.5% and total transmission ranged from 20% to 30%. Glued probes had sufficient mechanical strength to use their in vivo measurements of fluence rate. Because of influence of light coherency significant anisotropy increase was registered if the lamp was replaced by lasers.

Nd:YAG lasers emitting at 1064 nm are often used for coagulation of tissue in a non-contact mode, i.e. the treatment of verrucae, endometriosis, tumor coagulation and hemostasis. During this process an uncontrolled temperature rise of the irradiated area leads to vaporization and, finally, to a carbonization of the tissue surface. To prevent this, a dose controlled system was developed using an on-line regulation of the output laser power. The change of the backscattered intensity (remission) of the primary beam was used as a dose dependent feedback parameter. Its dependence on the temperature was determined with a double integrating sphere system and Monte-Carlo simulations. The remission of the tissue was calculated in slab geometry from diffusion theory and Monte-Carlo simulations. The laser control was realized with a PD-circuit and an A/D-converter, enabling the direct connection to the internal bus of the laser system. Preliminary studies with various tissues revealed the practicability of the system.

We performed an in-vivo study to identify and quantify the steps of volatilization. In all experiments, an infrared camera was used to record surface temperature during shot induced on in-vivo rat liver by a cw Nd:YAG laser. In a first group (5 animals), irradiation time varied from 1 to 9 seconds, power equals 20 watts and spot diameter equals 4 mm. Samples were immediately removed and fixed. In the second group (6 animals), time was fixed to 7 seconds. Liver from 2 animals was removed and fixed respectively at J0, J + 12 and J + 19. All sections were observed under microscope and damage depths measured. For irradiation time from 1 to 4 s, we noted blanching, temperature remained below 100 degree(s)C and damage depth was 850 micrometers . For durations from 5 to 7 s, we noted a dark red spot, temperature reached 145 degree(s)C and damage depth increased from 1800 to 5000 micrometers . For longer irradiation times, we noted coagulation, pop-corn effect, carbonization and tissue removal for 9 s. Damage depth was 5000 micrometers . Delayed histology showed that the necrosis was progressively separated from healthy tissue by a layer of conjunctive tissue. In-vivo volatilization could be described in 3 steps: coagulation, pop-corn effect, and tissue removal. We identified a relation between quantitative data and histological modifications.

Laser tissue welding has been applied successfully to several tissues using microscopic and macroscopic surgical techniques. The advantages of laser tissue welding include the formation of fluid tight bonds, decreased foreign body (suture) reaction scar formation, decreased anastomotic time and growth of the bond. The disadvantages compared to conventional suture and stapling techniques include decreased initial mechanical strengths, poor reproducibility and inadequate control of bond formation. These disadvantages have prevented general acceptance of laser-welding techniques by the general and specialty surgeon. Recently, several laboratories have introduced modified techniques to improve laser tissue welding. These include the use of exogenous dyes and bonding materials to make stronger bonds and computer driven temperature and optical feed-back systems to control bond formation. The advantages provided by the no-touch, fiberoptic delivery of precisely controlled laser light energy to limited endoscopic surgical fields are added reasons to reconsider the usefulness of laser tissue welding.

In vitro experiments on tissue of tympanic membranes of pigs have been performed to determine the threshold for thermal effects like coagulation and perforation with 633 nm laser radiation. An optical setup with a CCD camera was used to monitor the spot size of the laser beam. Up to 38 samples have been investigated by semi thin slides and visualized by HE coloring. The lowest intensity at which a damage occurred was 2.5 kW/cm². However even much higher intensities, for example 15 kW/cm², did not damage the tympanic membrane. Only in four cases laser induced damage occurred showing coagulation, carbonization, and perforation.

The goal of this work was to study the influence of pulse duration on acoustic transient generation in holmium laser ablation. For this, the generation and collapse of cavitation bubbles induced by Q-switched and free-running laser pulses delivered under water were investigated. Polyacrylamide gel of 84% water content served as a model for soft tissue. This gel is a more realistic tissue phantom than water because it mimics not only the optical properties but also the mechanical properties of tissue. The dynamics of bubble formation inside the clear gel were observed by 1 ns time resolved flash videography. A polyvinylidenefluoride (PVDF) needle probe transducer measured absolute values of pressure amplitudes. Pressure wave generation by cavitation bubble collapse was observed in all phantoms used. Maximum pressures of more than 180 bars at 1 mm from the collapse center were observed in water and high water-contents gels with a pulse energy of 200 mJ and a 400 micrometers fiber. A strong dependency of the bubble collapse pressure on the pulse duration for constant pulse energy was observed in gel as well as in water. For pulse durations longer than 400 microsecond(s) a 90% reduction of pressure amplitudes relative to 100 microsecond(s) pulses was found. This suggests that optimization of pulse duration offers a degree of freedom allowing us to minimize the risk of acoustical damage in medical applications like arthroscopy and angioplasty.

Erbium and Holmium lasers are ideally suited for cutting and drilling biological tissue. This is due to the fact that their wavelengths (Er:YSGG at 2.79 micrometers and Ho:YAG at 2.12 micrometers ) are strongly absorbed in water which is present in all tissues. Combined with an optical fiber these lasers seem to be optimal instruments for endoscopic and/or minimal invasive applications in surgery. In this study we focused our interest on cutting of human meniscus in the knee where, besides a very limited operation field, the standard arthroscopic treatment is performed in a liquid, highly absorbing environment. The bubble formation process, therefore, has to be well understood because it mainly determines relevant aspects of tissue ablation. The influence of the laser parameters in general and the influence of pulse duration in particular are determined in this paper for two different laser wavelengths. The goal was to determine the optimum laser parameters in view of a high ablation efficiency, a high precision and a minimal destruction of the adjacent tissue. To determine the optimum pulse duration for ablating tissue under water and to obtain a better understanding of the channel formation process, transmission and pressure measurements together with video flash photography were performed. Additionally, we determined experimentally the ratio between initial laser pulse energy and energy available for tissue treatment under water. To prove the results obtained, cuts in human meniscus were performed, sectioned and evaluated. The comparison between the results obtained with the Erbium and Holmium laser revealed a strong influence of the absorption coefficients on the tissue effects, especially on the ablation efficiency and on the zone of thermally and mechanically damaged tissue.

