Hard Plastic Clad Silica (HPCS) optical fibers were invented about a decade ago to improve on the original Plastic Clad Silica (PCS) optical fibers. Details of the invention/innovation process are reviewed along with the development of this new type of optical fiber structure. A compilation of the several types now offered in the USA, Japan and Europe is presented. The advantages and limitations of these fibers for a wide range of medical applications are reviewed. Finally a description of future developments and expanded products are suggested.

Silica-core/silica-clad fibers have become very popular tools for a variety of therapeutic and diagnostic applications. Two types of conventional silica/silica fibers having acrylate and polyimide coatings are reviewed. The properties of dual-waveguide silica/silica fiber are discussed; and the superior bend performance with this design is presented. Silicone/nylon and hard-fluoropolymer/Tefzel^TM dual-coated fibers are included as the dual-waveguide samples. Sample fibers of each of the four coating types were manufactured into 400/440 micrometers size, 0.22 NA fiber.

Power transmission of xenon chloride excimer lasers through optical fibers is necessary for medical applications where tissue removal is performed within the human body. The most important application at present is excimer laser coronary angioplasty. Typical levels of energy densities applied by optical fibers for this application cause color center generation in fused silica leading to transmission decrease called photodegradation. This effect depends essentially on the grade of the fused silica. Important parameters are fiber length, pulse duration, energy density, and the irradiated cross sectional area of the optical fiber endface. For a new grade of core material the influence of these parameters on the transmission performance is described. The obtained material improvement leads to a significant reduction of the observable transmission decrease as a function of the number of laser pulses applied. Thus continuous operation of the laser in the region of the typical transmission plateaus at considerably higher and constant energy levels at the distal fiber end becomes feasible. This offers a new option for more reliable dosimetry in medical applications.

Optical fibers have long been used for visual inspection inside the human body for medical diagnoses and treatment. By making use of sophisticated optical interferometric and ultra- small imaging techniques, combined with automated image processing, it is possible to extract significantly increased information for more accurate medical diagnoses. With support from NIH under the SBIR program, we have been developing a range of such instruments. One of these supported by the NIDCD is capable of providing detailed spatial information on the vibratory response of the tympanic membrane (TM). This instrument involves the examination of the TM by means of high speed electronic speckle pattern interferometry (ESPI). This provides a real time view of the vibration patterns of the TM for clinical diagnosis. This Interferometric Otoscope consists of mode conserving fiber optics, miniature diode lasers and high speed solid state detector arrays. We present the current status of the research including holography and ESPI of TM models and excised temporal bone preparations. A second instrument, also developed with support from NIDCD, is for application to the larynx. This system is also ESPI based but will incorporate features for direct vocal cord (VC) examination. By careful examination of the vibratory response of the VC during phonation, the characteristics of the mucosal wave may be examined. Adynamic regions of the cords can signal the start of lesions or cysts. Results of surgery can be evaluated in a quantitative manner. The design of a clinical prototype and preliminary electro-optic experiments on excised larynges and VC models will be presented.

Endoscope for stereoscopic vision is in great demand for medical field to diagnose and treat disease parts of patients more precisely. The authors are convinced that the silica based imagefiber is suitable for making a thinner fiberscope for stereoscopic vision. The structure of the fiberscope and the quality of transmitted image have been investigated. It has been found that stereognosis depends on the magnification of eyepiece, distance between left and right objective lenses and the image quality between two transmitting systems. On the basis of these results, the ultrathin fiberscope with silica based imagefibers for stereoscopic vision have been developed. The diameter of fiberscope is only 2 mm with two transmitting systems that consist of two imagefibers with 10000 pixels and lightguide for illumination and objective lenses. This fiberscope for stereoscopic vision can be used for the micro surgery, such as the laparoscopic surgery and the thoracoscopic surgery required for the thin diameter.

