k-t GRAPPA Accelerated Four-Dimensional Flow MRI in the Aorta: Effect on Scan Time, Image Quality, and Quantification of Flow and Wall Shear Stress

Purpose: The purpose of this study was to evaluate the utility of k-t parallel imaging for accelerating aortic four-dimensional (4D)-flow MRI. The aim was to systematically investigate the impact of different acceleration factors and number of coil elements on acquisition time, image quality and quantification of hemodynamic parameters. Methods: k-t accelerated 4D-flow MRI (spatial/temporal resolution 2.1 x 2.5 x 2.5 mm/40.0 ms) was acquired in 10 healthy volunteers with acceleration factors R = 3, 5, and 8 using 12- and 32-channel receiver coils. Results were compared with conventional parallel imaging (GRAPPA [generalized autocalibrating partial parallel acquisition], R 2). Data analysis included radiological grading of three-dimensional blood flow visualization quality as well as quantification of blood flow, velocities and wall shear stress (WSS). Results: k-t GRAPPA significantly reduced scan time by 28%, 54%, and 68%, for R 3, 5, and 8, respectively, while maintaining image quality as demonstrated by overall similar image quality grading. Significant differences in peak WSS (diff(12ch) = -5.9%, diff(32ch) = 18.5%) and mean WSS (diff(32ch) = 13.9%) were found at the descending aorta for both receiver coils for R = 5 (P-WSS < 0.04). Peak velocity differed for R=8 at the aortic root (-7.4%) and descending aorta (-12%) with P-peakVelo < 0.03. Conclusion: k-t GRAPPA acceleration with a 12- or 32-channel receiver coil and an acceleration of 3 or 5 can compete with a standard GRAPPA R 2 acceleration. (C) 2013 Wiley Periodicals, Inc.