直肠癌不仅在发达国家有很高的发病率，我国的直肠癌发病率也有逐年上升的趋势。除了非常早期的直肠癌可以局部切除外，直肠癌主要的治疗方法仍是根治性手术。全直肠系膜切除术(total mesorectal excision，TME)手术已被证实可减少直肠癌的局部复发率，但是手术方式在很大程度上依赖于术前对于肿瘤范围的准确评价。远处及局部复发的危险仍持续威胁着直肠癌患者的生命。TNM分期、疗效评价、复发监测是临床医生制定直肠癌治疗方案和评价预后的重要信息，也是影像学的研究热点。

There is a high incidence of rectal cancer in developed countries, there is an increasing trend in China.Apart from a very early rectal cancer with local excision, the treatment of rectal cancer is still radical surgery.TME(total mesorectal excision) surgery has been shown to reduce the local recurrence rate of rectal cancer, but the surgery is largely dependent on the accurate preoperative evaluation of the extent of tumor.The possibility of distant and local recurrence continue to threaten the lives of cancer patients.TNM staging, evaluation of tumor's response and recurrence monitoring, are all important factors for clinicians to develop the treatment program and make prognosis, and now emerging as imaging research focus.