John Allen
Dept. of Mech. Eng., Univ. of Washington, Seattle, WA 98105
Ronald A. Roy
Univ. of Washington, Seattle, WA 98105
Recent years have seen a host of direct experimental evidence of transient microcavitation in water produced by short pulses of megahertz-frequency ultrasound [Roy et al., J. Acoust. Soc. Am. 87, 2451--2458 (1990); and others]. However, to our knowledge there have been no published accounts of direct observations of such microcavitation activity in biological media. It is useful to relate the results of the aqueous experiments to the likelihood of producing cavitation in tissue. To do this, one must assess the relevant differences between the two media. As a first step in this process, a numerical implementation of the Gilmore equation for adiabatic bubble pulsations is employed [Church, J. Acoust. Soc. Am. 83, 2210--2217 (1988)] and compare predicted thresholds in water and in biological media modeled as a viscous fluid. Comparisons are made with the analytical theory of Holland and Apfel [IEEE UFFC 36, 204--208 (1989)]. The requirement that, at the threshold pressure, the bubble collapse temperature exceed 5000 K provides the rigorous comparison criterion. Results are viewed in light of recent experimental results obtained in water [Calabrese et al., J. Acoust. Soc. Am. 95, 2856 (1994)] and in tissue-mimicking phantom materials [Zheng et al., J. Acoust. Soc. Am. 95, 2855 (1994)]. [Work supported by NIH through Grant No. RO1 CA39374.]