"new method of performing virtual colonoscopy using a CT scan  which doesnt involve the dreaded laxative preparation to clear the colon the night before  may be about as effective as a standard colonoscopy at identifying the large polyps most likely to become cancerous according to research conducted at Massachusetts General Hospital Brigham and Womens Hospital and elsewhere. If the finding is confirmed by larger studies the technique could eventually serve as a firstline screening tool for colon cancer especially for the many people who avoid screening altogether. The new technique works by using a contrast agent  a tiny amount of this dye is ingested two days before the test  to highlight fecal matter in the colon which can then be digitally erased from the scan using a computer software program making it easier to see polyps.  Advertisement  In the study of  patients published Monday in the Annals of Internal Medicine the prepfree virtual colonoscopy was able to identify more than  percent of suspicious polyps that were  millimeters or larger compared with  percent identified when the same patients later had a standard colonoscopy.  ADVERTISING The research was partially funded by GE Healthcare manufacturer of the CT imaging device. Study participants reported an improved level of comfort with the new technique said study author Dr. Michael Zalis a radiologist at Massachusetts General Hospital primarily because it didnt involve the diarrheainducing prep that keeps most people in close range of a bathroom during the night before a colonoscopy. Of the study participants who expressed a preference  percent said they preferred the prepfree CT procedure over the colonoscopy.  Only sixty percent of Americans age  and over get the American Cancer Societys recommended screening for colon cancer a colonoscopy every  years fecal occult blood test every year or a flexible sigmoidoscopy virtual colonoscopy or barium enema imaging every five years. Surveys suggest that patients find the prep  required for both colonoscopy and traditional virtual colonoscopy  to be the worst part of screening. A number of folks who currently arent being screened because they fear the prep or arent willing to go through it again may be willing to have screening if theyre told they dont need to take laxatives and can still get a potent test said Dr. Durado Brooks director of prostate and colon cancer for the American Cancer Society. Advertisement  About  Americans die every year from colon cancer added Brooks and at least half of those deaths could be prevented if everyone followed the screening recommendations. Virtual colonoscopy with or without prep has some limitations. About one in five patients must undergo a standard colonoscopy after the imaging procedure to have suspicious looking polyps snipped off and biopsied. The CT scan also delivers a dose of radiation that  while only onefifth of the dose of an abdominal CT scan  was significant enough to raise the flags of the US Preventive Services Task Force.  The government advisory group decided in  not to recommend the use of virtual colonoscopy saying that evidence wasnt sufficient enough to prove that the tests benefits outweighed its harms which include a dose of radiation with every screening test. Standard colonoscopy also has rare complications such as an adverse reaction to the sedative perforation to the colon and bleeding from the site where the polyp was taken. Medicare doesnt provide coverage for the imaging test which Zalis said costs about onethird as much as the traditional scope screening.  Traditional colonscopy also trumps the virtual test when is comes to detecting smaller polyps less than  millimeters in size. The new study found that virtual colonosopy detected only  percent of polyps under  millimeters in size compared with  percent detected by a scope. Whats not clear though is whether missing these smaller polyps will make a difference in terms of catching growths before they turn into cancer.  Advertisement  Studies are underway right now said Brooks to track these smaller lesions to see what happens to them."