Excimer lasers with stimulated Raman scatteiing cell and Nd YAG laser with frequency doubler were employed to study the effect oflaser radiation both on intact and atheroscierotically damaged aortic wall. After inadiation,, samples of aorta were subjected to detailed morphologic study and sizes of craters, necrosis and tissue destruction zones were determined. Lipid content and spectra of the extracts affected by laser beam were under consideration as well. Key words: laser angioplasty, tissue ablation, photodissociation ofbiological molecules

Many aspects of the physical processes involved in a pulsed laser interacting with an occlusion in the intra-cranial vascular system, e.g., a blood clot, are included in the simulation codes LATIS and LATIS3D. Laser light propagation and thermo-mechanical effects on the occlusion can be calculated by these codes. The hydrodynamic response uses a realistic equation of state which includes melting and evaporation. Simple material strength and failure models now included in these codes are required to describe clot breakup. The goal is to ascertain the feasibility of laser thrombolysis, and to help optimize the laser parameters for such therapy. In this paper detailed numerical results for laser interaction with water is considered as an initial model for laser thrombolysis of soft blood clots which have high water content. Three regimes of water response to increasing laser energy are considered: (1) the linear stress pulse, (2) the nonlinear evaporation bubble, and (3) the nonlinear inertial bubble. It is shown that later in time the inertial bubble evolves into a slowly growing cavitation bubble. More physical processes will be added in the near future to better model realistic occlusion-vessel wall geometries.

We have implemented an interferometric method to probe the dynamics of transients induced in absorbing water solutions with nanosecond laser pulses delivered through an optical fiber. We examined two cases corresponding to strong absorption (deposition within 30 micrometers of the fiber tip) and moderate absorption (deposition within 500 micrometers of the fiber tip). With strong absorption the deposited energy leads to a strong stress transient followed by development of a thermally generated vapor bubble. Moderate absorption leads to a moderate stress transient and formation of a cavitation bubble cloud arising from tensile stresses that are produced in the absorbing fluid.

Laser thrombolysis uses microsecond laser pulses to remove thrombus-blocked arteries in the heart and the brain. Rapidly expanding and collapsing vapor bubbles are formed upon absorption of the laser energy by the thrombus. The goal of this study was to visualize the process of ablation and assess the effects of pulse repetition rate. The differences between contact versus non-contact of the laser delivery device with the thrombus were also investigated. Initial experiments were conducted with a gel-based clot model confined in 3 mm inner diameter silicone tubes. Subsequent experiments used 24 hour old porcine blood clots. Laser pulses of 50 mJ pulse energy were delivered via a quartz fiber contained in a flushing catheter. Pulse repetition rates of 1 Hz, 3 Hz, and 6 Hz were used. Wavelengths of 506 nm and 577 nm were used to ablate clot. Bubble action was captured by flash photography using a CCD camera and recorded on video. The amount of material removed was measured using a spectrophotometric technique. Bubble action was similar on clot and the clot model. No significant differences in bubble action or mass removal were observed at the three pulse repetition rates and the two wavelengths. Contact between the catheter and the clot did not result in a pistoning effect of the catheter at the pulse energy used.

To suppress restenosis after the percutaneous transluminal coronary angioplasty (PTCA), we experimentally investigated the optimum parameter setting on the combination of the balloon temperature and heating duration of our laser hot balloon catheter in rabbit model. The rabbit femoral arteries were treated by our laser hot balloon of 2.5 mm in diameter with various balloon temperatures and durations at the range from 60 to 90 deg., and from 15 to 30 seconds, respectively. The histological examination showed that high temperature (greater than 70 deg.) was necessary to suppress hyperplasia of the vessel in chronic phase. The angiography of pre- and post-treatment and of 2 months after the treatment showed that high temperature with short heating duration (15-30 s) was the best setting for chronic patency of the treated vessels. The laser hot balloon angioplasty with the above mentioned parameter setting might realize significant improvement on chronic patency after PTCA.

The perfusion of hibernating myocardium by oxygenated blood coming from transmyocardial channels to the left ventricular cavity has been considered as an alternative for patients unsuitable for bypass surgery. Channels created by lasers are believed to assure patency in the long term. At this moment, several laser systems have become available to create these channels with minimal thermal effects. The systems should be ECG triggered and the exposure should preferably be within the relaxation phase of the cardiac cycle (0.1 - 0.2 s). The lasers examined were an ultrapulsed carbon-dioxide laser with long focus delivery optics, a Holmium laser coupled to a 1 mm spot fiber and an Excimer laser coupled to a 950 fiber. Pieces of bovine myocardium (10 - 20 mm thickness) were exposed while the displacement during penetration was monitored. Pulse trains were delivered within 0.05 - 0.2 s with a repetition rate of 1 - 3 Hz. The fiber delivery devices were loaded with weights between 10 - 80 gram to study the influence of exerted force. For the carbon dioxide laser the creation of the channels was also recorded on high speed video and with a thermal imaging method in a model tissue to visualize explosive and thermal effects. With the Holmium laser immediate penetration of the fiber was obtained while with the Excimer laser the penetration of the fiber started only after several pulses within the train depending on force and energy. The carbon-dioxide laser beam created a channel instantly, up to 30 mm/pulse depending on spotsize and energy. We conclude that all three lasers are capable of creating a channel of 20 mm long on the heart within a few cardiac cycles. Histologic analysis showed that in contrast to the smooth channels of the carbon-dioxide laser, the Holmium and Excimer laser create irregular channels with ruptures to the sides with some thermal damage. It is not clear which kind of channels will have the best potentials to provide maximum perfusion of the myocardium.

The clinical procedure known as transmyocardial revascularization has recently seen its renaissance. Despite the promising preliminary clinical results, the associated mechanisms are subject to much discussion. This study is an attempt to unravel the basics of the interaction between 800 W carbon-dioxide laser radiation and biological tissue. Time-resolved flash photography was used to visualize the laser-induced channel formation in water and tissue phantoms. In addition laser-induced pressures were measured. Channel depth was shown to increase logarithmically with time (i.e. with pulse duration) in water, tissue phantoms and porcine myocardium. Pressure measurements show numerous small transients during the laser pulse which corresponded to the local and partial collapse of the formed channel already during the pulse. It was shown that in tissue, 20 mm of myocardium is perforated in 25 ms. Increasing the pulse duration only has a small effect on the maximum transversible thickness while histology shows that thermal damage around the crater increased with increasing pulse duration.

Texaphyrins are water soluble porphyrinoids which selectively localize in atheromatous plaque. The paramagnetic gadolinium texaphyrin is an excellent contrast agent which enables plaque detection by MRI. The diamagnetic lutetium texaphyrin, using fluorescence methods, was also shown to label atheromatous plaque. The chemical environment of bound lutetium texaphyrin within plaque was determined by fluorescence emission spectra to be predominantly lipophilic. The texaphyrin was found to bind to the lower density lipoproteins in the atherosclerotic-induced animals. Lutetium texaphyrin is an excellent candidate for photoatherolytic therapy.

