Parallel-plate waveguide for volume radio frequency transmission in MRI.

PURPOSE: Radiofrequency coils in MRI are narrowband resonant structures. The high-quality factor makes their performance sensitive to loading and other operating conditions. We developed a new coil to provide volume transmit in a broad frequency band.
METHODS: The proposed coil is a parallel-plate waveguide. When operating in the transverse electromagnetic mode, a uniform magnetic field is generated between the plates for imaging. The impedance of the transverse electromagnetic mode is matched by a broadband matching circuit. The two plates are actively driven with broadband Wilkinson power dividers and combiners. Re-entrant design is further applied to improve the overall efficiency.
RESULTS: We developed a prototype of a coil to image the human forearm with a bandwidth of more than one octave. Its feasibility was demonstrated by proton imaging and phosphorous spectroscopy at 7T.
CONCLUSIONS: The proposed coil structure is compact and relatively easier to construct. It can be applied for volume radiofrequency transmit in MRI in a broad frequency band.