PET-CT examination can be used for localization and qualitative diagnosis of many kinds of tumors: Diagnosis of malignant tumors, differential diagnosis of benign and malignant lesions; Detection of malignant tumor metastases, preoperative staging and restaging; Searching for tumor origin when metastasis is detected or paraneoplastic syndrome or elevated tumor markers appear; Monitoring the efficacy of malignant tumors, including judging the response to treatment and treatment effect; judging the sensitivity of tumors to radiotherapy and chemotherapy, guiding the selection of reasonable treatment plans and reducing the waste of medical resources; Detecting tumor recurrence, especially when tumor markers are elevated; Detection of residual abnormalities on physical examination or other imaging tests after treatment, deciding whether it is a tumor or fibrosis or necrosis after treatment; Selecting the area within the tumor for biopsy that is most likely to yield diagnostic information about the tumor; Guidance on radiotherapy planning and outlining of biological target areas prior to tumor radiotherapy. If you suspect a tumor, you should go to the hospital promptly.