The design of a confocal microscope including a fiber-optic imaging bundle is discussed, and experimental results are presented. The imaging bundle extends the range of the confocal microscope to image samples inaccessible to a conventional confocal system. The main advantage of this design over the single-fiber confocal microscope is the simplified mechanism required in the sample region. Applications of this design include biological research, industrial inspection, and potentially in-vivo medical systems.

Blood flow measurements were obtained with a laser Doppler fiberscope anemometer of our design. A specially designed steering mechanism enabled the positioning of the fiber probe in several points across the measured site. The anemometer was based on the reflected laser Doppler system, and the optical design allowed for a very small measuring volume. The system is shown to be a powerful and important tool for the in vivo analysis of blood flow.

Optical sectioning capability of fiber-optic scanning microscope using 9 cm long GRIN-rod lens probe has been demonstrated. Transverse resolution 1.3 micrometers and longitudinal resolution 30 micrometers were achieved. Dimensions of the probe allow the use of the device as an endoscope.

We developed the medical fiber cables which were designed for CO laser therapy, i.e., angioplasty and endoscopic therapy. As-S chalcogenide glass fibers were used for CO laser delivery. A 230 micrometers core-diameter fiber was used for the angioplasty laser cable. The outer diameter of this cable was 600 micrometers . The total length and insertion length of the angioplasty laser cable were 2.5 m and 1.0 m, respectively. Typically, 2.0 W of fiber output was used in the animal experiment in vivo for the ablation of the model plaque which consisted of human atheromatous aorta wall. The transmission of the angioplasty laser cable was approximately 35%, because the reflection loss occurred at both ends of the fiber and window. Meanwhile, the core diameter of the energy delivery fiber for the endoscopic therapy was 450 micrometers . The outer diameter of this cable was 1.7 mm. Approximately 4.5 W of fiber output was used for clinical treatment of pneumothorax through a pneumoscope. Both types of the cables had the ultra-thin thermocouples for temperature monitoring at the tip of the cables. This temperature monitoring was extremely useful to prevent the thermal destruction of the fiber tip. Moreover, the As-S glass fibers were completely sealed by the CaF₂ windows and outer tubes. Therefore, these cables were considered to have sufficient safety properties for medical applications. These laser cables were successfully used for the in vivo animal experiments and/or actual clinical therapies.

Silver halide polycrystalline MIR-fibers are coming to practical exploitation in CO-laser medicine through the development of core/clad fibers technology and design of suitable flexible delivery systems, convenient and reliable for operations. Recent results of such development and useful exploitation features are presented.

Infrared (IR) radiation emitted by lasers is a very important tool in surgery applications. This type of laser energy is used for cutting and soldering of tissues, cauterization, evaporation of growths, opening blocked passages and others. The most important lasers which give radiation in the mid-IR region are the CO₂ laser ((lambda) equals 10.6 micrometers ), CO laser ((lambda) equals 5 mm) and the Er-YAG laser ((lambda) equals 2.94 micrometers ). In our laboratory a plastic, flexible, hollow waveguide suitable for mid-IR energy transmission was devised. This waveguide is used successfully in surgery. The waveguide is made of a plastic tube covered internally with a thin metal layer (Ag) and a dielectric overlayer (AgI). A theoretical ray model was also developed which has described quantitatively the propagation of radiation through the waveguide under straight and bent trajectories. The thickness and index of refraction of the dielectric layer is the essential parameter which determines the attenuation of transmitted energy through the waveguide. Powers up to 50 watts of CO₂ laser can be transmitted through these waveguides for bending radii down to 2.5 cm.

Infrared optical fibers play a very important role in the advance using of lasers and chemical sensors in medicine. From various kinds of infrared optical fibers (crystalline, hollow) glassy optical fibers seem to have many advantages, namely in chemical and physical properties. In this paper the main attention is focused on chalcogenide (As_{24/S(subscript 3}, As₂Se₃, AsSeTe, GeSeTe) and chalcohalide glasses.

