The medical laser industry continues to be a complex industry to follow. In this presentation, the author provides an overview of the growing markets, the new laser technologies and the new applications that will shape the medical laser industry in the years ahead. The presentation covers both a conservative view of market growth as well as application breakthroughs that could greatly impact the sale of both conventional and new laser systems. These new applications include laser angioplasty, laser lithotripsy, corneal sculpting, and other new significant surgical and therapeutic uses for lasers. The new laser systems include excimer lasers, pulsed dye systems, new solid state lasers operating at fiber transmittable water absorption peaks, diode and diode pumped solid state lasers and tunable solid state lasers of the future. The presentation, based on a recently completed study of the industry (published by Arthur D. Little's Decision Resources, November, 1988), is a valuable overview for both established participants and those newly interested in the medical laser field.

Accuracy, reliability and cost requirements dictate the need to critically examine fiber optic approaches that are currently being pursued for detecting pressure in medical applications. Typical medical pressure measurements require only moderate sensitivity but high accuracy under environmental conditions. Temperature effects and fiber bending are the most frequently encountered environmental effects limiting achievable accuracy of the intensity encoded pressure sensors. This paper focuses on the effect of the fiber bending in a catheter-type fiber-optic pressure sensor and discusses the dual wavelength technique and additional improvements developed to minimize fiber effects and increase the accuracy and stability of the sensor.

This paper summarizes the design and performance of an assortment of fiberoptic temperature probes that may be used with the Luxtron Fluoroptic^® thermometer. These probes are made specifically for medical applications and most of them are available as commercial products. The probe types range from single sensors to linear arrays of multiple sensors. More recently, a catheter-borne sensor has also been developed. Prototypes of probes with very small tips (0.2 to 0.3mm in diameter) have demonstrated immunity to heating by both microwaves and ultrasonic waves. When used with Luxtron's Model 3000, the temperature precision of the probes is +/- 0.1°C and the accuracy is +/- 0.2°C. A simple low-cost connector has also been developed to facilitate convenient probe-to-extension-cable connection. All materials used are biocompatible and can withstand multiple cycles of ETO gas sterilization. Most of the probes have undergone clinical evaluation and have been proven practical for routine medical use.

The whole field of biosensing has been enhanced by the development of optical fibers CIA. They provide a means of activating the sensors and of carrying the sensor's signal back to the monitoring system. The small dimensions and flexibility of the fibers allow the development of the miniaturized sensor packages capable of introduction into a patient's vascular system. In a similar fashion optical fibers have revolutionized endoscopic techniques. Smaller, more flexible probes are permitting longer pathlengths and easier, less intrusive inspection of internal body areas. Standard fibers provide lighting while special optical fibers or bundles provide viewing capability. During the next decade real time sensing in vivo together with various endoscopic and laser techniques will provide doctors and patients with many new and delicate alternative procedures to common surgery. Not only will trauma be minimized, but with better and quicker knowledge of the patient's blood gas levels and other body conditions, doctors will be able to efficiently correct for unforeseen difficulties while controlling the known problems effectively. In both these application areas, the optimum fibers will need to have large numerical apertures (NA) to improve the sensing efficiency or the lighting efficiency and they must be sturdy/reliable as well as flexible. This places stringent requirements on the optical and mechanical porperties of the fibers. This paper describes a new type of fiber, Dual-Clad (Coat), High NA, Hard Clad Silica (HCS*) Fibers, which have the required optical and mechanical porperties for these application areas and very high core/clad/coat ratios.

We describe a fiber optic sensor based on a homogeneous fluorescence energy transfer immunoassay which operates in a continuous, reversible manner to quantitate the anticonvulsant drug phenytoin. B-phycoerythrin-phenytoin and Texas Red labeled anti-phenytoin antibody were sealed inside a short length of cellulose dialysis tubing which was cemented to the distal end of an optical fiber. When the sensor was placed into a solution of phenytoin, the drug crossed the dialysis membrane, displaced a fraction of the B-phycoerythrin-phenytoin from the antibody, and produced a change in fluorescence signal which was measured with a fiber optic fluorometer. The sensor had a concentration response of 5 to 500μmo1/L phenytoin with a response time of 5 to 15 min and precision of <2.5% CV. The chemical kinetics of the antibody-hapten indicator reaction were modeled mathematically and simulation showed that response time in the minutes range can be achieved when the dissociation rate constant is greater than approximately 10^-3 sec^-1. The dissociation rate constant influences the time to reach equilibrium and the unbound P* concentration range available for instrumental measurement. The ratio of the labeled and unlabeled hapten dissociation rate constants influences the analyte concentration range to which the sensor will respond.

