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CT Colonography


CT colonography is a minimally-invasive exam used to produce images that screen for cancer or polyps in the large intestine. Unlike traditional colonoscopy, the imaging is done from the outside by the CT scanner, not by a scope that is inserted into the rectum.

Colon cancer is one of the most common forms of cancer in adults. Early detection of colon cancer may help improve outcomes and increase your chances of survival. Be aware that, unlike colonoscopy, polyps or other abnormalities cannot be removed during a colonography. If polyps are found, you will have to schedule a colonoscopy to have them removed.

Please refer to the About CT section for more details about CT scanning and the associated risks and benefits.

Since early detection improves outcomes, professional organizations, such as the American Cancer Society, recommend colon cancer screening in adults starting at age 45. CT colonography is one of the tests suggested to be used for screening once every five years. The goal of screening is to detect pre-cancer or cancer at the earliest stage possible before symptoms appear. Individuals who are a higher than normal risk for colon cancer may start screenings at a younger age.

CT colonography may be recommended for you if you are reluctant to have a standard colonoscopy, if colonoscopy poses a risk for bleeding or other issues, if sedation is risky, or if you have bowel tumors or other obstructions.


  • CT colonography is minimally invasive and can detect polyps, cancers and pre-cancerous lesions with an accuracy comparable to conventional colonoscopy.
  • The risk of perforation of the colon is very low with conventional colonoscopy, and with CT colonography the risk is even lower.
  • Unlike conventional colonoscopy, CT colonography does not require sedation.
  • CT colonography is an excellent alternative for patients at higher risk of complications from colonoscopy, for example, due to age, chronic illness, medications (e.g. blood thinners) or severe lung disease.
  • If colonoscopy fails to visualize the entire colon, CT colonography can be done to improve visualization.
  • CT colonography may also provide images of abnormalities in the surrounding structures near the colon, such as the kidney, liver, pancreas and abdominal aorta.
  • The test is well tolerated and requires no sedation. You can return to your normal daily activities after having a CT colonography.


  • Excessive radiation can increase the risk for cancer. However, the amount of radiation received from CT colonography alone is unlikely to cause cancer or increase cancer risk significantly.
  • Pregnant women should be aware of the risk of radiation to the developing child. In some cases, doctors may recommend a different test instead of CT colonography.
  • Rarely, there may be a tear in the rectum or colon due to inflation with air.
  • CT colonography is available at multiple ARA imaging centers. The procedure takes about 15 minutes.
  • You will be asked to change into an exam gown.
  • Since metal can distort the CT images, all metal objects and jewelry should be removed prior to the procedure. This may include hearing aids, removable dental prostheses, eyeglasses, piercings, hairpins, etc.
  • Occasionally, it will be recommended that a contrast agent be injected to make the images clearer. After administering a small numbing injection, your paramedic or technologist will place an IV line into your arm or hand to administer the contrast. IV placement may be uncomfortable and may cause bruising later. Contrast may be delivered at a controlled rate by using a special injection pump and a saline solution drip may be used to help keep the IV line clear.
  • The CT scanner is a large box shaped machine with a large hole in the middle.
  • You’ll be placed on your back on a moveable exam table which may have straps or bolsters to help keep your head and body from moving. You will need to remain as still as possible so the images will be clear.
  • A small, flexible tube will be inserted into your rectum. Air, or carbon dioxide, will be gently pumped into your colon, and a small balloon may be inflated on the tube to keep it in place. The pumped air inflates your colon to smooth out the normal folds and wrinkles. This allows the radiologist to see any polyps or other abnormalities.
  • The technologist will leave the CT scan room where you are and conduct the exam from a computer in a nearby room. You will be able to talk with the technologist at all times.
  • The table will move your body into the CT scanner. You may be asked to hold your breath for about 15 seconds since breathing may distort the images. You may also be asked to lie face down while being scanned.
  • You may hear slight buzzing, clicking or rotating sounds during the scanning process.
  • When the scan is finished, you may be asked to wait a few minutes while the technologist checks the quality of the images. If needed, more images may be taken.
  • Be aware that, unlike colonoscopy, polyps or other abnormalities cannot be removed during a colonography. If polyps are found, you will have to schedule a colonoscopy to have them removed.
  • Like traditional colonoscopy, you will be required to do a bowel cleansing regimen before having a CT colonography. The day prior to the exam, your diet will be restricted to clear liquids. You will also be asked to take a laxative in a pill, liquid, or suppository.
  • Wear comfortable, loose fitting clothing. You may want to leave all jewelry, piercings and any other metal objects at home.
  • Be sure to tell your health care provider, ARA scheduler, and ARA technologist about any illness or allergies you may have. Also, provide a list of your current medications.
  • If you have a history of allergy to iodine-based contrast, you may need to take a steroid medication up to 12 hours before CT colonography. Inform you doctor if you have any contrast allergies.
  • In most cases, you should take all your medications as usual. Ask your doctor if you should make any adjustments to your medication during the bowel preparation period.
  • Inform your radiologist if you are pregnant. Although the risk of CT colonography is very low for the unborn baby, your doctor may choose an alternate exam. Depending on the circumstances, both the physician and patient may decide it is necessary to go ahead with the test.
  • CT colonography is fast and painless. If you feel like you might be anxious during the exam, tell your scheduler. ARA technologists and our clinical staff are experts at helping people through CT exams with minimum anxiety.
  • You can return to your normal activities after the exam.

To schedule a CT colonography, please use our online scheduling tool in the Patient Portal or you may call our scheduling team at (512) 453-6100 or toll free at (800) 998-8214. A referral from your healthcare provider is required to make an appointment.

A radiologist, a physician specifically trained to interpret radiological examinations, will analyze the images and send a signed report to the provider who referred you to ARA. The physician will then share the results with you.


Getting Your CT Exam at ARA

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