Effects of Simplifying Rf Coil 3-D EM Simulation Models on Power Balance and SAR

Mikhail Kozlov¹, Robert Turner

We have investigated the effect on power balance and SAR of simplifying rf coil 3-D EM simulation models, using co-simulation of the RF circuit and 3-D EM fields. We find that sufficiently accurate SAR and power balance estimation cannot be achieved for actual coils using simplified coil models and any renormalization approach. Simulations must converge by mesh refinement not only for B1+ values, but also for radiated and load absorbed powers, and must include simulation of the scanner gradient shield. The effect on SAR of distance to absorbing boundaries and gradient shield depends strongly on RF coil design. Thus coils and their environment need to be specified as accurately as possible, much better than current common practice. If simulation fails to give the correct power balance it is pointless to calculate SAR. In their current implementations, the Ansoft HFSS frequency domain solver provides much more reliable data, and much faster, than the CST time domain solver.