We have been studying endoscopic Nd-YAG laser therapies since 1979. In consequence, advantages of the contact method by using ceramic endoprobes were revealed¹²³. Various endoprobes were developed by our studies, and the experimental studies and clinical applications of ceramic frosted probe and chisel probe with Nd-YAG laser were studied. Frosted probe was able to thrombose in the artery of the canine gastric submucosal layer by Nd-YAG laser irra-diation, and was applied to endoscopic hemostasis. Chisel probe was able to cut canine gastric mucosa at the power of 20watts and duration of 2.Osec. with Nd-YAG laser, and was applied to endoscopic pyloroplasty and cutting complete biopsy of submucosal tumor.

Interstitial Nd-YAG laser irradiation has been successfully applied using an endo rod. The rod conected directly to a quartz fiber is made out of new ceramics and is driven into tumor under direct vision. The irradiation effect can be distinguished by a whitish dis-coloration of the cancer. This operation has been performed in 25 cases. In conclusion, it is considered to be a method, comparing conventional transurethral surgery, that the follow-ing advantages can be mentioned: 1. low laser energy is sufficient, 2. it can be applied also to large tumors (more than 3 cm in diameter), 3. damage to the surrounding tissue like an ureteral orifice is very slight, 4. there is no risk of bleeding and perforation, and 5. the technique is simple to practice and easy to manipulate.

We have been studying experimentally and clinically to evaluate the histological effects and safety of the therapeutic Nd-YAG laser endoscopy by the contact method with new ceramic endoprobes comparing wit Li those by the non-contact method with single quartz fiber. In this paper, we would like to discuss possibilities of clinical application of endoscopic local hyperthermia using Nd-YAG laser (Laserthermia) with computer control system. Newly developed computer controlled Laserthermia may possible to apply for the treatment of the malignant tumor in the gastrointestinal (GI) tract.

We have used photodynamic therapy (PDT) and local interstitial hyperthermia with low power Nd:YAG laser in nude mice in an attempt to study their therapeutic effects for further investigation. Pieces of solid tumor of human pancreatic carcinoma were subcutaneously transplanted in the backs of 28 nude mice which are 5-weeks old female. The fllowing experimental therapies were begun 5-6 weeks after the transplantation. 1) PDT:Argon dye laser was irradiated into a tumor with 300-400 mW in 72 hours after hematoporphyrine derivative (HpD) in a dose of 3 mg/kg was intravenously injected. Histological changes detected after 7 days were coagulated necrosis and fibrosis in the tissues ranging from 30 to 50% area ratio. 2) Local Interstitial Hyperthermia: The Frosted Probe for interstitial irradiation was punctured under controlling temperature near the margin of the tumor at 42°-43°C with 3W for 10-20 minutes. This therapy caused a marked amount of necrosis in the pancreatic tumors after 7 days. For mechanism, it seems that it is based on the effect of both thermal effect and direct effect of low power Nd:YAG laser energy on cancer cells, and the other is a damage of tumor vessels secondarily caused by this therapy in vivo.

The thermal response of an established animal tumor model to Nd:YAG laser-induced hyperthermia has been investigated. A variety of treatment parameters (dose, power density, and exposure time) and delivery techniques (focussed, unfocussed, defocussed, and intersti-tial) were studied in an attempt to optimize tumor eradication. The results presented indicate that the Nd:YAG laser operating at low output powers (1-2 W) may be used to induce local tumor hyperthermia.

We report the development of the first software driven medical laser system for tissue fusion. The laser system consists of a specially modified neodymium YAG laser head that operates at a wavelength of 1.319 μm rather than the fundamental 1.064 μm wavelength. Laser surgery software developed expressly for this system relieves the operating surgeon of the task of identifying the correct laser power levol, spot size, and time exposure for a. given laser wavelength and mode structure. For each tissue type, the above parameters vary from one thickness to another based on volume of tissue that requires heating and coagulation. This critical data is encoded on a floppy disk with hard disk back-up that is accessed by the laser microprocessor system. The surgeon inputs the tissue type and tissue thickness; and using that input, the microporocessor automatically adjusts the laser parameters for delivery by a fiber optic delivery system. Fiber optic delivery greatly increases operating flexibility and minimizes interference with standard surgical procedures.

