AUTHORS: Wenz D, Dardano T

Magnetic Resonance Materials in Physics, Biology and Medicine, 36: 227–243, April 2023


Objective: To determine whether a multi-feed, loop-dipole combined approach can be used to improve performance of rectangular dielectric resonator antenna (DRA) arrays human brain for MRI at 7 T.
Materials and methods: Electromagnetic field simulations in a spherical phantom and human voxel model “Duke” were conducted for different rectangular DRA geometries and dielectric constants εr. Three types of RF feed were investigated: loop-only, dipole-only and loop-dipole. Additionally, multi-channel array configurations up to 24-channels were simulated. Results The loop-only coupling scheme provided the highest B1 + and SAR efficiency, while the loop-dipole showed the highest SNR in the center of a spherical phantom for both single- and multi-channel configurations. For Duke, 16-channel arrays outperformed an 8-channel bow-tie array with greater B1 + efficiency (1.48- to 1.54-fold), SAR efficiency (1.03- to 1.23-fold) and SNR (1.63- to 1.78). The multi-feed, loop-dipole combined approach enabled the number of channels increase to 24 with 3 channels per block. Discussion This work provides novel insights into the rectangular DRA design for high-field MRI and shows that the looponly feed should be used instead of the dipole-only in transmit mode to achieve the highest B1 + and SAR efficiency, while the loop-dipole should be the best-suited in receive mode to obtain the highest SNR in spherical samples of similar size and electrical properties as the human head.