Two configurations of the four-ring birdcage coil for 1H imaging and 1H-decoupled 31P spectroscopy of the human head.

The four-ring birdcage resonator, a new class of dual-tuned birdcage resonators, is described. We report two configurations of the coil: the low-pass, high-pass (LP-HP) and the low-pass, low-pass (LP-LP), both of which can be operated in dual quadrature mode at 1.5 T. As head coils, both configurations exhibit greatly reduced tuning interactions between frequencies, permitting rapid, noniterative tuning. Compared with single-tuned, two-ring birdcage resonators of similar volume, the sensitivity and transmitter efficiencies of the resonators are better than 85% for the proton frequency and the same to within 5% for the phosphorus frequency. Circuit models have been developed to refine coil tuning and aid the calculation of B1 field contour plots. Both configurations have been used for integrated examinations involving acquisition of high-quality 1H images and 1H-decoupled 31P CSI spectra of the human head. A scaled-down version of the LP-LP configuration has been demonstrated for use with the human calf.