CT Enterography

What is CT Enterography?

CT enterography is a special type of computed tomography (CT) imaging performed with intravenous contrast material after the ingestion of liquid that produces images of the small intestine.

Computed tomography, more commonly known as a CT or CAT scan, is a diagnostic medical test that, like traditional x-rays, produces multiple images or pictures of the inside of the body.

The cross-sectional images generated during a CT scan can be reformatted in multiple planes, and can even generate three-dimensional images. These images can be viewed on a computer monitor, printed on film or transferred to a CD or DVD.

CT images of internal organs, bones, soft tissue and blood vessels typically provide greater detail than traditional x-rays, particularly of soft tissues and blood vessels.

What are some common uses of the procedure?

Physicians use CT enterography to identify and locate:

• small bowel inflammation
• bleeding sources within the small bowel
• small bowel tumors
• abscesses and fistulas
• bowel obstruction.

CT enterography is also used to diagnose Crohn's disease, and determine its location, severity and unexpected complications, in order to guide effective treatment.

How should I prepare?

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. Women will be asked to remove bras containing metal underwire. You may be asked to remove any piercings, if possible.

You should inform the technologist if you have a pacemaker. Pacemakers do not hinder the use of CT as in MRI as long as the scanner will not be taking images repeatedly over the area of the pacemaker device in the upper chest. This is usually not an issue for cardiac CT exams.

You will be asked not to eat or drink anything for four hours prior to the procedure.

You should inform your physician of any medications you are taking and if you have any allergies. If you have a known allergy to contrast material, or "dye," your doctor may prescribe medications to reduce the risk of an allergic reaction, or order a different test.

Also inform your doctor of any recent illnesses or other medical conditions, and if you have a history of heart disease, asthma, diabetes, kidney disease or thyroid problems. Any of these conditions may increase the risk of an unusual adverse effect.

Women should always inform their physician and the CT technologist if there is any possibility that they may be pregnant. See the Safety page (www.RadiologyInfo.org/en/safety/) for more information about pregnancy and x-rays.

What does the equipment look like?

The CT scanner is typically a large, box-like machine with a hole, or short tunnel, in the center. You will lie on a narrow examination table that slides into and out of this tunnel. Rotating around you, the x-ray tube and electronic x-ray detectors are located opposite each other in a ring, called a gantry. The computer workstation that processes the imaging information is located in a separate control room, where the technologist operates the scanner and monitors your examination in direct visual contact and usually with the ability to hear and talk to you with the use of a speaker and microphone.

How does the procedure work?

In many ways CT scanning works very much like other x-ray examinations. Different body parts absorb the x-rays in varying degrees. It is this crucial difference in absorption that allows the body parts to be distinguished from one another on an x-ray film or CT electronic image.

In a conventional x-ray exam, a small amount of radiation is aimed at and passes through the part of the body being examined, recording an image on a special electronic image recording plate. Bones appear white on the x-ray; soft tissue, such as organs like the heart or liver, shows up in shades of gray, and air appears black.

With CT scanning, numerous x-ray beams and a set of electronic x-ray detectors rotate around you, measuring the amount of radiation being absorbed throughout your body. Sometimes, the examination table will move during the scan, so that the x-ray beam follows a spiral path. A special computer program processes this large volume of data to create two-dimensional cross-sectional images of your body, which are then displayed on a monitor. CT imaging is sometimes compared to looking into a loaf of bread by cutting the loaf into thin slices. When the image slices are reassembled by computer software, the result is a very detailed multidimensional view of the body's interior.

Refinements in detector technology allow new CT scanners to obtain multiple slices in a single rotation. These scanners, called multislice CT or multidetector CT, allow thinner slices to be obtained in a shorter period of time, resulting in more detail and additional view capabilities.

For some CT exams, a contrast material is used to enhance visibility in the area of the body being studied.

How is the procedure performed?

Prior to the procedure, you will be asked to drink several glasses of a liquid solution that contains a contrast material. The total amount of fluid you will need to drink is approximately 1 to 1.5 liters. You should inform your doctor if you think you will not be able to drink this amount of contrast. You will drink the contrast material over a period of approximately one hour in order to fill the long small intestine. The fluid expands the small bowel so that abnormalities can be seen better.

The technologist begins by positioning you on the CT examination table, usually lying flat on your back or less commonly, on your side or on your stomach. Straps and pillows may be used to help you maintain the correct position and to help you remain still during the exam. Depending on the part of the body being scanned, you may be asked to raise your arms over your head.

If contrast material is used, depending on the type of exam, it will be swallowed, injected through an intravenous line (IV) or administered by enema (this is rare).

Next, the table will move quickly through the scanner to determine the correct starting position for the scans. Then, the table will move slowly through the machine as the actual CT scanning is performed. Depending on the type of CT scan, the machine may make several passes.

What will I experience during and after the procedure?

You may be asked to hold your breath during the scanning. Any motion, whether breathing or body movements, can lead to artifacts on the images. This loss of image quality can resemble the blurring seen on a photograph taken of a moving object.

When the examination is completed, you will be asked to wait until the technologist verifies that the images are of high enough quality for accurate interpretation.

