FAPI PET has been developed as a promising approach for the evaluation of fibroinflammatory, such as in inflammatory bowel disease. This prospective study aims to explore the value of 18F-AlF-FAPI PET/CT in assessing the activity of Thyroid Eye Disease (TED) and investigate whether FAPI PET/CT may be superior to 99mTc-DTPA SPECT/CT for the diagnosis, therapy response assessment, and follow-up of TED.

Subjects with TED underwent 18F-AlF-FAPI PET/CT and 99mTc-DTPA SPECT/CT for activity assessment within a 10-day period. On 18F-AlF-FAPI PET/CT, uptake in the extraocular muscles was quantified using SUV metrics and target-to-background ratio. On 99mTc-DTPA SPECT/CT, uptake in the extraocular muscles was semi-quantified using the uptake ratio. Activity of TED was determined through comprehensive clinical data. The correlation between SUV metrics and activity status was calculated to explore the value of 18F-AlF-FAPI PET/CT in assessing TED activity. The diagnostic accuracy of 18F-AlF-FAPI PET/CT and 99mTc-DTPA SPECT/CT in assessing TED activity was compared. Additionally, the correlation of changes in SUV metrics and therapy response will be calculated to explore the value of 18F-AlF-FAPI PET/CT in therapy response assessment of TED.

Inclusion Criteria:

1. Age ≥ 18 years;
2. Patients diagnosed with TED;
3. Complete understanding and voluntary participation in this study, with the signing of an informed consent form.

Exclusion Criteria:

1. Severe liver or kidney dysfunction;
2. Inability to maintain a supine position for 5 minutes to cooperate with the examination;
3. Suffering from claustrophobia or other psychiatric disorders;
4. Patients planning pregnancy or in the prenatal or lactation period;
5. Other conditions deemed unsuitable for participation in the trial by the investigator.