CT Colonography

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[lwptoc] What is CT Colonography or Virtual Colonoscopy? CT Colonography also called virtual colonoscopy is a diagnostic technique for the large intestines to detect the presence of cancer, polyps, or other abnormal formations. The test is conducted by exclusive X-ray equipment, involving the insertion of an appropriate tube in the colon, which is expanded by… Read More

CT Colonography


What is CT Colonography or Virtual Colonoscopy?

CT Colonography also called virtual colonoscopy is a diagnostic technique for the large intestines to detect the presence of cancer, polyps, or other abnormal formations. The test is conducted by exclusive X-ray equipment, involving the insertion of an appropriate tube in the colon, which is expanded by the administration of inflation gas. After that, CT images of the intestines and rectum are obtained.

How is CT Colonography different from a CT Scan and a conventional colonoscopy?

We all have heard about the CAT Scan or CT Scan; it is a medical imaging diagnostic test that utilizes the application of x-rays to produce images of the inside of the body.

Although, CT Scan is different from your traditional x-ray test. In an x-ray, the equipment used for diagnosis is less complex and the rays are useful to identify the dense tissues of the body, which are bones. Whereas, in a CT Scan the patient is placed on a bed and is rotated through the scanner, where high-intensity radiations are passed, with the ability to detect even the delicate parts of the body like blood vessels and tissues are detected, and can be produced as images.

These images are viewed on a computer as 3D images, can be printed, and even reformatted in multiple planes.

So, how do a CT Scan and a colonoscopy relate to each other? CT Colonography is a similar diagnostic procedure as a CT scan in which the patient is passed through a radiation scanner, and the large intestines of the patient are studied in the procedure, which was otherwise only possible through invasive procedures.

When is CT Colonography performed?

  • When an intestinal blockage is suspected, virtual colonoscopy is performed to detect the presence of a tumour or a polyp.
  • A virtual colonoscopy may also be performed when a conventional colonoscopy is ineffective or is potential for injury to the injury.
  • When a patient denies a traditional colonoscopy.

What is the principle behind Virtual Colonoscopy?

As we previously discussed, CT Colonography involves the patients being passed through specially designed equipment emitting x-ray radiations. Each body part, organ, and system will absorb radiations of only a specific value. Bones are identified as white on the x-ray, organs are identified as grey and the hollow space is identified in dark.

During a virtual Colonoscopy, the body rotates on the diagnosis field, passing through the scanners; the radiation detectors present, detect and emit the information, displayed on a monitor in the form of 2D images and 3D models.

The data is interpreted by an interventional radiologist, who gives their inference on the diagnosis. If an abnormal growth is detected through the scan, necessary measures are taken, to find out whether the growth is a polyp or cancer.

What are the benefits of Virtual Colonoscopy?

  • CT Colonography is a non-invasive process that is very effective when it comes to detecting even minor growths in the colon.
  • The procedure is ideal for patients who suffer from anxiety disorders, bleeding disorders, or other issues that may flare up, like hemorrhoids or fissure.
  • Conventional colonoscopy is not possible when bowel obstruction is present, CT Colonography is the only alternative in such cases.
  • Virtual colonoscopy is not only useful in detecting abnormalities in the colon, the diagnostic procedure can also detect malignancy in other organs and also abdominal aortic aneurysms.

What are the risk factors when it comes to CT Colonography?

  • Exposure to radiation is risky business. Although the radiation dose for each individual may vary, it is determined before the procedure by radiologists after a thorough study of the patient’s profile.
  • CT Colonography is a risky procedure for pregnant women, posing threat to the fetus.

How should you prepare for a CT Colonography?

  • As per the standard procedure, you will be asked to restrict your diet to fluids a day before your procedure.
  • You will also be asked to take an oral laxative the night before the procedure so that you empty your bowels. Laxatives like mucilage supplements, fiber supplements, magnesium citrate, or polyethylene glycol are commonly prescribed pre-procedure medications.
  • Many hospitals will ask you to come in for the procedure on an empty stomach and administer you an enema just before the procedure, to make sure that your bowel is empty and it doesn’t interfere with the test.
  • In case you are allergic to contrast media, then you will be given medication for it with instructions.
  • A patient can face discomfort when they are anxious and this causes involuntary motion in their colon. To arrest colonic motion, an IV/IM dose of hyoscine-N-butylbromide, an antimuscarinic drug is given.

Important Note: If you are on a certain medication, E.g., blood pressure medications, liver meds, blood thinners, medications that might affect your intestinal flora, then it is your duty to inform your doctor, to avoid any unwanted interactions.

How is the procedure carried out?

The technician will place on the CT exam table, positioning as per SOP. You will be lying flat on your back, your head rested against a pillow for comfort. Sometimes patients are strapped around their waist or lower body to maintain the desired position.

The next step involves pumping of air or carbon dioxide in the patient’s rectum, done by the gradual insertion of a flexible tube, two inches into the rectal cavity. Air is pumped so as to inflate the colon, easing the way for a comfortable CT colonography, and also hide wrinkles within the intestines, which hide the polyps.

What next? The table along with the patient is passed through the scanner, emitting x-rays. The patient might be required to change positions as directed by the radiologist. Once facing upwards, and other times face down on the bed. This allows for all-round scanning of the body and more scope for a virtual colonoscopy this way.

What equipment consists of a CT colonography system?

Scanner: This is a doughnut-shaped machine exhibiting an opening in the center through which the bed passes.

X-ray tube and detectors: These are separate formations opposite to each other present on a ring-like structure called the gantry. The detector detects the x-ray radiations absorbed by the body and transmits the information to the monitor.

Computer: The computer itself consists of the monitor, on which the information is transmitted and is interpreted in the form of 2D and 3D images.


Does CT Colonography cause pain?

A CT or virtual colonography is rarely considered painful because it is a non-invasive procedure. Patients might feel slight discomfort because of air pumped in their rectal cavity and an inflated colon.

How and when do you get your test results?

A radiologist is a person who oversees your CT colonoscopy, the radiologist is also the person who will interpret your results. You may receive reports of your results immediately after you are done with your tests. You might also be required to wait for a couple of days before your results are posted to you.

Will I have to do a conventional colonoscopy after doing a virtual colonography?

That depends on your diagnosis results. In case an abnormal growth in your colon is detected through the virtual colonoscopy, you will have to undergo the traditional colonoscopy, to identify the abnormality. If polyps are present, they will be removed in-process during colonoscopy.

Is CT Colonography safe?

The colonic perforation rate when it comes to virtual or CT colonography lies between 0.005% to 0.03%. This is less when compared to risks posed by conventional colonoscopy, which according to studies is placed between 0.06% to 0.19%.

What is the cost of the procedure?

The total cost of the procedure is between $330 to $1080, which is non-inclusive of other necessary and related fees.