High SNR full brain relaxometry at 7T by accelerated MR‐STAT

Abstract

AbstractPurposeTo demonstrate the feasibility and robustness of the Magnetic Resonance Spin TomogrAphy in Time‐domain (MR‐STAT) framework for fast, high SNR relaxometry at 7T.MethodsTo deploy MR‐STAT on 7T‐systems, we designed optimized flip‐angles using the BLAKJac‐framework that incorporates the SAR‐constraints. Transmit RF‐inhomogeneities were mitigated by including a measured ‐map in the reconstruction. Experiments were performed on a gel‐phantom and on five volunteers to explore the robustness of the sequence and its sensitivity to inhomogeneities. The SNR‐gain at 7T was explored by comparing phantom and in vivo results to MR‐STAT at 3T in terms of SNR‐efficiency.ResultsThe higher SNR at 7T enabled two‐fold acceleration with respect to current 2D MR‐STAT protocols at lower field strengths. The resulting scan had whole‐brain coverage, with 1 x 1 x 3 mm3 resolution (1.5 mm slice‐gap) and was acquired within 3 min including the ‐mapping. After ‐correction, the estimated T1 and T2 in a phantom showed a mean relative error of, respectively, 1.7% and 4.4%. In vivo, the estimated T1 and T2 in gray and white matter corresponded to the range of values reported in literature with a variation over the subjects of 1.0%–2.1% (WM‐GM) for T1 and 4.3%–5.3% (WM‐GM) for T2. We measured a higher SNR‐efficiency at 7T (R = 2) than at 3T for both T1 and T2 with, respectively, a 4.1 and 2.3 times increase in SNR‐efficiency.ConclusionWe presented an accelerated version of MR‐STAT tailored to high field (7T) MRI using a low‐SAR flip‐angle train and showed high quality parameter maps with an increased SNR‐efficiency compared to MR‐STAT at 3T.