Gary B. Hayes

Spectral diagnosis of atherosclerosis using an optical fiber laser catheter.

This communication demonstrates that fluorescence spectra of human aorta with good S/N ratios can be collected using an optical fiber laser catheter. The performance of this catheter is compared to a non-fiber optic collection system with an equivalent delivery/collection geometry. For a given sample, fluorescence lineshapes obtained using the two systems are identical; differences in peak fluorescence intensity are related to the different collection efficiencies of the two systems. It is shown that the fluorescence lineshape of arterial tissue depends on the delivery/collection geometry of the detection system, and that this is due to the interaction of absorption and fluorescence within the artery wall. This effect is investigated systematically using a specially designed collection system. Results are analyzed qualitatively using a simple, one-dimensional model of tissue fluorescence. With this analysis, we present design requirements for a collection system in which such geometric effects are eliminated, and show that our optical fiber laser catheter satisfies these requirements.

Controlled light delivery for laser angiosurgery

Controlled delivery of light is necessary for the precise removal of tissue in laser angiosurgery. We describe an optical fiber laser catheter incorporating a transparent, protective optical shield which provides such control. Tissue removal data characterizing the performance of the device are presented.

Portable Laser Spectrofluorimeter System for in Vivo Human Tissue Fluorescence Studies

A compact, portable spectrofluorimeter which measures broad-band fluorophores with high sensitivity is described. This instrument is specifically designed for acquisition of human tissue autofluorescence spectra in vivo. Pulsed excitation laser light at 337 nm and in the 370–700 nm wavelength range is provided, and the resulting fluorescence can be measured with 10-nm resolution. The system produces single-pulse spectra in human artery wall tissues with a signal-to-noise ratio of 100:1. An optically shielded fiber-optic probe for light delivery and collection permits calibrated intensity information to be obtained.

Time Dependence of Laser-Induced Surface Breakdown in Fused Silica at 355 nm in the Nanosecond Regime

Laser-induced surface breakdown in fused silica has been studied as a function of pulse width in the nanosecond regime. The third harmonic of a Nd:YAG laser was used to produce 7.5 ns duration pulses (FWHM) at 355 nm. A novel system using optical delay lines was used to extend these pulses to variable widths between 7.5 and 400 ns. At each pulse width, the beam was focused onto the surface of a commercially available fused silica flat and the breakdown fluence was determined. The breakdown fluence threshold was found to scale as the pulse width to the 0.8 power, significantly higher than the 0.5 power reported elsewhere for similar cases. Experiments were also performed on 200 jim core fused silica optical fibers and the results Obtained were consistent with a 0.8 power scaling law. This strong scaling law led to a dramatic increase in the amount of 355 nm light that could be transmitted through 200 p.m core fibers - from 1-2 mJ at 7.5 ns up to over 30 mJ at 400 ns. An experiment was also performed to probe the recovery time of fused silica (the time separation between pulses such that their effects are independent). This time was determined to be less than 25 ns.

Argon Ion Laser Angiosurgery In Different Animal Models Using A Multifiber Optical Delivery System

Stenotic or occlusive (two different techniques) lesions were surgically induced in the canine common carotid artery. The lesions were evaluated angiographically prior to as well as after laser angiosurgery (LAS). LAS was performed in 30 dogs using a continuous wave (CW) argon ion laser (Innova 20) coupled to a multifiber, quartz-shielded, fiberoptic catheter. Successful removal of lesion tissue was achieved in 89% of the animals with stenoses and in 40% and 82% in each of the two groups of dogs with occlusions. In the latter two groups, perforation of the vessel wall during LAS was encountered in 60% and 18%, respectively. No perforations occurred in the stenotic animals, where long-term follow-up was possible for up to 60 days with a patency rate of 63% and morphological evidence of excellent healing with complete reendothelialization.