In this work only first steps in blood glucose measurements were made and possibilities of tissue analysis were demonstrated with a MIR fiber probe. Spectroscopic measurements with the same objects by ATR (attenuated total reflectance) elements were made before, but advantages make fiber use more attractive.

The morphologic changes of the pulmonary artery have been observed by angiography, but angiography shows only the shadows of the changes actually occurring. Recent advances in fiberscopic technology enabled us to observe the coronary artery, great vessels, cardiac chambers and the pulmonary artery by angioscopy4 We report here angioscopic features of the pulmonary artery in patients with pulmonary thromboernbolism, pulmonary hypertension and rheumatic valvular disease.

Percutaneous angioscopic observation of the aortic luminal surface and aortic valve has not been established. Therefore, we performed percutaneous fiberoptic angioscopy of aorta and aortic valve using a balloon-tipped guiding catheter.

Recent advances in fiberoptic technology enables us to observe the cardiac chambers percutaneously in various categories of heart disease. We applied cardioscopy in 4 patients with HCM. Two of them presented excessive or good left ventricular function and no history of congestive heart failure (CHF). The other two patients showed reduced left ventricular function with a history of CHF. Cardioscopy was successfully performed in all patients. In patients with excessive or good left ventricular function, the color of the endocardial surface was light brown mixed with white. The trabeculae were significantly thick and contracted vigorously. In patients with reduced left ventricular function, the color was whiter, and the thickness and contraction of the trabeculae were reduced obviously. Myocardial biopsy revealed that interstitial fibrosis was prominent in the latters. These results indicate that (1) cardioscopy is safe and useful for evaluation of the internal surface of the ventricle in patients with HCM, and (2) cardioscopic characteristics of the ventricle are closely related to histopathological features.

Kawasaki disease is an acute systematic angiitis, specifically affecting the coronary arteries in young children. Coronary aneurysms develop in 10 to 15% of patients with Kawasaki disease. The coronary aneurysm frequently changes into coronary stenosis and obstruction. Hitherto, we could observe and access the severity of these coronary lesions with the use of two dimensional echocardiography and selective coronary angiography. Angiography is the most sensitive means available for diagnosing significant coronary lesions and their severity. However, it is insensitive for detecting intraluminal minute and pathologic changes such as intimal thickening, regeneration of endothelium and thrombus. Recent advance in fiberscopie technology, enabled us to observe the inside of coronary artery percutaneously. We tried to use this angioscopic technique for the observation of coronary lesions in eight patients with Kawasaki disease at chronic stage.

Recent advances in fiberoptic technology enabled us to observe percutaneously the cardiac chambers and valves. We examined left ventricular luminal and valvular changes by percutaneous fiberoptic angioscopy in patients with rheumatic valvular disease. Six patients with echocardiographic rheumatic changes in the mitral valves, underwent angioscopy during routine cardiac catheterization. The fiberscope 4.2 F in diameter, and the guiding catheter 9 F in external diameter with an inflatable balloon around the distal most tip were used for angioscopy. The left ventricular endocardial surface was diffusely white in color or white and brown in mosaic fashion. Echocardiography and angiography had low sensitivity for detecting the changes of the left ventricular luminal surface. Whitish changes which were observed by angioscopy were not related to the indices derived from echocardiography and angiography. The results indicate the possibility of percutaneous angioscopy in detecting left ventricular luminal changes in patients with rheumatic valvular disease.

We have been doing the basic experiments of UV laser beams and biotissue interaction with both KrF and XeCl lasers. However, the conventional optical fiber can not be available for power UV beams. So we have been investigating about UV power beam delivery systems. These experiments carry on with the same elements doped quartz fibers and the hollow tube. The doped elements are OH ion, chlorine and fluorine. In our latest work, we have tried ArF excimer laser and biotissue interactions, and the beam delivery experiments. From our experimental results, we found that the ArF laser beam has high incision ability for hard biotissue. For example, in the case of the cow's bone incision, the incision depth by ArF laser was ca.15 times of KrF laser. Therefore, ArF laser would be expected to harden biotissue therapy as non-thermal method. However, its beam delivery is difficult to work in this time. We will develop ArF laser beam delivery systems.

