Active Doppler monitoring of de novo cavitation induced by a dual-mode pulsed high-intensity focused ultrasound array

Abstract

Pulsed high-intensity focused ultrasound (pHIFU) is capable of inducing inertial cavitation in tissues without the need for microbubbles or other ultrasound contrast agents, thereby permeabilizing the tissue to enhance passive diffusion of systemically administered therapeutic agents. Here, we report on the use of ultrafast, synchronous power Doppler imaging to spatially map cavitation activity and resulting tissue disruption in ex vivo and invivo porcine tissues using a dual-mode imaging-therapy linear pHIFU array. The array (64 elements, aperture 51.2 mm × 14 mm, frequency 1.0MHz, 40% bandwidth) was driven by a power-enhanced Verasonics V1 system to deliver a series of 1 ms pulses at a 1% duty cycle while electronically scanning the pHIFU focus over an azimuthal range of ±1 cm. Plane wave Doppler ensembles were captured immediately after each pHIFU pulse to map the distribution and characteristics of the remnants of cavitation bubbles. The degree of resulting tissue disruption was assessed by histology and was correlated with cumulative Doppler power contours computed over the exposure region. The results show that ultrafast synchronous power Doppler is a promising approach for real-time quantitative monitoring of cavitational therapies. [Work supported by NIH R01EB023910 and T32DK007742.]