ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

3aPA4. Measurements of finite-amplitude acoustic pulses radiated from focused piston sources in water.

Michalakis A. Averkiou

Lawrence A. Crum

Appl. Phys. Lab., Univ. of Washington, Seattle, WA 98105

Mark F. Hamilton

Univ. of Texas at Austin, Austin, TX 78712-1063

Measurements of finite-amplitude acoustic pulses radiated by a focused piston source in water are reported. Pulses with center frequency of 2.25 MHz, durations ranging from two to ten cycles, and peak sound pressures up to 3 MPa were measured with a wideband (1--20 MHz) membrane hydrophone. The combined effects of focusing, diffraction, and finite-amplitude distortion on short pulses are demonstrated. Propagation curves for the peak positive and peak negative pressure along the axis of the source are shown. The peak negative pressure, which is an important factor in cavitation dynamics, is maximized in the prefocal region and shifts closer to the source with increasing source amplitude, as predicted earlier [Averkiou et al., 3306(A) (1993)]. Tissue images during treatment with a therapeutic ultrasound device that show increased cavitation activity in the prefocal region are presented. The measurements are compared with theoretical predictions based on the KZK equation and good agreement is found. [Work supported by the National Institutes of Health.]