FRAGMENTATION PROCESS OF CURRENT LASER LITHOTRIPTORS

Background and Objective: Flashlamp pumped dye (FPDL), Q-switched Nd:Y AG, and alexandrite lasers are the most clinically used laser lithotri ptors. Although calculi are fragmented by laser induced mechanical str esses for all lithotriptors, different fragment sizes and fragmentatio n efficiencies have been reported. In this work the effect of the puls e duration and pulse shape on the fragmentation processes is studied. Material and Methods: Fragmentation processes are characterized on mod el stones and on sensing target fibers. Stone fragmentation and cavita tion bubble generation are observed by video flash photography. Shock wave occurrence and strength are monitored with an hydrophone. Results : For the FPDL, stone fragmentation is induced by the collapse of the large cavitation bubble formed. For the Q-switched Nd:YAG, fragmentati on is already observed during the laser pulse, at the plasma onset, al though further fragmentation can occur at the bubble collapse. For pul se durations corresponding to the alexandrite, an intermediate fragmen tation regime is observed. Conclusion: For the first time the physical basis of the observed differences in the fragmentation efficiencies o f current laser lithotriptors is described. For nanosecond durations t he fragmentation processes are governed by plasma induced shock waves. On the contrary, for microsecond durations fragmentation is governed by cavitation. The high fragmentation efficiency of microsecond lasers is due to a high laser energy transfer into cavitation. (C) 1995 Wile y-Liss, Inc.