Mixed Imaging Sequences for Improved Spatiotemporal Resolution in Cardiac Imaging

Herrema, Blake

Graduate Thesis Or Dissertation

Mixed Imaging Sequences for Improved Spatiotemporal Resolution in Cardiac Imaging Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/k643b247v

Abstract

Ultrasound imaging of the heart is a vital diagnostic tool in modern medicine. The heart resides in a challenging imaging environment and exhibits a variety of tissue velocities. Therefore, high frame-rate ultrasound sequences are required that can penetrate depth and resolve motion. Modern imaging strategies often transmit either focused waves or broad waves. This work investigated the potential to use REFoCUS, an element-based beamforming method, to combine focused and broad transmissions within a mixed sequence. First, consistency of REFoCUS in the presence of motion was considered both in simulation and experimentally, as compared to virtual source beamforming. By imaging a moving point target, the point spread function (PSF) from differing motion cases was evaluated quantitatively. Each PSF was plotted as a contour plot in order to calculate the metrics of cystic contrast and cystic resolution. Second, REFoCUS was used to beamform mixed RF data that included transmissions from both focused and broad waves. The goal of designing a mixed sequence was to combine the reduced sensitivity to motion offered by focused waves with the ability to increase frame-rate offered by broad waves. The same metrics of contour plots, cystic contrast, and cystic resolution were used here. Applying weighting to mixed sequences reduced motion sensitivity in sequences incorporating broad waves, thereby improving the performance of select mixed sequences. Overall, this work showed that REFoCUS performs comparably to virtual source in terms of motion sensitivity, confirmed that focused transmissions are less sensitive to motion than broad waves, and created a mixed sequence that combines the benefits of focused and broad wave transmissions.

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