High-speed optical experiments demonstrate that the behavior of a polymer-shelled microbubble contrast agent in response to an acoustic pulse is qualitatively and quantitatively different from that of a lipid-shelled agent. The lipid-shelled agent expands in response to a two-cycle pulse, and at pressures approaching 1 MPa, both the shell and its contents fragment. The polymer-shelled agent remains largely intact at pressures up to 1.5 MPa and exhibits a different destruction mechanism: the polymer shell does not oscillate significantly in response to ultrasound; instead, a gas bubble is extruded and ejected through a shell defect while the shell appears to remain largely intact.

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