Anatomo-metabolic characteristics of atelectasis in F-18 FDG-PET/CT imaging

PURPOSE: To evaluate the structural and metabolic characteristics of atelectasis in FDG-PET/CT. METHODS: Twenty one consecutive patients (13 males, 8 females, median age 67 years) with CT features of atelectasis, undergoing PET/CT imaging for preoperative staging of histologically proven malignancies (20 lung cancer and 1 ovarian cancer metastasis to lung), were included in the study. RESULTS: Hounsfield units of atelectasis (-383.58+/-189, range -631 to 82) were significantly higher than in normal lung (-756+/-67.46, range -839 to -555; P=0.0001), and lower than in malignant tissue (35+/-19, range 4-77; P=0.0001). The main patterns of FDG uptake observed in atelectasis were diffuse and homogenous. The standard uptake value (SUV) in atelectasis was low to moderate (SUV(avg): 1.13+/-0.50; SUV(max): 1.44+/-0.54), and generally lower than in tumor tissue (SUV(avg): 6.25+/-3.58, range 2.0-16.5), but always higher than in normal lung (0.56+/-0.18 and 0.70+/-0.23, respectively) (P=0.0001). There was a positive correlation between the density of atelectatic lesions and the degree of uptake, with no relationship to size. CONCLUSION: There is a positive relationship between the density of collapsed lung and the intensity of FDG uptake. FDG uptake in atelectasis is higher than in normal lung, and generally lower than in tumor tissue.