Assessing disease activity in people with Takayasu's arteritis is difficult, as most people with the disease do not exhibit visible, measurable symptoms. Combination positron emission tomography/computed axial tomography (PET/CT) is a particularly sensitive, accurate scanning method that may improve researchers' ability to evaluate people with the disease. This study will determine the effectiveness of PET/CT in assessing disease activity in people with Takayasu's arteritis.

Takayasu's arteritis is a rare inflammatory disease that affects the aorta and its branches. The disease is much more common in females than in males, and disease onset typically occurs between the ages of 15 and 30. People with this disease often experience general discomfort, fatigue, fever, night sweats, weight loss, and joint pain. In the late stages of the disease, weak arterial walls may lead to aneurysms. Many patients do not exhibit any visible symptoms until this point, however. Because many people with Takayasu's arteritis do not have overt disease symptoms, the assessment of disease activity is difficult. Laboratory tests can help, but are often unreliable. Novel approaches to assessing disease activity are urgently needed to enhance and facilitate research on Takayasu's arteritis. This study will determine the effectiveness of combination positron emission tomography/computed axial tomography (PET/CT) in assessing disease activity in people with Takayasu's arteritis.

Participants in this study will enroll while their disease is active. The first PET/CT scan will take place upon study entry, while there is active disease. Participants will have a second PET/CT scan 3 months later, and a third scan 3 months after that if there is still active disease present. Participants will have a maximum of 3 scans unless a scan needs to be repeated because of technical failures, though this does not often happen. If there is no active disease at the time of the second scan, a third scan will not be done. All PET/CT scans will be scheduled within 10 days of participants' routine MRI scans. This study will not require any follow-up visits.

Inclusion Criteria:

• Diagnosis of Takayasu's arteritis, as defined by the VCRC Longitudinal Study #5503
• Currently enrolled in the VCRC Longitudinal Study #5503
• Active disease has occurred in conjunction with a disease relapse within 2 weeks before study entry (A detailed definition of "active disease" is available in the study protocol.)
• Willing and able to comply with the schedule for imaging studies and follow-up procedures

Exclusion Criteria:

• Pregnant or breastfeeding
• Unable to comply with study guidelines
• Unable to safely undergo MRI scanning

Participants in this study will have been diagnosed with Takayasu's arteritis and will be currently enrolled in the Vasculitis Clinical Research Consortium (VCRC) Longitudinal Study #5503.