The Nd:YAG-Laser in Laser-Lithotripsy: Possibilities and Limitations due to System Performance

Abstract

The Nd:YAG laser in its different modes of operation(cw, pulsed, Q-switched)turns out to become the standard laser system in a number of medical disciples, respectively is on the way to establish there. Regarding the endoscopic lithotripsy of urinary and biliary stones, its position however is contested as Q-switched laser pulses with nanosecond pulse duration can only be transmitted via relative inflexible optical fibers with core diameters of 400 urn or larger. An optical breakdown at the distal fiber end can thus only be achieved with additional optical or opto-mechanical components of reduced lifetime. To avoid this it is tried to stretch the pulsewidth of the Nd:YAG laser according to system performance into the microsecond region to produce similar fracturing results as with a flash lamp-pumped dye laser system.

The comparison of possible modes of operation of the Nd:YAG laser in the long-pulse region will show that this is feasible not easy in principal and technical only with great afford. In vitro investigations on synthetic plaster stones with variable pulse lengths to 150 μsec demonstrate the related problems to the endoscopic lithotripsy with microsecond Nd:YAG pulses. The results are compared with a newly developed alexandrite laser system that produces variable pulselengths in the range of 100 to 1000 nanoseconds.