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Abstract:
Purpose: 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.
Methods: We implemented a closed-form equation of the coil S-parameters and overall spatial B+1
field. We minimized a cost function, consisting of coil S-parameters and the B+1 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 B+1 homogeneity weighting. Using the known voltage range from the host console, we reconstructed the B+1
maps of the array and performed RF shimming with four realistic head models.
Results: As performed with B+1
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 B+1 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 B+1 homogeneity weighting, resulting in an improvement of 28.4 ± 7.5% in B+1
homogeneity with a small 1.9 ± 1.5% decline in power efficiency.
Conclusion: This co-simulation methodology accurately simulates the transceiver, predicting consistent S-parameters, component values, and B+1
field. The RF shimming of the calculated field maps match the in vivo performance.
