GASTROENTEROLOGY 1991;101:1391-1398 Lithotripsy of Gallstones by Means of a Quality-Switched Giant-Pulse Neodymium:Yttrium-Aluminum-Garnet Laser Basic In Vitro Studies Using a Highly Flexible Fiber System JiiRGEN HOCHBERGER, ERICH GRUBER, PETER WIRTZ, ULRICH DtiRR, ACHIM KOLB, ULF ZANGER, ECKHART G. HAHN, and CHRISTIAN ELL First Department of Medicine and Institute of Biomedical Statistics, Friedrich-Alexander-University, Erlangen-Nuremberg, Germany; Lasag A.G.. Thun, Switzerland; and Richard Wolf A.G., Knittlingen. Germany The quality-switched neodymium:yttrium-alumi- num-garnet laser represents a new instrument for athermal fragmentation of gallstones by transforma- tion of optical energy into mechanical energy in the form of shock waves via local plasma formation. A highly flexible 300-pm fiber transmission system was used in basic investigations to determine the influence of varying pulse repetition rates (5-30 Hz) and pulse energies (15 and 20 mJ) on shock wave intensity and stone fragmentation in vitro for 105 biliary calculi of known size and chemical composi- tion. After performance of 1200 shock wave pressure measurements using polyvinylidenefluoride hydro- phones, stone fragmentation was analyzed by deter- mination of fragment removal rates (volume of frag- ments removed per fragmentation time), ablation rates (mean volume removed per laser pulse), and median fragment sizes for each laser setting. With the quality-switched neodymium:yttrium-aluminum- garnet laser system, all concrements could be reli- ably disintegrated into small fragments (median diameter, 0.7-1.7 mm). Compared with pure choles- terol stones, a significantly higher fragment removal rate was achieved in cholesterol stones containing 30% calcium phosphate (P = 0.039), in cholesterol stones containing 20% pigment (P = O.O15), and in pure pigment stones (P = 0.007). Fragment removal rates, local shock wave pressures, and median grain sizes were significantly higher at a pulse energy of 20 mJ than with 15 mJ. Shock wave pressures showed a distinct dependence on pulse repetition rates at 20 mJ, yet not at 15 mJ. Because there is no evident hazard of thermal damage to tissue using the quality-switched neodymium:yttrium-aluminum- garnet laser, it appears to be a promising device for nonsurgical biliary stone therapy. L aser lithotripsy of giant common bile duct stones represents a new and promising nonsurgical tech- nique implemented via the endoscopic retrograde or percutaneous route. There are reports on successful stone fragmentation by pulsed lasers in preliminary clinical trials. Systems currently used include the free-running-mode solid state neodymium:yttrium- aluminum-garnet (Nd:YAG) laser with millisecond light pulse emission (1,2) and the dye laser in the microsecond pulse range used by other groups (3,4). The advantage of both laser systems lies in their thin and highly flexible 200-pm light transmission fibers that allow their endoscopic retrograde application via conventional duodenoscopes or mother-babyscopes. On the other hand, the thermal nature of the fragmen- tation mechanism of the free-running-mode Nd:YAG laser system presents certain hazards (5,6). Method- inherent thermal damage to the common bile duct can therefore not be excluded, if laser energy is acciden- Abbreviations usedin thispaper: Nd:YAG, neodymium:yttrium- aluminum-garnet: PVDF, polyvinylidenefluoride; Q-switched, quality-switched. LC 1991 by the American Gastroenterological Association 0016~5065/91/$3.00