Magnetic resonance imaging (MRI) provides a more tolerable alternative to conventional colonoscopy in screening colon cancer.
MRI colonography can detect polyps that have the potential for becoming cancerous. It involves taking MRI images of the colon and correlating them with those seen with colonoscopy. But unlike conventional colonoscopy, this doesn’t require the insertion of a long tube in the rectum. Moreover, with use of a special technique called faecal tagging, patients do not need to undergo the uncomfortable bowel cleansing required with conventional colonoscopy.
To assess the efficacy of MRI colonography, researchers at University Hospital Essen in Germany, studied 315 adults, above the age of 50, who had undergone MRI colonography screening. Two days before screening, the subjects drank a liquid with every main meal that tagged any stool in the bowel, allowing the stool to be virtually removed from the MRI images to make it easier for doctors to look for polyps. No bowel cleansing agents were given, although rectal water enema was administered prior to imaging. No sedative or analgesic medications were given. The findings on MRI colonography were compared with those obtained with conventional colonoscopy.
The results indicated that MRI colonography was fairly good at detecting polyps greater than 5 millimetres in diameter. However, MRI colonography nearly always missed smaller polyps. The overall sensitivity (detection of true positives) of this technique when compared to conventional colonography was 83% and specificity (detection of true negatives) was 90%.
Despite the encouraging results and patient comfort, conventional colonoscopy remains the first choice in screening colon cancer. An important advantage of conventional colonoscopy is that polyps that are detected can be removed or biopsied during the procedure.
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