Blood pH measurements present unique challenges due to the lack of a method to determine accuracy. Therefore an operational pH scale has been defined with the use of accepted pH standard buffer solutions in order to achieve precision and consistency. Historically, blood pH has been measured electrochemically with the glass electrode, in-vitro. The glass electrode is subject to drifts and to extraneous potentials that adds uncertainties to the measured values and must rely on frequent recalibrations to provide precision and consistency. A recent commercial entry, the fiber optic fluorescent pH sensor avoids these problems. The result is a stable sensor capable of continuous in-vivo monitoring of blood pH in spite of the intricacies introduced by the use of the operationally defined pH.

Evanescent fiber optic sensors are being developed for remote in situ immunoassay. The single reflection total internal reflection fluorescence (TIRF) geometry can serve as a well-defined model against which evanescent waveguide devices can be compared and evaluated. This paper addresses the problem of optimizing the sensitivity of an evanescent fiber optic sensor (EFOS). Two aspects are discussed: (1) the modes of exciting laser light in the fiber have an effect on the sensor efficiency and signal-to-noise ratio; (2) in a fiber biosensor, there is generally a protein layer attached to the core surface; the thickness of the layer is at least 5nm. If the refractive index of the protein layer can be made equal to the refractive index of the core, we can get a new fiber waveguide in which the core also contains the protein layer. The fluorescent emission sources are thus inside the core region and generate the highest signal collection efficiency. We also discuss the situation when the refractive index of the protein layer is larger or smaller than that of the optical fiber core.

Lipid monolayers have been studied by pressure-area relationships and fluorescence microscopy, revealing unique phase domain distribution patterns. Acetylcholine receptor and acetylcholinesterase were incorpoated into these membranes, Producing a change in lipid phase structure. Deposition of these membranes onto various substrates was successfully performed.

Reflection oximetry is usually performed by illumination of blood or tissues with monochromatic light at two wavelengths and measurement of the reflected light intensities. We investigated, whether an improvement in accuracy of measurement can be achieved by spectral analysis of the reflected light of a white light source. Flexible quartz fiber optic catheters were inserted in blood vessels. The reflected light was detected by an optical multichannel analyzer with a CCD array. The recording range was 400 to 1000 nm. All experiments were carried out in anaesthetized mongrel dogs. Oxygen saturation of arterial blood was varied by changing oxygen concentration of ventilation. Blood samples were drawn for reference measurements of oxygen saturation by an in vitro method. Three different configurations of quartz fibers were tested: 1) single fiber arrangement 2) double fiber arrangement; 3) statistically mixed fiber bundle. Below 600 nm reflection was only detectable with the monofiber configuration. Above 600 nm the reflection spectra showed considerable differences depending on fiber configuration. Highest sensivity to blood oxygenation was provided by the double and multifiber system. Analysis of blood reflection spectra can be done by two different mathematical models describing the optics of scattering and absorbing materials: 1) the theory of optical diffusion by ZDROJKOWSKI and 2) the two flux approach by KUBELKA and MUNK. It is shown, that both theories essentially yield the same results. Model computations revealed, that oxygen saturation can be determined by integrating the reflected light intensities in two wavelength ranges. This approach yielded excellent correlation with the in vitro method (r = 0.993).

