The aim of the present study was to assess age-related regional variations in skin function, by measuring the cutaneous microvascular response to histamine. Histamine was topically applied to the back and forearm of young and aged volunteers, and the response was quantified utilizing laser Doppler flowmetry. Each group comprised of 14 volunteers. The cutaneous vascular response to histamine was significantly greater on the back than on the forearm of young healthy volunteers, whereas in aged ones the response over these two sites did not significantly differ. These observations indicate anatomical or functional differences between old and young skin as relates to regional variations. They may underlie some of the differences in the manifestations of disease processes in various age groups.

In order to destroy selectively cutaneous vessels with a dye laser, the exposition time has to be shorter than the thermal relaxation time of the target tissue. Within this frame of time longer pulses are found to be more efficient in bleaching portwine stains than shorter ones. Two pulses of different length but with identical power density are compared in their therapeutical efficiency by means of reflectometry. There were no relevant differences neither in terms of lightness, redness nor in yellowness. If the increment and the irradiance is the same, a pulse stretching form 200 microsecond(s) to 260 microsecond(s) does not influence decisively the therapeutical effect in portwine stains.

The pulsed dye laser is the most efficient laser to treat port wine stains. Mathematical modeling predicts that the incident optical fluence required to coagulate small sized and/or deeply located vessels is larger than the threshold value for epidermal damage. Dynamic cooling has been reported to prevent epidermal damage caused by the absorption of laser energy in melanin. Further on, this cooling technique has proved to reduce the pain associated with laser therapy. The aim of our study was to examine possible clinical advantages of dynamic cooling. A flash lamp pumped dye laser emitting at 585 nm wavelength with pulse duration of 0.45 ms and a 5 mm diameter spot-size was used. In 12 port wine stains pairs of test sites were exposed to laser pulses with incident fluences of 6.0 to 10.0 J/cm². In all stains one of the sites in each pair received 20 ms cryogen spurts immediately prior to laser admission. In the cooled areas laser induced pain was significantly reduced, and the time period with skin discoloration was shortened by an average of 5 days. Post treatment hyperpigmentation was not prevented. Future studies will aim at improving the cooling technique in order to achieve optical protection of the epidermis.

The clinical objective in laser treatment of hemangiomas is to photocoagulate the dilated cutaneous blood vessels, while at the same time minimizing nonspecific thermal injury to the overlying epidermis. We present an in-vivo experimental procedure, using a chicken comb animal model, and an infrared feedback system to deliver repetitive cryogen spurts during continuous Nd:YAG laser irradiation. Gross and histologic observations are consistent with calculated thicknesses of protected and damaged tissues, and demonstrate the feasibility of inducing spatially selective photocoagulation when using cryogen spray cooling in conjunction with laser irradiation. Experimental observation of epidermal protection in the chicken comb model suggests selective photocoagulation of subsurface targeted blood vessels for successful treatment of hemangiomas can be achieved by repetitive applications of a cryogen spurt during continuous Nd:YAG laser irradiation.

Port wine stain birthmark removal is based on selective photothermolysis. The most common technique utilizes 0.45 ms laser pulses at 585 nm wavelength. High incident energy doses are often needed to reach the ectatic blood vessels in dermis. This might induce changes in pigmentation or even epidermal necrosis. However, the epidermis can be protected by selectively cooling it down prior to laser exposure. Short cooling pulses ensure epidermal protection while preserving the temperature in dermis. Visible reflectance spectra of the birthmark are dependent on the melanin content, the blood volume and the scattering properties. these parameters also determine the fluence underneath the skin during laser exposure. Threshold fluence values can therefore be predicted for each specific lesion. Eight Scandinavian patients with red to purple macular port wine stains were treated with a pulsed dye laser at the energy density 6 J/cm². Seven patients have developed hyperpigmentation in earlier treatments at this energy dose. One site in each lesion was cooled with a 20 ms cryogen spray immediately prior to laser exposure. Visible reflectance spectra were measured before and eight weeks after treatment. A simulation model based on diffusion approximation was used to estimate blood volume, skin pigmentation and scattering properties each time. The measured reflectance spectra, as well as the clinical observations, showed no significant differences between the cooled and uncooled sites. Estimated blood volume fractions and melanin pigmentations were about the same, and the short cooling spurts did not prevent hyperpigmentation. A light brown color was seen in both sites for 7 patients, and could be detected in the spectra for two patients. However, the estimated increases in pigmentation were small also for these patients. Calculated threshold fluence values were almost the same for cooled and uncooled sites after treatment.

The q-switched ruby laser has shown promising results in the treatment of blue and black tattoos. The red light of the ruby laser, 694 nm wavelength, selectively absorbed by dark pigments, is converted into heat and pigments are immediately vaporized. Energy levels range between 4, 5 and 12 J/cm². Short exposure time does not exceed the thermal relaxation time of the target structures. Thus, thermal damage of the surrounding tissue is minimal. Not only exogenous pigment as tattoo ink but also physiological pigmented structures as melanocytes, melanosome loaden keratinocytes, and melanophages are affected by this type of laser application. Therefore the ruby laser represents a new option in the treatment of a variety of benign pigmented lesions in cosmetic dermatology. The benefit of this source can be seen in efficient clearing of the lesions without scarring. As a side effect transient hypopigmentation may occur. Ruby laser treatment of melanocytic lesions cannot be recommended because unpigmented nevus cells do not absorb red light and persist unaltered. They still bear the potency of further transformation, as into malignancy.

