This paper presents the latest developments in CO₂, ancillary equipment, and advanced surgical techniques used in treating a variety of different dermatologic disorders. To improve our knowledge on the laser treatment of several cutaneous lesions, we have performed a study on 871 cases, of which 690 are benign skin tumors and 181 are malignant skin tumors. Based on this large number of cases, information on post-operative course, recovery time, the quality of scars and aesthetic results, recurrences and hemostasis of blood vessels is given. This study presents indications for performing laser surgery and describes how to avoid complications and limit the potential risks associated with lasers.

Four French laser centers worked together to elaborate a software able to give information on PWS treatment. It is based on a questionnaire describing PWS characteristics, laser treatment modalities, and results. The software was implemented in the four centers for evaluation. From October 1991 to June 1994, 893 patients' files were recorded and analyzed. Patients older than 15 years represented more than 50% of treatments. In all centers, the main location of PWS was the face (65%). Half of the PWS treated were under 30 cm². The distribution of PWS in 4 color groups differed widely from one center to another. The four centers used a Hexascan^R and more than half of the treatments were performed without anesthesia. The percentage of `good to excellent' fading was more important for PWS with initial color `red and purple,' for PWS with locations to `neck and face,' and increased with patients' age. In all centers, scarring occurrence was negligible. Treatment modalities were not discriminant for quality of fading. Evaluation of PWS color is very subjective but all participants agree on the evaluation of treatment results. This software is a first step to document the PWS laser treatment, but an objective method for characterization is strongly needed.

In order to characterize port-wine stains (PWS) before and after laser-therapy, a study using epiluminescence microscopy is achieved. The technique consists in placing a thin layer of mineral oil on the skin surface and inspecting the PWS with a Delta 10 dermatoscope (HEINE). A contact microphotography is then performed in a similar manner by means of a Dermaphot optical module (HEINE). One hundred and sixteen patients have been explored prior to laser treatment. Twenty eight have been explored at the same place three months after the first treatment and four three months after two treatments. The preliminary results are compared with Jones, Shakespeare, and Carruth's studies on transcutaneous microscopy. It is possible to classify PWS according to their epiluminescence microscopic aspect. The classification proposed by the English authors is not ideal and some adaptations are desirable, regarding particularly the background condition. Some correlation can be established between the macroscopic and microscopic aspect of PWS. It is far too early to correlate epiluminescence aspect before treatment and long term results of laser-therapy.

In treatment of port-wine stains with a pulsed dye laser, whether to deliver the pulses with or without overlap remains controversial. Therefore the effect of overlap on vascular damage was histologically objectivated by taking biopsies from normal human skin of 5 healthy volunteers, who had laser pulses delivered as follows: 1 single pulse, 2 completely overlapping pulses, 2 pulses with approximately 30% overlap, and 2 pulses with 1 - 2 mm normal skin in between. For these experiments a Candela SPTL-1 with a wavelength of 585 nm was used to deliver 5 mm diameter pulses at an energy level of 7.0 J/cm². Light microscopy of the biopsies taken 24 hours after delivering the pulses shows that in overlapping pulses the inflicted damage still seems to be confined to the vessels, but that it extends deeper into the dermis. A striking observation, however, is that concerning the depth of vessel damage, even in non- overlapping pulses, the adjoining pulses have an invigorating effect on each other.

We have been using a continuous dye laser (coherent medical) for more than two years. The wavelength is 585 nm, the power 1.8 W and the fluence 16 - 18 J/cm². We have treated 364 patients with port-wine stains and 15 children with ulcerated hemangiomas. The results were analyzed using a computer program developed by a team in Lille. The most frequent color was pale pink, followed by deep pink, red and purple. The mean number of laser sessions was 2.3.

During the period of January 1984 - July 1993, we have treated 611 children with more than 2000 lesions of congenital vascular disorders (CVD) such as hemangiomas and vascular malformations. This number does not include the patients with port wine stains, which also have been treated by means of laser. Most of the CVD patients (n equals 467) presented hemangiomas of the face, the anogenital region, and the extremities, some were located in the trachea or mouth or in the urogenital tract. All of these hemangiomas were growing prior to intervention or showed complications such as bleeding, ulceration, superinfection, or obstruction. Nearly a quarter (n equals 144) of the patients presented vascular malformations, either of singular vessel type involvement or of mixed vascular genesis (venous, arterio- venous, veno-lymphatic or lymphatic) with various complications like tracheal obstruction or recurrent thrombophlebitis. According to our step program, which is based on a clinical classification, the hemangiomas were treated as early as possible, while the vascular malformations were only treated with laser when no other therapeutic technique (embolization, resection) was suitable. All patients were referred for laser treatment from other centers. The lasers used were Nd:YAG and Argon lasers with transcutaneous application with or without continuous ice-cube surface cooling or interstitial laser application. The treatments were performed either on in- or outpatient basis according to age, localization and with good to excellent results in most cases and a complication rate of less than 2%.

Laser tissue welding is used to close wounds or to anastomose conducts such as arteries. The welding effect is due to tissue denaturation which depends on the irradiation parameters. An excessive laser irradiation leads to irreversible thermal damage. In conventional welding procedures, laser irradiation is controlled by visual inspection of the welded zone. A new device based on an 800 nm diode laser allowing an automated welding procedure is described here. The device measures the variation of the diffuse reflectance on the treatment area and stops laser irradiation when a given optimal value is reached. This allows the user to increase the reproducibility of the treatment by avoiding the subjective aspect of welding completion assessment by visual criteria. The system has been tested by in vitro welding an egg yolk membrane on mesenteric bovine arteries. The results have shown that for a given laser power, there is a specific reflectance decrease threshold value leading to an optimal welding. Reproducible welds with minimal thermal damage could be obtained.

This paper represents the method of contact zone effective temperature measuring by registering thermal radiation which is back propagated through the main laser radiation delivery fiber channel. The results of contact zone temperature measuring experiments for some different tissue types are also represented. The present method allows us to obtain a reliable real-time information about instant temperature in the contact zone using a reliable scale of time. The possibility of thermal feed-back control of an in contact laser destructor based on Ho laser is evaluated.

