Mercy Regional Health Center
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Computed Tomography (CT)

What is computed tomography?
How does a CT scanner work?
What happens during the exam?
How should I prepare for the procedure?
What should I wear?
What are the risks?
How long does a CT scan take?
Will I be able to feel the scan?
How is CT different than MRI?


What is computed tomography?
Computed tomography, or CT, is a testing procedure that creates pictures of the inside of your body. It is a painless, non-invasive way to obtain detailed information that helps your doctor evaluate your health.

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How does a CT scanner work?
A CT scanner is an x-ray machine that rotates a detector 360 degrees around your body as you lie on a table. The detector measures differences in density of body parts as x-rays pass through your body. The scanner uses a powerful computer to create multiple images — or image "slices" — that provide very detailed information about your body's health. CT allows imaging of organs not viewable by standard x-ray procedures. It is also useful for evaluating blood vessel health.

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What happens during the exam?
A technologist will escort you to the CT scanner room. You will be asked to lie on the scanner table. In some cases, you may be given an injection or drink containing a contrast agent before or during the scan. The agent will help the doctor better view certain body parts.
 
The table will move during the scan. You will be asked to stay still and not breathe for short periods while the machine is scanning. You will be able to hear and talk to the technologist, who will be in the next room.

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How should I prepare for the procedure?
Make sure you understand from your doctor exactly why you are having the exam, and which part of your body is going to be scanned.

Your doctor will let you know if there are any special steps you need to take before the exam.
 
Make sure you understand and follow directions carefully. Otherwise, your exam may need to be rescheduled.

  • If you have diabetes, you may be asked to temporarily alter your medication.
  • You may be asked to take a drink containing a contrast agent before your exam.

Please arrive at least 20 minutes before your appointment to be checked in for your exam. You may be asked to wear a hospital gown.

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What should I wear?
Wear comfortable, loose clothing. You may be asked to remove jewelry, metal objects, eyeglasses or dental pieces.

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What are the risks?
Rarely, some people have an allergic reaction to the contrast agent. This may cause a rash, low blood pressure or even some difficulty breathing. If a strong allergic reaction happens, it is treated as an emergency. If you are breastfeeding, ask your doctor how long you should hold off after the contrast agent is given.
 
With a CT, like a standard x-ray, there is a small exposure to radiation. The radiation from a CT scan may be slightly more than from a regular x-ray, but it is very small and unlikely to cause any harm.

  • Let your doctor know if you are allergic to iodine.
  • Let your doctor know if you are or may be pregnant, or if you are breastfeeding.

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How long does a CT scan take? 
It may take 15 to 30 minutes for the exam, depending on what scan your doctor has ordered. Once the exam is complete, any IV that was inserted to deliver the contrast agent will be removed. You can then go back to your normal activities.

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Will I be able to feel the scan?
No. The scan is painless, but you will hear a swirling noise while the scanner is on. You may feel some mild warmth if a contrast agent is injected.

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How is CT different than MRI?
CT uses x-rays to create high-resolution images, while MRI (magnetic resonance imaging) uses a strong magnet and radio waves. CT and MRI images provide slightly different information to doctors. These differences depend on the area being imaged. Your doctor may order one or both of these tests for you.

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