Effects of static and radiofrequency magnetic field inhomogeneity in ultra-high field magnetic resonance imaging

To characterize the severe static (B0) and radiofrequency (B1) magnetic field inhomogeneity in ultra-high field (≥7 T) magnetic resonance imaging, gradient echo (GE) and spin echo (SE) images of in vivo and postmortem human brains were acquired. The B0 and B1 inhomogeneity were experimentally mapped and/or numerically simulated, and correlated with the image artifacts. Whereas B0 inhomogeneity affects predominantly GE images near air/tissue interfaces, B1 inhomogeneity affects SE images more severely and shows nonintuitive patterns. Mapping of the B0 and B1 inhomogeneity is important in characterizing image artifacts. This will help develop better B0 and B1 inhomogeneity correction methods.