At ultra-high field strengths, e.g. 7 tesla, the homogeneity of the transmit B1+-field and the B0-field decreases compared to lower fields. This can strongly affect the contrast in images especially when imaging large volumes, such as the whole brain.
In this work we measure the mean and variance of B1+- and B0-fields in whole brain images acquired on four, whole-body human 7T scanners. We demonstrate that inter-subject differences dominate over inter-site differences in explaining the observed B0- and B1+-field variability. Inter-session differences are not significant.