We evaluated benzoporphyrin derivative verteporfin (BPD) photodynamic therapy (PDT) and dark effect on the intima (I) and media (M) hyperplasia (H) response of swine iliac arteries to balloon dilatation (Bdil) injury. Four month old Yucatan swine received bdil at 8 ATM pressure to all four iliac arteries. Pigs were randomly assigned to groups. PDT was performed with intraluminal 690 nm, cw laser (200 milliwatts and 30 joules per cm² tissue). Six weeks later, sites were pressure fixed, and excised at autopsy. Sections from each site were evaluated for I and M thickness, injury score (1 equals normal, 4 equals worst), and smooth muscle cell (SMC) intensity and distribution. Groups were compared using the Mann-Whitney U test. Means for each parameter were determined, and group means used for statistical analysis. Conclusions: (1) Bdil produced IH and MH. (2) PDT enhanced IH. (3) 2 mg/kg BPD reduced MH and produced a favorable trend in IH and injury. (4) No differences in SMC intensity and distribution were present.

Psoralen activated by UVA light (PUVA) was investigated as a means of inhibiting smooth muscle cell proliferation resulting from balloon injury. Twenty kilogram domestic swine were anesthetized and underwent balloon angioplasty to create a 133% overstretch injury. Assignments of treatment and control were randomized between the left anterior descending (LAD) and circumflex (LCX) coronaries arteries. The animals were given with 5 mg/kg of 8- methoxypsoralen eternally. Treatment vessels received 600 mJ/cm² of 364 nm light during balloon inflation to activate the psoralen. Control vessels received drug and balloon injury only. Serum was obtained during the light delivery to assess psoralen levels. At 30 days, animals were sacrificed and the coronary arteries perfusion fixed. Five sections per vessel were analyzed morphometrically to determine percent intimal area and extent of injury. The restenosis injury index was 0.21 plus or minus .02 in treatment vessels and 0.14 plus or minus .01 in the controls with a p-value less than .02. In this large animal model of balloon angioplasty injury, psoralen activated by ultraviolet light increased intimal hyperplasia.

We have been studying laser-induced fluorescence as a technique for identification of selected changes in the chemical composition of atherosclerotic plaque. Formulae for quantification of chemical changes have been developed based upon analysis of fluorescence emission spectra using multiple regression analysis and the principal of least squares. The intima of human aortic necropsy specimens was injected with chemical compounds present in atherosclerotic plaque. Spectra recorded after injection of selected chemical components found in plaque (collagen I, III, IV, elastin and cholesterol) at varying concentrations (0.01 - 1.0 mg) were compared with saline injection. A single fiber system was used for both fluorescence excitation (XeCl excimer laser, 308 nm, 1.5 - 2.0 mJ/ pulse, 5 Hz) and fluorescence emission detection. Average spectra for each chemical have been developed and the wavelengths of peak emission intensity identified. Curve fitting analysis as well as multiple regression analysis were used to develop formulae for assessment of chemical content. Distinctive identifying average curves were established for each chemical. Excellent correlations were identified for collagen I, III, and IV, elastin, and cholesterol (R² equals 0.92 6- 0.997). Conclusions: (1) Fluorescence spectra of human aortas were significantly altered by collagen I, collagen III, elastin and cholesterol. (2) Fluorescence spectroscopic analysis may allow quantitative assessment of atherosclerotic plaque chemical content in situ.

Photoacoustic drug delivery is a technique for delivering drugs to localized areas in the body. In cardiovascular applications, it uses a laser pulse to generate a cavitation bubble in a blood vessel due to the absorption of laser energy by targets (e.g., blood clots) or surrounding liquids (e.g., blood or injected saline). The hydrodynamic pressure arising from the expansion and collapse of the cavitation bubble can force the drug into the clots and tissue wall tissue. Time-resolved particle image velocimetry was used to investigate the flow of liquids during the expansion and collapse of cavitation bubbles near a soft boundary. A gelatin-based thrombus model was used to simulate the blood clot present during laser thrombolysis. An argon laser chopped by an acousto-optic modulator was used for illumination and photography was achieved using a CCD camera. The implications of this phenomenon on practical photoacoustic drug delivery implementation are discussed.

The first successful report using the neodymium:yttrium-aluminum-garnet (Nd:YAG) Laser to control hypermenorrhea was reported in 1981. Variations on the treatment technique have been attempted to improve the amenorrhea rate. Reports using the Nd:YAG laser with the blanching or non-touch technique seem to result in a better outcome and higher rate of total amenorrhea than using the dragging technique. Due to the report of improved rates of amenorrhea when using the blanching technique and the Nd:YAG laser, a fiber was developed to direct the laser energy at right angles to the axis of the fiber, therefore allowing a total treatment of the entire uterus in a perpendicular fashion. The theoretic benefit of this would be a more complete and predictable destruction of the endometrial lining, avoiding fluid overload by coagulating and sealing of the vessels and lymphatic. After a follow-up of 12 to 36 months, 56 of the 60 patients (93%) who underwent complete endometrial ablation with the SideFire^TM technique had excellent results. Total absolute amenorrhea resulted in 50 patients (83%). Contrary to earlier reports, using the rollerball electrode, this procedure technique resulted in no decrease in results in younger patients. In conclusion, this seems to be a reasonable alternative which offers improved results when compared to previously available methods using electrosurgery or the Nd:YAG laser without the use of the SideFire^TM device.

A mammographic stereotactic core biopsy instrument can be adapted for laser hyperthermic ablation of breast cancer. The object of this study is to characterize laser endohyperthermia ex-vivo and in-vivo to develop a reliable approach leading to human trials. Light of a Nd:YAG laser passed through a fiberoptic cable to a diffusing quartz tip upon entering surrounding tissues can bring about very high temperatures. This approach concentrating on the heat distribution to fat and fibrofatty tissue, first analyzed a physical model into which both the quartz tip and thermocouple needles were placed. Temperature recordings in volume through a time course demonstrated a progressive thermal increase around the tip. Additional light distribution studies in several media demonstrated the tip's output. The technique transferred to ex-vivo human breast and porcine fibrofatty tissue showed similar findings leading to an in-vivo analysis of subcutaneous porcine fibrofatty tissue. A step-down energy program beginning at 20 watts and decreasing to 15 watts, 10 watts, and to 7 watts, at 30 second intervals was held at the latter power for the remainder of 6 minutes. Three such cycles appear to be the optimal treatment program to develop temperatures between 60 degrees Celsius and 80 degrees Celsius (approximately equals 9700 joules). In-vivo experiments conducted on 5 occasions revealed no skin change. At necropsy the treated tissues demonstrated a circular sharply defined 3 cm volume of necrosis with no change in adjacent tissue. Time-temperature correlations between ex-vivo and in-vivo tissues showed great similarity. Nd:YAG laser energy distributed to a quartz tip through a fiberoptic cable is capable of uniform, complete tissue destruction to a 1 1/2 cm radius with no change beyond that field. This technique with further refinement will be appropriate to the treatment of small breast cancers that have been stereotactically biopsied.

