CT Scan of the Abdomen
CT imaging is particularly useful because it can show several types of tissue with great clarity, including organs such as the liver, spleen, pancreas and kidneys. Using specialized equipment and expertise to create and interpret CT scans of the lower gastrointestinal (GI) tract, the colon and rectum, an experienced radiologist can accurately diagnose many causes of abdominal pain, such as an abscess in the abdomen, inflamed colon or colon cancer, diverticulitis and appendicitis. Often, no additional diagnostic work-up is necessary and treatment planning can begin immediately.
What are some common uses of the procedure?
Because it is a non-invasive procedure that provides detailed, cross-sectional views of all types of tissue, CT is becoming the preferred method for diagnosing many diseases of the bowel and colon, including diverticulitis and appendicitis, and for visualizing the liver, spleen, pancreas and kidneys. In cases of acute abdominal distress, CT can quickly identify the source of pain. Especially when pain is caused by infection and inflammation, the speed, ease and accuracy of a CT examination can reduce the risk of serious complications caused by a burst appendix or ruptured diverticulum and the subsequent spread of infection.
CT is often the preferred method for diagnosing many different cancers, since the image allows a physician to confirm the presence of a tumor and to measure its size, precise location, and the extent of the tumor's involvement with other nearby tissue. CT examinations can be used to plan and properly administer radiation treatments for tumors, and to guide biopsies and other minimally invasive procedures. CT can also play a significant role in the detection, diagnosis and treatment of vascular disorders that can lead to stroke, gangrene or kidney failure.
How should I prepare for the procedure?
You should wear comfortable, loose-fitting clothing for your CT exam. Metal objects can affect the image, so avoid clothing with zippers and snaps. You may be asked to remove jewelry, eyeglasses, hearing aids and any removable dental work that could obscure the images. You also may be asked to refrain from eating or drinking anything for an hour or longer before the exam. Women should always inform their doctor or x-ray technologist if there is any possibility that they are pregnant.
What does the equipment look like?
The CT scanner is a large, square machine with a hole in the center, something like a doughnut. The patient lies still on a table that can move up or down, and slide into and out from the center of the hole. Within the machine, an x-ray tube on a rotating gantry moves around the patient's body to produce the images, making clicking and whirring noises as the arm moves. Though the technologist will be able to see and speak to you, you will be alone in the room during the exam.
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How does the procedure work?
In many ways, CT scanning works very much like other x-ray examinations. Very small, controlled amounts of x-ray radiation are passed through the body, while different tissues absorb the radiation at different rates. With plain radiology, when special film is exposed to the absorbed x-rays, an image of the inside of the body is captured. With CT, the film is replaced by an array of detectors, which measure the x-ray profile.
Inside the CT scanner is a rotating gantry that has an x-ray tube mounted on one side and an arc-shaped detector mounted on the opposite side. During each full rotation, as the fan-shaped x-ray beam is emitted through the patient's body, an image of a thin section is acquired. The detector records about 1,000 images—or profiles—of the expanded x-ray beam with each rotation. The profiles are then reconstructed by a dedicated computer into two-dimensional images of the sections that were scanned. Multiple computers are typically used to control the entire CT system.
You might think of it like looking into a loaf of bread by cutting it into thin slices. When the image slices are reassembled by computer, the result is a very detailed, multidimensional view of the body's interior.
With spiral—or helical—CT, refinements in detector technology support faster, higher-quality image acquisition with less radiation exposure. The current spiral CT scans are called multidetector CT and are most commonly four- or 16-slice systems. Using 8-slice scanner systems the radiologist can acquire 16 image slices per second. A spiral scan can usually be obtained during a single breath hold. This allows scanning of the chest or abdomen in 10 seconds or less. Such speed is beneficial in all patients, but especially in populations in which the length of scanning was often problematic, such as elderly, pediatric or critically-ill patients. The multidetector CT also allows applications like CT angiography to be more successful.
With conventional CT, small lesions may frequently go undetected when a patient breathes differently on consecutive scans, as a lesion may be missed by unequal spacing between scans. The speed of spiral scanning and single breath hold increases the rate of lesion detection.
How is the procedure performed?
The technologist begins by positioning the patient on the CT table. The patient's body may be supported by pillows to help him or her hold still and in the proper position during the scan. As the study proceeds, the table will move slowly into the CT scanner. Depending on the area of the body being examined, the increments of movement may be so small that they are almost undetectable, or large enough that the patient feels the sensation of motion.
A CT examination of the gastrointestinal tract requires the use of a contrast material to enhance the visibility of certain tissues. The contrast material may be swallowed or administered by enema. Before administering the contrast material, the technologist will ask whether the patient has any allergies, especially to medications or iodine, and whether the patient has a history of diabetes, asthma, a heart condition, or kidney problems. These conditions may indicate a higher risk of reaction to the contrast material.
A CT examination usually takes from five minutes to half an hour.
What will I experience during the procedure?
CT scanning causes no pain, and with spiral CT, the need to lie still for any length of time is reduced. For examinations of the abdomen and lower gastrointestinal tract, you may be asked to swallow contrast material, a liquid that allows the radiologist to better see the stomach, small bowel and colon. Some patients find the taste of the contrast material mildly unpleasant, but most can easily tolerate it.
You will be alone in the room during the scan; however, the technologist can see, hear and speak with you at all times. In pediatric patients, a parent may be allowed in the room with the patient, but will be required to wear a lead apron to prevent radiation exposure.
Who interprets the results and how do I get them?
A radiologist, a physician experienced in CT and other radiologic examinations, will analyze the images and send a signed report with his or her interpretation to the patient's physician. The physician's office will inform the patient on how to obtain their results.