| PrefaceCarcinoma of the lung is the leading cause of cancer death among men and women in most countries.Appproximately 660,000 new pulmonary lesions are identified each year all over the world.Early diagnosis of lung cancer is to be considered essential for proper therapy and increasing survival rate ,therefore,how to differentiating malignant tumor from benign pulmonary lesions is a question for discussion.PET/CT is an imaging technology that combines high-quality PET and CT in a single device and provides simultaneous structural and metabolic information under identical conditions. The aim of this study is to evaluate the diagnostic value of 18F-FDG PET/CT in differentiating malignant tumor from benign lesion in pulmonary nodules.Patients and MethodsPatient population: A total of 74 patient scans were included in the study. All patients with pulmonary lesions were known or suspected by chest radiology. All of them were proved pathologically or by follow-up. 55 patients were malignant and 19 patients were benign.Imaging methods: Scans were performed with the Discovery TMLS-16 PET-CT scanner ( GE Medical Systems, USA) .After fasting for at least 4 -6h, patients were injected intravenously with 222-555MBq 18F-FDG, followed by atracer uptake phase of 60 min. No specific breathing instructions were given to patients, and scan were performed during quiet tidal breathing. The CT scanner portion of the Discovery LS consists of a multidetector helical CT. Emission data were acquired for 3-4 min for each bed position, with six to seven bed positions.Diagnostic criteria were:①The SUVmax of pulmonary lesions≥2.5 ,②There were significant increasing of SUVmax(≥20%～30%) , and the information provided by thin planer canning with computed tomography (planer thickness 1.25mm) was considered ,③The location of pulmonary lesion was according to the CT data. We drew curves with changing of SUVmax from the center of every maliganant lesion to chest walls. The curve patterns and characteristics of malignancies were compared with benigns and normals. The summary of all of results were the final results of PET/CT.Statistical analysis: The difference in curves between malignan, benign and total normals was tested with vision; The difference in thin planer canning with computed tomography (planer thickness 1.25mm) between all kinds of classical characteristics was tested with a x2 test.ResultsThe final results of PET/CT indicated fifty-seven pulmonary lesions were malignant , there were 54 true-positive and 3 false-positive results, seventeen pulmonary lesions were benign, there were 16 true-negative and 1 false-negative results. Therefore, The sensitivity, specificity, accuracy and positive and negative predictive value of PET/CT for diagnosis of pulmonary lesions were 98.2%, 84.2%, 94.6%, 94.7% and 94.1%, respectively.DiscussionPosition emission tomography (PET) with 18F-fluorodeoxyglucose (FDG) has been shown to be useful in the detection of malignancy in pulmonary nodules. Different value of SUV have been established to distinguish malignant from benign lesions. However, it appears that too many factors can affect the level of SUV and therefore a diagnosis purely based on SUV level might not accurate enough. In all original CT scanners ,the role of CT is providing the information about anatomy, Thus PET/CT scanners which employ 16-slice CT with PET scanner aids in the evaluation of multiple pulmonary nodules. In addition to the shapes, borders ,and densities of the nodules, the distribution of the nodules can provide important clues to their etiology.In our study ,we maked curves with changing of SUVmax from the center of every maliganant lesion to chest walls, this indicated the invasion of periphery pulmonary tissue more directly. The pattener of the curves were parallel to the classical characteristics, for example shapes and borders .ConclusionFor pulmonary lesions, SUVmax and necessary delayed SUVmax suggest the uptake foci of FDG ,and typical morphological signs from thin planer spinal CT are important to differentiat malignant pulmonary tumor from benign lesions, these significantly reduce the diagnostic rate of false-positive and false-negative. Curves with changing of SUVmax from the center of every malignant lesion to chest walls also indicate the invasion of periphery pulmonary tissue more directly.
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