About CT Colonography
CT Colonography – or Virtual Colonoscopy – is a completely safe diagnostic medical test using low dose radiation CT scanning to obtain images of the colon (the large intestine).
For CT Colonography, sophisticated computer software combines the CT images to form a three dimensional image of the colon. The images are similar to what is seen during a conventional colonoscopy. All methods of screening for colon cancer require a cleansing program for the colon. With CT Colonography, a camera is not pushed through the colon as with a conventional colonoscopy. The colon does not need to be filled with liquid barium as it does with a barium enema. So, a CT Colonography tends to be significantly faster and more comfortable for patients than other common screening methods.
Conventional (fiber optic) colonoscopies have been considered the “gold standard” for colorectal cancer screening. Many studies have been conducted to compare the accuracy of virtual to conventional colonoscopies in finding tumors and polyps in the colon. Study results show that CT Colonography is as accurate as or even exceeds conventional colonoscopies at finding tumors and polyps of significant size. An additional benefit of CT colonography is that the radiologist can also see other abdominal structures in the CT scan images, helping to identify other health problems when examining the images.
A limitation of CT Colonography is that the radiologist cannot remove a polyp during the procedure. If polyps are found, the patient must undergo a conventional colonoscopy so they can be removed. Polyps are found in about 10% of the exams. So, CT Colonography is most appropriate for individuals who are not at high risk for colorectal cancer and not experiencing any symptoms of colorectal cancer.
CT Colonography vs. Conventional Colonoscopy
A patient may choose to have a CT Colonography over a conventional colonoscopy for the following reasons:
- Generally more comfortable than conventional colonoscopy
- Unable or unwilling to undergo conscious sedation for conventional colonoscopy
- Taking anticoagulation medication
- Had an incomplete conventional colonoscopy (occurs in 2-10% of conventional colonoscopies)
- Have an obstruction that prevents a conventional colonoscopy
Risks Involved in a CT Colonography
The risk of x-ray exposure does exist; however, it is well below the level that generally causes adverse affects. As with all colorectal screening methods including conventional colonoscopy, there is no guarantee that a virtual colonoscopy will identify all cancers and polyps. However, it is one of the most accurate colorectal cancer screening exams currently available.
Conditions to Let Us Know About
In advance of your exam, let your scheduler or technologist know if any of the following circumstances apply to you:
- Currently pregnant
- Diabetes
- Heart failure
- Blood in stool
- Unexplained weight loss
- Crohn’s disease
- History of colon cancer
- Previous colon surgery
Trial Results for CT Colonography
The ACRIN trial, sponsored by the National Cancer Institute (NCI), was conducted by Radiology Imaging Associates (RIA) at the Invision Sally Jobe sites in partnership with Rocky Mountain Gastroenterology Associates, as well as at 14 other national sites. It is the largest multi-center study to estimate the accuracy of state-of-the art CT Colonography involving 163 participants at Invision Sally Jobe and 2,600 participants total nationwide. The results of the study were published in the September 18, 2008 New England Journal of Medicine article titled “Accuracy of CT Colonography for Detection of Large Adenomas and Cancers.”
RIA’s Dr. Richard Obregon, M.D., principal trial investigator at Invision Sally Jobe, said, “We are honored to be part of such a prestigious ACRIN trial team and help validate the use of CT Colonography as a primary screening tool for colorectal cancer. As a pioneer in this field in the Rocky Mountain region, the Invision CT Colonography clinical team is confident these trial results will help further our efforts to educate the physician/provider community and the public about the values and benefits of CT colonography screening as an alternative to traditional colonoscopy.”
“As the ACRIN patient advocate who worked with the research team and as a research advocate with C3: Colorectal Cancer Coalition, I am pleased that CT Colonography can be added to the list of screening options. Having a method that is accurate and comprehensive while being minimally invasive is needed if we are to succeed in substantially reducing deaths from colorectal cancers,” said Pam McAllister, Madison, Wisconsin.
Colorectal cancer is the third most frequently diagnosed cancer and the second leading cause of cancer death in men and women in the United States. Although screening recommendations vary somewhat, many recommend that adults age 50 and older in the general population receive a colonoscopy every 10 years. Yet, despite the known benefits of screening, studies indicate that the majority of Americans age 50 and older are not being screened for the disease.