A CT Colonoscopy, also known as Virtual Colonoscopy, is a special type of CT scan used to examine the large intestine (colon and rectum). It uses X-rays and computer technology to create detailed 3D images of the inside of the bowel.
Unlike a standard colonoscopy, this test does not require inserting a long camera tube through the entire colon. Instead, it is minimally invasive and provides a clear view of the colon lining to check for polyps, growths, or signs of bowel disease.
This guide covers the purpose of a CT Colonoscopy and answers frequently asked questions to help you prepare and know what to expect.
Common Indications for CT Colonoscopy
Doctors may recommend CT colonography to:
- Evaluate selected patients with bowel symptoms or a positive screening test when conventional colonoscopy is incomplete, unsuitable, or unavailable.
- Check for polyps, tumors, or signs of colorectal cancer.
- Evaluate patients who cannot undergo or complete a standard colonoscopy.
- Follow up on abnormal results from other imaging tests or stool tests.
- Monitor the bowel after previous surgery or treatment.
What does a CT Colonoscopy show?
It provides clear images of the inside of the large intestine, allowing doctors to detect polyps, tumors, diverticulosis, narrowing (strictures), or other abnormalities.
What happens during a CT Colonoscopy procedure?
- You will lie on a CT table, usually on your back and side.
- A small flexible tube is gently inserted a short distance into your rectum to allow carbon dioxide or air to inflate the colon. This helps make the bowel visible on the scan.
- The CT scanner then takes pictures from different angles, often with you lying in two different positions.
- The entire scan usually takes 20-30 minutes.
Do I need to prepare for a CT Colonoscopy?
Yes. Preparation is important for clear results.
- You will need to follow a special diet for a day or two before the test.
- A bowel preparation (laxative or cleansing solution) is usually given to empty the colon.
- Sometimes a "faecal tagging" solution is also given to help highlight any leftover stool.
- Detailed instructions will be provided by your radiology center.
How long does a CT Colonoscopy take?
The scan itself is quick, usually 20-30 minutes, but preparation (bowel cleansing) is done the day before. Expect to spend about an hour at the radiology center.
Will the scan be painful?
The scan is generally not painful. You may feel some bloating or cramping from the air or carbon dioxide used to inflate the colon, but this usually settles shortly after the test.
Can I eat or drink before my CT Colonoscopy?
No, you will be given clear instructions. Typically, you’ll need to avoid solid foods and follow a clear-liquid diet the day before, along with taking bowel prep medicine.
Are there risks with a CT Colonoscopy?
- The test uses ionising radiation; dose varies with the scanner, patient, and protocol.
- Rarely, inflating the bowel with air or carbon dioxide can cause discomfort or, in extremely rare cases, bowel injury.
- Unlike standard colonoscopy, polyps cannot be removed during this test. If abnormalities are found, you may still need a standard colonoscopy for treatment.
Safety note (if contrast is used)
If IV contrast is planned, kidney-function testing is based on risk factors and local policy. Inform your radiographer if you have:
- Previous allergic reactions to contrast.
- Kidney problems.
- Diabetes.
Can I have a CT Colonoscopy if I am pregnant?
Pregnancy Precaution
CT colonography is generally deferred during pregnancy because it is usually elective and uses pelvic ionising radiation. Tell the referring clinician and CT team if you are pregnant or could be pregnant so a suitable alternative or timing can be chosen. Urgent bowel symptoms still require prompt clinical assessment.
Questions to ask your team
- What bowel preparation and stool-tagging instructions must I follow?
- What happens if the scan finds a polyp that needs conventional colonoscopy or biopsy?
- Is CT colonography suitable given my symptoms, pregnancy status, and bowel history?
Sources and further reading
Conclusion
CT colonography is a less invasive way to examine the colon and is particularly useful when conventional colonoscopy is incomplete or unsuitable. It still requires bowel preparation and rectal gas, uses ionising radiation, and cannot biopsy or remove a polyp. Discuss which test fits your symptoms and screening risk, and follow the preparation instructions closely.