Objective <p>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.</p> Material and methods <p>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.</p> Results <p>The phantom experiment demonstrated a strong linear relationship between sodium concentration and ²³Na signal intensity (<i>R</i>² = 0.996). In the clinical study, aTSC was significantly associated with T2 ratio (<i>β</i> = 154.5, <i>P</i> &lt; 0.001) and disc thickness (<i>β</i> = 3.38, <i>P</i> = 0.020), inversely correlated with age (<i>r</i> = –0.630, <i>P</i> &lt; 0.001), and not significantly correlated with BMI. aTSC significantly differed across Pfirrmann grades (<i>P</i> &lt; 0.001). Patients with severe back pain had significantly lower aTSC than those without pain (<i>P</i> = 0.005).</p> Conclusion <p>²³Na-MRI enables quantitative, clinically feasible evaluation of lumbar IDD and may serve as a non-invasive biomarker for disc degeneration severity.</p>