ASA 127th Meeting M.I.T. 1994 June 6-10

2pBV8. Thresholds for transient cavitation produced in phantoms by pulsed megahertz frequency ultrasound at various pulse conditions.

Xiaoyu Zheng

Qihong Xu

Robert E. Apfel

Ctr. for Ultrason. and Sonics, Yale Univ., New Haven, CT 06520-8286

The purpose of this work is to provide measurements in well characterized media in order to better understand transient cavitation phenomena and eventually to study cavitation-induced, in vivo bioeffects. In order to investigate the potential for transient cavitation generated by pulsed megahertz frequency ultrasound, a modified ``active detection'' system [Roy et al., J. Acoust. Soc. Am. 87, 2451--2458 (1990)] has been used. Highly focused transducers with megahertz center frequencies were used as driving transducers to cause cavitation. Experiments were first conducted in distilled water with polystyrene particles serving as nuclei for cavitation sites. Transient cavitation thresholds were measured for various nuclei concentrations and different sizes of nuclei. Measurements of the cavitation thresholds were then made in some tissue-mimicking (TM) phantom materials that are specially developed to exhibit attenuation coefficients similar to soft tissues. The dependence of the transient cavitation threshold on pulse characteristics (duty cycle, pulse length, pulse repetition frequency) were also investigated. [Work supported by NIH through Grant. No. R01 CA39374.]