The visual appearance of port-wine stain lesions is often a red to purple color due to an enlarged blood volume in the upper dermis. The purpose of the treatment is to re-establish normal skin coloration. Visual reflectance spectra should therefore, in principle, contain all relevant information about the lesion. The influence on the spectra from the different tissue parameters, such as melanin, blood content and scattering, is rather composite. However, a simple mathematical model can give a good understanding of the relevance of the different components. This knowledge can be used to optimize the laser treatment of port-wine stain. In vivo reflectance spectra were obtained using an integrating sphere spectrophotometer. A simple mathematical model based on the diffusion approximation was used to simulate port- wine stain and normal skin reflectance spectra. The absorption coefficients of epidermis and dermis are mainly due to melanin and blood. These parameters were measured in separate in vivo experiments and obtained from skin biopsies. The scattering coefficients were based on reported values. Simulated reflectance spectra show good agreement with the measured ones. Even though the diffusion model has limited validity for wavelengths shorter than 600 nm, the simulated spectra from 450 to 600 nm give a qualitative understanding of the influence of the tissue parameters. The results show that dark red to almost dark grey port-wine stains contain enlarged blood fraction in the entire upper dermis. The red port-wine stains appear when the abnormal density of blood is confined to a thin layer. High amount of epidermal melanin results in reduced reflectance throughout the visible spectrum. The characteristic spectrum due to the blood is suppressed. The reflectance spectra are strongly dependent on the dermal and epidermal scattering coefficient; even minor changes as naturally occurring with age, might have a significant impact. A permanently reduced scattering coefficient might result in a reddish coloration even when a normal blood content is restored. Correlation between measured and simulated spectra give a good understanding of the importance of the parameters determining the visual appearance of port-wine stain.

To study inherent differences in skin function related to regional variation, we tested the hypothesis that different reactivities of small blood vessels via their direct and indirect activation by histamine play an important role in the observed regional variation of processes. Histamine was administered to three cutaneous regions in 20 volunteers, and the induced response was quantified utilizing spectrophotometry and laser Doppler flowmetry. The back exhibited the greatest response, followed by the forearm and ankle in decreasing order of responsiveness. We suggest that the intensity of the wheal and flare response may partly be related to the local reactivity of the blood vessels once the histamine actually reached them, and to their indirect dilatation via the axonal reflex. These blood vessel response observations may provide initial insight into inherent functional differences influencing cutaneous manifestations of endogenous and exogenous diseases.

Specifying the distribution of laser energy within a tissue is the first step toward understanding and capitalizing on a variety of laser-tissue interactions. Whether photothermal, photochemical, or photomechanical in nature, laser-tissue interactions begin with the absorption of photon energy. The spatial distribution of photon absorption specifies the required laser exposure to be delivered and the extent of subsequent therapeutic action. Using infrared tomography (IRT), the broad, long term objective of this research is the development of a three-dimensional tomographic reconstruction algorithm (TRA) as a means to determine the: (1) initial space-dependent temperature increase in subsurface chromophores [(Delta) T_CHR((xi) ,(eta) ,(zetz) ,t equals 0)] immediately following pulsed laser exposure; and (2) depths and physical dimensions of discrete subsurface chromophores. Analysis of the recorded time sequence of infrared emission images [(Delta) M_CHR(x,y,t)] by longitudinal inversion and lateral deconvolution algorithms provides a direct means to determine the depths and physical dimensions of subsurface chromophores. Although our research is being shared with workers in a variety of disciplines, and pertinent to many clinical applications involving laser-induced photothermal mechanisms, we are particularly interested in addressing the problems associated with determination of the initial space-dependent temperature increase in subsurface chromophores in human skin in general, and port wine stain (PWS) blood vessels in particular.

The clinical objective in laser treatment of selected dermatoses such as port wine stain (PWS), hemangioma and telangiectasia is to maximize thermal damage to the blood vessels, while at the same time minimizing nonspecific injury to the normal overlying epidermis. 'Dynamic' cooling of skin, whereby a cryogen is sprayed onto the surface for an appropriately short period of time (on the order of tens of milliseconds), may offer an effective method for eliminating epidermal thermal injury during laser treatment. We present theoretical and experimental investigations of the thermal response of skin to dynamic cooling in conjunction with pulsed laser irradiation at 585 nm. Computed temperature distributions indicate that cooling the skin immediately prior to pulsed laser irradiation with a cryogen spurt of tetrafluoroethane is an effective method for eliminating epidermal thermal injury during laser treatment of PWS. Experimental results show rapid reduction of skin surface temperature is obtained when using tetrafluoroethane spurts of 20 - 100 ms duration. Successful blanching of PWS without thermal injury to the overlying epidermis is accomplished.

The liquid phase spectra of tatoo pigments are shown to be unreliable as a basis for mechanistic deductions. The reflectance spectra of the solids from 2000 nm to 500 nm (5000 to 20,000 cm^-1) are shown to accurately assess the relative loss of laser light for different pigments and to be useful in examining these to check for similarities in the pigments. The absorbance differences between the pigments are shown to be largely irrelevant in assessing the ease of tatoo removal by laser radiation of a variety of wavelengths. A multiphoton absorption mechanism with its concomitant shock wave is proposed to be responsible for the reduction of pigment particles to small sizes which the lymph system can remove. The different behavior of blue and green tattoos, treated by Q-switched ruby and Nd:YAG lasers, is attributed to the particle aggregation size of the pigments in the tattoo.

Laboratory and mathematical skin examination has played an important role in defining the clinical usefulness and limitations of laser, developing concepts and techniques that have further improved the effectiveness of laser treatment. In addition to this, new technological developments over the years, have helped define the specificity of laser-tissue interaction. Instantaneous conversion by thermal energy of water in a liquid state to a gaseous state when irradiation of skin is done by high power density carbon dioxide laser in short pulses, occurs so quickly that there is minimal thermal conduction to the adjacent tissues structures. The zone of thermal injury could be minimized to the order of only 50 micron thick. In spite of the limited effects of heat conduction, coagulation in vessels can be obtained as well, since small blood vessels are immediately sealed by the laser. Modern carbon dioxide systems can be programmed and make it possible to reproduce shots precisely to vaporize identically thin layers of soft tissue, since absorption by intracellular water limits the depth of penetration. Moreover, collimated handpieces make it possible to deliver a fixed beam diameter and a constant power density as the handpiece is steadily moved over lesions situated on uneven facial contours. The use of large spot sizes gives a more uniform vaporization thus damaging adjacent tissues to a lesser degree, but enlarging of the spot size requires higher energy levels per pulse so that the whole surface can reach a sufficiently high fluence for clean vaporization to take place. For this to be achieved, the fluence required is about 4 - 5 J/cm² and so UltraPulse^R carbon dioxide laser with a 3 mm spot size may be operated with optimal parameters for clean ablation. The resulting surface, covered by dry debris, can be removed by gently scrubbing to avoid thermal build-up, otherwise this remaining tissue can act as a refracting surface as the practical absence of water content means that the carbon dioxide laser light is not efficiently absorbed. This process is repeated layer-by-layer using the same laser parameters until all remaining abnormal tissue has been grossly removed. Utilized as a chain of rapid, short (approx. 1 ms) pulses, with high peak power, tissue can be effectively eliminated, taking advantage of the concept of the known thermal relaxation time of soft tissue. The current laser systems which are built according to the new concept of high technology based upon the knowledge of laser tissue interaction, known as UltraPulsed^R Carbon Dioxide Laser, are capable of precise ablation and also of being used in cosmetically sensitive areas with minimal thermal damage. Although the precise clinical role for this laser has yet to be accurately defined, the potential benefits offered by its use appear to be substantial.