It was in 1983 when we started to apply YAG laser to do experiments on animal and fresh internal organs off the body to confirm its effectiveness. Then we started to use it in clinical practice. Up to October 1995, in the twelve years, we treated 1075 cases, 2574 person times. Seven-hundred-seventy-nine cases of various esophagostenosis. Four-hundred-fifty-six of them were malignant stenosis, 295 anastomostenosis, 15 stenosis after radiotherapeutics, 7 corrosive anastomostenosis, 6 inflammatory anastomostenosis, plus we cured 5 cardia losses of relax, and 241 polyps in the alimentary canal. Among the 2154 polyps cured, 6 were that of esophagus, 6 that of cardia, 25 that of stomach, 10 that of duodenum, 194 that of large intestine. In addition, we treated 15 alimentary canal bleeding and 35 malignant colon and tectum cancers. Our experience in laser operating on the coelom has become richer and richer. The methods we used are being widened. The range of our laser application is being enlarged. We have gained our own experience in preventing complications and keeping the endoscopy from being damaged. The cure rate of the non-malignant had raised up to 98.7%. Cure rate of the malignant had raised up to 91%. The alimentary canal polyps can be cured perfectly. It is hard to tell whether YAG laser or high frequency electroresection has the advantage over the other. Besides, this paper is going to put forward several questions to discuss.

The ability of the 1.06 Nd:YAG laser and the 805 nm diode laser to transurethrally and interstitially ablate prostate has been well documented by this lab and others. With the introduction of lower cost and physically smaller diode laser systems, and the potential for transcatheter and laparoscopic delivery of laser energy through diffuser fibers, laser ablation of tumors of the liver is feasible and could prove to be a cost effective treatment for this and other soft tissue applications. This study examined the acute pathologic effect of 805 nm diode laser radiation delivered via diffuser fibers on normal porcine liver. After preliminary dosimetry parameters were established in cadaveric canine liver, laparotomies were performed to expose the liver on domestic swine. Histopathological samples taken 3 hours after lasing revealed 4 distinct zones of tissue change. The outermost zone showed a 2 mm band of hemorrhage with disruption of hepatic cords adjacent to a zone of disruption of hepatic cords without hemorrhage. Working toward the fiber the next zone was intact with no visible changes. The innermost zone that was in contact with the fiber exhibited a very thin area of necrosis and char. The diameter of the outermost zone seemed to increase with increased wattage.

A computer search and review of surgery logs, laser logs and case records was conducted to determine the number of horses that were presented and treated for upper respiratory abnormalities. This report concentrated on equine cases that had malignant and nonmalignant disease and whether the use of a laser affected the outcome. The report concluded that neoplastic or malignant cases were presented late in the course of the disease to be successfully treated but their demographics were helpful in distinguishing them from nonmalignant cases that had similar endoscopic findings and clinical signs. Having laser capability for treatment of nonmalignant diseases improved the success rate achieved with some diseases and influenced the selection of treatment, conventional surgery versus standing transendoscopic laser irradiation of the lesions.

This study evaluates tissue coagulation and ablation effects in the prostate gland of the canine model when a diode laser (805 nm-Diomed 25^R-Surgimedics/ESP, The Woodlands, Texas) and an angled fiber configuration (1000 (mu) 20 degree bent-Surgimedics/ESP, The Woodlands, Texas were used at specified power densities. Comparisons of therapeutic modalities included animals treated with noncontact coagulation alone, contact ablation alone, and noncontact coagulation and contact ablation in combination. The principal objective was to validate the effectiveness of coagulating prostatic tissue in a noncontact mode at a lower power, followed immediately with contact ablation of the prostatic urethra at a higher energy level. Applying laser energy with the fiber tip in noncontact mode created a deeper zone of coagulative necrosis with an increased level of cellular destruction (lower power 15 - 20 watts delivered to four quadrants for 200 seconds/quadrant) than did higher power modalities alone. An increased luminal diameter, which prevented immediate postoperative urodynamic abnormalities (stranguria, dysuria, and severe hematuria) in this model, was produced by ablating the prostatic urethra with the fiber tip in a contact mode (higher power: 23 - 60 watts for an additional 120 - 200 seconds for the ablative process) immediately following the coagulative procedure. Additionally, semen evaluations performed before and after laser surgery (8 weeks after coagulation/ablation) were performed on one dog and found to be normal with respect to number of spermatozoa and motility.

To evaluate the therapeutic applications of laser, 3 dogs and 26 horses were selected for the treatment of skin lesions, and 1 dog and 16 horses for analgesic treatment. The equipment used consisted of either red or infrared light laser apparatuses modified in order to increase the manageability and the power of the instrument. It was observed that He-Ne laser allowed a more rapid restitutio ad integrum with a lesser amount of J/cm² and so apparatuses were advantageous for the treatment of fistolous tracts complicated by abscess formation. In fact, by using sterilizable optical fibers, it was possible to reach the deeper parts of the tract. When considering the rapidity of the healing process of different body areas, the withers seems to necessitate the longest period of time to recover. Infrared laser is best used for pain relief and satisfactory results were observed without resting the animals. Significant and beneficial effects from laser therapy are obtained after 7 - 10 days of therapy.

This is a progress report on our ongoing fluorescence spectroscopy studies of diseased skin. A PC plug-in spectrometer has been used clinically to collect autofluorescence and diffuse reflectance spectral data from various skin lesions including skin cancer. To date, over 100 patients with a total of over 180 diseased skin sites have been measured and our database on the spectroscopic properties of diseased skin has been enlarged accordingly. Analysis of these preliminary data confirmed our preliminary observations that certain types of skin lesions possess consistent characteristic autofluorescence and diffuse reflectance properties. A new method of data analysis, spectra ratioing, provides new features to aid the optical diagnosis of skin lesions.

The movement of polarized light through the superficial layers of the skin was visualized using a video camera with a polarizing filter. This study constitutes a description of the impulse response to a point source of incident collimated linearly polarized light. Polarization images reject unwanted diffusely backscattered light from deeper in the tissue and the specular reflectance from the air/tissue interface. Two experiments were conducted: (1) Video polarization reflectometry used a polarized HeNe laser (633 nm) pointing perpendicularly down onto a phantom medium (0.900-micrometer dia. polystyrene spheres in water). The video camera was oriented 10 degrees off the vertical axis and viewed the irradiation site where the laser beam met the phantom. Video images were acquired through a polarizing filter that was either parallel or perpendicular with the reference plane defined by the source, camera, and irradiation site on the phantom medium's surface. The source polarization was parallel to the reference plane. The two images (parallel and perpendicular) were used to calculate a polarization image which indicated the attenuation of polarization as a function of distance between the source and point of photon escape from the phantom. Results indicated a strong polarization pattern within approximately 0.35 cm (approximately 2.2 mfp') from source. [mfp' equals 1/(micron_a plus micron_s')]. (2) Optical fiber reflectometry using a polarized diode laser (792 nm) coupled to a polarization-maintaining single-mode fiber, and a multi-mode fiber collector to collect regardless of polarization. Reflectance as a function of fiber separation was measured for the source fiber oriented parallel and perpendicular with the reference plane. Results indicated that the strongest polarization propagated within approximately 0.43 cm (2.2 mfp') from source. The polarization survived approximately 2.2 mfp', which for skin at 630 - 800 nm (mfp' approximately equals 0.066 cm) corresponds to 1.5 mm (or 6.4 ps of travel at the speed of light). Using 6.4 ps as a maximum time of survival, classical paths of photon transport (Feynman paths) were calculated to illustrate the expected depth of interrogation by polarized imaging. The expected mean depth of photons is about 0.36 mm at these longer wavelengths. Shorter wavelengths would result in a shorter mfp' and therefore more superficial imaging of the skin. Polarization images offer an inexpensive approach toward 2-D acquisition of time- gated images based on the early light escaping the tissue. Polarization imaging is an opportunity for a new form of optical image especially useful for dermatology.

