Evaluation of lumbar intervertebral disc degeneration using ²³Na-MRI in clinical settings

This study aimed to evaluate the clinical applicability of ²³Na-MRI for the quantitative assessment of lumbar intervertebral disc degeneration (IDD) by comparing ²³Na signal intensities with T2-weighted imaging (T2WI), Pfirrmann classification, and clinical findings.

A phantom experiment using NaCl solutions was conducted to validate the relationship between ²³Na signal intensity and sodium concentration. Lumbar ²³Na-MRI and T2WI were performed on 40 patients. Apparent tissue sodium concentration (aTSC) was calculated using cerebrospinal fluid (CSF) as a reference. Correlations between aTSC and T2 ratio, disc thickness, and Pfirrmann grade were assessed using linear mixed-effects models. Associations between mean aTSC across three discs and age and body mass index (BMI) were evaluated using Pearson's correlation, while differences by self-reported low back pain severity were evaluated using Welch's ANOVA. Differences across Pfirrmann grades were tested using Wald tests with FDR-corrected pairwise models.

The phantom experiment demonstrated a strong linear relationship between sodium concentration and ²³Na signal intensity (R² = 0.996). In the clinical study, aTSC was significantly associated with T2 ratio (β = 154.5, P < 0.001) and disc thickness (β = 3.38, P = 0.020), inversely correlated with age (r = -0.630, P < 0.001), and not significantly correlated with BMI. aTSC significantly differed across Pfirrmann grades (P < 0.001). Patients with severe back pain had significantly lower aTSC than those without pain (P = 0.005).

²³Na-MRI enables quantitative, clinically feasible evaluation of lumbar IDD and may serve as a non-invasive biomarker for disc degeneration severity.