Histotripsy: Controlled Mechanical Sub-Division of Soft Tissues by High Intensity Pulsed Ultrasound

Cain, Charles A.

Department of Biomedical Engineering, University of Michigan, Ann Arbor, USA

Our primary research goal is to develop a non-invasive image-guided ultrasound procedure for precise and effective tissue ablation for the treatment of many malignant and nonmalignant tumors. Current thermally based local ablation techniques have inherent limitations: (1) lack of reliable imaging feedback for targeting and lesion detection; (2) lack of precision often resulting in damage to the intervening and surrounding tissue; and (3) extensive treatment times for tumors larger than 3cm.  We have developed a new local ablation technique that addresses these limitations. This technique, which we call histotripsy, produces mechanical tissue fractionation using successive high intensity ultrasound pulses. These pulses form mircobubbles and the energetic microbubble activity (acoustic cavitation) that fragments and subdivides tissue structures. Our data show that histotripsy results in complete cellular disruption of treated volumes while preserving adjacent tissues, often leaving intact cells within microns of completely disrupted (fractionated) tissue. The level of tissue ablation depends on the histotripsy acoustic parameters (e.g., pulse intensity, pulse repetition frequency, and the number of pulses). Ultrasound imaging of histotripsy generated bubbles was used successfully for targeting and real-time monitoring of the treatment progress, and histotripsy generated lesions were clearly mapped using ultrasound and magnetic resonance imaging (MRI). Moreover, the imaging information promises to give reliable information on clinical outcome immediately after (or possibly during) treatment informing a clinician when a volume has been sufficiently treated.