Hollow waveguides are an attractive alternative to conventional solid-core IR fibers. The hollow core structure is well suited for the transmission of high laser powers as well as for some broadband sensor applications such as gas sensing and radiometry. Over the past 15 years a variety of fabrication techniques and hollow configurations have been studied. Today losses for these unique guides are as low as 0.1 dB/m and laser powers as high as 2.7 kW have been transmitted. In this paper we review the current status of hollow waveguides and indicate some of the most promising applications for this technology.

Silica-core optical fibers have long been the standard delivery medium for medical laser delivery systems. Their high strength, excellent flexibility, and low cost continue to make them the fiber of choice for systems operating from 300 to 2200 nm. An overview of the current fiber constructions available to the industry is reviewed. Silicone-clad fibers, hard- fluoropolymer clad fibers and silica-clad fibers are briefly compared in terms of mechanical and optical properties. The variety of fiber coatings available is also discussed. A significant product development of silica fiber delivery systems has been in side-firing laser delivery systems for Urology. These devices utilize silica-core fibers to project the laser energy at a substantial lateral angle to the conventional delivery system, typically 40 to 100 degrees off axis. Many unique distal tips have been designed to meet the needs of this potentially enormous application. There are three primary technologies employed in side-firing laser delivery systems: reflection off of an attached medium; reflection within an angle-polished fiber through total internal reflection; and reflection from both an angle-polished fiber and an outside medium. Each technology is presented and compared on the basis of operation modality, transmission efficiency, and power-handling performance.

The enhancement of polycrystalline MIR-fibers for 4 - 16 um range allows to spread their practical usage in medicine. The improved parameters of core/clad MIR-fibers are considered for the main areas of medical applications: power delivery for CO2-laser surgery; fiber probes for IR-spectroscopy diagnostics; and fiber pyrometry or IR-imaging with fiber bundles.

The success of a medical laser treatment is highly dependent on the optical, thermal and mechanical characteristics of an optical system or shaped tip on the end of a fiber '. Atpresent, this can be well illustrated by the laser delivery devices which are developed for the treatment of benign prostatic hyperplasia (BPH) 2 Thedesigns are based on either side-firing fibers or contact probes coupled to continuous wave (CW) laser systems. For the first, the optical properties are important and, for the latter, the thermal and mechanical properties.

Sapphire fibers grown at 20 mm/min in helium, using an improved laser-heated pedestal growth apparatus, have been shown to exhibit very low losses. The laser damage threshold and bending loss of these fibers have been evaluated. The best fiber forms for energy delivery may be a 100-micron diameter fiber with flared ends to increase the power handling capability while retaining the flexibility. Such a fiber has been successfully grown in our laboratory.

Er:YAG laser energy is highly absorbed by water, and therefore can provide excellent cutting precision with minimal thermal damage to surrounding tissue. Single crystal sapphire fibers are capable of transmitting Er:YAG laser energy with low loss and, additionally, they are chemically durable and bio-compatible. In this study, 300 micrometers diameter sapphire fibers were evaluated for use in surgical applications. Scattering and absorption losses, effective NA, and power handling capabilities were measured. The fibers had losses less than 1 dB/m, an effective NA of 0.2, and damage thresholds exceeding 1.2 kJ/cm². The high damage thresholds were achieved only after a laser conditioning process at the proximal end of the fiber.

Utilization of the promising Erbium:YAG laser has been hindered by the lack of a truly effective optical fiber delivery system. In a National Eye Institute funded Phase I SBIR, sapphire fibers produced by the Saphikon Edge-defined, Film-fed Growth (EFG_TM) technique were proven effective in delivering 2.94 micron Er:YAG laser energy in pre-clinical in-vitro ophthalmic procedures. A brief overview of the results of both the ab-externo sclerostomy and laser trabecular ablation procedures is given. A Design of Experiments methodology was used to significantly reduce average loss and variability of the EFG fibers, with losses below 1 dB/meter demonstrated in multi-meter lengths of 300 micron diameter fiber. Laser damage threshold levels above 1000 J/cm², and power handling capability over 8 watts has been demonstrated. Details of ongoing and planned pre-clinical and clinical studies in ophthalmic, otologic, and dental procedures are discussed, along with other, non- medical applications for the sapphire fibers. Introduction of additional fiber diameters and devices is also reviewed.

