A CT scan — also called Computerized Tomography or just CT—is an X-ray technique that produces images of your body that visualize internal structures in cross section. The scanner is comprised of a table and a gantry. The gantry is the donut shape part that houses the X-ray source. The X-ray source rotates inside the gantry as the patient moves through. Data is obtained and processed by a computer to produce a set of cross-sectional images, like slices, of the inside of your body.

How you prepare for a CT scan depends on which part of your body is being scanned. You may be asked to remove your clothing and wear a hospital gown. You'll need to remove any metal objects, such as jewelry, that might interfere with image results.

Some CT scans require you to drink a contrast liquid before the scan or have contrast injected into a vein in your arm during the scan. A contrast medium blocks X-rays and appears white on images, which can help emphasize blood vessels, bowel or other structures. If your test involves a contrast medium, your doctor may ask you to fast for a few hours before the test.

Before the CT scan, tell your doctor if you:

• • Are or might be pregnant.
• • Are allergic to any medicines, including iodine dyes.
• • Have a heart condition, such as heart failure
• • Have diabetes or take metformin (Glucophage) for your diabetes. You may have to adjust your medicine for a day before and after the test.
• • Have had kidney problems.
• • Have asthma.
• • Have a medical device, such as a pacemaker or an insulin pump.
• • Have had multiple myeloma.
• • Have had an X-ray test using barium contrast material (such as a barium enema) or have taken a medicine that contains bismuth (such as Pepto-Bismol) in the past 4 days. Barium and bismuth show up on X-ray films and make it hard to see the picture clearly.
• • Become very nervous in small spaces. You need to lie still inside the CT scanner, so you may need a medicine (sedative) to help you relax.

Yes, please take medicines before the CT scan. Consult your physician before the test for instructions.

Expect the exam to last no longer than an hour, depending on the preparation needed and whether it includes the use of a contrast medium. The scan itself may take less than a minute on the newest machines. Most scans take just a few minutes to complete.

CT scans are similar to those of conventional X-rays. During the CT scan, you’re briefly exposed to radiation. But doctors and other scientists believe that CT scans provide enough valuable information to outweigh the associated risks.

During the CT scan, you lie on a narrow table that slides through the opening in the CT machine. You may lie on your back, side or stomach, depending on the area to be scanned. The table can be raised or lowered. Straps and pillows may help you stay in position. During a CT scan of the head, the table may be fitted with a special cradle that holds your head still. CT scans are painless. If your exam involves use of an intravenous contrast medium, you may feel a brief sensation of heat or experience a metallic taste in your mouth. If you receive the contrast medium through an enema — to help highlight your lower gastrointestinal region — you may feel a sense of fullness or cramping.

Depending upon the body part being scanned, you may be required to hold your breath during the scan. It is important that you not move during the scan. The technologist will instruct you on breathing prior to the start of the scan.

The test will not cause pain. The table you lie on may feel hard, and the room may be cool. It may be hard to lie still during the test.

After the exam you can return to your normal routine. You may be asked to wait for a short time in the radiology department to ensure that you feel well after the exam. After the scan, you'll likely be told to drink lots of fluids to help your kidneys remove the contrast from your body.

It depends on which part of your body is being scanned. Although rare, the contrast medium involved in a CT scan poses a slight risk of allergic reaction. Most reactions are mild and result in hives or itchiness. For people with asthma who become allergic to the contrast medium, the reaction can be an asthma attack.

In rare instances, an allergic reaction can be serious and potentially life-threatening — including swelling in your throat or other areas of your body. If you experience hives, itchiness or swelling in your throat during or after your CT exam, immediately tell your doctor.

If you've had a reaction to a contrast medium in the past, and you need a diagnostic test that may require a contrast medium again, talk to your doctor. Be sure to let your doctor know if you have kidney problems, since contrast material that's injected into a vein is removed from your body by your kidneys and could potentially cause further damage to your kidneys.

If you have had a prior reaction to contrast media or have asthma or allergies, there's an increased risk of a reaction to the contrast medium.

No, the CT scan is a safe test that does not affect your ability to drive.

CT images are stored as electronic data files and usually reviewed on a computer. In most cases several hundred images are created during the scan, all of which will be reviewed by the radiologist. Previous examinations will also be reviewed and compared if applicable. The radiologist completes an in-depth review of all images and may at times consult with other physicians to provide an accurate report of your examination to your physician. The final report may take several days to complete.

No. If you are pregnant or suspect that you may be, you should not have a CT scan or any type of X-ray examination. You should inform the technologist if you suspect you may be pregnant. Alternative arrangements may be made to meet your medical needs.

CT and MRI images sometimes look very similar, but the equipment used to perform the scan is different. CT uses ionizing radiation just as with a routine X-ray, while MRI uses a magnetic field. Depending on the clinical indications, one may be preferred over the other, or both may be desirable. CT scanners are faster and as a result, claustrophobia and movement are not as problematic as with the MRI scanner.