Design and simulation of a dual-tuned H-1/Na-23 birdcage coil for MRS studies in human calf

Sodium magnetic resonance is a very promising tool for achieving biochemical information on tissue viability, cell integrity and function in quantitative and noninvasive manner. Although it has already been applied in vivo in most human tissues, the low detectable sodium signal gives rise to technological limitations in terms of data quality when using clinical scanners. The design of dedicated coils capable of providing large field of view with high signal-to-noise ratio data is a requirement for quantifying tissutal sodium. This work describes design, simulation, construction and test of a dual-tuned H-1/Na-23 birdcage coil for magnetic resonance (MR) studies in human calf performed with a 3-T MR scanner. Coil simulation was performed using an electromagnetic solver based on finite-difference time-domain (FDTD) method, while the design included matching, tuning and trap circuits' realization for H-1/Na-23 decoupling. Successively, a prototype of the coil was built and tested at workbench, for quality factors, Q ratio measurements and H-1/Na-23 channels' decoupling evaluation. Finally, the coil was employed in a 3-Tesla scanner for acquiring MR data. The results are presented as signal profiles for both coil channels extracted from the phantom chemical shift image and with in vivo imaging performed on human calfs. The designed dual-tuned coil provided good decoupling between H and Na channels, by permitting to maximize the homogeneity of the magnetic field at both the frequencies of interest. Moreover, the simulations accuracy was demonstrated by good agreement between the theoretical and experimental coil signal profiles.