Characterization of an HEM-Mode Dielectric Resonator for 7-T Human Phosphorous Magnetic Resonance Imaging

Goal: To design and characterize a new set-up for dual nuclei MRI combining an annular dielectric resonator filled with high permittivity material for phosphorous (P-31) and a traveling wave antenna for proton imaging. Methods: Recent studies have shown that an annular cylinder filled with water can serve as dielectric resonator for proton MRI of the extremities at 7 T. Using a very high permittivity material such as BaTiO3, this type of dielectric resonator can potentially be designed for lower gyromagnetic ratio nuclei. Combining this with a remote antenna for proton imaging, an alternative method for dual frequency imaging at ultra-high field has been implemented. Results: 3D electromagnetic simulations were performed to examine the efficiency of the dielectric resonator. The new dielectric resonator was constructed for 31P acquisition at 121 MHz on a human 7 TMRI system. Phantom and in vivo scans demonstrated the feasibility of the setup, although the current sensitivity of the dielectric resonator is only half that of an equivalently sized birdcage. Conclusion: The new approach offers a simple implementation for dual nuclei imaging at ultra-high field, with several possibilities for further increases in sensitivity. Significance: Utilizing high permittivity materials enables very simple designs for high field RF coils: in the current configuration the interactions between the proton and phosphorous resonators are very low.