CT colonography, also known as virtual colonoscopy, is a less invasive imaging test that uses CT scan technology to create detailed images of the colon and rectum. It helps doctors check for colon polyps, tumors, and signs of colorectal cancer, supporting early detection and appropriate follow-up when needed.
 
Colorectal cancer often develops silently. In many cases, there are no obvious symptoms in the early stages. Many colorectal cancers begin as small growths called polyps. Detecting these polyps early gives doctors the opportunity to monitor them or remove them before they become cancerous.
 
For some patients, CT colonography may be an alternative screening option to conventional colonoscopy, especially when a less invasive test is preferred or when colonoscopy is not suitable.
 
 

What is CT colonography?

CT colonography is a specialized CT scan that examines the large intestine without using a long camera tube. During the test, the colon is gently filled with air or carbon dioxide to help expand it. The CT scanner then takes detailed images, which are reviewed by a radiologist.
 
This test is commonly used to look for:

• Colon polyps
• Colorectal cancer
• Tumors or masses
• Narrowing or changes in the colon
• Abnormal findings after incomplete colonoscopy

 
Because CT colonography is performed using imaging from outside the body, it is often considered less invasive than conventional colonoscopy.
 
 

CT colonography vs colonoscopy: what is the difference?

Both CT colonography and colonoscopy are used to evaluate the colon, but they are not the same.
 
CT colonography uses CT imaging to create pictures of the colon and rectum. It usually does not require sedation, takes a short time, and allows most patients to return to normal activities soon after the test.
 
Conventional colonoscopy uses a flexible camera tube to directly view the inside of the colon. It usually requires sedation, so patients may need time to recover after the procedure and should arrange for someone to take them home. Its main advantage is that doctors can remove polyps and take tissue samples, or biopsies, from suspected areas during the same procedure.
In simple terms:

• CT colonography can detect polyps and suspicious findings.
• Colonoscopy can detect and remove polyps, and it can take biopsies from suspected areas.

 
If CT colonography shows a suspicious polyp or abnormal area, a follow-up colonoscopy is needed so your doctor can remove the polyp or take a biopsy.
 
 

Who may need CT colonography?

Your doctor may discuss CT colonography if you need colorectal cancer screening or further colon evaluation. It may be suitable for selected patients who:

• Need screening for colon polyps or colorectal cancer
• Prefer a less invasive colon screening test
• Cannot undergo sedation
• Had an incomplete colonoscopy
• Need evaluation because of symptoms or medical history
• Have medical reasons that make conventional colonoscopy more difficult

 
CT colonography is not suitable for everyone. Patients with active bowel inflammation, certain bowel diseases, recent colon surgery, or high-risk findings may need another type of test.
 
 

How do you prepare for CT colonography?

Preparation is important because a clean colon helps produce accurate images. Before CT colonography, patients are usually asked to follow bowel preparation instructions.
This may include:

• Eating a special low-fiber or clear-liquid diet
• Taking laxatives
• Drinking fluids as instructed
• Avoiding certain foods or medications before the test

 
Your healthcare team will provide specific instructions based on your condition. Good preparation helps the radiologist see the colon more clearly and reduces the chance of needing a repeat test.
 
 

What happens during CT colonography?

During CT colonography, you will lie on a CT scanning table. A small tube is placed into the rectum to gently inflate the colon with air or carbon dioxide. This may cause temporary bloating or pressure.
 
The CT scanner then takes images while you lie in different positions. The scan itself is usually quick. Sedation is usually not required, so most patients can leave soon after the examination.
 
 

What are the benefits of CT colonography?

CT colonography may offer several benefits for selected patients:

• Less invasive screening
  It does not require a long camera tube to pass through the entire colon.
• Usually no sedation
  Most patients do not need anesthesia or recovery time from sedation.
• Quick examination
  The scan is generally completed in a short time.
• Faster return to daily activities
  Patients can often resume normal activities soon after the test.
• Useful after incomplete colonoscopy
  It may help evaluate the colon when conventional colonoscopy cannot be completed.
• Helps detect larger polyps and suspicious changes
  It can identify abnormalities that need further investigation.

 

What are the limitations of CT colonography?

CT colonography is useful, but it has limitations.

• It cannot remove polyps or take biopsies. If polyps or suspicious findings are detected, you will need a follow-up colonoscopy so your doctor can remove the polyp or take a biopsy.
• CT colonography may be less effective in detecting small or flat polyps, particularly lesions smaller than 6 mm. Colonoscopy remains more sensitive for these subtle lesions and also allows immediate biopsy or polyp removal during the same procedure.
• The best screening test depends on your age, symptoms, family history, previous screening results, and overall health.

 

Key Takeaway

“CT colonography is a less invasive colorectal cancer screening option that may be suitable for selected patients, especially those who cannot undergo sedation or have had an incomplete colonoscopy. However, if polyps or suspicious findings are detected, a follow-up colonoscopy is still needed for biopsy or removal.”
— Asst. Prof. Veeravich Jaruvongvanich, M.D., Board-Certified Gastroenterologist at Bumrungrad International Hospital
 
 

When should you talk to a doctor?

You should consult a digestive disease specialist or gastroenterologist if you are due for colorectal cancer screening or if you have symptoms such as:

• Blood in the stool
• Ongoing abdominal pain
• Change in bowel habits
• Persistent constipation or diarrhea
• Unexplained weight loss
• Narrow stool shape
• Family history of colorectal cancer or colon polyps

 
Do not wait for symptoms before screening. Colorectal cancer can develop without early warning signs.

 

CT Colonography at Bumrungrad Digestive Disease Center

At Bumrungrad Digestive Disease Center (DDC), patients can consult with digestive disease specialists and gastroenterologists to discuss whether CT colonography is the right screening or diagnostic option. Based on your symptoms, risk factors, family history, and medical background, the specialist may recommend CT colonography, conventional colonoscopy, or another suitable test.
 
If CT colonography detects polyps or suspicious findings, colonoscopy is needed so your doctor can remove the polyp or take a biopsy.

 

FAQ

What is CT colonography?
CT colonography is a CT scan used to examine the colon and rectum for polyps, tumors, and signs of colorectal cancer. It is also called virtual colonoscopy.
 
Is CT colonography the same as colonoscopy?
No. CT colonography uses CT imaging from outside the body. Colonoscopy uses a flexible camera tube inserted into the colon, usually requires sedation, and can remove polyps or take biopsies from suspected areas.
 
Does CT colonography require sedation?
Usually, no. Most patients do not need sedation for CT colonography.
 
Can CT colonography detect colon polyps?
Yes. CT colonography can detect colon polyps, especially larger polyps. If polyps are found, a follow-up colonoscopy is needed to remove them.
 
Can CT colonography remove polyps?
No. CT colonography can detect polyps, but it cannot remove them. A colonoscopy is needed for polyp removal or biopsy.
 
Is bowel preparation needed for CT colonography?
Yes. Bowel preparation is usually required so the colon is clean and the images are clear.
 
Who should consider CT colonography?
CT colonography may be considered for selected patients who need colorectal cancer screening, prefer a less invasive test, cannot undergo sedation, or had an incomplete colonoscopy.