Pulsed Cavitational Ultrasound: A Noninvasive Technology for Controlled Tissue Ablation (Histotripsy) in the Rabbit Kidney

TLDR

Minimally invasive treatment of small renal masses is evolving, yet current thermal ablation methods are limited by uneven heating, perfusion, and tissue charring, hindering precise lesion creation. The authors developed a focused annular array ultrasound system delivering high‑intensity, short‑pulse cavitation to achieve controlled, nonthermal renal tissue ablation, with refinement underway for small renal mass treatment. The system emits 20‑µs pulses at >20 kW/cm intensity, repeated at 100 Hz for an average acoustic output of ~5 W, and was used for transcutaneous ablations in 10 rabbits. In rabbits, 10–100 pulses produced scattered damage, whereas 1,000–10,000 pulses produced complete, sharply demarcated, liquefied lesions with acellular cores and minimal surrounding injury, confirming effective nonthermal ablation.

Abstract

The optimal minimally invasive treatment for small renal masses continues to evolve. Current ablative technologies rely on thermal mechanisms for tissue destruction. However, the creation of precise lesions is limited by inhomogeneous heating/cooling due to tissue variability, perfusion effects and tissue charring. We hypothesized that nonthermal mechanical effects of ultrasound (cavitation) can be used to progressively homogenize tissue in controlled fashion with predictable results.We developed a focused annular array ultrasound system capable of delivering high intensity (greater than 20 kW/cm) short pulses (20 microseconds) of energy to a target volume. This system operates at a repetition frequency of 100 Hz, resulting in a low time averaged power output (approximately 5 W total acoustic output). Following approval from the institutional animal care committee a series of transcutaneous ablations were performed in the normal kidneys of 10 rabbits.Lesions created with a small number of pulses (10 or 100) produced scattered areas of damage characterized by focal hemorrhage and small areas of cellular injury in the targeted volume. Lesions created with greater numbers of pulses (1,000 or 10,000) demonstrated complete destruction of the targeted volume. Gross examination revealed that lesions contained a liquefied core with smooth walls and sharply demarcated boundaries. Histological examination demonstrated extensive areas of acellular debris surrounded by a narrow margin of cellular injury.This pulsed cavitational ultrasound system is capable of transcutaneous nonthermal destruction of renal tissue. Refinement of this technology for noninvasive ablation of small renal masses is currently under way.