What you can expect

Before the test

Before a virtual colonoscopy, you'll need to empty your colon. Any residue in your colon may obscure the images taken during the exam.

To empty your colon, follow your doctor's instructions carefully. You may be asked to:

• Follow a special diet the day before the exam. Typically, you won't be able to eat that day. Drinks may be limited to clear liquids. You may not be able to eat or drink anything after midnight the night before the exam.
• Take a laxative the night before the exam. You may also need to use a suppository to clear any remaining residue in your colon.
• Take medication to identify stool in your colon. The medication will help the doctor differentiate between colon abnormalities and stool residue.
• Adjust your usual medications. Remind your doctor of your medications at least a week before the exam. You may need to temporarily stop taking certain medications days or hours before the exam.

During the test

You'll wear a gown but likely no other clothes. Sedation usually isn't necessary, but you may be given medication to relax your colon.

You'll begin the exam lying on your side on the exam table, usually with your knees drawn toward your chest. A nurse or technologist will place a small tube (catheter) inside your rectum to fill your colon with air or carbon dioxide as you do a log roll on the table. The air or gas helps create clear images and may cause a feeling of pressure in your abdomen.

For the next part of the exam, you'll lie on your back. The exam table will be moved into the CT machine, and your body will be scanned. Then you'll turn over to lie on your abdomen or your side and your body will be scanned again.

You may be asked to turn and hold various other positions as well as hold your breath at times.

A virtual colonoscopy typically takes about 15 minutes.

After the test

You can resume your usual activities after your virtual colonoscopy. You may feel bloated or pass gas for a few hours after the exam as you clear any remaining air or gas from your colon.