MECHANISMS OF BILIARY STONE FRAGMENTATION USING THE HO-YAG LASER

We have investigated the fragmentation of gallstones using the pulsed Ho:YAG laser, comparing it to lithotripsy using the visible pulsed-dye laser. We find that the physical mechanisms of stone fragmentation ap pear to be quite different in the two cases. Using high-speed photogra phy, measurement of acoustic transients, time-resolved optical emissio n spectroscopy, and direct microscopic observation, we have analyzed t he interaction of the Ho:YAG laser with both water and gallstones. We propose a new model in which fragmentation begins with absorption of t he laser light by the stone surface. This is followed by melting and e jection of stone material, which is then swept away by the vapor bubbl e formed by the absorption of the Ho:YAG laser light by water. This mo del is in excellent agreement with our experimental observations, and differs substantially from the model developed by Teng et al. for lase r lithotripsy using the visible pulsed-dye laser.