In patients undergoing thoracic surgery central blood volume is subject to large variations and extravascular lung water (EVLW) may change critically due to fluid shifts. Therefore, an accurate monitoring of these parameters, in particular under perioperative conditions, seems to be desirable. The conventional method for determination of EVLW uses a bolus injection of cold indocyanine green dye into the right atrium and indicator detection on the arterial site. However, this technique is known to overestimate extravascular lung water to a considerable amount. In order to investigate the underlying mechanisms of this overestimation, an experimental study was performed with simultaneous measurements of indicator kinetics in the pulmonary artery and the aortic root by a specially designed double fiberoptic device. Experiments were carried out in 9 mongrel dogs under piritramide-N₂0 anesthesia. Pulmonary edema was induced by application of oleic acid. Cold indocyanine green dye was injected into the v. cava and indicator kinetics were recorded from the pulmonary artery and aorta using thermistor-fiberoptic catheters. The transport functions of cold and dye were computed by deconvolution of the corresponding pairs of dilution curves. The mean transit times of the intravascular (dye) and diffusible (cold) indicator were determined by transport functions. Then central blood volume and extravascular lung water could be calculated from these mean transit times together with cardiac output. Results: The average overestimation by the conventional analysis of curves (monoexponetial extrapolation) amounts to 55% under control conditions as well as in oleic acid edema. This overestimation is due to indicator recirculation (39%) and a reversible exchange of heat with prepulmonary structures (16%). More accurate measurements of ETLV can be obtained by deconvolution analysis, if pre- and postpulmonary indicator kinetics are recorded by fiberoptic catheters.

Infrared fiberoptic radiometry of thermal surfaces offers several advantages over refractive optics radiometry. Besides eliminating the need for a direct line of sight to the measured surface, it combines high capability of resolving small areas with high efficiency of power coupling. Those aspects are treated theoretically in this paper. Undesired effects in fiberoptic radiometry are discussed and quantified by a factor termed the figure of merit. We also describe a novel infrared multi-channel fiberoptic radiometer, useful for thermometry in strong electromagnetic fields. With this system, thermometry is possible either in contact or non-contact mode, in the temperature regime 0-70°C, which is attractive for medical applications. The radiometer signal is linearly dependent on temperature, simplifying the calibration significantly. This system was used to monitor and control the temperature of samples heated by microwave and radio-frequency fields.

Infrared signal transmission(1-5µm) trough zirconium fluoride glass fibers is used for non-contact temperature measurement. A radiometer was developed for temperature measurement between 30°C and 150°C. The output signal of the infrared detector, amplified by a lock in amplifier, is processed by a computer in function of controlled blackbody temperature. The dependence of the radiometer signal on the blackbody temperature is presented. Experimental and theoritical results are compared. Wider use of this device can be predicted for medical and biological applications.

The primary objective of this research is to discuss various applications and the pertinent results of an optical fiber thermography system which has been developed to measure temperatures of laser heated biological tissue. This presentation is intended as a follow up to a paper presented at SPIE's conference on laser surgery in 1987. That presentation addressed the actual system design concepts however and presently the theory of operation will be reviewed, system description provided and results presefited.

The depth of penetration (DOP) of a helium-neon (He-Ne) laser (wavelength of 633nm) in whole blood had been widely speculated to range from 0.5mm to 1.5mm. However, due to technical difficulties in determining the DOP, one of which is the problem of detecting the forward scattered light in blood, these speculations had not been quantitatively verified. A knowledge of the DOP as a function of haematocrit and oxygen saturation level is important in the development of a dual-fibre laser Doppler velocimeter for in vitro flow measurements when it is desirable to project the laser beam as far away from the fibre tip as possible. Using two multimode optical fibres, we were able to set up a simple system to measure the DOP in whole blood. The two fibres, potted and polished, were aligned inside a tube filled with blood and with its ends sealed. One fibre admits light from a 15mW He-Ne laser into the blood and the other detects the forward scattered light. The DOP is defined as the separation between the two fibres such that the signal, due to diffusion of red blood cells, disappears in the noise spectrum. Two properties of blood were varied separately while keeping the other constant. Haematocrit (HCT) was varied by dilutions with sodium chloride (saline) solutions and blood oxygenation varied by bubbling air into the sample. The DOP was found to vary with haematocrit in an approximately exponential manner with penetration at HCT 40 of ≈ 1.9mm and at HCT 5 of ≈ 6mm. The DOP also varies with oxygen saturation with a typical range of 1.6mm for desaturated blood to 3mm for saturated blood. These distances will enable sufficient penetration of a two fibre system to allow measurement of blood velocity especially in the arterial circulation.

