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

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Avdievich,  NI
Department High-Field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Max Planck Society;
Max Planck Institute for Biological Cybernetics, Max Planck Society;

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Citation

Li, X., Pan, J., Avdievich, N., Hetherington, H., & Rispoli, J. (2021). Electromagnetic simulation of a 16-channel head transceiver at 7 T using circuit-spatial optimization. Magnetic Resonance in Medicine, 85(6), 3463-3478. doi:10.1002/mrm.28672.


Cite as: http://hdl.handle.net/21.11116/0000-0007-E481-5
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.