Diagnostic value of 18F-FDG PET delayed imaging for patients with primary lung cancer

Objective: To discuss the diagnostic value of 18F-fluorodeoxyglucose (FDG) PET delayed imaging in primary lung cancers and distinguish them from tuberculosis. Methods: 18F-FDG PET early and 4 h delayed imaging were performed on seventy patients after intravenous injection of FDG, and the patients were defined into three groups: twenty-five subjects were with primary lung cancers , sixteen were with tuberculosis, twenty-nine were normal. Lung cancer patients were divided into subgroups of small-cell, squamous cell lung cancer and adenocarcinoma. Each image was analyzed by visual interpretation and semiquantitative method. FDG high uptake lesions as regions of interest (ROI) were drawn. ROI average FDG uptakes were evaluated and compared with that of the contralateral normal tissue (target/background, T/B) on the same plane of the images acquired at 1 and 4 h. Results: Standard PET imaging with a threshold standardized uptake value (SUV) of 2.5 found 22 positive and 3 negative cases. The resultant sensitivity, specificity and positive predictive value was 88.0%(22/25), 87.5%(14/16), 91.7%(22/24), respectively. Delayed imaging with a threshold SUV of 2.5 and increasing the positive cut-off by 10% than before found 23 positive and 2 negative cases. The sensitivity, specificity and positive predictive value was 92.0%(23/25), 93.8%(15/16) and 95.8%(23/24). The T/B ratio was closely relative to pathobiological types of primary lung cancers. In tuberculosis group, the mean SUV of lesions was 3.67 ± 2.17. Two high-FDG-uptake cases and one positive case were found on early imagings , the mistake rate was 12.5%(2/16) and 6.3%(1/16), respectively. All the T/B ratios of the malignant lesions in lung cancer group were significantly higher at 4 h than at 1 h. In the contrary, T/ B in normal and tuberculosis groups showed different uptakes of FDG at 1 and 4 h. Compared two imaging protocols, there was significant difference between lung cancer and tuberculosis group in delayed imaging (t=4.173, P=0.000) not in early imaging (t=0.945, P=0.347). Conclusion: Delayed FDG PET imaging is a better and more reliable imaging protocol for detecting and distinguishing lung cancer