An electro-optical system has been developed to monitor and control the temperature of the metal tip laser thermal angioplasty catheters. This system captures the infrared radiation (IR) emitted from the hot metal tip during the angioplasty procedure. The infrared energy travels through the same fiber that is used to deliver the laser energy and reaches the photodetector through special collection optics. The photodetector signal is further processed and correlated with the temperature of the probe tip. The temperature of these probes can be controlled in the range of 200 to 600 degrees centigrade. Additionally this infrared system allows performance of diagnostics on the fiber itself and detects conditions that may cause temperature fluctuations at the probe tip. This system has been tested with fibers ranging in core diameter from 116 to 600 micrometers and probe tip diameters from 0.5 to 5.0 millimeters.

To evaluate the usefulness of tissue fluorescence to distinguish normal from atherosclerotic regions in human arteries, we examined fluorescence spectral maps obtained over a wide range of excitation and emission wavelengths from 15 normal and 26 atherosclerotic human aorta specimens. After defining criteria to maximize safety, ease of use, reproducibility and predictive accuracy, we derived an optimum fluorescence discriminant function from this data set which reliably identifies normal and diseased arterial tissue, is independent of sampling device characteristics and vessel geometry, and utilizes simple, available methodologies. This discriminant function, the ratio of fluorescence intensity emitted at 380 nm to that emitted at 420 nm with excitation wavelength of 360 nm [I₃₈₀/I₄₂₀)₃₆₀] compared favorably to other fluorescent discrimination techniques previously described.

Development of a clinically acceptable laser angioplasty system has been hindered by the inability to adequately guide ablative laser radiation to atherosclerotic plaque. Low power laser-induced fluorescence spectroscopy is capable of discriminating normal and atherosclerotic arterial tissue. The purpose of this investigation was to develop and evaluate several spectral classification algorithms that would enable discrimination of atherosclerotic and normal arterial tissue by a computer controlled fluorescence guided laser angioplasty system.

The characterization of laser energy dosages for plaque vaporization using laser thermal-activated probe systems may provide a method to enhance efficiency of vaporization and limit excess thermal tissue damage. This study was conducted using two probe systems currently available for human use; the laser thermal probe or "hot-tip" and the laser thermal-optical probe system or "hybrid". Probe temperature was obtained using a K-type thermocouple. Atherosclerotic human cadaveric plaque was irradiated in air and in saline medium. In air, the volume of plaque vaporized rose with increasing power and exposure time for both probe systems. The mean volume of vaporized plaque at all energy levels was significantly higher for the thermal-optical system compared to the laser thermal system [2.9 μl vs 2.2 μl respectively; p < 0.01]. Also, with both probe systems, comparison of volume of tissue vaporized at the same energy levels showed that below 80 joules of total energy delivered, increasing the power parameter was more efficient in plaque vaporization than increasing the exposure time. Finally, the volume of plaque vaporized per °C was greater for the thermal-optical system as compared to the thermal system [0.0050 vs 0.0036 μl per °C ; p < 0.01]. Under saline medium, the laser thermal probe initiate vaporization only after 60 joules (J) versus 30 J for the thermal-optical system. Additionally, histologic studies showed that deeper plaque penetration occurred with the thermal-optical system compared to the pure thermal system. The results of this study suggest that the laser thermal-optical system is more efficient than the laser thermal system for plaque vaporization.

The effects of pulsed holmium-YSGG laser energy (2.1 μm) on arterial tissue were studied in vitro and in vivo. Delivered through silica optical fibers, the laser ablated calcified and noncalcified tissue in air and saline in a noncontact mode. Early in vivo healing studies in normal canine carotid arteries showed minimal chronic sequelae at 3 weeks.