Contact Nd: YAG laser surgery is assuming a gre ter importance in endoscopic and open surgery allowing coagulation, cutting and vaporization with greater precision and safety. A new contact probe allows a wider angle of irradiation and diffusion of low power laser energy (less than 5 watts) using the interstitial technique for local hyperthermia. Continuously monitoring temperature sensors are placed directly into the surrounding tissue or tumor. Using a computer program interfaced with the 1.ser and sensors, a controlled and stable temperature (e.g., 42°C) can be produced in a known volume of tissue over a prolonged period of time (e.g., 20-40 minutes).

As pump sources for Nd:YAG lasers, laser diodes have been shown to have significant advantages over other sources. This paper presents recent advances in the performance of laser diode pumped Nd:YAG lasers. Specific emphasis will be placed on those characteristics which offer unique advantages over conventional (lamp pumped) systems, including: size, weight, efficiency, stability, flexibility, reliability, and life.

Attempting a new method of laser irradiation for depressed gastric carcinoma, using a newly developed interstitial probe and laser attenuator, we applied local hyperthermia with prolonged low watt contact irradiation. Experimental studies were performed with this probe, using BDF1 mice injected hypodermically with Lewis lung carcinoma. A laser power of 2.0 w at the tip of fiber produced the most desirable temperature curve, about 43 - 60°C at the irradiation site. Clinical applications were carried out on 15 patients with early gastric carcinoma (mainly depressed), 10 preoperative pilot cases and 5 inoperable cases. In follow-up operations and biopsies gastric carcinoma was found to have completely dis-appeared in 2 of the preoperative and 4 of the inoperable cases. In the remaining 8 preoperative cases residual traces of carcinoma were found at the margin of the laser ulcer, but not at the bottom of it. We propose that endoscopic local hyperthermia using interstitial probe and low power irradiation (2.0 W) is the safest and most suitable method of dealing with depressed carcinoma.

An impact of the Q-switched Nd-YAG laser caused bleaching of stains and removal of deposits and pit & fissure contents of teeth. No chalky spots or craters were found microscopically on the enamel surface after irradiation. These results strongly suggested the clinical applicability of Q-switched Nd-YAG laser in removing dental deposits, intrinsic pigmentation of enamel, and pit and fissure contents of molar.

Attempts to model the thermal response of biological tissue to laser irradiation require an accurate description of the distribution of the light inside the tissue. This is difficult to describe theoretically because multiple scattering causes beam broadening. The Kubelka-Munk model is based on a model of two diffuse fluxes traveling in the forward and backward directions. This is unlike the directional laser source to be modeled. Multiple scattering theories are complex and add little intuitive insight to the light's behavior in the tissue. Our approach is to measure the growth of the beam as it is absorbed and scattered through our principal target, atheromatous plaque. We will describe an optical system that allows quantitative measurement of the 1/e² spot size as laser light is scattered in arterial plaque samples. The input beams used were: a) collimated lmm direct output from a laser and b) the diverging output of an optical fiber. The measurement is made by imaging the exit face of the tissue onto a scanning slit detector with unit magnification. By compressing the sample to calibrated thicknesses, readjusting the imaging to retain unit magnification, we obtain plots of exit spot size versus tissue thickness. The data indicate that the spot expands linearly as the sample's thickness is increased. However, the rate of beam expansion varied with different tissue samples. The linear beam expansion seen is in disagreement with the exponential growth previously assumed.

This approach to optical dosimetry in photodynamic therapy is based on the hypothesis that tumor eradication requires a minimum absorbed energy density by tissue-localized hematoporphyrin derivative. The required incident fluence is calculated from absorption profiles based on the diffusion approximation to radiative transfer. The results are in satisfactory agreement with empirical light dose levels reported in the clinical literature.

Hematoporphyrin derivative (HPD) is a mixture of porphyrins that localize in malignant tumors. The fluorescent emission of HPD was used in three animal tumor models to define tumor margins with gross imaging and to identify the microscopic distribution with fluores-cent photomicroscopy combined with standard histology. Fibroblasts within the tumor stroma were identified as the main cellular element retaining HPD. Our data indicate a barrier to diffusion of HPD containing it within the connective tissue capsule and preventing its up-take by malignant cells. A model for the uptake, retention and photodynamic action of HPD on tumors is proposed.

