Cardiorenal 23Na MRI at 7.0 Tesla using a 4/4 channel 1H/23Na RF antenna array

Purpose Cardiorenal syndrome describes disorders of the heart and the kidneys in which a dysfunction of 1 organ induces a dysfunction in the other. This work describes the design, evaluation, and application of a 4/4-channel hydrogen-1/sodium (H-1/Na-23) RF array tailored for cardiorenal MRI at 7.0 Tesla (T) for a better physiometabolic understanding of cardiorenal syndrome. Methods The dual-frequency RF array is composed of a planar posterior section and a modestly curved anterior section, each section consisting of 2 loop elements tailored for Na-23 MR and 2 loopole-type elements customized for H-1 MR. Numerical electromagnetic field and specific absorption rate simulations were carried out. Transmission field (B1+) uniformity was optimized and benchmarked against electromagnetic field simulations. An in vivo feasibility study was performed. Results The proposed array exhibits sufficient RF characteristics, B1+ homogeneity, and penetration depth to perform Na-23 MRI of the heart and kidney at 7.0 T. The mean B1+ field for sodium in the heart is 7.7 +/- 0.8 mu T/root kW and in the kidney is 6.9 +/- 2.3 mu T/root kW. The suitability of the RF array for Na-23 MRI was demonstrated in healthy subjects (acquisition time for Na-23 MRI: 18 min; nominal isotropic spatial resolution: 5 mm [kidney] and 6 mm [heart]). Conclusion This work provides encouragement for further explorations into densely packed multichannel transceiver arrays tailored for Na-23 MRI of the heart and kidney. Equipped with this technology, the ability to probe sodium concentration in the heart and kidney in vivo using Na-23 MRI stands to make a critical contribution to deciphering the complex interactions between both organs.