Gallstone lithotripsy with the pulsed dye laser: in vitro studies

The use of a pulsed dye laser to fragment human gallstones is reported. Laser energy was delivered by a 320 microns quartz fibre at wavelengths of 440, 480, 504, 560, 590, and 635 nm, in 1 microsecond pulses at energies of 5-60 mJ per pulse, producing peak powers of the order of 10(5) W. Cholesterol, pigment and mixed stones were fragmented. The shorter wavelengths were most efficient, using significantly less energy at 440 and 480 nm than at the longer wavelengths. Pigment stones were fragmented with significantly less energy than those in which cholesterol predominated. Thermal imaging during laser treatment showed no significant rise in temperature in the bulk of the stone. Absorption spectroscopy of bile revealed a peak at 450 nm, coinciding with the known absorption characteristic of bilirubin. Bile strongly attenuated light at shorter wavelengths, even at dilutions as great as 1:20 and protected samples of biliary epithelium from laser damage except when the optical fibre was in direct contact. The pulsed dye laser may offer significant advantages over current methods of biliary stone fragmentation.