A radially interleaved sodium and proton coil array for brain MRI at 7 T

The objective of the current study was to design and build a dual-tuned coil array for simultaneous Na-23/H-1 MRI of the human brain at 7 T. Quality factor, experimental B-1(+) measurements, and electromagnetic simulations in prototypes showed that setups consisting of geometrically interleaved H-1 and Na-23 loops performed better than or similar to H-1 or Na-23 loops in isolation. Based on these preliminary findings, we built a transmit/receive eight-channel Na-23 loop array that was geometrically interleaved with a transmit/receive eight-channel H-1 loop array. We assessed the performance of the manufactured array with mononuclear signal-to-noise ratio (SNR) and B-1(+) measurements, along with multinuclear magnetic resonance fingerprinting maps and images. The Na-23 array within the developed dual-tuned device provided more than 50% gain in peripheral SNR and similar B-1(+) uniformity and coverage as a reference birdcage coil of similar size. The H-1 array provided good B-1(+) uniformity in the brain, excluding the cerebellum and brain stem. The integrated Na-23 and H-1 arrays were used to demonstrate truly simultaneous quantitative H-1 mapping and Na-23 imaging.