Bader2018 IEEE Trans Med Imaging.pdf

Histotripsy utilizes focused ultrasound to generate bubble clouds for transcutaneous tissue liquefaction. Image guidance of histotripsy pulses is required to provide spatially resolved monitoring of treatment progress. The aim of this study was to investigate the feasibility of plane wave B-mode and passive cavitation images to be used as binary classifiers of histotripsy-induced liquefaction. Prostate tissue phantoms were exposed to histotripsy pulses over a range of pulse durations (5 – 20 μs) and peak negative pressures (12 – 23 MPa). Acoustic emissions were recorded during the insonation and beamformed to form passive cavitation images. Plane wave B-mode images were acquired following the insonation to detect the hyperechoic bubble cloud. Phantom samples were sectioned and stained to delineate the liquefaction zone. Correlation between passive cavitation and plane wave B-mode images and the liquefaction zone was assessed using receiver operating characteristic (ROC) curve analysis. Liquefaction of the phantom was observed for all insonation conditions. The area under the ROC (0.94 vs. 0.82), accuracy (0.90 vs. 0.83), and sensitivity (0.81 vs. 0.49) was greater for passive cavitation images relative to B-mode images (p < 0.05) along the azimuth of the liquefaction zone. The specificity was greater than 0.9 for both imaging modalities. These results here demonstrate a stronger correlation between histotripsy-induced liquefaction and passive cavitation imaging compared to plane wave B-mode imaging, albeit with limited passive cavitation image range resolution.