In this study, the interaction of picosecond and femtosecond pulsed laser radiation with human dental tissue was investigated experimentally, as this unexplored field is expected to be a potential alternative in powerful laser processing of biomedical structures. Dentin ablation rate experiments were performed by using teeth sections of different thickness. Dental tissue samples were irradiated in air with i) a regenerative amplifier laser at 1064 nm, pulse duration 110 ps, ii) the second harmonic laser at 532 nm, pulse duration 100 ps, and iii) a picosecond tunable dye amplifier at 595 nm, pulse width 800 fs. In all the experiments the pulse repetition rate was 10 Hz. The ablation rate per pulse at different energy fluence settings was calculated by measuring the time needed for the perforation of the whole dental sample thickness. Short laser pulses can confine thermal energy within the optical zone, which maximizes photothermal and photomechanical mechanisms of interaction. Tissue ablation rates were found to be comparable to or better than other nanosecond lasers, and left smooth surfaces, free of thermal damage.

The basic laser ablation processes of dental hard tissue will be reviewed. Pulse lengths covered in this presentation range from some femto seconds to the cw-mode, wavelengths from the ultraviolet to the infrared spectral domain. The underlying tissue removal mechanisms extend from surface evaporation, to photochemical processes, to mediated explosive ablation, to plasma processes. The most effective mechanism is the explosive process. Highly controlled tissue removal at low ablation rate can be obtained using plasma mediated ablation. Good tissue specivity characterizes the ablation in the near UV region of the spectrum.

Beagle dogs were utilized to assess the biologic effects of an Er, Cr:YSGG hard tissue cutting laser and results were compared with conventional mechanical preparations of enamel and dentin. Intraoperative pulpal temperature fluctuations were recorded with thermocouples. The laser cuts failed to induce inflammation in the pulps except in teeth with intentional pulp exposures for both methods. No increase in temperature was detected with the laser. It is concluded that this laser system may be safely employed for tooth preparations without causing adverse pulpal effects.

The purpose of this study was to evaluate the patient's response to cavity preparation using the Er:YAG laser in comparison to the mechanical drill. The study protocol contained the cavity depth and location, which had to be similar for both preparation methods. The patient's response was evaluated generally and according to the location and depth of the cavities. The study design was evaluated by statistical variance analysis and symmetrical tests. Within a time schedule of 9 months totally 103 patients with 206 cavities were treated conventionally and by laser. The drill was accepted as more inconvenient than the laser in 83 percent and 88 percent would prefer the laser for future cavity preparation. The local anesthesia needed for laser preparation could be reduced to nearly a half of the need for mechanical preparation. As a conclusion it can be stated that the Er:YAG laser partially can replace the drill for cavity preparation and contribute to a more comfortable caries therapy for the patient.

This study compares the effects of acid treatment and Er:YAG laser radiation on the enamel. The permanent human molars were used. Oval cavities in the buccal surface were prepared and the edges of cavities were irradiated by Er:YAG radiation. The energy of laser was 105 mJ and repetition rate 1 Hz. The radiation was focused by CaF₂ lens and the sample was placed in the focus. Ten samples were etched by 35 percent phosphoric acid during 60 s. Than cavities were filled with composite resin following manufacturers directions. By laser etching the structure enamel in section was rougher. The optimal connection between the enamel and composite resin was achieved in 75 percent by acid etching and in 79.2 percent by Er:YAG laser etching. Er:YAG laser etching could be alternative method for etching of enamel.

Aim of this study was to evaluate a handpiece with a special fiber tip for Er:YAG laser removal of subgingival calculus. The morphological changes of the treated areas were observed by light microscopy and SEM. To evaluate the efficiency, the time for complete removal of the calculi was measured. The temperature development in the pulp during laser treatment was investigated by a thermocouple inserted into a root canal. After calculi ablation, only smooth ablation traces are visible. The depth of the ablation traces is about 100 micrometers . Roughness of the treated area is similar to the untreated area. The ablation efficiency depends strongly on the shape and location of the calculi and varies between 4.6 and 20 mm²/min. During non stop preparation the maximum occurred temperature in pulp was 7.8 K. The results show that the Er:YAG laser with the used fiber delivery systems and handpiece is suitable for effective and sparing removal of subgingival calculus in periodontal treatment.

During prior studies it could be demonstrated that engaging a frequency double Alexandrite-laser allows a fast and strictly selective ablation of supra- and subgingival calculus. Furthermore, the removal of unstained microbial plaque was observed. First conclusions were drawn following light microscopic investigations on undecalcified sections of irradiated teeth. In the present study the cementum surface after irradiation with a frequency doubled Alexandrite-laser was observed by means of a scanning electron microscope. After irradiation sections of teeth were dried in alcohol and sputtered with gold. In comparison irradiated cementum surfaces of unerupted operatively removed wisdom teeth and tooth surfaces after the selective removal of calculus were investigated. A complete removal of calculus was observed as well as a remaining smooth surface of irradiated cementum.

