The sensitivity in NMR imaging can be enhanced by applying the higher static magnetic field. The appearance of the super-conducting magnet makes it easy to increase the resonance frequency as high as 80 MHz. At this range of frequency, the conventional RF coils such as saddle and cross-elliptical coils found to be difficult to operate due to the phase delay along the wire.
RF coil must have a high sensitivity characteristic in the receiving mode, and at the same time it should satisfy the excitation requirements with high RF field homogeneity over the imaging region during the transmitting mode. Under these considerations, several types of ring resonator RF coils for high-field NMR imaging are studied and suggested. Experimental study indicates close agreement with the theoretical analysis.
