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Which Radiology Tests are used in IBD?

Radiology tests can provide important information that endoscopy alone cannot provide. Many types of radiological tests used in IBD, including: 1) X-rays (with or without barium as a contrast, as in a small bowel follow through); 2) CT scan (“CAT scan enteropgrpahy”); 3) Magnetic resonance imaging (MRI enterography); 4) Leukocyte scintigraphy (“tagged white blood cell scan”); and 5) Abdominal ultrasound (echography). One of the risks of certain radiological studies is that it can result in exposure to relatively high doses of radiation. This is particularly problematic with young IBD patients who have repeated small bowel barium studies of CT scans. There is zero radiation with ultrasound or MRI examinations.

Plain abdominal X-rays

X-rays are the oldest way of imaging the inside of the body. Plain X-rays (without contrast) are a quick, inexpensive, and effective way of detecting signs of blockage in the small or large intestine. Females must remember to advise the technologist f there is any chance of being pregnant. It is important to avoid exposing your fetus to X-rays.

Patients with Crohn’s disease may have long-standing inflammation of the bowel that scars the wall and thus narrows the lumen (stricture) and prevents the easy passage of stool and air (Figure 14). This is called a bowel obstruction. People with very severe ulcerative or Crohn’s colitis can develop a widening of the large bowel (expanded by stagnant gas) called a megacolon (Figure 15). This serious complication is easily visible on a plain X-ray.

Abdominal X-rays with contrast

Contrast X-rays have long been used together with endoscopy to diagnose and monitor response to treatment of IBD. X-rays take images as a liquid contrast (usually barium) passes through the intestine, highlighting specific conditions. Barium contrast X-rays of the small intestine (small bowel follow through) are useful for looking at the lining of the small intestine that is beyond the reach of the endoscope. This is helpful to assess the extent of small bowel disease in Crohn’s disease (Image). Narrowing of the bowel (stricture) and an abnormal channel between the bowel and another organ (fistula) are two other complications of Crohn’s disease that can be detected with a contrast X-ray exam.

The preparation for a small bowel X-ray is not uniform. At a minimum, one must be fasting beginning at midnight before the test. The preparation for a barium enema of the large bowel is similar to that of a colonoscopy. It requires a liquid diet the day before, a bowel preparation to purge the colon of stool and debris, and no food or drink as of midnight before the test. It is important to follow the instructions your doctor gives you for your specific procedure.

After arriving for a barium contrast study, the technician will take a preliminary X-ray, called a scout film. For a small-bowel follow through, the patient drinks several cups of barium and then X-ray images are taken every 15-30 minutes as the barium travels down the small intestine, making its way to the large intestine. This can take as little as one hour or as long as 4 or more hours. A small bowel enteroclysis is similar, except that the barium is placed directly into the small intestine through a tube inserted via the nose or mouth. For a barium contrast enema, barium and air are introduced into the large intestine via a tube placed in the rectum. X-rays are taken to ensure that the entire large intestine is coated and well visualized. A barium enema takes about half an hour to complete.

Barium can cause constipation, so you should drink plenty of fluids after your test to maintain regularity. As the barium passes out of the body, it would be normal to notice that the stools are whitish-gray for a few days.

CT Scan

A CAT scan, or CT scan, takes multiple cuts, or X-rays from several different angles simultaneously to accurately reconstruct a realistic image of the internal organs. A contrast may be given by mouth, by rectum, or through the veins to provide the best images. During the test, the patient lies on a special table that advances through the scanner so that multiple images can be taken at different levels of the abdomen. Some patients undergoing a CT scan may have a feeling of claustrophobia (being “closed in”). They should advise the technician if they are prone to this feeling. The exam takes about 10 to 25 minutes to complete, depending on the information required.

Abdominal CT scans are used primarily to evaluate IBD patients who have considerable abdominal pain or fever. The test can confirm that inflammation is present in the small or large intestine. Moreover, it is used to rule out complications of IBD such as an abdominal abscess, areas of intestinal narrowing or strictures, bowel obstructions, fistulas, and bowel perforation. A CT scan is also useful in eliminating other diagnoses that can mimic IBD, such as an appendicitis, with or without perforation. Additionally, CT scan can guide the physician to drain an abscess. A small needle and a catheter can be passed through the skin into the abscess to drain the pus, avoiding surgery.

Although the contrast used for a CT scan is generally very safe, some patients can be allergic to the intravenous dye. Advise the technologist if you know that you have a contrast allergy. In addition, because the intravenous contrast is excreted by the kidneys, certain patients may be at risk. These include older, diabetic, or dehydrated individuals, as well as those known to have kidney disease. Patients taking metformin (Glucophage®) for diabetes must tell the doctor to avoid a rare but serious interaction with the contrast.

MRI

Magnetic resonance imaging (MRI) can provide very precise images of the internal organs, muscles, and soft tissues. It does not employ X-rays, and thus has the advantage of not exposing patients to any radiation. It detects the signal produced by the body’s tiny atoms in response to a strong magnetic field. It converts this signal into very realistic images of the body. During the test, the patient lies on a special table inside the MRI scanner while the magnet generates the images. As with CT scanners, some patients may experience feeling “closed in” or claustrophobia while inside the scanner. Let your physician know if you have a pacemaker or any metal implants, in order to avoid a serious complication when the magnet is turned on. The MRI scanner makes jackhammer like noises while capturing images.

MRI enteroclysis is a new technique that is a enhanced alternative to conventional enteroclysis. In addition to being radiation free, potential advantages of MRI scanning include the capability to detect disease outside the intestine. It also produces clear images that are free of interference from overlying bowel loops. CT scan enteroclysis is more readily available in most Canadian centres.

White Blood Cell Scan

Inflammation of the intestinal lining, with excessive number of white blood cells, is characteristic of both ulcerative colitis and Crohn’s disease. Leukocyte scintigraphy or “tagged white blood cell scan” is able to detect excessive accumulation of white blood cells in inflamed tissue. No preparation by the patient is required. It involves drawing a blood sample from the arm, and then isolating the patient’s own white blood cells. These cells are then labeled or tagged in the laboratory with a harmless amount of a radioactive substance. These white blood cells are then re-injected into the patient’s bloodstream. The labeled white blood cells travel through the bloodstream and migrate into the inflamed tissue. A special camera is used to detects where the white blood cells accumulate and therefore can assess where and how much inflammation is present.

Leukocyte scintigraphy can be used to detect the location of bowel inflammation (Figure 17), and to evaluate treatment response in IBD. It may not be able to distinguish the cause of the inflammation, such as between Crohn’s disease of the cecum versus an acute appendicitis. It is also not precise in defining anatomic details or looking at inflammation in the rectum. Its advantages are that it is relatively safe test and entails less radiation exposure than contrast X-ray or CT scan.

Ultrasound

Abdominal ultrasound, or echography, is used to investigate many organs in the abdomen, such as the liver, gallbladder, or ovaries. It is not as useful for hollow organs such as the bowel. Ultrasound is harmless and relies on the shadows cast by sound waves (too high for humans to hear). Although ultrasound studies usually do not require any preparation, patients should be fasting for a number of hours before the test.