We carried out the synthesis of the new compounds -- sulfonated mono- and diphthalocyanines of d- and f-elements (^sPcM, ^sPc₂M). The unusual geometry of these compounds leads to the appearance of new properties -- they are highly water soluble, non- toxic and in contrast to porphyrines they strongly absorb clinically useful light. Suitable methods for synthesis of unknown before water soluble Ga, In and Ti phthalocyanines have been developed. Our investigations show that these compounds are prospects for plastic surgery.

The present paper is devoted to the analysis of optical properties of hard tooth tissues in a wide range of light intensities. The main features of light reflection from enamel surface and light propagation in enamel and dentin are considered. The possibility of observation of various nonlinear effects in dental tissues are analyzed. The mechanisms of laser destruction of enamel and dentin are classified and the models of correspondent processes are considered.

Depth and profile cavity were studied after laser ablation with different energy of Er:YAG laser beam. Longitudinal sections of extracted human teeth were cut and polished to the flat surfaces. The thickness of layer of prepared teeth was from 3 to 5 mm. The check group contained glazed samples of ivory with the similar thickness. The Er:YAG laser drilling machine was operating in a free-running mode. For the preparation we used the energy up to 500 mJ. The repetition rate was 1 or 2 Hz. The laser radiation was focused on the tooth surface using CaF₂ lens (f equals 55 mm). During the experiment, teeth were steady and the radiation was delivered by the mechanical arm which was fixed in a special holder. The fine water mist (water - 50 ml/min with the pressure to atm, air-pressure three atm) was used. Samples with the flat surfaces from the enamel, dentin and ivory were irradiated with five different energies from 100 to 500 mJ. Quantities of one, five, ten, twenty and thirty pulses were used. The depth of cavity and its profile were observed and measured. It was found that depth of cavity depends on the value of energy, type of hard dental tissue and number of pulses. With increasing energy or number of pulses the saturation effect in depth of holes in dentine or enamel were proved.

Pulsed laser radiation in the range of very high water absorption near 3 micrometer is well known to be effective for the ablation of dental hard tissues. However ablation quality is limited by thermal side effects if using higher pulse repetition rates. This paper presents qualitative and quantitative results of dentin and enamel ablation with a scanned laser beam (emission wavelength 2.94 micrometer) and simultaneously, use of spray cooling. It is known that ablation of enamel is more problematic because of the low content of water. It was observed that the creation of unwanted 'recrystallizations' depended on a complex dependence of spot size, energy density, quantity of spray cooling and pulse duration. 'Recrystallizations' can be prevented by using optimized parameters.

Selective ablation is fixed to a range of fluences predicted by the ablation thresholds of infected and healthy tooth structures respectively. The aim of the study was to develop a dental handpiece, which guarantees homogeneous fluence at the irradiated tooth surface. Furthermore the point of treatment should be cooled down without energy losses due to the cooling system. We suggest the direct coupling of the laser radiation into a laminar stream of liquid, which may act in turn as a lengthened beam guide. The impacts of the laser radiation and of the cooling medium hit exactly the same point. Hot ablation debris is removed out of the crater by the flush of the water jet. While the surface of a bare fiber working on contact mode is destroyed after a few shots, it was shown that coupling the laser radiation into a stream of liquid prevents this destruction. Putting together the benefits of this special handpiece short overall treatment times seem to be possible. High average power can be applied to the tooth without the threat of thermal damage. Furthermore no time consuming cutting of the fiber prolongs the treatment time.

This paper is to originally present the results of a research of temporal and frequency structures of laser pulse and laser-induced acoustic one generated in human tooth enamel and dentine. An impact of tooth surface water spray on a deformation character of laser-induced acoustic signal frequency Fourier-spectrum has been defined also.

Ablation of dentin and tartar was studied under carbon dioxide-laser irradiation in cw and pulse mode with pulse length down to 150 microseconds. The specimens had been cut by a diamant blade to slices of thicknesses between 0.8 and 2.8 mm. The laser induced temperature rise was measured by an infrared camera monitoring the backside of the samples. The specimens shape and structure at the laser spot was analyzed by electron microscopy. Of special interest was the testing of the SwiftLase^TM to reducing the heat. The experimental results show the necessity of a water cooling in all application modes. The origin of the cracks which had been observed in many of the samples, is currently under investigation.

Because of their unique properties with regard to the absorption in organic tissue, pulsed Er:YAG lasers are of interest for various applications in medicine, such as dentistry, dermatology, and cosmetic surgery. The relatively low thermal side effects, and surgical precision of erbium medical lasers have been attributed to the micro-explosive nature of their interaction with organic tissue. In this paper, we report on preliminary results of our study of the thresholds for tissue ablation, using an opto-acoustic technique. Two laser energy thresholds for the interaction are observed. The lower energy threshold is attributed to surface water vaporization, and the higher energy threshold to explosive ablation of thin tissue layers.

The Er:YAG is currently used as an alternative instrument for the removal of dental decay. Safe laser parameters have been found, but in order to increase the preparation speed also higher pulse energies or repetition rates are under consideration. To investigate systematically the temperature effect of these parameters and of water spray, slices of dentine were perforated with the laser radiation, exactly towards a thermocouple placed in a hole at the back side. During and after preparation temperature was monitored, and maximum temperature rise reached at the moment of perforation (T_m) was evaluated. For preparation without water irrigation T_m was in the range of 30 to 40 K, increasing slightly with pulse repetition rate (prr). For low prr (2 Hz) the same was observed for the radiant energy, however for high prr (10 Hz) the effect was inverse. When moistening the slices during preparation by a fine water spray, T_m decreases. The temperature reduction is very pronounced for low prr, leading to a temperature rise of only 2 K at 2 Hz (200 mJ). When prr is enhanced the spray becomes less effective, even when higher flow rates are chosen. With respect to temperature, combinations of low pulse energy and high repetition rate are least favorable. For safe preparations in dentine low pulse repetition rates are recommended.

The aim of the study was the selective removal of dental calculus by means of pulsed lasers. In a first approach the optical characteristics of subgingival calculus were calculated using fluorescence emission spectroscopy (excitation laser: N₂-laser, wavelength 337 nm, pulse duration 4 ns). Subgingival calculus seems to absorb highly in the ultraviolet spectral region up to 420 nm. According to these measurements a frequency doubled Alexandrite-laser (wavelength 377 nm, pulse duration 100 ns, repetition rate 110 Hz) was used to irradiate calculus located on enamel, at the cementum enamel junction and on the root surface (located on dentin or on cementum). Irradiation was performed perpendicular to the root surface with a laser fluence of 1 Jcm^-2. During the irradiation procedure an effective water cooling-system was engaged. Histological investigations were done on undecalcified sections. As a result, engaging low fluences allows a fast and strictly selective removal of subgingival calculus. Even more the investigations revealed that supragingival calculus can be removed in a strictly selective manner engaging a frequency doubled Alexandrite-laser. No adverse side effects to the surrounding tissues could be found.

The purpose of this study was to evaluate the effects of the Er:YAG laser removal of subgingival calculi in periodontal treatment and to describe laser-induced cementum surface alterations. Freshly extracted human teeth with adherent plaques and mineralized calculi were laser treated using modified quartz fiber tips in direct contact to the root surface. For the fiber tip tested, the ablation threshold was 6.5 mJ. An effective removal of calculi was possible with 50 mJ resp. 150 mJ for a triple fiber. For the latter, a mass loss with a mean of about 5.1. mg/min was achieved. Histologic examinations of the cementum surface showed smoothed appearance alternately with rough depressions of the fiber tips, which can be discussed as a good precondition for periodontal tissue regeneration. Maximum temperature increase of 1.4 K was reached in the pulp, if an additional water irrigation was applied to the root surface. From these results it can be concluded that with the Er:YAG laser an effective removal of subgingival calculi can be performed without thermal risk for the pulp.

