There is a growing interest in the use of optical fibers in medicine. Three areas of interest are briefly reviewed: (a) Endoscopy - image transmission through fiberoptic bundles; (b) Diagnostics - physical and chemical measurements using fibers; (c) Power Transmission - delivery of high power laser beams through fibers. A thin and flexible endoscope may incorporate a fiberscope, diagnostic fibers and a power fiber. A physician would insert it into the body, and use it either as a diagnostic tool or for least invasive surgical procedures.

Infrared fluoride glass fibers less than 1 dB/m between 0.5 and 4.5 μm are now currently manufactured. They are drawn from multicomponent ZrF4-based glass preforms in various core to cladding ratios. These fibers may be used in several technological fields connected to medicine and biology : infrared spectrometry and in line gas analysis, remote I.R. spectrometry, thermal imaging and laser surgery.

Zinc Selenide (ZnSe) optical fibers 30 cm long by 1 mm in diameter have been fabricated by a grinding and polishing technique. The bulk transmission through a 30 cm length of these uncladded fibers is as high as 99 ± 2% at 10.6 pm. This corresponds to a bulk attenu-ation coefficient, a, as low as 0.2 dB/m. There appears to be no change in transmission within the uncertainty of the measurements when the fibers are bent to a radius of 115 cm. The minimum bend radius (fracture point) of the fibers was measured to be 60 ± 14 cm. As much as 14 watts of power for up to 5 min. was transmitted through the fiber without any damage or heating. Also power densities as high as 10 kW/cm² incident on the polished input end of the fiber caused no detectable damage to the surface. ZnSe can efficiently transmit radiation over a wide range of wavelengths (0.6 - 14 μm). Therefore, these ZnSe optical fibers can transmit radiation from He:Ne, Nd, HF/DF, CO and CO₂ lasers. The fabrication technique used to produce these fibers is scalable to longer lengths. Cladding techniques are currently under development. Such ZnSe fibers have potential application in catheters and endoscopes for CO₂ laser surgery, probes for remote optical measurements in hostile environments,and in various military infrared optical systems.

The high-intensity power delivery of CO laser with a As₂S₃ chalcogenide glass fiber for medical applications is described in this paper. The As₂S₃ glass fiber which had fluorinated ethylene propylene (Teflon FEP) cladding was used in this study. The fiber output of 1 5.3W was attained by means of the fiber which had 400μm core diameter without any degradation on the fiber. At the above condition, the light intensity of 16.9kW/cm² was obtained on the input end of the fiber. The maximum delivery power was restricted to melting of the core material at output end of the fiber. The allowable bending radius of the fiber was less than 30 mm. The applicability of this power delivery for medical applications, especially for the laser endoscopy and the laser angioplasty are discussed.

We have used two prototype fiberoptic angioscopes to visualize the interior of the right heart and pulmonary arteries to aid in the detection and localization of chronic pulmonary emboli, a difficult disease to diagnose with standardly available imaging techniques. The initial prototype was shorter, wider, and had less distal flexibility than the newer prototype. The initial prototype was used in eight patients and the angioscopic examination led to a change in the diagnosis in four. It also allowed more accurate localization of chronic emboli which aided the surgical approach in five patients. Use of this instrument was limited, however, because its diameter was too large to always permit insertion through the external jugular vein. The newer prototype is both longer and narrower allowing access through either the external jugular or an antecubital (arm) vein. This instrument has been used in two patients. In the first access was gained through the antecubital route when the external jugular was found to be inadequate. This patient could not have undergone angioscopy with the earlier prototype. Both instruments achieve good visualization. The earlier prototype is easier to manipu-late through the right heart, but more difficult to guide through the branching pulmonary arteries; the newer prototype is more difficult to guide through the heart because of the stiffness of its bundle, but easier to manipulate through branching arteries because of the greater flexibility of its distal tip.

Silver halide AgCl_xBr_1-x fibers were inserted into cardiological catheters to form CO₂ laser catheters. Human arteries which had been blocked by atherosclerotic plaque were transplanted into dogs. The laser catheter was used to recanalize the blocked arteries in an in vivo experiment.

Atherosclerotic vascular disease is a major cause of morbidity and mortality throughout the world. Surgical and pharmacologic agents have been used in the treatment of this disease with varying degrees of success. Recently, angiographically guided balloon dilatation of atherosclerotic vascular lesions has gained widespread use and acceptance because of efficacy, decreased cost, and reduced patient morbidity and mortality. There are, however, some lesions which cannot successfully be treated by this method because of their location, size, or configuration.