Pulsed photothermal radiometry (PPTR) of tissue based on the analysis of thermal radiation kinetics measured from tissue at laser heating is an effective method of laser-tissue interaction investigation. The processes of destruction under laser radiation action (coagulation, fusion and welding), which are characterized by definite dynamics of temperature in the region of laser heating, have been studied. The amplitude and kinetics of the thermal signal registered by PPTR technique depend on space and temporal temperature changes in the zone of heating, which is conditioned by the regime of laser action and internal processes in tissue. In the present study the investigation of thermal tissue destruction under action of high-power pulsed CO₂ and YAG:Er-laser radiation has been carried out using PPTR. Soft and hard tissues have been examined. The nonlinear dependencies of thermal emission kinetics, the thermal signal amplitude, and the integral absorption on laser energy density are presented and discussed. We represent PPTR as a technique which can be used for the definition of the destruction threshold and for the regulation of laser action on tissue. PPTR method has been applied in clinics with the aim of more accurate definition of CO₂ pulsed medical laser radiation dose for treatment of patients with different dermatological diseases.

The present in vivo study was undertaken in order to evaluate the patency rate and histological aspect on 30 venous anastomoses and 30 carotid anastomoses in Wistar rats using a laser. An argon laser was used with the following parameters: 100 mW, 3 s, continuous mode, spot equals 200 micrometers (fluence equals 950 J/cm², irradiance equals 320 W/cm²). The macroscopic aspect and patency rate were evaluated at different post-operative intervals (30 days and 60 days). In the venous group, the patency rate was 100% with no saccular pseudo aneurism. In the arteries group, the patency rate was 93% with 3 saccular pseudo-aneurisms and 2 thromboses. Histological studies noted slight and transitory modifications of the media in the arterial group. In the venous group, the modifications appeared under the endothelium with conjunctival hyperplasia. Since the procedure was similar in both groups the lack of pseudo-aneurism in the venous group can be explained by a lower intravascular pressure.

In this work we report our experiences on diode laser-assisted end-to-end microvascular anastomosis performed on femoral arteries and veins of rats and rabbits at very low laser power (30 - 40 mW). In the course of our trials we approached laser anastomosis with a reduced number of permanent stays to decrease foreign body reaction. Recently we demonstrated the possibility to perform anastomosis without supporting stays. Significant improvements in comparison with traditional procedures were also furnished by histology examination, which showed a better healing process in LAMA cases.

Diode laser assisted microvascular anastomosis (LAMA) versus control ateral conventional suture microanastomosis (CMA) were performed in 50 rats. The laser source (830 nm) was included into a micromanipulator without optical fiber connection. The beam was directly focused on a deviating mirror giving a 200 micrometers spot size. The LAMA was performed on the left common carotid by means of 3 laser shots of 360 mW power and 8 s exposure time regulated by an auto-stop system, the irradiance being 1,146 W/cm². CMA was performed on the right carotid by means of size 10.0 Ethilon stitches (BV 70, Ethnor, Neuilly, France). The anastomoses were evaluated by macroscopic controls and Doppler spectral analysis (D0 to D60). After LAMA, light and scanning electron microscopy visualized the rapid re-endothelialization of the anastomotic line with longitudinal migration of endothelial cells, while the media was repaired by collagen network due to tissular fusion. The procedure demonstrated the usefulness and the adaptability of our new laser system. The prototype, characterized by low weight (2,500 g), small size 30 X 10 X 6 cm), good laser transmission, equipped with a feed-back system is well adapted to microsurgery.

Dye enhanced laser welding has been recently proposed for skin closures to exploit the advantages of laser procedure (possible reduction of scar formation, no inflammatory reaction). In this preliminary study we used the diode laser-assisted technique to perform welding of rats' skin. In the pilot phase of the study we investigated the effect of the interaction between diode laser radiation and 20 full thickness skin wounds, performed on the shaved backs of 10 Wistar rats, using laser power in the range of 200 - 150 mW and, as the photoenhancing chromophore, Indocyanine Cardio-green (ICG) dye saturated solution in plasma. Ten wounds were sutured with 4.0 nylon thread, to provide a comparison with the traditional procedure. Wounds' samples were explanted on day 3 and 7 after the treatment, for histological evaluation. Clinical examination on the same days showed a high percentage of wounds dehiscence and presence of scales and crusts. Histologic examination demonstrated evidence of thermal injury and a heightened inflammation, superior to that of suture closures. In the second phase of the study, a lower laser power (150 - 80 mW), ICG-plasma-non saturated solution (ICG-sol) and ICG-plasma-saturated-sodium hyaluronate gel (ICG-gel), were used. Six wounds were filled with ICG-sol and six with ICG-gel, then irradiated at 150, 120 and 80 mW. Postoperative explants were performed on day 3 and 7. Clinical and histological results from this group were satisfactory: we recorded only one case of dehiscence, well healed wounds, no epidermal necrosis and a mild inflammatory reaction, reduced respect to that of traditional closure. We characterized the optimum range of parameters of diode laser-assisted technique to achieve an effective skin welding and the corresponding clinical and histologic pattern was described.

To study the possibility of using Nd:YAG laser to weld the tissues of the uterus experiments in rats and dogs have been conducted. With the biomicroscopy and the laser Doppler flowmetry we have evaluated the microcirculation in the uterus wall under traditional suture and laser welding suture. As a model of the wound, the dissection of serosa and muscles of the organ wall have been used. In laser welding suture we have welded the zone of tissue about 1 mm³ with the laser (power density 270 W/cm²). Histological control has been fulfilled on various phases of the healing process. The investigation of the uterus wall demonstrates that there are zones of microcirculation disorders in tissues: (1) the zone of coagulation of microvessels and adjacent tissues (about 100 micrometers ); (2) the zone of stasis (150 - 200 micrometers ); (3) the zone of reactive-destructive changes of microvessels (300 micrometers ), (4) the zone of malfunctional microcirculatory changes (600 micrometers ). The coagulation of microvessels changes the character of inflammation and the healing process, decreases the exudation phase and the leucocyte infiltration of tissues, and accelerates the capillary growth. In contrast with traditional suture, in the case of laser welding suture the edema and hemorrhagic signs are less expressed. The complete restoration of microcirculation under laser welding suture has been observed by the fourteenth day of the healing process. Under the traditional suture method normalization of tissue nutritious blood flow has been achieved by 21 days.