Pulsed Er:YAG and Er:YSGG lasers are well known to be effective instruments for the ablation of dental hard tissues. Developments in the last years made it possible to transmit the laser radiation at these wavelengths with flexible fibers. Therefore the application in the periodontal pocket may be possible. The aim of this study was to evaluate the in-vitro conditions to generate a bioacceptable root surface. Twenty extracted human teeth, stored in an antibiotic solution, were conventionally scaled, root planed and axially separated into two halves. Two main groups were determined. With the first group laser radiation was carried out without and in the second group with spray cooling. The laser beam was scanned about root surface areas. Laser parameters were varied in a selected range. The biocompatibility was measured with the attachment of human gingival fibroblasts and directly compared to conventionally treated areas of the root surfaces. The fibroblasts were qualified and counted in SEM investigations. On conventionally treated areas gingival fibroblasts show the typical uniform cover. In dependance on the root roughness after laser treatment the fibroblasts loose the typical parallel alignment to the root surface. With spray cooling a better in-vitro attachment could be obtained. Without spray cooling the higher increase in temperature conducted to less bioacceptance by the human gingival fibroblasts to the root surface. These results show the possibility of producing bioacceptable root surfaces with pulsed laser radiation in the range of very high water absorption near 3 micrometer.

For the first time the investigation results of acid resistance and microhardness of the dentin in root canals of the human tooth irradiated by Nd:YAG and Ho:YAG lasers are presented. The morphological changes in root dentin at the operated area were observed by SEM.

The aim of this study was to investigate the effect of a pulsed Nd-YAG laser on E. coli and S. aureus in suspensions. The temperature increased in the bacterial suspensions after each irradiation according to power and dye concentration. The bactericidal effect was evaluated by comparing the number of viable bacteria remaining after 24 h in the irradiated and the control specimens. Afterwards, an in vitro study of dentin permeability on horizontal sections of healthy dentin has been carried out following an original method derived from Pashley's experimentation. The results indicate the parameters (1,5 W; 20 Hz; with black dye) which should be used to obtain the bactericidal effect. An undesirable rise in temperature and in dentin permeability has been observed and a S.E.M. examination has been carried out in order to explain this result.

The structural changes in a human tooth enamel have been investigated by SEM method with action of submillisecond pulses of YAG:Nd and YAG:Cr;Tm;Ho lasers at the energy densities below the threshold of surface tissue ablation. The conditions of laser treatment leading to the essential increase of the acid resistance and microhardness of the intact enamel are defined. Influence of the laser radiation parameters on the acid resistance of the tooth crown in the pits and fissure area are investigated.

Recent studies focused on the ability of the laser light to enlarge the root canal during the endodontic therapy. The aim of this research is the experimental and theoretical study of the ablation rate of two infrared laser wavelengths on dentin. Thirty freshly extracted human teeth were longitudinally sectioned at thicknesses ranged from 0.5 to 2 mm, and irradiated on the root canal dentin. The measured ablation rates in dentinal wall of the root canal showed that the HF laser at 2.9 micrometer can more effectively penetrate into the tissue, whereas the carbon dioxide laser at 10.6 micrometer leads to high thermal damage of the ablation crater surroundings.

The displacement of human dried facial bone was measured and considered under static loads by real time holographic interferometry. Materials were dried human skulls. Various loads were applied to the zygomatic, maxillary and other facial bones by means of a loading apparatus. As the experimental result obtained from the load to the neighborhood of the fronto-malar suture on the zygomatic bone, density of interference fringes increased on the zygomatic bone more than on the other facial bones and parallel interference fringes were observed on the zygomatic bone. Densities of orbital maxillary and zygomatic bones were greater, when the load was applied to the center of infraorbital margin than when it was applied to the other facial bones. When the neighborhood of the front-malar suture on the frontal bone was loaded, coarse interference fringes occurred on the zygomatic, maxillary and orbital bones, while fine interference fringes appeared on the frontal bone. When the maxillary bone near infraorbital margin was loaded, concentric circular fringes were observed. The result shows that the displacement depends on the loading point. When the load applied to the zygomatic bone, parallel fringes appeared on the bone. This means that the bone deformed almost as a body.

The effects of laser-induced interstitial thermal therapy are based on the thermal effects in the tissue masses that are subjected to therapy. To conduct the therapy efficiently, it is necessary to function with optimum system parameters. As a result, these parameters have to be determined in advance. We introduce a software that allows us in different geometries to determine the distribution of the laser energy absorbed by the tissue and to undertake the calculations related to the thermal processes. This calculation follows as the function of up to three local coordinates selectively for the steady state and/or the transient processes. the method has been verified, and based on this, a planning system is presently being developed. A measuring device for the in-vitro determination of the thermal conductivity with dependence on the temperature change with respect to time will also be presented.

In the last decade substantial biological data and the oncologic effect on brain tumors of hyperthermia/thermotherapy have been documented. A new approach to a therapy for such tumors should meet the following requirements: effective destruction of expanded tumors by means of hyperthermia/thermotherapy; precise controllability of treatment; real-time checking or dosimetry; and careful treatment of normal tissue surrounding the tumor. In addition, an increase of the maximum power that can be supplied represents a measure of the largest possible tumor volume that can destroyed. In-vitro test results are presented that document a therapeutically relevant temperature rise up to 42 degrees Centigrade in the diameter range of 6 cm to 7 cm without occurrence of carbonization effects.

Interstitial laser coagulation is a new method of localized tissue destruction that may be used to eliminate solid tumors, such as hepatic metastases, an in-vitro study was performed to compare a cylindrical diffusing-tip (length 2 cm) with a bare-tip fiber. Fiber ends were positioned between two porcine liver slabs (37 degrees Celsius) and Nd:YAG laser light (1064 nm) was guided through either fiber with an output of 3 - 9 W and exposure times of 6 - 18 minutes. Lesions produced by the cylindrical diffuser-tip were significantly larger and more predictable at a higher laser output (greater than 6 W). With the diffuser tip lesions up to 36 mm in length and 23 mm in width could be produced at 7 W and 9 min without any central charring. Lesions produced with the bare-tip fiber were up to 32 mm in length and 20 mm in width at 6 W and 9 min with massive charring. These results indicate that at optimal laser settings the diffuser of 2 cm length produces a larger coagulation volume than a point light source and that charring should be avoided in interstitial laser coagulation.

Laser-induced thermotherapy is a method to treat pathologic sites of inner organs and oblique tissues with laser radiation. The radiation is transmitted via optical fibers and applied using specially designed laser applicators which are mounted to the distal fiber end. Different types of applicators have been developed recently for an effective treatment of large lesions in short periods of time. Two experimental set-ups are presented to measure the optical and thermal applicator patterns at various wavelengths and tissues. One set-up applies the integrating sphere technique to characterize the axial radiation distribution of LITT-applicators. The second set-up was developed to measure two-dimensional temperature distributions in-vitro during a laser application. It consists of a tissue phantom which could be opened like a book and enabled the uptake of thermocamera measurements. The applicator of interest was fixed between both slabs of the phantom. Measurements were carried out with various types of applicators (bare-fiber, diffusing tip, ring-mode, scattering-dome, internally cooled applicator) with a Nd:YAG laser (1064 nm) and a diode laser (980 nm). The results showed that the applicator designs yielded various maximum temperatures between 90 degrees Celsius and 260 degrees Celsius. The measurements for an internally cooled applicator were compared with theoretical calculations of photon- and heat diffusion in scattering media, applying Monte- Carlo simulations and finite difference methods. The measurements corresponded well with the theoretical simulations.

