Chop, grind, puree, liquefy—How to set the right dose on your new histotripsy blender

Exposure to cavitation during histotripsy incrementally mechanically fractionates targeted tissues and, given sufficient exposure, ultimately reduces them to liquefied acellular homogenates. While one-size-fits-all max exposure treatments can be utilized to ensure complete liquefaction in nearly all cases, recent evidence from animal tumor models suggests this is not ideal and indicates there may be dose-dependent anti-tumor immune responses. The “puree” setting (complete cellular necrosis, but with intact cell nuclei remaining) has generally been found to produce the strongest immune responses. Monitoring the level of damage generated during histotripsy, particularly quantitatively and in the sub-liquefied regime, has remained a challenge. While ultrasound (US) imaging-based methods have been demonstrated for detecting the presence of histotripsy ablations, and in select cases the binary identification of complete liquefaction, they generally only work for US-accessible and/or for in-plane targets. Here, we describe methods for measuring acoustic shockwaves emitted during cavitation nucleation and collapse using transmit-receive capable histotripsy transducers to assess the lifespans of generated cavitation (and localize it in 3-D), and quantitatively correlate lifespans with damage outcomes generated in ex vivo tissues, even in targets inaccessible to US imagers (e.g., through the skull). Preliminary results and challenges experienced in in vivo studies are also presented.