Capacitative radio frequency (RF) was met with little success when used to treat human cancer. Conductive rf needle hyperthermia (RFNH) is used successfully for human tissue ablation in neurosurgery, cardiology, and recently in urology. RFNH ablates tissue by causing thermal damage limited to the vicinity of the rf needle. We conducted a series of studies to evaluate the effect of RFNH on cancerous and normal tissue. RFNH was applied to normal porcine livers during open surgery. Liver function tests were elevated two days post treatment, then returned to normal. Pigs were sequentially sacrificed. RFNH induced lesions were found to be maximal in size on days 2 - 4 post treatment and later became smaller as liver regenerated. Phase 2 included mice bearing two subcutaneous murine bladder tumors (MBT2). The rf needle was inserted into both tumors of each mouse, but rf current was applied to one tumor only. Energies of 3 to 7.5 watts were applied for 30 seconds to 5 minutes using a 0.02 inch needle. Mice were sacrificed 0, 1, and 3 days after treatment. Necrotic lesions 0.5 - 1.2 cm in diameter were found within the treated tumors. In phase 3, mice bearing a single 8 - 18 mm subcutaneous tumor were treated by RFNH aiming for complete tumor destruction. All control mice died of huge tumors within 31 days. Treated mice were alive with no signs of tumor when sacrificed 60 days after treatment. In phase 3 RFNH is capable of complete tumor eradication with little damage to surrounding normal tissue. It may have clinical applications for percutaneous endoscopic and laparoscopic treatment of tumors.

Interstitial laser thermotherapy (ILT) has recently been applied for palliative ablation of tumors in different organs. The present animal experiments were conducted to evaluate the feasibility of ILT for tumor eradication. Twenty two rabbits, 8 normal and 14 with implanted VX2 tumors in the liver, were treated with Neodymium-YAG laser using interstitial thermotherapy (ITT) fibers. Single and/or multiple laser applications were performed either percutaneously (normal livers) or under laparotomy (VX2 tumors) and monitored with CT and visual inspection respectively. Laser energy was 3 or 4.5 watts during 600 or 300 seconds application. After therapy, all lesions were followed up by contrast enhanced MRI. Finally the animals were sacrificed at various intervals and the livers were evaluated by macroscopy, microangiography, and microscopy. With no exception, some vessels with surrounding tumoral tissue remained undestroyed inside the macroscopic limits of the laser induced lesions. This caused tumor relapse during follow up. In the liver, vessels have a cooling effect and can shield adjacent tissues. Therefore there is a discrepancy between the macroscopic area of necrosis and the area of radical treatment.

A computer model is presented enabling the determination of optimized laser parameters in advance of a LITT treatment. Besides, a real-time simulation of the spatial temperature- and damage distribution can be performed during the treatment. Input parameters for the simulation are the specific optical and thermal properties of the tissue. The optical properties of human liver and human prostate were measured at 850 nm and 1064 nm using a double- integrating sphere technique and inverse Monte-Carlo simulations. The thermal tissue properties were calculated from the individual water contents. The calculation of the spatial intensity distribution is carried out by performing a fast three-dimensional Monte-Carlo simulation in small time steps. The change of the optical tissue properties during the process of coagulation is taken into account. The corresponding temperature distribution is calculated by a numerical solution of the two-dimensional bio-heat transport equation in cylindrical geometry. Finally the degree of tissue damage is determined by solving the Arrhenius formulas numerically. Blood perfusion of the tissue can be considered as an internal cooling effect. Comparison of the calculated temperature behavior with experimental data shows good agreement.

A variable application-set was developed to enable a safe and effective LITT treatment. The set consists of various laser applicators, a protecting catheter and an introducing equipment. The laser applicator was developed with different radiation patterns to match the topological conditions of the diseased area. For MRI-controlled LITT treatments a special marker is mounted at the distal end of the glass fiber which facilitates its localization. To increase the patient's safety a special protecting catheter was designed which is temperature stable up to 250 degree(s)C and transparent for NIR-radiation. The catheter can be placed into the diseased area using the introducing equipment which consists of modified parts of standard interventional radiology equipment. The laser applicator is finally guided through the protecting catheter so that there is no direct contact between applicator and tissue. The system can be used both for intraoperative and for percutaneous treatments.

Since 1984 we use the interstitial application of laser induced thermotherapy (LITT) for the treatment of congenital vascular disorders (CVD) such as hemangiomas and vascular malformations. In most of the procedures a 600 micron core bare fiber is used to deliver the radiation of a cw Nd:YAG laser emitting at 1064 nm into the diseased tissue. As most of the CVD treated this way are located subcutaneously, the localization of the fiber and the interstitial laser coagulation (ILC) is controlled by transillumination and palpitation of the heat expansion of the skin surface, this way a crepitation can also be detected during the ILC. As the ILC in deeper body structures cannot be controlled directly we use color coded duplex sonography (CCDS), both for diagnostic and treatment control. In the procedures where we use the B-scan image for puncture control, a color signal is displayed representing tissue movements. These movements caused by degasification and vapor are those detectable as crepitations when using direct control. The color signal starts, changes, and moves in a reproducible pattern following the heat distribution and the subsequently occurring degasification in the tissue. Also the changes in perfusion are detectable by the means of CCDS. The precise extent of the coagulation is visible in the B-scan several minutes after laser exposure. The clinical experience and an extensive experimental evaluation has proven that CCDS is a valuable real time method to monitor the tissue reaction in ILC-procedures. For two years we have performed ILC-procedures with CCDS control in patients with CVD (n equals 65) successfully. Because of its reliable imaging and the clinical advantages recently we applied this type of ILC-control to the palliative treatment of nonresectable primary and secondary liver tumors (n equals 3) and subcutaneous metastases of mamma carcinoma. (n equals 6).

The goal of modern surgery is always to reduce the risks of surgery and anesthesia to a minimum. Our new method is carried out in local anesthesia, the surgical procedure is reduced to burrhole surgery and the procedure itself is real time controlled by the magnetic resonance tomography. The program allows the user to superpose at all times the isotherms to the recent MR picture with the brain tumor. The recent algorithm uses the water proton chemical shift. It possesses both a high sensitivity and a tissue independent effect and it also leads to an excellent method of monitoring temperature changes.

