Real-time elastography-based monitoring of histotripsy tissue fractionation using color Doppler

Histotripsy uses high intensity, μs-long ultrasound pulses to control cavitating bubble clouds for tissue fractionation. Ultrasound techniques exist to monitor this fractionation progress but due to acoustic interference from the histotripsy pulses and the presence of the hyper-echoic bubble cloud at the therapy focus, treatment must be halted for their application. This paper develops color Doppler as a real-time acoustic radiation force impulse (ARFI)-based feedback during histotripsy. This technique uses histotripsy pulses to apply ARFI and color Doppler to detect the ARFI-induced motion of the residual histotripsy bubbles in the increasingly softer tissue resulting from histotripsy fractionation. Various histotripsy treatments (0.75-1.25 MHz, 3-10 cycles, 50-100 Hz PRF) were applied to ex vivo tissue, with synchronized color Doppler acquisitions providing an estimate of the mean velocity of the focal region displacement in response to the histotripsy pulse using a 5 MHz linear array on a Verasonics imaging system. Depending on the specific Doppler parameters used, clear increasing or decreasing trends in mean velocity were observed as the treatment progressed. This study developed a real-time elastographybased feedback for histotripsy tissue fractionation and demonstrated its feasibility.