CT (computed tomography) colonography

Massachusetts General Hospital Imaging provides CT (computed tomography) colonography exams, sometimes called "virtual colonoscopy" exams, using the latest technology and radiation-dose-reduction techniques, Every scan is read by a radiologist with specialty training.
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About This Test


Before your appointment for a CT, please print and complete the Patient Procedure Screening Form.

Massachusetts General Hospital Imaging provides CT colonography exams at Mass GeneralMass General Imaging - Waltham and Mass General Imaging - Chelsea. No matter which facility you come to, our staff places priority on making your journey through the imaging process comfortable, safe, and successful. All images are read by a radiologist with specialty expertise in the area of the body being studied.

CT colonography overview:

  • A CT scanner rotates to take X-ray images from different angles all around your body. A computer puts these images together to form detailed, two-dimensional pictures.
  • CT provides clearer, more detailed pictures than traditional X-rays.
  • CT colonography, sometimes called "virtual colonoscopy," produces a 3D view of the colon in order to detect polyps and colorectal cancer. It is an alternative to traditional optical colonoscopy.
  • CT colonography is faster and less invasive than colonoscopy, requires less fasting beforehand, and does not require sedation.
  • The American Cancer Society has endorsed CT colonography as a screening test for colorectal cancer.
  • Exams typically take 20 minutes in total; the actual scanning takes just minutes.
  • Many exams involve contrast—a drink or injection that makes the images more informative.
  • If you are over 60 or have kidney disease, diabetes, lupus, or multiple myeloma, you’ll need a blood test beforehand to make sure the contrast will be safe for you.
  • The technologist performing your exam will be nearby and able to talk to you throughout the scan.
  • CT exams require that you lie still in a confined space. But because the scanning time is so short, most people tolerate the experience well.
  • Every exam is interpreted by a radiologist with specialty expertise in the specific area of the body under study. A specialist is capable of seeing and understanding subtle things due to advanced training and singular focus.
  • We use the latest technology, and the capabilities of our state-of-the-art scanners play a key role in tailoring each exam to your specific needs and reducing radiation exposure.
  • Patients and referring physicians should be aware that most insurance providers do not yet cover CT colonography for routine screening. Patients should expect to pay out-of-pocket unless a provider confirms coverage prior to the exam.

CT colonography in depth

What is CT colonography?

CT Colonography

A CT (computed tomography) scan is a noninvasive medical test that uses special X-ray equipment to produce multiple images or pictures of the inside of the body and a computer to join them together in cross-sectional views of the area being studied. CT scans provide greater clarity than conventional X-ray exams.

A CT colonography exam is a special type of CT scan that examines the colon and then uses the cross-sectional views to create a 3D view. CT colonography is designed to be easily tolerated by patients. The entire exam can be completed within twenty minutes, and most patients report that it causes little or no discomfort.

Colon cancer usually develops within benign growths called polyps, which arise from the colon wall. If polyps are detected early, removing them stops the development of cancer. A polyp can form at any time throughout life, but most commonly occurs in people over the age of 50. Most polyps grow slowly, and the risk that cancer will be found in a polyp is substantial only for polyps greater than 6mm in size. If your CTC shows no polyps, we will recommend that you wait five years before having another CTC.

Recently the American Cancer Society endorsed CT colonography as a screening test for colorectal cancer. It is now considered to be a valuable alternative to endoscopy because it is less invasive and does not require sedation or time off from work.


CT examinations, including CT colonography, improve health care and are an essential part of diagnosis and treatment planning. However, there are some risks associated with the level of radiation exposure during a CT and therefore the medical benefit of conducting the exam should always outweigh any risks involved.

No direct data have shown that CT examinations are associated with an increased risk of cancer; extrapolations from studies of radiation exposure suggest there is a very small incremental risk.

At Mass General Imaging, we pay special attention to minimizing radiation exposure—without giving up image quality. Radiation reduction has long been a priority for our entire staff, including radiologists, the technologists who administer most exams, researchers, and equipment engineers. We use many strategies to reduce radiation exposure, from employing the latest technology to customizing exams for each patient.


What to Expect

What should I expect BEFORE my CT scan?

