Clinical evaluation of cavitation thresholds in patients undergoing lithotripsy

Abstract

Thirty patients undergoing extracorporeal lithotripsy for renal and uteretic stone disease were included in a study of cavitation thresholds. A passive, focused hydrophone was used to detect the 1-MHz component of the broadband noise emmission from bubbles generated at depth in tissue close to the focus of a Stortz Monolith SL20 lithotripter. A theoretical model was used to obtain predictions of the peak negative pressure at the focus of the lithotripter at output settings corresponding to those used clinically. A detectable cavitation threshold was identified in 18 patients. As the output level of the lithotripter is reduced, multiple bubble collapses cease to be detected below a well-defined threshold which is similar in all patients. There is also some evidence that this threshold is dependent on the previous exposure history of the tissue. [Work supported by MRC.]