Abstract

Cavitation Control by Dual Frequency High Intensity Focused Ultrasound

M.R.Bailey, D.J.Halaas, R.Martin (Center for Industrial and Medical Ultrasound, Applied Physics Laboratory, University of Washington, Seattle, WA, USA); A.A.Chulichkov, V.A.Khokhlova (Department of Acoustics, Faculty of Physics, Moscow State University, Moscow, Russia)

e-mail: bailey@apl.washington.edu

Cavitation plays an important role in tumor necrosis, hemostasis, and drug delivery induced by high intensity focused ultrasound (HIFU). On the negative side, cavitation can cause unpredictable lesion distortion or form a barrier to deep sound penetration. On the positive side, cavitation creates hyperecho on B-mode ultrasound useful for targeting and monitoring treatment and is a major mechanism of stimulated local drug delivery. Elevated hydrostatic pressure has been used to suppress cavitation. However, the application of overpressure or underpressure to control cavitation clinically may be limited. Superposition of two different frequencies was used here to study the effect of acoustic waveform on cavitation. Two different cases were considered. First, high frequency 3.5 MHz HIFU pulses were superimposed on either the positive or the negative pressure phase of a low frequency 250 kHz continuous wave so that the local pressure in the tissue was adjusted as the HIFU was applied. Second, two high frequency, 1 MHz and 2 MHz, waves were superimposed with various relative phase shift to achieve the lowest cavitation threshold and to reveal the parameters of acoustic waveform that effect cavitation. The Gilmore-Akulichev model for bubble dynamics was used to numerically calculate the bubble dynamics. Work was supported by NSBRI/NASA, NSF, CRDF, and NIH.

Section : 5