SGER: Dynamics of Encapsulated Microbubbles for Medical Ultrasound

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AbstractCTS-0352829K. Sarkar, University of DelawareMicrobubbles are intravenously introduced into a patient's body to enhance the contrast of an ultrasound image. Our aim is to develop a reliable mathematical model for these microbubble contrast agents and characterize different agents with it. Specifically the focus of the modeling is the protective encapsulation of a contrast microbubble made of lipids, proteins or surfactants. Even though free microbubbles (without encapsulation) perform much better in reflecting ultrasound and enhancing image contrast, they issolve in blood stream in few seconds. The encapsulation stabilizes them making contrast imaging possible. Technical merit: A new interface model for the encapsulation with surface rheological properties will be developed. These properties will be determined by in vitro attenuation experiments with clinically approved contrast agents Definity and Optison. We claim that the proposed model of absorbed interface contains the essential physics, and will remain valid over a wider range of frequency and amplitude. We will test this hypothesis by comparing model predictions with scattering experiments (different from those used for model determination). The model parameters will be determined using a linearized version of the model appropriate for experiments with pulses of less energy. However, the developed models nonlinear dynamics will be compared with measured harmonic and subharmonic emissions. Our preliminary modeling with experimental data available in the literature for Optison shows encouraging agreement with measured subharmonic emission. We are collaborating on the clinical implementation of our research with Professors Flemming Forsberg and Barry Goldberg, MD of the Radiology Department at Thomas Jefferson Medical College and Hospital. Beyond contrast ultrasound the proposed research will provide critical understanding of interface dynamics in colloids and suspensions. Broader Impact: Ultrasound examination is the safest and the most popular means of imaging (one in every three imaging studies performed in the world is an ultrasound test). Utility of ultrasonography images however is limited due to poor contrast. For instance, 20 percent of the 17 million echocardiography performed in the United States in 2000 were suboptimal, i.e. did not provide definitive diagnosis for coronary heart disease. A good contrast agent will enable reliable imaging of abnormal blood flows leading to early reliable diagnosis. Use of contrast agent is not limited to heart; it also includes imaging kidney, liver and brain. Development of effective contrast agents and efficient modality can only be achieved through in vitro research with clinical collaboration such as proposed here. The proposed characterization will be used to provide useful guidelines to agent developers (e.g. Amersham Health, Bristol Myers Squibb) and scanner manufacturers (e.g. GE). The research will involve engineering graduate and undergraduate students in a non-traditional cross-disciplinary science of medical imaging.