Histotripsy produced by hundreds of microsecond focused ultrasound pulses in gels and tissue ex vivo

A two-stage treatment was performed to explore the feasibility of generating histotripsy using hundred-microsecond pulses. A single-element 1.06-MHz transducer was used at 8 MPa peak negative pressure with shockwaves. Stage 1 was performed to accelerate the rupture of local tissue structure by boiling bubbles. The pulse group had 500-μs/400-μs pulse duration (PD) and 100-Hz pulse repetition frequency (PRF) with 4.9%/3.9% duty cycle (DC). Stage 2 involved the mechanical homogenization of the lesion by inertial cavitation. Several locations in the lesion axial direction were treated simultaneously by the bubble clusters induced by multiple reflection of shocks. The pulse group had 500-μs/400-μs PD with 100-Hz PRF and 200-μs PD with 200-Hz PRF with 1%/0.88% DC. Experiments were conducted on polyacrylamide phantoms with bovine serum albumin and on rabbit liver tissues ex vivo. Final lesions had a cylindrical shape with smooth borders and total homogenate inside. These results demonstrated that hundred-microsecond pulses enabled controllable histotripsy with a lower acoustic pressure.