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Computed Tomography and Magnetic Resonance Imaging

By Walter W. Chan, MD, MPH, Assistant Professor of Medicine; Director, Center for Gastrointestinal Motility, Division of Gastroenterology, Hepatology, and Endoscopy, Harvard Medical School; Brigham and Women's Hospital

Computed tomography (CT—see Computed Tomography (CT)) and magnetic resonance imaging (MRI—see Magnetic Resonance Imaging (MRI)) 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) or diverticula (diverticulitis), is usually evident. Sometimes, these tests are used to help guide x-ray or surgical procedures.

For CT of the digestive tract, doctors usually give people substances that can be seen on x-rays (contrast agents) to help distinguish one tissue or structure from its surroundings. Contrast agents may be given by mouth, by vein, and/or by enema.

CT enterography

This test allows doctors to clearly see the lining of the small intestine and look for tumors or bleeding. For this test, people drink a liquid contrast agent such as barium.

CT colonography

This test (also called virtual colonoscopy) generates two-dimensional and three-dimensional images of the colon that may show tumors or other problems. Some doctors use this test instead of colonoscopy to screen for colon cancer. 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.