We have fabricated long lengths of low loss sulphide and telluride glass fibers for the 1 - 6 and 3 - 12 micrometers regions, respectively. Minimum losses for core/clad fibers are approximately 0.6 and 0.7 dB/m, respectively, while core-only fibers have exhibited losses of about 0.1 dB/m. The measurements have been performed on long lengths, typically 7 - 50 meters. Fiber strengths are reasonable for many short length applications, but improved processing will lead to stronger fibers for long length applications. These fibers are candidates for chemical sensors and for IR laser power delivery.

A new generation of infrared fibers, the TeX glass fibers, operating from 3 to 13 micrometers , exhibits a minimum attenuation of about 0.5 dB/m in the 7 - 9.5 micrometers range. A polymer coating on these fibers increases the mechanical properties and fibers with high flexibility have been obtained. CO₂ laser power delivery has been performed using a TeX glass fiber. More than 2.6 W has been transmitted through a 1 meter long fiber by injecting the maximum output power of the laser. One of the most promising applications of these glass fibers is the remote spectroscopy using either evanescent wave or direct absorption analysis. These technologies provide an opportunity to realize in situ and on-line control of chemical and biological processes. Our prototype system using a FTIR spectrometer allows quantitative and qualitative detection of organic species such as alcohol, cosmetic products which have their fingerprints in the spectral region from 3 to 13 micrometers . The detection efficiency using evanescent wave absorption has been studied as a function of the fiber's diameter. It has been found that this efficiency increases very rapidly when the fiber's diameter decreases.

Bundles of silver halide optical fibers have been fabricated by extrusion of preforms containing core-clad fibers. Silver halide fibers are transparent in the mid-IR spectral range (2 - 20 micrometers ), and therefore ordered arrays of such fibers have the potential to deliver thermal images at room temperature. Several kinds of bundles were prepared, consisting of 100 to 2500 fibers, with a fill factor of 0.34. Thermal images were delivered through the bundles and recorded using a IR cooled camera. This paper discusses the optical properties and the imaging characteristics of bundles with several fiber densities of 3 - 160 fibers per mm² and lengths up to 30 cm. The modulation transfer function of the bundles was measured by the knife edge sampling process, and by `bar-chart' imaging. The maximum spatial frequency that could be resolved after passing through a typical bundle was 3.5 lines per millimeter.

Heat-resisting polyimide-coated silver hollow glass waveguides have been fabricated for infrared medical laser light transmissions. The waveguides have inner diameters of 700 and 530 micrometers and the length of 1 m. The measurements of the guiding loss spectra show the low-loss property of the waveguides at the desired wavelengths. Moreover, Er:YAG laser light has been transmitted by the 700 micrometers -bore waveguide with the losses as low as 2.2 dB even when the waveguide is bent with a bending radius of 15 cm (180 degree(s)-bend).

KrF excimer laser (248 nm) is expected to be the new therapeutic instrument in the medical field. However, there is still not the optical fiber which has enough durability for the high power energy of KrF excimer laser. We have developed the optical fiber for transmitting the light of the high power KrF excimer laser. This fiber consists of the pure silica core with a large amount of OH, and also has been specially treated during fabrication. As a result, the newly developed fiber has achieved to transmit the light of KrF excimer laser efficiently.

We report the influence of growth atmosphere and purity of starting material on the uv-visible transmission characteristics of sapphire fibers grown by the laser-heated pedestal growth method. Improved performance in the visible has been achieved by annealing the fibers to remove color center absorption associated with an impurity, likely a transition metal.

Although non-invasive methods for in-situ analysis of laser-tissue interaction are not available yet, it continues to be an area of increased interest owing to its potential. This paper describes the development of an integrated diagnostic and therapeutic laser procedure through in-situ monitoring of the optical tissue characteristics in a non-invasive manner. Biological tissues are highly scattering media. The system under development uses a broadband (white-light) interferometer that derives the scattered signals obtained from different depths of the biological medium. The tissue light signature obtained in this manner will be curve fitted to the appropriate computer simulation resulting from the optical properties particular to well defined tissues, resulting from simulations within a range of optical parameters. The beam profile of the irradiation source appears to affect the ability to distinguish between certain tissues. A single mode fiber in tissue contact produces a statistically significant different light signature for at least three myocardial tissues. However, the theoretical resolution is limited to 4 to 8 mm depth. Identification of the local optical characteristics will provide discrimination between healthy and pathological conditions in addition to real time assessment of dosimetry.

