The imaging principle of abdominal MRI is different from that of CT, and nowadays, the use of MRI is becoming more and more widespread in clinical work. High-resolution MRI can perform T-staging of tumors in the abdominal cavity and N-staging of the surrounding lymph nodes. For example, if a tumor occurs in the gastrointestinal tumor or colorectal tumor, high-resolution MRI can determine the depth of tumor invasion, that is, T-stage, whether the tumor invades the mucosal layer, the submucosal layer, the muscular layer, whether it breaks through to the outside of the muscular layer or to the outside of the plasma membrane, and specifically stage the tumor. In addition, we can also stage the lymph nodes outside the tumor, whether there is one enlarged lymph node, or two, or even three or seven or more metastatic lymph nodes, to be able to make a preliminary assessment before surgery. Take rectal cancer as an example, for rectal cancer in the lower and middle segments, if the MRI stage before surgery is above T3N0, neoadjuvant radiotherapy is generally recommended, and after two courses of treatment, MRI will be performed again for evaluation; if there is a descending stage, radical surgery is needed; if there is no descending stage, comprehensive treatment may be continued.