Double-layered dual-tuned RF coil using frequency-selectable PIN-diode control at 7-T MRI

This article presents a dual-tuned (DT) radiofrequency (RF) coil for signal acquisition of 2 nuclei, namely, hydrogen (¹H) and sodium (²³Na), in the ultra-high magnetic field of a 7-T magnetic resonance imaging (MRI) system. The double-layered dual-tuned (DLDT) coil comprises a 2-loop coil configuration per single-pair geometry, with the ¹H and ²³Na coils being located on the outside and inside, respectively. The ¹H and ²³Na single-pair elements are tuned to resonance frequencies of 297.20 and 78.61 MHz, respectively. The single-pair geometry of the DLDT coil is extended to an 8-pair configuration to cover the human head, and the operation mode is transmission/reception (Tx/Rx). The 8-pair DLDT Tx/Rx coil array is designed with a non-overlapped single pair between the ¹H coil elements for geometric decoupling, and capacitive decoupling is implemented to minimize the mutual inductance coupling. The 2 resonance frequencies are fed through a single RF port to a common matching board, and each frequency is selected using the voltages at both ends of a PIN diode. Through use of the PIN diode in the DLDT coil configuration, with a voltage drop at both ends, different resonance frequencies can be selected for each coil element in accordance with the diode ON/OFF state. The experiments conducted showed that the proposed DLDT coil is effective in acquiring signals of ¹H and ²³Na in the MRI system.