A Comparison of FLASH-based Volumetric B1+ Mapping Methods in Phantom at 7 Tesla

Motivation: Fast and accurate B1+ mapping is critical for parallel transmission in ultra-high field MRI, but several options exist, and which is the most optimal is unknown. Goal(s): To evaluate three FLASH-based volumetric B1+ mapping methods; 2D SatTFL, 3D SA2RAGE and 3D Sandwich. Approach: We acquired fully sampled absolute B1+ maps at 7T in a realistic human head phantom across multiple transmission voltages to establish a ground truth and assess the dynamic range of each method. Results: SA2RAGE and Sandwich both enable low-power non-selective RF pulses and maintain accuracy for low B1+ regions. Sandwich has a 60% shorter acquisition time than SA2RAGE. Impact: This study will help to inform a choice of B1+ mapping sequences when imaging at ultrahigh field.