Asymmetric Field Distribution in B1+ & B1- Maps are Caused by Phase Differences in Field Components in the Laboratory Frame

Hidehiro Watanabe¹, Nobuhiro Takaya¹, Fumiyuki Mitsumori¹

Magnitude of B₁⁺ has an asymmetric profile in human brain at high field. We investigated the source of this asymmetry through simple change of the formula on the relationship of RF fields in the rotating and laboratory frames. |B₁⁺| can be expressed as the magnitude and the phase difference of the RF field components in the laboratory frame. While the former component has symmetric profile, the latter has asymmetry in human brains at 4.7 T. From these results, we concluded that the asymmetries in |B₁⁺| and |B₁^-*| maps are derived from the phase difference in the laboratory frame.