Patients have been successfully treated without complications, endoscopically using contact neodymium:YAG laser endoprobes for tumors and bleeding, and during open surgery with the laser scalpel. The contact probes made from a synthetic sapphire crystal with its optical properties, geometric design, thermal conductivity and high melting temperature (2030 C - 2050 C) have proven to be more effective than the current conventional non-contact method of delivering laser energy through a quartz fiber. Advantages include greater precision, sterility, avoidance of the tip melting and a requirement for lower neodymium:YAG laser energy with reduced tissue damage. The configuration of the probes allows coagulation, cutting or vaporization depending on the clinical condition being treated. Future uses will include interstitial local hyperthermia and photodynamic therapy. These contact probes can also be used with the argon laser and offer dramatic improvements in medical applications of the neodymium:YAG laser.

We have devised a system that will allow the optical sensing of high temperatures associated with the onset of optical fiber burnback, allowing immediate shuttering of the laser source. The shutter is triggered by an amplified signal obtained from the detected blackbody radiation that propagates back through the same fiber used to deliver the therapeutic laser energy. We will present some theory on the burnback phenomenon, describe the experimental setup used and discuss the results obtained.

Direct laser energy delivery was compared to fiber optic laser energy delivery by the performance of open laser endarterectomy in the rabbit arteriosclerosis model. In Group I, 6 open laser endarterectomies were performed with a hand-held CO₂ laser (10.6 pm). In Group II, 6 open laser endarterectomies were performed with an argon ion laser (488 nm and 514.5 nm) with the laser beam directed through a 400 μm quartz fiber optic. Gross and light microscopic examination revealed uneven endarterectomy surfaces and frequent perforations at the end points in Group I. In Group II, the endarterectomy surfaces were even and the end points were fused with a tapered transition. Energy density for Group I was 38 ±5 J/cm². Energy density for Group II was 110±12 J/cm². CO₂ laser energy was better absorbed by arteriosclerotic rabbit aortas than argon ion laser energy, but it could not be as easily controlled. We conclude that a more precise endarterectomy can be performed with fiber optic delivery of laser energy.

The method of fluorescence quenching is used to measure the concentration of molecular oxygen. The method is rapid, reversible, and does not consume oxygen. The method may provide the basis for a unique biomedical sensor. The key to developing such a device lies in the choice of a fluorophor/polymer composite matrix having the desired optical and transport properties. Experimental results will be presented for certain parameters essential for assessing device development. The properties of interest include the kinetics of fluorescence quenching, the biomolecular rate constants, the temperature dependence of oxygen solubility and diffusivity in the composite matrix, and the oxygen diffusion coefficient. Poly(dimethyl siloxane) [PDMS] was chosen as the polymer host because it is biocompatible, hydrophobic, has a high diffusivity for the simple gases, and is easily bonded to fused silica. 9,10-diphenyl anthracene [9,10-D] was selected since it is readily soluble in a number of organic solvents, has an excitation spectrum in the near UV, an emission spectrum in the visible, a long fluorescence lifetime, and a high quantum yield. When incorporated into PDMS, the optical spectra of 9,10-D does not alter appreciably. The response time of the device is determined by the solution/diffusion kinetics of oxygen in PDMS. The solubility of oxygen in PDMS decreases with increasing temperature and an enthalpy of solution of off = -3.0 kcal/mole. (1) The diffusion of oxyzen in PDMS is found to obey an Arrhenius relation over the temperature range of 5'C to 450C with D = Do exp (-ED/RT) (2) where Do = 0.115 cm²/s (3) and ED = 4.77 kcal/mole. (4) Results of these studies indicate that an appropriate device, based on a fluorophor/polymer composite, for the measurement of oxygen concentration should be sensitive over those ranges which are important for physiological monitoring.

The different absorption with temperature of a thermochromic solution is used as temperature sensing. The implemented version of the device is presented with technical data of the optoelectronic system and the experimental results.

Based on prior spectroscopical measurements of human skin, we developed a fiber optical measuring system for the diagnostics of peripheral venous disorders specially of the lower extremities. The method is based on the evaluation of the radiation beamed into the skin via a fiber optical sensor and scattered back from the tissue. The received light mainly comprises information about blood content and the surface area of the vesels and we can extract a signal which is nearly proportional to the changes of the blood pressure. The system allows painless diagnostics and a evaluation of peripheral venous disorders, even in an early stage.

