Design of a Quadrature 1H/31P Coil Using Bent Dipole Antenna and Four-Channel Loop at 3T MRI

MRI using nuclei other than protons is of clinical interest due to the important role of these nuclei in cellular processes. Phosphorous-31 (31P), for example, plays an important role in energy metabolism. However, measurement of 31P can be challenging, as the receive signal is weak compared with that of proton (1H). Consequently, it is often necessary to integrate 1H elements for localizations and B0 shimming in RF coils intended for 31P measurements. Good decoupling between the 1H and the 31P elements is therefore essential. In this paper, bent dipole antennas tuned to 1H were integrated with a four channel 31P loop coil array, in a manner providing strong geometric decoupling between dipoles and loops. As the physical length of a resonant dipole antenna is too long at 3T, the dipole antennas were bent around the load. The loss of 31P elements due to the presence of the dipole antennas was evaluated by measuring scattering parameters and comparing the SNR of 31P spectra with and without the presence of the dipole antennas. The performance of the bent dipole antenna was evaluated by simulation and sensitivity measurement. The Q-factors and the SNR of the four-loop array were reduced by less than 5% when the bent dipole antennas were introduced. The measured sensitivity of the bent dipole was higher (15%) than that of dual-tuned birdcage. The combined bent dipole and loop array is therefore a promising design for 1H/31P applications at 3T.