Effects of Temperature on the Histotripsy Intrinsic Threshold for Cavitation

Abstract

Histotripsy is an ultrasound ablation method that depends on the initiation of a dense cavitation bubble cloud to fractionate soft tissue. Previous work has demonstrated that a cavitation cloud can be formed by a single acoustic pulse with one high amplitude negative cycle, when the negative pressure amplitude exceeds a threshold intrinsic to the medium. The intrinsic thresholds in soft tissues and tissue phantoms that are water-based are similar to the intrinsic threshold of water over an experimentally verified frequency range of 0.3–3 MHz. Previous work studying the histotripsy intrinsic threshold has been limited to experiments performed at room temperature (~ 20°C). In this study, we investigate the effects of temperature on the histotripsy intrinsic threshold in water, which is essential to accurately predict the intrinsic thresholds expected over the full range of in vivo therapeutic temperatures. Based on previous work studying the histotripsy intrinsic threshold and classical nucleation theory, we hypothesize that the intrinsic threshold will decrease with increasing temperature. To test this hypothesis, the intrinsic threshold in water was investigated both experimentally and theoretically. The probability of generating cavitation bubbles was measured by applying a single pulse with one high amplitude negative cycle at 1 MHz to distilled, degassed water at temperatures ranging from 10°C–90°C. Cavitation was detected and characterized by passive cavitation detection and high-speed photography, from which the probability of cavitation was measured vs. pressure amplitude. The results indicate that the intrinsic threshold (the negative pressure at which the cavitation probability = 0.5) significantly decreases with increasing temperature, showing a nearly linear decreasing trend from 29.8±0.4 MPa at 10°C to 14.9±1.4 MPa at 90°C. Overall, the results of this study support our hypothesis that the intrinsic threshold is highly dependent upon the temperature of the medium, which may allow for better predictions of cavitation generation at body temperature in vivo and at the elevated temperatures commonly seen in high intensity focused ultrasound (HIFU) regimes.

For Whom the Bubble Grows: Physical Principles of Bubble Nucleation and Dynamics in Histotripsy Ultrasound Therapy

“…A monotonic decrease in the intrinsic threshold from 29.8 to 14.9 MPa was observed as the temperature of the medium increased from 10˚C to 90˚C. The measured temperature-dependent cavitation threshold matches the relative changes with temperature predicted by a CNT model (Arvengas et al 2011a;Vlaisavljevich et al 2016e). The surface tension was adjusted to 27.5% of its classical value in the CNT model to match the measured threshold values.…”

“…Cavitation probabilities in excess of 50% have not been measured in more viscous liquids (1,3-butanediol and olive oil, m = 97 and 84 cP, respectively, vs. 1 cP for water) (Arvengas et al 2011b;Maxwell et al 2013). The temperature dependence of the intrinsic threshold has been explored in vitro (Arvengas et al 2011a;Vlaisavljevich et al 2016e). A monotonic decrease in the intrinsic threshold from 29.8 to 14.9 MPa was observed as the temperature of the medium increased from 10˚C to 90˚C.…”

Selective detection of cavitation bubbles by triplet pulse sequence in high-intensity focused ultrasound treatment

“…30,31) The radius of the cavitation bubble is affected by the change in tissue elasticity even caused by acoustically induced tissue coagulation. 32) Since the size of the cavitation bubble affects nonlinear echoes, the analysis of bubble echoes may be effective for monitoring the progress of the treatment.…”

Comparative study of the dynamics of laser and acoustically generated bubbles in viscoelastic media

“…The dynamics of a single isolated, spherical, gas-filled bubble in both water and in homogeneous viscoelastic media (representative of the agarose gels) are numerically simulated using an approach similar to previous studies of histotripsy cavitation [25,26,[46][47][48]. In the present study, only acoustically nucleated bubbles are modeled.…”

“…The pressure amplitude, p A = −24 MPa, and frequency, f = 1 MHz (ω = 2πf ), correspond to experimental measurements. The time delay, δ = 5 µs, and fitting parameter, n = 3.7, were chosen as in previous studies [25,26,46,47]. Here, it is hypothesized that the largestamplitude cycle of the waveform gives rise to the bubble growth.…”