Experiments were performed to investigate the feasibility of combining laser heating of tissues while controlling the temperature changes by magnetic resonance imaging (MRI). A great potential exists for applications in cancer treatment and in scientific research.

Several recently proposed medical procedures involve intralumenal laser irradiation at power densities below the vaporization threshold. Typically the radiation is transported to the tissue to be treated by an optical fiber, and then applied to the inner wall by an energy diffusing source. The tissue is heated but not removed; in fact extensive tissue vaporization is potentially disastrous. The goal is therefore to elevate the tissue to a defined temperature within a range bounded by the threshold for effectiveness and the threshold for damage. The temperature reached is a function of the dimensions and properties of the tissue and of wavelength, exposure duration, power density, and certain boundary conditions. For example, a heat sink can be placed in contact with the inner surface, substantially altering the temperature distribution. We have constructed a simple model to calculate the radial temperature distribution in a cylinder of tissue subjected to continuous or long pulse optical irradiation from an axial source. The intent is to permit dosimetry based on experimentally supported calculations, rather than on trial and error. The temperature reached results from two competing effects: absorption of the radiation and conductive processes. The wavelength dependence is introduced through choice of absorption and attenuation coefficients, with tissue properties summarized in the thermal diffusivity. The effect of scattering is assumed to be no more than an alteration of the attenuation coefficient; the possibility of relaxing this assumption is considered. The model allows investigation of the effects of power density, pulse duration, and heat sinking on the time evolution of the temperature distribution.

Refractive defects such as myopia, hyperopia, and astigmatism may be corrected by laser milling of the cornea. An apparatus combining automatic refraction/keratometry and an excimer type laser for precision reshaping of corneal surfaces has been developed for testing. When electronically linked to a refractometer or keratometer or holographic imaging device, the laser is capable of rapidly milling or ablating corneal surfaces to preselected dioptric power shapes without the surgical errors characteristic of radial keratotomy, cryokeratomileusis or epikeratophakia. The excimer laser simultaneously generates a synthetic Bowman's like layer or corneal condensate which appears to support re-epithelialization of the corneal surface. An electronic feedback arrangement between the measuring instrument and the laser enables real time control of the ablative milling process for precise refractive changes in the low to very high dioptric ranges. One of numerous options is the use of a rotating aperture wheel with reflective portions providing rapid alternate ablation/measurement interfaced to both laser and measurement instrumentation. The need for the eye to be fixated is eliminated or minimized. In addition to reshaping corneal surfaces, the laser milling apparatus may also be used in the process of milling both synthetic and natural corneal inlays for lamellar transplants.

The authors report the design criteria and performance of the ExciMeda UV200 medical excimer laser system. A beam delivery system for controlled photoablative machining of variable power optical lenses in organic material is described. Some of the potential applications of this delivery system in corneal surgery are presented. The uses of the UV200 laser system in other areas of medical research are discussed and, in particular, its application i the field of laser angioplasty is outlined. There has been considerable interest recently in the use of excimer lasers in a variety of fields in medicine. The ultraviolet, high peak power beam emitted by an excimer laser has been shown to be capable of producing very clean and precise cuts in organic material. In particular, cuts can be made in biological material with minimal disturbance of the material adjacent to the cut. For example, tissue can be cut in such a way as to produce negligible charring or vacuolization in adjacent areas of the tissue. This is in marked contrast to the results when organic material is cut by a continuous wave laser such as an Argon ion laser, or c.w. CO₂ laser. The potential applications in clinical settings which are suggested by this feature of the interaction of tissue with excimer laser radiation have been largely unrealized outside the laboratory as yet. A primary reason for this is that, until recently, excimer lasers have been available only in a form that was suitable for the scientific laboratory. These lasers required large amounts of space, were not mobile once installed, and required con nection to external sources of water cooling, vacuum exhaust, a high current electrical supply, and a variety of gas bottles including the gases F₂ and C₁₂. These systems were not designed with clinical applications in mind, and thus provided unnecessary performance features at the cost of added complexity. They also posed potential electrical and gaseous safety hazards not suitable for a clinical environment. In addition, the output from these system could not be easily delivered to a target site due to the absence of any built-in beam delivery system such as an articulated arm, or fiber-optic delivery system . Several months ago, Summit Technology introduced the world's first medical excimer laser, the ExciMedTM UV200. This laser system is shown in Figure 1. It has been specifically designed for research applications in a clinical environment and incorporates a number of important design features.

