ASA 125th Meeting Ottawa 1993 May

3pPA6. Lithotripter shock wave propagation through layered media.

Joseph Jankovsky

P. Ted Christopher

E. Carr Everbach

Dept. of Eng., Swarthmore College, Swarthmore, PA 19081-1397

Recent advances in the computation of shock wave front propagation [P. T. Christopher and K. J. Parker, J. Acoust. Soc. Am. 90, 488--499 (1991)] have allowed the prediction of spark-gap lithotripter waveforms both on and off-axis for a variety of geometries and conditions. Since in both urinary and biliary lithotripsy, shock pulses must propagate through layered human tissues (e.g., fat, muscle, and other soft tissues) it is especially important to understand how waveforms evolve in layered media. Comparisons of computational predictions and experimental results are presented for a laboratory lithotripter of our own construction whose axis of symmetry is vertical. Measurements of waveforms were made using a novel PVDF membrane hydrophone [E. C. Everbach, J. Acoust. Soc. Am. Suppl. 1 87, S128 (1990)] immersed in oil--water layers horizontally stratified by buoyancy forces. The comparisons show sufficient agreement to allow the possibility of optimizing lithotripter reflector geometries so that waveforms could be tailored to accommodate tissue configurations of individual patients.