The results of comparative investigation for IR and visual absorption spectra of oral cavity bacteria are represented by this paper. There are also shown the main differences in absorption spectra of such pure bacteria cultures as : E- coli, Candida, Staph, Epidermidis, and absorption spectra of bacteria colonies cultured in tooth root canals suspected to harbour several endodontical problems. The results of experimental research targeted to investigate an effect of such combined YAG:Nd and YAG:Cr; Tm; Ho laser parameters like: wavelength, energy density, average power and etc., to oral cavity bacteria deactivation are given finally.

Previous studies on thermal effects of Er:YAG laser tooth irradiation have considered heat as an unwanted side effect of tissue ablation.In contrast, we now investigate the potential of the Er:YAG laser for controlled heating and surface sterilization. The methods include model calculations, temperature measurements, and the investigation of bactericidal effects on natural carious lesions. Due to the strong absorption, in the initial phase of subablative irradiation, there is steep temperature gradient in the tissue, subsequently fading off by heat conduction. Using repetitive pulses and irradiation times of a few seconds, it is possible to reach a surface temperature increase (Delta) T oscillating between 100 K and a few 100 K, while keeping (Delta) T in 1.5 mm depth below 6 K. Carious surfaces can be completely sterilized. Thus the Er:YAG laser offers a new potential for controlled and sparing sterilization in dentistry.

We demonstrate the killing of the oral bacteria Prevotella nigrescens using a photosensitizer and light from a 10 Hz, frequency doubled, Q-switched Nd:YAG pumped dye laser, with modified oscillator to increase output power. This system produced light at wavelengths close to 620 nm, the absorption maximum of the photosensitizing agent, malachite green isothiocyanate, a wavelength that is not significantly absorbed by tissue. A bacterial reduction of 97.5 percent was achieved at an energy density of 0.67 J/cm² and exposure times of 300 seconds.

Laser-doppler flowmetry (LDF) is a diagnostic method for checking and judging vitality in tissues. In dentistry, with the help of LDF, there can be investigated short-term or long-term changes of the oral microcirculation. Defects in the LDF equipment which go undiscovered lead to changes in the quality of the biosignals and hamper diagnosis. Reliable and reproducible results are only obtained if the LDF equipment concerned there exists a standardized quality assurance program. There has been developed and tested a method for constancy checks in LDF measurements. The investigation shows that before each clinical application of an LDF equipment careful testing is necessary.

The aim was to study the reproducibility of deposition conditions and physical parameters of thin hydroxyapatite (HA) layers created on flat Ti substrates and the deposition of HA layers on real tooth prostheses. Films were created by KrF excimer laser ablation from sintered HA target in Ar- water atmosphere. The small fluctuations in deposition parameters exhibited the greatest impact on the color of HA films; influence on XRD spectra and film morphology was smaller.

Ablative etch rates within human dentine using an Er:YAG laser have been measured with and without the application of additional water to the sample surface. Projection imaging techniques were found to be useful from both diagnostic and clinical aspects. Well-defined, spatially uniform laser pulses allow accurate determination of ablation threshold fluences as well as fluence-dependent effective absorption coefficients and material removal efficiencies. Etch rate dependency on sample water content is consistent with a thermal ablation mechanism. A model which accounts for this behavior, in view of the temporal pulse structure of the free-running Er:YAG laser, is put forward. The clinical implications of these results are also discussed.

The present paper is the first to results an investigation of parameters of acoustic wave accompanying human tooth enamel and dentine treatment provided with contact YAG:Er submillisecond pulse radiation. It is to define experimentally a dependence of laser-induced acoustic wave integral energy on radiation energy density. And at least, it is to identify Fourier deformations of laser-induced acoustic wave spectrum under contact and non-contact processing of human hard tooth tissue.

Influence of pulselength on mid-IR laser ablation of hard dental tissue was studied experimentally by applying free- generated Er:YAG laser pulses with pulselengths from 50 microsecond(s) to 1 ms and different energies to dentin slices in vitro with no spray cooling. The results show that for pulselengths between 50 and 300 micrometers , dentin ablation turns up abruptly at a well defined fluence value of approximately 4 J/cm², which is independent of the pulselength. Similarly, volumes of the resulting craters as a function of laser fluence at these pulselengths follow nearly the same curve, which corresponds well to a model of laser beam screening by the ejected debris. However, with 1 ms long laser pulses, the ablation tunes up at laser fluences above 4 J/cm² only gradually, reaching differential ablation efficiency similar as in previous cases at fluence values several times higher than the ablation threshold value. An estimate of this 'second threshold' fluence and the pulselengths at which it should in general be observed are derived from a simple model of heat diffusion and ablation front dynamics.

