Shot-to-shot variability of acoustic axis of a spark-source lithotripter

Abstract

The shot-to-shot spatial variability of acoustic and cavitation fields of a spark-source lithotripter was investigated. Spark jitter, variation in the arc strength and location is cited for lack of repeatability in laboratory experiments and is thought to contribute to the success of the Dornier HM3 in comminuting kidney stones, which tend to move during treatment. Transverse variability of the acoustic focus was assessed by measuring the location of the shock wave (SW) induced fountain. The water bath was lowered and a small cup half-filled with ink and having a gridded paper roof was placed at the level of the focus. An ink drop created by the fountain was recorded on the paper. Drop diameter varied from 0–12 mm, location of its center varied by about 1 mm. The extent and location of the cavitation field was measured by high-speed camera. The cavitation cluster was 1×10 cm at its largest extent but bubbles collapsed in a narrow 1–2 mm line. The location of the line was repeatable to within 2 mm. The results indicated that spark jitter affected SW amplitude but had little effect on the location of the acoustic axis. [Work supported by NIH (DK 43881), CRDF and RFBR.]