Information and Methods 1. Sources: The search was limited to “title, abstract, keywords”. In order to avoid omissions, a combination of online and manual searches was used, and additional searches were performed on the references in the retrieved literature. The retrieved literature was independently evaluated by a professor of respiratory medicine and a professor of nuclear medicine. Next, by reading the titles and abstracts, duplicates and literature that did not fit the research topic were excluded, and then literature that fit the topic was read in detail in full text, except for non-thesis literature such as reviews, syntheses, case reports, and other non-thesis literature, which was strictly limited according to the inclusion criteria. Finally, the literature that meets the requirements is identified. In the process of literature screening if encountered in the evaluation of inconsistency decided by discussion. 2, Inclusion criteria: (1) The study topic was the diagnostic value of 18F-FDGPET/CT for benign and malignant lung lesions; (2) The study population included nodular-like lesions of various morphologies in the lungs; (3) The sample size was >30 cases; (4) There was a pathological diagnosis or a clinical diagnosis with more than 1 year of follow-up; (5) There was a detailed raw data with the ability to extract the relevant data; (6) There was a 18F- FDPPET/CT method description for diagnosing benign and malignant lesions; (7) literature with detailed imaging methods and quality assurance. Literature quality grading: Literature quality grading was categorized into five grades: A, B, C, D, and E, with reference to the “Levels and bases of evidence grading” in the Evidence-Based Medicine Guidelines [5]. (1) Extraction of basic information of the literature: including the authors, research centers, publication time, number and age of the research subjects, continuity and type of research, statistical type, and diagnostic criteria. (2) Statistics acquisition: extract the diagnostic test four-cell table data of the included literature, i.e., true positive value, false positive value, true negative value and false negative value; establish the diagnostic test four-cell table, and calculate the indexes of sensitivity, specificity, positive likelihood ratio, and negative likelihood ratio; apply meta-analysis-specific statistical software to calculate the summarized value of the indexes of each study and draw their forest plots; make the summarized subjects’ work characteristic curves and calculate the The area under the curve, in order to prevent the ROC curve from producing detectable bias, the four-cell table of the diagnostic test was Cox-corrected [6]. (3) Heterogeneity test: according to whether the literature is heterogeneous or not, the statistical methods are categorized into deterministic model statistical methods and random model statistical methods. The heterogeneity of the literature is mainly caused by the threshold effect and non-threshold effect [7]. In this study, the threshold effect was tested by calculating the Spearman correlation coefficients of the logarithm of sensitivity and the logarithm of (1-specificity); the non-threshold effect was tested by the Cochran-Q value. If P<0,05, the homogeneity hypothesis test was rejected, indicating the existence of heterogeneity due to threshold and non-threshold effects, and a random effects model was chosen. On the contrary, the deterministic model was chosen. 5, Statistical processing: Meta-Disc1,4 and RewMan4,2 software were applied for statistical analysis and graphing. RESULTS 1. Search results: Through different combinations of search terms, 1250 English literature and 34 Chinese literature were initially retrieved. According to the inclusion criteria, 7 articles were finally included, including 5 articles in English and 2 articles in Chinese, which were completed by 6 independent research centers (of which articles 1 and 7 were the same research unit and counted as 1 research center). 3 articles were prospective studies and 4 articles were retrospective studies. There was continuity of cases included in each literature (Table 1). 2.Assessment of quality grading of the literature: Except for literature 4 and 6, which were classified as grade B without mentioning the application of blinding, the rest of the literature was classified as grade A. The majority of the included cases had a pathologic diagnosis. Most of the included cases had a pathologic diagnosis; for those without a pathologic diagnosis, they were followed up for more than 1 year. The inclusion of newer literature was considered to be related to the time when PET/CT was applied to the clinic. Criteria in the literature for diagnosing benign and malignant by 18F-FDP PET/CT include the semi-quantitative method of standardized uptake of FDG values and the graded method. Both the SUV value method and the grading method depend on the degree of 18F-FDP uptake in the lesion. 3, Data analysis: 795 cases were studied, including 506 males and 289 females, aged 54,9-64,3 years. The 8 cases that did not make a clear diagnosis in the literature 1 were characterized as misidentification after discussion in the group, and the original data in the text were merged, organized, and the sensitivity and specificity were recalculated. The information value of each diagnostic test parameter is shown in Table 2. 