Respiratory-gated imaging in metabolic evaluation of small solitary pulmonary nodules: 18F-FDG PET/CT and correlation with histology

ObjectiveThe aim of the study was to evaluate the effect of 2-(F-18)-fluoro-2-deoxy-d-glucose (F-18-FDG)-PET/computed tomography (CT) respiratory-gated imaging [four-dimensional (4D)] in the metabolic evaluation of small solitary pulmonary nodules and analyze the cutoff maximum standardized uptake value (SUVmax) of 2.5 in classifying and distinguishing benign/malignant pulmonary pathologies in 4D studies.Materials and methodsThirty-two patients with pulmonary lesions measuring 2cm or less were included during their scheduled F-18-FDG PET/CT examinations. The whole-body PET/CT acquisition (3D) was followed by a chest-centered PET/CT (4D) study synchronized with the respiratory cycle. The SUVmax percentage difference (%Diff SUVmax) was calculated. The nodule size, localization, and relationships with histological/cytological findings were studied.ResultsFifteen nodules were 10mm or smaller and 17 were larger than 10mm [mean size=12mm (7-20)]. The mean 3D-SUVmax was 2.5 (0.7-6.1) and the mean 4D-SUVmax 3.2 (0.9-7.2) (P<0.001). The mean %Diff SUVmax was 38% for all patients (7-90), 45% in subcentimetric (7-90%) and 31% (7-75%) in supracentimetric lesions (P=NS). Histology was obtained in 23/32 (72%) cases and the pathologic benign/malignant ratio was 4/19. Malignancies were diagnosed as lung adenocarcinoma, solitary metastases, large cell lung carcinoma, and sarcoma in 13 (41%), 3 (9%), 2 (6%), and 1 (3%) case, respectively. Malignant lesions showed mean 4D-SUVmax of 3.8 (1.2-7.2). The cutoff SUVmax of 2.5 did not classify and distinguish between benign/malignant pulmonary pathologies, neither in 3D nor in 4D studies.ConclusionRespiratory gating improves the detectability and metabolic evaluation of solitary pulmonary nodules, mostly those that are subcentimetric. However, as expected, the cutoff SUVmax of 2.5 does not distinguish between benign/malignant lesions in either 4D or 3D studies.