Visualization of flow patterns distal to aortic valve prostheses in humansusing a fast approach for cine 3D velocity mapping

The fluid dynamic performance of mechanical heart valves differs from norma l valves and thus is considered related to late clinical complications in p atients. Since flow patterns evolving around heart valves are complex In sp ace and time, flow visualization based on time-resolved 3D velocity data mi ght add important information regarding the performance of specific valve d esigns In vivo. However, previous cine 3D techniques for three-directional phase-contrast velocity mapping suffer from long scan duration and therefor e might hamper assessment In patients. A hybrid 3D phase-contrast sequence combining segmented k-space acquisition with short EPI readout trains is pr esented with its validation in vitro. The technique was applied to study fl ow patterns downstream from a bileaflet aortic prosthesis in six patients. Navigator echoes were incorporated for respiratory motion compensation. Bef ore flow visualization, spurious phase errors due to concomitant gradient f ields and eddy currents were corrected. Flow visualization was based on par ticle paths and animated velocity vector plots. Dedicated algorithms for pa rticle path Integration were implemented to account for the considerable mo tion of the ascending aorta during the cardiac cycle. A distinct flow patte rn reflecting the valve design was observed closest to the valve during ear ly flow acceleration. Reverse flow occurred adjacent to high velocity jets and above the hinge housings. Later in systole, flow became confined to the central vessel area and reverse flow along the inner aortic curvature deve loped. Further downstream from the valve, flow patterns varied considerably among patients, Indicating the impact of varying aortic anatomy In vivo. I t Is concluded that MR velocity mapping is a potential tool for studying 3D flow patterns evolving around heart valve prostheses in humans. (C) 2001 W iley-Liss, Inc.