The influence of the laser in biological and medical research is becoming increasingly more important. Laser systems which are utilized for basic research in chemistry and biology are described and examples of biological and medical research are presented.

√We developed a frequency-domain fluorometer which operates from 4 to 2000 MHz. The modulated excitation is provided by the harmonic content of a laser pulse train (3.76 MHz, 5 psec) from a syncronously pumped and cavity dumped dye laser. The phase angle and modulation of the emission are measured with a microchannel plate photomultiplier. Cross-correlation detection is performed outside the PMT. The performance was verified by measurement of known time delays and examination of standard fluorophores. The detector displayed no detectable color effect, with the 300 to 600 nm difference being less than 5 psec. The precision of the measurements is adequate to detect differences of 20 psec for decay times of 500 ps. This new instrument was used to examine tyrosine intensity and anisotropy decays from peptides and proteins. The data demonstrate that triply-exponential tyrosine intensity decays are easily recoverable, even if the mean decay time is less than 1 nsec. Importantly, the extended frequency range provides good resolution of rapid and/or multi-exponential tyrosine anisotropy decays. Correlation times as short as 15 psec have been recovered for indole, with an uncertainty of ± 3 psec. We recovered a doubly exponential anisotropy decay of oxytoxin (29 and 454 psec), which probably reflects torsional motions of the phenol ring and overall rotational diffusion. Also, the 2 GHz data reveal the time-dependent (√t) terms found in the presence of collisional quenching.

Applications of two laser-based quasi-elastic light scattering instruments to the characterization of aerodynamic diameter, diffusion diameter, and electrostatic charge of respirable particles for estimating lung retention of inhaled particles are discussed. The methods provide means of real time, noninvasive in-situ measurements of the size and charge distributions of both inspired and expired particles, permitting quantitative determination of the lung retention of inhaled particles. The two instruments used are: 1) electrical single particle aerodynamic relaxation time (E-SPART) analyzer; and 2) photon correlator employing a dual-beam laser Doppler velocimeter. Both have advantages over the conventional optical particle counter in that they measure equivalent diameter and electrostatic charge independent of the optical scattering properties of the particles, while providing data on a single particle basis. Applications of these instruments in estimating health hazards from atmospheric pollutants and in evaluating the efficacy of therapeutic aerosols in treating diseases are briefly discussed.

Photodynamic dose is defined as the area under the curve of sensitizer level plotted as a function of light dose. The photodestruction of sensitizer during photodynamic therapy is shown to result in an upper limit on the photodynamic dose which can be delivered by an unlimited light dose. This limit results in the opportunity to make total photodynamic dose uniform to considerable depths (one to two centimeters). The existence of thresholds for permanent tissue damage allows protection of normal tissue from the large light doses required to achieve this limiting dose deep in the tissue. Higher sensitizer levels in the tumor permit tumor destruction while the normal tissues are protected. A clinical trial to determine the proper level of injected dose necessary for these results is required. This theory of photodynamic therapy (PDT) dosimetry is tested in the DBA-SMT experimental mouse tumor system. Combinations of drug and light which are not reciprocal but are nearly equal by this theory are shown to give equivalent tumor control at seven days post treatment. Reciprocal combinations of drug and light fail to give equivalent results when they are selected using the theory to choose a combination where reciprocity should fail.

Picosecond spectroscopy has been used to study the excited state dynamics of metalloporphyrins and hemoproteins. The relative effects of intersystem crossing, low-lying charge transfer states and ligand ejection on the excited state lifetimes in various metalloporphyrins differs according to the properties of the central metal ion. Hemoproteins relax rapidly from the excited state but even in such fast processes ligand dissociation can occur, although not all axial ligands undergo photodissociation. In general, axial ligands, when present, can control the energy levels of the central metal and by doing so can control the rate of intersystem crossing and non-radiative decay through intermediate charge transfer states.

