Computed Tomography (CT or CAT) Scan of the Brain

(Head CT Scan, Intracranial CT Scan)

Procedure overview

What is a CT or CAT scan of the brain?

Computed tomography (CT or CAT scan) is a noninvasive diagnostic imaging procedure that uses a combination of X-rays and computer technology to produce horizontal or axial images (often called slices) of the body. A CT scan shows detailed images of any part of the body, including 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 be obtained from a standard X-ray, a lot of detail about internal organs and other structures is not available.

In computed tomography, the X-ray beam moves in a circle around the body. This allows 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 be seen more clearly. Contrast examinations may require you to fast for a certain period of time before the procedure. Your doctor will notify you of this prior to the procedure.

CT scans of the brain can provide more detailed information about brain tissue and brain structures than standard X-rays of the head, thus providing more information related to injuries and/or diseases of the brain.

Other related procedures that may be used to diagnose brain disorders include X-rays, magnetic resonance imaging (MRI) of the brain, positron emission tomography (PET) scan of the brain, and cerebral arteriogram. Please see these procedures for additional information.

Anatomy of the brain

The central nervous system (CNS) consists of the brain and spinal cord. The brain is an important organ that controls thought, memory, emotion, touch, motor skills, vision, respirations, temperature, hunger, and every process that regulates our body.

What are the different parts of the brain?

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The brain can be divided into the cerebrum, brainstem, and cerebellum:

• Cerebrum. The cerebrum (supratentorial or front of brain) is composed of the right and left hemispheres. Functions of the cerebrum include: initiation of movement, coordination of movement, temperature, touch, vision, hearing, judgment, reasoning, problem solving, emotions, and learning.
• Brainstem. The brainstem (midline or middle of brain) includes the midbrain, the pons, and the medulla. Functions of this area include: movement of the eyes and mouth, relaying sensory messages (hot, pain, loud, etc.), hunger, respirations, consciousness, cardiac function, body temperature, involuntary muscle movements, sneezing, coughing, vomiting, and swallowing.
• Cerebellum. The cerebellum (infratentorial or back of brain) is located at the back of the head. Its function is to coordinate voluntary muscle movements and to maintain posture, balance, and equilibrium.

More specifically, other parts of the brain include the following:

• Pons. A deep part of the brain, located in the brainstem, the pons contains many of the control areas for eye and face movements, facial sensation, hearing, and equilibrium.
• Medulla. The lowest part of the brainstem, the medulla is the most vital part of the entire brain and contains important control centers for the heart and lungs.
• Spinal cord. A large bundle of nerve fibers located in the back that extends from the base of the brain to the lower back, the spinal cord carries messages to and from the brain and the rest of the body.
• Frontal lobe. The largest section of the brain located in the front of the head, the frontal lobe is involved in personality characteristics and movement.
• Parietal lobe. The middle part of the brain, the parietal lobe helps a person to identify objects and understand spatial relationships (where one's body is compared to objects around the person). The parietal lobe is also involved in interpreting pain and touch in the body.
• Occipital lobe. The occipital lobe is the back part of the brain that is involved with vision.
• Temporal lobe. The sides of the brain, these temporal lobes are involved in memory, speech, and sense of smell.

Reasons for the procedure

A CT scan of the brain may be performed to assess the brain for tumors and other lesions, injuries, intracranial bleeding, structural anomalies such as hydrocephalus, infections, brain function or other conditions, particularly when another type of examination such as X-rays or physical examination are not conclusive.

A CT scan of the brain may also be used to evaluate the effects of treatment on brain tumors and to detect clots in the brain that may be responsible for strokes. Another use of brain CT is to provide guidance for brain surgery or biopsies of brain tissue.

There may be other reasons for your doctor to recommend a CT scan of the brain.

Risks of the procedure

You may want to ask your doctor about the amount of radiation used during the CT procedure and the risks related to your particular situation. It is a good idea to keep a record of your past history of radiation exposure, such as previous CT scans and other types of X-rays, so that you can inform your doctor. Risks associated with radiation exposure may be related to the cumulative number of X-ray examinations and/or treatments over a long period of time.

