Bubble translation due to radiation force in SWL

Abstract

The clustering of cavitation bubbles may lead to enhanced stone comminution and influence the extent of tissue damage during shock wave lithotripsy (SWL) treatment. Recent research has focused on changing the SWL pulse, or timing between pulses, to intensify or mitigate collapse or localize these clusters. Such research has targeted radial, not translational motion. We investigate whether bubble translation due to radiation force is sufficiently large to influence cluster formation. The translational dynamics of a single spherical bubble were modeled according to the formulation proposed by Watanabe and Kukita [Phys. Fluids 5(11) (1993)]. After radius-time data were obtained using the Gilmore equation, translational motion was calculated by numerical integration of the Watanabe equation. Calculations were performed for a range of bubble sizes (R0=2–20 μm) and pressure rise times (10−9–10−7 s). The results show that, during bubble growth and collapse induced by a single pulse or two pulses with microsecond delays, bubble translations are ∼0.1 mm. Although bubble translation from a single pulse may not have a noticeable effect on bubble distribution, the effect may be cumulative for the 1000+ shots fired during clinical SWL treatment. [Work supported by NIH DK43881, NSF, CRDF, and FIRCA.]