Various technologies based on different light—tissue interaction phenomena have been developed for medical applications. Now the progress in the area of laser medical technologies depends more and more from the design of a special fiber—optical tools1'2 . Thus the flexible fabrication technique for such fiber tools manufacturing is needed . These tools should serve for a laser beam forming ( local spot or volume irradiation, inclination of irradiation direction, spot size and the intensity distribution variation, etc.), for the most effective use of laser power in a distinct medical operations. Traditional optical elements ( i.e. lenses, prisms, mirrors ) could not be used as for laser treatment in local difficult—to-reach places of the body in the most of otolaringological,proctological, neurosurgery and eye microsurgery operations as for endo—, laparo- and torocoscopical laser operations as well. The creation of a number of fiber-end optical components FEOC ), such as lens—ended fibers, scatterers,side—fiber components, etc. gives a broad way for laser medicine applications independently from the localisation of an object of treatment (internal or external tissues of pacient). These fiber tools could be based on the fiber tip forming , its orientation relatively the fiber axis or/and on partial changing the total internal reflection conditions upon the determined length of fiber. These irradiation—forming FEOCs having about the fiber diameter size it is possible to include in endoscopic laser complexes for the solving of different tasks of modern medicine and diagnostics.

This study evaluated the acute and chronic effects of diode laser (960 nm) prostatectomy using a Prolase II fiber in a canine model (n equals 5). The laser fiber consists of a 1000 um quartz fiber which reflects a cone of laser energy, at 45 degree(s) to the axis of the fiber, into the prostatic urethra (Visual Laser Ablation of Prostate). Perineal access was used to guide a 15.5 Fr cystoscope to the level of the prostate. Under visual guidance and continual saline irrigation, 60 watts of laser power was delivered for 60 seconds at 3, 9, and 12 o'clock and 30 seconds at the 6 o'clock (posterior) positions for a total energy fluence of 12,600 J. One prostate received an additional 60 second exposure at 3 and 9 o'clock for a total fluence of 19,800 J. The prostates were evaluated at one day (n equals 1) and 8 weeks (n equals 4). The histopathology of laser effects at one day show areas of necrosis with loss of glandular structures and stromal edema. Surrounding this area was a zone of degenerative glandular structures extending up to 17.5 mm (cross sectional diameter). The histopathology of the 8 week laser treated animals demonstrated dilated prostatic urethras with maximum cross- sectional diameter of 23.4 mm (mean equals 18.5 +/- 3.9 mm). This study demonstrates the effectiveness of diode laser energy for prostatic tissue coagulation and eventual sloughing. The results also demonstrate the safety of diode laser energy, with similar tissue response as seen with Nd:YAG laser, for laser prostatectomy.

A high brightness laser-diode surgery system is described. As laser diode brightness is far below that of high-power gas or solid-state lasers, we designed a system by combining two high-power diode lasers of two different frequencies (patent pending). The combined power is coupled into a 600 micron fiber. We thus doubled the brightness at the distal end of the fiber. High power and high brightness are required in some medical procedures. Around this basic concept we built a 20 watt surgery system with emphasis on compactness and features. The system weighs only 7 kilograms, can be placed on a table or be hanged on a wall, offers optional three subcutaneous temperature measurement probes and has a rich menu of operating options displayed on an angle-adjustable LCD graphic display.

Semiconductor laser diodes are compact, efficient and reliable sources of laser light and 25 W fiber coupled systems developed by Diomed have been in clinical use for over three years. For certain applications, particularly in the treatment of benign prostatic hyperplasia and flexible endoscopy, higher powers are desirable. In these applications the use of flexible optical fibers of no more than 600 micrometers core diameter is essential for compatibility with most commercial delivery fibers and instrumentation. A high power 60 W diode laser system for driving these small core fibers has been developed. The design requirements for medical applications are analyzed and system performance and results of use in gastroenterology and urology with small core fibers will be presented.

