Medical Applications of Silver Halide Optical Fibers

Since the early eighties, when lasers were first used in cardiology, Intensive investigation has been carried on to develop a system consisting of a laser and an optical fiber for percutaneous transluminal laser angioplasty. Argon and Nd:YAG lasers were first used, since quartz fibers capable of transmitting visible light were commercially available (1). A persistent high rate of arterial wall perforation has jeopardized in vivo experiments with these two lasers. This arterial wall perforat ion has been attributed to the thermal mechanism by which the tissue was ablated (2). In the last two years it has been demonstrated that lasers such as dye, excimer, CO₂ TEA and Er:YAG -emitting ultrashort, energetic pulses of light, which are strongly absorbed by tissue — should be selected to obtain tissue ablation with minimal thermal damage (3–5). Yet excimer laser pulses shorter than 300 nanometer are poorly transmitted through fused silica optical fibers, while good optical fibers for the transmission of the Er:YAG light at 2.43 micrometer are not yet commercially available. The CO₂ laser was also considered a good candidate for cardiovascular applications. As a system, the CO₂ laser is extremely well developed, featuring continuous (CW), chopped and pulse modes of energy delivery and almost an unlimited variety of energy profiles in the pulsed mode including ultrashort high energy pulses. The lasers are small, efficient, reliable, easy to operate and thus do not require high technical skills.