Pulsed photothermal radiometry (PPTR) method based on analysis of experimentally measured kinetics of non-equilibrium infrared blackbody (thermal) emission from a specimen subjected to pulsed laser irradiation has been used to investigate optical properties of tissues. Detailed investigations of thermal emission kinetics and the relationship caused by pulsed YAG:Er and YAG:Ho laser irradiation of tissues with different pulse duration and over a broad energy range up to the evaporation threshold have been performed. The spectrum of dentine in the IR region is presented.

The results of investigation of interaction of YAG:Ho laser radiation with soft tissue in contact and non-contact modes of processing under fiber-optical delivery system application are presented. The laser wound is evaluated according to the criteria of efficiency (energy of laser radiation spent to removal of unit volume of tissue) and invasion (ratio of irreversibly necrotized tissue volume to removed tissue volume). The dependencies of destruction efficiency index and laser wound invasion on energetical parameters of laser radiation and destruction rate are presented. The considerable difference of destruction efficiencies of contact and non-contact modes is shown. The requirements for optimum parameters of Ho- laser for surgery are formulated.

The physical parameters of the plasma-induced ablation mechanism were investigated using a picosecond Nd:YLF laser system. The laser consists of a diode-pumped oscillator and a lamp- pumped regenerative amplifier. It operates at a wavelength of 1.053 micrometers with pulse durations of 30 ps and pulse energies up to 1 mJ. The laser beam was expanded to a diameter of 4 mm and focussed to spot sizes of about 30 micrometers . At these high power densities a localized plasma was induced at the focal spot. Surfaces of extracted human teeth were used as target material. In order to study the effect of accompanying shock waves, dye penetration tests, hardness tests and polarized microscopy were performed. At moderate pulse energies no significant impact of shock waves was observed. Because of this result, the terms `plasma- induced ablation' or `plasma-mediated ablation' are more appropriate for ablations solely induced by plasma ionization, and should be distinguished from photodisruptive ablations. In another series of experiments the generated plasma sparks were spectroscopically analyzed. From the measured spectra, mean plasma temperatures of about 5 eV and mean electron densities of about 10¹⁸/cm³ were estimated.

An inner ear model was used to demonstrate thermal and mechanical effects occurring during Erbium laser stapedotomy. Results of inverse schlieren optical flash photography and time resolved pressure amplitude measurements indicate the existence of safe laser parameters for stapes foot plate perforation. Due to the high absorption of 3 micrometers radiation in water, efficient bone ablation and precise fenestration with small thermally damaged zones is achieved. Pressure transients caused by the explosive ablation process correlate with the spiking of the laser intensity. The energy of a laser pulse, directly applied into the perilymph through an already existing perforation, creates a vapor channel which afterwards collapses, sending out a strong pressure transient. The maximal amplitude of this pressure transient depends on the geometry and dynamics of the vapor channel and is several times stronger than the pressure amplitudes generated by the bone ablation process. This study shows that no permanent hearing loss or damage of inner ear structures is expected using an Erbium laser fluence of 10 J/cm².

The interaction between a pulsed Holmium laser and bone was investigated by measuring the volume and the shape of laser craters, produced by single laser pulses. The mean ablation rate, as obtained from these data, was compared to predictions of theoretical models which calculate the ablation rate from the light distribution in the bone. Result of this comparison is that scattering has to be seen as the important factor for the interaction of the Holmium laser radiation and bone.

The processes of interaction of Ho-laser radiation with bone tissue were studied. The data have been obtained on ablation threshold and efficiency of ablation. The temperature response on laser radiation influence has been investigated. The influence of water irrigation on temperature distribution has been accomplished. 3

A numerical combined model with movable boundary conditions having been used for the evaluation of Er-laser dental treatments is presented. This model facilitates the simulation of heat flows and temperature distribution in different kinds of human teeth caused by Er-laser irradiation with arbitrary orientation of laser beam axis. This model can be used for simulation and optimization of exposure parameters to minimize pulp overheating and procedure duration in the application of lasers for dental treatment.

We devised a diagnostic technique based on a pump-and-probe scheme that provided time- resolved imaging of photofragmentation effects during laser lithotripsy. The evolution of the cavitation bubble induced on kidney stone samples by underwater irradiation with a XeCl excimer laser is presented and analyzed.

In-vitro ablation experiments of calf brain tissue with ultrashort lasers are reported. Excisions have been performed by the mechanism of plasma-mediated ablation with focused picosecond laser pulses. Results achieved with a 35 ps oscillator/regenerative amplifier Nd:YLF laser at 1053 nm and its second and fourth harmonic at 526 and 263 nm, respectively, are presented. Preliminary experiments with 19 ps laser pulses at wavelengths near 3 micrometers generated by optical parametric amplification are reported. Here, during the ablation with low photon energies no plasma was induced. Furthermore, the spectrum of laser-induced plasma sparks on the surface of fresh calf brain tissue was recorded. Atomic line widths were measured and used to determine the electron density of the plasma. With energy densities of about 100 J/cm² values between 2 (DOT) 10¹⁷ and 5 (DOT) 10¹⁸ cm^-3 were found.

