Comparative Evaluation of 68Ga-FAPI and 68Ga-DOTATATE PET/CT and PET/MRI in Thyroid Eye Disease

Thyroid eye disease is an autoimmune disorder that can cause inflammation and fibrosis of the extraocular muscles and orbital tissues. Accurate assessment of disease activity is important for treatment planning, but commonly used clinical scores and conventional imaging each have limitations. This prospective single-center cohort study will evaluate two molecular imaging approaches, gallium-68-labeled fibroblast activation protein inhibitor (68Ga-FAPI) PET/CT and PET/MR and gallium-68 DOTATATE somatostatin receptor PET/CT and PET/MR, in adults with thyroid eye disease and in a control group without thyroid-related or orbital disease. The study will compare visual and quantitative imaging findings, including maximum standardized uptake value and target-to-background ratio in the extraocular muscles, and examine their associations with clinical activity score and extraocular muscle thickness. The study aims to characterize the ability of these imaging methods, separately and in combination, to assess thyroid eye disease activity.

Inclusion Criteria: * For the thyroid eye disease cohort: diagnosis of thyroid eye disease according to European Group on Graves' Orbitopathy criteria. * For the thyroid eye disease cohort: scheduled to undergo 68Ga-FAPI PET/CT and PET/MR and 68Ga-DOTATATE PET/CT and PET/MR within one week. * For the control cohort: clinically recommended to undergo FAPI or somatostatin receptor PET imaging for another reason, with no history of thyroid-related disease or orbital disease; orbital PET/MR is added to the existing examination without additional radiation exposure. Exclusion Criteria: * Previous bilateral orbital surgery. * Treatment with glucocorticoids, monoclonal antibodies, or radiotherapy within the previous month. * Inability to remain supine. * Contraindication to MRI, including incompatible metallic implants or claustrophobia. * Planning pregnancy, currently pregnant, or breastfeeding.