During the scan, a thin beam of x-rays is focused on a specific part of your body, such as the head, chest, liver, spleen, pancreas, adrenal glands, kidneys, or spine. The x-ray tube moves rapidly around this site, enabling multiple images to be made from different angles to create a cross-sectional picture. The x-ray beam is picked up by an electronic detector which records the information and feeds it into a computer.
The computer then analyzes the information and constructs an image on a TV screen. During some CT scans, a contrast medium (commonly called “dye”) is used to outline blood vessels or highlight organs of the body (eg, liver, kidneys) so that they can be seen more easily.
As with other important diagnostic procedures, you may be asked to sign an informed consent to undergo a CT scan. That is your opportunity to ask any questions following a description of the risks, benefits, and alternatives of the procedure. The contents of this guide are for your information only and are not to be interpreted as taking the place of informed consent. Do not hesitate to discuss your upcoming CT exam with your physician or the radiologist.
Following are a few steps that your doctor may ask you to take before you go to the hospital or radiologists office for your exam. These same general steps may be recommended if you are a hospitalized patient.
You may need to fast for a few hours
If a contrast medium is to be used during your CT scan, your doctor will probably ask you not to eat anything for three or four hours or more before the exam. In addition, you may be asked not to drink anything for one hour before the exam.
You may need to wear a hospital gown
If you are having a body scan, you will probably be asked to undress and put on a hospital gown for the exam. You will also be asked to remove any jewellery so that it does not interfere with the x-ray imaging.
If you are having a CT scan of your head, you may be asked to wear loose, comfortable clothing for the exam. And you will need to remove dentures, glasses, hearing aids, earrings, hairpins, and any other objects that may be in the path of the x-ray beam.
You will be asked to lie on a table that is connected to the CT scanner. Then the part of your body that is to be scanned will be positioned in the middle of the large, doughnut-shaped scanner ring. This ring holds the x-ray tube and the electronic detector that sends information to the computer.
The technologist may take preliminary scans
If a contrast medium is to be used during your exam, the technologist will probably take some preliminary scans before the radiologist injects the material.
The radiologist may administer a contrast medium
If a contrast medium is used, the radiologist or technologist will inject it into a vein, probably in your arm. Some or all of the solution may be injected by a syringe or by an automatic injector. Some or all of it may run slowly into your vein from an intravenous (IV) bottle that hangs on a pole next to the table. A tourniquet may be used to make the vein stand out for easier injection. A tourniquet is simply a band that is wrapped tightly around your arm, similar to, but smaller than, the cuff that is wrapped around your arm when you have your blood pressure taken.
The table may move
You will remain alone in the room after the procedure begins, but the radiologist and the radiologic technologist will watch you closely through an observation window and you can talk to them through a two-way intercom.
The table may move a short distance every few seconds to position you for each new scan, or the table may move continuously very slowly. You will hear clicking or buzzing sounds as the mechanism in the scanner moves around your body, making images from many different angles. It is important that you lie very still during the procedure so that the scanner can get the best possible pictures.
The entire procedure may take about an hour for a body scan and a half-hour for a head scan.
After the exam is over, the radiologist will look at all the images to make sure they contain all the needed information. You will be asked to wait while this is done because sometimes it is necessary to do repeat scans or take additional scans.
Dress and return home
After the radiologist has a complete set of scans, you may change back into your clothes and go home. If you are a hospitalized patient, you may go back to your room.
Drink plenty of fluids
Unless you have other tests scheduled, you may eat normal meals after the exam and your doctor will suggest that you drink plenty of fluids. Fluids will help eliminate the contrast medium from your body.
Meet with your physician