Pulsed Er:YAG and CO₂ lasers should be suitable instruments for dentin and enamel ablation because both tissues have absorption peaks for radiation at 2.9 and 9.6 micrometers wavelengths. This is the context of our research that emphasizes the way in which the diameter and the depth of the crater made in enamel and dentin with the laser Er:YAG and CO₂ is influenced in quantity and quality. Freshly extracted human third molar were used for this experiment. The laser source is Er:YAG Kavo Key dental model 1240 and CO₂ Laser Sonics LS 860. The dimensions of the obtained craters were measured using the optical microscopy method. The obtained results were modelled experimentally with programs: GRAPHER and STATGRAPHICS. After the mathematical processing to the results what we obtain is relevant regarding the influence of the key parameters in the efficiency of the ablation according to the type of laser. On the whole, from our research results that both lasers ablate efficiently the dentin when the laser energy is between 200 and 300 mJ.

This paper represents a complex of investigations concerned with temperature dynamics of pulp chamber for various temporal and power parameters of YAG:Ho laser. Comparison of overheating values at various modes of water cooling system operation is performed. Method of pulp chamber temperature measuring based on temperature monitoring of a checking point of a tooth surface is advanced. Moreover, the results of a special sub-research concentrated on thermal feedback signal at tooth tissues under YAG:Nd laser radiation treatment are offered also. Finally, method of recognizing of any diverse tooth tissue types, such as:bone, dentine, enamel and gum against a thermal response is demonstrated within the limits of this research.

This paper investigates a behavior of tissue remittance in the process of laser pulse. The results for various tissue remittance obtained under the treatment of middle IR laser radiation.

To consider the dynamic response of implant bridge caused by occlusion, the deformation of the bridge and the near mandible subjected to occlusional force was measured by holographic interferometry. In the study, the mandibles of Japanese monkeys were used. A screw type ceramic implant was placed in the site of the second molar, when it was about one year since the mandibular first and second molars were extracted. An implant bridge was then fabricated and placed between the implant and the first and second premolars. After the mandibular bone was extracted, double exposure holographic interferograms were recorded under various loads for the mandible. It was found that the stress on the implant bridge concentrated on the mesial of the pontic when the vertical load was applied to the second premolar. This shows that the mandible near the implant receives most of stress and suffers frequent damage such as the bone resorption, when the loads were applied to its mesial side.

Free electron laser (FEL) gives high efficiency for the photo-induced effects when the laser is tuned to the absorption maximum of target materials. The effect on dentine was investigated using the FEL tuned to 9.4 micrometers , which is an absorption maximum of phosphoric acid in infrared region. As a result, irradiated dentine surface which was amorphous had changed to the recrystalized structure by the spectroscopic analysis of IR absorption and x-ray diffraction. Furthermore, the atomic ratio of P/Ca had reduced from 0.65 to 0.60. These results indicated that 9.4micrometers -FEL irradiation caused the selective ablation of phosphoric acid ion and the reconstruction of disordered atoms.

This paper presents in vitro investigations to compare three different wavelengths used to LITT on the basis of coagulation efficiency, maximum temperature and maximum coagulation volume. The results led us to the conclusion that wavelengths with a smaller penetration depth show a higher coagulation efficiency but a smaller maximum coagulation volume.

Laser-induced interstitial thermotherapy (LIlT) is an alternative method of treatment for BPH which can be applied either transurethrally under direct vision or transperineally under sonographic guidance 1,3,4 Since large prostate glands require longer treatment sessions (1 stickl5 g volume) 1, it is necessary to evaluate means of reducing actual treatment time. When treating larger prostate glands with the perineal or transperineal approach, it became obvious that synchronous stick application could reduce total treatment time. Therefore we connected a specially -designedbeam splitter with a Nd:YAG laser.

The laser-induced interstitial thermotherapy (LITT) is a new treatment modality for advanced recurrent malignancies of the upper aerodigestive tract. Since 1993 26 patients with an incurable tumor recurrence of the head and neck region were treated at the Department of Otorhinolaryngology, Head and Neck Surgery at the University of Kiel. In nine patients tumor progression was stopped or a partial regression was observed. Eight patients showed slowed down tumor growth and nine patients displayed an unchanged tumor progression. No severe complications were noted. These preliminary results show that the LITT is a suitable method for the palliative treatment of advanced tumor recurrences of the head and neck region. Through optimization and standardization of radiation parameters and application of the laser fibers the success rate could be improved.

A preliminary assessment was made of the effect of interstitial laser photocoagulation on normal lung parenchyma. Using rats lesions were created by passing the laser fiber percutaneously into the normal lung under general anaesthetic. The lungs were removed post mortem at 3 days. The lesions were ellipsoid in shape and well circumscribed. Histology showed central charring surrounded by zones of coagulative and hemorrhagic necrosis. there was a clear margin between the treated and normal tissue. These results indicate that further examination is warranted of the use of ILP for treatment of small primary lung tumors in patients unsuitable for surgery.

Twenty VX2 tumors were grafted on 10 rabbit livers. The animals were randomized in two groups when tumor size reached 8 mm. Thermotherapy was performed by delivering the 830 nm output of a diode laser in the center of the tumor using a 300 micrometers fiber. Irradiation conditions were 1.5 W over 900 s. On day 7 or day 14 tumors were removed, stained using hematoxylin eosin and picrosirius red F3BA. Electronic microscopy examination was also preformed. Among the treated tumors, recurrences were found both at the periphery and within the tumors. All recurrences were located near biliary structures. The thermal damage was evaluated by the picrosirius red F3BA stain. Electronic microscopy indicated the thermal resistance of the biliary ducts in the vicinity of coagulative necrosis. The biliary ducts themselves or the vasculature surroundings the ducts lead to a heat sink, thus limiting the tissue temperature elevation. Thermal dosimetry as MRI using thermo sequences should be developed to insure efficient thermotherapy.