The spatial irradiance distribution of optical modified fibers with beveled tips which can be used for lateral-aiming delivery systems was calculated using 3-D ray tracing. Light refraction and reflection at the front surface and second refraction at this surface after reflection by cylindrical fiber surface were taken into account. The results were compared to measurements using CCD-camera and goniometric measurements performed for silica (n equals 1.457) 0.6 mm-fibers in air and in water. The slope angle was varied from 18 degree(s) to 60 degree(s). To prevent a forward lighting, gold coating of the front fiber face was considered. Measured damage threshold of this coating yielded 2 W in air and 30 W in water for continuous wave Nd:YAG laser. For the Ho:YAG laser (250 microsecond(s) , 2 Hz) the measured threshold was 60 mJ in water and in air. To increase the focusing effect the front side of the fiber can be modified as a beveled spherical surface.

Cylindrical light diffusion is a key element in a variety of medical applications which require the controlled administration of light to a treatment site within the body. Applications such as photodynamic therapy (PDT), laser induced hyperthermia (LHT), and photoatherolytic (PAL) therapy may all require that light be diffused in this manner. Cylindrical diffusers are typically used in tubular cavities, such as the bronchus, trachea, or the esophagus, and in interstitial applications where uniform illumination over a specified length is required to maximize the therapeutic response. A third generation of cylindrical diffuser with improved performance has been developed to more effectively meet these needs. This paper will discuss the evolution of cylinder diffusers and will describe the characteristics and performance of this new generation device.

To predict the outcome of laser therapy it is important to possess, among other things, an accurate knowledge of the intensity and distribution of the laser light incident on the tissue. For irradiation of the internal surfaces of hollow organs, modified fiber tips can be used to shape the light distribution to best suit the treatment geometry. There exist bulb-tipped optical fibers emitting a uniform isotropic distribution of light suitable for the treatment of organs which approximate a spherical geometry--the bladder, for example. For the treatment of organs approximating a cylindrical geometry--e.g. the oesophagus--an optical fiber tip which emits a uniform cylindrical distribution of light is required. We report on the design, development and testing of such a device, the CLD fiber tip. The device was made from a solid polymethylmethacrylate (PMMA) rod, 27 mm in length and 4 mm in diameter. One end was shaped and 'silvered' to form a mirror which reflected the light emitted from the delivery fiber positioned at the other end of the rod. The shape of the mirror was such that the light fell with uniform intensity on the circumferential surface of the rod. This surface was coated with BaSO₄ reflectance paint to couple the light out of the rod and onto the surface of the tissue.

Anti-thrombotic and thrombolytic effects of anti-thrombin agent (Argatroban;Arg 0.5 mg/kg) was evaluated by angioscopy and compared with heparin (250 U/kg). Occlusive thrombus was produced in canine iliac artery by balloon injury. At another side, balloon denudation was attempted at 20 minutes after the administration of the agent. One hour thrombus was control. Angioscopic percent luminal obstruction with thrombus reduced by Arg (from 69 to 32%, P < 0.0001), but not by heparin (from 53% to 59%). Both agents had antithrombotic effects and prevented thrombus formation. The activated partial thromboplastin time (APTT) prolonged to 190% with argatroban and 1253% with heparin (P < 0.0001). Thus, antithrombin agent has both preventive effect of thrombosis and thrombolytic effect without marked prolongation of the APTT.

