Abstract

Influence of the Direct Wave on Bubbles in Electrohydraulic Lithotripters: in-Vitro Observations

T.Matula, P.R.Hilmo, M.R.Bailey (Center for Industrial and Medical Ultrasound, Applied Physics Laboratory, University of Washington, WA, USA)

e-mail: matula@apl.washington.edu

In shock-wave lithotripsy, or SWL, an acoustic pulse is used to destroy kidney stones. The acoustic pulse for an electrohydraulic shock wave lithotripter is initiated with an underwater spark discharge. A portion of the expanding shock wave is reflected and focused at the stone using an elliptical reflector, resulting in large positive and negative peak pressures. The mechanisms for stone comminution by this shock wave are currently being debated; however, most researchers neglect the effect of the unfocused direct wave, propagating directly from the spark discharge to the stone. Although the direct wave is much smaller in amplitude than the focused wave, it remains sufficiently large to affect bubble dynamics at the lithotripter focus in vitro. Using light scattering techniques recently developed to measure the radial oscillations of a bubble in SWL [T. J. Matula, et. al., Phys. Fluids 14, 913-921 (2002)], we have examined the influence of the direct wave on bubbles at the lithotripter focus. By using an aperture stop, we have been able to remove the direct wave component. This talk will focus on measurements of bubble dynamics from the direct wave, and potential effects that the direct wave can have on existing bubbles.

Section : 5