The beam characteristics and spot geometry of a short pulsed (15 - 1000 microsecond) carbon- dioxide, multimode laser were measured. At a distance of 1.0 - 3.0 cm from the handpiece the laser produced a 5 mm² square spot with an even fluence across the entire spot area (Mesa Mode). Human eyelid skin was irradiated both in vivo and ex-vivo immediately after excision with 1, 2, 3, or 4 pulses, a pulse duration of 62.5 microseconds, and at a fluence of 6 J/cm². H&E stained sections showed an even removal of tissue across the impact site. The depth of thermal damage was measured as 38 micrometer plus or minus 22.7 with a range of 0 - 100 micrometer.

Treatment of leg telangiectasia with a pulsed laser is investigated theoretically. The Monte Carlo method is used to calculate light propagation and absorption in the epidermis, dermis and the ectatic blood vessel. Calculations are made for different diameters and depths of the vessel in the dermis. In addition, the scattering and the absorption coefficients of the dermis are varied. On the basis of the considered damage model it is found that for vessels with diameters between 0.3 mm and 0.5 mm wavelengths about 600 nm are optimal to achieve selective photothermolysis.

The exposure of human skin to near-infrared radiation is numerically simulated using coupled laser, thermal transport and mass transport numerical models. The computer model LATIS is applied in both one-dimensional and two-dimensional geometries. Zones within the skin model are comprised of a topical solder, epidermis, dermis, and fatty tissue. Each skin zone is assigned initial optical, thermal and water density properties consistent with values listed in the literature. The optical properties of each zone (i.e. scattering, absorption and anisotropy coefficients) are modeled as a kinetic function of the temperature. Finally, the water content in each zone is computed from water diffusion where water losses are accounted for by evaporative losses at the air-solder interface. The simulation results show that the inclusion of water transport and evaporative losses in the model are necessary to match experimental observations. Dynamic temperature and damage distributions are presented for the skin simulations.

It is known that aqueous solutions of indocyanine green (ICG) are not stable -- the dye degrades over time, especially in the presence of light. Addition of protein or other partially- hydrophobic compounds (e.g., surfactants) to the solution act to stabilize the ICG, presumably by binding the dye and preventing occurrence of the degradation reaction. Solutions of ICG in other, less polar solvents, such as methanol, are also stable under normal conditions of handling and storage. We have discovered, however, that both protein-stabilized and methanol solutions of ICG will degrade when exposed to high-intensity monochromatic illumination. We irradiated 10 (mu) M aqueous solutions of ICG, containing human serum albumin (HSA) as a stabilizer, with light from an alexandrite laser (wavelength: 750 nm; pulse energy: 100 mJ; pulse repetition rate: 20 Hz). While the HSA did act to slow the degradation process somewhat, even concentrations as high as 3% were not sufficient to prevent measurable degradation after as little as 30 seconds of irradiation. We obtained similar results with methanol solutions. Our results suggest that it is important to consider the type of illumination used during tissue welding in order to control ICG degradation. We present our measurements of the intensity dependence of ICG degradation in the presence of stabilizers. In addition, we discuss nonlinear effects (saturable absorption and multi-photon absorption and fluorescence) exhibited by ICG during high-intensity pulses irradiation.

This study focused on meniscal cartilage repair by using the laser-activated photoactive 1,8- naphthalimide dye N,N'-bis-{6-[2-(2-(2- aminoethoxy)ethoxy)ethoxyethyl]amino-1H-benz (de)isoquinolin-1,3(2H)-dion-2- yl}-1,11-diamino-3,6,9-trioxaundecane. Harvested cadaveric human menisci were debrided and carved into strips 1 mm thick, 10 mm long, and 3 mm wide. Each strip was divided into two flaps, the surface painted with photoactive dye, the painted surfaces overlapped, the sample wrapped in Saran film, and the composite sandwiched between two glass slides at a pressure of approximately 3 kg/cm². The sample then was transilluminated by argon ion laser light of 457.9-nm wavelength at a power density of 200 mW/cm² with exposure times up to 5 h (3902 J/cm² energy density). Essentially, the same procedures were performed for human femoral articular cartilage samples. Control experiments were conducted with laser irradiation alone and with dye alone. All the specimens were stored in isotonic saline solution for 2 h after irradiation to ensure hydration. The bond shear-strength was then tested and samples prepared for optical and electron transmission microscopy. Shear strength values of up to 1.8 kg/cm² for meniscal tissues and 1.2 kg/cm² for articular cartilaginous tissues were obtained for exposures of 3902 J/cm². Shear strength values of approximately 0.9 kg/cm² and 0.4 kg/cm², respectively, for meniscus and cartilage were obtained with 459 J/cm² exposure. Dye- and light-only controls exhibited 0 kg/cm² shear strength values. Microscopy revealed close contact at the bonded surface in the laser-activated, dye-treated-specimens. This study shows that the laser-activated photoactive dyes have the capability of athermally bonding the meniscal and articular cartilage surfaces.

A study of laser tissue welding mediated with an indocyanine green dye-enhanced protein solder was performed. Freshly obtained sections of porcine artery were used for the experiments. Sample arterial wall thickness ranged from two to three millimeters. Incisions approximately four millimeters in length were treated using an 805 nanometer continuous- wave diode laser coupled to a one millimeter diameter fiber. Controlled parameters included the power delivered by the laser, the duration of the welding process, and the concentration of dye in the solder. A two-color infrared detection system was constructed to monitor the surface temperatures achieved at the weld site. Burst pressure measurements were made to quantify the strengths of the welds immediately following completion of the welding procedure.

Temperature feedback control (TFC) of cw argon ion and cw Ho:YAG laser-assisted anastomoses of severed rat intestines increased wound stability during the first 72 hours after surgery when compared to laser anastomosies formed without temperature control. Comparisons of in vitro bursting pressures measurements and qualitative and quantitative histopathology observations of wound healing were performed to discover the factors associated with this increased stability. Close apposition of the wound edges and decreased abscess formation were found to be associated with good wound healing. No differences in bursting pressure measurements and wound healing patterns were associated with the laser (wavelength) used or between the TFC and non-TFC groups.

