Virtual Colonoscopy

Medically Reviewed By William C. Lloyd III, MD, FACS
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What is a virtual colonoscopy?

A virtual colonoscopy is a CT (computed tomography) or MRI (magnetic resonance imaging) scan of the colon and rectum. CT relies on X-rays to generate the image and MRI uses a different type of technology not involving X-rays. Your doctor may recommend a virtual colonoscopy to screen for colon cancer and possibly look for other diseases of the colon. A virtual colonoscopy is an important test that can help detect colorectal cancer in its earliest, most curable stage and other serious conditions.

The colon and the rectum make up the large intestine, sometimes called the large bowel. The large intestine is a long, hollow organ in your abdomen that plays an important role in digestion by removing water from digested material and forming feces. In addition to looking for signs of colorectal cancer, a virtual colonoscopy can help your doctor find the reason for unexplained intestinal symptoms you may be having, such as changes in your bowel movements, abdominal pain, or rectal bleeding.

Virtual colonoscopy, also known as a CT colonography, is only one method used to screen for colon cancer. A conventional colonoscopy is also used to screen for colon cancer and to help detect other diseases of the colon. A colonoscopy is a more invasive procedure that allows your doctor to see the lining of your colon and rectum using a thin, flexible instrument with a camera, called a colonoscope. This instrument is inserted through the rectum into the colon. 

Certain procedures can be done during a colonoscopy that cannot be performed during a virtual colonoscopy. These include taking a biopsy, controlling bleeding, and removing polyps (growths that can become cancerous). You should discuss all of your diagnostic and colon cancer screening options with your doctor or healthcare provider to best understand which option is right for you.

Why is a virtual colonoscopy performed? 

Your primary care doctor or a gastroenterologist may recommend a virtual colonoscopy to screen for colon cancer and colon polyps, growths that can become cancerous. Your doctor may also recommend the procedure to help diagnose a variety of other diseases and conditions of the colon and rectum including:

  • Abdominal pain, which can be caused by many different conditions including inflammatory bowel disease, diverticulitis, and intestinal ulcer

  • Abnormal changes in your bowel movements, which can be caused by a variety of conditions from intestinal inflammation to colon cancer

  • Anemia (low red blood cell count) if the underlying cause has not been found through less invasive testing. A virtual colonoscopy may be used to identify potential bleeding sites.

  • Bleeding symptoms, such as bloody stool, or black, tarry feces. Potential causes of such bleeding include colon cancer and intestinal inflammation or damage.

  • Poor colonoscopy results, such as the inability to see the entire colon during a traditional colonoscopy.

Who performs a virtual colonoscopy?

Radiologists and diagnostic radiologists perform virtual colonoscopies. Radiologists specialize in using radiation and other imaging techniques to diagnose and treat a wide variety of conditions from broken bones and birth defects to cancer. Diagnostic radiologists specialize in performing and interpreting imaging tests, such as ultrasounds, X-rays, angiograms, CTs, nuclear scans, and MRIs.

A radiologic technologist may perform the actual procedure under direction from the radiologist or diagnostic radiologist.

How is a virtual colonoscopy performed?

A virtual colonoscopy is performed in a hospital radiology department or outpatient radiology clinic. It takes about 30 minutes and generally includes these steps:

  1. You dress in a patient gown and lie on an examination table.

  2. The radiologic technologist positions you on the table and inserts a small flexible tube about two inches into your rectum.

  3. Air is pumped into the colon. This expands the colon to help create the clearest images of the entire organ.

  4. The table you’re lying on moves you through a tunnel-like structure as a series of images are taken. You may be placed in a variety of positions during this process. You will also need to hold your breath briefly during the procedure to help avoid blurry images.

  5. After all the images have been taken, you will wait briefly while the pictures are checked for quality.

Will I feel pain?

Your comfort and relaxation are very important to both you and your care team. You may feel pressure, abdominal fullness, or brief cramping when air is pumped into the colon. Take a few long, deep breaths to help yourself relax, but if any discomfort does not pass quickly, tell a member of your care team.

