Local cavitation suppression using cavitation nuclei preconditioning for precise treatment in histotripsy

Our previous work has shown that a highly confined lesion with an area smaller than the natural focal zone can be generated using a cavitation nuclei preconditioning strategy. A cavitation nuclei preconditioning pulse was delivered to the periphery of the focus before each therapy pulse. It was hypothesized that this nuclei preconditioning pulse would destabilize appropriately sized cavitation nuclei in the periphery, therefore suppressing peripheral cavitation. To gain more insight into this phenomenon, this study investigated the effects of nuclei preconditioning pulses on cavitation bubble cloud, cavitation nuclei, and lesion development process. Using high speed photography, we observed that: 1) a narrower and denser bubble cloud was formed within 200 pulses; 2) the cavitation nuclei in the periphery grew to a larger size and migrated out of the periphery after application of the preconditioning pulses; and 3) application of the preconditioning pulses resulted in more efficient treatment in the center of the focus and highly confined lesions. This study supports our hypothesis and furthers our knowledge in the spatial control of cavitation bubble cloud, allowing for active protection of regions immediately surrounding the treatment zone.