異方性を有する膜に覆われた超音波造影気泡の集団としての非線形音響特性

抄録

Using microbubbles coated by a thin shell as Ultrasound Contrast Agents (UCAs) for ultrasound diagnosis improves image resolution. Since numerous microbubbles are used in clinical practice, understanding the acoustic properties of liquids containing multiple microbubbles is important. However, interactions between ultrasound and numerous coated microbubbles have not been fully investigated theoretically. Additionally, ultrasound contrast agents with shells made of various materials have been developed. Recently, Chabouh et al. proposed an equation of motion that considers the anisotropy of the shell [Chabouh et al., J. Acoust. Soc. Am., 149 (2021), 1240] and reported that the anisotropy of the shell affects the resonance of the oscillating bubbles. In this study, we derived a nonlinear wave equation describing ultrasound propagation in liquids containing numerous coated microbubbles based on the method of multiple scales by expanding Chabouh’s equation of motion for a single bubble. This was achieved by considering shell anisotropy in the volumetric average equation for the liquid and gas phases. The anisotropy of the shells was observed to affect the advection, nonlinearity, attenuation, and dispersion of the ultrasound waves. In particular, we have discovered an anisotropic case that suppresses attenuation and promotes nonlinearity.