Solvated electrons are formed in high yield and can be detected by transient absorption spectroscopy when calf thymus DNA is irradiated with laser pulses at 266 nm having peak intensities above 10¹⁴ W/m². Approximately 20% of the initially appearing absorption strength decays with a time constant of 400 ps, while the remaining 80% is long-lived (> 10 ns). The decaying component may indicate geminate recombination of the photoejected electron. Spectral evidence suggests that the bases are the site of ionization. The signal is observed to depend nonlinearly on the excitation pulse energy, indicating that two (or more) excitation quanta at 266 nm are required to ionize DNA. An equimolar mixture of nucleosides shows a much lower quantum yield for electron formation; this is discussed in terms of an exciplex model for the DNA excited state.

Laser/microscope fluorescence methods for studying adsorption/desorption kinetics and surface diffusion of molecules reversibly associated with biological membranes are discussed. These methods, which include fluorescence excitation by evanescent waves generated by total internal reflection, and fluorescence quenching by thin metal films, may also find application in the design of in vivo biosensors and in studies of transmembrane transport and chemical kinetics.

The photosensitizing properties of hematoporphyrin derivative (HPD) have been investigated using egg phosphatidylcholine liposomes and resealed bovine erythrocyte membranes (ghosts) as model membranes. The results demonstrate that incorporated HPD photosensitizes lipid peroxidation in liposome and ghost membranes and protein cross-linking in ghosts via the Type 2, singlet oxygen mechanism.

Sensitized photooxidation causes a change in the tertiary structure of lens crystalline. The subtle variations observed in the nature of these changes are attributed to the difference in the inherent tertiary structure of the crystallins. Each active species of oxygen, a product of the sensitized reaction, has a distinct role in this process. Sensitizer molecules also exhibit a certain specificity regarding the photoinduced conformational changes of these proteins.

Pulsed-dye-laser fragmentation of biliary and urinary calculi is associated with a bright flash, an acoustic transient and material removal. Time-resolved spectroscopic studies of the flash have demonstrated the presence of a plasma when fragmentation occurs. A model is proposed in which the plasma absorbs the optical energy of the laser, and expands, and generates mechanical forces that fragment the stone.

We have developed and tested a quasi-elastic light scattering (QELS) microscope spectrometer. Microscopic scattering volumes in single cells can be studied using the QELS microscope spectrometer. The scattering properties of model systems and various biological preparations have been examined.

Quasi-elastic light scattering is a useful method to determine the size distribution of sub-micron particles in fluids. We have applied this technique to measure in vivo changes in the association of human lens protein constituents that occur with aging and cataractogenesis. The autocorrelation function of the scattered light has been analyzed by a two component exponential where each component is characterized by an intensity and decay rate. Each pair of parameters is associated with one of two major protein compo-nents in the lens. Our results seem to be consistent with the model of progressive aggregation of the lens proteins as detected in vitro by other biochemical methods.

The technique of quasi-elastic light scattering spectroscopy or photon correlation spectroscopy has been used to non-invasively monitor changes in the lens of the eye which could lead to lens opacification and cataract development. We have made quasi-elastic light scattering measurements from the eyes of normal and cholesterolemic rabbits. This report describes an exploratory investigation of the effects of a high cholesterol diet on the lens of the rabbit eye. The goal in making these measurements was to provide a non-invasive assessment of systemic atherosclerotic involvement in these rabbits.

Quasielastic light scattering technology provides a means of obtaining a linear measure of the total light scattered by the lens or cornea. This technology has been applied to a population of normal volunteers and a group of patients with different types of cataracts. The replicate errors have been measured for 5 and 50 microsecond sample times in both the cortex and the nucleus of the human crystalline lens in vivo, and they vary from 10-13%. The regional error associated with a change in the location of the pickup, a variation over an area of 225 square microns, is 18-20%. The change from a clear to a cataractous cortex is associated with wide fluctuations in total light scattered; in our population, the mean decreased slightly. In the nucleus, the total light scattered by opaque nuclei was 400% greater than that scattered from non-cataractous, age-matched control nuclei. It appears as if the signal-to-noise ratio for this instrument applied to humans is likely to be 10-20/1. This should enable one to detect small changes in the light scattering properties of the lens in vivo and should make clinical trials of anticataract drugs tolerably short in duration and affordable. Other film-based technologies for in vivo objective measurement of cataractous change along with their strengths and weaknesses are also discussed. Specifically the Topcon SL-45, the Topcon SL-5D/6E, the Neitz CTR and the Zeiss-Kawara cameras are discussed.

