Considering the ionizing radiation exposure is it safer to have an mri instead of ct scan in the colon cancer follow up after surgery ?

YES: Good question! Many doctors do not appreciate the very real risks from the high doses of radiation used in CT scans so I advise doing CT scans only when absolutely necessary. Research shows MRI's are at least as accurate as CT scans for assessing colon cancer so I see no goos reason to choose a CT scan when a MRI gives the needed assessment without any exposure to ionizing radiation.