The progress of the previous four years of this program has been substantial. New beams have been discovered and evaluated, new ceramics have been evaluated, novel arrays have been built and studied, and new methods of aberration correction and flow estimation have been demonstrated. Our goal continues to be to develop new beams for improving the quality of medical ultrasound imaging. In this phase of the research we will develop new approaches to velocity estimation based on signal processing techniques developed in the sonar and radar literature collectively called direction-of-arrival (DOA) methods. Our general hypothesis is: Special transducer geometries (for transmit) combined with special beamforming in receive, derived from DOA concepts, will produce quality improvements in blood and tissue velocity imaging. The hypothesis will be tested through four Aims: 1) High-resolution velocity discrimination. Very high velocity resolution methods are developed from dOA theory; 2) Novel clutter rejection approaches which also ensue from DOA theory; 3) True- velocity flow mapping. Doppler flow-mapping process is described as a convolution of the true velocity map and a generalized ambiguity function; and 4) Quantitative schlieren beam imaging. The Doppler beams will be characterized using a specially modified schlieren system. Successful completion of this collaboration between imaging scientists at Mayo and signal processing experts at the University of Minnesota will result in improved medical ultrasound imaging of tissue and blood motion.
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