Abstract
PURPOSE: The spoiled gradient recalled echo (SPGR) sequence with variable flip angles (FAs) enables whole liver T1 mapping at high spatial resolutions but is strongly affected by B1+ inhomogeneities. The aim of this work was to study how the precision of acquired T1 maps is affected by the T1 and B1+ ranges observed in the liver at 3T, as well as how noise propagates from the acquired signals into the resulting T1 map. THEORY: The T1 variance was estimated through the Fisher information matrix with a total noise variance including, for the first time, the B1+ map noise as well as contributions from the SPGR noise. METHODS: Simulations were used to find the optimal FAs for both the B1+ mapping and T1 mapping. The simulations results were validated in 10 volunteers. RESULTS: Four optimized SPGR FAs of 2°, 2°, 15°, and 15° (TR = 4.1 ms) and B1+ map FAs of 65° and 130° achieved a T1 coefficient of variation of 6.2 ± 1.7% across 10 volunteers and validated our theoretical model. Four optimal FAs outperformed five uniformly spaced FAs, saving the patient one breath-hold. For the liver B1+ and T1 parameter space at 3T, a higher return in T1 precision was obtained by investing FAs in the SPGR acquisition rather than in the B1+ map. CONCLUSION: A novel framework was developed and validated to calculate the SPGR T1 variance. This framework efficiently identifies optimal FA values and determines the total number of SPGR and B1+ measurements needed to achieve a desired T1 precision.