Maksymowych WP, Lambert RG, Baraliakos X, et al. - This study was carried out to ascertain quantitative sacroiliac joint (SIJ) MRI lesion cut-offs that optimally define a positive MRI for inflammatory and structural lesions typical of axial spondyloarthritis (axSpA) and that predict clinical diagnosis. In the analysis, the ASAS MRI group evaluated MRIs from the ASAS Classification Cohort in two reading exercises: 169 cases and 7 central readers, 107 cases, and 8 central readers. Sensitivity/specificity was estimated for the number of SIJ quadrants or slices with bone marrow edema (BME), erosion, fat lesion, where a majority of central readers had high confidence there was a definite active or structural lesion. They offer cut-offs for definite active and structural lesions typical of axSpA that have high PPV for a long-term clinical diagnosis of axSpA for application in disease classification and clinical study.