Laser induced thermotherapy (LITT) has been recently developed for treating deep seated tumors. Diode laser (830 nm) is suitable for LITT, because of its high penetration in tissue. The present animal experiment was conducted to evaluate the performance of a diode laser for treating liver tumors in rabbits. Fifty-two New Zealand rabbits were grafted in liver with a Vx2 tumor model. They were treated at a tumor size of 8 mm diameter. A laser energy of 1 350 J (power: 1.5 W; irradiation time 900 s) was delivered through a 300 micrometer fiber implanted in the center of the tumor. Our experiment was divided in two parts: (1) A survival study: we compared the medians survival between untreated tumors (Group A, n equals 21) and irradiated tumors (Group B, n equals 21), (2) An evaluation of LITT efficiency on day 7 (Group C, n equals 5) and at day 14 (Group D, n equals 5). We compared at day 7 and day 14 the radiologic data (ultrasonography and MRI realized before and after irradiation) to the microscopic examinations (haematoxylin eosine stain and picrosirius red F3BA). The results were a median survival not significantly different in group B (laser) than in group A (control) and an efficiency only at short time (on day 7). There was a good correlation between radiologic data and microscopic examinations in groups C and D. The picrosirius red F3BA estimated the extent of thermal damage. In conclusion, these disappointing results are due to an insufficient irradiation of peritumoral tissue and to the Vx2 aggressivity (undifferentiated). Using multiple optical fiber could improve the LITT efficiency. The correlation between radiological and microscopic findings would allow us to quantify the results of LITT.

Thermal ablation techniques are experiencing application in many different fields of medicine. Recently, experimental studies have been performed by various authors concerned with dosimetry and laser-tissue interaction. In order to study the effects of interstitial laser energy on biological tissue, we examined different tissue models which compared important parameters during laser application. We have performed the following in vitro, in vivo and ex vivo studies by comparing a neodymium: YAG (1064 nm) and diode laser (830 nm) equipped with interstitial laser fibers. In vitro studies which examined the influence of changes in power and time duration of application were performed on potato, muscle, liver and kidney. In vivo studies (porcine model) also examined different power settings at designated time intervals. Ex vivo studies with isolated perfused kidney (IPK) investigated the effects of power, application time, perfusion pressure and different perfusion mediums (saline solution, anticoagulated blood). In vitro studies revealed necrotic lesions in all tissues. Although no power threshold could be obtained for liver tissue (early onset fiber damage), potato, kidney and muscle tissue demonstrated their own respective power threshold. Furthermore, when using the Nd:YAG laser, we observed that higher power settings had permitted a quicker necrosis induction, however within its own treatment power spectrum, the diode laser was capable of inducing larger lesions. In vivo studies demonstrated that early onset diffuser tip damage would prevent exact documentation of laser-tissue interaction at higher power levels. Results obtained with our standardized ex vivo model (IPK) revealed smaller necrotic lesions with saline than with blood perfusion and also demonstrated the important role which perfusion rate plays during laser-tissue interaction. We found that pigmented, well vascularized parenchymal organs with low stromal content (kidney, liver) and a higher absorption coefficient induced larger necrotic volumes than organs without these characteristics. Higher power settings demonstrated side effects, (e.g. popcorn effect or uncontrollable vaporization induced by extreme hyperthermia) in every animal tissue in all three trials. Our experimental interstitial laser studies have shown that many factors influence the size outcome of the necrotic lesion and that treatment parameters (treatment time, power setting) must be optimally combined to obtain a controlled and predictable necrotic lesion in certain tissues.

This paper discusses the feasibility of radio-frequency current in bipolar technique for interstitial thermotherapy (rf-ITT). A short survey of established methods for interstitial tissue coagulation, e.g. the interstitial laser photocoagulation (ILP) and microwave exposure are given. In addition, a new concept for interstitial application of bipolar or quasi-bipolar radio- frequency alternating current is presented. Theoretical investigations of the electrical field distribution generated by a dipole model come together in the different mechanisms of heat generation by using radio-frequency alternating current. New concepts of bipolar or quasi- bipolar coaxial layered applicators are presented. This bipolar needle electrode enables the surgeon to use a partial and homogeneous exposure of radio-frequency current for interstitial thermotherapy, e.g. for the treatment of BPH or for concha coagulation in ENT. Less power is needed due to the limited current exposition at the immediate operation site and a highly safe procedure is possible. Therefore, to determine the thermal damage of tissue, depending on the rf parameters, a computer model for a real-time simulation of the spatial electrical field distribution especially for a multiple probe application is currently being developed. This is an appropriate tool for dosimetry. A similar program for LITT, called LITCIT, developed at the Laser-Medizin-Zentrum Berlin has already shown its efficiency in clinical use. Furthermore the feasibility of a 'cross-over' applicator is discussed which combines ILP and rf-application by using metallized optical fibers for a simultaneous application of electrical energy and laser radiation.

In medical literature no significant studies have been published on the effectiveness of laser compared with traditional procedures in two series of cerebral gliomas; for this reason we have studied 220 tumors (200 supratentorial -- 20 brain stem gliomas), 110 operated upon with laser, 100 with conventional techniques. Four surgical protocols have been carried out: (1) traditional techniques; (2) carbon dioxide laser free hand; (3) carbon dioxide laser plus microscope; (4) multiple laser sources plus microscope plus neurosector plus CUSA. Two laser sources have been used alone or in combination (carbon dioxide -- Nd:YAG 1.06 or 1.32). Patients have been monitored for Karnofsky scale before and after operation, 12 - 24 and 36 months later; and for survival rate. Tumors were classified by histological examination, dimensions, vascularization, topography (critical or non critical areas). Results for supratentorial gliomas: survival time is the same in both series (laser and traditional). Post- op morbidity is significantly improved in the laser group (high grade sub-group); long term follow-up shows an improvement of quality of life until 36 months in the low grade sub-group.

Chronic unilateral and bilateral back pain with pseudoradicular symptoms, is a common clinical syndrome, which in many cases can be related to the facet joint syndrome. The pain is caused by mechanical affection of synovial and capsular nerve terminals. Therefore, current therapeutical attempts including physical therapy, intra-articular injection of local anesthetics and steroids and thermocoagulation of the facet joint with a thermocoagulator, are performed. We confirmed laser coagulation of the facet joint. Porcine cadaveric spines were treated immediately after death by intra-articular facet joint laser radiation. With the pulsed Nd:YAG laser (1064 nm) altogether 600 J were applied in three different places 4 mm apart at the top of the facet joint. The results showed that facet joint laser radiation leads to a small (about 1 - 2 mm diameter) lesion restricted to the facet joint cavity and its synovia. Histologically, we found a central carbonization zone and necrosis, including almost the whole cartilage and approximately 0.2 mm of the adjacent bone. These changes are similar to Nd:Yag-laser applications in other skeletal regions. It is suggested that these changes may lead to facet joint denervation by coagulation of the synovial nerve terminals. Cicatration of the laser lesion might cause ankylosis of this joint. In sum, facet joint laser radiation could be an alternative therapeutical tool for lower back pain of the facet joint syndrome type. Therefore, future clinical application of this technique seems to be very promising.

Nd:Yag laser radiation is used for the treatment of protrusion of intervertebral discs. It is known that laser radiation leads to coagulation, vaporization and carbonization of the disk. Little is known about the early changes in vertebral discs after laser radiation. Therefore, we exposed cadaveric porcine vertebral discs by Nd:YAG laser radiation immediately after death. The discs were quartered and either formalin fixed after laser radiation or kept in culture for 1, 4 and 7 days and then formalin fixed. Immunohistochemistry was performed with antibodies directed against vimentin and amyloid precursor protein (APP). Results showed a jerky leak of notochordial remnant cells and mucopolysaccharides at the distal end of the application needle during laser radiation, which was interpreted as a bursting extrusion of damaged but not vaporized tissue. Histology and immunohistochemistry revealed an incomplete loss of nucleus pulposus and a large, almost complete necrosis of the notochordial remnant cells. In surviving notochordial remnant cells after laser radiation a slight increase of vimentin and APP could be seen without any other cellular reactions. The annulus fibrosus showed no significant changes except a defect with a small necrosis zone at the site of the application needle. Therefore, it can be concluded that Nd:YAG laser radiation leads to an increased volume reduction by the leak of nucleus pulposus and to a slight cellular reaction of surviving notochordal remnant cells detectable by vimentin and APP increase.

