Recently, collaborations between medical industries and academia have directly benefitted the development of ultrasound contrast agents (UCAs). First generation UCAs consisted of stabilized air-filtered microbubbles. A lack of persistence, led to second generation UCA's, consisting of microbubbles containing high molecular weight gases. Third generation agents are now being pursued. These agents provide, in addition to good sensitivity and long persistence, Selective Fragility, useful in imaging and in drug delivery. The physics of Selective Fragility is complex, and not well understood. The applicants propose to study these microbubbles destruction mechanisms by constructing custom microbubbles, and evaluating them using improved measurement tools and theoretical models. Point Biomedical Corp. will supply custom microbubbles (biSphere(tm)) to the Applied Physics Laboratory (APL) along with acoustic scatter data and high temporal resolution microscope images. The response of these microbubbles to pulsed ultrasound will be characterized at APL by adapting a unique light scattering system that has been used to study cavitation dynamics. This system is capable of real-time direct measurements of a bubble's radial oscillation. "Clumps" of UCAs will also be, measured to access the backscatter amplitude and cavitation thresholds. Successful completion of this project will lead to significant innovations in both diagnostic and therapeutic ultrasound
