Subwavelength dielectric waveguide for human head travelling-wave MRI at 7T

Motivation: Radiative excitation (e.g., travelling-wave, TW) has strength in large coverage and low SAR. It’s well compatibility with single-channel (clinical-mode) makes it promising as whole-body excitation solution at UHF. But it has apparent weakness in efficiency. Goal(s): Improve excitation efficiency as well as homogeneity of TW MRI under clinical-mode. Approach: Subwavelength dielectric waveguide was designed to enhance excitation efficiency as well as homogeneity through mode conversion, power-focusing, wave-impedance-matching and phase-velocity-matching. Results: The excitation efficiency was improved by 114% over brain compared to classic TW . SAR efficiency was 10.8% higher than birdcage. The B1+ RMSE in brain was reduced by 21.9% compared to birdcage. Impact: Our results offered insights into the design of new generation TW MRI excitation systems at UHF. The improved TW MRI systems operated under single channel may hold promises to whole-body imaging at UHF in clinical scenarios.