 The purpose of this study is to determine if MR colonography with fecal tagging is better using air or water for distension of the colon. Patients referred to colonoscopy are offered MR colonography before colonoscopy. Two days before colonography, patients ingest a 200 ml Barium sulfate solution 2 four times a day, which will render fecal masses invisible on the following MR colonography. Air or water randomised trial is used for distension of the colon. The examinations are evaluated by two independent blinded readers. 