In vivo soft tissue aberration correction for histotripsy using acoustic cavitation emissions

Phase aberration by heterogeneous soft tissues decreases the focusing quality of transabdominal histotripsy, thereby increasing the energy required to generate cavitation for therapy and elevating the risk of unsafe tissue heating. In vitro studies have shown that the acoustic signals emitted by histotripsy cavitation bubbles can serve as ‘point sources’ for aberration correction (AC). This study assessed the efficacy of cavitation emission-based AC in vivo. A 750-kHz, 260-element, receive-capable histotripsy phased array was used to generate cavitation at 3 locations in the livers of 3 pigs (n = 9). For each location, cavitation emission signals were received and cross correlated to determine a set of corrective phase delays. Then, the array was re-fired at increasing increments of driving power both with and without aberration correction. It was found that AC decreased the transducer power required to generate cavitation by 16%–48%. This result suggests that AC using the cavitation emissions from an initial test pulse can substantially reduce the energy delivered to intervening tissues during histotripsy therapy and thus increase treatment safety.