The use of real-time passive cavitation imaging for monitoring boiling histotripsy treatments

Abstract

Boiling histotripsy (BH) is a high intensity focused ultrasound method that induces mechanical tissue liquefaction and relies on the formation of a mm-sized vapor bubble at the focus. One challenge of transcutaneous BH is to confirm the presence of such bubble and to differentiate it from prefocal cavitation. Strong prefocal cavitation can shield the focus, prevent initiation of boiling, and lead to unsuccessful treatment, although an echogenic region would still be present on B-mode ultrasound images. Here, a methodology for real-time monitoring of different bubble activity during BH treatment is proposed. Custom BH systems of 1 and 1.5 MHz with inline ultrasound imaging probes connected to a Verasonics V1 system were used for BH treatments in pigs in vivo and in ex vivo tissues. Backscattered signals arriving to the imaging probe were recorded during the 10 ms BH pulses delivered at 1 Hz and passive cavitation imaging (PCI) reconstruction was performed and displayed on top of the B-mode images to identify and classify the regions of bubble activity. Spectral analysis of the PCI signals promoting prefocal cavitation and lack thereof was performed to identify the spectral features corresponding to prefocal cavitation and vapor bubble formation. [Work supported by NIH R01EB007643, R01GM122859, and R01EB25187.]