When patients with psoriasis develop joint pain, it is often hard to decide whether or not the pain is due to psoriatic arthritis (PsA). At this time, doctors use information from the history and physical exam to determine the diagnosis. X-rays, magnetic resonance imaging (MRI) and ultrasound have been used to help with the diagnosis but all three have limitations. A newer imaging technique, whole body Positron Emission Tomography/Computed Tomography (PET/CT) uses the idea that inflammatory cells take up sugar to locate inflammation in the body. Because patients with PsA have inflammatory cells in their joints and tendons, this type of scan allows the physician to take a picture of the whole body and locate inflammation. The investigators have found that some patients with psoriasis (but without arthritis) have inflammation in joints and tendons even before the patient has symptoms. In this study, the investigators will explore how well PET/CT works for assessing inflammation in patients with PsA. This would be a very exciting tool that could be used to find and treat inflammation before it causes damage or pain.