For the interstitial treatment of pathologic tissue, e.g. tumors, the benign prostate hyperplasia or the concha hyperplasia in otorhinolaryngology, the method of interstitial laser photocoagulation and the monopolar RF- needle coagulation can be used as well as other methods, e.g. the microwave exposure, alcohol injection, ultrasound or hot water irrigation. This article will present latest results of interstitial thermotherapy with radio-frequency alternating current in bipolar technique. Therefore basic investigations of the thermal field distribution in in vitro samples were performed. THe efficiency of the developed applicators were examined using egg white and in in vitro experiments with porcine liver tissue. Bipolar needles with different diameters were built and tested. Carbonization and dehydration can be avoided by irrigation of the tissue during treatment through an integrated central flushing port. A bipolar needle has been developed for the treatment of concha hyperplasia which can be used as the monopolar pendant with similar results in partial tissue coagulation but without current flow in the sensitive head region. First pathologic investigations pointed out that with the use of the bipolar technique the surface of the concha with the ciliary epithelium is less affected due tot he limited spatial current distribution. Furthermore the design of a multi-electrode needle is presented which could probably offer an additional increase of safety and a simplification of performing a concha coagulation procedure. The new design of a bipolar needle electrode enables the surgeon the use of a partial application of radio frequency current for ITT. Less power is needed due to the limited current distribution at the immediate operation site, which means that a neutral electrode is not needed. Thus a highly safe procedure can be performed by the surgeon.

This study evaluated a single-laser approach for simultaneous ablation and fluorescence excitation for spectroscopic guidance of laser angioplasty. A spectroscopy system was developed and coupled to a clinical XeCl excimer laser. Ablation of 162 human aortic samples in saline and blood with 45 mJ/mm² per pulse yielded 676 fluorescence spectra validated histologically. Five types of spectra could be differentiated: atheroma, fibrous plaque, calcified lesion in saline, normal media and calcified lesion in blood. Discriminant analysis prospectively classified 576 validation spectra with a sensitivity between 83.5 and 100 percent and a specificity between 96.8 and 100 percent. Subsequently, the equipment was used in 16 patients for angioplasty of 18 coronary stenoses applying 500 to 1725 pulses with 45 to 60 mJ/mm² under saline flushing. A total of 783 spectra were recorded and validated by intracoronary ultrasound. Except for the media spectrum, all types of spectra were observed in vivo, too. The predominant sonographic category also prevailed in spectroscopy. In conclusion, using an excimer laser for angioplasty allows combining ablation and fluorescence excitation without a diagnostic laser. Principal types of atherosclerotic lesions and the media can be differentiated spectroscopically with this approach.

Despite the widespread application of balloon angioplasty for the treatment of coronary artery disease, restenosis limits the clinical benefits of the procedure. Restenosis is a complex process and may be partly attributed to the inability of the vascular endothelium to regenerate and cover the denuded area at the site of arterial injury. We previously demonstrated that low power red laser light (LPRLL) stimulates endothelial cell proliferation in vitro and contributes to rapid endothelial regeneration following balloon injury in nonatherosclerotic rabbits. We evaluated the long term impact of intravascular LPRLL on restenosis in an atherosclerotic rabbit mode. Rabbit abdominal aortas were subjected to balloon dilatation and balloon dilatation plus laser illumination. Intravascular laser therapy was performed using a 3.0 mm laser-balloon catheter. All rabbits received a single dose of 10 mW for 3 minutes generated from a He-Ne laser. Angiography was performed before and after treatment, and repeated at 60 days prior to harvesting the aortas. Quantitative angiography, morphometric, and histologic analysis revealed that LPRLL treatment prevented balloon-induced adverse changes including intimal proliferation. We conclude that intravascular LPRLL reduces restenosis following balloon angioplasty.

Numerous reports suggest that low power red laser light (LPRLL) is capable of affecting cellular processes in the absence of significant thermal effect. The objective of the present study was to determine the effect of LPRLL on viability, growth, and attachment characteristics of rabbit and human aortic endothelial cells (EC) and smooth muscle cells (SMC) in vitro. All cell cultures were irradiated with single dose LPRLL using a He-Ne continuous wave laser with different energy densities. Assessment of effect on cell viability, growth, and attachment was performed utilizing Alamar Blue assay. Based upon our experiments, we conclude that: 1) stimulation and/or inhibition of cell growth and death can be obtained with LPRLL by varying the energy level, 2) LPRLL increases EC attachment, and 3) EC are more sensitive to photobiomodulation with LPRLL than SMC. These data may have significant importance leading to the establishment of new methods for phototherapy of atherosclerosis and restenosis.

When lasers were introduced to general surgery in the late sixties great expectations were cherished and abundant optimism developed. A great amount ofbasic research and clinical trials were peformed and indications for the new surgical device gradually defined. Only detailed evaluation and comparison with established forms oftreatment was able to describe the place oflaser application in surgery (1,2).