Plasma mediated ablations of calf brain tissue and corneal tissue have been performed with ultrashort pulses provided by different laser systems: A 30 ps Nd:YLF amplified laser with up to 1.5 mJ of pulse energy and a powerful 180 fs Ti:Sapphire oscillator/regenerative amplifier laser system capable of pulse energies of up to 300 (mu) J. With the femtosecond pulses the threshold in energy density needed for initiating the ablation process was found to be significantly lower than with longer pulse durations. Furthermore, the amount of ablated material is by a factor of two greater with the femtosecond pulses compared to the results obtained with the picosecond pulses. Histological examinations did not show any thermal or structural damage in adjacent tissue with pulses in the pico- and femtosecond range as it could be found after irradiation with longer pulses. The morphology of the excisions is of a very high quality.

The shock wave generation in stapes models during laser ear surgery is experimentally investigated. The intensity absolute measurements of shock waves generated by excimer laser in the treated bone are performed. It is shown that the roughness of the crater bottom profile depends on the laser beam fluence. It is revealed that in the pulse repetition regime of bone drilling there exists an optimal laser beam fluence, which provides as high a rate of drilling as the smooth bottom of the crater. For ArF and KrF excimer lasers the optimal fluence is equal to about 0.4 - 0.5 J/cm² at the repetition rate 5 Hz. The amplitude of shock wave induced at these parameters of laser beam in the back side of the bone sample of 1.1 mm thickness was measured to be about 25 bar and the corresponding pressure gradient 0.35 bar/micrometers .

Pulsed laser ablation of biological tissues under confined stress conditions (PACS) is demonstrated to be precise tissue removal with minimal thermal and mechanical damage to adjacent tissue layers. PACS was described based on results obtained with four complementary techniques: (1) laser-flash photography, (2) time-resolved stress detection (TRSD), (3) laser Michelson interferometry, and (4) pendulum recoil measurements. Comparison of ablation process was made between aqueous solutions and collagen gels. Experiments demonstrated two distinct ablation stages with different ablative forces that drive material ejection at temperatures substantially below 100 degree(s)C. The first stage is associated with the ejection of thin subsurface layer of the irradiated volume. The material ejection from a superficial layer (d << 1/(mu) _eff) is caused by a rapid growth of cavitation bubbles produced by laser-induced thermoelastic expansion in irradiated volume. The second, delayed stage of material removal occurs due to the collapse of coalesced cavitation bubbles in the depth (d <EQ 1/(mu) _eff) of irradiated volume. Collapse of large cavities with subsequent generation of turbulent motion toward medium surface can stimulate jets in liquids and plumes of debris in gels. Depending on water content and mechanical properties of a medium, the second stage may be either very pronounced (aqueous solutions) or practically absent (stiff gels). Estimates predict the possibility to remove precisely only a monolayer of cells employing PACS with an appropriate combination of laser wavelength and pulse duration.

For a few years promising techniques have been worked out for microsurgery of cells and organelles by laser micro-cutting and micro-drilling. In this paper the specific requirements for controlled and safe laser surgery at this scale are addressed. Laser micro-drilling is investigated for various interaction parameters. For this a Nd:YAG laser ((lambda) equals 1064 nm) in Q-switched (7 ns) mode and a cw diode laser ((lambda) equals 1.48 micrometers ) in pulsed mode are used. The lasers are coupled to an inverted microscope and focused through the microscope objective (40X and 45X) in a spot of 1 to 3 micrometers in diameter. Ablation of biological targets (mouse zygotes zona pellucida) is compared with ablation of model targets (ink films), all in liquid environment. Possible generation of acoustical transients and cavitation bubbles is monitored with a PVDF pressure transducer and by time resolved video flash photography. The results show that, for the pulse durations investigated, a large absorption coefficient is a necessary condition for controlled micro-drilling. In liquid environment, short pulse lasers in combination with a low light absorption coefficient of the target induce unacceptable mechanical effects related to the generation of a cavitation bubble. These effects are due to a too high energy threshold for ablation in these processes. Video images of the drilled holes reveal walls of regular shape with small surrounding damage immediately after laser irradiation, which are completely destroyed at the bubble collapse. By contrast, with the 1.48 micrometers laser diode, which is strongly absorbed by the target, reproducible micro-drillings without mechanical effects are performed.

The dynamic process of ablation during continuous laser irradiation was simulated using a finite-difference model. A summary of experimental results suggested a typical ablation velocity and the parameters of the model were adjusted to match this value. Then the model was perturbed by systematically varying each parameter to observe how sensitive ablation velocity was on that particular parameter.

Energy absorption, heat transfer, thermodenaturation and vapor blanket formation under the action of laser radiation pulse on pigmented spherical granules in heterogeneous laminated biotissues are investigated theoretically.

Various model calculations on the light transport at the ocular fundus are used in the literature either for interpretation of in-vivo reflectance measurements or for the prediction of photocoagulation effects. All these models take into account the absorption spectra of the pigments, known to be located at the eye ground: melanin, hemoglobin, xanthophyll and the receptor pigments. However light scattering inside the single fundus layers has not been investigated in detail and is therefore neglected in the calculations or is only considered by very rough approximations. This paper presents measurements at specimen of retina, retinal pigment epithelium, choroid and sclera using double integrating sphere technique. Absorption coefficients, scattering coefficients, and anisotropy of scattering were calculated by an inverse Monte-Carlo simulation from the measured collimated and diffuse transmittance and diffuse reflectance. Additional goniophotometric measurements were performed to determine the effect of the parallel aligned photoreceptors on the radiation transport. Conclusions are drawn for the interpretation of fundus reflectance measurements, which are a potentially useful tool in diagnostics and photocoagulation dosimetry, and for the calculation of temperature profiles, modelling the effect of coagulation.

