context: There are many different types of imaging tests used to diagnose diseases of the digestive system. A CT scan, computed tomography, takes multiple X-rays of the body from different angles in a very short period of time. These images are collected by a computer to give a series of "slices" of the body, which can help doctors determine what is causing your symptoms. This test combines a CT scan with the injection of a contrast dye that highlights blood vessels and tissues in the abdomen. New technology has made it possible for a computer to take CT images of the colon and reconstruct a three-dimensional model of your colon -- called a virtual colonoscopy. The inside of this model can be inspected, obviously without causing any pain to you, while searching for abnormalities. However, if an abnormality is found, a scoping test, either sigmoidoscopy or colonoscopy, will be needed to get a tissue sample. MRI produces very clear pictures of the human body without the use of X-rays. MRI uses a large magnet, radio waves, and a computer to produce these images. The MRI examination poses no risk to the average person if appropriate safety guidelines are followed. Also called nuclear scanning, radionuclide scanning is a test in which the patient either swallows, inhales, or is injected with a small amount of radioactive material. A special camera is used to detect the radioactivity, producing images of organs and areas of the body that can't be seen well with standard X-rays. Many abnormal tissue growths, or tumors, are particularly visible using radionuclide scanning. In addition to showing the structure of an organ, radionuclide scanning allows the doctor to see how the organ is functioning. A diseased or poorly working organ will appear differently on the scan than will a healthy organ. The information from this test is valuable in diagnosing many diseases, including cancer. Because this test shows internal areas that are not visible on standard X-rays, radionuclide scanning can also help identify problems very early in the progression of a disease. Although radiation is used in this scanning technique, the test is very safe. The actual dose of radiation you receive is quite low and stays in your body only for a short time. Drinking plenty of fluids after your scan will help to eliminate any radioactive material from your system. Upper and Lower GI Tests Upper GI tests use X-rays to examine the esophagus, stomach, and first part of the small intestine (the duodenum). For these tests, you need to drink a chalky liquid called barium. As the barium passes through the digestive tract, it fills and coats the esophagus, stomach, and first part of the small intestine making them more visible with X-ray. Then a fluoroscope machine is held over the part of the body being examined and transmits continuous images to a video monitor. This upper GI test is used to diagnose: Hiatal hernias Ulcers Tumors Esophageal varices Obstruction or narrowing of the upper GI tract Lower GI tests or barium enemas are used to examine the large intestine and the rectum. For this test, barium or an iodine-containing liquid is introduced gradually into the colon through a tube inserted into the rectum. As the barium passes through the lower intestines, it fills the colon, allowing the radiologist to see growths or polyps and areas that are narrowed. The fluoroscope machine is held over the part of the body being examined and transmits continuous images to the video monitor. The lower GI test is used to detect: Colon polyps Tumors Diverticular disease Gastroenteritis Strictures or sites of narrowing and obstruction Ulcerative colitis or Crohn's disease Other causes of abdominal pain or blood, mucus, or pus in the stool Abdominal ultrasound The ultrasound machine sends out high-frequency sound waves that reflect off body structures, sending them to a computer that creates a picture of organs and structures in the abdomen. This is done with a handheld probe, called a transducer, which is moved over the abdomen. There is no exposure to radiation with this test. Abdominal X-ray A small amount of radiation is used to take a picture that is recorded on film or a computer.