Common Procedures

Common Procedures > CT Colonography

CT Colongraphy Frequently Asked Questions

What is CT colonography?  

CT colonography uses a machine called a ‘Computed Tomography’ (CT) scanner to produce images of the large bowel. The CT scanner uses sequential X-rays to do this.

Several days before the CT scan, you will be asked to observe dietary restrictions to reduce the number of faeces in your bowel. One day before the scan, you will also be asked to take oral medication to help clear the bowel of as much faecal matter as possible. This will help to increase the accuracy of the scan.

Before the CT scan, a thin tube will be placed into your anus, through which gas will be passed to inflate your large bowel. Images will then be obtained with you in two different positions (lying on your back and on your tummy).

A specialist doctor (called a radiologist) will then use dedicated software to analyse the images and look for signs of colon cancer. If the radiologist detects an abnormality, additional tests may be suggested.

How is CT colonoscopy different from regular colonoscopy? 

Regular (optical) colonoscopy involves putting a camera into the large bowel, while in CT colonography, the ‘camera’ is outside the body, and it creates virtual images of the colon. This is why CT colonography is also called ‘virtual colonoscopy’.

CT colonography allows other organs in the abdomen to be assessed as well (abnormalities in other organs may be a cause of the patient’s symptoms), while optical colonoscopy only evaluates the colon.

In an optical colonoscopy, if an abnormality in the large bowel is identified, the doctor can proceed to directly obtain tissue for further analysis. In CT colonography, if an abnormality in the colon is detected, the patient will be offered optical colonoscopy for further analysis

This test involves the use of X-rays. Is it dangerous? 

As this test involves the use of X-rays, the patient will be exposed to radiation. The radiation dose is however very low. The radiation dose of a CT colonography is approximately equivalent to 1 year of background radiation.

What happens when something abnormal is found on CT colonography? 

If the abnormality is in the large bowel, your primary doctor will discuss with you the need for an optical colonoscopy to obtain tissue for diagnosis.

If the abnormality is outside the large bowel (in another organ in the abdomen), your primary doctor will discuss with you the need to do other tests (for example other CT scans, MRI) to confirm the diagnosis.

Is this test as accurate as optical colonoscopy? 

Several international large studies have shown that CT colonography is as accurate as colonoscopy. Flat lesions or lesions < 5mm, however may be missed.

Do I need to go for this test if I do not have any bowel symptoms? 

Like optical colonoscopy, CT colonography is recommended for everyone above the age of 50 who have a stool FIT positive as colon cancer may not result in any symptoms in the early stages.

What are the risks? 

CT colonography is considered a very safe procedure. Minor side effects include abdominal bloatedness or dizziness. Serious side effects (which are extremely rare) include damage to the large bowel wall (the chance of this happening in CT colonography is much lower than in optical colonoscopy) and severe allergic reactions to dye injected into the blood vessels during the CT scan.