[Imaging in Large-Vessel Vasculitis. What Works Best in Giant Cell Arteritis and Takayasu Arteritis?].

Giant cell arteritis (GCA) is the most common primary systemic vasculitis and can present with a cranial, large-vessel, or mixed phenotype. Rapid and secure diagnosis is essential to prevent irreversible visual loss. Imaging has fundamentally transformed the diagnostic pathway. Vascular ultrasound is the first-line modality, enabling high-resolution assessment of both cranial and extracranial vessels, detecting pathological findings such as the halo sign, compression sign, and increased intima-media thickness. Magnetic resonance imaging (MRI) serves as an important complementary modality without radiation exposure. However, persistent mural signal abnormalities in large vessels limit activity assessment. Imaging with [18F]FDG positron emission tomography-computed tomography (PET/CT) enables whole-body assessment and identification of extracranial involvement but is constrained by limited specificity for inflammation and frequent persistent uptake in remission. Emerging tracers such as [18F]FAPI and [68Ga]Ga-DOTA-Siglec-9 may further improve imaging of inflammation in GCA. Similarly, novel ocular imaging modalities, including transorbital ultrasound and optical coherence tomography angiography, offer promising tools for detecting macro- and microvascular ophthalmologic involvement. Takayasu arteritis (TAK), the second major large-vessel vasculitis, is predominantly affecting young women, involving only the aorta and its major branches. Early diagnosis is crucial, as ongoing inflammation leads to stenosis, occlusion, aneurysm formation, and ischemic complications. Imaging with MRI is the diagnostic gold standard, enabling detailed assessment of mural inflammation and luminal pathology without radiation exposure. Ultrasound supports rapid evaluation of accessible arteries, though it is limited for the thoracic aorta. Radiation-based imaging with [18F]FDG PET/CT and CT-angiography may complement MRI, but their use is constrained by radiation exposure which is particularly relevant in this young patient population. Disease activity monitoring remains challenging, as persistent mural thickening, IMT elevation, and [18F]FDG uptake may reflect vascular remodeling rather than active vasculitis.