Abstract
ObjectiveTo analyze the two major components of the intervertebral disc (IVD) in an ex vivo phantom, as well as age-related changes in patients.MethodsCollagen 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).ResultsDECT 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).ConclusionsDECT-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).
Highlights
MethodsCollagen and chondroitin sulfate were imaged at different concentrations in agar solution
Analysis of different concentrations of collagen solution yielded a high correlation of density and mass at 120 kVe with r = short-tau intensity recovery 0.9610, p = 0.0023 (Fig. 2)
Chondroitin sulfate displayed a significant concentrationdependent density in conventional computed tomography (CT) scans with a positive linear correlation at 120 kVe with Pearson’s r = 0.9583, p = 0.0026, and r = 0.9646, p = 0.0019, in chondroitin maps (cMaps), respectively
Summary
Collagen and chondroitin sulfate were imaged at different concentrations in agar solution. The intervertebral disc connects two vertebral bodies and consists of cartilaginous and fibrous elements—the central nucleus pulposus (NP) and the surrounding anulus fibrosus [3] Collagen and proteoglycans such as chondroitin are the main biochemical components of the disc and are thought to play a significant role in the development of DDD [4, 5]. Several contraindications limit the use of MRI in patients, with an ongoing debate about cardiac implants [10, 11] Another diagnostic modality to assess for discogenic pain would be provocative discography, with contrast application after placing a needle in the IVD [12, 13].
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