A new method to determine optical properties of biological tissue, time-resolved stress detection (TRSD), was tested on albino rat skin, heated in vitro. The TRSD method is based on the detection of pressure waves that are generated by short laser pulses. The pressure waves carry information about the optical properties (absorption and effective attenuation coefficients) of the medium. The evaluation was done in a systematic way by comparing the results of the TRSD method with results obtained using an integrating sphere. Measurements for both methods were performed on the same skin samples to minimize biological variations. The TRSD method proved to be reasonably successful to determine optical properties of tissue for the used wavelength of 355 nm: (1) The effective attenuation coefficients of both methods agreed very well; (2) The TRSD method gave absorption coefficients of a factor 2 + 0.5 times higher than the integrating sphere method; and (3) The reduced scattering coefficients were sensitive to error.

For this research the spectral optical characteristics (diffuse spectral reflectance and transmittance) for a number of human teeth were measured in the 250 to 1500 nm region of the electromagnetic spectrum. From the reflectance and transmittance of the dental enamel the spectral absorptance and thus the attenuation coefficient can be determined. The optical characteristics of the human incisor/molar samples were measured with a Hitachi U3400 spectrophotometer and 60 mm (Phi) integrating sphere (IS) attachment, using a photomultiplier tube and PbS detectors. The characteristics of the IS attachment restricted the effective range of wavelengths that could be used to 250 - 1500 nm, which is also the wavelength range of interest. It is clear from the reflectance and transmittance characteristics of dental enamel that absorption is significantly higher in the UV and NIR regions than in the visible, with the attenuation coefficient the highest in the UV region from 250 to approximately 400 nm. The UV wavelengths may therefore prove to be extremely beneficial for laser dental procedures as a result of (1) better absorption, (2) simpler delivery systems than for CO₂, (3) possible germicidal effects at approximately equals 250 nm, (4) higher optical resolution attainable, and (5) reduced stray reflections from the tooth surfaces.

This study aimed to evaluate the interest of several liposome compositions (DPPC, DSPC, DPPA) to control specific ranges of temperature and to assess the possible use of temperature sensitive liposomes in an established model such as the liver as a new approach to monitor tissue temperature under laser irradiation. Temperature sensitive liposomes (DPPC or DSPC or DPPA) loaded with carboxy-fluorescein were injected to Wistar rats. The liver was exposed and irradiated with a 100 W Nd:YAG laser (single pulse mode, pulses ranging from 100 to 260 ms, spot diameter: 4 mm) to avoid direct absorption by the dye entrapped in the liposomes. The temperature was measured with an infrared camera during laser irradiation. The animals were then sacrificed and the liver was surgically removed. Immediately after, the fluorescence was measured -- ex vivo -- with a fluorescent imaging system. We were not able to prepare stable high transition temperature liposomes (DPPE). Concerning DPPC, the mechanism of dye release at the basal temperature led to a complete leakage of the dye in less than 5 minutes. Only background fluorescence was observed but no specific response due to laser irradiation. Nevertheless the results obtained using DSPC liposomes meet to a large extent our requirements since a useful monitoring of temperature is feasible from 42 degree(s)C to 62 degree(s)C. In fact the critical temperature of most tissues varies from 53 degree(s)C to 58 degree(s)C.

The new model of biotissue as a medium with two kinds of inhomogeneities -- small-scale, representing randomly placed scatterers and absorbers, and large-scale, corresponding to the macroscopic structures -- is proposed. The first and second moments of space-angle intensity distribution of the optical beam propagating in such medium are considered. It is shown that the possibility exists to define parameters of each scale inhomogeneity separately through the moments measurements for conditions often realized in medicine. The results are suitable for development of optical non-invasive diagnostic methods.

Noncontact high-accuracy techniques are very actual in real time in medicine and biology. An analysis of laser light fluctuations may indicate a state of a muscle tissue. In the study spectral characteristics of a dynamic speckle field scattered by skin over a muscle are investigated in detail. Among them: a power of fluctuations, a ratio of spectral amplitudes for two different harmonics, an average frequency of fluctuations, a spectral highwidth, and so on. A variation of these parameters during tonus changing are discussed. The power of fluctuations has the largest dynamic range.

Optical properties of human hair are the subject of great interest for the realization of any possible cosmetic applications. This paper represents the results of hair microstructure as an optical substance investigation, indicates melanin and keratin absorption spectra, and shows experimentally discovered anisotropia of optical properties of human hair. Radiation weakening coefficient value at the range from 450 up to 800 nm is estimated. Thresholds of hair destruction by Nd, Ho, Cu, and Er laser radiation are obtained. Perspectives of laser application for epilation and other medical purposes are evaluated.

Most biological tissues consist of layers with different optical properties. A few examples are the skin, the esophagus, the stomach and the wall of arteries. An understanding of how the light propagates in such layered systems is a prerequisite for any light based therapy or diagnostic scheme. In this study we investigate the influence of different kinds of layers on time resolved reflectance measurements. Experiments were performed on layered gel phantoms and the results compared to Monte Carlo simulations and diffusion theory. It is shown that when a low absorbing medium is situated on top of a high absorbing medium, the absorption coefficient of the lower layer is accessible if the differences in the absorption coefficient are only small. In the case of large difference the optical properties of the upper layer dominate the signal and shield information on the lowest layer. The degree of this shielding effect depends on layer thickness as well as optical properties. In the case of an almost absorption and scattering free layer in between two normal tissues, an overall increase of the signal is visible. However, the overall shape of the curve is about preserved. The apparent scattering coefficient is slightly decreased, while the apparent absorption coefficient is unaltered.

