Quantification of B0 homogeneity variation with head pitch by registered three-dimensional field mapping.

In this study, we quantify the extent to which B(0) homogeneity in adult humans is dependent on head pitch relative to the B(0) vector. Three-dimensional, whole-brain B(0) field maps were acquired in five normal subjects for three generalized head pitch angles. Optimal first- and second-order shimming of the experimental B(0) maps were simulated numerically. The spatial B(0) distribution within the brain was analyzed following automated volumetric co-registration of all data. Increasing head pitch improves both the resonance offset and local homogeneity in the inferior frontal lobes, but introduces inhomogeneities in other regions of the brain which cannot be compensated by first-order shimming but are further improved by second-order shimming.