Coupling investigation of different RF coil elements for 7-tesla magnetic resonance imaging based on characteristic mode analysis

Here in this paper we propose an approach to investigate the coupling mechanism of different RF coil elements based on characteristic mode analysis. The coil element with lumped-element-connection to the shielding plate focuses the magnetic field below the strip-line due to a loop current from the dominant mode. Denoted by a negative characteristic mode eigenvalue, the coil element without direct connection to the shielding plate behaves more like an electric dipole and the field is distributed mainly above the strip-line. A compromise between these two scenarios which suffers neither from the field below nor above the strip-line achieves an optimal decoupling. FDTD simulation and experimental measurement confirmed the conclusion from characteristic mode analysis.