CT colonography is a CT scan of the bowel that looks for polyps and cancer without a colonoscope. Learn how it works, bowel preparation and when it is advised.
CT colonography (virtual colonoscopy) uses CT and a little gas in the bowel to make 2D and 3D pictures of the colon and rectum. It can find polyps and cancers and is a useful option for people who cannot have, or do not want, a standard colonoscopy. If polyps are found, a colonoscopy is needed to remove them.
Who May Choose CT Colonography?
- People who cannot tolerate colonoscopy or sedation
- After an incomplete colonoscopy because of a long or twisted bowel
- People on blood thinners that cannot be stopped easily
- Elderly or frail patients
- Those who prefer a non-invasive screening test
See CT abdomen and pelvis for the standard belly scan.
FeatureCT colonographyColonoscopyMethodCT scan with gas in the bowelCamera tube through the anusSedationNot neededOften neededPolyp removalNoYes, during the testRadiationLow doseNoneBowel preparationYes, with a tagging agentYes, full preparationTime10 to 15 minutes30 to 60 minutesHow Is It Done?
A small soft tube is placed in the rectum to gently fill the colon with carbon dioxide or air. You then lie on the CT table, first on your back and then on your front or side, and hold your breath for a few seconds in each position. Contrast may be given in a vein in selected cases. The scan itself takes minutes, and you can go home right after.
Bowel Preparation
You need a low-residue diet for a day or two and a laxative to clear the bowel. A special oral agent (tagging) marks leftover stool so it is not confused with polyps. Drink plenty of fluids. Follow the centre's exact instructions, and tell them about kidney disease, diabetes and medicines. See CT scan preparation.
What It Can and Cannot Find
CT colonography finds most polyps larger than 10 mm and many 6 to 9 mm ones, and detects most cancers. Very small polyps and flat lesions may be missed. It can also show changes outside the colon, such as in the kidneys, liver and arteries. Polyps of 6 mm or more usually lead to a colonoscopy for removal.
A Practical Example
Hari, 71, is on blood thinners for a heart valve and had a failed colonoscopy as the bowel was long and twisted. A CT colonography shows a 12 mm polyp in the sigmoid colon. A colonoscopy is then done with a safe plan for the blood thinners, and the polyp is removed. The scan avoided repeated sedation and showed exactly where to go.
Understanding Your Report
The report lists the number, size and position of polyps and uses a scoring system called C-RADS. C0 means incomplete, C1 normal, C2 intermediate and C3 or C4 need colonoscopy or surgery. Your doctor will advise accordingly.
After the Scan and Next Steps
Take the report to a gastroenterologist. If the scan is normal, your next screening is usually in five years, depending on your risk. If polyps or masses are seen, a colonoscopy with biopsy or removal is advised. Report blood in stool, changes in bowel habit, weight loss or anaemia early, and do not wait for the next screening.
Questions to Ask Your Doctor
- Is CT colonography suitable for me or do I need colonoscopy?
- Which bowel preparation should I follow?
- What will happen if a polyp is found?
- When is my next screening due?
Common Mistakes to Avoid
- Not following the bowel preparation.
- Ignoring blood in stool.
- Assuming a normal scan ends the need for any future screening.
Booking, Timing and Report
Most CT scans can be booked on the same day, and the visit takes 20 to 40 minutes. Carry your prescription, old scans and a recent creatinine report if contrast is planned. Reports are usually ready within 24 hours, and images can be provided on a CD or digital link for your doctor.
Frequently Asked Questions
What is CT colonography?
A CT scan of the colon to find polyps and cancer.
Can polyps be removed during it?
No, colonoscopy is needed.
Do I need sedation?
No.
Do I need bowel preparation?
Yes, with a tagging agent.
Is it painful?
Mild bloating or cramps can occur.
How long does it take?
About 10 to 15 minutes.
Is it as accurate as colonoscopy?
Good for larger polyps, less for tiny ones.
Is it safe in pregnancy?
Not advised.
When is the report ready?
Usually within 24 hours.
Book Your Test at Ganesh Diagnostic
Ganesh Diagnostic & Imaging Centre in Rohini, Delhi offers this test with trained radiology staff and clear reports. You can book an appointment online, check our branches across Delhi NCR, contact us for current rates, or explore all our services. Reports can be downloaded online through our patient portal, so you do not need to make a second trip just to collect them.
This article is for general information only. It does not replace advice from your doctor. Always follow your doctor's instructions for your test.
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