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© Dirk Biddle
Computed Axial Tomography (CT or CAT) scans are a less invasive method than an angiogram, however, as in an angiogram, injected radiopaque dyes (contrast mediums) are often used. CAT scans can image nodules and other pathology of the blood vessels caused by the inflammatory process.
In preparation for a CAT scan, patients are often asked to avoid food, especially when contrast material is to be used. Contrast material may be injected intravenously, or administered by mouth or by an enema in order to increase the distinction between various organs or areas of the body. Therefore, fluids and food may be restricted for several hours prior to the examination. All metallic materials and certain clothing around the body are removed because they can interfere with the clarity of the images.
A CAT scan is performed in a hospital or an outpatient centre. You will put on a gown and asked to lie down on a table that moves into the middle of a large, donut-shaped x-ray machine. It is important that you lie very still or the picture will be blurry. Right outside of the CAT scan room is a smaller room with a window in it. The radiologist sits in this room and controls the scanning equipment. A microphone allows the radiologist to talk to you throughout the procedure. A CAT scan technologist will tell the patient when to breathe or hold his/her breath during scans of the chest and abdomen.
The scanner is able to move around your body to take the pictures at different angles, which are then seen on a computer monitor. This recorded image is called a tomogram. "Computerized Axial Tomography" refers to the recorded tomogram "sections" at different levels of the body. Many x-ray pictures are taken, and each one provides a view of a different layer or “slice” of your body. CAT scans thus provide rapid, detailed cross-sectional imaging of patient anatomy which can then be reconstructed into three-dimensional models, as needed. A CAT scan will take approximately 30 to 90 minutes to complete, however, newer CAT scans called "spiral" or "helical" CAT scans can provide more rapid and accurate visualisation of internal organs. For example, many trauma centres are using these scans to more rapidly diagnose internal injuries after serious body trauma.
Types of CAT scan utilised can include: i) Cranial - used to detect tumours and evaluate cysts, cerebrovascular accidents, intracranial haemorrhage, skull and facial fractures, ii) Chest – used to detect acute and chronic changes in the lung parenchyma, airspace disease (eg; pneumonia), emphysema, fibrosis, pulmonary embolism, iii) Cardiac – imaging of coronary arteries, heart abnormalities, iv) Abdominal and pelvic – to investigate acute abdominal pain, kidney stones, appendicitis, pancreatitis, diverticulitis, abdominal aortic aneurism, bowel obstruction, tumours, pelvic fractures and sometimes osteoporosis, and v) extremities – complex fractures.
If your test requires a contrast agent, the dye will usually be injected through an intravenous tube in your vein. Some contrast agents are however given in liquid form. Intravenous contrast enhanced scans allow for evaluation of vascular structures and further evaluation of masses and tumours.
There are usually no side effects to this procedure. Allergic reactions to the contrast dye usually occur immediately, but are unusual. Signs of an allergic reaction include swelling and difficulty breathing. Patients with a history of allergy to iodine or contrast materials should notify their physicians and radiology staff. If any problems are experienced during the CAT scan, the technologist should be informed immediately.
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