Spectral CT electron density for evaluation of lumbar intervertebral disk degeneration

OBJECTIVE: This study aimed to investigate the ability of spectral CT parameters to evaluate lumbar intervertebral disk degeneration (LIDD). SUMMARY OF BACKGROUND DATA: LIDD is the most prevalent cause of low back pain. However, the usefulness of spectral CT for LIDD evaluation remains unclear. METHODS: This retrospective study included consecutive patients who underwent spectral CT and Magnetic resonance imaging for spinal disease examination from February 2018 to June 2021 on a single center. The conventional polyenergetic 120-kVp computed tomography value (CTconv), electron density (ED), and effective atomic number (Zeff) were measured in the annulus fibrosus (AF) and nucleus pulposus (NP) in each disk. Additionally, differences in each spectral CT parameter were obtained between the anterior AF and NP and between the posterior AF and NP. These parametric values were correlated with modified Pfirrmann grade (mPG) using Spearman's rank correlation coefficients. The receiver operating characteristic curve analysis was used to assess diagnostic performances for differentiating between normal and degenerative disks. RESULTS: Three hundred thirty-eight lumbar intervertebral disks of 100 patients were analyzed. The CTconv and ED were negatively correlated with mPG in AF (ρ = -0.29 to -0.36) and positively correlated with mPG in NP (ρ = 0.16-0.45), whereas Zeff in NP was negatively correlated with mPG (ρ = -0.29 to -0.38). The ED differences between the anterior AF and NP and between the posterior AF and NP were strongly correlated with mPG (ρ = -0.71 and -0.64, respectively) and demonstrated high diagnostic performances in differentiating between normal and degenerative disks (area under the receiver operating characteristic curve values = 0.92 and 0.88, respectively). CONCLUSION: Spectral CT parameters, particularly ED, can diagnose lumbar intervertebral disk degeneration.