Computed tomography (CT or CAT scan) is an imaging test that uses X-rays and a computer to make detailed images of the body. A CT scan shows details of the bones, muscles, fat, and organs. CT scans are more detailed than standard X-rays.
In standard X-rays, a beam of energy is aimed at the body part being studied. A plate behind the body part captures the variations of the energy beam after it passes through skin, bone, muscle, and other tissue. While much information can come from a standard X-ray, MRI captures much more detail about internal organs and other structures.
In a CT scan, an X-ray beam moves in a circle around the body. This provides many different views of the same organ or structure. The X-ray information is sent to a computer that interprets the X-ray data and displays it in a two-dimensional (2D) form on a monitor.
CT scans may be done with or without "contrast." Contrast refers to a substance taken by mouth or injected into an intravenous (IV) line that causes the particular organ or tissue under study to show up more clearly on the scan.
CT scans of the brain can give more detailed information about brain tissue and brain structures than standard X-rays of the head. CT scans can give healthcare providers more information related to injuries or diseases of the brain.
A CT scan of the brain may be used to check the brain for tumors or other lesions, injuries, bleeding in the brain, structural anomalies, infections, brain function changes, or other conditions. A CT scan may be done when another type of exam, such as an X-ray, MRI, or physical exam, is not conclusive.
A CT scan of the brain may also be used to see if treatment is working for brain tumors and to look for clots in the brain that may cause a stroke. Another use of brain CT is to guide brain surgery or biopsies of brain tissue. A biopsy is when a small piece of tissue is removed so it can be examined in the lab.
There may be other reasons for your healthcare provider to recommend a CT scan of the brain.
You may want to ask your healthcare provider about the amount of radiation used during the CT procedure and the risks related to your situation. It is a good idea to keep a record of your radiation exposure, such as previous CT scans and other types of X-rays, so that you can inform your healthcare provider. Risks associated with radiation exposure may be related to the cumulative number of X-ray exams and/or treatments over time.
If you are pregnant or think you may be, tell your healthcare provider. Radiation exposure during pregnancy may lead to birth defects. If it’s necessary for you to have a CT of the brain, special precautions will be taken to reduce the radiation exposure to the fetus.
Nursing mothers should talk with the radiologist about when to resume breastfeeding after contrast material is injected.
If contrast dye is used, there is a risk for allergic reaction to the dye. Tell your healthcare provider if you are allergic to or sensitive to medicines, contrast, or iodine. Most people will not have a bad reaction from iodine contrast. However, let your healthcare provider know if you have ever had a reaction to any contrast dye, or have kidney problems.
There may be other risks depending on your specific medical condition. Be certain your healthcare provider knows all of your medical conditions.
Make a list of questions and discuss any concerns with your healthcare provider before the procedure. Consider bringing a family member or trusted friend to the appointment to help you remember your questions and concerns and to take notes.
- Your healthcare provider will explain the procedure to you and ask if you have any questions.
- If your CT scan involves the use of contrast dye, you will be asked to sign a consent form that gives permission to do the procedure. Read the form carefully and ask questions if anything is not clear.
- Generally, you won’t need to fast before a CT scan, unless a contrast dye is to be used. Your healthcare provider will give you special instructions ahead of time if contrast is to be used and you will need to withhold food and drink.
- Tell your healthcare provider of all medicines (prescribed and over-the-counter), vitamins, herbs, and supplements that you are taking.
- Tell the technologist if you have ever had a reaction to any contrast dye, or if you are allergic to iodine.
- Tell the technologist if you are pregnant or think you may be.
- Based on your medical condition, your healthcare provider may request other specific preparation.
CT scans may be done on an outpatient basis or as part of your stay in a hospital. Procedures may vary depending on your condition and your healthcare provider’s practices.
Generally, a CT scan of the brain follows this process:
- You will be asked to remove any clothing, jewelry, or other objects that may interfere with the procedure, such as eyeglasses, hairpins, dentures, and possibly hearing aids.
- If you are asked to remove clothing, you will be given a gown to wear.
- If you are to have a scan done with contrast, an intravenous (IV) line will be started in your hand or arm for injection of the contrast dye.
- You will lie on a narrow scan table that slides into a large, circular opening of the ring-shaped scanning machine. Pillows and straps may be used to help keep your head still during the scan.
- The technologist will be in another room where the scanner controls are located. However, you will be in constant sight of the technologist through a window. Speakers inside the scanner will allow the technologist to talk to you and hear you. You will have a call button so that you can let the technologist know if you have any problems during the scan. The technologist will be watching you at all times and will be in constant communication.
- The scanner will rotate around you, and X-rays will pass through your body for short amounts of time. You will hear clicking and whirring sounds, which are normal.
- The X-rays absorbed by the body's tissues will be detected by the scanner and transmitted to the computer. The computer will transform the information into an image to be interpreted by the radiologist.
- It will be very important for you to stay very still during the scan. You may be asked to hold your breath for a short time at various times during the scan.
- If contrast dye is used, you will be removed from the scanner after the first set of scans has been completed. A second set of scans will be taken after the contrast dye has been given.
- If contrast dye is used, you may feel some effects when the dye is injected into the IV line. These effects include a warm flushing sensation, a salty or metallic taste in the mouth, a brief headache, and/or nausea. These effects usually only last for a few moments.
- You should tell the technologist if you feel any breathing difficulties, sweating, numbness, or heart palpitations.
- When the procedure is done, you will be removed from the scanner.
- If an IV line was inserted, it will be removed.
- You may be asked to wait for a short time while the radiologist examines the scans to make sure they are good images
While the CT procedure itself causes no pain, having to lie still for the length of the procedure might cause some discomfort or pain, particularly if you’ve recently been injured or had surgery. The technologist will use all possible comfort measures and complete the procedure as quickly as possible to minimize any discomfort or pain.
If contrast dye was used, you may be monitored for a period for any side effects or reactions to the contrast dye, such as itching, swelling, rash, or difficulty breathing. Tell the radiologist or your healthcare provider right away if you notice any of these symptoms.
If you notice any pain, redness, and/or swelling at the IV site after you go home, tell your healthcare provider as this could be a sign of infection or other type of reaction.
Otherwise, there is no special type of care needed after a CT scan of the brain. You may go back to your usual diet and activities unless your healthcare provider tells you differently.
Your healthcare provider may give you other instructions after the procedure, depending on your particular situation.Before you agree to the test or the procedure make sure you know:
- The name of the test or procedure
- The reason you are having the test or procedure
- What results to expect and what they mean
- The risks and benefits of the test or procedure
- What the possible side effects or complications are
- When and where you are to have the test or procedure
- Who will do the test or procedure and what that person’s qualifications are
- What would happen if you did not have the test or procedure
- Any alternative tests or procedures to think about
- When and how will you get the results
- Who to call after the test or procedure if you have questions or problems
- How much will you have to pay for the test or procedure
January 16, 2018
Approach to Neuroimaging in Children. UpToDate
Grossman, Neil, MD,Moloney, Amanda Jane (Johns), PA-C, MPAS, BBA