The statistics of backscattered light are used for tissue discrimination. The time series of the detected light is considered as realization functions of weak stationary processes. Auto- and cross-spectra, as well as squared coherencies, are computed. The validity of the method is demonstrated by differentiation between normal tissue and tumor and for detection of therapy efficacy in photodynamic therapy.

The clinical objective in treatment of port wine stains is to maximize thermal damage to the abnormal blood vessels without introducing thermal damage to the normal overlying epidermis. The rationale of dynamic cooling is to protect the epidermis from thermal damage by selectively cooling this layer down immediately before delivering the laser pulse. This work discusses the thermal dynamics of epidermal cooling by milliseconds cryogen spurts and melanosomal heating by the laser pulse.

Monte Carlo (MC) simulation model and the thermoindicative tissue phantom were applied for evaluation of a depth of tissue necrosis (DTN) as a result of quasi-cw copper vapor laser (578 nm) irradiation. It has been shown that incident light focusing angle is essential for DTN. In particular, there was a significant rise in DTN parallel to elevation of this angle up to +20 degree(s)C and +5 degree(s)C for both the MC simulation and tissue phantom models, respectively, with no further increase in the necrosis depth above these angles. It is to be noted that the relationship between focusing angles and DTN values was apparently stronger for the real target compared to the MC-derived hypothetical one. To what extent these date are applicable for medical practice can be evaluated in animal models which would simulate laser-assisted therapy for PWS or related dermatologic lesions with converged 578 nm laser beams.

Some biophysical and mathematical aspects of development of a computer model of low- intensity laser radiation influence on the dynamics of the x-irradiated bone marrow tissue hemopoiesis are discussed.

In this work the mathematical model presented describes the processes in the epidermis sensitized by the furocoumarins under UVA-radiation of pulse laser.

For the study of some primary photochemical mechanisms of neuron response to laser microirradiation it was modified with quenchers of intermediate photochemical products. Dibunol (0.02 mM), inhibitor of lipid peroxidation, did not shift impulse activity itself, but changed neuron response to microirradiation: impulse frequency acceleration was lower than control, spike generation ceased at higher frequency levels, and neuron lifetime increased by 1.7 times. Hence, impulse acceleration phase is probably connected with membrane lipid peroxidation induced by blue light and dibunol protects cells from laser injury. The study of hydroxyl radicals (important in ionizing radiation cell damage) participation using quencher D- mannite (10 mM) did not show reliable changes of neuron response parameters, i.e., these radicals were not significant for blue laser light induced neuron activity changes. Observation of flavin-like action spectrum with a maximum near 460 nm forced us to use a flavin triplet quencher. Ten mM NaJ did not shift impulse frequency level but changed neuron response to irradiation: cell lifetime increased by 1.4 times due to inhibition phase increase. It is not proved that flavin triplets were involved in neuron response and its lifetime increase was due to rather physiological than photochemical causes.

Vapor generation initiating by the action of laser radiation pulses on pigmented granules in biotissue is investigated theoretically.

Laser angioplasty as a method of removal of atherosclerotic plaque from arterial walls is still being developed as a reliable medical procedure. Problems encountered are thermal damage to surrounding tissue, perforation of the arterial wall, and identification of the atherosclerotic plaque that is to be removed. This study concentrates on the problem of distinguishing between the atherosclerotic and normal arterial tissue. Spectral optical characteristics, such as reflectance and fluorescence of the atherosclerotic tissue, could provide useful information to be implemented for identification purposes. The total reflected light (specular and diffuse reflectance plus fluorescence) of atherosclerotic arterial tissue and unaffected arterial tissue were measured between the wavelengths of 250 nm and 800 nm, using a double beam spectrophotometer, Hitachi U3400. The results show significant differences between the affected and unaffected aorta samples in the ultraviolet region, especially at the wavelengths 315 nm and 400 nm. These differences can be used as criteria to identify atherosclerotic plaque from normal arterial tissue. An instrument can be developed to be used with laser angioplasty. This instrument can combine the identification and ablation processes by using a 308 nm excimer laser, which emits light close enough to the 315 nm identification criteria and removes atherosclerotic plaque successfully.

There has been much interest in the biological effects of low energy visible and near infrared lasers. Most of the experiments show that low energy visible and near infrared lasers do have specific bioeffects which seem to change from stimulatory to damaging with increasing doses. In the present work we irradiated keratinocytes with various light sources (360 nm, 540 nm, 630 nm, and 780 nm) and found that at a specified, relatively low energy dose there is an accelerated cell mitosis. The percentage of dividing cells 24 hrs following exposure increased by 2 - 3 fold. Cell number in the treated cultures increased between 48 and 72 hrs by a factor of 1.3 - 2. We have suggested that the effect is due to light absorption by either endogenous porphyrins or cytochromes in the cell. Porphyrins and cytochromes are photosensitizers. At low irradiation doses, small amounts of singlet oxygen (¹O₂) or other oxyradicals are produced, providing the energy needed for cell proliferation. We have examined our assumption by introducing very small amounts of hematoporphyrin derivatives (HPD) into the fibroblast cells, measuring their proliferation after light irradiation. We have found that in comparison to previous results a smaller energy dose of 360 nm light is needed to enhance proliferation. These preliminary results have important implications in phototherapy and in photodynamic therapy.

