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.
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.
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.
Participants will be selected from adults evaluated in the Department of Nuclear Medicine at the Army Medical Center of PLA between November 2025 and December 2027. The thyroid eye disease cohort will consist of patients meeting European Group on Graves' Orbitopathy diagnostic criteria. The control cohort will consist of patients without thyroid-related or orbital disease who undergo clinically indicated FAPI or somatostatin receptor PET imaging for another reason.
Cohort
Prospective
68Ga-FAPI PET/CT and PET/MR Imaging
Diagnostic testParticipants receive 3 to 5 mCi of 68Ga-FAPI intravenously. PET/CT and PET/MR imaging of the head and orbits is performed approximately 50 minutes after injection, with PET acquisition of approximately 5 minutes per bed position. PET/MR includes routine T1-weighted, T2-weighted, and FLAIR sequences. The exact FAPI compound should be added if specified by the radiopharmacy documentation. Required confirmation: the protocol does not identify the specific FAPI compound, such as FAPI-04.
68Ga-DOTATATE PET/CT and PET/MR Imaging
Diagnostic testParticipants receive 3 to 5 mCi of 68Ga-DOTATATE intravenously. PET/CT and PET/MR imaging of the head and orbits is performed approximately 50 minutes after injection, with PET acquisition of approximately 5 minutes per bed position. PET/MR includes routine T1-weighted, T2-weighted, and FLAIR sequences.
Extraocular Muscle SUVmax on 68Ga-FAPI and 68Ga-DOTATATE PET Imaging
Maximum standardized uptake value will be measured separately in the superior, medial, lateral, and inferior rectus muscles on PET/CT and PET/MR images for each tracer. Values will be summarized by tracer, imaging platform, eye, and participant group.
Extraocular Muscle Target-to-Background Ratio on 68Ga-FAPI and 68Ga-DOTATATE PET Imaging
For each extraocular muscle, target-to-background ratio will be calculated as extraocular muscle SUVmax divided by background SUVmax measured using a 1-cm region of interest in occipital soft tissue. Values will be summarized by tracer, imaging platform, eye, and participant group.
Diagnostic Accuracy for Thyroid Eye Disease Activity
Receiver operating characteristic curves will be used to estimate the area under the curve for quantitative 68Ga-FAPI and 68Ga-DOTATATE PET/CT and PET/MR measures in relation to clinically defined thyroid eye disease activity. Required confirmation: specify the reference standard and exact Clinical Activity Score threshold used to define active disease before submission.
Association Between PET Uptake Measures and Clinical Activity Score
Pearson correlation coefficients will be used to assess associations of extraocular muscle SUVmax and target-to-background ratio with Clinical Activity Score.
Association Between PET Uptake Measures and Extraocular Muscle Thickness
Pearson correlation coefficients will be used to assess associations of extraocular muscle SUVmax and target-to-background ratio with extraocular muscle thickness measured on anatomic imaging. Required confirmation: specify the sequence, measurement plane, muscle-specific rule, and unit for extraocular muscle thickness.
Visual Positivity of Extraocular Muscle Uptake
Each eye will be classified as positive when any extraocular muscle demonstrates 68Ga-FAPI or 68Ga-DOTATATE uptake greater than background and negative otherwise. At participant level, a participant will be classified as positive when at least one eye is positive. Positivity will be compared between imaging approaches using categorical analyses.
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