PET-CT, also known as positron emission computed tomography, is an imaging device that reflects the genetic, molecular, metabolic, and functional status of a lesion. PET-CT is a combination of both PET and CT devices, with complementary advantages, but is not a simple superposition of the two functions. CT can precisely locate the lesion and show the morphological and structural changes. Its unique fusion image, which fuses PET and CT images, can reflect the pathological state and morphological and structural changes of the lesion at the same time, significantly improving the diagnostic accuracy, especially in identifying benign and malignant tumors, as well as systemic metastasis and staging of tumors. This test has the advantages of being safe, non-invasive, accurate, rapid and cost-effective. However, it is not recommended for routine medical checkups because of its relatively high price and high radiation dose.