BACKGROUND: Rheumatoid arthritis (RA) is a common chronic, inflammatory autoimmune disease, and early clinical diagnosis is crucial for its treatment. CXCR4 expression was characterized in arthritic mouse models and joints of RA patients, and [ RESULTS: CXCR4 expression was significantly increased in the inflamed joints of collagen-induced arthritis (CIA) and collagen-antibody induced arthritic (CAIA) mice, and in synovial tissues of RA patients. [ CONCLUSION: The CXCR4-targeted PET probe [