According to the statistical results of the national authority, the incidence of cancer in China has been increasing year by year, and now, cancer has become the number one killer. before 1975, the first cause of death among urban residents in China has been respiratory diseases, in 1975 the first is cerebrovascular disease, and in 1985 it was heart disease. In the 1990s, malignant tumors became the number one killer of residents. One out of every four deaths in large cities is due to cancer. The most important treatment for cancer is early detection, as most early cancers can be cured. The results of numerous studies show that 1/3 of cancers can be prevented; 1/3 of cancers can be treated if they are diagnosed early; reasonable and effective treatment can prolong the survival period and improve the quality of life of the remaining 1/3 of cancer patients. How to make early diagnosis of tumor is a hot issue in medical research today. PET-CT is an emerging “in vivo biochemical” imaging technology. It combines PET imaging, a functional molecular imaging technology that reflects physiological and pathological characteristics at the cellular and molecular levels, with CT imaging technology that reflects physiological and pathological anatomical structural changes at the tissue level. The combination of PET imaging and CT imaging technology reflects the physiological and pathological anatomical structural changes at the tissue level. PET-CT can provide PET images and CT images at the same time, and realize the real sense of image fusion with the same machine, playing the role of 1+1>2. It can both accurately characterize the lesion and accurately locate it, and its diagnostic performance and clinical value are higher. It is the most perfect and highest grade medical imaging technology today. PET-CT provides an effective means for early detection and reasonable treatment of cancer. Identification of benign and malignant tumors or lesions As we all know, it is very important to identify the benign and malignant tumors, which is not only related to the treatment plan, but also directly affects the patient’s prognosis. For example, if a patient has a single nodule in the lung, after PET-CT examination, if the nodule has low metabolic activity, it indicates a high possibility of benign lesion and the choice of surgery should be cautious; on the contrary, if the nodule has increased metabolic activity, it indicates a possibility of malignancy and active treatment measures, including surgery, should be taken. Tumor staging Tumor staging is an important basis for deciding the patient’s treatment plan. a PET-CT whole-body imaging of the patient, a single PET-CT whole-body imaging can provide information on the presence or absence of metastases in various organs of the body, such as brain, lung, lymph nodes, liver, adrenal glands and bones, which is helpful for accurate clinical staging of various tumors such as lung cancer, breast cancer, colon cancer, ovarian cancer and lymphoma. Taking the diagnosis of lymph node metastasis as an example, PET-CT is more accurate because CT or MRI is to consider enlarged lymph nodes (>1cm) as metastases, which are not infrequently enlarged due to chronic inflammation or misjudge normal-sized lymph nodes that have been invaded by tumor tissues as normal, while PET is more accurate than considering only lesion size to determine whether metastasis is present based on the metabolic activity of lymph nodes.