Positron emission tomography (PET) is a nuclear medicine imaging technique that reflects biochemical changes and metabolic information in living organisms through the tracer principle by using positron-emitting nuclide labeled biologically active molecules, such as glucose, amino acids, and nucleotides. In tumor PET imaging, the most commonly used tracer is 18F-labeled deoxyglucose (18F-FDG). It is an analogue of glucose, replacing the oxygen atom at the 2-position of the glucose molecule with the positron-emitting nucleophile 18F. It is taken up by cells via the same pathway as glucose and is acylated to fluoro-2-deoxyglucose-6-phosphate by the action of hexokinase, a product that does not match the substrate of the enzyme and cannot be further metabolized like normal glucose and is trapped in the cell. Intracellular fluoro-2-deoxyglucose-6-phosphate reflects the glucose utilization of that cell. The biological features of rapid cell proliferation, increased cell membrane glucose carriers and increased activity of intracellular phosphatases prevalent in malignant tumor tissues result in a significantly higher rate of glycolytic metabolism in tumor cells. the degree of intracellular concentration of 18F-FDG is positively correlated with the high level of intracellular glucose metabolism. Malignant tumors tend to have increased uptake of 18F-FDG and can therefore be used to diagnose malignancy and identify benign and malignant lesions. However, some acute inflammatory lesions may also show increased uptake of 18F-FDG, but not as much as in malignant tumors, in which case they can be identified with a delayed scan, i.e., a second scan 2 hours after the first scan. Generally, 18F-FDG uptake is reduced in benign lesions, whereas in malignant tumors it is not reduced but may be increased. There are two common methods to determine whether FDG uptake is abnormal: one is the visual image method, with the degree of uptake of the mediastinal blood pool as a reference. Grade 1 is no significant uptake on the image, grade 2 is uptake below the mediastinum, grade 3 is uptake equal to the mediastinum, grade 4 is uptake above the mediastinum, grade 5 is uptake much higher than the mediastinum, grades 4 and 5 are judged as malignant lesions, while 1, 2 and 3 are considered benign lesions; the other is a semi-quantitative analysis to identify the nature of the lesion by the level of FDG standardized uptake value (SUV), a parameter that reflects the glucose metabolic rate of the tissue. Using the increased ability of tumor cells to uptake FDG, not only can the site, size, and degree of metabolic abnormality of the primary lung lesion be detected and determined early, but the lymph nodes and distant metastases of the tumor can also be accurately determined. PET is also applied to evaluate the response of tumors to treatment. At present, the commonly used clinical method to monitor tumor response to treatment is the comparison of CT examination before and after treatment, and the criteria used for evaluation are whether the tumor volume is reduced and the proportion of reduction. However, the number and proliferation activity of residual tumor cells do not necessarily correspond to the change in tumor volume. The degree of FDG concentration on PET reflects the proliferative capacity of cells, which correlates with the number of viable cells and the proliferative activity of cells; therefore, the status of FDG uptake in the tumor after induction therapy can provide a more accurate evaluation of the treatment response.