Evaluation of lumbar intervertebral disc degeneration using dual energy CT virtual non-calcium imaging

Abstract

Purpose: To clarify the utility of dual energy CT (DECT) virtual non-calcium (VNCa) imaging for investigating lumbar intervertebral disc degeneration.

Method: Fifty-three patients who underwent both DECT and MR imaging were retrospectively reviewed. Midsagittal T2-weighted imaging findings of all discs were classified based on modified Pfirrmann grade (mPG). Quantitative evaluation of VNCa maps was achieved by setting volumes of interest on each disc. We compared VNCa CT values with mPG using Spearman's rank correlation and one-way ANOVA. VNCa imaging findings of each disc were classified by two neuroradiologists into one of three categories based on the attenuation of nucleus pulposus (NP) compared to that of annulus fibrosus (AF) or muscle. The relationship between the visual categories for each rater and mPGs was analyzed by chi-square test. Statistical significance was established at P < 0.05.

Results: Among the included 171 lumbar discs, significant positive correlation was found between VNCa CT values for NP and mPGs (R² = 0.574, P < 0.05), whereas no significant correlation was found between those for AF and mPGs (R²= -0.015, P = 0.846). Mean VNCa CT values for NP were significantly different among each mPG (P < 0.05 for each), except between grades 3 and 4 (P = 0.111). Mean VNCa CT values for AF were not significantly different among each mPG (P = 0.160-1.000). Statistically significant difference was observed among the visual categories for VNCa maps and mPGs in each rater (P < 0.05 for both).

Conclusions: VNCa imaging acquired by a single DECT scan and post-processing has potential as an imaging biomarker of lumbar intervertebral disc degeneration.

Keywords: Annulus fibrosus; Dual energy CT; Intervertebral disc degeneration; Modified Pfirrmann grade; Nucleus pulposus; Virtual non-calcium imaging.