Prepare for a Virtual CT Colonoscopy scan

Virtual colonoscopy uses CT scanning to obtain an interior view of the colon (the large intestine) that is ordinarily only seen with an endoscope inserted into the rectum.

Important Information Prior to Your Exam

  • Please let us know if you have any allergies or adverse reactions to medications.
  • If you are pregnant or may be pregnant, please tell your doctor or technologist.
  • Inform your doctor, if you have heart, liver or kidney disease to be certain that the bowel prep is safe for you.
  • Also let us know if you have had prior colon surgery.
  • Please let us now if you need interpreting services, this can be arranged for you.
  • You will need to contact the UCSF Ambulatory Pharmacy at (415) 353-1544 to have the preparation packet mailed to you.
  • The preparation packet costs approximately $100 and is available only by credit card payment.
  • It is extremely important that you follow the preparation instructions closely in order for your virtual colonoscopy to be successful.

What is the preparation for a virtual CT colonoscopy procedure?


You will need to purchase ALL the following laxatives (in addition to the Omnipaque) before starting the preparation. The laxatives should be available at your local pharmacy. You do not need a prescription for the laxatives. 

  1. One 10oz. bottle of magnesium citrate (commonly sold as Citroma). This is NOT the same as “Milk of Magnesia.” 
  2. Four 5mg bisacodyl oral tablets (commonly sold as Carter’s Little Pills or Dulcolax). 
  3. One 10mg bisacodyl suppository (commonly sold as Dulcolax, Fleet Bisacodyl, or Magic Bullet). DO NOT keep this in your pocket or anywhere warm – it will melt and become unusable. 

On the day before the virtual colonoscopy:

  • No solid food all day.
  • Drink clear liquids only (i.e., water, tea, coffee, juice, soda, broth, jello, etc.).
  • Drink 8 oz of water (about 1 glass) at least every hour (try to never be thirsty). Over the course of the day, drink at least 2 quarts of liquids.
Time Instruction
8 am Mix 2 tsp of Omnipaque in 1 glass of water and drink it.
12 pm Mix 2 tsp of Omnipaque in 1 glass of water and drink it.
5 pm Drink the 10 oz bottle of Magnesium Citrate.
7 pm

Mix 2 tsp of Omnipaque in 1 glass of water and drink it.

Also take all four 5mg oral bisacodyl tablets with a large glass of water. Do not chew the tablets. Bisacodyl tablets take generally 6-12 hours to produce bowel movements. 

12 am MIDNIGHT No food or liquid.

On the day of the virtual colonoscopy:

  • Do not eat or drink anything. This includes medications. Bring your medications with you and take them after the virtual colonoscopy is completed.
Time Instruction
At least 2 hours before your exam

Mix 4 tsp of Omnipaque in 1 glass of water and drink it.

Also unwrap the 10mg bisacodyl suppository and discard the foil/wrapper. While lying on your side with your leg raised, insert the suppository into the rectum and gently push in as far as possible. 

What happens during the virtual colonoscopy?

After changing into a gown, you will be placed on the CT scanner table. The technologist will distend your colon with air by inserting a small rectal tube that is connected to an insufflator. As your colon fills with air, you may feel bloating and mild discomfort. Please let us know if you feel uncomfortable.

You will be scanned initially lying on your back. We will then ask you to turn onto your belly and we will scan a second time. You will be asked to hold your breath during each scan for about 20 seconds. If you have to breathe out, do so shallowly. We may need to give additional air through the rectal tube when you turn onto your belly.

Then you are done! You will return to the dressing room to change back into your clothes.

Day before virtual colonoscopy:

Day before virtual colonscopy


Morning of virtual colonscopy

If you have any questions, please call UCSF Imaging Center at China Basin at (415) 353-4500 and ask to speak to a nurse.