The results are presented of investigating the influence of intravenous laser irradiation of blood (ILIB) on the immunity T-systems in animals with peripheral nervous system traumas in dynamics. It is shown that ILIB produces a positive effect on T-lymphocytes. After the second course of irradiation the proliferative activity of lymphoid cells increased compared with the original level by a factor of two on the average.

The irradiation of large surfaces or the whole body with copper vapor or ultraviolet lasers causes the structural changes of the bone marrow, skin, and intestine cells indicating the acceleration of their proliferation and differentiation. The increase of migration of the bone marrow cells in stroma and epithelial layers of organs indicates the intensification of intercellular intertissue interactions. This phenomena takes place in doses not more than 0.2 J/cm² for ultraviolet and 0.5 J/cm² for copper vapor lasers. The greater of the doses cause the damages of bone marrow, skin, and intestinal cells.

To understand the effects of laser radiation on live cells and tissues it is important to take into account not only the laser parameters but also the temporal and spatial peculiarities of the live objects. The temporal dynamics of the parameters of a live cell or tissue should be taken into consideration when making the prognosis of the effects of any laser. The chronobiological approach allows us to automatically take into account the individual peculiarities and the current functional state of the live objects, which makes it possible to exclude `nonstandard' effects of laser action and to diminish their poor determinability and high variability. Modulation of the intensity of laser irradiation by the signals of registered biorhythms of the irradiated cell or organism enables us to guarantee stable amplification of plastic processes, restoration of the levels of function and biosynthesis.

The action of laser radiation on arbitrary selected points of skin in the wavelength range 440 - 1060 nm and power range 40 mW - 4 W caused threshold and near threshold skin sensations. The warm sensations and skin pain were observed. The skin pain sensations are probably related to the radiation action on free nerve endings in the epidermis (specific skin pain) or upon the receptor system situated under the epidermis (nonspecific skin pain). The warm sensations are related to the radiation action on temperature-sensitive points of skin. The dependence of stimulus intensity on its duration for the threshold thermal sensations was revealed.

In experiments on white rats the influence of He-Ne laser radiation ((lambda) -- 632.8 nm, power density -- 1.5 mW/cm²) and electromagnetic field of extremely high frequency (42.0 - 43.3 GHz, 1 mW/cm²) on transplantability and growth of fibroadenomas of mammary glands, and influence of low power laser irradiation on transplantability and growth of Walker carcinosarcoma were investigated. Skin at the site of future transplantation underwent irradiation. He-Ne laser and EHF-radiation were stated to change properties of tissue accepting tumor cells. A single laser irradiation of the inoculation site of Walker carcinosarcoma cells produced no effect on tumor transplantability, but increased the average life span of animals. Laser and EHF irradiation increase the transplantability of fibroadeonomas but depress growth and rate of multiplication of tumor cells.

It was observed in some experiments that visible laser radiation activates the enzymatic function of mitochondria, while infrared laser radiation affects the enzymatic activity of cellular membranes. The aim of the study was to estimate the activity of some membranous as well as mitochondrial enzymes of hepatocytes in rats irradiated with infrared laser. Experimental material consisted of 38 Wistar rats divided into 2 groups -- a studied group exposed to infrared laser radiation and a control group, in which no irradiation was made. A semiconductive infrared laser (wavelength -- 904 nm, mean power -- 8.9 mW) was used. The clean-shaven skin of the right infracostal region of animals was irradiated 5 minutes daily for 15 consecutive days. After finishing the experiment in the preparations from obtained segments of the left liver lobe, the enzymatic activity of succinate dehydrogenase (SDH, EC 1.3.99.1), lactic dehydrogenase (LDH, EC 1.1.1.27), Mg²⁺ dependent ATP-ase (ATP-ase Mg²⁺, EC 3.1.3.2.) and acid phosphatase (AcP, EC 3.6.1.8.) was estimated with the use of histochemical methods. In the case of SDH and LDH the increase of enzymatic activity was observed in all 3 zones of liver cluster, especially in male rats. In the case of ATP-ase Mg²⁺ and AcP the increase of enzymatic activity in biliary canaliculi of hepatocytes in all zones of the liver cluster was observed. On the basis of the obtained results it was proved that infrared laser radiation activates significantly the enzymatic activity of most of the analyzed enzymes, which means that it affects not only properties of biological membranes but also activates the oxidoreductive processes of organism, as it has been observed for visible laser radiation. On the basis of the spectrum of energetic levels in macromolecules (Jablonski's diagram) the mechanisms of availed results are discussed both for enzymes possessing and not possessing chromatophores.

The simple molecules, water, carbon dioxide, carbon monoxide, and hydrocyanic acid, as well as volatile organic substances have been used to investigate fundamental processes arising during laser tissue interaction. The compounds have been determined by gas chromatography (GC), by gas chromatography in combination with mass spectrometry (GC/MS), and by help of an ion selective electrode. Especially, the dependence of the emitted substances, irradiating porcine tissue (bone, muscle, and liver) with XeCl, TEA CO₂, and cw CO₂ laser radiation, on different reaction gases are appropriate to obtain information on basic processes. The results demonstrate that oxidation is a process effective in rivalry to the formation of such toxic substances as carbon monoxide, hydrocyanic acid, and styrene as a typical volatile organic compound. The moisture content of tissue is another parameter influencing the interaction processes characteristically. It is possible to reduce the emitted amount of harmful chemicals working in an oxygen containing atmosphere or with a high water content in the reaction zone.

