Full-wave modeling of lithotripter fields

Abstract

The propagation of extracorporeal shock wave lithotripter pressure pulses is considered. A computational modeling must account for the effects of diffraction, nonlinear steepening and generation, and propagation of shock waves. Some commercial lithotripters are reflector focusing systems. Therefore, reflections at curved boundaries have to be considered. For specific interests in the propagation through and the interaction with human tissue structures, refraction, absorption, and scattering must be included. A full-wave model based on a set of nonlinear acoustic time domain equations is applied. This system is discretized to obtain a finite difference representation of broad bandwidth and low dispersive character. To enable an accurate shock wave computation an algorithm that modifies the temporal and spatial resolution adaptively is developed. Exemplary a reflector focusing lithotripter is modeled. To validate the model resulting computed wave profiles are compared with measured ones. The measurements are performed using a fiber-optic probe hydrophone. Excellent agreements show the method to provide an accurate and flexible tool for field predictions of complex devices. Characterizing parameters like −6-dB focal regions and energy quantities can be obtained, too. A human tissue model is applied to obtain predictions of the relevant parameters inside the human body.