PET-CT belongs to the category of ECT, and we know that PET-CT relies on the metabolism of glucose in the human body. The tracer we use is equivalent to the imaging agent, and after the glucose is injected into the body through a vein, different tissues in the body will absorb it differently. For example, tumors are absorbed more than normal tissues, and benign and malignant tumors have different degrees of malignancy and different degrees of absorption. Therefore, it will form a bright spot in the body, which we call a different degree of concentration: First, the higher the malignancy of the tumor, the more tracer is taken up, forming a bright spot, which we can find out from the imaging. Second, we can see the size, extent and degree of the concentration and identify the disease. Thirdly, we can evaluate the efficacy, whether there is residual tumor after treatment or whether there is recurrence, by doing imaging we can evaluate and use different glucose uptake rate to make differential diagnosis. It is mainly used for the diagnosis and differential diagnosis of brain, lung, liver, kidney and other tumors, and has an important role.