Homogeneity of the RF Field in MRI TEM Coils

摘要

The transverse-plane B1⁺homogeneity in TEM RF coils is shown to be frequency invariant and solely dependent on the excitation purity of the fundamental m=1 mode. It is demonstrated that the capacitive coupling introduced by the interconnecting lumped capacitors should maximize the separation between the resonance frequency of the fundamental mode and that of all other higher order modes in order to maximize this purity. A full-orthogonal excitation of the coil, if possible, would also mitigate this design challenge, especially if high-Q operation cannot be guaranteed. The presented optimization of the capacitive coupling is based on a field theoretical technique of TEM coils, which offers simple analytic design equations. Simulation results are presented to validate the presented approach.