Abstract: Objective:To study the correlation between 18fluorine deoxyglucose(18F-FDG) positron emission tomography/computerized tomography(PET/CT) scan and bronchoalveolar lavage fluid(BALF)in patients with thoracic sarcoidosis,and explore the mechanism of 18F-FDG uptake in sarcoidosis.Methods:Nineteen patients with thoracic sarcoidosis underwent 18F-FDG PET/CT scan and BALF.The CD4+/CD8+ T cell ratio and serum angiotensin converting enzyme(sACE),tumor necrosis factor-(TNF-) and soluble interleukin-2 receptor(sIL-2R) levels in bronchoalveolar lavage fluid were detected.18F-FDG PET/CT scan was semi-quantitatively analyzed by maximum standardized uptake value(SUVmax) and mean standardized uptake value(SUVmean).The correlation between SUVmax,SUVmean,CD4+/CD8+ T cell ratio,sACE,TNF- and sIL-2R levels was also analyzed.Results:SUVmax was significantly correlated to SUVmean(P0.01).SUVmax was significantly correlated to sACE(P0.01) and TNF-(P0.01),respectively;SUVmean was also significantly correlated to sACE(P0.01) and TNF-(P0.01),respectively.SUVmean was correlated to CD4+/CD8+ T cell ratio(P0.05).Conclusions:The 18F-FDG uptake capacity is high in high load of sarcoidosis granuloma;its ability to 18F-FDG uptake may be associated with T cell activation.SUVmean may be superior to SUVmax in determining the activity of sarcoidosis.