Electromagnetic simulation of a 16-channel head transceiver at 7 T using circuit-spatial optimization

With increased interest in parallel transmission in ultrahigh-field MRI, methods are needed to correctly calculate the S-parameters and complex field maps of the parallel transmission coil. We present S-parameters paired with spatial field optimization to fully simulate a double-row 16-element transceiver array for brain MRI at 7 T.

We implemented a closed-form equation of the coil S-parameters and overall spatial $$ field. We minimized a cost function, consisting of coil S-parameters and the $$ homogeneity in brain tissue, by optimizing transceiver components, including matching, decoupling circuits, and lumped capacitors. With this, we are able to compare the in silico results determined with and without $$ homogeneity weighting. Using the known voltage range from the host console, we reconstructed the $$ maps of the array and performed RF shimming with four realistic head models.

As performed with $$ homogeneity weighting, the optimized coil circuit components were highly consistent over the four heads, producing well-tuned, matched, and decoupled coils. The mean peak forward powers and $$ statistics for the head models are consistent with in vivo human results (N = 8). There are systematic differences in the transceiver components as optimized with or without $$ homogeneity weighting, resulting in an improvement of 28.4 ± 7.5% in $$ homogeneity with a small 1.9 ± 1.5% decline in power efficiency.

This co-simulation methodology accurately simulates the transceiver, predicting consistent S-parameters, component values, and $$ field. The RF shimming of the calculated field maps match the in vivo performance.