PET-CT can determine whether a tumor has metastases and where they have metastasized, allowing for clinical staging of the tumor. Solid tumors are usually staged using the specifics of T (degree of tissue infiltration) N (degree of metastasis in lymph nodes) M (degree of metastasis in other organs or tissues). For example, bladder cancer is usually divided into 4 stages: T1 stage is confined to the mucosal layer of the bladder without metastasis to lymph nodes and other organs and tissues; T2 stage tumor invades the deep muscular layer, which may be accompanied by metastasis to lymph nodes; T3 stage tumor invades fat tissue around the bladder through the muscle layer, which can be determined by CT and has metastasis of peripheral lymph nodes; T4 stage tumor invades other organs and tissues (e.g. prostate, uterus, vagina, etc.), which can be examined by both CT/PET-CT. If any of the above situations occurs, it is recommended to seek timely medical treatment for reasonable and standardized diagnostic and therapeutic behaviors.