Participants with JIA will have a definitive clinical diagnosis of JIA according to established clinical criteria.9 Patients will be divided according to subtype - patients with ERA will be recruited into groups A (DWI and FF) and / or Group B (WB MRI) along with the polyarthritis and extended oligoarthritis groups. Once the WB MRI protocol is defined, for ERA patients recruited to both arms of the study the intention is to combine the DWI and WB MRI scan together to limit participation to 6 months scans only for this group.