Parametric mechanism of subharmonic generation by the microbubble contrast agents

• Published in: The Journal of the Acoustical Society of America 2003-04, Vol.113 (4_Supplement), p.2323-2324
• Main Authors: Genis, Vladimir, Oboznenko, Igor, Tran, Dat
• Format: Article
• Language: English
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.4780799

Contrast agents, consisting of gas-filled microbubbles, are widely used in biomedical ultrasound for enhancing the capabilities of ultrasound imaging. The behavior of contrast agents has been shown to lead to the generation of harmonic and subharmonic components in the backscattered signal. The mechanism of subharmonic generation is not quite understood. It is known that the oscillation of gas-filled bubbles is described by nonlinear equations. In this work, the parametric approach to solving this problem is introduced, where the nonlinear equation is substituted by the linear equation with time-varying parameters, such as flexibility of the bubble. The equation describing the oscillation of the bubble is reduced to the Mathieu equation, and conditions for unstable solutions are presented. It has been demonstrated that the regions of instability occur in the vicinity of the frequencies w=1/2 wo, w=3/2 wo, etc., which correspond to generation of the first and higher subharmonics. Criteria for determining the relationship between the acoustic pressure, required for subharmonic generation, and the radius of the air-filled bubble are also determined.