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.

Although your personal physician requests the CT scan, a radiologist performs the actual examination. A radiologist is a medical doctor who specializes in the use of imaging for diagnosis of medical conditions. The radiologist is assisted by a radiologic technologist, a person who has extensive training in the use of x-ray equipment. Together, these highly skilled professionals will make sure that your CT scan pictures are of the best quality possible and that you are as comfortable as possible throughout the procedure.

A CT scan of the body can take from 15 to 30 minutes, while a scan of the head alone can take about 5 minutes. In case injection of contrast is required, the procedure may take longer. However, you may need to allow extra time for each procedure in case there are delays or a need to repeat some scans. Your doctor or the office nurse will advise you how to plan your schedule for the day of the exam.

A CT scan is usually completely painless. The machine does not touch you and you do not feel the x-rays. Occasionally, some patients who are administered a contrast medium experience a side effect, usually involving only slight discomfort. This rarely occurs today because newer, safer products called nonionic contrast media have been developed, and they reduce most discomfort.

You can help assure a successful, comfortable procedure by carefully following the instructions of your physician, the radiologist, and the radiologic technologist. Be sure to answer carefully any questions they may ask about your general health. For example, tell them if you are pregnant, diabetic, and/or allergic to any foods or drugs. Let them know if you have had any contrast media in the past and if you had any side effects. Give them a complete list of any medications you may be taking now, including nonprescription medications. Also indicate if you have had or are presently being treated for an infection in any part of your body.

You lie quietly on a table

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.

Wait for the radiologist to review the scans

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