Virtual Colonoscopy (CT Colonography)

Written & reviewed by the BestDoctors.sg editorial team · Last updated 2 Sep 2026 · General information, not medical advice

A virtual colonoscopy, also known as CT colonography, is a way of examining the large bowel without passing a camera all the way through it. It is a useful option when a standard colonoscopy cannot be done or completed, or when a less invasive test is preferred. This guide explains what the scan involves, how to prepare, and what your results might mean, in the Singapore setting.

What it is

A virtual colonoscopy is a CT scan that produces detailed, three-dimensional pictures of the large bowel (the colon and rectum). A radiologist reviews the images to look for polyps, cancer and other changes in the bowel wall. The term “virtual” reflects that the pictures are built from the scan rather than from a camera physically travelling through the bowel. Because it uses CT technology, it can also show nearby structures in the abdomen and pelvis, which the radiologist will comment on if relevant.

How it differs from a standard colonoscopy

In a standard colonoscopy, a doctor passes a flexible tube with a camera through the whole length of the large bowel, usually with sedation. A virtual colonoscopy involves no sedation and no scope inside the bowel, so it feels less invasive. The important trade-off is that if a polyp or other abnormality is found during a virtual colonoscopy, it cannot be removed or biopsied at the same time. In that case a standard colonoscopy may still be needed to take a tissue sample or remove the polyp. A virtual colonoscopy is particularly useful when a full colonoscopy is not possible or could not be completed.

Why it’s done

A doctor may recommend a virtual colonoscopy to investigate symptoms such as a change in bowel habit, bleeding, or unexplained abdominal discomfort. It is also commonly used to follow up an incomplete colonoscopy, for example when the scope could not reach the whole bowel because of a narrowing or a difficult loop. In some screening situations it may be offered as an alternative when a standard colonoscopy is not suitable. Your gastroenterologist or colorectal surgeon will explain why it is the right choice for your situation.

How to prepare

Good preparation is essential because any leftover stool can hide or mimic a polyp. You will be asked to follow a bowel-cleansing preparation and to make diet changes in the days beforehand, similar to the preparation for a standard colonoscopy. This usually means eating a low-residue diet, then taking a laxative preparation so the bowel is as empty as possible. You may also be given a drink that “tags” any remaining stool or fluid so the radiologist can tell it apart from the bowel wall. Follow the instructions from the imaging centre closely, and tell the team about your medicines, allergies, kidney problems, diabetes or the possibility of pregnancy.

What happens during the scan

You will lie on the CT scanner table. A thin, soft tube is gently placed into the back passage, and a little gas or air is passed through it to expand the bowel so the walls are smooth and the pictures are clear. The scan itself is quick. You will usually be scanned in more than one position, such as lying on your back and then on your front or side, so the radiologist can see all parts of the bowel and move any fluid around. You may feel some fullness or the urge to pass wind as the bowel is inflated. The procedure does not usually need sedation, so you can normally travel home on your own afterwards.

After the scan

Most people feel some bloating, cramping or wind for a short while as the gas settles and is passed naturally. This usually eases soon after the scan. Because sedation is not normally used, you can generally return to your usual activities, eating and drinking straight away unless you are told otherwise. If you were given a contrast injection as part of the scan, the team will advise you on drinking fluids afterwards.

Results and next steps

A radiologist studies the images and prepares a report for the doctor who arranged the scan. A normal result means no significant polyps or worrying changes were seen. If findings such as polyps are picked up, you may be advised to have a standard colonoscopy so they can be removed or biopsied, since this cannot be done during the virtual scan. The radiologist may also note other findings in the abdomen or pelvis that need follow-up. Your doctor will discuss the report with you and explain the recommended next steps.

Benefits and limitations

The main benefits are that a virtual colonoscopy is less invasive, needs no sedation, and can examine the whole bowel even when a standard colonoscopy could not be completed. There are limitations to weigh up. The scan uses a small amount of X-ray radiation. It may miss very small or flat lesions that a camera examination could detect. Most importantly, it cannot treat anything it finds, so an abnormal result often leads to a standard colonoscopy anyway. Your doctor will help you decide which test suits your needs.

When to see a doctor

Some bloating and wind after the scan is normal and settles quickly. See a doctor promptly if you develop severe or persistent tummy pain, a hard or swollen abdomen, or any bleeding from the back passage after the procedure. Go to the nearest A&E or call 995 if you feel severely unwell, for example with worsening pain, breathlessness, or fever. Serious problems are uncommon, but it is always safer to be checked.

Common questions

Is a virtual colonoscopy better than a standard colonoscopy?

Neither is simply “better” — they suit different situations. A virtual colonoscopy is less invasive and needs no sedation, but it cannot remove polyps or take biopsies. A standard colonoscopy can both find and treat problems in one sitting. Your doctor will recommend the option that fits your symptoms and circumstances.

Do I still need bowel preparation?

Yes. Even though no camera is passed through the bowel, it must be clean and empty so the radiologist can see the bowel wall clearly. You will follow a bowel-cleansing preparation and diet changes similar to those for a standard colonoscopy.

Is the scan painful?

It is not usually painful. You may feel fullness, cramping or an urge to pass wind while the bowel is gently inflated with gas or air. This eases soon after the scan, and sedation is not normally required.

Will I need a standard colonoscopy afterwards?

Only if something is found that needs to be removed or biopsied, such as a polyp. If the scan is normal, you will not usually need a follow-up colonoscopy straight away. Your doctor will advise based on your report.

Can I go back to work the same day?

Usually yes. Because sedation is not normally used, most people can drive home and return to their normal activities soon after the scan, unless the team advises otherwise.

Related guides

• Colonoscopy
• Colorectal cancer
• FIT test
• Blood in stool
• Colonoscopy Cost in Singapore: Prices, MediSave & Colorectal Cancer Screening

Sources

• Singapore General Hospital
• HealthHub
• NHS
• National Cancer Centre Singapore