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Computed tomography (CT or CAT) scans provide information about the status not only of soft tissue structures like organs, nerves and the brain, but also exquisite detail of even the smallest bony structures such as the vertebrae.
CT scans are considered to be one of the best ways to evaluate the sinuses. They are also helpful for evaluating swelling, inflammation and tumors.
During a CT scan, you will lie flat on a table that automatically slides into a doughnut-shaped piece of equipment. Most scans take only a few minutes and have a low risk of radiation exposure.
As X-rays pass through your body, different tissues absorb different amounts. Detectors inside the gantry measure the radiation leaving your body and convert the radiation into electrical signals. A computer gathers these signals and gives them a color ranging from black to white, depending on the signal's strength. The computer then puts the images together and displays them on a computer monitor. A technician in a separate room supervises your exam and watches the images on the computer. He or she can see and talk with you through an intercom.
Depending on what information is needed, the doctor may order a CT scan that is done using a contrast fluid or dye. This requires injecting a small amount of a colorless fluid (called dye or contrast) into a vein in your arm or hand before the CT scan. (If you have any allergies to drugs, iodine or other contrast agents, let your doctor know.)
A CT scan is painless. It can be done on an infant or toddler. Unlike magnetic resonance imaging (MRI) , a CT scan can be done even if you have a pacemaker or cardioverter defibrillator.
Usually having a CT scan done takes less than an hour. Most of that time is spent preparing for the actual scan. As with an X-ray, a radiologist who is specially trained to read the images will look at the scan and send a report to your doctor or surgeon.
A CT scan is about as safe as an ordinary X-ray. There is some brief exposure to radiation. However, the information that a CT scan provides outweighs the risks of the radiation exposure.
If any of the following apply to you, please tell your doctor:
- You are or think you might be pregnant. In this case, your doctor may want to recommend another type of diagnostic test.
- You have asthma or allergies. If it is necessary for you to have a contrast medium while the CT scan is done, there is a small possibility that you would have an allergic reaction to the medium.
- You have medical conditions such as diabetes, asthma, heart disease, kidney problems or a thyroid condition. These also may increase your risk of an allergic reaction to any contrast medium that may be needed during your CT scan.