Temporal power spectra of the speckle signal detected by a simple optical fiber probe for the blood flow monitor system are analyzed theoretically and experimentally as a function of the laser spot size at a moving scatter plate, the moving velocity of the plate, the core diameter of the detecting fiber and the numerical aperture of it.

In order to assess the effect of laser energy on the heart's rhythm, 7 newborn pigs each had 3 two-second applications of laser energy directly to the left ventricular epicardial surface. A quartz fiberoptic delivery system was used. All piglets (in all 21 applications) had ventricular arrhythmia induced. This varied from single premature ventricular contractions to sustained(112 seconds) ventricular tachycardia (6/7 piglets). The sustained ventri-cular tachycardia exhibited electrophysiologic criteria of a "re-entrant" mechanism. Fifteen minutes following lasing, programmed ventricular stimulation, a technique that indicates whether a substrate may be present for spontaneous re-entrant arrhythmias, showed induced arrhythmia in only 2/7 pigs, neither sustained. We conclude that epicardial application of laser energy frequently results in significant ventricular arrhythmia. This arrhythmia appears to be re-entrant in nature. Fowever, shortly following lasing, sustained arrhythmia could not be induced. Therefore, we feel that more knowledge about the arrhythmogenic potential of laser lesions is needed prior to wide-spread clinical application.

Fresh myocardial segments from fetal and adult sheep, and from newborn and adult pigs were exposed to continuous mode argon laser irradiation in saline medium. Additionally, myocardial segments from newborn pigs were exposed to laser irradiation in fresh, heparin-ized blood medium. The irradiation distance from the tip of the quartz fiber to the tissue varied between contact and 20 mm, and power output at the fiber tip varied between 1 and 8 watts. Exposure time was kept constant at 2 seconds. Tissue debris was also processed for study by scanning and transmission electron microscopy. There was no difference in myocardial tissue response between sheep and pigs, nor was there a difference in response between young and adult animals. In both saline and blood media, there was a sharp decrease in burn depth with increasing irradiation distance. With increasing irradiation distances in saline medium, burn diameter increased initially and then plateaued; while with increasing irradiation distance in blood medium, the burn diameter decreased sharply. When the fiber tip was in contact with the tissue, the diameter of burn was greater in blood than saline, while the depth of burn was similar. Filtration of the tissue bath demonstrated particles as large as 3 mm in length which were composed of deformed and coagulated whole tissue segments. Electron and scanning micrography of the bath media identified intracellular components and fragments of burst cells. In conclusion, we have found no difference in adult vs. newborn, or sheep vs. porcine myocardial response to fiberoptic argon laser irradiation. The most critical factors affecting width and depth of burn were the distance of the fiber tip from the tissue, and the medium in which the tissue was bathed. Of particular clinical importance was the fact that the burn width and depth drastically decreased when blood was present between the laser fiber and the tissue.

We describe a novel all-fibre optic laser Doppler velocimeter (FOLDV) which utilizes a low power stabilized single-mode laser and an optical fibre tap. After fundamental experiments to correlate the FOLDV signal to electromagnetic flowmeter (EMF) output, in vivo measurements of erythrocyte velocities have been made in both femoral and coronary veins and arteries. In experiments in which coronary blood flow was changed by electrical stimulators of sympathetic nerves, the FOLDV was able to measure velocity before, during and after the intervention where EMF failed to provide velocity information during intervention. In addition, the pulse wave velocities in femoral arteries were determined by referencing the FOLDV signal to vascular pressure. The FOLDV was also used to measure velocity profiles and vessel dimensions.

A fiber-coupled laser is proposed for an internal mirror type system, in which the fiber is directly connected to the coupling-hole of a resonator mirror by taking exact matching of their diameters each other. This is, on trial, experimentally demonstrated for a CO₂ laser combining with a KRS-5 fiber, obtaining the peak power up to 3 watts with the KRS-5 fiber having the diameter of 1 mm in a conventional compact laser. The theoretical estimates for optimum design is also described, especially on the optimum coupling of a mirror in hemispherical configuration. Furthermore, advantages of the proposed scheme are discussed.

A digest of applications of optical fibre technology in biology and medicine is presented. We describe the topic from several main (according to our opinion) points of view, namely: place of optical fibre and some kinds of optoelectronic equipment among other optical biomedical apparatus, requirements imposed by biomedical environments on the construction of apparatus, possible areas of applications, main confinements of applications and further development. We present here our arbitrary understanding of directions of development of debated field. The bibliography of this problem is quoted and some works carried in this country are emphasized.