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

Abstract

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.