Flexible acoustic waveguides for selective tissue fragmentation are not yet commercially available. Experimental studies have shown the possibility of transmission of acoustical transients via optical silica glass fibers. The aim of this project is the development of a new endoscopic application system that would enable surgeons to use the laser and the ultrasound technique for therapy simultaneously. The concept of this application system is based on the transmission of laser radiation and ultrasound power via flexible silica glass fibers. Theoretical and experimental results on the feasibility of such an application system for an ultrasonic power delivery system are presented. Piezo-electric transducers are used to provide a high efficiency in generating the ultrasonic power. With reference to the CUSA-technique, a special flexible guiding system has been designed for providing aspiration at the tip and for protection of the fiber. The system transmits via an optical fiber up to 100 Watt Nd:YAG laser radiation. The axial oscillation of the fiber tip is +/- micrometers at a frequency of 27 kHz. First results of in vitro experiments are presented. The parenchymatous cells of liver can be fragmented without destruction of the collagenous matrix. The laser can be optionally used to coagulate bleedings or to cut collagenous tissues in contact. Applications for an acoustical and optical waveguide in ultrasonic surgery are demonstrated. This new approach in developing a first application system for the therapeutical use of laser radiation and power ultrasound in minimal invasive surgery via optical waveguides offers new possibilities in surgery. The laser ultrasonic surgical therapy (LUST) with its thin and flexible applicator provides new working fields especially for neuro or liver surgery. The tip can be bent and thus areas which could not be treated before have now been made accessible. Without changing the instrumentation, the surgeon can use the laser for tissue coagulation or cutting, next to the selective ultrasonic tissue fragmentation, where nerves or vessels will not be affected. Such a LUST-application system could be ready for clinical use in two to four years.

High grade dysplasia in columnar lined oesophagus is a premalignant condition. Yet oesophageal resection in these patients carries significant risks and is associated with considerable morbidity in often asymptomatic patients. Endoscopic photothermal ablation of these areas is possible using the laser. Three lasers were compared for the thermal destruction of superficial areas of dysplastic tissue in the oesophagus. A thermal imaging system was used to measure the depth of penetration and the thermal profile in tissue produced.

Duodenal and periampullary cancer present with jaundice, bleeding and obstruction. Many patients are unsuitable for radical surgery. Endoscopic palliation of jaundice can be achieved using endoscopic sphincterotomy or stent insertion. However, the problems of bleeding and obstruction can be difficult to manage. Ten patients were treated using superficial Nd:YAG laser ablation and lower power interstitial laser therapy. After initial outpatient endoscopic therapy, treatment was repeated at 4 monthly intervals to prevent recurrent symptoms. Bleeding was controlled in all patients and only one patient developed obstructive symptoms between treatment sessions. This responded to further endoscopic laser therapy. The median survival was 21 months. Laser treated patients were compared with a historical series of 22 patients treated with endoscopic sphincterotomy or stent insertion. The complication rate was less in patients treated with the laser.

Nd : YAG laser has been used in the treatment of colorectal cancer since the 80 s. The first results were published in 1980 by Frank and company/li. Authors have been nade with the technique since 1986,when the first experinents with laser started/2/- In the 1986 the laser was worked on wavelenghts of 106 urn and 1319 unThe goal of these experiments was to setup an optimal usage of both wavelenghts, and to establish a safe schedule of outputs with the minimum of perforations of intestines- Since January 1988 our clinic has been using the laser in the therapeutic program. In clinical treatments laser with the wavelenght of 1064 urn and the power of 40 - 50 V is used. Only in rare cases we use the power over 50 V The ratio of energy for one treatment depends only on the 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 a short-tine anestezy Our patients were hospitalized for 2 or 3 days- For the actual treatment.s, we used a rigid endoscopic technique and also a flexible technique (coloskop)- We preferred the flexible technique definitely Since January 1991 we have been practicing almost all treatments in ambulant schedule without general anestezia Only in the cases where treatments reach under linea dentata, we choose short-term inhale anestezia. The patients are hospitalized for one day In the actual treatments we take advantages of the Nd:YAG laser- We try to evaporize the most of the tumor masses during great hemostazis The hemostazis is defined by the zone of coagulation-

The 980 nm Ceralas D50 diode laser, produces homogeneous lesions on tissues of different nature. In our endourological tests we used the Ceralas D50 coupled with Comeg 24 ch laser resectoscope, and we treated 22 patients: n.5 bladder cancers, n.3 uretero pelvic junction obstructions, with hydronephrosis, n.3 urethra stenosis, n1 ureter stenosis, n.4 multiple upper tract transitional cell carcinomas, n.6 BPH treatments with VLAP modalities. Using the 1000 micrometers delivery fibers with different shaped tips, we obtained a bloodless sharp cut and easily vaporizations with minimum carbonizations, with power output in the range of 8-12 W, and 18-24W for VLAP.

