Crohn's and Colitis. Dr. Hillary Steinhart

than having to fast on the day of the examination.

       Small-Bowel Enema, or Enteroclysis

      In some cases, a small-bowel follow-through X-ray doesn’t provide enough detail because of problems with the movement of barium through the small intestine or because the images are captured only every few minutes and important information can be missed. To solve this problem, the barium is administered directly into the small intestine by means of a tube placed through the nose into the esophagus, stomach, and duodenum. The radiologist can watch continuously as the barium flows through the entire small intestine. This examination also requires only fasting prior to the procedure.

       Barium Enema

      Barium enema provides images of the large intestine (colon). Liquid barium solution and air are pumped into the large intestine. A barium enema is rarely performed, however, having been replaced by colonoscopy and CT scan. Conversely, a normal calprotectin level makes the likelihood of IBD much lower, and the doctor and patient or family may then decide against further testing. This decision can be of value when it comes to children, for whom a test such as endoscopy is more difficult to do.

       X-Ray Risk

      All X-rays involve some degree of exposure to radiation, but, as long as the tests are not repeated frequently, the amount of radiation exposure is relatively small compared to the amount that one is exposed to every day from background sources.

       Imaging Studies

      Imaging studies provide “pictures” of the intestines and other internal organs without having to open up the abdomen by performing surgery. Imaging studies have been the mainstay of IBD diagnosis for many years. X-rays provide two-dimensional pictures of the intestine, while other types of imaging studies also provide information about surrounding structures within the abdomen, something which conventional X-ray studies cannot do. These include ultrasounds, computer-assisted tomography (CT, or CAT) scans, and magnetic resonance imaging (MRI). They provide multiple images of the abdomen in “slices” that can be positioned crosswise or lengthwise through the abdomen. In this way, it is possible to provide a three-dimensional representation of the intestines, other abdominal organs, and even blood vessels. Because of this capability, these imaging studies can provide improved diagnostic information compared with conventional X-ray studies.

       Ultrasound

      Ultrasound examinations are very safe and widely available. A probe that transmits a high-frequency sound wave is moved over the abdominal wall. That sound wave is reflected off structures within the abdomen and back to the probe, which has a sensor to detect the reflected sound waves, or echoes. These echoes are then converted into an image. Patients must fast before an abdominal ultrasound study. There are certain modifications of the ultrasound technique that can allow the radiologist to determine the rate of blood flow within the intestine. An increased blood flow may give an indication that the bowel is inflamed.

      One particular type of ultrasound, a transanal ultrasound, is used to evaluate patients for possible anal abscesses and fistulas. This involves putting a special ultrasound probe into the anus in order to obtain images of the surrounding tissues. Although this may provide excellent detail, the procedure may be very difficult or impossible for patients with painful anal conditions associated with Crohn’s disease.

       Detecting Complications

      Ultrasound may be helpful in detecting complications of IBD, such as abscesses, but it is not the most sensitive imaging study, particularly when the intestines are to be evaluated.

       Computer-Assisted Tomography (CAT scan, or CT scan)

      Computer-assisted tomography is a very safe and widely used imaging technique. This technology, along with MRI, has virtually replaced the small bowel follow-through and small-bowel enema procedures.

      During a CT scan, the patient lies on a table, which is surrounded by a large donut-shaped structure that produces and detects X-rays. These X-rays are converted into very detailed images when processed in the machine’s computer.

      Patients undergoing CT scans of the abdomen are often given a contrast solution to drink 1 to 2 hours before the scan to provide better diagnostic images or an intravenous injection of another contrast material to show blood supply to the intestine and other tissues.

      CT scans are generally not needed for routine follow-up of a patient’s clinical disease activity. If an abscess is detected by CT scan, the images can be used by the radiologist to insert a needle or plastic tube through the skin and into the abscess in order to allow it to drain properly.

      CT scans involve radiation exposure, which is always a concern, particularly in young people. However, newer “low-dose” CT scans expose patients to a fraction of the radiation that they would be exposed to with a standard CT scan, without losing much of the important diagnostic information.

       Sensitive Test

      CT scans are very sensitive at detecting IBD complications, such as abscesses and intestinal obstructions. They do involve some radiation exposure and so should not be repeated too frequently or unnecessarily.

       Magnetic Resonance Imaging (MRI)

      Magnetic resonance imaging is relatively new in IBD diagnosis. It uses a large magnet to create images based on the different water content and molecular makeup of different tissues. A patient undergoing an MRI scan lies on a table that slides into the machine. The patient lies very still during the procedure, which can last up to 20 or 30 minutes. Like a CT scan, the MRI provides cross-sectional images, but because the intestines are continuously contracting in the abdomen during the procedure, the images of the intestines may not be as clear as they are in CT scans, where the image is obtained in a fraction of a second. Some studies are done after patients are administered an injection of a contrast agent into the vein. Because it does not involve any exposure to radiation, MRI may become the investigation of choice once the technology has advanced to the point where it provides images that are comparable in quality to CT scans.

       Assessing the Anus

      MRI is particularly useful for assessing the anus and the surrounding tissue for complications, such as fistulas and abscesses, in Crohn’s disease.

      MRI is particularly useful for assessing the anus and the surrounding tissue for complications, such as fistulas and abscesses, in Crohn’s disease. MRI is also useful in determining whether areas of the intestine are inflamed or whether the changes seen are due to scarring. This is a particularly helpful distinction because tissue that is inflamed may respond to therapy with medication, whereas areas of scarring will likely not improve with medical therapy.

       Endoscopy

      In endoscopy, a long, narrow tube with a light and a camera on its tip is passed into the gastrointestinal tract. The endoscope can be steered in the desired direction to provide very detailed images of the inner lining of the gastrointestinal tract on a video monitor. When the procedure examines the esophagus, stomach, and duodenum, it is called an upper gastrointestinal endoscopy or, more commonly, a gastroscopy. When the instrument is inserted through the anus into the rectum and colon, it is called a colonoscopy. When doing a colonoscopy, the physician can often also examine the ileum (last part of the small intestine). This is one of the areas most commonly involved in Crohn’s disease.

       Gastroscopy

      Gastroscopy is a relatively straightforward procedure, but is done much less commonly in IBD than is colonoscopy, with the possible exception of individuals first diagnosed in childhood. In that case, gastroscopy is frequently carried out at the time of diagnosis. Gastroscopy is usually carried out following an overnight fast so that the stomach is empty. The back of the throat is sprayed with a local anesthetic so that the gag reflex is reduced, and, in some cases, a mild sedative is given intravenously to relax the patient.