Laser angioplasty of atherosclerotic iliac arteries of Yucatan miniature swine was performed with an argon laser source coupled to a 200 gm silica quartz fiber with 1.0 mm, 1.2 mm, or 1.5 mm silica ball-tips fused to the distal end of the fiber. After initially failing to cross the lesion with a guide wire, laser angioplasty was attempted in 41 lesions in 22 animals. The laser energy was delivered with the ball-tip in contact with the lesion in 1 to 5 second pulses at a mean power of (±SD) of 2.9 ± 0.2 watts. The average energy delivered per pulse was 8.6 ± 3.7 joules for 7.9 ± 6.5 pulses per lesion. Successful recanalization was determined angiographically. Following laser recanalization balloon angioplasty was attempted to further improve the lumen size. Successful laser recanalization was observed in 35 of 41 (85%) lesions and laser-induced perforation occurred in 5 (12%). No instances of mechanical perforation occurred due to the atraumatic, blunt nature of the ball-tip laser fiber. Laser angioplasty with this modified fiber tip is an effective method for recanalizing obstructed arteries which otherwise would not be amenable to balloon angioplasty.

We successfully demonstrated usefulness of CO laser angioplasty. We investigated in vivo CO laser angioplasty using contact irradiation under visualization by a thin endoscope in atheromatous rabbit aorta, which was temporary filled by saline during the irradiation. 4W, 4s contact irradiation via 400μm As-S glass fiber to atheromatous aorta wall made a fine ablation hole with the minimum heat injuries to remained vascular tissue. A small amount of char was found on ZnSe contact tip after approximately 20 irradiations. But no damage was occurred in the tip. We think the visualization in the arterial lumen by the thin endoscope may be useful for pre-diagnosis and targeting of laser therapy.

A clinical trial was performed to study the efficacy of the percutaneous excimer laser angioplasty system and to develop and modify the technique and equipment for this system. Follow-up data on the treated patients was obtained and long-term results for different anatomic subgroups were studied.

Pulmonary angioscopy has been shown to have a clinically useful role in the diagnosis of causes of chronic pulmonary artery obstruction and in determining operability. These results are based on the use of traditional medical endoscope technology and a distal view-ing balloon. While the technique is clinically useful, modifications are needed to make the technique more readily available to clinicians. Needed modifications include narrower bundles, improved flexibility of the bundle, and a secure (preferably disposable) mechanism of balloon attachment. These changes need to occur without sacrifice of current optics or distal tip deflection. These changes appear to be possible and would facilitate the wide-spread use of angioscopy in a large volume, branching vascular bed.

I have been asked to talk about the clinical problems encountered when performing coronary angioscopy. By definition, this discussion will reflect negatively on the procedure. Nevertheless, after presenting some of the data, I hope you will leave thinking optimistically about the future of coronary angioscopy. The first topic that I would like to address, as shown in Figure 1, concerns the goals for coronary angioscopy. What great discoveries might we ekpect from this tool? Is the potential benefit worthy of a large research and development investment? Then, assuming these goals are meritorious, I will compare the difficulties of percutaneous angioscopy with that of a more fully explored technique- intraoperative angioscopy. I will next describe the differences between percutaneous angioscopy of peripheral vasculature, a procedure enjoying more widespread use, and percutaneous coronary angioscopy (a technique less often utilized). I will then outline the basic requirements for any percutaneous coronary angioscopy system whose attributes can resolve some of the inherent challenges of the technique. Even if this hypothetical instrument were developed and proved to be safe and functional, angioscopy will always have intrinsic limitations. I will next outline these shortcomings. This will be followed by a more optimistic topic- a review of the published studies that have utilized percutaneous coronary angioscopy. Finally, I will speculate on developments in coronary angioscopy for the near future.

The development of high density ultra-thin image guide is described. For this development a quantitative evaluation system and actual scope evaluation system were adopted. 2000, 3000 and 6000 pixels ultra thin image guides were introduced.

The image transmission characteristics of shorter silica based imagefiber has been investigated. It has been found that the image quality strongly depends on the length and the suitable structure to the fiber length exists for the imagefiber. And as a result, it has been clarified that the most part of the unwanted waves can be removed by twisting or bending the imagefiber.

