In conventional X-rays, a beam of energy is aimed at the body part being studied. A plate behind the body part captures the variations of the energy beam after it passes through skin, bone, muscle and other tissue.
With computed tomography scan (also called a CT or CAT scan), the X-ray beam moves in a circle around the body. This allows for many different views of the same organ or structure, and provides much greater detail. The images are sent to a computer which interprets and displays the data in two-dimensional form on a monitor. CT scans may be done with or without contrast.
Learn how to prepare for a CT scan and what to expect before, during and after the procedure.
Before the Procedure
If your doctor decides to use contrast dye, you will need to fast (nothing by mouth) for four hours prior to the procedure. Women should always inform their radiologist if there is any possibility they may be pregnant.
Wear comfortable, loose-fitting clothing to your exam. Metal objects, including jewelry, eyeglasses and dentures, may affect the CT images and should be left at home. You will be given a gown to wear and asked to remove jewelry, hearing aids and removable dental work. Women will be asked to remove bras containing metal underwire.
During the Procedure
The technologist begins by positioning you on the exam table, usually lying flat on your back. Straps and pillows may be used to help you maintain the correct position and remain still. Electrodes will be attached to your chest to record the electrical activity of the heart.
If your radiologist wants to use a contrast dye during your CT scan, an intravenous (IV) line will be put in a vein in your hand or arm and the dye will be injected into the IV line during the scan.
You will be alone in the room during the CT scan. Sometimes a parent may stay in the room with their child. However, the technologist will always be able to see, hear and speak with you through an intercom system.
The table will move quickly through the CT scanner, a large machine with a hollow, circular tube in the middle, to determine the correct starting position for the scans. Then the table will move slowly through the machine as the CT scan takes pictures.
Patients are asked to hold their breath for small moments while images are recorded. The entire scan is usually completed within 10 minutes.
After the Procedure
When the exam is complete, you will be asked to wait until the technologist verifies that the images are of high enough quality for accurate interpretation. Once this has been confirmed, you can return to your normal activities.
After the images have been interpreted, your radiologist or referring physician will discuss the findings with you. Depending on the results of the CT scan, additional tests or procedures may be scheduled to gather further diagnostic information.