Fast dynamic parallel phase contrast MRI with high acceleration factors and optimized SNR

Introduction: Time-resolved phase contrast (PC) MRI is important for many clinical applications and requires fast data acquisition. In order to increase spatiotemporal resolution or reduce total acquisition times, parallel imaging techniques such as kt-SENSE, kt-BLAST [1] and kt-Grappa [2] have been introduced. For kt-BLAST/ kt-SENSE it has been shown that high reduction factors of the order of R=8 may introduce discrepancies in the measured velocities in PC MRI [3]. Generally, all techniques suffer from decreased SNR and/or increased temporal blurring with increasing acceleration factors. In this study, a method called PEAK-Grappa (Parallel MRI with Extended and Averaged Grappa Kernels) was applied to phase contrast MRI for the evaluation of blood flow in the thoracic aorta. PEAK-Grappa is based on an extended spatiotemporal Grappa kernel in combination with temporal averaging. Qualitative and quantitative results of in-vivo experiments illustrate that the temporal fidelity of timeresolved flow measurements are preserved while SNR was considerable improved compared to conventional Grappa. Most noticeable, the integration of the temporal domain into estimated Grappa reconstruction in conjunction with temporal averaging even permitted imaging with enhanced SNR compared to full k-space reconstruction without temporal averaging.