We successfully made visualization of 81 human coronary arteries in 75 patients by newly developed 5F coronary balloon endoscope catheter. In all case, patient target lesions were directly visualized as one of ordinary diagnosis. 80% of the success percentage for sufficient visualizaion to clinical diagnosis was attained.

A new ball-tip fibre optic device has been assessed for the purpose of laser angioplasty. A pulsed Neodymium-YAG laser producing 100 p.s pulses at a repetition rate of 10 Hz was used to ablate human cadaver arterial tissue using approximately 500 mJ per pulse at a wavelength of 1064 nm or 300 mJ at a wavelength of 1.3 μm. Both wavelengths are capable of ablating atheroma with little histological evidence of surrounding thermal damage. Crater depths of about 5 μm per Joule were produced using 1064 nm with normal tissue exposed under saline. Crater depth increases by about 50% when exposures are carried out under blood and when diseased arterial tissue is exposed the crater depth is almost doubled. Depth of ablation with a wavelength of 1.3 μm is 3 to 4 times greater than with 1064 nm for the same exposure and a similar increased response is seen for diseased tissue or in the presence of blood. Further experiments at 1064 nm have shown that the ball-tip device has advantages over bare fibre or sapphire tipped devices in the recanalisation of occluded femoral vessels in an artificial circulation.

Currently there is no available system capable of providing real-time absolute dimensional analysis of features within the field of view of conventional angioscopes. This paper describes a method which utilizes computer-based image processing equipment and novel algorithms to address this problem. By analyzing the magnification characteristics of an angioscope and analyzing any single feature from multiple angioscopic views, the cross-sectional area of the feature may be calculated. Experimental results indicate both a high accuracy and the feasibility of this approach.

As is well known visible and near infrared beams are able to use ordinary quartz fiber. There are needed some technique about ultraviolet beams. We have been investigating about that, one of the technique is to OH on added to high purity quartz fiber. So in our laboratory, we have obtained 85%/m 248nm beam transmittance in over 200ppm 0 ion added quartz fiber at the milliwatt power regions. On the other hand, we have investigating 308nm beam delivery with the OH ion unadded high purity quartz fiber. The transmittance was over 85%/m , therefore the high purity quartz fiber is usable to XeC1 laser beam delivery systems,we have been investigating also UV-beam delivery with the metal-polymer compound he tube.

Recently many researchers, doctors and instrument companies have begun developing fiber optic laser delivery systems to accomplish less traumatic surgery or localized irradiation treatmentE13. With high power levels, particularly in short bursts, fibers with cores larger than telcom are needed to keep the power densities from approaching the damage threshold of silica. Among the many advantages of using optical fibers in laser surgery are the following: microsurgery can be employed, trauma is reduced, access to interior through catheter introduction into vascular, gastrointestinal or respiratory tracts, accurate application of laser power through a lightweight medium to provide localized irradiation as well as surgical removal , and the devices are sterilizable and of moderate cost permitting one-time use (disposable) probes.

Transmission characteristics of silica based large core fibers ( SLF ) have been investigated. Concerning with the spectral loss in ultra violet region, a pure silica core and B,F doped silica cladding fiber showed the lowest value approximately 3 dB/m at 200 nm wavelength. It has been clarified that the bending loss of SLF strongly depends on the Numerical Aperture and core diameter. It has been found that excess loss due to bending has the methodical relations with core diameter and bending diameter. On the other hand, a fiber was fractured by about 20 times of its diameter. As a result, it has been clarified that large NA fiber has the advantage in laser surgery. This paper describes the details of the transmission characteristics and the mechanical reliability of SLF for medical usage.

In this paper only the problems regarding to the input-coupling and transmission properties of the fibre are discussed. For a given Excimer laser system (Technolas MAX 10) the laser beam was prepared to transmit pulse energy densities up to 25 J/cm² to fibres of 200 - 600 μm core diamter. Coupling of Excimer radiation into Q/Q fibres is limited by destruction of the front surface or the core of the fibre (Fig. 1). This limit is of the order of 40 - 50 J/cm² for 308 nm and 50 nsec pulse length. To reach this limit it is necessary that the laser beam fulfills the following three demands: 1. The laser beam should have a diameter slightly less than the fibre core diameter and he should have flat intensity profile. 2. The beam divergence (^θ_B) should about the same as the fibre aperture (^θ_F). 3. The point 1 and 2 can be fulfilled, if the beam parameter product d ^θ_B(d = waist radius) is equal or less than the parameter product of the fibre.

