Extracorporeal shock wave lithotripsy: Method, application, and physical foundation

During the last years a new device has been put into the medical health system allowing for noninvasive treatment of kidney and gall stones: the Dornier lithotripter. The principle methods of shock wave generation are discussed, such as underwater spark discharge, dielectric laser breakdown, electromagnetic and piezoelectric method, and their suitability to disintegrate body concrements effectively. For practical applications, careful choice of system parameters has to be made to fulfill all requirements: good stone disintegration and low pain and side effects for the patients simultaneously. Based on the theory of focusing the relevant physical effects like diffraction, nonlinear propagation, and attenuation (absorption) are explored both qualitatively and quantitatively, so far as possible. It will be shown that a full time-dependent profile calculation can be given within simple diffraction theory accounting for a proper description of the dependence of focusing on aperture, including stress and tensile. The relevance of pulse shape forming will be explored. Additionally nonlinear propagation in relation to damping and pulse deformation in soft tissue is important. Within a simple model the propagation of highly unharmonic pulses will be calculated including nonlinear steepening, anomalous tissue absorption, and dispersion.