Age-dependent microstructural changes of the intervertebral disc: a validation of proteoglycan-sensitive spectral CT

OBJECTIVE: To analyze the two major components of the intervertebral disc (IVD) in an ex vivo phantom, as well as age-related changes in patients. METHODS: Collagen and chondroitin sulfate were imaged at different concentrations in agar solution. Age-related changes in disc density were retrospectively analyzed in normal-appearing discs in dual-energy computed tomography (DECT) images from a patient cohort with various spinal pathologies (n = 136). All computed tomography (CT) scans were acquired using single-source DECT at 80 and 135 kVp with automatic exposure calculation. In 136 patients, the attenuation of normal-appearing discs on collagen/chondroitin maps (cMaps) correlated with the patients’ age with Pearson’s r using standardized regions of interest in the anterior anulus fibrosus (AAF) and nucleus pulposus (NP). RESULTS: DECT collagen mapping revealed concentration-dependent Hounsfield units (HU) of IVD components. For collagen, we found Pearson’s r = 0.9610 (95% CI 0.6789–0.9959), p = 0.0023 at 120 kVe, and r = 0.8824 (95% CI 0.2495–0.9871), p = 0.0199 in cMap. For chondroitin sulfate, Pearson’s r was 0.9583 (95% CI 0.6603–0.9956), p = 0.0026 at 120 kVp, and r = 0.9646 (95% CI 0.7044–0.9963), p = 0.0019 in cMap. Analysis of normal-appearing IVDs revealed an inverse correlation of density with age in the AAF: Pearson’s r = − 0.2294 at 135 kVp (95% CI − 0.4012 to − 0.04203; p=0.0141) and r = − 0.09341 in cMap (95% CI − 0.2777 to 0.09754; p = 0.0003). In the NP, age and density did not correlate significantly at 135 kVp (p = 0.9228) and in cMap (p = 0.3229). CONCLUSIONS: DECT-based collagen mapping allows microstructural analysis of the two main intervertebral disc components—collagen and chondroitin sulfate. IVD density declines with age, presumably due to a reduction in collagen and chondroitin sulfate content. Age-related alterations of disc microstructure appear most pronounced in the AAF. KEY POINTS: • DECT-based collagen mapping allows precise analysis of the two main intervertebral disc components—collagen and chondroitin sulfate. • Intervertebral disc (IVD) density declines with age, presumably due to a reduction in collagen and chondroitin sulfate content. • Age-related alterations of disc microstructure are most pronounced in the anterior anulus fibrosus (AAF). SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00330-021-08028-z.