  • Medications: Questions surrounding your current medication usage will be addressed at the time of scheduling.
  • Food and Drink: The bowel preparation that you take the night before your appointment is essential for a good exam. The colon needs to be prepared so that the radiologist can clearly see if any polyps are present. The special liquid that you drink passes through you and is not absorbed by your body. Because the liquid is not absorbed, it causes most people to have diarrhea on that evening only. On the morning of the exam, you should strictly limit your diet to clear liquids, such as tea or apple juice.
  • What to wear: You should wear comfortable, loose-fitting clothing to your exam. You may be given a gown to wear during the procedure. Metal objects including jewelry, eyeglasses, dentures and hairpins may affect the CT images and should be left at home or removed prior to your exam. You may also be asked to remove hearing aids and removable dental work.
  • When to arrive: If you are having a CT scan of your abdomen or pelvis, you need to arrive one hour before your scheduled appointment. This is to allow time for you to drink barium sulfate before your exam and to ensure that the barium fluid completely coats your gastrointestinal tract. The barium helps to highlight body areas for the CT scan. If you are having a scan other than the abdomen you should arrive at your appointed time.

What will I experience DURING my CT colonography scan?

  • Scanning: To begin, you will lie comfortably on the CT scanner table. A very small, flexible tube will be inserted into your rectum and some air gently blown into the colon to hold it open. After the tube is inserted, your privacy will be maintained and you will be in control of the amount of air. You may experience a temporary sense of fullness and bloating, but nearly all patients report that the air insufflation is not painful.
  • Length of scan: A CT colonography typically takes about 20 minutes. The actual scanning takes about two minutes to perform the actual CT scan. The first series of pictures will be taken with you lying on your back, followed by another set lying on your stomach. After the pictures are taken, the tube is removed and the exam is complete.

What should I expect AFTER my CT colonography scan?

  • Instructions: Because no sedation is required for the test, you can drive or return to work after the exam is completed. Immediately following the exam, you may resume your regular diet.
  • Exam results: All CT scans are read by a Mass General radiologist specialty trained in CT colonography.

    Rapid results are essential not only for your peace-of-mind, but also for your physician to begin planning your treatment immediately, if necessary. If we detect a polyp on your CTC, we will inform your doctor, and he or she will likely recommend a conventional colonoscopy (endoscopy) to have the polyp removed.


Conditions & Diseases

  • Colorectal Cancer

    Colorectal cancer is malignant cells found in the colon or rectum.


  • New test offers hope for easier colon screening - 5/15/2012, Clinical

    A new method of performing virtual colonoscopy using a CT scan - which does not involve the dreaded laxative preparation to clear the colon the night before - may be about as effective as a standard colonoscopy at identifying the large polyps most likely to become cancerous, according to research conducted at Massachusetts General Hospital, Brigham and Women’s Hospital, and elsewhere.

  • New laxative-free colonoscopy shows promise - 5/15/2012, Clinical

    If you're turning 50 or you're already there, colorectal screening is in your future. Although you would only have to be screened every 10 years (if no polyps are found), the prospect of getting prepped for procedure is a big turn-off for many. You've probably heard some of the horror stories about the pre-screening laxatives, the taste, the amount, the ensuing "cleansing."


  • The Webster Center for Advanced Research and Education in Radiation

    Webster Center takes on radiation-dose reduction

    Dr. James H. Thrall, Department of Radiology chairman emeritus, discusses The Webster Center for Advanced Research and Education in Radiation, a unique research effort dedicated to reducing radiation dose for every exam Mass General Imaging performs.

  • Radiation reduction: Our ongoing objective

    Radiation reduction: Our ongoing commitment

    As CT (computed tomography) technology has transformed the practice of medicine, Mass General Imaging has dedicated itself to making sure each exam exposes the patient to the lowest achievable amount of radiation. Department of Radiology Chairman Emeritus James H. Thrall, MD, discusses our decade-long commitment—and our success—regarding this issue.

  • Decision tools support radiation-reduction efforts

    Decision tools support radiation-reduction efforts

    One effective way to reduce radiation exposure is to avoid unnecessary exams. That's why Mass General Imaging has been a leader in developing software tools that guide referring physicians by not only making sure the selected exam matches the patient's needs but also suggesting radiation-free alternatives when appropriate.

  • Imaging specialists, focused on you

    Imaging specialists, focused on you

    Each radiologist at Mass General Imaging is a specialist in a particular area of the body. Department of Radiology Chairman Emeritus James H. Thrall, MD, explains how patients benefit from the additional specialty training our physicians have completed.

Request an Appointment

Call to request an appointment 617-724-9729

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