An 8Tx/32Rx head-neck coil at 7T by combining 2Tx/32Rx Nova coil with 6Tx shielded coaxial cable elements

Standard head coils used at 7T MRI suffer from high signal loss at lower brain regions and neck. This study aimed to increase the field of view (FOV) of a birdcage coil to image the lower brain regions and neck with a straightforward approach of using add-on transmit shielded coaxial cable coil (SCC) elements.

A new head-neck coil was modeled as a combination of the 2Tx/32Rx Nova head coil and 6Tx SCC elements. The add-on transmit SCC elements have been produced. The full wave electromagnetic simulations were performed to analyze the coil geometry and estimate the local specific absorption ratio (SAR). The $B_1^{+}$ field maps and structural images were acquired in a phantom and in vivo on a 7T scanner.

The computed SAR histogram revealed a peak ${\text{SAR}}_{10g}$ of 4.08 W/kg. The simulated and measured $B_1^{+}$ maps are in good agreement. The manufactured coil's S-parameters are below $-$ 10 dB. The $B_1^{+}$ field measurements on a subject presented the increase in the FOV. The T1-weighted structural images of three subjects acquired with the head-neck coil showed increased coverage compared to the head coil only.

Combining the 2Tx/32Rx Nova head coil and 6Tx SCC elements allowed imaging of the whole brain with an increased FOV down to the C4 spine. The coil stayed fully functional when different subjects were scanned. We conclude that the SCC transmit-only coils are a robust adjunct to conventional coil designs and can meaningfully enhance and expand their field of view.