Ultrasound-induced microbubble coalescence by parametric instability
Résumé
Micrometer-sized gas bubbles in a liquid will oscillate upon insonification by ultrasound. During the expansion phase, bubble coalescence is frequently observed. We give a description of the microbubble coalescence mechanism, based on high-speed optical observations and theoretical modeling.Ultrasound-induced microbubble coalescence is the fusion of two or more microbubbles. As adjacent bubbles expand, the following stages can be distinctly observed: flattening of the bubble surfaces prior to contact, drainage of the interposed liquid film toward a critical thickness, rupture of the liquid film, and formation of a single bubble. Locally the critical thickness is more quickly reached than might be explained from film drainage alone, due to thickness perturbations induced by secondary radiation forces and amplified by a parametric instability. The coalescence process is thus sped up to durations of less than 1 μs for ultrasound contrast agent microbubbles in the micron diameter range.The coalescence mechanism presented here has potential clinical applications in harmonic imaging, noninvasive blood pressure measurements, and targeted drug delivery.
Domaines
Physique Médicale [physics.med-ph]
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