Influence of finite wall impedance on contrast agent bubble behavior near a membrane.

Abstract

Experiments investigating the radial dynamics of ultrasound contrast agent (UCA) microbubbles in the vicinity of an optically transparent membrane show that bubble oscillation amplitude and frequency of peak response decrease as bubbles move closer to the membrane (Overvelde et al. Proc. 19th Intl. Congr. Acoust., 2007). However, treating the membrane as a rigid wall predicts that the peak oscillation amplitude should increase at small standoff distances, contrary to experimental observations. Here we present a model describing UCA bubble dynamics near a locally reacting wall having finite acoustic impedance. If finite wall impedance is included in the model, the predicted bubble behavior is in good agreement with observations. The hybrid time‐frequency domain model is based on a linear frequency domain solution [Ingard, J. Acoust. Soc. Am. 23, 329 (1951)] which has been adapted to account for weakly nonlinear bubble oscillations and UCA shell dynamics. Wall impedance parameters are derived from independent experimental measurements. Comparisons between the model and data from microbubble spectroscopy experiments will be presented. [Work supported by the ASA Hunt Fellowship and NIH DK070618.]