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Brain CT Scan
(Computed Tomography of the Brain, Intracranial CT Scan)


A body scanner delivers x-rays to the head at many different angles. A computer then compiles this information to construct highly detailed, cross-sectional images of the brain. In some cases, a contrast dye may be injected to better define tissues and blood vessels on the scans and enhance the images.

Purpose of the Test

To help diagnose disorders affecting the brain, including tumors; infarction (an area of dead tissue caused by interruption of blood flow); bleeding within the brain; hematoma (collection of blood on the brain); and hydrocephalus (accumulation of fluid within the ventricles of the brain).

To determine the stage of brain tumors and to monitor them after treatment for cancer.

Who Performs It

A radiologist and/or a trained technician.

Special Concerns

CT scans are not usually done during pregnancy because exposure to ionizing radiation may harm the fetus.

People with allergies to iodine or shellfish may experience an allergic reaction to the iodine-based contrast dye.

People who experience claustrophobia may find it difficult to undergo a CT scan, which takes place in a narrow, tunnel-like structure.

This test may not be possible for severely overweight individuals (over 300 lbs).

Before the Test

Inform your doctor if you have an allergy to iodine or shellfish. You may be given a combined antihistamine-steroid preparation to reduce the risk of an allergic reaction to the contrast dye.

Tell your doctor if you suffer from claustrophobia. He or she may prescribe a sedative to help you tolerate the procedure.

If a contrast dye is to be used or if sedation is anticipated, you will be instructed to fast for 4 hours before the test and drink large amounts of fluids on the day before the test to prevent dehydration. If a dye is not being used, fasting is unnecessary.

Just before the test, remove all jewelry and metal objects.

What You Experience

You are asked to lie on your back on a narrow table. Your head is immobilized in a brace (but your face is left uncovered) and then advanced into the CT scanner.

The scanner takes pictures at different intervals and varying levels over your head, so you will feel the table move during the test. The resulting images are displayed on a viewing monitor and recorded on x-ray film.

You must remain still because any movement can distort the image on the scan.

A contrast dye may be administered through an intravenous (IV) needle or catheter inserted into a vein in your arm. (Upon injection of the dye, you may experience a mild nausea, flushing, warmth, or a salty taste in the mouth.) The scanning process is then repeated.

The test usually lasts 10 to 20 minutes. If a contrast dye is used, it may take up to 40 minutes because scans are taken before and after the dye is given.

Risks and Complications

Although radiation exposure is minimal, you will receive a higher dose of radiation than during standard x-ray procedures.

Some people may experience an allergic reaction to the iodine-based contrast dye, which can cause symptoms such as nausea, sneezing, vomiting, hives, and occasionally a life-threatening response called anaphylactic shock. Emergency medications and equipment are kept readily available.

Patients who are dehydrated or those with impaired kidney function may experience acute renal failure from infusion of the contrast dye. Adequate hydration before the test can reduce this risk.

After the Test

If contrast dye was used, you are encouraged to drink clear fluids to avoid dehydration and help flush the dye out of your system.

You are free to resume your normal diet and activities.

If contrast dye was injected, blood may collect and clot under the skin (hematoma) at the injection site; this is harmless and will resolve on its own. For a large hematoma that causes swelling and discomfort, apply ice initially; after 24 hours, use warm, moist compresses to help dissolve the clotted blood.

Delayed allergic reactions to the contrast dye, such as hives, rash, or itching, may appear 2 to 6 hours after the procedure. If this occurs, your doctor will prescribe antihistamines or steroids to ease your discomfort.


A radiologist will examine the CT images for evidence of any abnormality.

If a definitive diagnosis can be made based on the images, appropriate treatment will be initiated, depending on the specific problem.

In some cases, additional tests, such as an MRI or a PET scan of the brain, may be needed to establish a diagnosis and determine the extent of the problem.


From The Johns Hopkins Consumer Guide to Medical Tests. You can order this book now on our secure server.


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