Axial Spondyloarthritis: Dual-Energy Virtual Noncalcium CT in the Detection of Bone Marrow Edema in the Sacroiliac Joints

Purpose: To determine the diagnostic performance of dual-energy virtual noncalcium (VNCa) CT in the detection of bone marrow edema in study participants with sacroiliitis associated with axial spondyloarthritis. Materials and Methods: In this prospective study, 47 consecutive participants (mean age, 27 years; age range, 14-41 years [28 male; mean age, 24 years; age range, 14-37 years] [19 female; mean age, 29 years; age range, 17-41 years]) underwent dual-energy CT and 3.0-T MRI between April 2016 and December 2017. Two independent readers visually evaluated all sacroiliac joints for the presence of abnormal marrow attenuation on dual-energy VNCa images using a four-point classification system (0, no edema; 1, mild edema; 2, moderate edema; 3, severe edema). CT numbers on VNCa images were determined with region-of-interestbased quantitative analysis. MRI was the reference standard for presence of bone marrow edema. Results: Sensitivity, specificity, and accuracy of readers 1 and 2, respectively, in the identification of bone edema at CT were 87% and 93% (48 and 51 of 55), 94% and 91% (32 and 31 of 34), and 90% and 92% (80 and 82 of 89). Interobserver agreement was excellent (kappa = 0.81). CT numbers from VNCa images increased from no edema to severe edema (P<.001). The area under the receiver operating characteristic curve was 0.93 for reader 1 and 0.91 for reader 2 in differentiation of the presence of bone marrow edema from no edema. A cutoff value of 233 HU derived from reader 1 yielded overall sensitivity, specificity, and accuracy of 90% (49 of 55), 83% (28 of 34), and 87% (77 of 89) in the detection of any extent of edema in the sacroiliac joints. Conclusion: Dual-energy VNCa CT images had excellent diagnostic performance in evaluation of the extent of bone marrow edema in study participants with sacroiliitis associated with axial spondyloarthritis. (c) RSNA, 2018