The Kentuckiana Cancer Institute offers diagnostic radiology services. Computed Tomography scanning—sometimes called CAT scanning—is a noninvasive, medical test that helps physicians diagnose and treat medical conditions.Computed tomography (CT) combines the latest computer technology with the use of general X-rays. Using a thin beam of radiation, the CT scanner creates a cross-sectional image of the area being imaged and is repeated throughout the specified body region. The computer then reconstructs the “slice” to create the actual image being viewed. CT scans of internal organs, bone, soft tissue and blood vessels provide greater clarity than conventional x-ray exams.
What are some common uses of the procedure?
CT imaging is:
- one of the best tools for studying the chest and abdomen because it provides detailed, cross-sectional views of all types of tissue.
- often the preferred method for diagnosing many different cancers, including lung, liver and pancreatic cancer, since the image allows a physician to confirm the presence of a tumor and measure its size, precise location and the extent of the tumor's involvement with other nearby tissue.
- invaluable in diagnosing and treating spinal problems and injuries to the hands, feet and other skeletal structures because it can clearly show even very small bones as well as surrounding tissues such as muscle and blood vessels.
- an examination that plays a significant role in the detection, diagnosis and treatment of vascular diseases that can lead to stroke, kidney failure or even death.
Physicians often use the CT examination to:
- plan and properly administer radiation treatments for tumors
- guide biopsies and other minimally invasive procedures
- plan surgery
- measure bone mineral density for the detection of osteoporosis
- quickly identify injuries to the liver, spleen, kidneys or other internal organs in cases of trauma
How should I prepare for the CAT scan?
You should wear comfortable, loose-fitting clothing to your exam. You may be given a gown to wear during the procedure.
Metal objects including jewelry, eyeglasses, dentures and hairpins may affect the CT images and should be left at home or removed prior to your exam. You may also be asked to remove hearing aids and removable dental work.
You may be asked not to eat or drink anything for several hours beforehand, especially if a contrast material will be used in your exam. You should inform your physician of any medications you are taking and if you have any allergies, especially to contrast materials.
95 percent of the CT scans performed will require you to have two types of contrast media (X-ray dye).
- Gastroview contrast is taken orally prior to the exam to allow better definition of the bowel structure.
- Isovue 370, an IV contrast is administered during the exam. This may cause a slight warming sensation throughout the body and may leave a metallic taste in your mouth just for the length of the injection.
Also inform your doctor of any recent illnesses or other medical conditions, and if you have a history of heart disease, asthma, diabetes, kidney disease or thyroid problems. Any of these conditions may increase the risk of an unusual adverse effect.
What does the equipment look like?
The CT scanner is typically a large machine with a hole, or tunnel, in the center. You will lie on a table which slides into and out of this tunnel. The x-ray tube and electronic x-ray detectors rotate around you. They are opposite each other in a ring, called a gantry. The computer workstation that processes the imaging information is located in a separate room.
How does the procedure work?
In many ways CT scanning works very much like other x-ray examinations. X-rays are a form of radiation—like light or radio waves—that can be directed at the body. Different body parts absorb the x-rays in varying degrees.
In a conventional x-ray exam, a small burst of radiation is aimed at and passes through the body, recording an image on photographic film or a special image recording plate. Bones appear white on the x-ray; soft tissue shows up in shades of gray and air appears black.
With CT scanning, numerous x-ray beams and a set of electronic x-ray detectors rotate around you, measuring the amount of radiation being absorbed throughout your body. At the same time, the examination table is moving through the scanner, so that the x-ray beam follows a spiral path. A special computer program processes this series of pictures, or slices of your body, to create two-dimensional cross-sectional images, which are then displayed on a monitor.
CT imaging is sometimes compared to looking into a loaf of bread by cutting the loaf into thin slices. When the image slices are reassembled by computer software, the result is a very detailed multidimensional view of the body's interior.
Refinements in detector technology allow new CT scanners to obtain multiple slices in a single rotation. These scanners, called "multislice CT" or "multidetector CT," allow thinner slices to be obtained in a shorter period of time, resulting in more detail and additional view capability.
Modern CT scanners are so fast that they can scan through large sections of the body in just a few seconds. Such speed is beneficial for all patients but especially children, the elderly and critically ill.
How is the CAT scan performed?
The technologist begins by positioning you on the CT examination table, usually lying flat on your back or possibly on your side or on your stomach. Straps and pillows may be used to help you maintain the correct position and to hold still during the exam.
Next, the table will move quickly through the scanner to determine the correct starting position for the scans. Then, the table will move slowly through the machine as the actual CT scanning is performed.
You may be asked to hold your breath during the scanning.
When the examination is completed, you will be asked to wait until the technologist determines that the images are of high enough quality for the radiologist to read.
CT scanning of the body usually lasts between five and 30 minutes.
What will I experience during and after the procedure?
Most CT exams are painless, fast and easy. With spiral CT, the amount of time that the patient needs to lie still is reduced.
If an intravenous contrast material is used, you will feel a slight pin prick when the needle is inserted into your vein. You may have a warm, flushed sensation during the injection of the contrast materials and a metallic taste in your mouth that lasts for a few minutes. Occasionally, a patient will develop itching and hives, which can be relieved with medication. If you become light-headed or experience difficulty breathing, you should notify the technologist or nurse, as it may indicate a more severe allergic reaction.
If the contrast material is swallowed, you may find the taste mildly unpleasant; however, most patients can easily tolerate it. You can expect to experience a sense of abdominal fullness and an increasing need to expel the liquid if your contrast material is given by enema. In this case, be patient, as the mild discomfort will not last long.
When you enter the CT scanner, special lights may be used to ensure that you are properly positioned. With modern CT scanners, you will hear only slight buzzing, clicking and whirring sounds as the CT scanner revolves around you during the imaging process.
You will be alone in the exam room during the CT scan, however, the technologist will be able to see, hear and speak with you at all times.
After a CT exam, you can return to your normal activities. If you received a contrast material, you may be given special instructions.