B‐scan ultrasound monitoring of cavitation acitivity in and around the kidney during shock wave lithotripsy

Acoustic cavitation is thought to play a major role in both stone comminution and tissue injury during shock wave lithotripsy (SWL). Although ultrasound machines cannot directly observe cavitation events, remnant gas bubbles appear as echogenic regions. We treated young pigs in an unmodified Dornier HM3 and used a standard clinical ultrasound machine (Bruel and Kjaer 3535) to image the kidney while SWL was being administered. We observed large regions of in vivo echogenicity within the renal pelvis (collecting system), which has not been reported before. When the ureter was blocked, up to 30% of the renal pelvis was covered with echogenicity. Clouds of echogenicity progressed through the collecting system with consecutive shots. The echogenic regions in the renal pelvis could be temporarily enhanced when nondegassed fluid was injected through a ureter catheter. Echogenicity was observed on the posterior and anterior surfaces of the kidney and appeared to occur at sites of subcapsular hematomas. The presence of echogenicity is consistent with the claim that cavitation plays an important role in both stone comminution and tissue damage. [Work supported by NIH and the Hunt Fellowship.]