2pPAa1. The demographics of cavitation produced by medical ultrasound.

Session: Tuesday Afternoon, May 14

Author: Ronald A. Roy
Location: Appl. Phys. Lab., Univ. of Washington, Seattle, WA 98105


A frequent consequence of moderate-to-high intensity ultrasound is the nucleation and proliferation of acoustic cavitation activity. Nucleation refers to the formation of a gas/vapor bubble resulting from acoustic stress. Cavitation activity is the subsequent energetic motion of these bubbles, and the associated mechanical and thermal effects. The process is very nonlinear. It is appropriate to view the family of cavitation as occupied by distinct, yet related phenomena. For example, if one drives a bubble at moderate amplitudes, stable motion results accompanied by fluid microstreaming. If the same bubble is driven hard, explosive growth is followed by inertial collapse, together with the formation of shock waves, free radicals, etc. When assessing the likelihood of a mechanical bioeffect, one must consider the characteristics of the cavitation field, which can be estimated knowing the properties of the medium, and the properties of the sound field. A tutorial description of basic cavitation dynamics is presented. Attention is given to those aspects of bubble motion that are relevant to medical ultrasound conditions. Associated mechanical and thermal effects are discussed, and the relationships between the characteristics of the sound field and the expected cavitational response of the medium explored. [Work supported by NIH Grant PO1 DK43881-01.]

from ASA 131st Meeting, Indianapolis, May 1996