How to Prepare for Your Virtual Colonoscopy

This information will help you prepare for your virtual colonoscopy at Memorial Sloan Kettering (MSK).

About Your Virtual Colonoscopy

A virtual colonoscopy (VC), also known as a computed tomography (CT) colonography, is done to take pictures of your colon (large intestine) and rectum (the last part of your colon) to look for signs of cancer. Adults ages 50 years and over should be screened for colon polyps. Colon polyps are growths attached to the inner wall of your colon. They are usually benign (not cancerous), although some can be cancerous or precancerous.

During your VC, your technologist will use a CT scan to take 3-D pictures of the inside of your colon and rectum. A VC is different from a regular colonoscopy because your doctor can look at the inside of your colon without using a colonoscope (flexible tube placed in the rectum during a colonoscopy).

Your doctor will use the 3-D pictures to:

  • Look for signs of colorectal cancer
  • Look for growths (polyps) in your colon and rectum

If you have any questions, call 212-639-7280. If the office is closed, call 212-639-2000 and ask for the Radiology Body fellow on call.

 
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Before Your Procedure

Pick up your prep kit

Before your VC, you’ll need to clean out (empty) your colon. To do this, you will need to pick up the following supplies from an MSK pharmacy:

  • 2 (5 milligram) tablets of bisacodyl (Dulcolax®). You will get a box of 10 tablets, but you will only need to take 2.
  • 1 (50 milliliter) bottle of iohexol (Omnipaque®). This is a contrast dye that will make your colon easier to see during your VC.
    • Don’t put the iohexol in the refrigerator.
    • Don’t store the bottle in direct sunlight.
  • 1 (225 milliliter) bottle of liquid barium sulfate suspension. This is another contrast dye.
    • You can keep the barium sulfate in the refrigerator or at room temperature.
  • 2 (296 milliliter) bottles of magnesium citrate. This is a laxative that will clean out your colon.
    • You can keep the magnesium citrate in the refrigerator or at room temperature.

You will also need:

  • 64 ounces of any clear liquid that isn’t red, purple, or orange.
    • We recommend that you get a sports drink like Gatorade® or Powerade®.
    • If you have diabetes, be sure to get sugar-free clear liquids.

Ask about your medications

You may need to change the time you take your regular medications so it’s not at the same time as the medication needed for your bowel preparation. If you usually take your medications at the time you’re supposed to take one of your bowel preparation medications, plan to take your other medications 1 hour before or 1 hour after. If you’re having trouble planning your medication time, call your doctor or nurse.

If you take medication to thin your blood, such as to treat blood clots, do not stop taking it unless your doctor tells you to stop. Some examples of blood thinners include warfarin (Coumadin®), dalteparin (Fragmin®), dabigatran (Pradaxa®), enoxaparin (Lovenox®), clopidogrel (Plavix®), prasugrel (Effient®) and cilostazol (Pletal®). There are others, so check with your doctor if you aren’t sure.

Contrast dye

Contrast is a special dye that makes it easier for your doctor to see abnormalities in your body. Oral contrast dye will be part of your bowel preparation for your VC. Please talk to your doctor if you’ve had a reaction to any contrast dye used for a CT in the past. This includes barium and iodinated contrast.

If you will be having a VC without oral contrast, ask your nurse for the resource How to Prepare for Your Virtual Colonoscopy Without Oral Contrast, or search for it on www.mskcc.org/pe.

For people with diabetes

  • If you take insulin or other medications for diabetes, you may need to change the dose. Ask the doctor who prescribes your diabetes medication what you should do the day before and the morning of your procedure. Tell your doctor you will be drinking a clear liquid diet the day before your procedure.
  • If you monitor your blood sugar (glucose) level, ask your doctor if you should stay on the same monitoring schedule. Call your doctor if your blood sugar falls below 70.
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3 Days Before Your Procedure

Avoid certain foods

Don’t eat foods that are hard to digest. Food may make it difficult to see your organs in the pictures taken during your VC. If this happens, you may need to repeat the procedure.

 

Examples of foods that are hard to digest are:

  • Raw fruits and vegetables. You can have vegetables that are cooked or canned.
  • Whole kernel corn
  • Popcorn
  • Potato skins
  • Grains or seeds, such as poppy or sesame seeds
  • Nuts
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The Day Before Your Procedure

Begin your bowel preparation

During your bowel preparation, you’ll take laxatives and contrast medication. Be sure to follow these instructions carefully. It’s very important that your colon is empty for your VC. If your colon isn’t empty, it will be difficult to see polyps or other problems inside your colon. If this happens, you may need to repeat the procedure.

If you have any questions, call your doctor’s office.

Follow a clear liquid diet

You will need to follow a clear liquid diet the day before your procedure. Examples of clear liquids are listed in the table below. While you’re following the clear liquid diet:

  • Don’t eat any solid foods.
  • Don’t drink anything red, purple, or orange.
  • Make sure to drink plenty of liquids in addition to water, coffee, and tea. Try to drink at least 1 (8-ounce) glass every hour while you’re awake.

You can drink as many clear liquids as you like between each step of your bowel preparation. Stop drinking clear liquids at midnight.

