Nonlinear behavior of ultrasound-insonified encapsulated microbubbles
Résumé
Ultrasound contrast agents consist of small encapsulated bubbles with diameters below 10 µm. The encapsulation influences the behavior of these microbubbles when they are insonified by ultrasound. The highly nonlinear behavior of ultrasound contrast agents at relatively high acoustic amplitudes (mechanical index>0.6) has been attributed to nonlinear bubble oscillations and to bubble destruction. For microbubbles with a thin, highly elastic nanoshell, it has been demonstrated that the presence of the nanoshell becomes negligible at high insonifying amplitudes. From our simulations it follows that the Blake critical radius is not valid for microbubble fragmentation. The low maximal excursion observed and simulated for a thick, stiff-shelled microbubble is in agreement with previous acoustic analyses. The ultrasound-induced gas release from stiff-shelled bubbles has been reported. However, we also observed gas release from microbubbles with a thin, elastic shell.
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