Acoustic removal of cavitation nuclei to enhance stone comminution in shockwave lithotripsy

Abstract

Cavitation bubbles are formed by shockwaves as part of the normal SWL procedure and can assist in fragmentation when they collapse against a stone. However, following collapse, the bubble cloud leaves behind a large population of residual micron sized bubble “nuclei” that can interfere with subsequent shockwaves. This often manifests as more efficient fragmentation at lower shockwave repetition rates where there is sufficient time for nuclei to dissolve. This study will show how the application of low amplitude, unfocused ultrasound bursts can be used to stimulate bubbles to coalescence or dispersion from the shockwave path by the primary and secondary Bjerknes forces. Applying these bursts in between shockwaves reduces the bubble nuclei shielding effect allowing more energy to reach the stone and increasing efficacy. Our results will show this technique is effective at reducing the number of shocks required for stone comminution on a clinical electromagnetic lithotripter with a simple supplemental transducer to generate the low amplitude field.