Acoustical And Optical Feedback Guidance For Pulsed Laser Lithotripsy And Angioplasty

Abstract

The feasibility of using acoustic and plasma optical feedback emissions for guidance during pulsed laser lithotripsy and angioplasty procedures was studied in-vitro. A flash-lamp pumped tunable dye laser operating at a wavelength of 504 nm (coumarin green) was used as the laser source. Acoustic signals were recorded with a hydrophone which has a useful frequency response of up to 350 KHz. Plasma optical emissions were transmitted retrograde along the laser fiber and reflected through a beam splitter to an optical detection system consisting of a series of spectral filters (to transmit plasma radiation from 380 to 440 nm and block any 504 nm laser light) and a photomultiplier tube. Measurements of the laser-induced acoustic and the plasma optical emission signals were obtained from urinary and biliary calculi, ex-vivo bovine ureters, blood, blood clots, bile, atheromatous plaque and normal arterial wall. Results of monitoring show that it is possible to know without direct vision whether the laser energy is being discharged in the lumen, on healthy soft tissue, or on calculus or atheromatous plaque. Blood, blood clots, bile produced strong acoustic signals but no plasma signals; calculi and plaque produced strong plasma and strong acoustic signals. Neither plasma nor significant acoustic signals were produced by normal ureteral or arterial wall. These distinctions may allow clinical laser fragmentation of calculi or ablation of plaque to be performed with fewer complications.