k-t accelerated aortic 4D flow MRI in under two minutes: Feasibility and impact of resolution, k-space sampling patterns, and respiratory navigator gating on hemodynamic measurements

PurposeTo assess the performance of highly accelerated free-breathing aortic four-dimensional (4D) flow MRI acquired in under 2 minutes compared to conventional respiratory gated 4D flow. MethodsEight k-t accelerated nongated 4D flow MRI (parallel MRI with extended and averaged generalized autocalibrating partially parallel acquisition kernels [PEAK GRAPPA], R=5, TRes=67.2 ms) using four k(y)-k(z) Cartesian sampling patterns (linear, center-out, out-center-out, random) and two spatial resolutions (SRes1= 3.5x2.3x2.6mm(3), SRes2=4.5x2.3x 2.6mm(3)) were compared in vitro (aortic coarctation flow phantom) and in 10 healthy volunteers, to conventional 4D flow (16mm-navigator acceptance window; R=2; TRes=39.2 ms; SRes= 3.2x 2.3x2.4mm(3)). The best k-t accelerated approach was further assessed in 10 patients with aortic disease. ResultsThe k-t accelerated in vitro aortic peak flow (Qmax), net flow (Qnet), and peak velocity (Vmax) were lower than conventional 4D flow indices by 4.7%,11%, and 22%, respectively. In vivo k-t accelerated acquisitions were significantly shorter but showed a trend to lower image quality compared to conventional 4D flow. Hemodynamic indices for linear and out-center-out k-space samplings were in agreement with conventional 4D flow (Qmax13%, Qnet13%, Vmax17%, P>0.05). ConclusionAortic 4D flow MRI in under 2 minutes is feasible with moderate underestimation of flow indices. Differences in k-space sampling patterns suggest an opportunity to mitigate image artifacts by an optimal trade-off between scan time, acceleration, and k-space sampling. Magn Reson Med 79:195-207, 2018. (c) 2018 International Society for Magnetic Resonance in Medicine.