Design principles and rules are currently being formulated for building intelligent machines for `factories of the future'. The intelligent machine is one which has control functions that resemble the `brain', `eyes' and other anthropomorphic substitutes for the skilled expert. These skills are related to the expert's knowledge and abilities to plan complex actions and to detect errors with a continual upgrade of machine understanding. A craft related language enables a high level of communication between the system and the operator. These same capabilities can be embodied in a medical laser system. This paper will define the key characteristics of a smart medical laser and will describe the advantages of an intelligent system based on diode laser technology. System control functions and software architecture will be explained and the main subsystems highlighted.

Interstitial photothermal coagulation has long been recognized as a potential important, minimally invasive modality for treating a variety of pathologic conditions. We present two different technologies for interstitial photothermal coagulation of tissue with infrared lasers: An optical fiber with a radially symmetric diffusing tip for deep coagulation, and a flat bare fiber for the coagulation of thin and long lesions by longitudinally moving the fiber while lasing in concert. Urology and Gynecology Fibers: The fibers are 600 microns diameter with 20 - 40 mm frosted distal tips protected by a smooth transparent cover. When used with a Neodymium:YAG (Nd:YAG) laser, the active fiber surface diffuses optical radiation in a radial pattern, delivering up to 40 W power, and thus providing consistent and uniform interstitial photothermal therapy. Coagulation depth ranges from 4 to 15 mm. Animal studies in the United States and clinical studies in Europe have demonstrated the feasibility of using these fibers to treat benign prostatic hyperplasia and endometrial coagulation. Rhinology Fiber: The fiber is an 800 micron diameter flat fiber operated at 8 W power level while being interstitially pushed and pulled along its axis. A long and thin coagulated zone is produced. The fiber is routinely used for the shrinking of hypertrophic turbinates without surrounding and bone mucusal damage in ambulatory environments.

Commercial CO₂ surgical lasers introduced in the early 70's employed continuous-wave operation only. Following several years of clinical research and applications, it was realized that for some procedures surrounding thermal necrosis was too excessive. The Superpulse mode, adapted from industrial CO₂ laser ceramic scribing techniques, was found to be advantageous and was thus incorporated in surgical systems. Over the years, additional modes such as the Pulser (chopped) mode were adapted. However, only recently a better understanding of CO₂ laser-tissue interactions has led to significant improvements in char- free techniques, especially for non-focused, tissue surface treatments. These techniques are based on high energy pulse modes such as the Sharpulse^TM as well as innovative beam scanning devices like the SwiftLase^TM and SilkTouch^TM. The evolution of these different techniques and their basic physical principles will be discussed, and histologies showing reduced tissue carbonization and thermal necrosis will be presented.

Researchers at the University of Texas at Austin's Biomedical Engineering Laser Laboratory investigating the medical applications of lasers have worked toward the development of a retinal robotic laser system. The ultimate goal of this ongoing project is to precisely place and control the depth of laser lesions for the treatment of various retinal diseases such as diabetic retinopathy and retinal tears. Researchers at the USAF Academy's Department of Electrical Engineering have also become involved with this research due to similar interests. Separate low speed prototype subsystems have been developed to control lesion depth using lesion reflectance feedback parameters and lesion placement using retinal vessels as tracking landmarks. Both subsystems have been successfully demonstrated in vivo on pigmented rabbits using an argon continuous wave laser. Work is ongoing to build a prototype system to simultaneously control lesion depth and placement. The instrumentation aspects of the prototype subsystems were presented at SPIE Conference 1877 in January 1993. Since then our efforts have concentrated on combining the lesion depth control subsystem and the lesion placement subsystem into a single prototype capable of simultaneously controlling both parameters. We have designed this combined system CALOSOS for Computer Aided Laser Optics System for Ophthalmic Surgery. An initial CALOSOS prototype design is provided. We have also investigated methods to improve system response time. The use of high speed non-standard frame rate CCD cameras and high speed local bus frame grabbers hosted on personal computers are being investigated. A review of system testing in vivo to date is provided in SPIE Conference proceedings 2374-49 (Novel Applications of Lasers and Pulsed Power, Dual-Use Applications of Lasers: Medical session).