 
  Drink Do Not Drink
Soups
  • Clear broth, bouillon, or consommé
  • Clear packaged vegetable, chicken, or beef broth-mix
  • Any products with particles of dried food or seasoning
Sweets
  • Gelatin, such as Jello®
  • Flavored ices
  • Sweeteners, such as sugar or honey
  • Anything red, orange, or purple
Drinks
  • Water
  • Clear fruit juices, such as white cranberry, white grape, apple
  • Soda and sports drinks, such as 7-Up®, Sprite®, ginger ale, seltzer, or Gatorade®
  • Black coffee
  • Tea
  • Clear liquid protein drinks
  • Juice with pulp
  • Nectars
  • Milk or cream
  • Alcoholic beverages

Follow your bowel prep medication schedule

The day before your VC, you will begin taking your bowel preparation medication. Follow the medication schedule in this section.

You may need to change the time you take your regular medications so it’s not at the same time as the medication needed for your bowel prep. If you usually take your medications at the time you’re supposed to take one of your bowel prep medications, plan to take your other medications 1 hour before or 1 hour after. If you’re having troubling planning your medication time, call your doctor or nurse.

If you have any questions, call 212-639-7280. If the office is closed, call 212-639-2000 and ask for the Radiology Body fellow on call.

Bowel prep schedule

Use the table at the end of this resource to write down the time you take each medication.

Remember that you can drink clear liquids between each of these steps. Stop drinking clear liquids at midnight.

 

Step 1: Bisacodyl tablets

Anytime in the morning before 11:00am, take 2 (5 milligram) bisacodyl tablets.

  • Take them with 1 (8-ounce) glass of clear liquids.
  • Don’t chew or crush them.
  • Don’t take them within 1 hour of taking an antacid (medication to relieve heartburn or stomach pain), including calcium carbonates (such as Tums®) and histamine-2 blockers (such as Zantac®). Ask your doctor for more information.

The bisacodyl tablets will cause you to have a bowel movement about 6 to 8 hours after you take them. This will help the laxative taken in Step 2 work better. You can take these tablets and still do normal activities because they will rarely cause diarrhea (loose or watery bowel movements).

Step 2: First bottle of magnesium citrate

Between 2:00 pm and 6:00 pm, drink the first bottle of magnesium citrate.

  • You may want to drink it with a straw to lessen the taste.
  • This is a laxative, so you should begin having bowel movements more frequently. Your stool will become more and more loose and clear as you continue with your bowel prep. You will want to be near a bathroom. The time it takes for the laxative to start working varies for each person.
  • If you don’t start having bowel movements within 2 hours after completing Step 2, call your doctor.
  • Apply petroleum jelly (Vaseline®) or A & D® ointment to the skin around your rectum after every bowel movement. This helps prevent irritation.

Drink at least 4 to 6 cups (32 to 48 ounces) of clear liquids over the next 2 to 3 hours.

 

Step 3: Liquid barium sulfate suspension and second bottle of magnesium citrate

Two to 3 hours after drinking the first bottle of magnesium citrate, drink the bottle of liquid barium sulfate suspension and the second bottle of magnesium citrate.

Drink at least 4 to 6 cups (32 to 48 ounces) of clear liquids over the next 2 to 3 hours.

Step 4: Iohexol

Two to 3 hours after drinking the liquid barium sulfate suspension and second bottle of magnesium citrate, drink the bottle of iohexol.

  • You can mix the iohexol with 8 ounces of clear juice, water, or soda. You can also drink the iohexol and then follow it with 8 ounces of clear juice, water, or soda.
  • The plastic bottle has a pull-tab on the top, but you don’t need to pull it. Instead, twist the entire top to remove it. Remove the black rubber stopper before drinking the contrast.
  • The iohexol bottle says it’s for injection, but it can also be taken orally (by mouth). We want you to drink this medication so that it will be in your colon by the time of your VC.

Now your stool should be more liquidy and yellowish-clear. This is a sign that your bowels are getting cleared. If your bowels aren’t getting cleared, call 212-639-7280 and ask to talk with a nurse or the fellow on call.

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Do not eat or drink anything after midnight except for your medications with a small sip of water.

 
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The Day of Your Procedure

You may take your usual daily medications as prescribed with small sips of water.

What to expect

Once you arrive at the hospital, nurses, and other staff members will ask you to state and spell your name and date of birth many times. This is for your safety. People with the same or similar names may be having procedures on the same day.

When it’s time to change for your procedure, you will be asked to change into a hospital gown.

You will be taken into the CT exam room where you will lie on the CT exam table. A small tube will be gently placed into your rectum and secured to your leg or buttocks. It will feel like you’re having a rectal exam. The tube will inflate your colon with air or gas so that your technologist can get a better view. To help move the air or gas throughout your colon, you will be asked to change positions frequently. You will lie on your side, back, and abdomen (belly).

The VC isn’t painful, but you may feel some bloating, discomfort, or cramping. You may also feel like you’re going to have a bowel movement. These feelings should go away after your procedure.

You will be asked to hold your breath for about 10 seconds while the CT scanner takes pictures. Your technologist will take pictures of your abdomen and pelvis in at least 2 different positions (usually while you’re on your back and stomach).

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Bowel Prep Schedule

Step Scheduled Time Actual Time Taken Medication(s) to Take
1 Before 11:00 am  
  • 2 (5 milligram) bisacodyl tablets
2 Between 2:00 pm and 6:00 pm  
  • 1 (296 milliliter) bottle of magnesium citrate
3

2 to 3 hours after Step 2

 
  • 1 (225 milliliter) bottle of liquid barium sulfate suspension
  • 1 (296 milliliter) bottle of magnesium citrate
4

2 to 3 hours after Step 3

 
  • 1 (50 milliliter) bottle of iohexol
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