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CT Colonography – What It Is and How It Works

Feb 25, 2021 | Articles, CT

You’ve probably heard of MRIs, x-rays, and CT scans, but have you ever heard of CT Colonography? Of the many tests and medical equipment, CT Colonography isn’t as well-known as the other. To understand what this procedure entails, we need to lay down all the facts.


CT Colonography Explained

Computed Axial Tomography (CAT), more commonly known today as CT scan, is a diagnostic medical imaging test performed using a CT scanner. Much like x-rays, a CT scan produces multiple images of the body’s insides to aid a doctor’s diagnosis.

CT scans can detect fractures and tumors on the bone and joints. Patients with heart disease, cancer, or emphysema also undergo CT scans to help doctors spot any changes. They can also be used to locate any blood clots, infections, excess fluid, and internal bleeding. Lastly, it can also be used to diagnose various conditions in the colon or if you’re having difficulty completing a colonoscopy.

In layman’s terms, CT colonography (CTC) is just a CT scanner used to take pictures of the inside of a patient’s colon and rectum. They’re like a more beefed-up x-ray that focuses mainly on obtaining a clearer cross-sectional image of the colon.


CT Colonography and Its Uses

The main reason for performing CTC is to look for cancer or polyps in the large bowel. Polyps are tiny clumps of cells that grow in the lining of the colon. Doctors resort to the use of CT colonography to find those polyps in their early stages to prevent cancer from developing.


Colonoscopy vs. Colonography

A traditional colonoscopy involves inserting a small camera affixed on a flexible metal tube into the colon through the rectum. Since the tube is inserted throughout the entire colon, patients can feel some discomfort during the procedure with a slight risk of perforation and bleeding.

On the other hand, a CT colonography involves merely inserting a small tube a few inches into the rectum to gently inflate the colon with gas or air. This procedure uses a CT scan machine to produce hundreds of cross-sectional images of the colon. CTC is also known as Virtual Colonoscopy, as it is a more minimally invasive test compared to traditional colonoscopy.


CT Colonography Procedure

CT scans work very similarly to x-rays. An X-ray machine uses a small amount of radiation to project an image of the body to a recording plate. Bones will appear white on an x-ray, while soft tissue like the heart or the liver will have shades of gray.

With CT scanning, several x-ray beams rotate around the patient to capture images of the human body. Imagine a high-speed camera rotating around the patient.  It will then be displayed on a monitor where the two-dimensional cross-sectional images captured are processed by a specialized computer.

It takes 15-20 minutes for the entire procedure to complete. In some cases, the CTC technologist will use a special dye called contrast material to produce a clearer image. While the procedure itself doesn’t cause any side effects to the patient, some are allergic to the contrast material. Pregnant women are also not recommended to undergo CTC. Other than those mentioned, the procedure is entirely safe.



CT Colonography is a revolutionary diagnostic technique used by doctors to detect colon abnormalities like cancer and polyps. It’s a lot less invasive than colonoscopy as it mainly uses a CT scanner to produce images of the inside of a patient’s body.

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