Influence of Pulse Repetition Rate on Cavitation at the Surface of an Object Targeted by Lithotripter Shock Waves

Abstract

Stone breakage in shock wave lithotripsy is improved by slowing the rate of shock wave (SW) delivery. Previous studies have shown that increased cavitation at fast pulse repetition frequency (PRF) reduces the tensile phase of the SW, while the leading positive wave is virtually unaffected. Since the tensile component of the SW drives cavitation, and since cavitation at the stone contributes to breakage, it seems likely that increased cavitation along the path to the stone affects cavitation at the stone. Here we present preliminary data suggesting that PRF influences bubble dynamics at the stone. High-speed imaging showed that as PRF increased, bubble density of cavitation clouds increased, and the size of individual bubbles decreased. A new method to measure stresses generated by cavitation was used to show that locally induced stresses from bubble collapse can be greater than the incident SW, and were higher at 0.5Hz than at 2Hz PRF.