If you are pregnant or suspect that you may be pregnant, you should notify your doctor. Radiation exposure during pregnancy may lead to birth defects. If it is necessary for you to have a CT of the brain, special precautions will be made to minimize the radiation exposure to the fetus.

Nursing mothers should wait 24 hours after contrast material is injected before resuming breastfeeding.

If contrast dye is used, there is a risk for allergic reaction to the dye. Patients who are allergic to or sensitive to medications should notify their doctor. Studies show that 85 percent of the population will not experience an adverse reaction from iodinated contrast; however, you will need to let your doctor know if you have ever had a reaction to any contrast dye, and/or any kidney problems. A reported seafood allergy is not considered to be a contraindication for iodinated contrast.

Patients with kidney failure or other kidney problems should notify their doctor. In some cases, the contrast dye can cause kidney failure. The effects of kidney disease and contrast agents have attracted increased attention over the last decade, as patients with kidney disease are more prone to kidney damage after contrast exposure. Also, patients taking the diabetes medication metformin (Glucophage) should alert their doctor before having IV contrast, as it may cause a rare condition called metabolic acidosis. If you take metformin, you will be asked to stop taking it 24 hours before and for 48 hours after your procedure. A blood test may be required before you can start taking metformin again.

There may be other risks depending on your specific medical condition. Be sure to discuss any concerns with your doctor prior to the procedure.

Before the procedure

• Your doctor will explain the procedure to you and offer you the opportunity to ask any questions that you might have about the procedure.
• If your procedure 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 something is not clear.
• Generally, there is no fasting requirement prior to a CT scan, unless a contrast dye is to be used. Your doctor will give you special instructions ahead of time if contrast is to be used and if you will need to withhold food and drink.
• Notify the technologist if you have ever had a reaction to any contrast dye, or if you are allergic to iodine.
• Notify the technologist if you are pregnant or suspect you may be pregnant.
• Based on your medical condition, your doctor may request other specific preparation.

During the procedure

CT Scan

CT scans may be performed on an outpatient basis or as part of your stay in a hospital. Procedures may vary depending on your condition and your doctor's practices.

Generally, a CT scan of brain follows this process:

1. 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.
2. If you are asked to remove clothing, you will be given a gown to wear.
3. If you are to have a procedure done with contrast, an intravenous (IV) line will be started in the hand or arm for injection of the contrast dye. For oral contrast, you will be given medication to swallow.
4. You will lie on a scan table that slides into a large, circular opening of the scanning machine. Your head may be immobilized to prevent movement during the procedure.
5. 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 enable the technologist to communicate with and hear you. You will have a call button so that you can let the technologist know if you have any problems during the procedure. The technologist will be watching you at all times and will be in constant communication.
6. As the scanner begins to rotate around you, X-rays will pass through the body for short amounts of time. You will hear clicking sounds, which are normal.
7. 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.
8. It will be very important for you to remain very still during the procedure.  You may be asked to hold your breath at various times during the procedure.
9. If contrast dye is used for your procedure, 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 administered.
10. If contrast dye is used for your procedure, you may feel some effects when the dye is injected into the IV line. These effects include a flushing sensation, a salty or metallic taste in the mouth, a brief headache, or nausea and/or vomiting. These effects usually last for a few moments.
11. You should notify the technologist if you feel any breathing difficulties, sweating, numbness, or heart palpitations.
12. When the procedure has been completed, you will be removed from the scanner.
13. If an IV line was inserted for contrast administration, the line will be removed.
14. You may be asked to wait for a short period of time while the radiologist examines the scans to make sure they are clear.

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 in the case of a recent injury or invasive procedure such as surgery. The technologist will use all possible comfort measures and complete the procedure as quickly as possible to minimize any discomfort or pain.

After the procedure

If contrast dye was used during your procedure, you may be monitored for a period of time for any side effects or reactions to the contrast dye, such as itching, swelling, rash, or difficulty breathing. Notify the radiologist or your doctor if you experience any of these symptoms.

If you notice any pain, redness, and/or swelling at the IV site after you return home following your procedure, you should notify your doctor as this could indicate an infection or other type of reaction.

Otherwise, there is no special type of care required after a CT scan of the brain. You may resume your usual diet and activities unless your doctor advises you differently.

Your doctor may give you additional or alternate instructions after the procedure, depending on your particular situation.