Multi-feed, loop-dipole combined dielectric resonator antenna arrays for human brain MRI at 7 T

Abstract

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 loop-only 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.

Dipolectric antenna for high‐field MRI

“…Although dielectric pads were introduced to address $$$ {\mathrm{B}}_1^{+} $$$ inhomogeneities, they were also found suitable to improve SNR in human brain MRI at 7 T 18 . Development of DRAs is still an active area of research, and there is an evidence showing that they can be considered an encouraging alternative to loop coil arrays at 7 T and above 19–22 . DRA can be designed as a ceramic block with a desired dielectric constant ε r and low loss tangent (or electrical conductivity σ ).…”