Study Of [¹⁸F]AIF-FAPI PET/CT For Targeting Fibroblast Activating Protein In Sarcoidosis :comparison With ¹⁸F-FDG PET/CT

Purpose:Sarcoidosis is a granulomatous disease with an uncertain etiology,which may be the manifestation of tissue damage and fibrosis caused by acute and chronic inflammatory process caused by autoimmune abnormalities in various parts of the body,particularly when the thoracic lymph nodes are involved.Despite being a benign disease,sarcoidosis is very challenging to diagnose and differentiate from other diseases.The purpose of this study is to evaluate the potential clinical application value of ¹⁸F-FAPI-42 PET/CT in the diagnosis and treatment of sarcoidosis by head-to-head comparison of ¹⁸F-FDG and ¹⁸F-FAPI-42 PET/CT results of sarcoidosis patients.Methods:A single center retrospective clinical study was conducted in the First Affiliated Hospital of Guangzhou Medical University.Twenty-seven patients with sarcoidosis were included for ¹⁸F-FAPI-42 PET/CT and ¹⁸F-FDG PET/CT imaging.1.study the distribution of sarcoidosis lesions throughout the body;2.by visual analysis of PET/CT images,the differences of the positive rates of the above two imaging agents in displaying different parts of lesions on PET/CT images were compared;3.take the semi-quantitative analytical indicators of the maximum standardized uptake value（SUVmax）and target to background ratio（TBR）of the lesions to compare the differences between ¹⁸F-FAPI-42 PET/CT and ¹⁸F-FDG PET/CT;4.immunohistochemical FAP staining was used to quantify the expression of FAP in sarcoidosis,and the connection between FAP expression and SUVmax of ¹⁸F-FAPI-42 PET/CT was investigated.Results:1.Among the 27 patients with sarcoidosis,the location of lesion involvement was as follows:lymph nodes in 26 cases（96.2%）,lung in 13 cases（48.1%）,subcutaneous in 4 cases（14.8%）,spleen in 4 cases（14.8%）,bone in 3 cases（11.1%）,heart in 2 cases（7.4%）,muscle space in 2 cases（7.4%）,liver in 2 cases（7.4%）,kidney in 1 case（3.7%）.2.The positive rates of ¹⁸F-FDG and ¹⁸F-FAPI-42 for the lesions of involved lymph nodes were equivalent（100%vs.96.0%）.3.¹⁸F-FDG showed that SUVmax and TBR of lymph node lesions were slightly higher than ¹⁸F-FAPI-42（SUVmax:11.4 vs.5.5,TBR:6.5 vs.4.4）.The positive rates of the two PET/CT imaging agents for lung involvement and lesions were the same（100%vs.100%）;¹⁸F-FAPI-42 was superior to ¹⁸F-FDG（100%vs.0%）for cardiac involvement lesions（n=2）.4.Immunohistochemical FAP staining analysis showed that FAP expression in sarcoidosis was moderately correlated with SUVmax of ¹⁸F-FAPI-42 PET/CT（r=0.827,P<0.001）.Conclusion:¹⁸F-FDG PET/CT reflects the level of glycolysis in sarcoidosis lesions,while ¹⁸F-FAPI-42 shows the amount of activated fibroblasts in sarcoidosis lesions.As a result,this study compared how the two different imaging agents displayed lesions in the same sarcoidosis patient,and it discovered:1.The two imaging agents are better able to show the lesions associated with various systems and sarcoidosis sites;¹⁸F-FAPI-42 performed better than ¹⁸F-FDG in the cardiac lesions.2.Through the comparative study of immunohistochemical FAP staining results and ¹⁸F-FAPI-42 PET/CT imaging,it was found that SUVmax of lesions was positively correlated with FAP expression.