Since 1991, we have undertaken extensive laboratory and clinical studies of the Neodymium:YAG (Nd:YAG) laser for surgical treatment of bladder outlet obstruction due to prostatic enlargement or benign prostatic hyperplasia (BPH). Side-firing optical fibers which emit a divergent, relatively low energy density Nd:YAG laser beam produce coagulation necrosis of obstructing periurethral prostate tissue, followed by gradual dissolution and slough in the urinary stream. Laser-tissue interactions and Nd:YAG laser dosimetry for prostatectomy have been studied in canine and human prostate model systems, enhancing clinical application. Ongoing studies examine comparative Nd:YAG laser dosimetry for various beam configurations produced by available side-firing optical fibers and continue to refine operative technique. We have documented clinical outcomes of Nd:YAG laser prostatectomy in 230 consecutive patients treated with the Urolase^TM side-firing optical fiber. Nd:YAG laser coagulation the prostate produces a remarkably low acute morbidity profile, with no significant bleeding or fluid absorption. No postoperative incontinence has been produced. Serial assessments of voiding outcomes over more than 3 years of followup show objective and symptomatic improvement following Nd:YAG laser prostatectomy which is comparable to older but more morbid electrosurgical approaches. Nd:YAG laser prostatectomy is a safe, efficacious, durable and cost-effective treatment for BPH.

Purpose: We evaluated the ability of KTP laser to evaporate prostatic tissue in vivo and compared the results with historical Nd:YAG treated controls. Methods: Five dogs underwent anterograde transurethral evaporation of the prostate (TUEP) with KTP laser at 38 watts and were sacrificed 48 hours after surgery. Results: All procedures were hemostatic and without complications. Laser evaporation produced cavities within the prostate ranging from 2.5 to 3.2 cm in diameter (average equals 2.9 cm) that were free of necrotic tissue. Conclusions: Preliminary findings in this initial canine study of laser evaporation of the prostate, show that KTP laser produces large spherical cavities within the prostate in a hemostatic fashion. These cavities are free of necrotic tissue. In addition, these cavities are comparable in size to those that have been observed 4 to 8 weeks following Nd:YAG VLAP and are significantly larger than the acute cavities produced by Nd:YAG TUEP.

Holmium:YAG (Ho:YAG) laser vaporization and resection of the prostate offers advantages in immediate tissue removal compared to the Neodymium:YAG (Nd:YAG) laser. Ongoing development of appropriate operative techniques and Ho:YAG laser delivery systems suitable for endoscopic prostate surgery, including side-firing optical delivery fibers, have facilitated this approach. We performed Ho:YAG laser prostatectomy in 20 human subjects, including 2 men treated immediately prior to radical prostatectomy to assess Ho:YAG laser effects in the prostate. A total of 18 men were treated in an initial clinical trial of Ho:YAG prostatectomy. Estimated excess hyperplastic prostate tissue averaged 24 g (range 5 - 50 g). A mean of 129 kj Ho:YAG laser energy was delivered, combined with a mean of 11 kj Nd:YAG energy to provide supplemental coagulation for hemostasis. We have observed no significant perioperative or late complications. No significant intraoperative changes in hematocrit or serum electrolytes were documented. In addition to providing acute removal of obstructing prostate tissue, Ho:YAG laser resection allowed tissue specimen to be obtained for histologic examination. A total of 16 of 18 patients (90%) underwent successful removal of their urinary catheter and voiding trial within 24 hours following surgery. Immediate improvement in voiding, comparable to classic transurethral electrocautery resection of the prostate (TURP), was reported by all patients. Ho:YAG laser resection of the prostate appears to be a viable surgical technique associated with minimal morbidity and immediate improvement in voiding.

Alternatives to the side-firing laser method include controlled destruction of prostatic adenoma by an atraumatic saline cooled laser fiber introduced endoscopically into the prostate under visual and transrectal ultrasound (TRUS) control. Laser light produces intense heating and interstitial laser coagulation (ILC) occurs with characteristic TRUS changes which are used to control the volume of tissue destruction. The prostatic urethral lining is preserved which may reduce laser side effects). Thirty-six men with symptomatic BPH were treated by ILC between April 1994 and September 1995. All were discharged home on the first post-operative day and reviewed periodically to 12 months post-treatment with measurement of IPSS, flow rate (FR), residual volume, complications, potency and TRUS. Seventeen men (47%) voided immediately, 15 (42%) performed intermittent self-catheterization (ISC) for 3.5 days (2 - 5). Four men (11%) required catheterization for 1/52. Thirty-five men tolerated the treatment well, requiring only mild oral analgesia. One man developed dysuria and required early transurethral resection revealing a large volume of coagulative necrosis. Improvement in symptoms and flow rate developed from 1 - 30 days later. There were no significant complications. Hyperechoic and cystic zones developed at the ILC site which persisted to 12 months. This clinical study indicates the feasibility and safety of intense heating by ILC with visible and ultrasound control to coagulate the adenoma while preserving the urethra. Changes are easily seen on TRUS, symptomatic improvement is good and there have been minimal urethral symptoms or complications.

Benign prostatic hyperplasia (BPH) can significantly impair quality of life in older men. Most men over 60 experience some symptoms due to BPH and it is thought that essentially all men would eventually be affected by it if they lived long enough. At present, transurethral resection of the prostate (TURP), a surgical treatment for BPH, is one of the more common procedures performed in the developed world, particularly in the United States. A number of other treatments are also often used, including open prostatectomy, side-firing lasers, and drug therapy. With the population in the developed world rapidly aging, BPH is expected to affect an even larger group of men in the future. Current methods of therapy carry significant disadvantages. Open prostatectomy carries a fairly high risk of impotence and incontinence, as well as sometimes significant risk of death depending on the patient's age and medical conditions. TURP also carries similar risks, albeit reduced, including the risk of substantial blood loss and a small but meaningful risk of death. Side-firing lasers are thought to have a reduced risk of death compared to TURP due to significantly reduced bleeding; however, patients often experience an extended period of pain during voiding due to prolonged tissue sloughing. Drug treatment, although useful for some patients, does not strongly improve symptoms in the majority of patients. Even with the current range of treatments, many patients with symptomatic BPH elect to avoid any current treatment due to risks and side effects. As a possible solution to this problem, previous writers have suggested the possibility of treating BPH through interstitial thermotherapy. In this treatment, prostatic tissue is heated from within the prostate to the point of irreversible necrosis. Healing processes then reduce the volume of the affected tissue, even in the absence of sloughing. This study covers initial human use of such a device, using an 810 nm wavelength diode laser not previously used for such therapy.

