Juvenile Arthritis Quantitative Imaging

Inclusion Criteria: * Participant is willing and able to give informed consent for participation in the study. * For cases, patients will have clinical diagnosis of JIA: enthesitis-related arthropathy, extended oligoarthritis or polyarthritis (defined according to ILAR criteria) * For controls, patients will have a diagnosis of mechanical back pain (though to arise from muscles, bones, ligaments or discs), with normal inflammatory markers * Age 12-24 Exclusion Criteria: * Contra-indication to MRI scan (e.g. metal foreign object) * Unable to give consent * Unable to speak English * Unable to tolerate an MRI scan (e.g. due to claustrophobia, contrast allergy) * Renal or hepatic failure (eGFR \< 30ml/min for renal failure, where applicable)