Reactions of biological tissues treated with either laser or electrosurgery devices are mainly governed by the temperature field in the area of treatment. The dependence of the emission rate of volatile organic compounds (VOC) on the temperature of the reaction zone was determined in vitro for these devices. Different kinds of tissue (porcine liver, muscle and skin) were vaporized under standard conditions. Power settings of a Nd:YAG laser and a CO₂ laser and those of an electrocauter were varied in different measurements. The temperature development in the area of treatment was determined with a thermocamera. VOCs were collected simultaneously under realistic conditions during the treatment. The samples were evaluated and analyzed using a multisorbent sampler and capillary gas chromatograph system (GC).

Toxic and carcinogenic substances were produced during laser application in medicine for the cutting and evaporation of tissue. The laser smoke presents a danger potential for the medical staff and the patients. The laser tissue interaction process was investigated by means of laser spectroscopic measurements which give the possibility of measuring metastable molecular states directly as a prerequisite to understand and to influence fundamental laser tissue interaction processes in order to reduce the amount of harmful chemicals. Highly excited atomic and molecular states and free radicals (CN, OH, C₂, CH, CH₂) have been detected applying spontaneous and laser induced fluorescence methods. It was found that the formation of harmful substances in the laser plumes can be reduced significantly by optimization of the surrounding gas atmosphere. A high content of oxygen or water in the interaction zone has been found, in agreement with the results of classical and analytical methods, as a suitable way to decrease pollutant emission. The experimental methods and the principal results are applicable not only in laser medicine but in laser material treatment generally.

Liver and muscle tissue have been irradiated with a surgical CO₂-laser. The prefiltered fumes were adsorbed on different sorbents (activated charcoal type NIOSH and Carbotrap) and desorbed with different solvents (carbondisulphide and acetone). Analysis was done by gas chromatography/mass spectrometry. An updated list of identified substances is shown. Typical Maillard reaction products as found in warmed over flavour as aldehydes, aromatics, heterocyclic and sulphur compounds were detected. Quantification of some toxicological relevant substances is presented. The amounts of these substances are given in relation to the laser parameters and different tissues for further toxicological assessment.

A total of 148 volatile compounds were identified from the laser plume produced by a 10 W CO₂ laser upon irradiation of pig liver. Structure elucidation was carried out by coupled gas chromatography mass spectrometry using reference samples. The identified compounds include hydrocarbons, alcohols, aldehydes, acids, esters, amides nitriles, ketones, furans, phenols, pyrazines, pyridines, and sulphur-compounds. Toluene, styrene, methylpyrazine, benzaldehyde, benzylcyanide, 4-methylphenol, indol and scatol for the major components of the pyrolysis products; derivatives may also reach higher concentrations. An interesting group of O/N-compounds with closely related chemical structures remained unknown.

Systematic investigations of the consistence of laser plume need reproducible conditions in terms of geometrical, optical and time scale parameters, which are to be quite well-defined in a carefully set up in vitro experiment. However, the conditions of plume production differ significantly in the surgical environment. Moreover, the sampling procedure for examinations of plume during laser operations is governed by the priority of the patient's treatment and must not disturb the progression of the operation. This has to be taken into account for estimations of the possibly existing hazard for the patient and the operating room staff on the basis of results of in vitro experiments. For laser-microlaryngoscopic operations in the ENT- clinic an intra-operational sampling procedure was designed. In comparison to other areas of laser surgery, laser-microlaryngoscopies allow a relatively well controlled trapping of the plume, using a microlaryngoscope especially developed for efficient laser plume evacuation. The results are compared to those obtained by application of the intraoperational sampling procedure in an in vitro simulation and to those yielded by in vitro experiments.

A common application of the Neodymium:YAG laser (1064 nm) is the treatment of nasal polyps. The polyps are treated endoscopically with laser power settings of 5 to 10 watts delivered via a flexible fiber with a core diameter of 600 micrometers . Coagulation and vaporization are accompanied by a severe development of dust and plume during the treatment. These products are normally aspirated during the treatment together with cooling fluent via the working channel of the endoscope. Due to the rather low efficiency of the aspiration the products are partly aspirated by the patient. Volatile organic compounds (VOC) were adsorbed and evaluated with a gas chromatography system (GC). The calibration of the system together with geometrical considerations of the adsorption allows for a quantitative determination of several products. Among these toluene is used as a marker substance. Besides the plume samples collected during the treatment of polyps investigations of VOCs were carried out of samples received during Nd:YAG laser treatment of nasal warts and CO₂ laser treatment of leucoplakia. The evaluated data led to an estimation of the patient's health risk assuming aspiration of the products by the patient. Improvements of the aspiration system are suggested.

Aerosols, vapors, and gases in smoke produced during laser treatments of tissue can be a nuisance to the operating team and the patient and may be the source of potential health hazards. This paper provides information on distribution models as a link between aerosol and gaseous emission and immission to persons in the operating room. In vitro measurements according to this model were performed in an operating scenario. During vaporization of porcine liver with a CO₂ laser (20 W cw) respirable fine dust was collected at several measuring points in a typical operating room. The fine dust concentration was acquired at three measuring points both as the mean value of 30 minutes and as six consecutive measurements of five minutes each. Since the maximum concentration was measured above the treated surface the operating surgeon is likely to aspirate most of the dust. Thus the immission concentration of volatile organic compounds (VOC) typically produced during vaporization was also determined at this measuring point. The measured values were compared to theoretically predicted developments of concentrations of dust and VOC. To estimate the potential health hazards the measured concentrations were related to threshold limits given by the European authorities.

