Virtual Colonoscopy or CT Colonography

Virtual colonoscopy, also called CT colonography is a minimally invasive diagnostic technique that utilizes CT (computed tomography) scans to inspect the colon (large intestine or large bowel) and the rectum (back passage) for cancers and other conditions affecting the colon and rectum.

The virtual colonoscopy procedure involves using a high-technology X-ray scanner and advanced computer programs to create detailed images of the tissues inside the colon and rectum. Unlike standard colonoscopy or optical colonoscopy, virtual colonoscopy or CT colonography does not require sedation, injections, or the insertion of a camera into the colon, and the procedure takes less time than an optical colonoscopy. Virtual colonoscopy or CT colonography can also visualize certain segments of the colon that are hard to view during a standard optical colonography.

Indications

In general, your physician may recommend a virtual colonoscopy or CT colonography for:

• Screening for colorectal cancer
• Screening for abnormal growths called polyps before they turn cancerous
• Evaluation of the colon after unsuccessful or incomplete optical (standard) colonoscopy
• Assessment of intestinal strictures
• Individuals with contraindications to or who do not want a standard colonoscopy
• Better examination of neoplasms or growths identified by standard colonoscopy

Preparation

In general, preparation for CT virtual colonoscopy or CT colonography will involve the following:

• You will be given a clear liquid or low-fiber diet for at least 24 hours prior to the procedure.
• Laxatives (medication), or sometimes a special liquid drink (contrast medium), are given over 1 or 2 days to empty your bowels completely before the procedure.
• Inform your doctor of any medications or supplements you are taking
• Disclose any recent illnesses or other medical conditions you have, which may impact the procedure
• Inform your doctor of any allergies to medications, contrast dye, or latex (which can be found in surgical gloves)
• Sign an informed consent form

Procedure

Virtual colonoscopy or CT colonography is typically performed as an outpatient procedure in the radiology (CT scanning) department at the hospital. A specialist doctor (radiologist) or a radiographer performs this test using a CT scanner machine. The CT scanner is generally a large, donut-shaped machine with a short tunnel in the center. You will be placed on a table that slides in and out of this short tunnel. Rotating around you, the X-ray tube and electronic X-ray detectors are positioned opposite to each other in a ring known as a gantry. The computer workstation that processes the imaging information is in a separate control room. This is where your technologist operates the scanner and monitors your exam in direct visual contact. Your technologist will be able to hear and talk to you using a speaker and microphone.

In general, CT colonography will involve the following steps:

• Your radiographer will place you on the scanning table in a position that is best suited for conducting the exam.
• A small tube is then inserted into the rectum, and a carbon dioxide gas or air is used to distend (inflate) the colon and rectum to obtain clear visualization of the inside of your bowel. You may feel uncomfortable and bloated as a result of the gas.
• Your radiographer will then move the scanning table into the CT scanner machine. Several X-ray beams and electronic X-ray detectors rotate around you. Each rotation yields several images of thin slices of your colon. You may hear buzzing and whirring noises.
• A special computer program processes this large volume of data to generate a detailed, three-dimensional model of your colon, which your radiographer utilizes to see the colon in a way that simulates traveling through the colon. This is why the procedure is often referred to as a virtual colonoscopy. Two-dimensional images of the inside of the colon, as well as the rest of the abdomen and pelvis, are taken and reviewed at the same time.
• A radiologist, a physician specially trained to supervise and interpret radiology exams, will analyze the images and send an official report to the doctor who ordered the exam.

Post-procedure care

After the exam, you will be shifted to an observation room where you will stay for a short time to ensure that you feel well after the exam. You can return to your normal activities once comfortable. If you were administered contrast material, you may receive special instructions. You will likely be told to drink lots of fluids to help your kidneys flush the contrast material from your body after the scan.

Risks and Complications

Some of the possible risks of virtual colonoscopy/CT colonography include:

• Dehydration
• Nausea
• Stomach bloating
• Stomach pain
• Diarrhea
• Blurred vision
• A tear in the bowel
• Radiation exposure

Benefits

Some of the benefits of virtual colonoscopy/CT colonography over standard colonoscopy include:

• Provides clearer and more detailed images than a conventional colonoscopy
• Excellent alternative for individuals with a risk of complications from a colonoscopy
• A better diagnostic alternative for elderly patients who cannot tolerate a standard colonoscopy
• Much lower risk of colon perforation compared to colonoscopy
• Less expensive than colonoscopy
• Less exposure to radiation
• Requires no sedation or pain reliever, and is well tolerated by most patients
• Can detect abnormalities outside of the colon

Summary

Virtual colonoscopy or CT colonography is a test that utilizes special x-ray equipment to check the colon and rectum for cancer and other colorectal disorders. It is a simple outpatient procedure that typically takes around 30 minutes, and allows you to go home on the same day of the procedure, or return to work immediately following your exam.