Objective: To assess the efficacy of PDT to: Palliate symptoms, control disease and extend survival in patients with advanced inoperable cancer. Subject and Method: 55 Males and 23 females aged between 45-81 years (mean 66 years) with inoperable and advanced lung cancer with > 5O. obstructive lesions of the main, lobar or segmental bronchi. Patients had pre-treatment routine clinical radiological, functional and endoscopic assessment with proven histological diagnosis. Protocol of PDT was; Intravenous injection of 2 mg/Kg bodyweight Polyhaematoporphyrin (equivalent to Photofrin) or Photofrin followed 24-72 hours later by illumination of tumour using 630 nm light (Oxford Laser) delivered via an optical fibre with end diffuser. Treatments were carried out under general anaesthesia as a day case procedure. Patients were rebronchoscoped for debridement/retreatment 4-7 days later. Results: There was no treatment related mortality. Two patients developed mild photosensitivity reaction. All patients showed symptomatic improvement with good initial functional and radiological amelioration. Every patient responded to treatment. Seven patients had complete response and negative histology for 3-12 months. After the first treatment average Forced Vital Capacity (FVC) and Forced Expiratory Volume in one second (FEV1) improvement was 0.5 litres and 0.4 litres respectively. Twenty five percent of patients (nr 19) survived more than 2 years, 10'. (nr=8) between 1-2 years and the remaining 51 patients less than a year. Conclusion: PDT should be considered as a therapeutic modality for all stages of lung cancer and is an excellent treatment modality for palliation in advanced bronchial malignancies.

Different assemblies have endeavored to develop arthroscopic laser surgery. Various lasers have been tried in the treatment of orthopaedic problems, and the most useful has turned out to be the Hol-YAG laser 2.1 nm which is a near- contact laser. By using the laser as a powerful tool, and cutting back on the power level, one is able to better achieve the desired treatment effect. Clinical studies to evaluating the role of the laser in different arthroscopic knee procedures, comparing to conventional techniques, showed that the overall outcome attains a momentous confidence level which is shifted to the side of the laser versus the conventional for all maneuvers, barring meniscectomy where there is not perceiving disparity between laser versus the conventional. Meniscectomy continues to be one of the most commonly performed orthopaedic procedures. Laser provides a single tool which can ablate and debride meniscal rims with efficiency and safety. Chondroplasty can also be accomplished with ease using defocused laser energy. Both lateral release and soft tissue cermilization benefit from the cutting effect of laser along with its hemostatic effect. Synovial reduction with a defocused laser is also easily accomplished. By one gadget, one can cut, ablate, smooth, coagulate, congeal and with authentic tissue depth control The future of laser arthroscopic surgery lies in its ability to weld or repair tissues. Our research study has shown that laser activated photoactive dyes can produce a molecular bonding of collagen fibers, and therefore a repair 'weld' can be achieved with both meniscal tissues and with articular cartilage lesions.

At the first time, the CO2 laser was utilised in infective neurosurgical pathology as a surgical cutting instrument to remove inflammatory pseudomembranes in chronic osteomyelitis, and as a vaporising instmment on the dura mater surface. Successively, the instrument, defocused and at a low power, was used for prolonged and diffuse photo coagulation ofthe surgical cavity, particularly, ofthe dural surface and ofthe osteomyelitic bone edges, with the aim to sterilise tissues. So, we saw a shortening of the average time of wound healing and a lack of recurrence of the septic pathology. Then, we have treated, with CO2 laser, intracranial infective pathology: i.e. primary abscesses, capsulated or not, circumscribed purulent encephalitis, secondary abscesses in surgical cavities (patients operated for intracranial hematomas and tumors). In these cases we have obtained a lack of septic recurrences and an improvement ofneurological post-operative course. Thank to these results, we have continued to use laser in infective pathology; for giving an experimental support to these results we have carried on researches in vivo (on the experimental animal) to see the interaction between the laser and inflammatory tissue, and in vitro (on bacterial culture: in solid and liquid media) to see the laser effect on the bacterial cell. The bacterial cell has been also sensibiized to the photo dynamic effect of the laser (Argon, He-Ne), with hematoporphyrin. The goal of these experiments is to understand the role of thermal, photochemical, and mechanic resonance laser effects in the interaction between laser radiation and bacterial cell.

Cranial rat bone was irradiated by 2,1 micrometers Holmium Yag laser radiation. Quantitative edge rates were calculated. Histologic sections were investigated by light and electron microscopy. 20 cases of hard fibrous or calcified spinal and cranial meningeomas and neurinomas were operated upon using pulsed laser beam. In rat cranial bone ablation rate ranged between 3-5/10 mm per pulse. Perifocal thermal damage was observed in a zone of 20-90 micrometers around the lesion. In all human cases tumors could be removed totally without additional neurological deficit. In vivo heat development was measured by an IR-camera.

Different lasers are today used in many neurosurgical centers, in clinical practice or in basic and clinical research. Even if the laser effects have been studied in other pathological conditions, the laser technology has been mostly applied to the treatment of intracranial tumors. This paper will be mainly concerned with the aspects of surgical technique regarding the supratentorial meningiomas of the skull base, derived from our experience with a series of skull base meningiomas operated on between January 1981 and July 1996. The subject of our analysis are 110 patients who underwent a total of 121 operations. In addition to simple bipolar coagulation and removal of the mass in small coagulated fragments, we have utilized various lasers with different sources of emission, namely CO₂, Argon and Nd:YAG. The CO₂ laser was utilized in 10 cases, the Argon laser in 2 cases and the Nd:YAG laser in 27 cases in both the contact and remote modalities. Among these last 27 patients a total removal was achieved in 96 percent, against 86 percent obtained in the remaining 83 meningiomas. Six patients were reoperated on for recurrences; none of them had been operated on using the Nd:YAG laser.

