A shielded 32-channel body transceiver array with integrated electronics for 7 T.

Abstract

Purpose: Develop a 32-channel transceiver array for 7 T body imaging that incorporates an RF shield, improves SNR, lowers g-factors, and is robust to external loading.

Methods: The addition of a local RF shield was first investigated for single resonant blocks consisting of either one loop and a dipole (LD) or three loops and a dipole (3LD). A 32-channel array consisting of eight shielded 3LD blocks (32LD-SH) was constructed and validated for in-vivo use. The SNR, parallel imaging, and transmit performance were compared to a previously published 16-channel LD array (16LD). The effect of top loading was investigated by placing arms on top of the coils and measuring S-parameter changes. In vivo imaging of multiple anatomies was performed.

Results: In single block experiments, the RF shield impacted SNR and $B_1^{+}$ performance by <5%. The 3LD blocks had 80% higher peripheral SNR and 25% higher SNR at a depth of 10 cm. The 32LD-SH array had 18% lower $B_1^{+}$ /W^0.5 efficiency and 30% higher central SNR compared to the 16LD array and supported threefold acceleration in the foot-head direction. Arm placement had no effect on the 32LD-SH array but reduced the 16LD match to 5.4 dB.

Conclusion: A 32-channel transceiver array was developed for 7 T body imaging that is insensitive to top loading and has higher SNR and lower g-factors compared to an existing 16-channel transceiver array. Despite lower transmit performance, parallel transmit optimization permitted the 32LD-SH to achieve flip angles necessary for high-quality gradient and spin echo acquisitions of target organs in the chest, abdomen, and pelvis.