Multi-modal assessment of histotripsy liquefaction

Abstract

Histotripsy is an emerging therapeutic ultrasound modality for mechanical tissue liquefaction via bubble cloud activity. Image guidance schemes for histotripsy necessitate both quantification of the bubble cloud activity and accurate delineation of the treatment zone. In this study, magnetic resonance (MR) and passive cavitation imaging (PCI) were combined to assess histotripsy treatment in vitro and ex vivo. Bubble cloud emissions were monitored with PCI. Changes in the medium structure were assessed with T1-, T2-, and diffusion-weighted MR images. Liquefaction zones generated in agarose phantoms and porcine livers were correlated with passive cavitation and MR images through receiver operating characteristic (ROC) analysis. Strong bubble activity was observed for all samples. Histotripsy-induced changes in sample structure were evident on T2-weighted images for all samples, and T1- and diffusion-weighted imaging for liver samples. The locations of the strongest MR pixel values did not necessarily coincide with the locations of the most intense bubble activity. The area under the ROC curve for predicting liquefaction was significantly greater than 0.5 for all imaging modalities, and PCI provided the best prediction of histotripsy damage. These results indicate PCI and MR imaging provide complementary sets of information, demonstrating the utility of multimodal imaging for monitoring of histotripsy.