Evaluation of Coaxial Dipole Antennas 

The aim of this work was to evaluate a new 8-channel transceiver (TxRx) coaxial dipole array for imaging of the human head at 9.4T developed to improve SAR-performance and provide for a more compact and robust alternative to the existing state-of-the art dipole arrays.

First, the geometry of a single coaxial element was optimized to minimize peak SAR and sensitivity to the load variation. Then, a multi-tissue voxel model was used to numerically simulate a TxRx array coil that consisted of eight coaxial dipoles with the optimal configuration. Finally, we compared the developed array to other human head dipole arrays.

In conclusion, as a proof of concept, we developed and constructed a prototype of a 9.4T (400 MHz) human head array consisting of 8 TxRx coaxial dipoles. The developed 8-element coaxial dipole TxRx array coil showed up to 1.1 times higher SAR-efficiency than a similar in geometry folded-end and fractionated dipole array while maintaining whole brain coverage and low sensitivity of the resonance frequency to variation in the head size. To the best of our knowledge, this is the first example of using coaxial dipoles for human head MRI at UHF.