Controlled cavitation to augment SWL stone subdivision: Mechanistic insights in-vitro

The presence of cavitation activity has been identified as a crucial component for SWL stone subdivision. However, its exact role in the comminution process remains somewhat weakly defined, in part due to the fact that it is difficult to isolate the cavitational component from shock waves. In this study, we further explored the importance of cavitation in SWL stone comminution through the use of histotripsy ultrasound therapy. Histotripsy was utilized to target cystine-mimicking model stones with controlled cavitation at strategic time points in the SWL comminution process. Ten model stones were sonicated in-vitro with each of five different treatment schemes: A. SWL with histotripsy interleaved; B. SWL followed by histotripsy; C. Histotripsy followed by SWL; D. SWL-only; E. Histotripsy-only. Following sonication, debris was collected and sieved. It was found that the combination of histotripsy and SWL (A, B, and C) produced a higher degree of comminution than either modality in isolation. When histotripsy controlled cavitation was applied following SWL (B), the increase in exposed stone surface area afforded by shock wave stone subdivision led to enhanced cavitation erosion. When histotripsy controlled cavitation was applied prior to SWL (C), it is likely that stone surface defects induced by cavitation erosion provided sights for crack nucleation and accelerated shock wave stone subdivision. Both these effects are likely at play in the interleaved therapy (A), although shielding of shock waves by remnant histotripsy microbubble nuclei may have limited the efficacy of this scheme.