A CT (computed tomography) or CAT (computerized axial tomography) head scan looks at the inside of your head and neck. Special X-ray technology gives your doctor a clear picture of your skull, brain, eyes, nasal passages (sinuses), veins, arteries, and tissue. It’s a common test used for a serious head injury, stubborn headaches, physical birth defects of the brain and skull, brain disease (cancerous and noncancerous growths, infection, fluid, bleeding), and stroke. Doctors decide when a person needs a CT head scan. Your doctor may recommend one for mild symptoms (fainting, dizziness, hearing loss, and strange changes in behavior) if you are experiencing other things that may be more serious.
A CT machine is shaped like a giant circle. It is attached to a long table that slides in and out of the machine. The technology takes multiple X-ray views of your head and layers them on top of one another to create a 3-D image for your doctor to review. If you are having a CT head scan, you will lie on the table during the procedure and you will 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 will not be given the results of the test by the technician.
Path to improved health
An injury or illness related to your head can be frightening. However, the clear images provided by CT head scans can help your doctor better diagnose and treat head- and brain-related conditions. It also may reduce the need for you to have other medical procedures involving tubes, needles, or surgery. A CT head scan is a safe way for your doctor to see inside your head and neck. If you are seeing your doctor for a head-related problem, he or she will do a careful office exam and discuss your symptoms before deciding whether to recommend a CT head scan. Your doctor also will look at the seriousness of your symptoms before deciding if you need a CT head scan. If your CT 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 an emergency room setting. In those types of health emergencies, timing is critical. An emergency room doctor may need to do a CT 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 a stroke has a better chance at recovery and survival when examined and treated early. An emergency room CT head scan helps doctors confirm that it was a stroke, evaluate the damage, and decide on further treatment.
For the test, you will be asked to undress, put on a hospital gown, and remove all jewelry and metal items. Some people must have a dye injected into the vein in their arm for the CT head scan. This is to make it easier for certain parts and functions in your head or neck to show up better on the image. Once the dye is inside your body, you may feel a short burning sensation, the taste of metal, and a warm feeling throughout your entire body. It lasts only a few seconds. Some people are allergic to the dye (see “Things to consider”). Tell your doctor if you know you are allergic to dye or if you are experiencing any problems breathing during the test.
Things to consider
Like an X-ray, a CT head scan will expose you to a small dose of radiation. One CT 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 CT head scan exposes you to more radiation than a single X-ray. The exposure to radiation is small with one CT head scan. Repeat exposure to CT scans over a long period of time can increase your risk of cancer. Talk with your doctor about whether the benefits of a CT head scan outweigh the risk of radiation exposure. The detail from the CT head scan can help your doctor make a more informed diagnosis, reduce surgical procedures to get a look inside your head, and decide on an effective treatment. Today’s CT scan technology is faster than it used to be. Therefore, your exposure to radiation is even less than it once was.
Some people who need a CT head scan must get an injection of dye (contrast) before the test. The dye (which contains iodine) shows up inside your head and gives your doctor a better view of problems, such as blockages or growths. If you know you have an allergy 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 you to have difficulty breathing. If you have trouble breathing during the test, tell the scan technician immediately.
Something your doctor will consider is whether or not a CT head scan is necessary. Because the test involves radiation exposure, potential overuse, time, and expense, the Orenschools (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
- Will a CT head scan expose other parts of my body to radiation?
- Can a CT head scan be harmful to my pregnancy?
- How many CT head scans is too many when considering radiation exposure?
- 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?