4. Heterogeneity test: The Spearman correlation coefficient of the logarithm of the sensitivity and the logarithm of the (1-specificity) is -0,436, P=0,328, P>0,05, which suggests that the existence of a threshold effect can not be thought of yet; the Cochran-Q of the DOR is 11,95, P=0,0631, P>0,05, which suggests that a non-threshold effect can not be thought of yet. consider that there is a non-threshold effect. Therefore, it was considered that the included literature had chi-square, and the deterministic model was applied for meta-analysis. As shown in Figure 1. 5. Meta-analysis: Through the indirect combination of samples, the pooled sensitivity was 95% (93%~97%), and the pooled specificity was 77% (71%~82%), as shown in Fig. 2. The pooled PLR was 4,12 (3,25~5,22), and the pooled NLR was 0,08 (0,05~0,11), as shown in Fig. 3. 6. Creation of SROC curves: Discussion Despite the fact that a large number of clinical studies have suggested that PET/CT is useful for tumors, it is not yet possible to make SROC curves. suggest that PET/CT has an important role in the diagnosis and differential diagnosis of tumors, they are mostly retrospective analyses from independent research institutions and lack large-sample, multicenter prospective studies. The incidence and death rate of lung cancer are located in the first place of malignant tumors, and the benign and malignant differential diagnosis of lung lesions is the main indication for PET/CT. In this study, the value of 18F-FDPPET/CT in the differential diagnosis of benign and malignant lung lesions was meta-analyzed according to the methodology of evaluating diagnostic tests in evidence-based medicine. A total of 7 papers were included in this study. The methodological bias caused by the experimental design was controlled by excluding small samples and literature with grade C or lower; the heterogeneity test was applied with Meta-Disc1,4 software to confirm that there was no heterogeneity in the included literature; and good consistency and reproducibility of the included studies were ensured by the limitation and control of the diagnostic criteria of the cases, the diagnostic criteria of PET/CT, and the imaging conditions. The results of this study showed that 18F-FDPPET/CT had a high sensitivity for diagnosing benign and malignant lung lesions, but its specificity was not satisfactory. The reasons for this may be related to the subjectivity of the reviewer and the limitations of PET/CT [18]. The application of PET/CT for diagnosis requires not only a solid knowledge of nuclear medicine and radiography on the part of the reviewer, but also a comprehensive grasp of the patient’s clinical information. However, PET/CT has been used in the clinic for a relatively short period of time, and a high-level team of readers has not yet been formed. In PET/CT tumor imaging, the uptake of tracer by some benign lesions and normal tissues can cause false positives; clinical practice and the literature have shown that false positives can also occur in inflammatory pseudotumors, tuberculosis, pneumonia, and granulomas. Due to the different origins and heterogeneity of tumors, some malignant tumors do not use glucose as a substrate for energy supply, and no or small amount of tracer uptake can cause false negatives; false negatives can be seen in adenocarcinomas, alveolar carcinomas, and carcinoid tumors; PET/CT is affected by respiratory motion during image acquisition, and lesions with a diameter of <5 mm can be easily missed [18]. Likelihood ratio is a composite index reflecting both sensitivity and specificity, which is not affected by the prevalence rate, and can comprehensively reflect the value of diagnostic tests, which is very stable.The larger the PLR is, the smaller the NLR is, and the higher the diagnostic value of diagnostic tests is. The results of this study showed that the pooled PLR was 4,12 and the pooled NLR was 0,08, indicating that 18F-FDPPET/CT has a greater value for the differential diagnosis of benign and malignant lesions in the lungs.The SROC curve is not affected by changes in thresholds [19], and the diagnostic tests are compared directly through graphs and areas, which more accurately reflect the linear relationship between the sensitivity and the specificity; the AUC stands for the accuracy of the diagnostic test, the AUC of this study was 94%, which further affirmed the diagnostic value for identifying benign and malignant lung lesions. In summary, by mining, organizing and analyzing the information of the included literature, it is confirmed that it has high diagnostic value for the identification of benign and malignant lesions in the lungs. However, there are still some shortcomings in this analysis. Because PET/CT has been used in clinical practice for a short time, most of the included literature is from the past 5 years, which may lead to publication time bias; the included literature contains only two languages, Chinese and English, which may lead to bias due to the limitation of the language. Therefore, larger samples, multicenter, randomized, double-blind, controlled prospective studies are still needed to more accurately evaluate its clinical value, and the training of high-quality PET/CT diagnostic physician teams is also an important factor in improving the diagnostic rate.