Prior to a possible clinical application of photodynamic therapy (PDT) for prostatic diseases such as benign prostatic hyperplasia and prostate cancer, optical properties of the prostate gland need to be studied. The specific objectives of this study were (1) to determine the light penetration depth, (2) to document the photosensitizer levels in the prostate, and (3) to document the lesion size after PDT. Sixteen dogs were injected with Photofrin II (1, 3 and 5 mg/kg) 24 hrs prior to laser application. After laparotomy and exposure of prostate, monochromatic light (630 nm, via an argon pumped dye laser) was applied through an isotropic fiber at 100 mw for a total dose of 400 joules. Continuous light fluence and temperature were documented. Prostates were harvested at 1 week and examined histologically for the lesion size. Four sham dogs were treated without Photofrin II. At Photofrin doses of 1, 3 and 5 mg/kg the mean prostatic Photofrin levels were 1.78 plus or minus 0.33, 1.47 plus or minus 0.08 and 1.95 plus or minus 0.44 (mu) gm/ml. The mean light penetration depths were 2.08, 1.37 and 1.64 mm respectively. Photofrin dose escalation (1, 3 and 5 mg/kg) increased the lesion size to radius of 4.1 plus or minus 0.9 mm, 4.4 plus or minus 0.8 mm and 6.3 plus or minus 0.9 mm. There were no lesions seen in sham dogs. These results demonstrate that light penetration in prostate is consistent and therapeutic levels of photosensitizer are achieved in prostatic tissue. Moreover, increasing size of the lesions were documented with dose escalation.

Photodynamic therapy (PDT) and interstitial thermotherapy are well known treatment modalities in urology. The approach of this study is to combine both to achieve a selective treatment procedure for benign prostatic hyperplasia (BPH) and prostate carcinoma. Measurements of thy in-vivo pharmacokinetics of 5-ALA induced porphyrins by means of fiber assisted ratiofluorometry showed a maximum fluorescence intensity at time intervals of 3 - 4 h post administration. Fluorescence microscopy at that time showed bright fluorescence in epithelial cells while in the stroma fluorescence could not be observed. Interstitial PDT using a 635-nm dye laser with an irradiation of 50 J/cm² resulted in a nonthermic hemorrhagic lesion. The lesion size did not change significantly when an irradiation of 100 J/cm² was used. The usefulness of PDT for treating BPH as well as prostate carcinoma has to be proven in further studies.

We determined the optical properties of the human prostate, in vivo, over multiple wavelengths for 6 men, in an outpatient setting. Analysis of these data reveal reliable determination of the optical properties in the 650 - 800 nm range, however, values in the shorter wavelengths (400 - 625 nm) were not interpretable due to a low signal to noise ratio. To the best of our knowledge, this is the first report of the optical properties i.e. reduced scattering coefficient [(mu) _s^' (cm^-1)], absorption coefficient [(mu) _a (cm^-1)], and penetration depth [(delta) (cm)], for the in vivo human prostate over multiple wavelengths in the white light spectrum.

Laser induced interstitial thermotherapy is a new minimally invasive procedure for the treatment of benign prostatic hyperplasia. Since high power laser diode lasers became available for clinical use a comparison of tissue effects of different wavelengths under controlled conditions is needed. In this study three different laser wavelengths were compared at output powers of 4 W and 8 W with 10 min and 90 s irradiation time, respectively, resulting in applied energies of 2700 J and 720 J. The results in both groups showed that the use of a wavelength close to the relative water absorption peak at 980 nm gave tendentiously but not significantly larger coagulated areas. Furthermore it became obvious that the use of 8 W for 90 sec results in higher maximum temperatures and larger lesions compared to the application of 4 W over a period of 10 min, although the energy used in the latter group was 4 fold higher.

An excellent knowledge of histopathological risk factors of superficial bladder transitional cell carcinoma is mandatory to establish the prognosis of the disease. Presence or absence of carcinoma in situ (CIS) in superficial bladder cancer is one of the most powerful risk indicators. This study examines the usefulness of fluorescence photodetection of neoplastic urothelial foci in bladder cancer following intravesical instillation of delta-aminolevulinic acid (5-ALA). Following bladder instillation of an aqueous solution of 5-ALA in 43 cases, a Krypton ion laser and a Xenon arc-lamp were successively used as excitation source of the PPIX fluorescence. Tissular samples were respectively taken during bladder wall photodetection, either by the means of a video camera, or under direct endoscopic observation. A good correlation was observed between the fluorescence findings and the histopathological diagnosis. On a total of 298 biopsies, 49/110 carcinomatous lesions were detected by the fluorescence, whose more than 36% were CIS. PPIX induced fluorescence with topical bladder instillation of 5-ALA is an efficient and useful method of mapping the mucosa in bladder carcinoma. Moreover, in case of a multifocal disease, this method seems very helpful in finding and treating any residual malignant spots at the end of a transurethral bladder resection.

Endourologic intervention has become widely considered the initial procedure of choice for short segment ureteral strictures. Techniques employed in conjunction with endourologic access to manage the strictured area have included balloon dilation, cold knife and electrosurgical incision. More recently laser incision with the potassium titanyl phosphate (KTP) laser has been employed. The holmium:YAG laser with a wavelength of 2100 nm has recently become available for urologic use. This wavelength is able to precisely vaporize and incise tissue. In this presentation we describe our results with holmium:YAG laser incision of ureteral strictures. Seventeen patients were treated including 12 patients with distal ureteral strictures, 4 patients with ureteroileal anastomotic strictures and 1 patient with a stricture in the ureter of a transplanted kidney. The holmium:YAG laser was employed using a 400 (mu) end-firing quartz fiber placed in contact with the tissue. Clinical and radiologic follow-up of at least 3 months post-surgery (range 3 - 21 months) is available in 14 patients. At last follow-up in these patients, 10/14 (71%) of strictures have remained open. While the ultimate success of endourological techniques of stricture management are determined by the inherent nature of the stricture rather than the technique employed, the holmium:YAG laser for endoureterotomy demonstrates short term efficacy and safety comparable to that reported for other minimally- invasive techniques of stricture management.

The gold standard surgical treatment of benign prostatic hyperplasia (BPH) is transurethral resection of the prostate (TURP). Over the past few years, TURP has been challenged by laser prostatectomy, a technique that offered many advantages including minimal bleeding, short hospital stay, no fluid absorption, rapid learning curve and better change to preserve antegrade ejaculation. Laser prostatectomy can be done by vaporizing or coagulating prostatic tissue and more recently by using a combination of both: The hybrid technique Nd:YAG lasers have been used, (coupled with contact tips or with side firing or even bare fibers) to either coagulate or vaporize prostatic tissue. Recently semiconductor diode lasers have become available and offer certain advantages. They are compact portable units with no need for water cooling, yet they have sufficient power for tissue vaporization. Diomed (Cambridge, U.K.), produces a 60 W gallium aluminum arsenide semiconductor diode laser emitting at 810 nm. We report the first clinical experience using a semiconductor diode laser for prostates using a combination of contact tip and sidefiring.

