The broad objective of this project is to increase the efficacy of vascular diagnosis by magnetic resonance imaging (MRI). The specific goal is to develop rapid magnetic resonance angiography (MRA) encoding techniques that are robust for flow patterns with spatially and temporally varying motion. These encoding techniques will be employed in sequences which create vessel contrast via either of two mechanisms: 1) inflow enhancement, also called time-of-flight (ToF) contrast, and 2) T1-weighted contrast, used in conjunction with intra-vascular injection of a T1 shortening contrast agent (contrast-enhanced). Applications will be in the carotid arteries and peripheral vasculature, although improvements in pulse sequence design may well be useful in other MRA and non-MRA applications. The first two years of this project will involve implementation, characterization, and optimization of two encoding methods.The first method is spiral scanning and reconstruction for in-plane encoding. The second method, which is the more unique and important part of this grant, is localized quadratic (LQ) encoding with a shifted modulation transfer function (MTF) for through-plane encoding. The combination of these two encoding techniques will serve as the basis for sequence development. The final three years will be used for further sequence development and initial in-vivo studies on normal volunteers and clinical patients. The sequences will be specifically compared to current techniques to assess the following properties: 1) reduction in imaging time, 2) reduction of motion artifacts, 3) reduction of flow voids, and 4) reduction of oblique flow artifact. It is hypothesized that the sequences can achieve all of these improvements with respect to current techniques for both ToF and contrast-enhanced MRA.
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