Different laser-optical waveguide laser system suitable for effectiv tissue ablation are analysed. The emphasis is made on excimer, erbium, CO and CO₂ lasers operating with optical fibers or hollow metal waveguides.

Infrared (IR) fibers and delivery systems for use with surgical lasers have been or are being developed by at least three dozen competitors worldwide. Clad and unclad chalcogenide, fluoride, metal halide and single crystal fibers, and rigid and flexible metal, polymer, glass, and ceramic waveguides have been investigated. While there are now half a dozen flexible waveguides and an equal number of rigid waveguides marketed for surgical laser applications, there are still no commercially available IR fiber delivery systems. At least two 10µm IR fiber developers, in the author's opinion, have produced surgical-grade fibers, and one of these has completed development of and received FDA marketing approval for a surgical laser delivery system incorporating a novel, disposable, flexible IR fiber. However, neither of these developers is currently pursuing commercialization of the fibers or delivery systems; nor has there been significant interest from medical laser competitors or large healthcare companies. Development of fluoride fibers for use with mid-IR lasers, such as Erbium-YAG, continues, but no commercial medical products using this technology have yet been announced. It is ironic that there seems to be little business interest currently in surgical IR fibers, despite the identification of numerous potential surgical applications where the use of a flexible delivery system could make a procedure less invasive, or allow new procedures to be performed.

The existence of a threshold photodynamic dose has been postulated because of the sharp demarcation between an area of PDT necrosis and normal undamaged tissue 1. An experiment was designed to measure the light intensity at various distances from the source of irradiation during PDT. Experiments were performed on normal rodent colon using a standard intravenously injected dose of the photosensitiser aluminium sulphonated phthalocyanine (A1SPc). Irradiation was performed 1 hour after injection of 5mgkg^-1 using an argon pumped dye laser delivering 100mW from the end of the fibre. The time of irradiation was varied and the amount of necrosis measured 72 hours after treatment. The light intensity at specific points could be correlated with the amount of necrosis. Threshold photodynamic effects are important, if a total photodynamic dose (light fluence x photosensitiser concentration) is considered, since selective tumour destruction may be possible if the dosimetry is carefully adjusted to allow a photodynamic thresholdto be reached in the tumour and not in the normal colon. Adjustment of the light or photosensitiser dose can be used to manipulate the effect. Under apprpriate circumstances A1SPc can be photodegraded so that a total threshold photodynamic dose may never be reached in normal colon.

Most current applications of lasers at high or low power use a single fibre. There are many uses for such delivery systems for tumour debulking, and at low powers for interstitial laser hyperthermia and photodynamic therapy. However, there are limitations due to the comparatively small amount of necrosis that can be achieved in photodynamic therapy and interstitial laser hyperthermia with a single fibre. With multiple fibre application, larger areas of tissue can successfully be irradiated, affecting a volume similar to that of clinical tumours, making this extention of laser usage of potential in the clinical treatment of some cancers. There is a need for further developments in fibreoptic technology to allow more efficient application of multiple fibre systems both for power delivery and also to use the same system for simultaneous fibreoptic sensory measurements to monitor tissue changes during irradiation.

Plastic hollow fibers for the transmission of CO₂ laser energy in curved path were produced by plating the inner face of plastic tubes with a metal film and a dielectric film. These fibers could transmit high power (25 watts) with low losses even through bendings. Bleeding ulcers in dogs' stomachs were successfully treated with the fibers which were inserted into the stomach through the oesophagus.