The skin microhaemodynamics and the tonic state of muscles, which provide myohypertonus in patients with radicular and reflex syndromes of lumbar osteohondrosis at moderate and pronounced musculotonic manifestations, have been studied with the help of a laser specklometer whose principle of operation is based on speckle-optical measurements of states of the human skin. When investigating the skin in these patients, asymmetry of speckle-optical indices has been revealed on the sick and the normal limbs, which was more pronounced in zones of the affected root primary innervation. The speckle-optical studies have revealed asymmetry of the vibrational properties of paravertebral muscles in patients at rest and in various postural reactions.

For several years laser tissue welding has appeared as a new alternative technique for tissue repair instead of manual sutures. It has been evaluated in different experimental models including blood vessels, skin, nerve, intestine, bile ducts, vas and fallopian tube. Different types of lasers with different sets of parameters have been used: carbon dioxide laser, Nd:YAG laser, argon and KTP laser and diode laser. Recent trends in tissue fusion promote near infrared lasers at low irradiance with intraoperative enhancement of light absorption by specific chromophores. As far as microvascular reconstruction is concerned, successful clinical applications are currently published. Although the molecular mechanism involved in welding is not completely understood, the tissular fusion is considered as a thermal phenomena. In laser assisted microvascular anastomosis, the best experimental model, the ultrastructural examination of arteries anastomosed with Nd:YAG, argon or diode laser revealed interdigitation of collagen fibers which appeared swollen, with modified striation and organized in irregular network. The mechanism of welding involving the formation of non covalent bands between collagen strands, is generally induced by a temperature of 60 - 63 degrees Celsius well adapted to collagen denaturation.

This in-vivo study examines the interest of vessel anastomosis with a 1.9 micrometer diode laser. Ten end-to-end carotid anastomoses and 10 end-to-end jugular anastomoses are performed in Wistar rats. The technique requires brief applications (20 to 25 spots) with a diode laser (lambda equals 1.9 micrometer, (phi) equals 220 micrometer, P equals 60 mW, t equals 0.7 s, F equals 110 J/cm²) after placement of three equidistant stay sutures. The macroscopic aspect and patency are evaluated at different post-operative intervals. Vessel histology is performed at 15, 21, and 30 days after the procedure. These anastomoses reveal minimal thermal damage in the adventitial layer only at depth of 200 micrometer. No medial or intimal thermal damage is identified. No thrombosis is observed, giving a permeability of 100% for both arteries and veins. The mean clamping time is 9 plus or minus 3 min. For 1.9 micrometer, the water extinction length is 0.15 mm. The welded thickness is comparable to the extinction length of the wavelength giving consequently a weld strength of 4 multiplied by 10⁶ dynes/cm² comparable to the strength of suture repairs: 5 - 6 multiplied by 10⁶ dynes/cm². These findings suggest that a low-energy 1.9 micrometer diode laser has potential clinical application for anastomosis of small vessels.

A new computer program, LATIS, being developed at Lawrence Livermore National Laboratory is used to study the effect of pulsed laser irradiation with temperature feedback on endovascular patch welding. Various physical and biophysical effects are included in these simulations: laser light scattering and absorption, tissue heating and heat conduction, vascular cooling, and tissue thermal damage. The geometry of a patch being held against the inner vessel wall (500 micrometer inner diameter) by a balloon is considered. The system is exposed to light pulsed from an optical fiber inside the balloon. The laser power is adjusted during the course of a pulse. This is done automatically in the simulation by temperature feedback. A minimum in the depth of damage into the vessel wall is found. The minimum damage zone is about the thickness of the patch material that is heated by the laser. The more ordered the tissue the thinner the minimum zone of damage. The pulse length which minimizes the zone of damage is found to be the time for energy to diffuse across the layer. The delay time between the pulses is determined by the time for the heated layer to cool down. An optimal pulse length exists which minimizes the total time needed to weld the patch to the wall while keeping the thickness of the damaged tissue to less than 100 micrometers. For the case that is considered, a patch dyed with light absorbing ICG on the side next to the vessel (thickness of the dyed layer is 60 micrometer), the best protocol is found to be 33 - 600 ms pulses applied over 1.6 min.

Since 1984, the author used a low output carbon dioxide laser for microsurgical anastomoses in the experimental investigation with rats. The series of experiments demonstrates the following characteristics, in comparison with conventional microsurgical anastomoses: ease in technique; less time consumption; equivalency of patency rate and bursting pressure; but only about 50% of the tensile strength of manual suture anastomosis. These findings suggested that low output carbon dioxide laser has the potential for clinical application. Then this technique has been applied in six clinical cases with digital replantations and free vascularized flap since 1988. The procedure offers increased safety and speed in reconstructive microsurgery.

A series of carotid end-to-end diode laser assisted microvascular anastomosis (LAMA) versus control ateral conventional suture microanastomosis (CMA) were performed in 120 Wistar rats (in the same animal, LAMA performed in the left side and CMA in the right). The optic and scanning electron microscopic examinations were assessed from day 0 to day 210. The results revealed that on day 0 LAMA gave rise to proteins deneturation and collagens fusion of the media and adventitia in the arterial wall. Re-endothelialization of anastomotic line began at day 3, as well as a large number of inflammatory aggregated in the adventitia. On day 10 the endothelial cells were restored on the anastomotic site and collagenous network developed in the media. On day 90 proliferation and disorientation of the elastic fibers appeared. A part of elastic laminae had been reconstructed on day 210. In the group CMA, the re- endothelialization developed later than LAMA, and the reconstruction of the elastic laminae failed to happen until day 210. These data suggest that the results of long term healing process after diode LAMA is better than that of CMA in normal artery repair.

A 100 micrometer core optical fiber-coupled 75 mW diode laser operating at a wavelength of 800 nm has been used in conjunction with a protein solder to stripe weld severed rat tibial nerves, reducing the long operating time required for microsurgical nerve repair. Welding is produced by selective laser denaturation of the protein based solder which contains the dye indocyanine green. Operating time for laser soldering was 10 plus or minus 5 min. (n equals 24) compared to 23 plus or minus 9 min (n equals 13) for microsuturing. The laser solder technique resulted in patent welds with a tensile strength of 15 plus or minus 5 g, while microsutured nerves had a tensile strength of 40 plus or minus 10 g. Histopathology of the laser soldered nerves, conducted immediately after surgery, displayed solder adhesion to the outer membrane with minimal damage to the inner axons of the nerves. An in vivo study, with a total of fifty-seven adult male wistar rats, compared laser solder repaired tibial nerves to conventional microsuture repair. Twenty-four laser soldered nerves and thirteen sutured nerves were characterized at three months and showed successful regeneration with average compound muscle action potentials (CMAP) of 2.4 plus or minus 0.7 mV and 2.7 plus or minus 0.8 mV respectively. Histopathology of the in vivo study, confirmed the comparable regeneration of axons in laser and suture operated nerves. A faster, less damaging and long lasting laser based anastomotic technique is presented.

This study aimed to evaluate the interest of a 1.9 micrometer diode laser for corneal wound suture. Six adult albino rabbits were anesthetized. A 7 mm corneal incision was practiced on the right eye. For 3 animals (laser plus stitch) the incision was surgically sutured with 2 stitches of a nylon monofilament and laser impacts were performed between the stitches. For 3 animals (laser only) juxtaposed lasers impacts were realized to suture the wound. After the procedure the animals were examined daily for signs of inflammation, infection and for healing of the corneal wound. Material was obtained for histological examination 1 month after the procedure. Approximation of the edges of the would was successfully obtained in the (laser plus stitch) group. In the (laser only) group this approximation remained troublesome. After the procedure, one cornea of the (laser only) group disclosed a little leakage during 2 days. Histological examination assessed the welding of the corneal wound in the two groups provided structural modifications and some inflammatory signs. Corneal welding using a 1.9 micrometer diode laser is possible either with laser and stitch or with laser only. The approximation of the edges of the wound with additional stitches is an evident drawback. The use of additional stitches should be avoided to keep the theoretical advantages of corneal would suture using laser welding.