Interstitial laser photocoagulation (ILP) is becoming an established treatment for hepatic metastases. Per-procedural ultrasound does not accurately define the tissue coagulated and dynamic computed tomography, while an accurate form of assessment, must be delayed until 24 hours after therapy; it too is, therefore, no use for per-procedural confirmation of total tumor ablation. By virtue of its good contrast, spatial and temporal resolution and the fact that T1 weighted images are temperature sensitive magnetic resonance imaging (MRI) is, theoretically, applicable to the per-procedural guidance of ILP. Our ex vivo porcine, and in vivo rat liver experiments showed good imaging-pathological agreement. We have treated with ILP two patients suffering from hepatic metastases using MRI guidance. Four to eight 400 micrometers optical fibers were passed through the lesion down Teflon sheaths under local anaesthetic and intravenous sedation using ultrasound guidance. Sets of 400 second laser burns at 1.5 - 2.0 W per fiber were then performed, with a 1 cm fiber withdrawal between each set, until the entire tumor had been coagulated. Therapy was monitored with dynamic MRI using a T1 weighted FLASH sequence. MRI showed an enlarging bright rimmed low signal area which correlated with the region of devascularization seen on enhanced helical computed tomography at 24 hours. MRI can monitor ILP of hepatic metastases and confirm tumor ablation at the time of treatment.

An experimental procedure of antitumoral interstitial diode laser hyperthermia was achieved in a series of 30 Swiss nu/nu mice (10 weeks old, 25 g weight). The tumor model was a subcutaneous HT29 colonic carcinoma. The diode laser (830 nm) was applied through a 300 micrometers optic fiber implanted in the tumor and delivered at different powers as follow: group 1 -- 0.2 W (n equals 5); group 2 -- 0.5 W (n equals 4); group 3 -- 0.8 W (n equals 4); group 4 -- 1.0 W (n equals 4); group 5 -- 1.2 W (n equals 4); group 6 -- 1.5 W (n equals 4); group 7 -- 1.8 W (n equals 5). The exposure time was 900 sec (360 to 1 620 J). According to the different laser applications the temperature range was 48.2 degree(s)C to 73.7 degree(s)C in the center of the tumor and 42.0 degree(s)C to 63.5 degree(s)C in its peripheral part. The tumor was removed 24 h after laser treatment. The largest necrosis diameter evaluated by macroscopic and histological sections were 8, 11, 13.25, 17.65, 18, 18.25 and 18.5 mm in the group 1, 2, 3, 4, 5, 6, 7, respectively. In the groups 6 and 7 (1.5 and 1.8 W) all animals died after treatment, the death being explained by extensive hyperthermia. Our results suggest that 1.0 W/900 sec might be the most effective condition for treating this tumor model in Swiss nu/nu mice.

Urinary outflow obstruction by prostatic enlargement is usually treated by resection or, recently, less invasively by thermal `ablation' of tissue through the urethra. With the latter technique, the amount of tissue that can be removed is limited by the limited penetration depth of suitable radiation sources, e.g. lasers, or conduction of heat. Interstitial thermotherapy was expected to overcome this problem. Our initial in vitro and animal studies with different light guides for interstitial application of Nd:YAG laser radiation showed small carbonized lesions with bare fibers, but large homogeneous coagulation zones with special `ITT' (interstitial thermotherapy) fibers. Further studies using these applicators resulted in a technique to be apt for clinical routine in the treatment of symptomatic prostatic enlargement. The tip of the light guide was repeatedly inserted into the prostate either transurethrally through a cystoscope under direct vision or percutaneously from the perineum under transrectal ultrasound guidance. The number of fiber placements depended on the size and configuration of the gland. Irradiation was performed either for 10 min with 5 or 7 W or in the advanced `turbo'- mode for 5 or 3 min per fiber placement using automatically stepwise reduced power (20 W for 30 s, 15 W for 30 s, 10 W for 30 s, and 7 W for 210 or 90 s). By optical feedback control the laser was switched off automatically in the case of carbonization to avoid fiber damage. From July 15, 1991 to October 1, 1993 239 patients with BPH and 14 patients with advanced prostate cancer, suffering from severe urinary outflow obstruction, were treated by laser induced interstitial thermotherapy. The results and complications of treatment are reported.

The use of thermal energy in order to cause damage to obstructing prostate tissue is a recently introduced alternative to transurethral resection of the prostate (TUR-P). In order to assess the efficacy of perineal interstitial laser treatment, we report on 22 patients (operative high risk category), with a 6 month follow up, who have been treated with the Dornier ITT laser fiber. Treatment protocol designates the perineal approach for side lobe hypertrophy, transurethral approach for middle lobe hypertrophy, and the continuous application of decreasing increments of energy within specific time intervals. Results were evaluated by flow rate, residual urine, symptom score, reduction in prostate size, and cystomanometric studies. The overall success rate was 61%, flow rate improvement > 15 ml/sec in 50%, mean symptom score reduction from 26 to 7, residual urine decrease to < 50 ml within 12 weeks in 40%, and prostate volume decrease in 47%. Interstitial laser coagulation can be considered a safe alternative to TUR-P in a select number of patients, however a larger series of patients must be treated before the efficacy of the method is finally established.

A new sensor using fiber optics is suggested for blood flow measurements in small vessels. The sensor principle and a first evaluation on a flow model are presented. The new sensor uses small CO₂ gas bubbles as flow markers for optical detection. When the bubbles pass an optical window, light emitted from one fiber is reflected and scattered into another fiber. The sensor has been proven to work in a 3 mm flow model using two 110 micrometers optical fibers and a 100 micrometers steel capillary inserted into a 1 mm guide wire. The evaluation of a sensor archetype shows that the new sensor provides a promising method for intravascular blood flow measurement in small vessels. The linearity for steady state flow is studied in the flow interval 30 - 130 ml/min. comparison with ultrasound Doppler flowmetry was performed for pulsatile flow in the interval 25 - 125 ml/min. with a pulse length between 0.5 and 2 s. The use of intravascular administered CO₂ in small volumes is harmless because the gas is rapidly dissolved in whole blood.

Pulsed laser ablation of atheromatous arteries was studied at three wavelengths in the near ultraviolet, visible, and near infrared regions of the spectrum. The experiments were done with an Nd:YAG laser, 9 nsec pulse duration. The wavelength could be fixed at 1064 nm, 532 nm, or 355 nm through KDP crystals. Laser fluences ranged up to 80 J/cm² and repetition rate was 8 Hz. Ablation fluence thresholds increased with wavelength from UV to the visible region and dropped again near (lambda) equals 1064 nm. Maximum ablation efficiency at 355 nm was measured to be 0.6 mg/J, three times higher than the corresponding value at either 532 or 1064 nm, which was approximately 0.20 mg/J. The results are in good correlation with the optical properties of cardiovascular tissue, assuming that the absorption coefficients are equal to (mu) _a approximately equals 24 cm^-1 at 355 nm, and (mu) _a approximately equals 1.32 cm^-1 at 532 or 1064 nm. Corresponding the scattering coefficients assumed to be equal to 8 cm^-1 at 355 nm and 20 cm^-1 at 532 and 1064 nm. Taking into consideration the composite nature of calcified lesions, the optical properties of cardiovascular tissues, and the different possibilities of the three wavelengths the choice of pulsed Nd:YAG laser with KDP crystals capability seems to be a good choice for angioplasty.

