Effects of temperature on the histotripsy intrinsic threshold for cavitation

Abstract

A histotripsy cavitation cloud can be formed by a single acoustic pulse with one high amplitude negative cycle, when the negative pressure exceeds a threshold intrinsic to the medium. The intrinsic threshold in water-based soft tissues, which is similar to the intrinsic threshold of water, has been experimentally verified in the range of 24-30 MPa over a frequency range of 0.3-3 MHz at 20°C. In this study, the effects of temperature on the intrinsic threshold was investigated both experimentally and theoretically. Single pulses with one high amplitude negative cycle at 1 MHz were applied 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 indicated that the intrinsic threshold 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, this study supports 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.

The effects of ultrasound pressure and temperature fields in millisecond bubble nucleation

“…Similar experiments have been performed more recently up to 90˚C [29]. The latter reported similar results, however with a scaling value ranging from 25% to 27.5% for the surface tension of water.…”

“…The nucleation pressure threshold has also been referred to as tensile strength, cavitation pressure or intrinsic threshold in the literature [24,29,38,42,45]. In this paper, the terminology "cavitation pressure/threshold" is avoided.…”

“…The classical theory has been put aside in the field of biomedical ultrasound due to overestimated predictions for pressure thresholds under poor physical assumptions. Nevertheless, it has been recently shown that ultrasound cavitation can be modelled with the aid of CNT provided that the surface tension of water is corrected to an effective value [15,28,29]. A similar approach has been successfully applied to therapeutic ultrasound [15].…”

“…A similar approach has been successfully applied to therapeutic ultrasound [15]. This resulted in the development of what is referred to as the intrinsic threshold for cavitation in HIFU [29].…”

“…Nonetheless, this methodology can be extended to the study of HIFU-induced bubble nucleation in most systems with high water content given appropriate parametrisation. Such a fundamental approach was chosen due to the unsuitability of macro-scale fluid dynamics to explain bubble formation, leaving reasonably complicated experiments as the only source of insight into HIFU-induced bubble nucleation [15,28,29]. Likewise, understanding the thermodynamics of bubble nucleation in HIFU pressure and temperature fields is arguably a key component in the planning of HIFU protocols in terms of defining safety windows and establishing best practices.…”