The multi-YAG laser is a multi-purpose surgical laser designed with the ability to emit 1440 nm light in the pulsed mode for ablation of tissue. Preliminary studies have shown that this laser can rapidly ablate urinary calculi. To define the optimal parameters for laser lithotripsy, 60 uric acid (UA) stones and 60 calcium oxalate monohydrate (COM) stones were ablated in a controlled in vitro study. Each stone was fragmented to less than 1.5 mm while varying the pulse energy (0.3 J to 1.5 J) and the pulse frequency (5 Hz to 15 Hz). The mean energy required to fragment a milligram of stone (fragmentation efficacy - J/mg) was calculated for each experimental level and then compared. The pulse frequency did not significantly affect the fragmentation efficacy for the UA stones (p equals 0.4069) or the COM stones (p equals 0.2560) but, it was significantly affected by the pulse energy for both groups (p less than 0.001). In addition, a plateau in the fragmentation efficacy occurred for both stone groups with respect to the pulse energy. For the UA stones, there was no improvement in the efficacy of fragmentation beyond 0.3 J/pulse and for the COM stones, this plateau did not occur until 0.9 J/pulse. Overall, the COM stones required more energy for fragmentation (p equals 0.001), but efficient and rapid ablation was achieved at energies between 0.6 J and 0.9 J/pulse. These results suggest that the multi-YAG laser has the ability to efficiently ablate urinary calculi of variable composition.

The dual wavelength Nd:YAG (multi-YAG) laser has excellent stone ablating properties. To investigate the safety of this laser for fragmenting ureteral calculi, an ex vivo animal study was undertaken to study acute tissue interactions associated with multi-YAG laser lithotripsy. Human ureteral calculi were implanted in ureters harvested from swine (n equals 42). Direct vision ureteroscopic laser lithotripsy was performed while varying pulse energy (0.3 to 1.5 Joules) and pulse frequency (5 to 15 Hz). All ureters were then examined histologically, graded for tissue injury, and compared to controls. Photofragmentation was associated with mucosal denudation and/or focal mucosal necrosis (grade 0 and 1) in 37/42 cases. Four treatments caused necrosis involving up to two thirds of the ureteral wall (grade 2) and 1/42 had grade 3 changes (transmural necrosis). Ureteroscopic examination alone produced grade 0 to 1 injuries. Logistic regression analysis revealed that pulse energy (p equals 0.47), total energy used for fragmentation (p equals 0.82), and stone weight (p equals 0.64) were not significant predictors of higher grade tissue injury. Pulse frequency (p equals 0.14) began to approach significance. Of the five ureters with grade 2 or greater injury, four were associated with a pulse frequency of 15 Hz. Our findings show that multi-YAG laser lithotripsy is associated with acute tissue changes ranging from mucosal denudation to different levels of coagulative necrosis. Low grade injury is most common and would have minimal potential for strictures. Although higher grade tissue injury is possible, all grade 2 and 3 injuries were microscopically focal in nature. Therefore, multi-YAG laser lithotripsy can be performed with acceptable levels of acute tissue injury at pulse energies up to 1.5 Joules and at pulse frequencies less than 15 Hz.

Many novel treatments for BPH are predicated on depositing power, for example using a laser, microwave, or rf source, to generate heat. In order to be useful and effective a requisite amount of power must be deposited in the tissue so that a reasonable amount of tissue can be necrosed in a reasonable time. The potential to be effective is fundamentally effected by the electromagnetic frequency. The frequency of the power source dictates the penetration characteristic in tissue, and thus the size of the heat source that can subsequently conduct further into the tissue. Because tissue char limits the peak temperature accessible for any power source, a particular frequency can only effectively heat a certain amount of tissue, given similar conditions. Too large a penetration of power can be as ineffective as too shallow.

Laser prostatectomy is at present an established alternative for transurethral electroresection of the prostate (TUR-P). To compete with the different laser techniques, new electrosurgical modalities were developed as replacement for the standard electrosurgery tools for TUR-P. These modalities consist of a grooved cylinder fitted at the end of a TUR-P-element and are designed to combine both vaporization and coagulation in one device. The aim of this study was to investigate the potentials of the new 'rollerbar' devices and compare them with contact laser devices. Four different 'rollerbars' (Ciron, Storz and Prosurg), standard rollerball (Storz), and contact fibers (SLT) were applied to bovine myocard tissue submerged in glycine (electro) or saline (laser). The Valley Laboratory Force 40 and Force 300 were used as electrosurgical units; an MBB 4060 as Nd:YAG laser. Power settings ranged from 100 to 300 Watt (pure cut mode) for the electrosurgery device. The laser settings ranged from 10 to 60 Watt. The devices were moved over the tissue with a constant speed, while constant force was applied. The direct thermal effect of the devices was studied with a special thermal imaging technique on phantom tissue. Results show the vaporizing and coagulating power of the different devices. The rollerball (adjusted to high electrical power, i.e., 200 Watt) and the contact fibers provide similar vaporizing potential as the special-developed 'rollerbar' devices. Coagulation, necessary for hemostasis, is in all cases limited to a depth of about 2 mm. Increasing the electrical power from 200 to 300 watt only slightly increased the affected volume. The presented 'rollerbars' have a clear vaporizing and coagulating effect on tissue. The standard rollerball and contact laser fibers show similar capacities as the special-designed rollerbars.

Conventional side-firing fiber technology exhibits performance limitations and utilizes expensive single-use only devices which often require multiple fibers for laser prostatectomy. Another limitation of existing side-firing fiber technology is its inability to focus the beam to create incisions for urologic applications such as laser TURP (transurethral resectional prostatectomy), tumor necrosis, lithotripsy, genital warts, and photodynamic therapy. Newly introduced variable-focus side-firing endoscopic device utilizes either one or two lenses and a mirror, onto a single cylinder of molded glass. The laser beam exits the optical fiber, passes through the lens, strikes the cylindrical mirror, and traverses the cylindrical surface. Depending on the design, the laser beam is reflected at the angles ranging from 30 degrees to 120 degrees out of the cylindrical lens. A second lens can be formed onto the side of the cylindrical surface at the beam's exit point. Another advantage of the innovative side-firing device is its capability to provide versatile matching to multiple laser wavelengths from 360 nm to 2.5 microns, and achieve power densities great enough to perform vaporization, incision and coagulation of tissue. Precise focusing of the laser beam results in reduced tissue necrosis of surrounding the treatment area as well as in decreased laser radiation back-scattering. Surgeons can very the focus by adjusting the distance from the tip to the target area. The variable focus side-firing device provides a focused beam at the range of 1.0 to 1.5 mm, for incision. Outside this range, it produces a defocused beam for coagulation.

For the last 50 years, electrosurgical transurethral resection of the prostate (TURP) has been the 'gold standard' surgical treatment for male urinary outflow obstruction, despite its high morbidity rate. Recently, in an attempt to decrease the morbidity associated with electrosurgical TURP, the Nd:YAG laser has been widely used to treat outflow obstruction by coagulating prostatic tissue. Although morbidity due to post-operative bleeding is significantly decreased by the Nd:YAG laser, the need for an indwelling catheter for up to one week and dysuria lasting for up to two months have limited the acceptance of this approach. More recently, contact laser prostatectomy, utilizing patented Wavelength Conversion ^TM Effect (WCE) technology, has demonstrated a significant reduction in morbidity compared with TURP and provides immediate symptom improvement and catheter removal typically within 24 hours. With WCE surface treatments on large round probes that are reusable and made of fused silica, a small portion of the Nd:YAG wavelength from a Contact Laser System is absorbed at the probe surface, increasing its temperature, while the remaining native wavelength radiates into the tissue. The temperature gradient in the tissue resulting from this dual effect provides precise and hemostatic vaporization with depth of tissue necrosis as shallow as 0.5 mm when desired. Contact laser prostatectomy can be accomplished by vaporizing with WCE probes alone or in combination with a free-beam coagulation approach, in a procedure known as Laser CHRP^TM (coagulation and hemostatic resection of the prostate). Precise hemostatic incision and vaporization with WCE technology and a variety of other probe shapes have also proven effective in sphincterotomy, urethral strictures, transurethral incision of the prostate, bladder neck contracture and treatment of condyloma.

