The effect of boundary proximity on the fundamental and subharmonic emissions from individual microbubbles at higher frequencies

• Published in: The Journal of the Acoustical Society of America 2013-05, Vol.133 (5_Supplement), p.3586-3586
• Main Authors: Helfield, Brandon, Leung, Ben, Goertz, David E.
• Format: Article
• Language: English
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.4806607

It is recognized that the proximity of a boundary can influence the dynamic behavior of acoustically stimulated microbubbles. In a biomedical ultrasound context, this is relevant to molecular imaging with targeted microbubbles, and when microbubbles are near vessel walls or contained within microvessels. Theoretical models have recently been developed to examine these effects, but experimental work has been more limited and primarily focused on the assessment of resonant frequency effects rather than its impact on nonlinear behavior, which is perhaps more relevant to imaging applications. Understanding this behavior is important to improving microbubble detection and for the quantitative interpretation of contrast images. With the use of an optical trap, this study experimentally investigates the effect of boundary proximity (0 to 200 µm) and boundary stiffness (Opticell and agarose) on fundamental and subharmonic emissions from individual Definity and MicroMarker bubbles at 11 MHz. The scattered pressure dependence on proximity from an Opticell boundary resulted in an oscillatory dependence, while from an agarose boundary resulted in a decreasing fundamental and an increasing subharmonic response with increasing distance from the boundary. These experimental findings are not entirely captured by basic analytical simulations, likely suggesting that more complex numerical models may be required.