MR IMAGING AND COMPUTER RECONSTRUCTION OF FLOW PATTERNS

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MRI velocity encoded phase imaging has the potential for rapid, accurate and precise determination of 3-D blood flow patterns. It is believed that if the capability to display and quantitate these flow patterns were readily available, routine diagnostic utilization would emerge. immediate diagnostic applications include improved measurement of traditional cardiovascular parameters such as cardiac output, stroke volume, regurgitant fractions, pressure gradients, and quantitative assessment of vascular aneurysms and malformations. A new application is the measurement of total left and right coronary artery flow from measurements of velocity in the ascending aorta, aortic root, and proximal portions of these vessels. The broad, long term objective of the application is the development of rapid, accurate and precise MR imaging techniques for reconstruction and visualization of 3-D blood flow patterns. The application will develop (1) cardiac gated, limited field of view (FOV) 3-D velocity encoded pulse sequences for generation of velocity data, and (2) algorithms based on fluid mechanics for reconstruction and display of the flow patterns. Selective RF signal suppression or excitation will be used to allow collection of 3-D data with a small FOV and small number of phase encode steps in each direction. Accuracy and precision of the velocity data will be achieved by adapting 2-D pulse sequence methodology. Time-coded streamlines will be used to visualize the flow patterns. Fluid dynamics conservation laws, vessel boundary, and constant flux constraints will be imposed on the 3-D velocity data to significantly improve the internal consistency of the data and the accuracy and precision of reconstructed streamlines. The new techniques will be applied to the measurement of coronary artery flow. While several groups have developed optimized pulse sequences to visualize the coronary arteries, measurement of total flow is not yet reliable. Differences in pulse sequence design for flow measurement are the need for (I) high temporal resolution to eliminate errors due to pulsatility, (2) thin slices to minimize partial volume errors, and (3) data acquisition through the entire RR interval. The 3-D pulse sequences will measure, in a single sequence, the blood velocity in the ascending aorta, sinuses of Valsalva leading into the coronary arteries, and within the coronary arteries. The reconstruction algorithms will improve the internal consistency of the velocity data and generate flow patterns that are consistent with fluid dynamics constraints.