A simple and analytical way to correct for ΔB0 inhomogeneity in the evaluation of B1 maps relying on flip angle measurements and non-selective square pulses

Introduction: Efficient mitigation of the radiofrequency (RF) inhomogeneity at high field using coil arrays relies on the accurate knowledge of the individual B1 maps. Based on these maps, algorithms using diverse k-space trajectories can return RF waveforms which homogenize the flip angle (FA). The algorithms initially aimed at counteracting the B1 inhomogeneity only [1, 2], until the spatial domain approach was introduced to include B0 variations as well [3]. To date, no simple recipe has been formulated to correct for the latter in the evaluation of the B1 maps themselves. Here we derive a simple analytical approximation to increase the accuracy of the B1 mapping techniques which rely on the measurement of the FA using non-selective square pulses, in the presence of B0 inhomogeneity.