We will present a thermal model for laser pulses with pulse widths small compared to the material's thermal time constant. This model will then be used to generate computer plots of the zones of vaporized tissue as well as the predicted tissue temperature rise. Using published values of absorption coefficients, we will predict the vaporization energy thresholds for Er:YAG (2.94μm), Ho:YAG (2.1μm) and CO₂ (10.6μm) laser pulses. We will also examine the extent of the thermally denatured zone surrounding the zone of vaporization. Using typical energies available from these lasers we will then predict material removed per pulse, and per second.

The effectiveness of the continuous wave hydrogen fluoride laser for cutting animal skin; skeletal and heart muscle; and liver tissue was tested. Histological studies demon strated that it is comparable to the CO₂ laser in tissue cutting action. Importantly, the hydrogen fluoride laser can be delivereg through mid-infrared fiber optics, making it a potential tool for opthiamic applications, intravascular surgery, and for laser myocardial revascularization. It was not felt to be practical for general surgical applications.

The trivalent Erbium transition,⁴T_11/2 ^{4[/supI_13/2 has an emission wavelength close to , 3 μm in a variety of host laser crystals. The fundamental 0-H vibrational stretch in water occurs at approximately the same wavelength. It is therefore expected that the absorption coefficient of water near 3 μm would be of the order of 104cm-1. In order to measure this value precisely with a transmission spectrometer, it is necessary to have a film with a thickness of the order of the reciprocal of the absorption coefficient of water. This implies a thin film of water of about one micron. It is also desirable to measure the water absorption coefficient in the infrared out to wavelengths as long as 12 μm. This would require cell thicknesses up to 20 μm. A special cell has been designed and constructed to meet these criteria of variable thickness, IR transmission and compatibility with high purity water samples. The cell is shown in cross section in Figure 1. It is designed to provide a variable thickness film of water and a liquid filled space adjacent to the film that acts as a reservoir. The IR transparent ZnSe windows are attached to the Invar holders which are separated by two Teflon gaskets and a Invar spacer with inflow and outflow ports. The two Invar holders are squeezed together, compressing the Teflon gaskets. This not only changes the film thickness, but provides a positive seal with the gaskets. The film thickness is adjusted to the desired value, the transmission of the water film is measured and the film thickness is verified after the transmission measurement. The sequence can then be repeated for different thicknesses of the cell.}

351 nm, 20-nsec XeF excimer laser irradiation has previously been shown to selectively target and damage melanosomes in human skin. In the following studies selective targeting with melanosomal photodisruption has been demonstrated in pigmented guinea pig skin with a Q-switched 40-nsec ruby laser, and a 750-nsec pulsed dye laser but not with a 400-usec pulsed dye laser. The pulse width dependence of melanosomal disruption, occurring only at pulsewidths shorter than the thermal relaxation time of the melanosome (0.5 - 1.0 usec), is in accordance with the theory of selective photothermolysis. Possible mechanisms of melanosomal photodisruption include development of sudden thermal gradients leading to cavitation or shock wave production.

Cherry angiomas, small red spots found on normal skin, usually 1-3 mm in diameter, were used as a model to evaluate the Ofect on cutaneous vascular lesions of a cw laser treatment applied through a Dermascan delivery system. This device permits effective laser exposure times of 1 millisecond, thus limiting thermal diffusion damage in tissues adjacent to the optically absorbing vasculature. Treatment requires no anesthesia and produces no burn/blister response. Clearing of the lesion is complete about five weeks after treatment.

Melanin bearing cutaneous lesions have been successfully treated with a cw argon laser applied through a Dermascan* delivery system. This device permits effective laser exposure times of the melanin bearing cells of 1 millisecond, thus limiting thermal diffusion damage to adjacent tissues. Clearing of the lesions occurs in one to two weeks, resulting in normal skin color and texture.

One of the authors has performed 162 arthroscopic laser surgeries in the knee joint without any major complication. Other investigators have recently proposed diagnostic arthroscopy and arthroscopic surgery for "non-knee" joints. The authors have proposed that arthroscopic laser surgery he extended to "non-knee" joints. The authors have performed arthroscopic laser surgery on "non-knee" joints of twelve cadavers. One of the authors have performed one successful arthroscopic surgery on a shoulder joint with only a minor, transient complication of subcutaneous emphysema. Is laser arthroscopic surgery safe and effective in "non-knee" joints? The evolving answer appears to be a qualified "Yes," which needs to be verified by a multicenter trial.