Photodynamic therapy (PDT) of proliferative vascular smooth muscle cells (SMC) reduces intimal hyperplasia. We asses the effects of PDT on contractile SMC In normal arteries using aluminum disulphonated phthalocyanine (AlS₂Pc) sensitization. Rats sensitized with intravenous AlS₂Pc underwent carotid artery fluorescence measurement. More rats had carotid artery irradiation with different laser energies 30 minutes after sensitization with AlS₂Pc 5.0 mg/kg and sacrificed at 3 days. Additional rats were irradiated with 50 J/cm² after sensitization with different AlS₂Pc doses and sacrificed at 3 and 14 days. Histological analysis was by light microscopy. Rats treated with PDT and sacrificed at 3 and 6 months were also analyzed. The results show AlS₂Pc induced high and dose dependent fluorescence within the arterial media. All PDT light doses (50 - 250 J/cm²) produced arterial SMC depletion. In contrast, PDT sensitizer doses produced complete cell depletion only at high doses of AlS₂Pc. These treated arteries were acellular after 3 days. At 14 days the media remained acellular but the endothelial lining regenerated. The arterial media remained acellular even at 6 months -- however, no hemorrhage, thrombosis or aneurysm formation was seen. Arterial PDT causes media contractile SMC depletion in vivo and the artery retains its structural and functional integrity.

To study a possibility of selective laser action on atherosclerotic plaques and normal vessel wall a set of laboratory experiments was performed. We used XeCl-laser with a Raman shifting cell and Nd-YAG laser with a frequency doubler, tripler, and quadrupler. It allows us to compare the results of laser action on tissue in a broad spectral range. The laboratory setups permit us to vary parameters of laser radiation such as pulse repetition rate, duration, energy, and power density. All samples were subjected to detailed morphological study. In particular, experiments with XeCl-laser demonstrate that the specific vaporization energy decreases when the laser energy increases. The penetration depth of laser radiation was considerably less than is to be expected from the measurement of absorption factor at 308 nm. Moreover, the absorption spectrum of the tissue after irradiation was absolutely different from the initial tissue absorption spectrum. Therefore, the two-photon processes play the main part in the interaction of high-power laser-light with tissue. Thus the laser pulse duration is to be considered as one of the most important parameters in this case. It is shown also that IR radiation at 1.06 mkm is quite effective to penetrate into calcified plaques. Laser angioplasty is still to be considered as a promising technique for treatment of vascular diseases. However, the discussion about the type of laser to be used for this purpose has not yet been finished.

Recent progress in biomedical optics resulted in increased activity in this area at a number of different centers. Reported are the first results of the program directed to incorporate at Tomsk Cardiology Center experience gained in Tomsk optical profile research institutions in areas of light-matter interaction, high resolution spectroscopy, laser physics and relevant software and their usage in cardiac therapy, surgery, and diagnostics. To coordinate research work in this direction the special unit-laboratory of laser medicine is organized at the Center. Laboratory activity goes in the following directions: study of spectral properties of vessel walls in norm and atherosclerosis, comparative study of different wavelength laser radiation action on normal and atherosclerotically damaged tissues, novel approach to intravascular imaging, and usage of high sensitive laser spectroscopy for early diagnosis of cardiac diseases. The spectroscopic study of AP and normal tissue is aimed at understanding of differences in internal energy structures and ways of energy migration which are of critical importance for reaching selective laser action on normal and deceased tissues. To compare thermal, mechanical, and photo-chemical variations of tissues caused by laser radiation the XeCl excimer laser with Raman shifting cell and Nd:YAG laser with second, third, and fourth harmonic converters are employed. Fine influence of pulse duration, intensity, and repetition rates on AP removal is considered in laboratory experiments with vessel samples. Preliminary results on theoretical consideration for determination of spectroscopically detectable markers of some cardiac diseases are reported as well.

Photodynamic therapy (PDT) of proliferative vascular smooth muscle cells (SMC) reduces intimal hyperplasia (FCIH). We assess the effects of adjunctive balloon injury and immediate PDT on contractile SMC, using aluminum disulphonated phthalocyanine (AlS₂Pc) sensitization, on intimal hyperplasia. Groups of 5 Wistar rats underwent tail vein injection with 2.5 mg/kg of aluminum disulphonated phthalocyanine (AlS₂Pc). Standard carotid artery balloon injury was performed with a 2FG Fogarty embolectomy catheter and the artery irradiated with 50 J/cm². Control groups were also studied. Rats were killed at 2 and 4 weeks after treatment and perfusion fixed H&E stained cross-sections assessed by computerized morphometric measurements. Three sections per rat were analyzed. PDT treated arteries were free of FCIH formation in all cases. Laser alone (and to a lesser extent sensitizer alone) produced some reduction in the levels of FCIH compared to untreated but balloon injured vessels. The ratio of the area of intimal hyperplasia in treated vessels to the area of intimal hyperplasia in untreated (balloon only) rats were sensitizer only 98%, laser only 68% and PDT 0% at 4 weeks. PDT given at the time of angioplasty may be affective in the management of restenosis.

The quality of microendoscopic images ((phi) < 0.5 mm) results from numerous factors. The microlens, the optical interfaces, and the multicore fiber (MCF) play a role. The intercomparison of the performances of these various components requires a precise evaluation of their modulation transfer function (MTF). The MTFs of a representative sample of MCFs have been evaluated in detail and the results presented in previous communications. The sampling density, the cross-talk, and to a lesser extent the leaky modes and propagation in the cladding have been found to be the main factors worsening the MTF. The Selfoc Grin lens also limits, in a non-negligible proportion, the overall quality of the microendoscopic image. Comparative data have been obtained with a slightly modified evaluation procedure for the MTF. This synthetic analysis results in a global understanding of the factors limiting the performances of microendoscopes.

