Adam Calabrese
Dept. of Phys., Univ. of Mississippi, Oxford, MS 38677
Ronald A. Roy
Univ. of Washington, Seattle, WA 98105
Previously, cavitation due to pulsed megahertz-frequency ultrasound was detected using a technique that only looked for the onset of detectable cavitation [Calabrese et al., Advances in Nonlinear Acoustics, edited by H. Hob(ae ligature)k, pp. 394--399 (1993)]. This method provides little information about cavitation production rates, which may be better correlated to a mechanical bioeffect than the threshold alone. A modified approach using a passive cavitation detector [Roy et al., J. Acoust. Soc. Am. 87, 2451--2458 (1990)] is used to determine the rate of cavitation as a function of acoustic pressure amplitude. Measurements are repeated for a variety of pulse lengths (from 3 to 100 (mu)s) and duty cycles (from 0.1% to 20%) and at frequencies of 1, 2.25, and 5 MHz. Initial results suggest that the threshold pressure for cavitation is weakly dependent on pulse length and decreases with increasing duty cycle. [Work supported by NIH through Grant No. RO1 CA39374.]