Abstract

Linkage of Cavitation with Spall Failure in Lithotripsy: in Vitro and in Vivo Results

J.C.Williams, J.A.McAteer (Department of Anatomy, Indiana University School of Medicine, Indianapolis, IN, USA); R.O.Cleveland (Department of Aerospace and Mechanical Engineering, Boston University, Boston, MA, USA); Y.A.Pishchalnikov, I.V.Pishchalnikova (Department of Acoustics, Faculty of Physics, Moscow State University, Moscow, Russia)

e-mail: williams@anatomy.iupui.edu

Theoretically, SW's should be able to break kidney stones via tensile forces produced by internal reflection (spall). However, overpressure greatly reduces SW damage to stones, suggesting that cavitation plays an important role in stone breakage. We examined the role of cavitation in a non-overpressure model by using Mylar to block bubble contact with the proximal face of the stone. After 300 SW (20 kV), stones without Mylar showed proximal pitting and distal spall crack, while stones with Mylar showed no pitting and no spall. Model stone cylinders exposed to SW's at different fixed orientations showed a consistent pattern of proximal pitting and distal spall. Examination of stones placed intra-renally into living pigs for SW exposure showed similar results: Stones had sites of erosion and cracks distal to those sites. In addition, the degree of stone comminution was the same between stones treated in vitro and those treated within animals. Conclusion: Spall fracture is linked to cavitation action, both in vitro and in vivo.

Section : 5