Diagnostic accuracy of MRI-based synthetic CT compared to conventional CT in spinal and sacroiliac disorders: a systematic review.

BACKGROUND

Spinal and sacroiliac disorders, such as disc herniation, sacroiliitis, and spondylarthritis, require precise imaging for diagnosis. Conventional computed tomography (CT) is widely regarded as the reference standard for evaluating cortical bone and certain structural lesions due to its superior spatial resolution and accurate Hounsfield unit quantification, whereas MRI remains superior for marrow edema, soft tissue involvement, and early inflammatory changes. MRI-based synthetic CT (sCT) offers a radiation-free alternative by generating CT-like images from MRI data. This systematic review evaluates the diagnostic accuracy of sCT compared to conventional CT in these disorders.

METHODS

Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) for diagnostic test accuracy studies (PRISMA-DTA) guidelines, we searched databases (PubMed, Embase, Cochrane, Scopus, Web of Science, CINAHL, IEEE Xplore) and gray literature. Eligible studies compared sCT to CT in patients with spinal/sacroiliac disorders, reporting metrics like sensitivity, specificity, and agreement. Two reviewers screened records, extracted data, and assessed risk of bias using QUADAS-2. Narrative synthesis was performed due to heterogeneity.

RESULTS

Ten studies (n = 1028 participants) were included, focusing on degenerative spinal conditions and axial spondyloarthritis. sCT showed sensitivity of 47-94% and specificity of 83->95% for lesions (e.g., erosions, ankylosis), often superior to MRI and comparable to CT. Geometric measurements (e.g., vertebral dimensions) had high concordance (ICC = 0.788-0.978). Inter-observer agreement was moderate to excellent (κ = 0.41-0.98). Risk of bias was low in four studies but high in six, mainly due to small samples and selection issues.

CONCLUSIONS

MRI-based sCT demonstrates promising diagnostic accuracy for spinal and sacroiliac disorders, potentially reducing radiation exposure. However, methodological limitations warrant larger, multicenter trials for validation.