Excimer laser ablation (308nm) of canine aortic samples was performed via an UV grade fused silica fiber. The influence of the repetition rate (2-20 Hz) and of the applied pressure (1-6 Atm) on the ablation rate was studied. Operative fluences between 30mJ/mm² to 40mJ/mm² were used. Results show a linear dependence of the ablation rate on the repetition rate for all fluences. The linearity was also preserved at various applied pressures and at low repetition rates for the same range of fluences. A saturation effect was observed at increased values of repetition rate. No dependence of the ablation rate on the repetition rate was observed when the experiment was performed using direct irradiation with a mask instead of a fiberoptic.

The primary goal of this study was to devise an Optical Fiber based monitoring scheme of the arterial wall ablation by the use of laser induced fluorescence. Preliminary results indicate that the time evolution of the fluorescent light follows complex exponential decays. A comparison of the time characteristics of the decays with the findings of other investigators suggests that these decays may be related to the ablation of the successive arterial wall main layers.

Clinical studies in photodynamic therapy (PDT) have utilized lasers to take advantage of coupling efficiencies to optical fibers allowing light to be delivered to many areas of the body. This is particularly true in endoscopic PDT. Both interstitial and superficial delivery techniques can be applied using one of a variety of delivery fibers available. A fiber with an optically flat end with a lens to produce a spot with a homogeneous intensity is used for superficial applications. Diffusers of various lengths, at the tip of a fiber, produce a cylindrical isotropic pattern and are suited for either intraluminal or interstitial illuminations.

The newest developments in the evaluation of fluorescence detection in photodynamic therapy deal with the ability to distinguish tissue autofluorescence from that of injected photosensitizers. The ability to make this distinction as well as detect fluorescence slightly above background emanating from occult metastases is paramount for the diagnosis of disease. The delivery of light to excite and detect background fluorescence as well as photosensitizer fluorescence in tissues has been accomplished using two HeNe lasers emitting at 632.8 nm and 612 nm delivered through a single quartz fiber optic. Chopping at different frequencies, contributions of fluorescence may be separated. Fluorescence is picked up via a 400 micron quartz fiber optic positioned appropriately near the target tissue. Extraction procedures to quantitate Photofrino II concentration in tissues correlated with fluorescence measurements from instrumentation developed for in vivo fluorimetry were applied for the detection of low drug levels in occult metastases of the lymph nodes. These techniques have been initially applied to detect low levels of drug in DRA mice bearing the SMT-F tumor, which has been extensively studied in our laboratory. The data show the ability of the techniques to detect very low levels of porphyrin in the tumors after low, non-therapeutic doses of injected photosensitizer. The Pollard rat prostatic adenocarcinoma (PA-III) model was chosen for this study because of its characteristic pattern of metastases involving only ipsilateral lymph nodes. Early studies on this lymph node model have shown the ability of the detection device to measure low levels of drug in non-palpable occult metastases in the nodes. The findings show that the detection of small numbers of metastatic cells is possible (<100 cells) with injected DHE doses of 0.25 mg/kg.

The use of single fibre for interstitial low power laser hyperthermia (1-2 W) is associated with the development of a lesion of thermal necrosis measuring 1.4-1.8 cm in liver, pancreas and prostate. These lesions heal safely and can be well visualised with ultrasound. The use of a multiple fibre (4) system has enabled the production of larger lesions in all these organs which take a longer time to heal than single fibre lesions, but do so safely. Again, ultrasound enables these lesions to be studied in their creation and in their resolution. Following this experimental work early clinical application to a variety of otherwise untreatable tumours (breast, skin, pancreas and liver) has been carried out. This has resulted in a partial response in all treated and complete response in a smaller number of cases. The method appears to be safe and practical for the treatment of some tumours.

We investigated a fiber-optic infrared radiation diagnosis for in vivo urinary tract tissue discrimination during laser urinary stone fragmentation. Such in vivo analysis may be useful for preventing mis-irradiation to surrounding tissue. Since we plan to use infrared lasers and infrared fibers to the urinary stones photofragmentation, the pulsed photothermal radiometry(PPTR) was employed in this study due to its simplicity and benefit of common use of the infrared laser and fiber to therapy and diagnosis. We successfully demonstrated a discrimination between urinary stones and urinary tract tissue, by a chalcogenide glass fiber-optic CO laser induced PPTR analysis.