Interrater reliability and radiation dosage of oblique coronal computed tomography for sacroiliitis in comparison with axial computed tomography.

Objective: Sacroiliitis, a prerequisite to the diagnosis of ankylosing spondylitis, can be ascertained by CT when MRI is not available. Oblique coronal CT is an increasingly popular approach when examining sacroiliitis. The goal of this study was to understand how oblique coronal CT compared with axial CT scanning in terms of raters' concordance when diagnosing sacroiliitis.

Methods: 52 subjects < 45 years of age at onset of their chronic lower back pain were sequentially scanned by X-ray, axial CT and oblique coronal CT. The acquired images were graded by two experienced, double-blinded physicians.

Results: Sacroiliitis in the oblique coronal view was sensitive enough for grading disease severity and/or detecting improvement. Interrater reliability for CT (axial + oblique coronal) was higher than X-ray. The diagnosis based upon oblique coronal CT was consistent, while the radiation dose delivered to the gonads was significantly reduced, compared with axial CT.

Conclusion: When MRI is not available, oblique coronal CT should replace axial CT when diagnosing sacroiliitis. Advances in knowledge: When evaluating sacroiliitis, oblique coronal CT is as accurate as conventional axial CT, yet more advantageous owing to reduced radiation dosage.