Radiofrequency Coil Tuning Using Matching Circuit Co-Simulation with Magnetic Resonance Integral Equations

Abstract The proposed extension to the conventional circuit co-simulation (CCS) method reliably and efficiently introduces arbitrary matching networks into CCS routines and is here dubbed as matching circuit co-simulation (MCCS). It further achieves coil tuning for resonance and an optimum scattering parameters condition that resembles a fully matched coil. Combined with magnetic resonance integral equations (MARIE), the proposed MCCS further accurately produces a full EM simulation of the coils. We first validated MARIE with the MCCS routine to use it to model simple single-channel coils and parallel transmit (pTx) head arrays coupled with Duke, a digital human body model. Having successfully validated the MCCS routine, we swept through both tuning and matching network parameters to optimize the coil. While optimizing for all parameters simultaneously is a viably efficient option for coil models of low complexity, these models are not realistic, and we found that it becomes a highly computationally expensive problem to solve for more complex coil geometries, such as birdcage coils and pTx coils with higher number of channels, especially when shielding is included. Consequently, we separated tuning and matching into two steps, by first tuning the coil to the right frequency, and then introducing matching networks to enhance the power transmission into the body. We observed lower on-diagonal S-parameters after matching in all pTx coils, but 1 coil still had strong cross-coupling. Finally, electromagnetic fields obtained via MARIE for separate port excitation were successfully combined using MCCS.