The goal of this study was to examine acoustical mechanisms that manipulate cavitation events in order to improve the efficacy of shockwave lithotripsy (SWL) at higher rates. Previous work has shown that applying low amplitude acoustic pulses immediately after each shockwave (SW) can force cavitation bubbles to coalesce and enhance SWL efficacy. In this study, the effects of applying low amplitude acoustic pulses at different time delays is investigated before and after each SW, which would result in different interactions among residual microbubbles producing forced coalescence and dispersion. Utilizing forced coalescence and dispersion was hypothesized to mitigate the shielding effect of residual bubbles, further improving efficacy particularly for higher SWL rates. A set of in vitro experiments was performed in a water tank so that the behavior of bubbles, coalescence and dispersion, could be observed with a high-speed camera. Model kidney stones were treated by a clinical Dornier lithotripter with firing rates of 30 shocks/min and 120 shocks/min, along with an in-house made transducer to generate low amplitude acoustic pulses fired at different pressures and time delays. The average percentage of untreated stone fragments greater than 2 mm was 15.81% for 120 shocks/min without mitigation and significantly reduced to 0.19% for the optimum mitigation protocol.

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