The actual mechanism for production of laser welding of tissue is presently unknown, but collagen plays an important role is tissue welded after laser irradiance. The quantity change in collagen extracted from the abdominal aorta of Wistar rats after tissue welding using an 830 nm diode laser was investigated. The collagen contents following repeated pepsin digestion after acetic acid extraction were determined with Sircol collagen assay. Compared with untreated aorta, the collagen content of the treated vessel was obvious decreased immediately after laser irradiation and following an initial increase on day 3, there was a peak at day 10. The results suggest that a part of collagen molecules is denatured by the heat of laser. There is an effect of stimulating collagen synthesis after laser welding with parameters used in this study.

We describe healing results of our 6 month study of a repair procedure which evokes the healing response in meniscal tears and partial thickness defects in articular cartilage by a non-thermal tissue sparing photochemical weld using 1,8-naphthalimide dyes. Welds of incisional flaps in adult sheep meniscus and femoral articular cartilage were made using the dye MBM Gold 012011012 at 12 mM in PBS, 457.9nm Argon ion laser radiation at 800 mW/cm², 7.5 minutes with approximately 1 kg/cm² externally applied pressure. Gross appearance of tissues in all welded knees appeared normal. Hematoxylin and eosin stained sections disclosed close bonding of welded areas and continuing healing response as cellular recruitment.

3D finite difference computerized model was developed to simulate the thermal behavior of biological tissue irradiated with a CO₂ laser beam. The model uses standard thermal processes and in addition takes into consideration water evaporation and the corresponding changes in the thermal properties of the tissue. The results contain a temperature and biological damage map of the irradiated tissue. Experimental results of test made on Lucite irradiated with CO₂ laser fit very well the theoretical predictions. The model was then used for simulations of tissue welding and the results indicate that an improved method could be used for CO₂ laser welding.

An experimental study on the applicability of diode laser welding to assist corneal transplantation is presented. Fusion of corneal tissue was accomplished by low power laser irradiation at 810 nm in association with Indocyanine Green (ICG) as the photoenhancing chromophore. Twenty freshly enucleated eyes obtained from young goats were used. In the preliminary experimental phase we examined the effects of laser welding on cuts produced by the scalpel on the cornea. Then we tried to design and test a novel diode laser- assisted corneal transplantation procedure. Our experimental results indicate that this procedure is affordable, but some technical aspects, as the application of ICG to the cut as well as the control of laser action are very critical issues.

The speckle-optical methods and the methods of electroneuromyography were used to study the myotonus, the contractional activity of leg muscles and the neuromotor system functional state in intact rabbits and 3 months after the sciatic nerve (SN) neurorrhaphy in conditions of intravenous laser irradiation of blood (ILIB). The blood of animals was exposed to laser radiation with the help of a quartz-polymeric light guide, which has been inserted into the earvein the next day after SN stitching. The radiation power at the light guide output was 2-2.5 mW. Two courses of treatment with a two-week interval have been conducted. It has been established from the speckle-optical study data that ILIB increases the contractional activity of skeletal muscles in animals. The ILIB-therapy after the SN neurorrhaphy normalizes the latent period of M-response and neural cation potential. A tendancy has been revealed to an increase in impulse conduction velocity in motor nerve fibers and in maximal amplitude of the neural action potential. Thus, the ILIB-therapy after SN trauma improves the neuromotor system functional state in experimental animals in the early reinnervation period.

It is found that in rabbits with the injured sciatic nerve irradiation of blood with low-intensity laser radiation stimulates the mechanism of hemoglobin and thrombocyte formation. Normalization of the lymphocytic composition in blood of the animals with the injured nerve shows that it is possible to prevent development of the process of lymphocytopenia. Changes in the albumins/globulins ratio, the stimulating effect of same biochemical parameters and increase of the hemopoiesis in blood of the animals with the damaged peripheral nerve can probably be considered as evidence of the positive effect of intravenous irradiation of blood with low-intensity laser irradiation on living organisms.

Common audiometry often does not really allow a reliable and objective differential diagnosis of hearing disorders such as otosclerosis, adhesive otitis, ossicular interruption or tinnitus, even though several methods might be used complementarily. In recent years, some experimental studies on middle ear mechanics established laser Doppler vibrometry (LDV) as a useful method allowing objective measurement of human tympanic membrane displacement. The present study on LDV investigated the clinical use of this new method under physiological conditions. LDV proved to be a fast, reproducible, non-invasive and very sensitive instrument to characterize ear-drum vibrations in various middle ear dysfunctions, except in tinnitus patients. For future applications, improved optical characteristics of the vibrometer might result in a better differential diagnosis of subjective and objective tinnitus, otoacoustic emissions or Morbus Meniere.