Though the scanning itself causes no pain, there may be some discomfort from having to remain still for several minutes and with placement of an IV. If you have a hard time staying still, are very nervous or anxious or have chronic pain, you may find a CT exam to be stressful. The technologist or nurse, under the direction of a physician, may offer you some medication to help you tolerate the CT scanning procedure.

For exams (excluding head and neck) your head will remain outside the hole in the center of the scanner. The scanner is approximately 24 inches wide, therefore, your entire body will be "inside" the scanner at one time such as with MRI.

If an intravenous contrast material is used, you will feel a pin prick when the needle is inserted into your vein. You will likely have a warm, flushed sensation during the injection of the contrast materials and a metallic taste in your mouth that lasts for at most a minute or two. You may experience a sensation like you have to urinate; however, this is actually a contrast effect and subsides quickly.

If the contrast material is swallowed, you may find the taste mildly unpleasant; however, most patients can easily tolerate it. You can expect to experience a sense of abdominal fullness and an increasing need to expel the liquid if your contrast material is given by enema. In this case, be patient, as the mild discomfort will not last long.

When you enter the CT scanner room, special light lines may be seen projected onto your body, and are used to ensure that you are properly positioned. With modern CT scanners, you will hear only slight buzzing, clicking and whirring sounds as the CT scanner revolves around you during the imaging process.

You will be alone in the exam room during the CT scan, unless there are special circumstances. For example, sometimes a parent wearing a lead shield may stay in the room with their child. However, the technologist will always be able to see, hear and speak with you through a built-in intercom system.

With pediatric patients, a parent may be allowed in the room but will be required to wear a lead apron to minimize radiation exposure.

After a CT exam, you can return to your normal activities. If you received contrast material, you may be given special instructions.

The oral contrast material you will ingest for your enterography exam is not absorbed by the body and will be expelled through the rectum. Therefore, loose stools will be present for a couple of hours after the examination. The oral contrast agent may cause nausea, diarrhea and abdominal cramps. You should tell your doctor if these mild side effects become severe or do not go away within a short time period.

See the Safety page (www.radiologyresource.org/en/safety/index.cfm?pg=sfty_contrast) for more information about contrast materials.

Who interprets the results and how do I get them?

A physician, usually a radiologist with expertise in supervising and interpreting radiology examinations, will analyze the images and send a signed report to your primary care physician or physician who referred you for the exam, who will discuss the results with you.

What are the benefits vs. risks?

Benefits

• CT scanning is painless, noninvasive and accurate.
• A major advantage of CT is its ability to image bone, soft tissue and blood vessels all at the same time.
• Unlike conventional x-rays, CT scanning provides very detailed images of many types of tissue as well as the lungs, bones, and blood vessels.
• CT examinations are fast and simple; in emergency cases, they can reveal internal injuries and bleeding quickly enough to help save lives.
• CT has been shown to be a cost-effective imaging tool for a wide range of clinical problems.
• Compared to other imaging procedures of the small intestine, CT enterography is able to visualize the entire thickness of the bowel wall and to evaluate surrounding soft tissues. The other examinations, some of which are invasive, are only able to image the inner lining of the small intestine.
• CT enterography has been shown to diagnose and/or rule out certain conditions/diseases that could help determine your future medical care.
• CT enterography may eliminate the need for video capsule endoscopy (VCE) and the potential complications of that procedure.
• CT enterography allows other organs in the abdomen to be seen.
• CT is less sensitive to patient movement than MRI.
• CT can be performed if you have an implanted medical device of any kind, unlike MRI.
• No radiation remains in a patient's body after a CT examination.
• X-rays used in CT scans should have no immediate side effects.

Risks

• There is always a slight chance of cancer from excessive exposure to radiation. However, the benefit of an accurate diagnosis far outweighs the risk.
• Women should always inform their physician and x-ray or CT technologist if there is any possibility that they are pregnant. See the Safety page (www.RadiologyInfo.org/en/safety/) for more information about pregnancy and x-rays.
• CT scanning is, in general, not recommended for pregnant women unless medically necessary because of potential risk to the baby in the womb.
• Manufacturers of intravenous contrast indicate mothers should not breastfeed their babies for 24-48 hours after contrast medium is given. However, both the American College of Radiology (ACR) and the European Society of Urogenital Radiology note that the available data suggest that it is safe to continue breastfeeding after receiving intravenous contrast. For further information please consult the ACR Manual on Contrast Media and its references. (www.acr.org/Quality-Safety/Resources/Contrast-Manual)
• The risk of serious allergic reaction to contrast materials that contain iodine is extremely rare, and radiology departments are well-equipped to deal with them.
• Advancements in CT technology now allow CT enterography to be performed with even lower radiation doses.

• Because children are more sensitive to radiation, they should have a CT exam only if it is essential for making a diagnosis and should not have repeated CT exams unless absolutely necessary. CT scans in children should always be done with low-dose technique.

What are the limitations of CT Enterography?

A person who is very large may not fit into the opening of a conventional CT scanner or may be over the weight limit—usually 450 pounds—for the moving table.

Certain bowel obstructions, small tumors and early inflammation may not be visualized with CT enterography. Another procedure, CT enteroclysis, provides greater filling and distension of the small intestine and may allow better detection of abnormalities. However, it requires placement of a tube into the small bowel through the nose.