Inclusion Criteria:  Age ≥ 50 years, capable and willing to provide informed consent and can tolerate PET/CT. ESR ≥ 50 mm/h and/or CRP ≥ 10mg/L within 1 week of PET/CT referral. New suspected giant cell arteritis according to at least one of the following criteria:  Cranial GCA symptoms (new-onset localized headache, scalp or temporal artery tenderness, ischemia-related vision loss, masseter pain on prolonged mastication) PMR symptoms: shoulder and/or hip girdle pain associated with inflammatory stiffness.  Suspected large-vessel vasculitis based on angiography, MRA, or CTA.  Exclusion Criteria:  Initiation of corticosteroid or immunosuppressive therapy >4 days before PET/CT. Prior TAB or treated GCA with suspected relapse. Non-fasting or hyperglycemia (>11.1 mmol/L) resulting in altered FDG biodistribution.