Accuracy of transmission CT and FDG-PET in the detection of small pulmonary nodules with integrated PET/CT

Purpose: The purpose of this study was to determine the accuracy of detection of small pulmonary nodules on quiet breathing attenuation correction CT (CTAC) and FDG-PET when performing integrated PET/CT, as compared with a diagnostic inspiratory CT scan acquired in the same imaging session. Methods: PET/CT scans of 107 patients with a history of carcinoma (54 male and 53 female, mean age 57.3 years) were analyzed. All patients received an integrated PET/CT scan including a CTAC acquired during quiet respiration and a contrast-enhanced CT acquired during inspiration in the same session. Breathing CTAC scans were reviewed by two thoracic radiologists for the presence of pulmonary nodules. FDG-PET scans were reviewed to determine accuracy of nodule detection. Diagnostic CT was used as the gold standard to confirm or refute the presence of nodules. Results: On the CTAC scans 200 nodules were detected, of which 183 were true positive (TP) and 17, false positive. There were 109 false negatives (FN). Overall, 51 (48%) patients had a false interpretation, including 19 in whom CT was interpreted as normal for lung nodules. The average size of the nodules missed was 3.8 +/- 2 mm (range 2-12 mm). None of the nodules missed on the CTAC scans were detected by PET. In the right lung there were 20 TP, 42 true negative (TN), 11 FP, and 34 FN interpretations with a sensitivity in nodule detection of 37% (CI 24-51%) and a specificity of 79% (CI 66-89%). In the left lungs there were 16 TP, 65 TN, 3 FP, and 23 FN interpretations, with a sensitivity of 41% (CI 26-58%) and a specificity of 96% (CI 88-99%). Conclusion: The detection of small pulmonary nodules by breathing CTAC and FDG-PET is relatively poor. Therefore an additional diagnostic thoracic CT scan obtained during suspended inspiration is recommended for thorough evaluation of those patients in whom detection of pulmonary metastases is necessary for management.