The purpose of this study is to diagnose possible synchronous carcinomas and polyps with MR colonography in patients booked for operation because of carcinoma in the descending or sigmoid colon, where a preoperative full colonoscopy is not possible. Two days before colonography, patients ingest a 200 ml Barium sulfate solution four times a day, which will render fecal masses “invisible” on the following MR colonography. The study is primarily a feasibility study with altered operative strategy as a secondary end-point. Gold standard is colonoscopy and operation.