Design of an 8-Channel Transmit 32-Channel Receive 11.7T Head Coil and Evaluation of SNR Gains

To design and develop an 8-channel transmit 32-channel receive 11.7T head coil for the strongest human MRI scanner to date, demonstrate safety, and evaluate signal-to-noise ratio (SNR) gains compared to 7T, the most used ultra-high-field (UHF) platform.

The transmit array design incorporated a folded-end radiofrequency (RF) shield to mitigate wave propagation in the scanner bore. The receive array consisted of 32-overlapped loops constructed on a helmet size-matched with the industry standard 7T head coil. The transmit array was characterized using B₁ ⁺ mapping and MR thermometry, whereas the receive array performance was evaluated by measuring SNR at 7T and 11.7T using a lightbulb-shaped phantom filled with a tissue equivalent solution.

Loss due to wave propagation was 4.5% of the input power for the chosen RF shield. The mean magnitude of the complex correlations between the simulated and measured single channel B₁ ⁺ maps was 94%, which highlights minimal interaction between the transmit and receive arrays. An SNR gain of three-fold was achieved in the phantom centre. In the periphery, representing the cortex, the SNR gain was 2.65-fold, and the average gain over the whole volume was a factor of 2.69. The g-factors of the 11.7T array were lower than the reference 7T coil due to the distinct coil sensitivities at higher frequency.

We report substantial SNR gains over the whole volume at 11.7T using a fully overlapped 32-channel loop array. The central SNR gain of B₀ ^2.14 agrees with the theoretical prediction, while we also gain supra-linearly in the periphery.