Size Measurement of Tissue Debris Generated from Mechanical Tissue Fractionation by Cavitational Pulsed Ultrasound Therapy — Histotripsy

Our investigations have shown that short (⩽50 μsec) high intensity, low duty cycle ultrasound pulses can achieve significant breakdown of tissue structure. We call this technique “histotripsy”, and inertial cavitation is its hypothesized mechanism. The potential medical applications of histotripsy are vast. There is a concern that erosion debris generated by histotripsy at a tissue‐fluid interface might be an embolization hazard. Therefore, it is essential to measure the size distribution of this tissue debris. A large aperture 512‐element 1‐MHz phased array and a 788‐kHz single element transducer were used to deliver ultrasound pulses. Tissue debris created by erosion at a tissue‐fluid interface and inside lesions in bulk tissue was collected and measured with a particle sizing system. In resulting samples, debris smaller than 6 μm constitutes >99% of the total number of tissue debris particles, and >70% of the total volume. Exposures with shorter pulses produce higher percentages of small tissue debris (<6μm) in comparison to longer pulses. Over 90% of the total number of residual particles is found to be smaller than 2 μm, which is unlikely to be an embolization hazard.