Characterization of an electromagnetic lithotripter using transient acoustic holography

Abstract

Shock wave lithotripters radiate high intensity pulses that are focused on a kidney stone. High pressure, short rise time, and path-dependent nonlinearity make characterization in water and extrapolation to tissue difficult. Here acoustic holography is applied for the first time to characterize a lithotripter. Acoustic holography is a method to determine the distribution of acoustic pressure on the surface of the source ("source hologram"). The electromagnetic lithotripter characterized in this effort is a commercial model (Dornier Compact S, Dornier MedTech GmbH, Wessling, Germany) with 6.5 mm focal width. A broadband hydrophone (HGL-0200, sensitive diameter 200 µm, Onda Corp., Sunnyvale, CA) was used to sequentially measure the field over a set of points in a plane in front of the source. Following the previously developed transient holography approach, the recorded pressure field was numerically back-propagated to the source surface and then used for nonlinear forward propagation to predict waveforms in different points in the focal region. Pressure signals predicted from the source hologram coincide well with the waveforms measured by a fiber optic hydrophone. Moreover, the method provides an accurate boundary condition from which the field in tissue can be simulated. [Work supported by RSF 14-15-00665 and NIH R21EB016118, R01EB007643, and DK043881.]