Laser welding of corneal incisions was performed using two different diode laser wavelengths. Tissue fusion was attempted both with direct absorption of radiation at 1950 nm radiation and with ICG dye-enhanced technique at 810 nm. Thirty deep (not full thickness) corneal incisions of 15 fresh-enucleated porcine eyes were treated. Semiconductor diode lasers emitting in continuous wave at 1950 nm and at 810 nm were used. Both were coupled to an optic fiber handpiece. Wound samples were explanted on day 0 after treatment for histological evaluation. The group of corneal wounds treated with the ICG-enhanced technique revealed tissue welding in 70% of treated wounds. Using 1950 nm tissue fusion was observed in 50% of treated wounds. Macroscopic evaluation revealed a pronounced thermal damage of the epithelium in the samples treated with 1950 nm radiation. Wound closures obtained using 1950 nm were characterized by superficial welding of corneal layers. (Abstract truncated.)

Injuries involving division of the flexor tendons of the hand are a common surgical problem. Sutured repairs must be strong enough to withstand early active movement. Experiments were designed to assess the strength of bonds formed between tendon sections as a result of heating (1) under controlled conditions in a water bath and (2) using a carbon dioxide laser (laser tissue welding). The load (N) and stress (N/cm²) required to disrupt thermal bonds between bovine tendon sections heated for 4 minutes in water peaked at 62 degrees Celsius (13N, 11.3N/cm²). Further experiments revealed the optimal time period for heating to be 9 minutes (21.5N, 20.6N/cm²). A threshold effect was apparent at these parameters. The in vitro strength of sutured, laser welded and sutured and laser welded tendon repairs was compared in a rabbit model. Laser welding alone did not produce repairs as strong as sutured repairs. It did, however, augment the strength of sutured repair. This effect was maximal at a power of 0.1 W.

End-to-end carotid artery anastomoses and aorta arteriotomy closure in rats have been performed using a diffraction limited semiconductor MOPA laser, coupled to an operating microscope and emitting a 1 watt continuous power output at a wavelength of 985 nm. Laser aiming was performed using an eye-guided laser targeting prototype, which allows the user to direct the laser with a beam steering unit controlled by the surgeon's eye movements. Preliminary results show that efficient welds can be obtained with the MOPA laser with irradiances of 670 and 1195 W/cm². The ease and efficiency of the eye-guided procedures enabled the user to close up to 5 mm long arteriotomies in the rat aorta and to accurately perform laser assisted microvascular anastomoses of rat carotid arteries These laser welding procedures demonstrate the feasibility of eye-guided laser targeting in laser microsurgery.

Statistically significant results on positive effects of low-energy intercardiac blood irradiation, based on observation of 354 patients suffering from Q-MI, are presented. The He-Ne laser and a catheterized flexible fiber-optic lightguide were used to perform the blood irradiation. The data obtained make it possible to draw a conclusion that the positive clinical effect of the laser blood irradiation is realized via stress-limiting mechanisms.

Failed rescue coronary angioplasty is a high risk situation because of high mortality. Coronary stent has given us the chance of improving and maintaining the patency of the artery. We report our preliminary experience of rescue stenting after unsuccessful coronary angioplasty.

A comparison between the laser angioplasty techniques preliminary expectations and verified limits with ten years of research on the laser technology and six years experience in clinical utilization is reported. Both early enthusiasm and present criticism have been found excessive because the limits of the techniques were intuitable from the beginning and on the other hand a significant clinical usefulness is verifiable in a selected group of patients.

Low-energy He-Ne laser (0.5 - 83 Hz) of changeable frequency specifically increases the resistance of erythrocytes of patients after acute stroke to lipid peroxidation (LPO) induced by hydrogen peroxide. Increase in frequency of illumination increases the efficiency. The same treatment does not affect the LPO process in erythrocytes prepared from healthy donors. Laser beam treatment suggests to provide a reorganization of membrane structure resulting in increase of the antioxidant defense of the cell.

Usage of laser therapy for complex treatment of patients with unstable stenocardia allows one to increase efficiency of medicines. This results in pronounced anti-quinsy and anti-arrhythmia effects, prophylactic effect with respect to acute myocardium infarction (AMI), shortens the patient's stay in hospital and prolongs the remission period. In the methods developed the He- Ne-therapy makes no complications and lateral effects. It is of great importance to determine the individual doses of intravascular laser irradiation of blood (ILIB). The work in this field has gone on for 10 years. The dose is chosen in accordance with the treatment purpose: training reaction, quite or high activation. The duration of one ILIB session is calculated to provide the maximum inhibition of the products of peroxidation of lipids. The method is sufficiently accurate, and its results correlate with those obtained by clinical observations and cytodiffractometry.

A set of laboratory experiments was performed to study a possibility of selective laser action on different classes of atherosclerotic plaques and samples of normal vessel walls were performed. To this end Nd:YAG-laser with frequency doubler and quadrupler as well as XeCl-laser with SRS cell were employed which allows us to compare results of laser action in broad spectral range. The laboratory setups permit us to vary parameters of laser radiation, such as the pulse duration, energy and density of the energy in process of experiments. All samples were subjected to detailed morphological study. Experiments performed indicate the possibility of initiation of photochemical destruction of plaques by UV laser radiation. Such a possibility is supported also by semi-empiric quantum chemistry calculations performed for fat acids. All this allows us to suggest a sort of optimal strategy for laser destruction of atherosclerotic plaques with minimal site effects.

Laser ablation of the prostatic tissue or laser prostatectomy, is used as an alternative method to traditional endoscopic resection of the prostate (TURP). Recently, there have been reports of transurethral coagulation of the prostate using various sidefiring laser systems. These devices can be classified into two groups: one that uses total internal reflection, and one that has a gold-plated metal reflecting mirror. We have developed a new Albarran bridge with these characteristics in order to minimize the restrictions presented by the other delivery systems. Laser coagulation of the prostate has been performed using a conventional bare fiber passed through a sidefiring Albarran bridge containing a distal gold-plated reflector with a deflecting mechanism. The complete device passes through a 21 F. rigid cystourethroscope. The system and the fiber can be used for several dozen treatments. Transurethral laser coagulation was performed on 65 patients for obstructive symptoms caused by begnin prostatic hyperplasia. The dosimetry was 1000 J per 1cc of prostatic tissue at 60 W for 60 seconds. Successful results were obtained in 55 patients (85%). A significant reduction in obstructive symptoms from a mean AUA-6 Symptom Score of 21.2 preoperatively to 9.1 at 3 months and 7.6 at 6 months was associated with an increase in the peak urine flow rate from 6.1 mL/sec preoperatively to 13.1 mL/sec at 3 months and 15.7 mL/sec at 6 months. The residual urine volume averaged 190 mL preoperatively and 365 mL at 6 months. Transurethral laser coagulation of the prostate represents a useful alternative to transurethral resection, especially in high-risk patients with an enlarged median lobe or a small prostate. Treatment is bloodless and, with the aid of the modified Albarran bridge, can be performed with standard urological instrumentation and conventional Nd:YAG laser system. The new Albarran bridge also can reduce the cost of laser treatment.

