Computed tomography (CT—see also Computed Tomography (CT) Computed Tomography (CT) In computed tomography (CT), which used to be called computed axial tomography (CAT), an x-ray source and x-ray detector rotate around a person. In modern scanners, the x-ray detector usually... read more ) and magnetic resonance imaging (MRI—see also Magnetic Resonance Imaging (MRI) Magnetic Resonance Imaging (MRI) In magnetic resonance imaging (MRI), a strong magnetic field and very high frequency radio waves are used to produce highly detailed images. MRI does not use x-rays and is usually very safe... read more ) scans are good tools for assessing the size and location of abdominal organs. Additionally, cancerous (malignant) or noncancerous (benign) tumors are often detected by these tests. Changes in blood vessels can be detected as well. Inflammation, such as that of the appendix (appendicitis Appendicitis Appendicitis is inflammation and infection of the appendix. Often a blockage inside the appendix causes the appendix to become inflamed and infected. Abdominal pain, nausea, and fever are common... read more ) or diverticula (diverticulitis Diverticulitis Diverticulitis is inflammation of one or more balloon-like sacs (diverticula). Infection may or may not develop. Diverticulitis usually affects the large intestine (colon). Left lower abdominal... read more ), usually can also be detected. Sometimes, these tests are used to help guide x-ray or surgical procedures.
For CT and MRI of the digestive tract, doctors may give people substances that can be seen on the imaging test (contrast agents) to help distinguish one tissue or structure from its surroundings. Contrast agents may be given by mouth, by vein, by enema, or in combination.
Regular CT does not show the lining of the intestines well. A variation of the test, called CT enterography, allows doctors to clearly see the lining of the small intestine and look for tumors or narrowing of the intestines resulting from inflammation (strictures). For this test, people drink a large volume (about 1.6 quarts [1.5 liters]) of a liquid contrast agent such as barium. The contrast agent distends the small intestine so that doctors can see it better.
Magnetic resonance (MR) enterography is similar to CT enterography in that people drink a contrast agent before pictures are taken of their small intestine. It helps doctors see inflammation, bleeding, and other problems. This test is typically reserved for younger people, especially those with inflammatory bowel disease, so they are not exposed to radiation.
This test generates two-dimensional and three-dimensional images of the colon that may show tumors or other problems.
For this test, people drink a contrast agent, and their colon is inflated with gas from a tube inserted in the rectum. Before the test, people are given laxatives or enemas similar to those required for a regular colonoscopy to thoroughly remove stool. Although CT colonography is able to detect abnormal growths (intestinal polyps Polyps of the Colon and Rectum A polyp is a projecting growth of tissue from the wall of a hollow space, such as the intestines. Some polyps are caused by hereditary conditions. Bleeding from the rectum is the most common... read more ) or even colon cancer Colorectal Cancer Family history and some dietary factors (low fiber, high fat) increase a person’s risk of colorectal cancer. Typical symptoms include bleeding during a bowel movement, fatigue, and weakness... read more , people still need to have a colonoscopy to remove any polyps or abnormalities detected during the test.