A 128-channel receive array with enhanced signal-to-noise ratio performance for 10.5T brain imaging.

PURPOSE

To develop and characterize a 128-channel head array for brain imaging at 10.5 T, evaluate signal-to-noise ratio (SNR) relative to ultimate intrinsic SNR (uiSNR) and lower field strengths, and demonstrate human brain anatomical and functional imaging with this unique magnetic field and high-channel-count array.

METHODS

The coil consists of a 16-channel self-decoupled loop transmit/receive (16Tx/Rx) array with a 112-loop receive-only (Rx) insert. Interactions between the 16Tx/Rx array and the 112Rx insert were mitigated using coaxial cable traps placed every 1/16 of a wavelength on each feed cable, locating most preamplifier boards outside the transmitter field, and miniaturizing those placed directly on individual coils.

RESULTS

The effect of the 112Rx insert on the circumscribing 16Tx/Rx array was minimized, leading to similar transmit field maps obtained experimentally with and without the 112Rx array in place and by electromagnetic simulations of the 16Tx/Rx array alone. The 128-channel array captured 77% of uiSNR centrally. Significantly higher 1/g-factor values across the whole brain was achieved compared with 7 T. Excellent SNR, high parallel-imaging performance, and minimal Tx-Rx interactions collectively facilitated acquisition of high-quality, high-resolution, proof-of-concept functional and anatomical images, including with power-demanding sequences in the human brain.

CONCLUSIONS

Counterintuitive to expectations based on magnetic fields less than or equal to 7 T, the higher channel counts provided SNR gains centrally, capturing about 80% uiSNR. The fraction of uiSNR achieved centrally in 64Rx, 80Rx, and 128Rx arrays suggested that a plateau was being reached at 80%. At this plateau, B-dependent SNR gains for 10.5 T relative to 7 T were approximately linear to quadratic for the periphery and the center, respectively.