Effects of acoustic parameters on bubble cloud dynamics in ultrasound tissue erosion (histotripsy)

Abstract

High intensity pulsed ultrasound can produce significant mechanical tissue fractionation with sharp boundaries ("histotripsy"). At a tissue-fluid interface, histotripsy produces clearly demarcated tissue erosion and the erosion efficiency depends on pulse parameters. Acoustic cavitation is believed to be the primary mechanism for the histotripsy process. To investigate the physical basis of the dependence of tissue erosion on pulse parameters, an optical method was used to monitor the effects of pulse parameters on the cavitating bubble cloud generated by histotripsy pulses at a tissue-water interface. The pulse parameters studied include pulse duration, peak rarefactional pressure, and pulse repetition frequency (PRF). Results show that the duration of growth and collapse (collapse cycle) of the bubble cloud increased with increasing pulse duration, peak rarefactional pressure, and PRF when the next pulse arrived after the collapse of the previous bubble cloud. When the PRF was too high such that the next pulse arrived before the collapse of the previous bubble cloud, only a portion of histotripsy pulses could effectively create and collapse the bubble cloud. The collapse cycle of the bubble cloud also increased with increasing gas concentration. These results may explain previous in vitro results on effects of pulse parameters on tissue erosion.

Prediction of far-field acoustic emissions from cavitation clouds during shock wave lithotripsy for development of a clinical device

“…In the years since its discovery, several laboratories around the world have found ways to exploit this interpretation of the two peak structure by the Gilmore model to characterize responses as a result of lithotripsy [61][62][63][64][65][66]. Indeed, application of the technique to in vivo data [46] identified the initial bubble size to be used in the CFD simulations in this and earlier papers in the series [14,15,21].…”

Non-thermal ablation of rabbit liver VX2 tumor by pulsed high intensity focused ultrasound with ultrasound contrast agent: Pathological characteristics

“…These include forming non-thermal lesion [12] , damaging DNA, promoting cell apoptosis, inhibiting cell proliferation [13] and even causing histotripsy [14] . Thermal and non-thermal effects can be effectively controlled by adjusting exposure parameters of PHIFU; short duty cycle and high intensity favor the occurrence of cavitation [4] .…”

The influence of gas diffusion on bubble persistence in shock-scattering histotripsy

“…2 Bubbles thought to be nucleated from nanoscale sources expand tens of micrometers in diameter under the tensile phase of the histotripsy pulse. 3 Bubble clouds can persist for more than 50 ms after the acoustic excitation pulse, [4][5][6] even in highly degassed media. Persistent bubbles shield the focal zone from subsequent pulses, preventing complete liquefaction of the target tissues.…”