Rheumatoid and psoriatic arthritis patients benefit from anti-TNF-α therapy, once it is effective in reducing joint and skin manifestations in 60-70% of patients with inflammatory articular joint and skin diseases. Thus, identifying the presence and amount of TNF-α in the joint or skin in these patients may help in guiding the course of treatment more efficiently. The investigators research group has developed a novel approach to label anti-TNF-α with technetium-99m. Here the investigators compare the results obtained with scintigraphy and MRI in rheumatoid and psoriatic arthritis. The 99mTc-anti-TNF-α scintigraphy might recognize the molecule involved in the inflammatory process and provide crucial information to help physicians taking decisions about the drugs to be used based on biological evidence and which are cost-effective and appropriate for the treatment of choice. It allows direct identification of the monoclonal antibody anti-TNF-α in the articular joints and skin while it also ensures that the drug has reached its therapeutic target. It also allows correlation between the presence of the drug and clinical responses.