Optical fiber systems with lateral emission of laser radiation are currently used for laser treatment of benign prostatic hyperplasia (BPH). They can be classified in reflective or refractive systems in which a mirror or a prism, respectively, is connected to the fiber tip. Both systems are disposable making the cost of treatment too high. An alternative solution for refractive systems is the prismatic cut of the fiber tip. A side fiber of this type was conceived at the Department of Chemical Physics of the University of Venice and then patented. An Olympus 27ch transurethral resectoscope was also modified for use with our side fiber as well as with the resecting blade. Our modified resectoscope with a Nd-YAG laser has been clinically used for the laser treatment of BPH (6 cases), as well as in high risk patients with bulky bleeding bladder tumors (4 cases), and in transitional tumors of the prostate infiltrating the parenchyma (2 cases). Laser treatment with our resectoscope resembles traditional endoscopic treatment, guarantees the precision of fiber tip translation, and permits combined treatments with laser and traditional blade.

This present work reports the long term results after endoscopic laser treatment in 474 patients with benign rectosigmoid villous adenomas revealed by biopsy. Two types of wavelength were used: The 1.06 micrometers infrared light from the Nd:YAG laser and the green light from the argon laser or the Nd:YAG frequency doubled laser. In some patients, both wavelengths were used. Treatment was completed in 415 patients. Total tumor destruction was obtained in 92.8% of them, a carcinoma was detected in 6.5% on biopsy specimens obtained during laser treatment, and benign villous tissue persisted in 0.7%. During the average 30 mo. follow up period of the patients with total tumor destruction, 18% had a tumor recurrence. Treatment was well tolerated with a 1.8% complication rate (one perforation, one hemorrhage, and 7 stenosis requiring dilatation). Because treatment is long and difficult and cancer rate is high, endoscopic laser should be limited in patients with a circumferential villous adenoma to nonsurgical candidates. The risk of complication after surgery (some being fatal) has to be balanced against the risk of undetected carcinoma in the other patients and the indication for endoscopic laser treatment should be discussed case by case.

Laparoscopic cholecystectomy (LC) is a minimally invasive method of removing the diseased gallbladder. It was introduced into Lithuania in December 1992 and has gained wide acceptance. While LC offers many advantages over the conventional laparotomy procedure one of its drawbacks is delayed biliary complications. Those complications may be avoided with appropriate precautions. The aim of this research is to maximize the safety of LC. The potential way to solve this problem is to minimize the possible heat damage and electrical injury remote from the site of surgery during dissection of the cystic duct, cystic artery, and the gallbladder. Neodymium:YAG laser applications with endoscopic fiber have been investigated. The possibilities to use it as a scalpel and as coagulator to release the gallbladder from all its peritoneal attachments during LC have been investigated. The controversy over optimal sources for thermal dissection of the gallbladder has been performed. The potential benefits of Nd:YAG laser in surgery -- precise cutting, limited collateral tissue damage, and improved capillary and arteriole hemostasis -- have been found.

A picosecond Nd:YLF laser system was used to remove sound and carious enamel by the mechanism of plasma-induced ablation. The plasma spark was optically imaged onto the entrance pupil of a spectrometer. The spectra were scanned between 400 - 700 nm with a typical resolution of 0.2 nm. Calcium in neutral and singly ionized states and the sodium doublet at 589 nm were observed. The second harmonic of the laser wavelength was generated in an external BBO crystal, thereby converting about 10 (mu) J of the pulse energy to radiation at 527 nm. The amplitude of the diffuse reflected second harmonic was used as a reference signal for normalization of the spectra. Several sound and artificial caries regions of different teeth were investigated. The spectra obtained from caries always showed a strong decrease in amplitude of all mineral lines, if compared to sound enamel. These results can be explained by the demineralization process of dental decay. Thus, caries infected teeth are easily distinguished from sound probes, enabling a computer controlled caries removal in the near future. The possible setup of such an automated system is discussed.

Engaging four different pulsed laser systems emitting in the near ultraviolet (wavelength 355 nm, wavelength 377 nm), in the near infrared (wavelength 755 nm), and in the mid infrared (wavelength 2.9 micrometers ) spectral region ablation thresholds of healthy dentin were determined. During experiments with an Alexandrite-laser (wavelengths 377 nm and 755 nm) a pulse duration of 200 ns was used, whereas at wavelength 355 nm pulse duration was fixed at 9 ns and at wavelength 2.9 micrometers pulse duration was set to 200 ns again. Using laser wavelengths which are well absorbed by the target (near UV, mid infrared) two well defined ablation thresholds could be detected. Due to low absorption of near infrared wavelengths in healthy dentin, high fluences must be engaged for ablation of healthy dentin. In this spectral region only a more or less statistically appearing ablation threshold can be observed. Caused by high fluences unpredictable plasma formation takes place. Even so, short pulse duration leads to high peak power, thus originating plasma.

The aim of the study was to describe the effects of different surrounding media -- water and air -- during application of a caries selective laser system on healthy dentin, the substance which should be preserved. Fluences used in this study were chosen with respect to the previously described ablation thresholds of healthy dentin. Fiber optics (0 400 micrometers , N.A. 0, 12) were used for transmission of the laser radiation. Luminescence emission was recorded time resolved in order to differentiate between fluorescence and plasma emission. Hot plasma seems to be rigorously reduced if the irradiation is performed under water. Scanning electron microscopical investigations were performed. Craters irradiated in air show cracks and signs of melting whereas crater walls after irradiation under water demonstrated rough surfaces and open dentinal tubules. Cracks did not occur if irradiation was performed in water. As long as water cooling is provided a Q-switched, frequency-doubled Alexandrite-laser providing fluences of 5 Jcm^-2 at the tooth surface does not produce hot plasma during the ablation of healthy dentin.

In recent years the dental use of the Er:YAG has found increasing interest. Most of the papers published so far concentrate on in vitro studies on cavity preparation, including the determination of ablation rates, measurements of temperature increase, microscopical analysis, and studies on the effect of water spray. The results are qualitatively in agreement and reveal a combination of high ablation efficiency and small side effects superior to other laser systems. Quantitative results, however, e.g., on ablation threshold or crater depths, sometimes differ. Some of these differences now can be explained and related to laser parameters or experimental conditions. Besides increasing the understanding on laser tissue interaction, the actual research enlarges the potential applications of the Er:YAG laser, such as for condition of enamel or dentin surfaces to enhance the bonding of composites. With the use of fibers, additional perspectives are given in periodontics and endodontics, e.g., for concrement removal or root canal preparation or sterilization.

