Imaging diagnosis of outlet obstructive constipation                   SHEN Hui, WANG Wei-xing, TIAN Bing, et al. Department of Medical Imaging, Changhai Hospital, the Second Military Medical University, Shanghai 200433, China
Corresponding author：HAO Qiang，E-mail: haoqiang@189.cn
Abstract    Outlet obstructive constipation (OOC) is the most popular reasons of chronic constipation, and also hardly diagnosed by imaging. Defecography is the major modality for constipation, and its images are still the evidence of surgery.  X-rays defecography is the gold standard for evaluating OOC. On the contrary, MR-defecography is expensive nowadays and has an unphysiological defecation way, but it will be an extensive examination and has broad prospects in the future. Ultrasound defecography is seldom applied for diagnosing OOC, and its exact role remains to be evaluated.