Improved quantification of skin sodium through rapid biexponential relaxation measurement and signal loss compensation

Motivation: Sodium MRI detects abnormal skin sodium accumulation in many metabolic disorders, but current methods vastly underestimate actual sodium concentrations because of signal loss from rapid biexponential T2 relaxation. Goal(s): To improve skin sodium concentration measurement accuracy through individual relaxation measurement and compensation. Approach: A spin-3/2 simulation dictionary-based skin sodium relaxometry method including blood sodium contribution was used to compensate signal loss in high-resolution surface-coil images of healthy human calf. Results: Relaxation compensated skin sodium concentration of ~81 mM is much higher than typically reported (~20 mM) and is similar to ~85mM from atomic absorption spectroscopy and skin density. Impact: Previous MRI studies of skin vastly underestimate sodium concentration. Rapid biexponential T2 relaxation measurement enables signal loss compensation to correct skin sodium concentration values.