What are the risks and potential complications of a virtual colonoscopy?  

Complications after a virtual colonoscopy are not common. However, any procedure involves risks and the possibility of complications that may become serious in some cases. Complications can develop during or after the procedure and include: 

  • Dehydration due to taking enemas and laxatives before the procedure

  • Gastrointestinal disturbances, such as nausea, vomiting, and rectal discomfort

  • Perforation of the colon (rare)

  • Small risk of cancer due to radiation exposure. Your radiology team follows strict standards for X-ray techniques and will use the lowest amount of radiation possible to produce the best images. Your doctor will generally not order an X-ray procedure if you are pregnant due to danger of radiation to an unborn child.

Reducing your risk of complications

You can reduce the risk of certain complications by: 

  • Following activity, dietary and lifestyle restrictions and recommendations before your procedure and during recovery

  • Informing your radiologist if there is any possibility that you may be pregnant

  • Notifying your doctor immediately of any concerns, such as rectal bleeding or increase in pain

  • Taking your medications exactly as directed

How do I prepare for my virtual colonoscopy?

If you dread the thought of undergoing testing for colorectal cancer, you are not alone. You are an important member of your own healthcare team. The steps you take before your procedure can improve your comfort level and help your doctor obtain the most accurate results. You can prepare for a virtual colonoscopy by:

  • Answering all questions about your medical history and medications you take. This includes prescriptions, over-the-counter drugs, herbal treatments, and vitamins. It is a good idea to carry a current list of your medical conditions, medications, and allergies at all times.

  • Completely cleansing your intestines as directed by your doctor. This may include a combination of enemas, laxatives, and not eating solid foods for a day before the test.

  • Drinking plenty of clear fluids to be well hydrated 

  • Removing all jewelry and metal on the day of your test

  • Taking or stopping medications exactly as directed

Questions to ask your doctor

Preparing for a virtual colonoscopy can be stressful. It is common for patients to forget some of their concerns during a doctor’s office visit. You may also think of other questions after your appointment. You should contact your doctor with concerns and questions before the procedure. 

It is also a good idea to bring a list of questions to your appointment. Common questions include:

  • Why do I need a virtual colonoscopy? Are there any other options for diagnosing or treating my condition?

  • How long will the procedure take? When can I go home?

  • What kind of restrictions will I have after the procedure and when can I return to work and other activities?

  • What kind of assistance will I need at home? Will I need a ride home?

  • What medication plan should I follow before and after the procedure?

  • How will my pain or discomfort be managed?

  • When should I follow up with you?

  • How should I contact you? Ask for numbers to call during and after regular hours.

  • When and how will I get the results of my test?

What can I expect after my virtual colonoscopy?

Knowing what to expect after a virtual colonoscopy can help you get back to your everyday life as soon as possible. 

How will I feel after the virtual colonoscopy?

You may have mild abdominal cramping and you may pass the gas that was inserted during the procedure. Take slow deep breaths to relax your abdominal muscles and reduce discomfort. You should not be in pain. Tell a member of your care team if you have discomfort that does not go away quickly or if you are in pain, because this may be a sign of a complication.

When can I go home?

In general, you should be able to go home and get back to your normal activities and diet immediately after the examination. You may be instructed to drink extra water and fluids for 24 hours to ensure good hydration.

When should I call my doctor?

It is important to keep your follow-up appointments after a virtual colonoscopy. Call your doctor if you have concerns or questions between appointments. Call your doctor if you have:

  • Fever (you should not have any fever after a virtual colonoscopy)

  • Pain

  • Rectal bleeding, bloody stools, or black tarry stools

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2020 Nov 19
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
  1. CT Colonography. American College of Radiology.
  2. Learn About Cancer. American Cancer Society.
  3. Virtual Colonoscopy. National Digestive Diseases Information Clearinghouse (NDDIC).