(515f) Buckling of Phospholipid-Coated Microbubbles in Response to Ultrafast Oscillations

In medical ultrasound imaging, the echo of the blood pool is enhanced using ultrasound contrast agents. The contrast agent studied here consists of a suspension of microbubbles (1 to 5 μm in radius) of an inert gas coated with a phospholipid monolayer, which undergo radial oscillations when excited by the applied ultrasound field. We characterize the dynamics of individual microbubbles through combined manipulation with optical tweezers and ultrahigh speed imaging at 15 million frames per second. The viscoelastic parameters of the monolayer are extracted from a fit to the numerical solution of the evolution equation for the bubble radius. The experiments furthermore reveal that buckling of the phospholipid monolayer increases the nonlinear response of the bubbles at low acoustic pressure, a feature that is highly desirable for contrast enhancement.