Transceiver 16-Channel Coaxial-End Dipole Array for Combined Head and C-Spine MRI at 9.4 T

This work aims to design a double-row transceiver array consisting of 16 folded-end coaxial-end dipoles for combined C-spine and brain imaging. The curved coaxial-end dipole elements were aligned on a tight-fitting, ergonomically shaped conformal holder optimized for subject comfort. Transmit efficiency, B₁ ⁺ field homogeneity, and tissue-specific absorption rate (SAR) were numerically evaluated using electromagnetic simulations and optimized with respect to several configurations of the array geometry. After identifying the optimal array configuration, the array was built and tested on a bench and in the MRI scanner, using anatomical imaging and transmit field mapping on a phantom and healthy volunteers. The designed array provided RF excitation over the entire brain and cervical spinal cord down to the C7 region, covering a field of view of more than 365 mm in head-foot direction. Measured in a region covering the cerebrum, cerebellum, brainstem, and C-spine, it achieved B₁ ⁺ field homogeneity of ~31% (coefficient of variation), mean transmit efficiency of ~0.38 μT/√W, and SAR efficiency of 0.65 μT/√W/kg when driven in the circularly polarized mode. The acquired anatomical MR images confirmed that the constructed array provided coverage of the brain and C-spine.