From January 1985 to December 1994, 23 early stage carcinomas of the esophagus were treated by photodynamic therapy in 21 patients. The stage of the tumors was assessed by esophagoscopy with multiple biopsies, CT scan and, from June 1991, also by endoscopic ultrasonography: 7 lesions were classified as carcinoma in situ (Tis) and 16 as invasive (T1). The photosensitizers used for PDT were hematoporphyrin derivative 3 mg/kg in 4 patients and dihematoporphyrin ether 2 mg/kg in 17. Light irradiation was performed using an Argon-dye laser system at a wavelength of 630 nm with an average energy of 50 J/cm² and 70 J/cm² for the treatment of Tis and T1, respectively. A complete response was achieved in 17/23 (74%) tumors, 15/21 (71%) patients. In the follow-up period from 6 to 78 months (median 36 months) 3 recurrences occurred 6, 12, and 14 months after PDT, respectively. Seven patients died due to concomitant diseases, not related to tumor progression. The actuarial survival rate was 95%, 75% and 37% at 1, 3, and 5 years, respectively. Complications included 1 case of sunburn and 2 cases of esophageal stenosis at the treatment site, that gradually responded to endoscopic bougienage.

The purpose of this study was to evaluate the efficacy and safety of endoscopic Nd:YAG laser photocoagulation for the treatment of flat colorectal adenomas. From January 1982 to December 1994, 222 lesions were treated in 216 patients. Initial eradication was obtained in 96% of lesions with a diameter less than 1 cm, in 89% of lesions with a diameter between 1 and 4 cm, and in 64% of lesions with a diameter greater than 4 cm. According to the histology, a complete disappearance was obtained in 94% of tubular, in 89% of tubulovillous, and in 80% of villous adenomas. Adenomas with severe dysplasia or foci of invasive carcinoma were eradicated in 76% and in 75% of cases, respectively. During a median follow- up of 24 months (3 - 129 months), recurrences developed in 46 of the 186 initially cured lesions (25%). All recurrent lesions were submitted to Nd:YAG laser photocoagulation, obtaining eradication in 37/46 (80%) of the cases. Malignant degeneration occurred in 6% of lesions. Complications related to laser treatments were observed in 5% of patients.

Nd:YAG laser has been used in the treatment of colorectal cancer since the 80s. Since January of 1988 our clinic uses laser in therapeutic program. In clinical treatments laser with the wavelength of 1064 micrometer and power of 40 - 50 W is used. Only in rare cases do we use power over 50 W. the ratio of energy for one treatment depends only on clinical effect, there are no other limits. In the first period of our clinical practice, from 1988 to 1991, all the laser treatments were held under short-term anesthesia. Our patients were hospitalized for 2 or 3 days. For the actual treatments, we used the rigid endoscopic technique and also the flexible technique (coloscop). We preferred the flexible technique definitely. Since January of 1991 we practice almost all treatments in ambulant schedule without general anesthesia. Only in the cases where treatments reach under linea dentata, we choose short-term inhale anesthesia. The patients are hospitalized for one day. In the actual treatments we take advantage of Nd:YAG laser. We try to vaporize most of the tumor masses during great hemostasis. The hemostasis is defined by the zone of coagulation.

This paper presents the results of theoretical and experimental investigation of lithotripsy processes by means of Ruby laser. The possibility of obtaining smooth microsecond pulse by two-photon absorption and negative feedback techniques is investigated. The methods of increasing of lithotripsy processes efficiency had been considered.

An infrared camera was used to measure the temperature rise which takes place in endotracheal tubes under laser irradiation. It was seen that a metallic tube was heated up within a second to temperatures of 200 degrees to 300 degrees Celsius which was very destructive to the PVC conduits inside of the tube. A compound tube, on the other hand, reached temperatures of only 38 degrees Celsius at its inner surface. The thermal induced destruction of the conduits inside of the metallic tube is seen as the reason for complications like airway blocking. Furthermore preliminary results of a randomized clinical study are presented, showing that the metallic tube needed higher pressure levels than the compound tube.

The carbon dioxide laser is a well established tool in the surgical treatment of laryngeal and tracheal stenosis. Usually the laser beam is applied by a microscope/micromanipulator device. Different types of rigid laryngoscopes and bronchoscopes provide access to nearly every area of larynx, trachea and main bronchi. In order to be treated with this equipment the target tissue has to be in a straight optical axis with the laser beam output at the micromanipulator. We report about one patient who presented with severe dyspnea due to granulation tissue directly below his left vocal cord. He was suffering from tracheomalacia for several years and was successfully treated by tracheostomy and a Montgomery's silicone T-tube as a stent. Then granulation tissue blocked the upper orifice of the Montgomery's T-tube. First removal by a carbon dioxide laser beam through the laryngoscope would have required sacrificing his intact left vocal cord. We removed the obstructing tissue by using the ArthroLase^TM System: the carbon dioxide laser beam was conducted through a 90 degree bent rigid probe, using the tracheostomy as an access. This ArthroLase^TM System was originally designed for arthroscopic surgery. In this special case however it successfully extends the use of the carbon dioxide laser in otolaryngology.

The design of head mounted displays (HMD) for functional endoscopic sinus surgery (FESS) is discussed. Head mounted displays (HMD) have been advocated as a replacement or complement to the operating room video monitors and also have the capability for true stereo- endoscopic image display. Though video monitors have greatly enhanced surgical endoscopy by re-involving nurses and assistants in the actual mechanics of surgery, video monitors require the operating surgeon to be focused on the screen instead of the patient, often with awkward hand-eye relationships. Several factors are critical in the design and selection of a surgical HMD. Typical values for resolution, angular subtense, and field of view are discussed for standard video monitors, HMDs, and for comparison a 35 mm slide projection. The relationship between field of view and angular subtense is described and correlated to visual acuity properties of the human eye. The UC Irvine surgical experience with HMD assisted endoscopic surgery is discussed. The advantages and limitations of the system used in this study are discussed.

By using moire topography video, the feature of facial expression can be well analyzed. The dynamic change of moire strips pattern enables the observation of facial movement in three dimensions and contributes to the better evaluation of patients with facial palsy. Using this method, several special features on the facial expression of patients with facial palsy were demonstrated.

We examine thermal effect of a 2.1 micrometer Holmium laser on the internal stress and shape of cartilage. For 2.1 microns radiation, the absorption depth is more by an order of magnitude than that, for 10 micrometer radiation. We have studied the influence of laser intensity, pulse duration, pulse repetition rate, and of cartilage thickness on its shaping conditions. Spatial and temporal locality of Ho laser radiation as well as the bulk character of the heating allow us to produce the stress relaxation without overheating of the surface irradiated and to prevent undesirable effects of tissue carbonization and destruction.

We have established that the phenomenon of cartilage shaping under the laser irradiation is connected with the bound-to-free transformation of water at a temperature around 70 degrees Celsius. The process of laser-induced stress relaxation in cartilage is accompanied and may be detected by the (1) mechanical, (2) thermal, and (3) optical effects. No pronounced structure effects were observed, for optimal conditions of the laser shaping of cartilage. The significance for otolaryngology of new laser applications for the shaping of cartilage is discussed.

As a high number of metastases grow in the liver, new treatment methods have been developed. Laser-induced thermotherapy (LITT) has recently applied for a minimally invasive technique in local treatment of liver metastases. Laser light was performed using Neodymium yttrium aluminum garnet (Nd-YAG, wavelength 1064 nm) delivered through a quartz fiber optic with a diameter of 400 micrometer with diffuse light emission. Laser light is converted into heat in the target area with an ensuing coagulative necrosis, secondary degeneration and atrophy, tumor shrinkage with minimal damage to surrounding structures. The size of heated volume depends on laser power, laser irradiation time, the way it reaches the target area and optical and thermal characteristics of the treated tissue. Pilot clinical studies have demonstrated that this technique is practical for the palliation of hepatic tumors. The clinical success of the thermotherapy depends on the optimal localization of the laser applicator in the center of the lesion, an optimal 'online monitoring' of thermal changes in the treated tissue and an exact documentation of the therapy effect and the local tumor controlrate. The individual optimization of two special developed thermosensitive sequences allows an exact monitoring of the progress of LITT to the treated lesion and surrounding structures. The purpose of this paper is to describe our experimental and clinical experience with MR-guided LITT for treatment of liver metastases and follow-up evaluation in larger series.

