Optimal flip angles for in vivo liver 3D T1 mapping and B1+ mapping at 3T

Abstract

Purpose: The spoiled gradient recalled echo (SPGR) sequence with variable flip angles (FAs) enables whole liver (Figure presented.) mapping at high spatial resolutions but is strongly affected by (Figure presented.) inhomogeneities. The aim of this work was to study how the precision of acquired (Figure presented.) maps is affected by the (Figure presented.) and (Figure presented.) ranges observed in the liver at 3T, as well as how noise propagates from the acquired signals into the resulting (Figure presented.) map. Theory: The (Figure presented.) variance was estimated through the Fisher information matrix with a total noise variance including, for the first time, the (Figure presented.) map noise as well as contributions from the SPGR noise. Methods: Simulations were used to find the optimal FAs for both the (Figure presented.) mapping and (Figure presented.) 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 (Figure presented.) map FAs of 65° and 130° achieved a (Figure presented.) 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 (Figure presented.) and (Figure presented.) parameter space at 3T, a higher return in (Figure presented.) precision was obtained by investing FAs in the SPGR acquisition rather than in the (Figure presented.) map. Conclusion: A novel framework was developed and validated to calculate the SPGR (Figure presented.) variance. This framework efficiently identifies optimal FA values and determines the total number of SPGR and (Figure presented.) measurements needed to achieve a desired (Figure presented.) precision.