Objective: Our objective was to evaluate the diagnostic role of dual-phase 18F-fluorodeoxyglucose (18F-FDG) PET/computed tomography (CT) in the characterization of solitary pulmonary nodules (SPNs).
Patients and methods: A total of 48 SPNs in 48 patients were included in this retrospective study. The final diagnosis was confirmed histopathologically or by follow-up CT. Two PET/CT scans were performed: the first (early scan) was performed 1 h after injection and the second (delayed scan) was performed 2 h later. Standardized uptake values (SUVs) [early and delayed SUVmax and SUVmean adjusted to body weight, body surface area (BSA), lean body mass (LBM) and blood glucose level (Glc)], retention index and nodule-to-mediastinum (nodule activity/subcarinal region of interest activity) ratios were calculated, along with the receiver operating characteristic curve. Intraobserver and interobserver variabilities among nuclear medicine physicians were analysed for the two phases.
Results: Eighteen patients had malignant tumour, whereas 30 had benign lesions. The median (min−max) SUVmax was 1.5 (0.5–4.1) in the benign group and 3.6 (1.3–38) in the malignant group. With the threshold value of early SUVmax as 2.5 and 2.75 using the receiver operating characteristic curve, a sensitivity of 94–75%, specificity of 75–80% and an accuracy of 83–78% were calculated. With the same threshold values for delayed images, 94–100% sensitivity, 77–80% specificity and 83–88% accuracy were obtained. BSA-SUVmax, LBM-SUVmax and Glc-SUVmax did not show any advantage over other quantitative parameters in the SPN characterization. There was no variability in the results obtained between the two nuclear medicine physicians.
Conclusion: Dual-phase PET/CT may increase the diagnostic potential of PET/CT in the characterization of SPNs. In this particular study group, a threshold value could not be determined for the retention index, but higher retention indices may show higher malignant potential in SPNs.