ObjectiveTo assess the diagnostic accuracy of radiography (X-ray, XR), CT and MRI of the sacroiliac joints for diagnosis of axial spondyloarthritis (axSpA).Methods163 patients (89 with axSpA; 74 with degenerative conditions) underwent XR, CT and MR. Three blinded experts categorised the imaging findings into axSpA, other diseases or normal in five separate reading rounds (XR, CT, MR, XR +MR, CT +MR). The clinical diagnosis served as reference standard. Sensitivity and specificity for axSpA and inter-rater reliability were compared.ResultsXR showed lower sensitivity (66.3%) than MR (82.0%) and CT (76.4%) and also an inferior specificity of 67.6% vs 86.5% (MR) and 97.3% (CT). XR +MR was similar to MR alone (sensitivity 77.5 %/specificity 87.8%) while CT+MR was superior (75.3 %/97.3%). CT had the best inter-rater reliability (kappa=0.875), followed by MR (0.665) and XR (0.517). XR +MR was similar (0.662) and CT+MR (0.732) superior to MR alone.ConclusionsXR had inferior diagnostic accuracy and inter-rater reliability compared with cross-sectional imaging. MR alone was similar in diagnostic performance to XR+MR. CT had the best accuracy, strengthening the importance of structural lesions for the differential diagnosis in axSpA.

BackgroundTo analyse the added value of susceptibility-weighted imaging (SWI) compared with standard T1-weighted (T1) MRI for detecting structural lesions of the sacroiliac joint (SIJ) in patients with axial spondyloarthritis (axSpA) using CT as reference standard.Material and methodsSixty-eight patients with suspected or proven axSpA underwent both MRI and CT of the SIJ on the same day. Two readers separately scored CT, T1 and SWI for the presence of erosions, sclerosis and joint space changes using an established 24-region SIJ model. Disagreement was resolved by a third reader. Diagnostic accuracy (McNemar test), Cohen’s kappa (k), sensitivity (SE) and specificity were calculated on the joint level using CT as reference.ResultsIn CT, 38 joints showed erosions, 67 sclerosis and 37 joint space changes. Agreement with CT for erosions was 92.6% (k=0.811 (0.7–0.92)) in SWI and 87.5% (k=0.682 (0.54–0.82)) in T1 (p=0.143) and agreement for sclerosis 84.6% (k=0.69 (0.57–0.81)) and 62.5% (k=0.241 (0.13–0.35)) (p<0.001), respectively. This resulted in superior SE of SWI (81.6% vs 73.7%) for erosions and sclerosis (74.6% vs 23.9%) at a minor expense of SP. No differences were detected for joint space changes.ConclusionIn patients with axSpA, SWI depicts erosions and sclerosis more accurately than T1 spin echo MRI at 1.5 T.

ObjectivesTo propose a data-driven definition for structural changes of sacroiliac (SI) joints in the context of axial spondyloarthritis (axSpA) imaging on a large collective of CT datasets.Methods546 individuals (102 axSpA, 80 non-axSpA low back pain and 364 controls without back pain) with SI joint CTs were evaluated for erosions, sclerosis and ankylosis using a structured scoring system. Lesion frequencies and spatial distribution were compared between groups. Diagnostic performance (sensitivity (SE), specificity (SP), positive predictive values, negative predictive values and positive and negative likelihood ratios) was calculated for different combinations of imaging findings. Clinical diagnosis served as standard of reference.ResultsAnkylosis and/or erosions of the middle and dorsal joint portions yielded the best diagnostic performance with SE 67.6% and SP 96.3%. Inclusion of ventral erosions and sclerosis resulted in lower diagnostic performance with SE 71.2%/SP 92.5% and SE 70.6%/SP 90.0%, respectively.ConclusionsSclerosis and ventrally located erosions of SI joints have lower specificity on CT of the SI joint in the context of axSpA imaging. Ankylosis and/or erosions of the middle and dorsal joint portions show a strong diagnostic performance and are appropriate markers of a positive SI joint by 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).

Objective MRI findings of the sacroiliac joint space in axial spondyloarthritis (axSpA) include inflammation and fat metaplasia inside an erosion; the latter is also termed “backfill”. We compared such lesions with CT to better characterize them whether they represent new bone formation. Methods We identified patients with axSpA who underwent both CT and MRI of the sacroiliac joints in two prospective studies. MRI datasets were jointly screened by three readers for joint-space-related findings and grouped into three categories: type A: high short tau inversion recovery (STIR) and low T1 signal; type B: high signal in both sequences; type C: low STIR and high T1 signal. Image fusion was used to identify MRI lesions in CT before we measured Hounsfield units (HU) in each lesion and surrounding cartilage and bone. Results Ninety-seven patients with axSpA were identified, and we included 48 type A, 88 B, and 84 C lesions (maximum 1 lesion per type and joint). HU were 73.6 ± 15.0 for cartilage, 188.0 ± 69.9 for spongious bone, 1086.0 ± 100.3 for cortical bone, 341.2 ± 96.7 for type A, 359.3 ± 153.5 for B, and 446.8 ± 123.0 for C lesions. Lesion HU values were significantly higher than those of cartilage and spongious bone but lower than those of cortical bone (p&lt; 0.001). Type A and B lesions showed similar HU values (p= 0.93), whereas type C lesions were denser (p&lt; 0.001). Conclusion All joint space lesions show increased density and might contain calcified matrix, suggesting new bone formation, with a gradual increase in the proportion of calcified matrix towards type C lesions (backfill).