A comparison of commercial extracorporeal shock wave lithotripters based on measurements in the acoustic field

Abstract

A survey of five, presently available, commercial extracorporeal shock wave lithotripters is reported. As part of the survey, a detailed examination of the acoustic field of the Dornier HM3, Wolf Piezolith 2200, Technomed Sonolith 2000, EDAP LT‐01, and Siemens Lithostar was carried out using the same 25‐μm, bilaminar PVDF membrane hydrophone. The absolute pressure has been estimated from the voltage waveforms (recorded on a digital scope with a 30‐MHz single‐shot bandwidth) using the 1‐MHz calibration factor for the hydrophone. The peak positive focal pressure at clinically used power settings of the different lithotripters is found to vary in the range 20–115 MPa. The peak negative focal pressure ranges from 3–10 MPa. The width of the focal region (defined as the region in which the peak positive pressure may be greater than 50% of that at the focus) varies from 0.1–2.5 cm. The rise time of the main pressure peak (defined as the time from 10%–90% of the peak positive pressure) is found to vary from less than 30 ns to 500 ns and the full width at a half‐maximum of the positive pressure half‐cycle from 250–500 ns. The estimated peak positive pressure gain of the different systems range from 10 to above 1000. Some of the parameters reported can be related to the relative clinical performance of the lithotripters. [Thanks to the companies and hospitals who provided the facilities for this survey.]