Dipole RF element for 7 tesla magnetic resonance imaging with minimized SAR

The coupling between a centrally fed dipole element and a metal (ground) plate used for shielding can be controlled via the termination of the meandered (lower-current) end-sections of the dipole. Here we investigated three different terminations, a lumped chip-capacitor and a distributed open-circuit with and without a high-dielectric substrate around the meander. Based on a novel figure of merit (FoM) for the performance of MRI coils, where the magnetic and the electric field are considered, the length of the three differently loaded dipole elements is optimized systematically using a full-wave FDTD simulator. For the version with high-dielectric (ε_r = 11.2) substrates above and beneath the meanders, a 41 cm-long dipole element exhibits a distinct improvement in the FoM compared to the other two loading strategies. This optimal FoM-behavior is due to an eigen-resonant shielding plate which contributes significantly to the excited electro-magnetic field. The proposed approach to achieve an improvement in the FoM has confirmed by near-field measurement.