Ronald A. Roy
Appl. Phys. Lab., Univ. of Washington, Seattle, WA 98105
J. Brian Fowlkes
Univ. of Michigan Medical Ctr., Ann Arbor, MI 48109
A recently published study reports the direct observation of transient microcavitation in water produced by clinical diagnostic ultrasound [Holland et al., IEEE UFFC 39, 95--101 (1992)]. Results are presented from a similar study in which an aqueous suspension of 0.2-(mu)m-diam polystyrene spheres was insonated by an ATL UM9 scanner operating in the pulse Doppler mode at 3.5 and 5.0 MHz. The suspension was degassed to approximately 90% of saturation. Using a computer automated active cavitation detector [Roy et al., J. Acoust. Soc. Am. 87, 2451--2458 (1990)], cavitation production rates were obtained for a variety of pulse parameters such as intensity, peak negative pressure, pulse length, and pulse repetition frequency. Results suggest a cavitation threshold which is fairly well predicted by the mechanical index calculated from the various pulse waveforms obtained in situ. [Work supported by NIH through Grant No. RO1 CA39374.]