Quantitative iodine-mapping of photon-counting CT detects large-vessel vasculitis: A case report.

Diagnosis of large-vessel vasculitis can be challenging because clinical symptoms and early imaging findings are often nonspecific. A 69-year-old woman presented to the emergency department with severe headache and markedly elevated inflammatory markers. Initial brain CT, brain MRI, and ultrasound examinations revealed no significant findings. On repeat presentation, photon-counting-detector CT (PCCT) was performed to search for an infectious focus and demonstrated concentric mural thickening of the aorta and supra-aortic branches. Retrospectively reconstructed iodine maps, exploiting the intrinsic spectral capabilities of PCCT, showed increased iodine concentration within the aortic wall, raising suspicion of active large-vessel vasculitis. The diagnosis of giant cell arteritis was subsequently corroborated by MRI, 18FDG PET/CT, and repeat ultrasound of the temporal artery. Corticosteroid therapy led to rapid clinical and biochemical improvement. PCCT with spectral postprocessing may provide valuable additional information for the early detection of large-vessel vasculitis, particularly in cases with initially inconclusive imaging.