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

Sodium (23Na) MRI provides complementarycellular and metabolic information. However, the intrinsicMR sensitivity of 23Na is considerably lower comparedwith that of the proton, making it difficult to measureMR-detectable sodium signals. It is therefore importantto maintain the signal-to-noise ratio (SNR) of the sodiumsignal as high as possible. Double-tuned coils are oftenemployed in combinationwith a 1H coil, providing structuralimages and B0 shimming capability. The double-tuned coildesign can be achieved with the use of two geometricallydecoupled coilswhoseB1 field directions are perpendicularto each other. This can be used to design quadrature-driven,single-nucleus coils to improve SNR, and additionally, thiscoil can also be utilized as a linear-driven double-resonantmode. Here,we have developed and evaluateda quadratureenhanced,double-tuned coil. The novel coil usesPIN-diode switches, inserted only in the loop coil, toshift the resonance frequency between 1H and 23Na sothat 23Na signals can be acquired in quadrature and thecapability of using 1H function remains. Consequently,the 23Na SNR values obtained with the double-tunedcoil are nearly 33% and 17% higher in comparison withgeometrically identical single-tuned coils. SNR plots alsoshow the superiority of double-tuned coil in 23Na