The investigators aim to recruit a minimum of 12 patients with known, active rheumatoid or psoriatic arthritis in the feet and ankles. Patients will first undergo a screening genotyping test; low affinity binders for PBR28 PET will be excluded from this pilot study. Those patients meeting inclusion criteria, will then undergo a PET-CT localised to feet and ankles that have been identified to be clinically inflamed (on examination and ultrasound at the screening visit). After PET-CT, patients will undergo synovial biopsy of one joint imaged. After 6 patients have undergone PET-CT, an interim analysis will be undertaken, to optimise PET scan duration and to alter the group of joints being imaged with CT.
