PET-CT is a kind of whole-body examination, which is mainly used in the following aspects: 1. whole-body examination: for some high-end medical examinations, PET-CT can be used for whole-body examination to determine whether there are any tumor diseases in various parts of the body. 2. screening for tumor metastases: it can be used for tumor patients to check whether there are metastases in other parts of the body, such as whether breast cancer patients have metastases in other parts of the body. PET-CT can also be used to check whether there is recurrence after tumor treatment. 3.Checking other lesions: PET-CT can be used to check lesions that are not detected by other imaging methods, such as patients with lymph node metastasis, but no primary lesions are found and not detected by other examination methods. PET-CT can be used to detect lymph node metastases.