1. Malignant tumors are one of the major diseases that endanger human health and lead to human death. In China, there are more than 1.6 million new cancer patients every year, and the number of people suffering from cancer increases year by year. The occurrence and development of malignant tumors often start from the changes of proto-oncogenes, through metabolic abnormality, functional abnormality, anatomical structure abnormality, and finally clinical symptoms, so the metabolism and functional abnormality of the tumor cells are earlier than the anatomical form changes. When clinical symptoms appear or lumps are found in the body, most of the patients are in the middle or late stage of the tumor, losing the best time for treatment.PET-CT has unique advantages in early qualitative and localized diagnosis of tumors, and it is an indispensable means for early diagnosis of tumors and implementation of scientific and effective treatment. 2.PET-CT can be used as a health checkup to find hidden early tumor lesions and make them cured. 3.For clinically suspected tumor lesions, PET-CT can make differential diagnosis and identify benign and malignant lesions. 4.For patients with confirmed malignant tumors, PET-CT can accurately detect systemic metastatic foci and assist in the formulation of treatment plans. 5.For those who clinically find metastatic foci but the primary tumor foci are unknown, PET-CT can help detect the primary tumor foci. 6.For diagnosed malignant tumor foci, PET-CT can accurately locate them in space, implement and optimize radiotherapy or X, γ knife resection plan. 7.For scar, residual or recurrent foci after tumor treatment PET-CT can effectively identify.