Characterization of pulmonary lesions with low F-18 FDG uptake using double phase F-18 FDG PET/CT: comparison of visual and quantitative analyses.

Background of the present study was to assess the usefulness of double phase positron emission tomography/computed tomography (PET/CT) to differentiate malignant from benign pulmonary lesions with low fluorine-18 fluorodeoxyglucose (F-18 FDG) uptake. Of 218 consecutive patients who underwent double phase F-18 FDG PET/CT to evaluate pulmonary lesions found on CT, we retrospectively analyzed 30 who had focal pulmonary lesions with an SUV of <2.5. All patients underwent PET/CT of the thorax at two time points: scan 1 at 60 min and scan 2 at 120 min after the intravenous injection of 2.5 MBq F-18 FDG. The F-18 FDG PET/CT images were analyzed visually and quantitatively. Of 30 evaluated nodules, 13 (43%) proved to be malignant and 17 (57%) benign. The SUVmax1 (maximal SUV of early image), SUVmax2 (maximal SUV of delayed image), %DeltaSUVmax (percent change of maximal SUV), CR1 (contrast ratio of early image), and CR2 (contrast ratio of delayed image) of malignant pulmonary lesion were significantly higher than those of benign. However, %DeltaCR (percent change of contrast ratio) revealed no statistical differences. Among the quantitative indices, SUVmax1, SUVmax2, and CR2 were superior to the visual analysis for differentiation of malignant from benign pulmonary lesions. The SUVmax1, SUVmax2, and %DeltaSUVmax were superior to %DeltaCR for differentiation of malignant from benign pulmonary lesions. Based on the presented results, the quantitative indices except %DeltaCR were higher in malignant nodules than benign pulmonary nodules. However, the diagnostic performances were similar between visual and quantitative analyses. Further studies are needed to confirm these results and improve statistical accuracy. Key words: F-18 FDG, PET/CT, double phase, SUV.