As part of our Computer-Assisted Surgical Techniques (CAST) program, we use computers to guide surgical lasers, create minimal incision widths, regulate the rate of tissue ablation, monitor the types of tissue being ablated with photo-acoustic feedback, and track and compensate for patient motions due to respiration and heart beat. The union of the computer, robotics and lasers can assist the surgeon and permit several new applications. Although these advances in laser surgery appear to have obvious benefits, it is important to evaluate and quantify the clinical advantages. We have compared the CAST system to manually controlled laser surgery and studied the wound healing after laser incision. We have found definite advantages to the CAST system. However, the computer, alone, cannot compensate for the thermal damage lateral to the incision site. The results suggest the need for motion tracking and compensation to be a part of the CAST system.

The authors have introduced laser phototherapy for the treatment of neonatal jaundice. Clinical trials have demonstrated its high efficacy compared to the conventionally used fluorescent phototherapy. In this paper a new modification to laser irradiation in phototherapy can be achieved by scanning the laser output beam in the selected wavelength of irradiation (488 nm) through a fiberoptic bundle which irradiate the skin of the baby. Scanning of the laser beam provides intermittent irradiation at high frequency, which can provide the same therapeutic efficacy with almost half the power of laser irradiation.

We describe layer-by-layer char-free ablation of hemorrhoids and other rectal lesions at very low CO₂ laser power levels with a miniature `SwiftLaser' optomechanical flashscanner. Increased speed with excellent control, very shallow thermal damage, and less postoperative pain are the main advantages of the flashscan technology in rectal surgery.

We are privileged to be living in an era in which surgery is undergoing a profound change. Technology is a major part of this advance. The old `surgical interface', the eye and hand of the surgeon, is being replaced by a technologically advanced interface that will enhance the surgeon's capabilities while preserving the benefits of the minimally invasive approach. In this presentation we will review the technologies that are contributing to this progress.

Today's presentation discusses where the medical laser market is today; what the near-term future looks like; some of the specialties/applications that will lead the way; and a brief discussion of future trends.

Many laser medical procedures can be improved by dispensing exogenous fluids onto the tissue during irradiation. Examples include the dispensing of coolants, photoabsorptive enhancers, photoreflective tissue shields, photoactivated tissue solders, fillers, or surface sealants. The main obstacle to the use of such auxiliary fluids is the difficulty of dispensing them in a convenient, interactive fashion while operating the laser. We have adapted ink-jet printing technology to this problem of dispensing auxiliary fluids during laser procedures. The technology can dispense fluids with exquisite volumetric, spatial, and temporal precision. In principle, one or more fluids can be dispensed interactively from nozzles similar in size to the optical fibers and microlenses that are used for the lasers. Compact handpieces or endoscopic tools that will incorporate fluid MicroJets and laser optics can be envisioned. The enhancements to laser surgical technology that could be afforded by the use of fluid jetting will be discussed. Examples from ongoing work in dentistry, orthopedics, and dermatology are presented. Supported in part by NIH SBIR's DE10687 and GM50602.

Pulsed laser output, when coupled to a microscope, is a powerful tool for microablation of samples. Applications range from ablation to cellular material to destruction of conducting traces in integrated circuits. Coupling the laser to the microscope for optimum performance, however, is not a simple exercise. The optical characteristics of both the laser and the microscope must be carefully considered. This paper discusses the techniques which are important when coupling a laser to a microscope.

