In order to properly scan the colon two conditions must be met.
First, bowel cleansing must take place. Stool within the colon needs to be removed because CT images cannot see through stool and stool adheres to the colon wall. Your doctor will instruct you on the type of bowel cleansing laxative you should use.
In addition to bowel cleansing, there are some dietary restrictions:
- One week prior to the exam, no eating of hard nuts and seeds, such as peanuts, cashews, popcorn, sunflower, poppy, and sesame seeds.
- Three days prior to the exam, no eating of high residue foods such as bran cereal and raw vegetables.
- One day before the procedure:
- Only clear liquids are to be ingested
- An afternoon / evening bowel cleansing laxative and contrast preparation needs to be completed.
If you have diabetes, you must discuss adjusting your diabetes medication dose with your doctor prior to beginning a clear liquid diet.
Second, the colon walls must be distended in order to see colon polyps. The colon is inflated with carbon dioxide gas. This is the same gas as in gingerale or soda pop; therefore, following the procedure the gas will either be quickly absorbed or passed out of the rectum within approximately 5 to 10 minutes. Once the colon is distended, two separate CT scans (one lying on the stomach and one on the back) will be taken in order to view the entire colon.
After the procedure, a normal diet and activity may be resumed unless a screening virtual CT colonoscopy detects a large polyp and the requirements to have a conventional colonoscopy procedure later in the day are met.