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

Abstract

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 (¹ H/²³ Na) 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 ²³ Na MR and 2 loopole-type elements customized for ¹ H MR. Numerical electromagnetic field and specific absorption rate simulations were carried out. Transmission field ( $B_1^{+}$ ) uniformity was optimized and benchmarked against electromagnetic field simulations. An in vivo feasibility study was performed.

Results: The proposed array exhibits sufficient RF characteristics, $B_1^{+}$ homogeneity, and penetration depth to perform ²³ Na MRI of the heart and kidney at 7.0 T. The mean $B_1^{+}$ field for sodium in the heart is 7.7 ± 0.8 µT/√kW and in the kidney is 6.9 ± 2.3 µT/√kW. The suitability of the RF array for ²³ Na MRI was demonstrated in healthy subjects (acquisition time for ²³ Na 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 ²³ Na MRI of the heart and kidney. Equipped with this technology, the ability to probe sodium concentration in the heart and kidney in vivo using ²³ Na MRI stands to make a critical contribution to deciphering the complex interactions between both organs.

Keywords: MRI; RF coil; cardiac MRI; cardiorenal syndrome; renal MRI; sodium.