Current modalities for treating a herniated lumbar disc include standard open discectomy, microsurgical discectomy, chemonucleoysis and percutaneous discectomy. The Food and Drug Administration has not yet approved percutaneous laser discectomy for clinical investigation. The investigators believe that percutaneous laser discectomy combines the efficacy of both chemonucleoysis and percutaneous discectomy with the safety of both open standard discectomy and microsurgical discectomy. The investigators removed two lumbar discs from a cadaveric spine and weighed each of them. The two lumbar discs weighed in the range of 13.654 grams and 15.713 grams, respectively. The investigators initiated several series of 10 firing cycles from a surgical carbon dioxide laser system. In each firing cycle the surgical carbon dioxide laser system delivered a beam of light energy having an output power of 18.0 watts at pulse duration of 0.045 second at the rate of 15 pulses per second for a period of 6 seconds and vaporized approximately 325 milligrams of disc material. Based on the findings of other investigators reported in the literature relating to percutaneous discectomy the investigators postulated that 10 to 20 firing cycles are required to vaporize 30 to 40% (2.4 to 6.4 grams) of the disc material. The investigators initiated two series of 10 firing cycles in order to perform laser discectomy in a third lumbar disc of the cadaveric spine in situ. The investigators harvested and then bisected the laser-treated third lumbar disc for gross review. Their gross findings indicated a high probability of success For percutaneous laser discectomy.

With the increasing pressures being put on the medical system to reduce treatment costs, the use of lasers in surgery is fast becoming an effective means for achieving beneficial treatment at lowered overall treatment costs. For this and other reasons, the medical field is about to undergo a revolution in surgical therapy and in the use of laser diagnostics. This paper discusses the past, present and future outlook for medical lasers, including the markets, changes occurring in both lasers and fiber optic delivery systems, new surgical applications likely to become important and some of the leading systems suppliers.

When we were first confronted with the laser, in 1975, it was not considered useful for neurosurgery¹²³. We were nonetheless fascinated by the potential of a non-touch instrument and attempted to demonstrate its applicability. After theoretical considerations and experimenting on animals, we performed the first laser operation on a patient on July 28, 1976. Since then we have performed nearly 1000 procedures with the CO2 and Nd:YAG lasers ^4,56,7. Our early hopes for the laser have been realized and new indications have been added.

Bowed tendons in the horse can greatly hinder it's racing career. A pulsed, 904 nm, infrared GaAs laser, peak power 2 watts, averaging .4 mW, 10 diodes per head, was used in reducing the area of the bowed tendon. This treatment proved to capacitate the horse for better race performance. Before application of the laser the wound area was shaved. A cast of playdoe was formed over the affected area. The cast was then removed and spread over a sheet of paper which consisted of a drawing of a grid in square centimeters. The squares were then counted.

Two experiments were performed using male rats. (Winstar Strain, 300 gm.) Dorsal cutaneous nerves were cut from approximately T1 0 through T1 3. The denerved tissue was identified in 0.65 cm²/squares and counted.

Veterinary medicine is a latecomer in benefiting from the advent of surgical lasers. It is ironic that although most of the basic work in lasers is carried out in animal species with which we are most conversant, veterinary medicine as a profession has not been very extensively involved.

The therapeutic benefits of light-energy is not a new concept to the modern world. Documented applications from ancient times tell of the therapeutic effects of ordinary sun-light to treat such common ailments as painful body joints, wounds, compound fractures and tetanus. The discovery of laser light in the 1960's, opened up new prospects for the medical use of light. Laser light differs from other forms of electromagnetic spectrum in that a single wavelength rather than a spectrum of wavelengths is emitted. Since the early 1970's, low-energy laser radiation has been reported to enhance wound healing rates, reduce edema, and relieve musculoskeletal pain. There is no detectable thermal effect of this laser on the tissue being treated. The effects are considered to occur as a result of photochemical, non thermal effects of the laser beam. Photons are absorbed by the tissue being treated and, in turn, produce positive therapeutic effects such as reduction of pain and edema. Pre-clinical and clinical evaluations are, presently, underway to document the safety and efficacy of low energy laser therapy, which represents a significant advance in the non-invasive treatment of pain.