Interstitial laser-induced thermotherapy (LITT) is a recently developed, minimally invasive technique for local tumor destruction within solid organs. Low-power laser, with delivery of light energy through thin optical fibers, results in a well-defined area of coagulative necrosis. Thus, laser can destroy tumor by direct heating, while greatly limiting damage to surrounding structures. Experimental work has shown that a well defined area of coagulative necrosis is obtained around the fiber tip, with minimal damage to surrounding structures. Pilot clinical studies have demonstrated that this technique is practical for the palliation hepatic tumors. The success of LITT is dependent on delivering the optical fibers to the target area, real time monitoring of the effects of the treatment and subsequent evaluation of the extent of thermal damage. The key to achieving these objectives is the imaging methods used. The magnetic resonance (MR) findings of LITT in the experimental setting have been described, but the clinical role of MRI during and after LITT has been only described in a small series of patients.

We performed diode-laser assisted skin welding on Wistar rats by using a sodium hyaluronate gel mixed with Indocyanine Cadio-green (ICG) as photoenhancing chromophore. Laser treatment was accomplished with a 'side' irradiation technique, taking advantage of the fact that diode laser radiation at 810 nm is well transmitted by tissue on distances of some millimeters. Clinical and histological results were compared with those of conventionally sutured wounds.

We present the preliminary results of an experimental study on diode laser-assisted end-to-end anastomosis of the vas deferens in rats. Laser irradiation was associated with a photoenhancing chromophore to produce welding of the stumps at low laser power supported by only 2 suture says. The reduction of suture material is aimed to minimize foreign body reaction during the healing process.

Fluorescence spectroscopy has been reported as a very promising approach for the discrimination between healthy and atherosclerotic arteries, as far as both, the spectral shape and the intensity of the corresponding spectra seem to be useful parameters for the diagnosis, at specific wavelengths. Nevertheless there are some difficulties in the precise diagnosis, mainly between the different categories of atherosclerotic arteries (fibrous, calcified, heavy calcified). These difficulties are based on the one hand on biophysical factors, such as the necessity for the preknowledge of tissue fluorophores or the complexity of tissue optics. On the other hand, different spectral classification algorithms have been used, such as multivariate linear regression, decision plane analysis and Bayesian decision analysis, each one with certain disadvantages. In this work, two different classification algorithms were developed and evaluated. During the first procedure, simple dimensionless functions were formed by the ratio of the intensities at selected wavelengths and the logistic model was used for statistical analysis. Decision surfaces were drawn and it was estimated that the probability of correct classification is 88%. The algorithm correctly discriminates 97% of healthy from diseased samples and 80% of fibrous from calcified coronary arteries. During the second procedure, a proper ratio was selected in the sense that the ratio groups of the populations P₁ and P₂ might be separated with an essential considerable veracity probability. The separability was confirmed by testing the validity of specific statistical hypotheses. The demonstration has been made by means of the Kolmogorov-Smirnov goodness of fit method. Therefore by applying statistical methods on proper parameters obtained from the specimens spectra, it has been able to automatically classify the arterial specimens into healthy (normal), fibrous, calcified and heavily calcified, with more than 99.9% probability (less than 0.1% confidence interval). The different classifications algorithms are thoroughly discussed and evaluated.

Uterine leiomyomas (fibroids) are common benign tumors which may cause heavy or painful periods, may present as a pelvic mass and are associated with infertility. Local excision of symptomatic lesions can be difficult and hazardous, and the alternative is hysterectomy. We are investigating interstitial laser photocoagulation (ILP) as a less invasive alternative. Initial experiments were undertaken on 40 fibroids after surgical removal. One or two bare tipped, precharred fibers from a 25 W semiconductor laser (805 nm) were inserted into the center of the fibroid and treatment delivered with 2 - 10 W for 100 - 1000 sec. Specimens were subsequently sectioned perpendicular to the fiber track. Fibroids are very pale and apart from occasional charred tracts there was little evidence of thermal coagulation macroscopically or after haematoxylon and eosin staining. However, using a diaphorase stain technique we were able to demonstrate ellipsoid zones of devitalized tissue up to 20 mm across (15 mm for single fibers). These results suggest that ILP is producing gentle, uniform coagulation which could lead to resorption of treated areas. With appropriate numbers of treatment sites, this could permit minimally invasive management of clinically significant lesions. Clinical studies have commenced treating fibroids with ILP at the time of surgical excision by myomectomy or hysterectomy.

The absence of a hard tissue model reflecting the properties of the inner and middle ear has made it difficult to draw consistent conclusions on the many experimental laser studies in ear surgery. Porcine otic capsule tissue has been studied by our group extensively in a wide variety of laser-tissue interaction studies and is an economically attractive and simple to use hard tissue source. Porcine otic capsule was harvested from the temporal bone of freshly sacrificed domestic pigs via a craniotomy approach. The technique when performed with power instruments takes less than 5 minutes and the entire otic capsule bone is removed intact as the suture line is not fused to the remaining petrous apex. The tissue specimen contains a vestibule, cochlea, oval and round windows, and internal auditory canals which can be used as an intact middle ear/inner ear system. The tissue can also be micromachined into thin slabs of bone varying for 100 - 1000 micrometers in thickness. In order to quantify more precisely the laser-tissue interactions in otic capsule, optical properties (absorption and scattering) and physical properties were determined (acoustic impedance). The tissue has been used in a wide variety of basic studies investigating the laser-tissue interactions with argon, KTP, (Nd:YAG), carbon dioxide, Ho:YAG, Er:YAG, and XeCl lasers. Porcine otic capsule is an ideal tissue on which standardized test can be performed to compare the relative effects of various laser in otosurgical models.

The range of application of Nd:YAG laser is now wide and of particular interest in the treatment of neoplastic lesions of the large bowel, both benign and malignant, which, besides the debilitating of vegetative lesions, may also provide a good hemostasis of the bleeding ones. Yag laser treatment of malignancies is indicated in patients not suitable for surgery due to the extent of the disease or to the high anesthesiologic/surgical risk. The treatment of choice for benign neoplasms is represented by endoscopic polypectomy, being Yag laser therapy reserved to patients with very large polyps and with a high anesthesiologic risk. Yag laser therapy is also recommended in teleangiectasies with active or previous bleeding, since it allows the complete ablation of such lesions with subsequent outstanding hemostasis. Furthermore this treatment may be advantageously associated to other operative endoscopic procedures, such as diatermotherapy, dilatation and injection therapy. It is also to be outlined that Yag laser therapy is currently used to cure benign diseases and for the palliation of advanced cancer in inoperable patients. Our laser instrument is an Nd:Yag laser MBB Medilas 2 with maximum power of 100 watts at the tip, with 'non-contact' laser fibers. We use flexible optic fiberendoscopes of several sizes, according to the type of lesion to be treated. Moreover we have employed both Savary dilators of progressive caliber from 5 to 15 mm and Rigiflex pneumatic balloons. Adequate bowel preparation by means of isosmotic solution was achieved in patients with non stenotic neoplasm, or evacuative enemas and fluid diet in patients with bowel neoplastic stenoses. The patients were premedicated with benzodiazepines. Stenotic malignant lesions have been treated with endoscopic dilatation before laser treatment. At each session 4,000 - 8,000 joules of energy were administered; all patients received an average of 5 - 6 laser sessions. Followup laser sessions have then been preformed every 2 months. From November 1st, 1992 to February 28th, 1995, 130 patients (78 males and 52 females) with an average age of 65 years (range 39 - 91) underwent Nd:Yag laser therapy of the large bowel for a total of 722 laser sessions. In 91 patients suffering from colorectal cancer with a mean extension of 5 cm 492 Nd:YAG laser sessions were performed with an average of 5.4 sessions per patient (range 1 - 19).