We propose a simple Actual Flip angle Imaging (AFI) modification to an existing multi-echo 3D-EPI implementation with flexible segmented CAIPIRINHA sampling. The free EPI factor choice makes more efficient use of the long optimal TRs than traditional AFI. Whole-head B1 maps at 5mm isotropic resolution can be acquired in less than 2s, however at the expense of increased signal dropouts at 7T. We explore the benefits of both reduced TEs and increased resolutions to counteract this. We find that a 2.5mm isotropic resolution single-echo protocol acquired in about 10s results in robust whole-head B1 maps with negligible dropouts and distortions.
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