This study investigates the checks of cavity margin after enamel and dentin ablation. The Er:YAG laser enamel and dentin ablation can be directly connected with the danger of cracks originating in the enamel near the cavity. This study evaluates the quality of the enamel edges after Er:YAG laser preparation. The enamel and dentin of buccal surfaces were ablated by the Er:YAG laser radiation. An Erbium:YAG laser system with the energy of 200 mJ was used to generate 200 microsecond(s) long pulses of mid-infrared 2.94 micrometers light in multimode configuration. The laser was operating in a free running mode, the repetition rate being 0.5 Hz with average laser power of 100 mW. Laser radiation was focused on the tooth tissue. Water cooling was used during the procedure in order to prevent tooth tissue destruction. The time of laser preparation was 5 minutes. A cavity of class V was prepared. The teeth were immersed into 0.5% basic fuchsin and then centrifuged at 6000 rev/min for 20 minutes. The microphotographs of the margins stained with 0.5% basic fuchsin were made and then the longitudinal section of the teeth were evaluated. The micrographs of the longitudinal section were checked and measured afterwards. The effect of the investigated laser irradiation on the origin of cracks was analyzed in the scanning electron microscope. Micrographs of each tooth before and after the laser ablation were compared. Micrographs of the intact teeth after extraction present the cracks of the enamel. They depend on the pressure exerted during extraction. The influence of the laser ablation proper is it bears no signs of new cracks. The conclusions of this study demonstrate the non-invasive nature of the Er:YAG laser ablation of the hard dental tissues.

Optoacoustic method is a very useful tool for studying laser induced processes in hard dental tissues. In principle, the method can also be used for on-line monitoring of laser drilling. Our study, however, shows that at high laser energies the optoacoustic energy is not proportional to the volume of the ablated hard dental tissue. In addition, the optoacoustic signal depends critically on the presence of water on the tooth surface. These observations must be taken into account when attempting to use the optoacoustic method for on-line monitoring of the laser drilling process.

The present work represents the results of research of mechanical strength formed by submillisecond pulses of Er-laser at the border of enamel-seal and dentine-seal in a cavity. Comparative research of an adhesion of three of the most widespread types of modern seal materials (cement, amalgam, polymer) to walls of the laser cavity are conducted. The comparison of `laser adhesion' with adhesion of these materials to the walls of the cavity has been made by the usual mechanical tools. The dependence of free adhesion energy from the geometry of the cavity and energy density of laser radiation is considered. This work informs the reader about the results of research removal efficiency of some modern seal materials. The influence of water-spray on the efficiency of seal materials laser treatment process is considered.

Side effects of root canal preparation with lasers such as the generation of acoustic shockwaves and heat transfer were investigated. Shockwaves may cause disintegration of root hard substance and too high temperatures may damage the periodontium. Three types of pulsed lasers with different ablation characteristics were chosen for the study. (1) Excimer laser 308 nm/120 ns. (2) Er:YSGG laser 2.78 micrometers /500 microsecond(s) . (3) Nd:YAG laser 1.06 micrometers /180 microsecond(s) . Delivery systems for all lasers were quartz fibers with 400 micrometers core diameter. Canals were pretreated up to size 40 to obtain a comparable root canal shape. The teeth were positioned with the root in chicken egg protein as a heatsink during the laser operation. Shockwaves were measured with a needle hydrophone and visualization of the ablation process was made with high speed flashlamp photography. Temperatures were measured with a fiberoptic device. Results show that lasers with medium pulse length, operating at wavelength highly absorbed by hard and soft tissue, caused minimum side effects. The ablation process with lasers emitting at a low absorbed wavelength rapidly shifts from an initial heat transfer at the beginning of preparation to a noncontrollable ablation and temperature rise when carbonization occurs in the canal. Very short pulsed lasers such as excimer lasers cause stronger shock waves than lasers with a pulse length in the microsecond(s) region. One can conclude that Er:YSGG lasers offer the best ratio between efficiency and side effects.

The high level of efficiency of hard tissue ablation with Er:YAG and Er:YSGG lasers is well known. Of these lasers it is possible only to transmit Er:YSGG laser radiation with OH reduced quartz fibers. Most of the fibers we use in this study were prepared as hemispherical fiber tips. Fifty single rooted teeth were divided into ten groups (n equals 5). After conventional opening of the pulp chamber, root canal preparation was performed in five groups under water only using the laser. In the other five groups preparation with K-files to size 35 was performed before treatment with laser radiation. All teeth were axially separated with direct access to the root canal and examined in SEM investigations. The groups were compared by measuring the areas with patent dentin tubules. Representative areas were examined by TEM. The temperature at the root surface was measured during laser irradiation with thermocouples positioned at several points. The in-vitro study of the effect of the high delivered energy (50 - 100 mJ per pulse) in the root canal showed a good ablation effect. Most of the dentin tubules were opened. The increase in temperature at the root surface was tolerable.

The purpose of this study was to establish an operative method in endodontics. The effect of a pulsed Nd:YAG laser on root canal dentin has been examined with a scanning electron microscope. Our first experimentation was to observe the impacts carried out perpendicularly to root canal surface with a 200 micrometers fiber optic in the presence of dye. Secondarily, the optical fiber was used as an endodontic instrument with black dye. The irradiation was performed after root canal preparation (15/100 file or 40/100 file) or directly into the canal. Adverse effects are observed. The results show that laser irradiation on root canal dentin surfaces induces a nonhomogeneous modified dentin layer, melted and resolidified dentin closed partially dentinal tubules. The removal of debris is not efficient enough. The laser treatment seems to be indicated only for endodontic and periapical spaces sterilization after conventional root canal preparation.

The indications of lasers in oral surgery are defined by the laser-tissue interaction types. These are mainly thermal effects depending especially on the absorption of laser light in varying biological tissues. In histological sections different laser effects are demonstrated on oral mucosa, bone and cartilage, which have a great influence on wound healing and subsequently on clinical indications of the different wavelengths. On the one hand the good coagulation effect of the Nd:YAG laser is wanted for hemostasis in soft tissue surgery. On the other hand, for the treatment of precancerous dysplasias or neoplasias an effective cutting with a coagulation effect like using the CO₂ laser is necessary. However, the excision of benign mucosal lesions as well as performing osteotomies or shaping of cartilage should be undertaken with the Er:YAG laser without greater coagulation and consequently without any delay of wound healing.