Some physical phenomena which occur during the fragmentation of calculi by laser induced optical break down are presented. With in vitro experiments it could be shown that the energy of the laser induced plasma and of the cavitation bubble (induced by the plasma) depends by the nature of the tissue. The laser induced plasma and the cavitation bubble generate shock waves. These sound waves are transferred via the laser fiber and detected with a piezo- electrical sensor at the proximal end. The acoustic signal contains information on the potential energy of the bubble, which depends on the energy of the plasma. The possibility of measuring the energy dependent acoustic transients allows to distinguish between hard and soft tissue and by this it is suitable for controlling the laser lithotripsy process. The transmission of acoustic transients through silica glass fibers is investigated by theoretical calculations. It shows the feasibility of silica glass fibers as an acoustic wave guide.

Sapphire and fluoride glass fiber optics were tested for their ability to deliver pulsed infrared laser energy. Commercial fluorozirconate fibers were found to experience laser-induced aging at fluences far below their measured laser damage thresholds. Irradiation of these fibers with even modest fluences (30 mJ/cm²) of Er:YAG laser radiation at 2.94 micrometers wavelength (200 microsecond(s) pulses at 6 Hz) caused pitting and melting of the end-faces within 30 minutes. A tunable free electron laser was used to show that this deterioration is directly related to the absorption of radiation near 3 micrometers wavelength by adsorbed water on the fiber faces. Sapphire fibers did not show any evidence of laser-induced aging.

We have developed a theoretical model for describing the light intensity distribution of fiber optic diffusers. By using this model the light distribution at any radial distance from fiber axis can be calculated from that of the near field. Different types of fiber diffusers were quantitatively measured and compared with theoretical model.

The newly developed optical fibers are described designed to transmit intense radiation in the visible and near IR spectral regions. The main characteristic feature of the fibers is a core made of unique purity silica with extremely low OH content not exceeding 20 ppb. As a result, the fiber spectral attenuation in the infrared is substantially reduced: the absorption spectrum is a smooth monotonously rising curve with typical loss levels of less than 0.2 dB/m at 2.1, 10 dB/m--at 2.7 and 27 dB/m--at 2.8 microns. Thin (approx. 10% of the fiber diameter) fluorinated silica cladding together with the high purity core ensure excellent optical damage resistivity of the fibers and greatly facilitate their coupling to high power lasers. The plasma outside deposition technology used for clad fabrication can provide fluorine doping levels sufficient to produce the fibers with numerical aperture NA up to 0.24. The fibers can have either hermetic metal (In, Sn, Pb, Zn, Al) or plastic protective coating. For the Al-coated fibers the mechanical properties and environmental durability are characterized by the following figures: tensile strength--more than 7 GPa, minimal bend radius--40 times the fiber radius (long term), operating environment--from--196 up to 400 degree(s)C, 100% humidity.

In a previous research project a flexible plastic hollow waveguide has been developed in our laboratory. The waveguide was prepared by depositing silver (Ag) layer and silver iodine (AgI) overlayer on the inner surface of a plastic tube. The said waveguide proved to be a very suitable means for delivering high power CO₂ laser energy ((lambda) equals 10.6 micrometers ) in any desired tortuous path, having small attenuation. Through the same waveguide it is possible to transmit non-coherent infrared energy from a thermal energy source to a detector. In this paper we present a new type of waveguide which is suitable for the transmission of Er- YAG laser radiation ((lambda) equals 2.94 micrometers ). Such energy can be employed for drilling and operating in hard tissues (bone, tooth). The essential factor which made this device possible for use as Er-YAG laser energy delivery system is based on the known data from the CO₂ waveguide research was the control over the thickness and the index of refraction of the dielectric layer (AgI). Another important factor was to avoid the roughness of the plastic substrate and of the Ag/AgI layers. Reducing the roughness enabled us to reduce the scattering of the transmitted radiation to a low value, which is essential for the good functioning of the waveguide. The performed experiments have shown that an energy of up to 900 mJ could be coupled into the flexible waveguide and delivered to a target in straight or bent trajectory. The transmission was 55% in straight and 40% in bent trajectory (waveguide length 1 m, internal diameter 1.9 mm minimum radius of bending 20 cm).