A laser system can be coupled to a light microscope for laser microbeam ablation and trapping of single cells in vitro. We have extended this technology by sensitization of target structures with vital dyes to provide selective ablation of specific subcellular components. Isolated auditory receptor cells (outer hair cells, OHCs) are known to elongate and contract in response to electrical, chemical and mechanical stimulation. Various intracellular structures are candidate components mediating motility of OHCs, but the exact mechanism(s) is currently unknown. In ongoing studies of OHC motility, we have used the microbeam for selective ablation of lateral wall components and of an axial cytoskeletal core that extends from the nucleus to the cell apex. Both the area beneath the subsurface cistemae of the lateral wall and the core are rich in mitochondria. OHCs isolated from guinea pig cochlea are suspended in L- 15 medium containing 2.0 (mu) M Rhodamine 123, a porphyrin with an affinity for mitochondria. A spark-pumped nitrogen laser pumping a dye cell (Coumarin 500) was aligned on the optical axis of a Nikon Optiphot-2 to produce a 3 ns, 0.5 - 10 micrometers spot (diameter above ablation threshold w/50X water immersion, N.A. 0.8), and energy at the target approximately equals 10 (mu) J/pulse. At short incubation times in Rh123 irradiation caused local blebbing or bulging of cytoplastic membrane and thus loss of the OHC's cylindrical shape. At longer Rh123 incubation times when the central axis of the cell was targeted we observed cytoplasmic clearing, immediate cell elongation (approximately equals 5%) and clumping of core material at nuclear and apical attachments. Experiments are underway to examine the significance of these preliminary observations.

With the recent availability of Beta Barium Borate (BBO) crystals in useful sizes at acceptable market prices, the promise of Optical Parametric Oscillators (OPOs) becoming practical tunable systems is finally being realized. Wavelength coverage from such systems extends from 420 nm to over 2400 nm when pumped in the UV. For medical applications their usage will be limited in the near term to low repetition rates (< 50 Hz) nanosecond pulsed systems. The pump lasers of choice will be flashlamp pumped Q-switched Nd:YAG lasers. As higher repetition rate (kHz) Q-switched diode pumped solid state continue to increase in energy and decrease in price, they are likely to also become viable pump sources for lower energy OPO systems. Energy output in excess of 100 mJ from low repetition rate OPO systems may make them suitable for selective absorption applications in medicine such as colored tattoo removal or treating vascular lesions. For such high energy devices peak powers necessitate the use of articulating arms for beam delivery. For high repetition rate systems, energy outputs will be in the range of 100 to 500 (mu) J at kHz frequencies (up to 1 W average power). Peak powers are low enough that fiber optic delivery is possible. These systems may find selective absorption applications in ophthalmology.

A pulsed erbium garnet laser (30 Hz at 2.78 micrometers ) was used to characterize cutting on various soft tissues. Bovine heart, porcine liver and chicken breast were cut, and the resultant craters cut were microscopically examined. The variation of crater depth with average power settings and number of pulses was studied in detail. The second part of the study was to evaluate the coagulation effect of the erbium laser on surgical cuts induced into mucosal soft tissues. Conclusions of this study will be provided from qualitative analysis of the histopathological data.

In our research, the Er:YAG laser has demonstrated a wide range of clinical capabilities based on its various mechanisms of cutting. In this article, I will discuss three of those mechanisms, presenting supportive research studies to define these laser-tissue interactions. To illustrate the clinical significance of this basic research, I will present specific clinical results in dentistry, both hard and soft tissue, and ophthalmology.

In vitro study on extracted human teeth of the influence of Er:YAG laser power on the ablation efficiency and thermal damage has been carried out. Dependence of the diameter and depth of ablation holes in dentin and enamel was measured as a function of laser pulse energy and repetition rate. The drilling speed per pulse was found to be independent of the repetition rate in the range of 1 - 20 Hz. In the studied laser power range, and under water spray cooling, no visible damage was observed in enamel. In dentin, carbonization was observed only at very high laser powers. Experimental results show that at high laser powers thermal damage occurs more readily at higher energies per pulse than at higher repetition rates. The experiment therefore seems to indicate that dental lasers which allow higher repetition rates are better suited for laser drilling of hard dental tissue.

At the end of the 19th century, when physicians were just learning about sterilization of surgical implements, the introduction of x-rays was met with suspicion and fear. One hundred years later, the x-ray is handled with great respect, but it would be hard to imagine a medical or dental health clinic without it. Today, as we approach the end of the 20th century, we stand on the cusp of several embryonic technological surges. As in the past, there are some who are reticent about embracing new ways of diagnosing and treating disease. Lasers, robotics, imaging and virtual reality, the interactive information superhighway--I want to share with you my views of how these terms that didn't exist 100 years ago will impact medicine over the next 100 years beyond belief. And how that impact will begin much sooner than you think...by the year 2001.