There have been 4,032 laser surgical operations for the last 7 years with available first generation lasers (CO₂, Nd:YAG, argon, combo (CO₂ + Nd:YAG). The most important experience, the advantages and disadvantages of application are shown by the evaluation of results and complications. In oral soft tissue surgery the most important indicational circles of the use of first generation lasers have been established. The clinical introduction of a second generation of surgical lasers (Ho:YAG, Er:YAG, excimer, etc.) brings new possibilities in not only hard tissue surgery, but it also widens the advantages of the use of surgical lasers in the surgery of oral soft tissues.

A constantly growing number of patients turning to toxicological centers with oral mucous chemical burns after acute poisoning made us take up the research of this problem. A high level of fatalities made it necessary to work out new more effective methods of treatment. The aim of this research was to study the peculiarities of the clinical picture of the oral mucous chemical burns and work out more affective methods of treatment and their tests.

Dealing with laser-tissue interaction, it is essential to investigate both the morphology of laser- induced effects and the ablation rate. The conventional methods, like HE-stained histological sections, have various disadvantages as regards artifacts or spatial crater morphology assessment. A confocal laserscanning microscope was applied to investigate the laser effects of a Ho:YAG laser on bovine bone. With this instrument it is possible to scan the object both along the xy-plane and the z-axis, thus `optically cut' the specimen without damaging them, yielding exact crater profiles, 3D images, and crater volume calculations. In the delicate region of the skull base area it is of fundamental importance to know exactly which kind of affect will take place regarding both ablation rate and morphology.

The danger of ignition of ventilation tubes during CO₂-laser surgery in the larynx region has been described several times in the literature. It was found that tubes of polymers, like PVC, have a low ignition threshold and, even worse, evaporate toxic gases when they were irradiated accidentally by the laser beam. So far, a pure metal tube was described as the safest endotracheal tube. A newly developed compound tube built up by a rubber tube surrounded by an ondulated silver foil and a layer of white Merocel^R-foam, was tested for its laser stability against various types of lasers, like CO₂ Holmium:YAG, Nd:YAG, Ar⁺ and excimer laser. The damage threshold of this tube at approximately 3 (DOT) 10⁶ W/cm² is significantly higher than the damage threshold of the metal tube and far above the power density used for coagulation or ablation of tissue. Beside these experimental results, this contribution describes the experiences which have been obtained with this tube in the clinical routine.

Based on a laser scanning endoscope via an imaging fiber bundle, a new approach for a tumor diagnostic system has been developed to assist physicians in the diagnosis before the actual PDT is carried out. Laser induced, spatially resolved fluorescence images of diseased tissue can be compared with images received by video endoscopy using a white light source. The set- up is required to produce a better contrast between infected and healthy tissue and might serve as a constructive diagnostic help for surgeons. The fundamental idea is to scan a low-power laser beam on an imaging fiber bundle and to achieve a spatially resolved projection on the tissue surface. A sufficiently high laser intensity from the diode laser is concentrated on each single spot of the tissue exciting fluorescence when a dye has previously been accumulated. Subsequently, video image of the tissue is recorded and stored. With an image processing unit, video and fluorescence images are overlaid producing a picture of the fluorescence intensity in the environment of the observed tissue.

The treatment of benign prostatic hyperplasia (BPH) using Nd:YAG laser light has become an accepted alternative to TURP. However, there is no consensus to the dosimetry using the various laser devices. In our study, we evaluate the optical and thermal characteristics of 7 commercially available side firing laser probes. For the thermal analysis, an optical method was used based on `Schlieren' techniques producing color images of the temperature distribution around the laser probe in water. Absolute temperatures were obtained after calibration measurements with thermocouples. Laser probes using metal mirrors for beam deflection heated up entirely. The local temperature rose up to 100 degrees centigrade, thus inducing vapor bubble formation that interfered with the emitted beam. Laser devices, using total internal reflection for deflection, showed far less heating primarily at the exit window, though Fresnel reflections and secondary beams indirectly heated up the (metal) housing of the tip. After clinical application, the absorption at the probe surface and hence temperature increased due to probe deterioration. Color Schlieren imaging is a powerful method for the thermal evaluation of laser devices. The thermal behavior of laser probes can be used as a guidance for the method of application and as an indication of the lifetime of the probes.

Interstitial laser photocoagulation (ILP), which is a new method of low power laser destruction of tumors, has been used to treat laparoscopically 50 consecutive patients with symptomatic uterine leiomyomas which were difficult or impossible to remove via laparoscopy. The KTP/YAG laser, with wavelengths of 532 and 1064 nm respectively, was employed. Holes 2 cm apart were drilled with a 600 micrometers quartz laser fiber employing the KTP component at 8 W and subsequent coagulation of the surrounding myoma tissue was accomplished during the withdrawal of the fiber over the course of 10 - 30 s but using the YAG component at 8 W until the whole myoma had been treated. Thirty seven became symptom free and have remained so. Six were lost to follow up. Of 10 complaining of subfertility 4, in whom uterine myomas were the only etiological factor, have become pregnant. Seven patients required further treatment: Two were retreated because their myomas were excessively large and did not completely disappear with the initial ILP, 2 received further ILP because of the development of new myomas and 3 were subjected to laparoscopically assisted vaginal hysterectomy at patients' request (2 because of the development of new myomas and 1 because of the development of further endometriosis). Finally, in 7 cases, residual tumor or scar tissue was biopsied and examined for the presence of oestrogen and progesterone receptors. None was discovered and in 2 subsequent pregnancy did not cause further growth of residual myoma tissue.

The Q-switched Nd:YAG laser is the most recent in a series of pulsed laser systems for plastic surgery. The 532 nm wavelength has been shown to be absorbed by a variety of chromophores. These include tattoo pigments, oxygenated hemoglobin and melanin-containing epidermal cells. A simple multi-line solid state laser module pumped by double-frequency Q- switched YAG laser is presented. This solid state multi-line module enables tuning of the wavelength in the yellow spectral range to 560 nm or to 580 nm for dermatology applications. Conversion efficiency in excess of 70% was achieved at 10 Hz pulse repetition frequency and output energy per pulse of approximately 200 mJ.