PET-CT is to install PET and CT in the same frame and the same examination bed, so that the patient does not need to move during one scan, and PET and CT images can be obtained separately, and then by computer processing, PET images providing functional imaging and CT images providing anatomical information can be aligned and matched into PET-CT fusion images to achieve perfect unity of function and morphology, while CT can both CT can provide fast and accurate attenuation correction for PET, as well as localization and characterization of lesions, which greatly improves the diagnosis. Solitary pulmonary nodule (SPN) is a round solid lesion ≤ 3 cm in diameter in the lung without atelectasis or pneumonia and without hilar lymph node enlargement; it can be distinguished when other lesions are present in the lung. Glucose metabolism varies greatly in different tumors, and FDG metabolism differs in different pathological types of tumors; therefore, SUV also varies greatly depending on the tumor type; some tumors with lower metabolism, better differentiation, slow growth, and low malignancy can show false negatives; studies have found that the most frequent false negative lung cancer in the diagnosis of SPN with FDG-PET is highly differentiated fine bronchoalveolar carcinoma; the most The most frequent false positives were for tuberculoma and inflammatory pseudotumor. The study also found that the qualitative diagnosis of SPN is difficult to make based on FDG-PET alone, and must be based on a combination of history, physical examination, and serial imaging data. Also considering the cost of the examination, patients with pulmonary nodules need to decide on a case-by-case basis whether PET-CT is needed.