The detection and quantification of the concentration of exogenous chromophores in-vivo by their fluorescence is complicated by many physical and geometrical parameters. Measurement of such signals is advantageous in determining the pharmacokinetics of photosensitizers such as those used in photodynamic therapy (PDT) or to assist in the diagnosis of tissue histological state. To overcome these difficulties a ratio based fiber optic contact fluorometer has been developed. This fluorescence detection system (FDS) uses the ratio of the fluorescence emission peak of the exogenous chromophore to that of endogenous chromophores, i.e. autofluorescence, to correct for a variety of parameters affecting the magnitude of the measured signals. By doing so it also minimizes the range of baseline measurements prior to exogenous drug injection, for various tissue types. Design of the FDS and results of its testing in animals and patients using the second generation photosensitizer Tin ethyletiopurpurin (SnET2) are presented. These results support the feasibility and usefulness of the Ratio FDS system.

Near infrared optical imaging is emerging as a potentially important imaging modality, because it offers real time data access, portability, cost-effectiveness, and the relatively safe use of non-ionizing radiation. Reconstruction of images by optical tomography is complicated by the diffusive character of light propagation in optically heterogeneous tissue. The spatial volume element probed by the light path between the light source and optical detector is rather wide and depends on a variety of experimental and instrumental factors. We have published an optical image of the hand in air based on photon density wave distribution characteristics, using both steady-state (intensity) and frequency-domain (phase and modulation) experimental conditions. Since then, we have developed new instrumentation, better measurement protocols, some reconstruction algorithms and a more complete theoretical understanding of photon diffusion in both homogeneous and heterogeneous media. We have now performed frequency-domain measurements (at a modulation frequency of 160 MHz with 760 nm near infrared light) with the hand immersed in a scattering fluid (the infinite geometry arrangement). The advantages of our current approach include the spectroscopic resolution of physiologically interesting tissue regions, greater spatial resolution, the generation of absorption and reduced scattering coefficient maps of the image, rapid data acquisition, real time simultaneous display of the experimental parameters and calculated optical parameters and the possibility of obtaining some tomographic reconstruction.

We have introduced a computer-based endoscopic camera which includes (a) unique real-time digital image processing to optimize image visualization by reducing over exposed glared areas and brightening dark areas, and by accentuating sharpness and fine structures, and (b) patient data documentation and management. The image processing is based on i Sight's iSP1000^TM digital video processor chip and Adaptive Sensitivity^TM patented scheme for capturing and displaying images with wide dynamic range of light, taking into account local neighborhood image conditions and global image statistics. It provides the medical user with the ability to view images under difficult lighting conditions, without losing details `in the dark' or in completely saturated areas. The patient data documentation and management allows storage of images (approximately 1 MB per image for a full 24 bit color image) to any storage device installed into the camera, or to an external host media via network. The patient data which is included with every image described essential information on the patient and procedure. The operator can assign custom data descriptors, and can search for the stored image/data by typing any image descriptor. The camera optics has extended zoom range of f equals 20 - 45 mm allowing control of the diameter of the field which is displayed on the monitor such that the complete field of view of the endoscope can be displayed on all the area of the screen. All these features provide versatile endoscopic camera with excellent image quality and documentation capabilities.

Since the introduction of functional endoscopic sinus surgery (FESS), the procedure has undergone rapid change with evolution keeping pace with technological advances. The advent of low cost charge coupled device 9CCD) cameras revolutionized the practice and instruction of FESS. Video-based FESS has allowed for documentation of the surgical procedure as well as interactive instruction during surgery. Presently, the technical requirements of video-based FESS include the addition of one or more television monitors positioned strategically in the operating room. Thought video monitors have greatly enhanced surgical endoscopy by re- involving nurses and assistants in the actual mechanics of surgery, video monitors require the operating surgeon to be focused on the screen instead of the patient. In this study, we describe the use of a new low-cost liquid crystal display (LCD) based device that functions as a monitor but is mounted on the head on a visor (PT-O1, O1 Products, Westlake Village, CA). This study illustrates the application of these HMD devices to FESS operations. The same surgeon performed the operation in each patient. In one nasal fossa, surgery was performed using conventional video FESS methods. The contralateral side was operated on while wearing the head mounted video display. The device had adequate resolution for the purposes of FESS. No adverse effects were noted intraoperatively. The results on the patients ipsalateral and contralateral sides were similar. The visor did eliminated significant torsion of the surgeon's neck during the operation, while at the same time permitted simultaneous viewing of both the patient and the intranasal surgical field.

