Use of Gallium-68 HA-DOTATATE PET/CT in Giant Cell Arteritis (GCA)

Inclusion Criteria: Participants must: 1. Meet the revised GCA diagnosis criteria (modified from ref 1) 2. Have either newly-diagnosed or relapsing disease 3. Have active disease (modified from ref 1, to remove ESR/CRP requirements) 4. Have been empirically started on glucocorticoid treatment (or had baseline glucocorticoid dose increased, in the case of relapsers) ≤ 2 weeks of enrolment 5. Participant must be have had (or will be willing to undergo) an urgent FDG-PET/CT as part of routine clinical care. GCA diagnosis criteria (modified from ref 1, to remove ESR requirement). 1. Age ≥ 50 years 2. And at least 1 of a. or b. : 1. Unequivocal cranial symptoms of GCA (new headache, scalp or temporal artery tenderness, ischemia-related vision loss, jaw/mouth claudication 2. Unequivocal symptoms of polymyalgia rheumatica (PMR), defined as shoulder and/or hip girdle pain associated with inflammatory stiffness 3. And at least 1 of a. or b.: 1. Temporal artery biopsy revealing features of GCA 2. Evidence of large-vessel vasculitis by angiography or cross-sectional imaging study such as magnetic resonance angiography (MRA), computed tomography angiography (CTA), or positron emission tomography-computed tomography (PET-CT) Exclusion Criteria: * Patients not meeting the above criteria or who are unable to provide informed consent will be excluded.