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.]