ASA 126th Meeting Denver 1993 October 4-8

2aPAa11. Cooling effect introduced by acoustic streaming.

Junru Wu Andrew J. Winkler Timothy P. O'Neill

Dept. of Phys., Univ. of Vermont, Burlington, VT 05405

It is believed that a fetal exposure to focused ultrasound during the second and third trimesters of pregnancy represents one of the worst-case situations for thermal effects introduced by ultrasound. This is because (1) the ultrasound beam may pass through a distended bladder that is filled with low attenuating fluid, and (2) heating effects may be most pronounced near well-ossified bone of high attenuation coefficient. It was found in recent in vitro experiments that acoustic streaming in low attenuating fluid may dramatically reduce the temperature rise generated by ultrasound at the surface of bone if the ultrasound path contains a low-attenuating-fluid/thin-soft-tissue/bond structure. [Work supported by Hewlett-Packard Co.]