Estimation of skin sodium content via ²³Na magnetic resonance imaging at 3 T using a single-loop surface...

To assess the feasibility of performing quantitative in vivo tissue sodium concentration measurements in the skin with MRI using a sodium-tuned single-loop transmit/receive surface coil at 3 T.

Proton and sodium imaging of skin at the lower back was performed in 17 healthy volunteers on a clinical 3 T system using an anisotropic (1 x 1 x 10 mm) 3D cones sequence. B₁ mapping via the double-angle method was used to account for spatial variation in transmit and receive sensitivity. Apparent tissue sodium concentration (aTSC) was estimated relative to a concurrently imaged phantom of known concentration.

The mean and standard deviation of B₁-corrected aTSC across all subjects were 28 ± 7 mM, approximately 63% higher than previously published studies at 3 T. Although the study was not originally powered to detect gender or racial differences, a higher aTSC was observed in males relative to females (31 ± 5 mM vs. 23 ± 7 mM, distribution 11M/6F).

The skin aTSC values recorded were slightly higher than in some previous studies, which possibly arose from the higher spatial resolution and coil sensitivity utilised here. The recorded values remain lower than those measured at 7 T or via direct tissue sampling. Sex-linked differences in ²³Na-MRI-derived aTSC are consistent with biopsy results described in the literature. A scan duration of ~40 minutes was considered clinically acceptable.