Development and Implementation of a PIN-Diode Controlled, Quadrature-Enhanced, Double-Tuned RF Coil for Sodium MRI.

Sodium (Na) MRI provides complementary cellular and metabolic information. However, the intrinsic MR sensitivity of Na is considerably lower compared with that of the proton, making it difficult to measure MR-detectable sodium signals. It is therefore important to maintain the signal-to-noise ratio (SNR) of the sodium signal as high as possible. Double-tuned coils are often employed in combinationwith a H coil, providing structural images and B shimming capability. The double-tuned coil design can be achieved with the use of two geometrically decoupled coils whose B field directions are perpendicular to each other. This can be used to design quadrature-driven, single-nucleus coils to improve SNR, and additionally, this coil can also be utilized as a linear-driven double-resonant mode. Here, we have developed and evaluateda quadrature-enhanced, double-tuned coil. The novel coil uses PIN-diode switches, inserted only in the loop coil, to shift the resonance frequency between H and Na so that Na signals can be acquired in quadrature and the capability of using H function remains. Consequently, the Na SNR values obtained with the double-tuned coil are nearly 33% and 17% higher in comparison with geometrically identical single-tuned coils. SNR plots also show the superiority of double-tuned coil in Na.