PET-CT for — Large-Vessel Vasculitis

Each gives different information, and they are often used together rather than as alternatives. Ultrasound is quick and shows wall thickening and blood flow in arteries near the surface, particularly the carotid and temporal arteries. MRI shows wall oedema and thickening across a wider area. PET-CT adds metabolic information — where inflammation is most active across the whole aorta and its branches in one scan. EULAR guidance supports PET-CT as a complementary tool, particularly when the extent of disease is unclear or treatment response needs to be assessed across the full arterial tree.

Yes, and this matters. Corticosteroids reduce FDG uptake in inflamed vessel walls, which can make active vasculitis appear less active than it truly is. Your team will ask about your dose and the timing of your last tablet before scheduling the scan. In some situations they may recommend scanning before steroids are started, or during a lower-dose period, to get the clearest picture of disease activity. Do not change or stop your medication without advice — let your team make that timing decision.

Not from the scan image alone. Both conditions cause FDG-avid uptake in vessel walls and lymph nodes, and the patterns can look very similar. Your team will read the report alongside your blood tests, chest imaging, symptoms, and risk factors for infection. In some cases, a tissue sample is needed before a definitive diagnosis can be made. If your report describes large-vessel uptake or enlarged lymph nodes, what that finding means in your specific situation is a question for your rheumatologist or treating physician — not a conclusion to draw from the report alone.

The physical steps are essentially the same — fasting, a blood sugar check on arrival, radiotracer injection, and a rest period before scanning. The important difference is what your team needs to know beforehand. For a vasculitis scan, your steroid dose and the timing of your last tablet directly affect when the scan should be scheduled, because corticosteroids reduce FDG uptake in inflamed tissue. Tell your team exactly what you are taking and when, so the scan gives the most useful result.

Allow around three hours from arrival to leaving. Most of that is the resting wait after the radiotracer injection — usually about an hour — during which you sit quietly while the tracer distributes through your body. The scan itself takes around half an hour. You can leave when it is complete and resume normal activities. You do not need someone to drive you home, though having a companion for the wait is fine.

Yes, and this is one of its recognised uses alongside initial diagnosis. Comparing a scan taken before treatment with one taken after several months of therapy shows whether FDG uptake in the vessel walls has reduced, stayed the same, or increased. A reduction in uptake generally suggests the inflammation is responding. EULAR guidance supports repeat PET-CT for this purpose in appropriate situations. Your rheumatologist will decide whether a follow-up scan adds useful information for your case, or whether blood markers and clinical assessment are sufficient.