Use of laser systems in minimal invasive surgery results in formation of laser aerosol with volatile organic compounds of possible health risk. By use of currently identified chemical substances an overview on possibly associated risks to human health is given. The class of the different identified alkylnitriles seem to be a laser specific toxicological problem. Other groups of chemicals belong to the Maillard reaction type, the fatty acid pyrolysis type, or even the thermally activated chemolysis. In relation to the available different threshold limit values the possible exposure ranges of identified substances are discussed. A rough estimation results in an exposure range of less than 1/100 for almost all substances with given human threshold limit values without regard of possible interactions. For most identified alkylnitriles, alkenes, and heterocycles no threshold limit values are given for lack of, until now, practical purposes. Pyrolysis of anaesthetized organs with isoflurane gave no hints for additional pyrolysis products by fragment interactions with resulting VOCs. Measurements of pyrolysis gases resulted in detection of small amounts of NO additionally with NO₂ formation at plasma status.

We present the process controlling of a high-frequency surgery generator during tissue treatment. Hereby, the temporal behavior of the voltage and the current are measured and then the finger print of the generated light arc in the electrical characteristic is analyzed by the control unit. This unit forces the high-frequency generator to supply an appropriate electrical power for different kinds of tissue. The functional ability is verified by cuts with different set points of the controlled variable, therefore, different degrees of slough, and cuts through tissue heterojunctions.

Laser plume and particulate debris distribution during laser ablation of tissue can vary strongly depending on laser type and laser parameters. Investigations were made by means of particle flow visualization and particle density monitoring for both cw- and pulsed lasers. It turns out that the dynamics of fine dust particles are quite different from those of larger particles consisting of aggregates of cell fragments or complete cells. Consequences for the design of plume suction units and other safety means are discussed.

Efficiency and precision of intraluminal laser incisions of soft tissue were investigated particularly for reopening ureteral strictures. We used mid-IR laser radiation and an application system which nearly tangentially performed the contact incision via a low-OH quartz fiber to achieve a longitudinal cut through the whole ureter wall up to the periureteral fat tissue. With pulsed Holmium and Thulium laser radiation we investigated in vitro (using the model of pig ureters) the cutting efficiency and coagulation zone with respect to laser power, pulse length, cutting speed and fiber diameter. The thermo-mechanical mechanism of tissue ablation was evaluated by fast flash photography showing a growing influence of the cavitation bubble towards shorter pulse lengths. In a first clinical study 14 patients underwent the laser therapy. We used the Holmium laser in the free running mode at a pulse repetition rate of 10 Hz and with an average power of 3 W at the end of a 300 micrometers fiber. The reopening of the stenoses took about 19 min. with an average laser energy of 819 J applied. The whole procedure was observed by videoscopy. No bleeding could be seen and no complications during the laser treatment occurred.

The effect of water content on ablation rates in hard tissue is considered. Two wavelength regimes and two types of tissue (dentin and bone) are compared. In the UV (XeCl excimer at 308 nm) the ablation rate is lower in dehydrated dentin than in fresh dentin. In dehydrated dentin the ablation rates at 2.5 J/cm² and 7.0 J/cm² are 0.6 and 0.8 micrometers /pulse, respectively. In fresh dentin the rates are nearly three times as large. A logarithmic increase is indicated. Dentin ablation with the IR (Ho:YAG, 2.1 micrometers ) showed a similar trend to that of dentin XeCl ablation: fresh samples ablated faster then dehydrated samples. Ablation rates are considerably higher in this case and range, from 1.7 micrometers /p at 20 mJ/p to 21.5 micrometers /p near 230 mJ/p in dehydrated dentin. In fresh samples for the same energy range the ablation rates were 5.1 to 213 micrometers /pulse. This effect was reversed in cortical bone. Here ablation rates of dehydrated bone were higher than those of fresh bone. In fresh bone, ablation rates ranged from 1 micrometers /p at 50 mJ to 48 micrometers /p near 300 mJ/p and in dehydrated bone from 7 micrometers /p at 30 mJ to 68 micrometers /p near 280 mJ/p. Possible explanation of these observations are discussed.

A set-up with an integrating sphere and a narrow-beam arrangement was used in order to derive the optical properties in vitro of 1 mm thick tissue slabs. The measured macroscopic quantities, the reflectance, and the total transmittance were correlated to the tissue optical properties by Monte Carlo simulations. Mie calculations were performed to be able to calibrate the set-up with a solution of latex spheres and ink. Finally, the optical properties of rat liver samples were measured, before and after photodynamic therapy, showing approximately a 40% increase of the absorption coefficient at 650 nm due to the treatment.

Hysterectomy is the most common major operation performed in the United States with dysfunctional uterine bleeding being a major indication. Endometrial destruction by photodynamic therapy (PDT) has been suggested as a possible alternative to invasive surgical procedures for abnormal uterine bleeding due to benign changes. Effective destruction of the endometrium during PDT requires a sufficient amount of light to be delivered to the entire endometrium in a reasonable time. To satisfy these criteria, we have developed a trifurcated optical applicator consisting of three cylindrical diffusing fibers. The applicator was inserted into freshly excised, intact human uteri and the optical distribution was measured with an isotropic fiber probe at various locations in the uterus. The results were in good agreement with the predictions of a mathematical model based on diffusion theory. The results indicate that irradiation of the endometrium by the trifurcated applicator can destroy tissue to a depth of 4 mm given an optical power of 100 mW per cm of diffusing tip (100 mW/cm) for an exposure time of less than 20 minutes.