Trusted medical advice from the
American Academy of Family Physicians.

CT Head Scan

A CT (computed tomography) or CAT (computerized axial tomography) head scan looks inside your head and neck. CT and CAT scans are the same test. Special X-ray technology gives your doctor a picture of your skull, brain, eyes, nasal passages, veins, arteries, and tissue. It’s a common test. It’s used for a serious head injury, stubborn headaches, brain and skull birth defects, brain diseases, and stroke. Doctors decide when a person needs a CT head scan.

A machine is used for a CT scan. The machine is shaped like a giant cylinder. It’s attached to a long table that slides in and out of the machine. The technology takes multiple X-ray views of your head. It layers them on top of each other to create a 3-D image for your doctor.

If you’re having a CT head scan, you’ll lie on the table during the procedure. You’ll be asked to remain still. It could take 30 minutes to complete. The machine is noisy; however, the test is painless. Children often have difficulties remaining still, so they may be given an injection of a medicine to make them sleep through the test. You won’t be given the results of the test at the time of the test.

Path to improved health

An injury or illness related to your head can be scary. However, the images provided by CT head scan can help your doctor better diagnose and treat head and brain conditions. It also may reduce the need for you to have other medical procedures, including surgery.

Your doctor will first do an office exam and discuss your symptoms. Your doctor also will look at the seriousness of your symptoms. That will help him or her decide if a head scan is necessary. If your head scan is not an emergency, it will be scheduled in a hospital or imaging center.

In the event of an emergency, such as an accident, a serious injury, or stroke, doctors can do a CT head scan in the emergency room. In those types of health emergencies, timing is critical. An emergency room doctor may need to do a head scan in order to diagnose, treat, and evaluate the damage a person may have suffered. For example, CT head scans are used to diagnose stroke. A person who has had a stroke has a better chance at recovery when examined and treated early. An emergency room head scan helps doctors confirm that it was a stroke, evaluate the damage, and decide on further treatment.

For the head scan test, you will need to undress and put on a hospital gown. Some people must have a dye (contrast) injected into the vein in their arm for the CT head scan. The dye contains iodine. This makes it easier for certain parts and functions in your head or neck to show up on the image. Once the dye is injected, you may feel a burning sensation, the taste of metal, and a warm feeling in your body. These last only a few seconds. Some people are allergic to the dye (see “Things to consider”). Tell your doctor if you know you’re allergic to dye.

Things to consider

Some people who need a CT head scan must get an iodine dye injection before the test. If you know you’re allergic to iodine, tell your doctor. He or she may prescribe medicine before the test to reduce your allergic reaction. Some people with poor kidney function caused by kidney disease or diabetes may need extra fluids after the test to help remove the iodine from their kidneys. People who have diabetes and are taking the medicine metformin should tell their doctor before the test. Metformin and the dye can result in a serious drug interaction. The most serious allergy to the dye could cause difficulty breathing. If you have trouble breathing during the test, tell the scan technician immediately.

Like an X-ray, CT head scans will expose you to a small dose of radiation. One head scan image is made up of multiple X-rays. That’s how the technology creates a clear image of the inside of your head or neck. Therefore, a head scan exposes you to more radiation than a single X-ray. The exposure to radiation is small with one head scan. Repeat exposure to scans over a long period of time can increase your risk of cancer. Today’s CT scan technology is faster than it used to be. Therefore, your exposure to radiation is even less than it once was. Talk with your doctor about whether the benefits of a head scan outweigh the risk of radiation exposure.

Your doctor will consider whether or not a CT head scan is necessary. Because the test involves radiation exposure, potential overuse, time, and expense, the American Academy of Family Physicians (AAFP) follows the recommendations of the Choosing Wisely campaign for CT scans. Choosing Wisely is an effort that promotes patient-physician conversations about unnecessary medical tests and procedures. According to Choosing Wisely, children and adults who come to the emergency room with a minor head injury and have a low risk of developing serious complications do not need a CT head scan. A CT head scan should not be performed on a person for sudden hearing loss, unless that person has signs of a brain injury or disease, a history of trauma, or serious ear disease. Additionally, Choosing Wisely recommends that doctors should not order a CT head scan for people who come to the emergency room for fainting or feeling lightheaded without additional signs of a more serious issue.

Finally, if you weigh 300 pounds or more, check with your doctor to see if the CT machine has a weight restriction.

Questions for your doctor

  • How many CT head scans is too many when considering radiation exposure?
  • Will a CT head scan expose other parts of my body to radiation?
  • Can a CT head scan be harmful to my pregnancy?
  • When is a CT head scan better than an X-ray?
  • What’s the difference between a CT head scan and a magnetic resonance imaging (MRI) test?

Resources

Centers for Disease Control and Prevention: Radiation and Your Health: CT-Scans

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