The cellular response of arterial wall to in vivo exposure to continuous wave argon and xenon chloride Excimer laser irradiation was examined. Acutely, argon irradiation created vaporization of atherosclerotic material with the formation of craters surrounded by zones of thermal and acoustic injury. Thermal and acoustic damage was not noted with the Excimer exposures. Over nine weeks, both types of laser burn demonstrated complete healing. Argon irradiation was associated with damage to normal surrounding tissue which could not be appreciated at the time of laser application.

This study compared the histology, biochemistry, and tensile strength of laser welded and sutured canine venotomies, arteriotomies and arteriovenous fistulas. Bilateral femoral, carotid or jugular vessels were studied with one repair (control) closed with interrupted 6-0 polypropylene sutures, and the contralatral repair (experimental) welded with the argon laser. Specimens were examined at weekly intervals from 1 to 4 weeks for each type of repair and evaluated histologically by hematoxylineosin, elastin and trichrome stains, biochemically by the formation of [3H] hyaroxyproline as an index of collagen synthesis, ana mechanically by tensile strength determinations. At removal, all experimental closures were patent without hematomas, aneurysms or luminal dilatation. Histologic and biochemical examination and tensile strength determinations suggest that laser welaing may be an alternative to sutures for repair of large diameter venotomies, arteriotomies and arteriovenous fistulas, as they heal comparable to suture repairs up to 4 weeks postoperatively.

In an attempt to overcome some of the problems associated with conventional wound closure, i.e. suture or mechanical device closure, the laser has been used for "tissue welding" ,(sealing and fusion), of wound edges. Early attempts at laser tissue fusion were centered on microvascular anastomosis and recent studies have extended to include most soft tissues. It has been demonstrated in animal studies, that the process of healing after laser wound closure is very similar in most tissues. Within the past year alone, the experimental work in this area has progressed rapidly; limited clinical trials are now under way. Based on detailed animal studies and limited clinical experience, laser tissue fusion may soon replace many conventional techniques of wound repair.

Various mechanisms have been proposed for laser induced vascular welding. The conflict is partly due to the different laser parameters being used, different techniques, and the possible dual thermal and photochemical effects of lasers on tissues. This study examines the thermal aspects of welding medium diameter (4-8 mm) blood vessels. Six canine arteriovenous (A-V) fistulas were created by argon laser vessel fusion. Thermal images were concurrently recorded with a AGA thermal camera and computer analyzed. The welding was done at an energy fluence of 1100 J/cm², using continuous saline irrigation for cooling. The thermal profiles revealed a maximum temperature of 48° C. In previous experiments, welding of microvessels has been achieved with CO₂ , Na:YAG and argon lasers. In our experience, welding of medium diameter arteriotomies and A-V fistulas was possible only with argon lasers. The thermal component induced by different laser wavelengths may be partly accountable for these observed differences in welding properties. Further studies are required to delineate the role of photochemical and thermal reactions in vascular tissue fusion by lasers.

Shortly after the ruby laser was introduced, in 1959, a study for the use of this ruby laser for the in-vitro dissolution of arteriosclerotic plaque was performed.' With subsequent advances in laser technology and with refined delivery techniques, laser applications to the treatment of arteriosclerosis in the coronary arteries and peripheral vascular system is a reality. This report reviews the disease process, arteriosclerosis, and the ef-forts towards laser treatment of this disease. We conclude with a review of the technical barriers to the routine application of laser energy in arteriosclerotic cardiovascular disease and the progress being made to overcome these obstacles.

Laser thermal angioplasty involves the use of a novel fiberoptic delivery system, the Laserprobe, in which argon laser energy is converted to heat in a rounded metallic cap at the end of a flexible fiberoptic system in order to provide thermal energy for vaporization of obstructive atherosclerotic lesions. Experimental studies in animals have demonstrated improved safety and efficacy of this device compared to bare fiberoptic delivery systems. Preliminary clinical trials demonstrate its feasibility as an adjunct to balloon angioplasty in patients with obstructing peripheral arterial lesions.