Role of cavitation in stone fragmentation by shock wave lithotripsy

Abstract

Several strategies were used to assess the importance of cavitation in the breakage of stones by an electrohydraulic lithotripter in vitro. (1) Stones exposed to SWs at atmospheric pressure broke readily. However, stones treated at high overpressure (OP∼125 atm) sufficient to eliminate cavitation did not break into fragments even with twice the number of SWs. Stones at OP did, however, develop transverse fractures typical of spall. This suggests that cavitation contributes to stone fragmentation, but is clearly not the only mechanism involved in stone breakage. (2) Cylindrical model stones positioned vertically in the acoustic field of a research-EHL showed proximal erosion and spall. However, placement of a mylar disk against the flat leading face of the stone eliminated cavitation-erosion, and spall did not occur. This suggests that cavitation may contribute to stone fracture by spall. (3) Time reversal of the lithotripter wave form using a pressure release reflector (Prel) also prevented stone fragmentation. With the Prel insert the tensile phase of the SW preceding the compressive wave bubble growth is interrupted by P+ and, thus, cavitation is suppressed. Together, these results suggest that cavitation plays an important role in the breakage of stones by lithotripter shock waves. [Work supported by NIH P01-DK43881.]