Acoustic bubble coalescence and dispersion for enhanced shockwave lithotripsy

Abstract

The goal of this study is to develop methods to improve shockwave lithotripsy (SWL). Although cavitation on the surface of a stone may aid fragmentation, cavitation away from the stone may block subsequent shockwaves or cause tissue damage. In previous work, we have shown low amplitude acoustic bursts immediately after each shockwave can force cavitation bubbles to coalesce enhancing SWL efficacy. In this study we examined the feasibility of acoustically dispersing bubbles away from the propagation path immediately before the arrival of the next shockwave. A clinical Dornier lithotripter was used with an in-house made transducer to generate Acoustic Bubble Coalescence and Dispersion (ABCD) pulses fired at different timing with respect to each shockwave. Model stones were treated with 2500 shockwaves at 30 shocks/min or 120 shocks/min and four different ABCD pulse sequences in-vitro. Results showed fragments larger than 2 mm were significantly reduced for all four ABCD sequences cases at 120 shocks/min. The remnant mass of fragments larger than 2 mm was 0.16% at low rate of 30 shocks/min, and 15.81% at 120 shocks/min without ABCD, and 0.19% at 120 shocks/min with ABCD. These results suggest that dispersing residual bubbles can aid in fragmentation efficiency allowing faster SWL treatments.