The optical beam profile, power transmission efficiency, and tissue effects on the Idaho potato model of 1.064-micrometer Nd:YAG radiation were determined using a fiber with the 3M High-Power Side-Firing Tip. The results suggest that a single mechanically and thermally robust beam-focusing tip may be used for both ablation and coagulation in the treatment of benign prostate hypertrophy.

A field where fluorescence spectroscopy might be of great interest for diagnosis, is coronary atherosclerosis and therefore spectroscopic characterization of cardiovascular tissues has been extensively studied. Nevertheless there are several limitations in the precise interpretation of the spectroscopic differences, between normal and atherosclerotic arteries since the tissue is a complex and multilayer structure. Therefore the spectra of individual chromophores could overlap and re-absorption phenomena could occur, too. Another major difficulty arises from the necessity of convenient classification algorithms and the assessment of their feasibility to use fluorescence information, for accurate diagnosis. As a result in order to assess the feasibility of utilizing spectral information to discriminate arterial tissue type several classification algorithms were developed and evaluated. In this work the following pattern recognition techniques have been tested and evaluated: (1) Distance measure (or norm, or metric) based pattern recognition techniques. Methodologically speaking, based on the histopathological diagnosis, a training set of spectra has been classified into four different categories (healthy, fibrous, calcified, heavy calcified) and in each of these four training groups a representative spectrum has been recorded. (2) A pattern recognition method based on statistical considerations. Discrimination between either the four aforementioned classes (categories) or pairs of them is achieved since peak intensities in appropriate wavelengths appear to correlate efficiently with tissue type. The difference of each training set member from the corresponding representative has been defined by using various appropriate distance measures and the sample statistical properties for each category of the training group has been found. Appropriate statistical analysis has been performed in order to deduce the distribution of the distance measures and of the coefficients of the whole population for each one of the four categories, with at least 99% confidence interval. A validation set of samples has been used in order to test and compare the aforementioned pattern recognition algorithms. A performance comparison of the aforementioned algorithms has been undertaken.

In medical experimental and clinical treatment modalities of light, laser photocoagulation of ventricular tachycardia amongst others, the success of the application relies on whether or not the procedure operates in the optical window of the light-tissue interaction. The optical window of biological tissues can be determined by spectral scans of the optical properties. Optical anomalies may result from the irradiance, the wavelength, or from the tissue composition itself. The transmission of cw Nd:YAG laser light on myocardial tissue showed a nonlinearity in the transmission curve at approximately 3 kW/mm² irradiance. The total attenuation coefficient dropped sharp from 1.03 plus or minus 0.04 mm^-1 to 0.73 plus or minus 0.05 mm^-1 at this point in the curve. On the other hand, aneurysm tissue has a highly organized fiber structure, which serves as light-guides, since the transmission of light along the length of the collagen fibers is approximately 50% higher than the transmission perpendicular to the fiber orientation. In addition, changes in optical properties due to tissue phase changes also influence the penetration depth. These phenomena can be utilized to manipulate the optical penetration to an advantage.

Visual laser ablation of the prostate (VLAP) has been shown to be as effective with fewer complications than TURP in the treatment of bladder outlet obstruction secondary to benign prostatic hyperplasia. Questions have been raised about VLAP regarding prolonged irritative and obstructive voiding symptoms postoperatively. It is postulated that these symptoms are due to the slow slough of necrotic debris following VLAP. In an effort to improve upon the technique of VLAP, patients underwent lasing of the prostate in the routine manner (2, 4, 8, and 10 o'clock positions with sixty watts for sixty seconds) using Nd:YAG free beam energy. A bladder neck incision was then performed using a contact laser fiber. International prostate symptom score assessments were done preoperatively; one week and six weeks postoperatively. Post void residual urine volumes and prostate size were also evaluated. The findings indicate that symptom scores and post void residual urine volumes have significantly improved within ten days postoperatively using this technique.

Clinical reports of transmyocardial laser revascularization (TMLR) suggest that this procedure is effective in relieving angina. However, experimental evidence of nutritive blood flow through the TMLR channels is not available. The purpose of this study was to test whether blood could flow through the TMLR channels created with the carbon-dioxide laser.

Since 1993, radiofrequency ablation of the prostate has been studied as a potential treatment for symptomatic bladder outlet obstruction due to benign prostatic hyperplasia. Two transurethral radiofrequency delivery systems have been developed to the point of undergoing initial human clinical trials. The TUNA^TM system involves focal interstitial radiofrequency energy application, while the TURAPY^TM system involves a circumferential application of radiofrequency energy to the prostatic urethra via a simple delivery catheter. Experimental studies in animal models and human prostate tissue have demonstrated the nature of radiofrequency induced tissue heating and thermal injury. Observed thermal effects are relatively focused, with steep temperature gradients occurring over a few millimeters from the radiofrequency emission source. This allows precise and focused tissue treatment with little or no danger of injury to surrounding structures. Early human clinical experience in the treatment of benign prostatic hyperplasia has demonstrated efficacy in the relief of voiding symptoms and safety and minimal morbidity associated with this technology. The existing operative approaches are relatively simple. Ongoing development of more versatile delivery systems for radiofrequency ablation of the prostate is expected. Results from larger clinical trials with longer term followup will eventually allow adequate assessment of the role of radiofrequency ablation in the surgical management of benign prostatic hyperplasia.

The applicability of modern numerical hydrodynamic methods for modeling the bubble dynamics occurring in laser thrombolysis is addressed. An idealized test problem is formulated and comparisons are made between numerical and analytical results. We find that approximately 23% of the available energy is radiated acoustically in one cycle with larger fractions likely to be radiated under more realistic conditions. We conclude that this approach shows promise in helping to optimize design parameters.

Lasers are currently limited in their ability to remove hard tissue. Furthermore, many laser systems, such as the long pulse infrared lasers used to ablate bone or hard dental tissue, also generate unacceptable heat levels and cause collateral tissue damage. Ultrashort pulse lasers, however, are highly efficient, quiet and relatively free of damage. With recent development now allowing operation at high pulse repetition rates, ultrashort pulse systems can yield significant material volume removal which can potentially match or even exceed conventional technology while still maintaining the minimal collateral damage characteristics. In this paper, we report on preliminary studies of 350 fs pulse interactions with hard tissue and compare our results to the nanosecond ablation regime.