Virtual colonoscopy

A virtual colonoscopy is a test that uses a CT scanner and X-rays to produce images of the large bowel and look for any abnormalities inside your abdomen and bowel.

Why you might need a virtual colonoscopy

Your large bowel is the lower part of your intestines. It absorbs water and nutrients from digested food that passes through it. If you have unexplained changes in your bowel habits, anal bleeding or persistent stomach pain, you may have a virtual colonoscopy to check for signs of bowel cancer.

The procedure provides a clear picture of what’s going on inside your large bowel, so that your doctor can identify any changes.

They can also check for other conditions like:

• Diverticular disease
• Inflammation
• Polyps (non-cancerous growths)

A polyp is extra tissue that grows inside your bowel wall. While these are usually harmless, they can sometimes turn into cancer. To be safe, polyps are removed and tested for cancer.

Finding any issues early means that your healthcare team can decide the next steps as soon as possible. You may need further treatment, monitoring, or reassurance that nothing serious is happening.

Is a virtual colonoscopy right for you?

Your doctor may recommend a virtual colonoscopy to check inside your large intestine for any abnormalities, such as growths, inflammation or any other changes that might occur.

A virtual colonoscopy may be more suitable than a traditional colonoscopy, where a small camera is inserted into the rectum, for a number of reasons. For example, if you:

• Are at risk of bleeding or other complications
• Don’t want to be sedated
• Have a blockage in your bowel
• Need to drive yourself home after the procedure

A virtual colonoscopy may not be suitable if you are pregnant as it uses X-rays, which could harm the unborn baby. It may also not be suitable for you if you have:

• A higher than average risk of colon cancer
• A history or family history of colon cancer
• A history or family history of polyps
• Acute diverticulitis
  An active flare-up of bowel disease
• Significant abdominal pain

Radiation exposure carries a higher risk for children and young adults, so virtual colonoscopy is not generally recommended for this age group.

You’ll have your virtual colonoscopy in the hospital’s imaging department, using a CT scanner. This will take images of your bowel to create a detailed 3D model of your colon — the radiologist will use this to examine your bowel as if a camera were travelling through it.

The scan will also create 2D images of your colon, abdomen and pelvis, which can help detect any other issues that may be causing your symptoms. 

Before the procedure

You may be asked to follow a low-fibre or restricted diet in the days leading up to the scan. Your admissions letter will explain whether you need to avoid certain foods or only drink clear fluids.

You may need to stop taking medications or supplements, such as iron tablets, in the run-up to your scan. Your care team will advise you whether you need to pause or adjust your dose.

If you have diabetes, your doctor will give you specific advice on how to prepare, especially if you take insulin or other medicines that affect your blood sugar.

How to prepare for the surgery

To capture the clearest images, your bowel will need to be as clean and empty as possible. You’ll be given an iodine-based liquid to drink the day before your procedure. This acts as both a laxative and a dye.

Who will be involved?

A highly-skilled radiographer will carry out your scan. They will typically not be in the room with you while the scan is running, however, they will be able to communicate with you through an intercom.

The procedure

How long does a virtual colonoscopy take?

A virtual colonoscopy typically takes less than 30 minutes.

What happens during the scan?

You’ll change into a hospital gown and lie down on the scanning table. Your healthcare team will gently insert a thin, flexible tube into your rectum and pass carbon dioxide through it to slightly inflate your bowel.

This allows the CT scanner to take clear and detailed images of the lining of your bowel by smoothing out any folds or wrinkles that may hide polyps from view. The gas may cause a sensation similar to trapped wind or the urge to go to the toilet but, as the colon is empty, this won't be possible.

The scanner table will move slowly through the CT scanner while it takes pictures of your bowel. You may have to change positions a few times so that the scanner can get images of your bowel from all angles. You’ll have to lie perfectly still as the scanner takes the images, as it can take several minutes to generate each picture. You may be asked to hold your breath for a couple of seconds during the scan.

What happens immediately after your scan

When your radiologist has all the pictures they need, your care team will gently remove the tube inflating your bowel. You’ll be taken into a recovery room that has a toilet and your clothes so you can get dressed.

The gas used to inflate your bowel may cause mild bloating or discomfort, but this should resolve when you use the toilet or pass gas naturally.

You can usually go home straight after the procedure if your care team is happy for you to do so.

Your results

In most cases, your radiologist will complete their report within 5 working days. Your results will be sent to the doctor who referred you for the scan, who will arrange a follow-up appointment to talk you through them. They will explain what the scan revealed and the best treatment options for you, if necessary.

A virtual colonoscopy is generally considered a very safe procedure and has fewer associated risks than a traditional colonoscopy (also called an endoscopy). You may experience discomfort and bloating from having your bowel inflated. You may also feel faint when you first sit up after having the procedure. 

In fewer than 1 in 10,000 people, inflating the bowel with carbon dioxide causes an injury.

If a virtual colonoscopy isn’t suitable for you, you may be offered a standard colonoscopy instead. This is also called an endoscopy of the bowel. It involves passing a long, flexible tube with a camera on the end through your colon and moving it carefully around your bowel.

This doesn’t use X-rays, but is more invasive than a virtual colonoscopy, and usually needs sedation to keep you comfortable. However, an advantage of this procedure is that doctors can take biopsies or remove polyps during your colonoscopy, which they can’t do with a virtual one.

Capsule endoscopy

This involves swallowing a tiny disposable camera inside a capsule the size of a large vitamin pill. As it travels through your bowel, it takes pictures that are transmitted wirelessly to a small recorder for your radiologist to review. This is a relatively new technology and is only offered at some hospitals.