Recent advances in high resolution color spatial light modulators and light weight optics together with application specific integrated circuits enable true stereoscopic visualization on a head mounted display (HMD). The development of precision stereo displays with comfortable long duration wear characteristics are critically dependent on incorporating key human factors into the HMD design. In this paper we discuss the development of a VGA format (640 X 480 pixel) full color video and graphics stereo display. Its primary application is as an element of an integrated, interactive visualization system for surgeons performing minimally invasive surgery and endoscopic laser surgery. Additional uses include endoscopic and open surgical training and rehearsal. The high resolution, wide field of view displays combined with true stereoscopic imagery enhances the surgeon's visualization, ability to navigate and manipulate in the surgical field.

The scattering phenomenon of infrared and visible radiation from hollow waveguides, made of teflon or fused silica, having Ag and AgI guiding layers, was measured by two methods; Total Integrated Scattered and Backscattering. The root means square roughness was evaluated by both methods. It was found that the roughness of the silver layer is influenced by the substrate. The AgI is the main contributor to roughness and this is a function of its preparation method.

Plastic and fused silica waveguides suitable for transmitting CO₂ and Er-YAG laser radiation were prepared and characterized. The temperature of several points on the waveguide was measured. Optical parameters (transmission, focussing, misalignment) of the two types of waveguides were determined and compared.

Existing numerical methods of optical waveguide modeling are generally not applicable to the multimode regime because of the enormous computing power required. We have found that a ray tracing algorithm can be useful in modeling multimode waveguides. To test the method, a commercial ray tracing software package was used. Two sets of numerical data from literature on multimode waveguide bending losses were compared with predictions of the ray tracing models; results agree well with the data. This technique can be applied in multimode waveguide design where previous methods were too computing-intensive.

In order to introduce Er:YAG lasers at 2.94 micrometers into medical applications such as minimally invasive surgery, appropriate infrared transmitting fibers are necessary. Because of their cheapness, variability in diameter, high flexibility, mechanical stability and regenerability, liquid core fibers have been taken into consideration as one type of conceivable lightguides. In this work IR absorption effects of water in the core and permeation of atmospheric water and of the solvent through the cladding are studied. The absorption of 2.94 micrometers which is due to the unresolved rotational structure of the stretching vibrations of dissolved water at 3617 and 3708 cm^-1 increases when the water content rises. According to preliminary permeation measurements, keeping a liquid-filled plastic fiber under normal atmospheric conditions leads to an increasing water concentration in the core and, simultaneously, to a loss of the solvent. On the other hand the water content could be reduced when the lightguide was stored in a desiccator. These problems could be solved by using a liquid lightguide with an appropriate jacket. Compared to unjacketed counterparts it has a better long time transmission at 2.94 micrometers . Meanwhile the transmission could be improved to up to 55% (pathlength: 1 m). As these first results are thought to be further improvable they are well promising towards the realization of a liquid lightguide for medical purposes.

Usually for study and to analyze the nystagmus eye movements is used a non invasive method for eye movements with an infrared limbus reflection technique, based on an IR-LED emitter and photo diodes detectors, also using a scleral search coil in a magnetic field and digital image processing. We use a new technique, silica-based fiber optic system with rod lens that consist in two pairs, a pair for horizontal eye movements and another for vertical eye movements and a circular array in order to detect torsional nystagmus. This fiber optics bundle was made on a spectacle mounted differential reflectivity device. The electrical signals detected are introduced to two instrumentation amplifiers (horizontal and vertical), an amplifier-multiplex for torsional nystagmus and we use an interface of eight channels A/D connected to the PC. The software is developed to analyze: position, velocity, acceleration, cross correlation, FFT based processing for frequency analysis and power spectral density determination. The results obtained were in these areas: nystagmus, eye tracking (X - Y), saccadic eye movements related to visual stimulus on a visual perimeter then compared with the IR-LED and photo transistors techniques and application for disabled.