MRI: Development of a Micro- and Macro- particle Image Velocimetry System for Opaque Flows

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ABSTRACTProposal No. CTS-0421461Principal Investigator: R. Shandas, University of ColoradoDetermination of the velocity field of opaque fluid flows is a challenge in many areas of fluids research, ranging from the imaging of flows in complex shapes that are difficult to render in transparent media, to the demanding constraints of flow in the aerated surf zone. In the context f cardiovascular research, the added requirements of measurements made in living creatures limit the choices and capabilities of flow field instrumentation even further. This grant is to develop a system to meet these needs, based on the synthesis of two existing technologies, Particle Image Velocimetry (PIV) and Brightness-Mode (B-mode) contrast ultrasound echo imaging: Echo PIV. Medical B-mode contrast echo imaging is achieved by the backscatter of ultrasound from "contrast agent", thin-shelled microbubbles of gas that have been injected into the bloodstream. Two sequential images are then subjected to PIV analysis, in which a cross correlation between the two images gives the displacement of the particles, allowing a velocity vector field to be determined based on the time between images. A prototype system is currently in use, but the off-the-shelf components result in spatial resolution and dynamic range inadequate for the current research program in cardiovascular fluid dynamics at the University of Colorado (CU). Advances in ultrasound technology will be required, but are feasible. This system will be used in support of a range of studies of cardiovascular flow at UCHSC. In particular, this system will enable the measurement of fluid shear near the walls of small arteries, answering many questions about the role of shear in vascular diseases. It will enable the measurement of the complex, time dependent flows in the large vasculature, such as the main pulmonary artery and aortic arch in vivo, allowing the validation of modeling efforts that seek to combine realistic solid mechanics models of the walls with pulsatile 3-d flows. It will also be used to increase understanding of ventricular flows, where fluid-physics-based analysis may lead to the differentiation of changes due to age from those due to illness. This work will be disseminated into both the biomedical and experimental fluid dynamics communities via presentations and publications. The PIs are recipients of an NIH training grant, and University of Colorado is the recipient of a grant promoting underrepresented groups in biomedical research: the combination ensures the participation of a wide range of graduate and undergraduate students in the development of this system. Also, this system will be used as examples in both freshman and graduate design courses.