Preclinical Assessment of an Image-Guided Histotripsy System for Renal Ablation

This work presents the development and evaluation of a preclinical ultrasound imaging-guided histotripsy system for non-invasive renal ablation. A primary design consideration for the system was to integrate the therapy source with imaging sequences that provide effective visualization of bubble activity.

A custom focused transducer was manufactured to enabled targeting of the lower and upper poles of the kidney in pig, a common pre-clinical model for renal applications. The transducer included a coaxial opening to integrate a curvilinear imaging probe. An ultrafast imaging sequence that combined subharmonic chirp-coded excitation and Volterra filtering was used for active bubble detection. Passive images of bubble activity were also formed with a pth root algorithm. Bubble detection with these sequences was assessed in a tissue-mimicking phantom and in vivo porcine kidney.

The ultrafast sequence provided improved active bubble detection compared to conventional B mode imaging, with increased bubble-to-tissue and bubble-to interference ratios. Trends captured with passive imaging differed from those collected with ultrafast imaging, providing complementary information on bubble activity. In vivo experiments confirmed these sequences provide improved bubble visualization relative to conventional B-mode imaging. Further, the successful detection of bubble activity with ultrafast imaging was concurrent with visible ablation observed in gross examination and histology.

The system provides safe and effective image-guided histotripsy in the kidney, addressing prior limitations with bubble cloud detection.

This work demonstrates the feasibility of integrating advanced ultrasound imaging onto a histotripsy platform to monitor renal ablation and support accurate and effective treatment.