CT Scan of the Head

During a CT scan of the head, the head is positioned inside a cylinder that is part of the CT scanner. The entire scanner can tilt, and the X-ray scanning cylinder within it can rotate to obtain the views needed. For a head scan, 10 to 30 slices are usually taken. The results are highly-detailed images of the head, including the brain, eyes, bones of the skull, and the air-filled cavities (sinuses) within the bones around the nose.

Sometimes a special dye (contrast material) that contains iodine is injected into the blood during a CT scan of the head. The dye makes blood vessels and certain structures inside the head more visible on the CT scan images.

You may also want to see our info on CT scans of the body.

Why It Is Done
A CT scan of the head is done to:

• Evaluate certain symptoms (such as confusion, paralysis, numbness, vision problems, or severe, persistent headaches) that might indicate a brain injury, brain tumor, or bleeding within the skull.
• Determine the extent of damage caused by a stroke and help determine the effectiveness of treatment for a stroke.
• Help determine the cause of a loss of consciousness or a decreasing level of consciousness.
• Detect blood clots, tumors, bleeding, infection, or increased pressure in the skull or brain.
• Evaluate the effectiveness of treatment for a brain tumor.

CT scans of the head may also be done to:

• Investigate problems of the eyes and the optic nerve. The test may detect fractures of the bones around the eyes or foreign objects in the eye.
• Investigate problems of the middle ear bones and the auditory nerve.
• Evaluate problems or diseases of the air-filled cavities (sinuses) within the bones around the nose.
• Evaluate problems with the bones and joints of the jaw, face, and skull (such as temporomandibular disorder or Paget's disease).

How to Prepare
Before the CT scan, tell your doctor if:

• You might be pregnant.
• You become very nervous in confined spaces. You need to lie very still inside the CT scanner, so you may need medication to help you stay relaxed. However, this is uncommon because the cylinder within the scanner is not long enough to enclose very much of your body.
• You are allergic to shellfish (shrimp, scallops, lobster), the iodine dye used in the contrast material that is injected into your blood, or any other substance that contains iodine. You should also tell your doctor if you have asthma, are allergic to any medications, or have ever had a serious allergic reaction (anaphylaxsis) from any substance (such as the venom from a bee sting).

If you will be given an injection of contrast material, you may need to avoid eating and drinking for 4 hours before the test.

How It Is Done
A CT scan is usually done by a radiology technologist. The resulting pictures are usually interpreted by a doctor who specializes in evaluating X-rays (radiologist). However, some other types of doctors (such as a surgeon or an internal medicine doctor) may review a head CT scan to help guide a person's care.

You will need to remove jewelry that might interfere with the X-ray picture.

During the test, you will lie on your back on a table that is attached to the CT scanner. The scanner is a large square machine with a circular opening that contains the X-ray tube and detector. Movement of your head will be limited by using straps or tape, but your face will not be covered.

The table will slide into the hole in the scanner while a cylinder lining the hole rotates around your head. If a standard CT scanner is used, the table will move a small distance every few seconds to reposition you for each new "slice" of the CT scan. If a spiral (helical) CT scanner is used, the table will glide in a smooth, continuous movement. You may hear clicking or buzzing sounds as the table moves and the cylinder turns.

It is very important to hold completely still while your head is being scanned. Otherwise, repeat scans may be needed.

During the test, you are usually alone in the scanner room. However, the technologist will watch you through an observation window, and you will be able to talk to him or her through an intercom.

If contrast material is needed, it will be injected into a vein (usually in your arm) over 1 to 2 minutes. Then additional pictures are taken.

This test usually takes about 30 minutes, but because of delays that can occur, you should allow at least an hour for the test.

How It Feels
You will feel no discomfort from the X-rays during the CT scan. However, the table you lie on may feel hard and the room may be chilly because air-conditioning is used to keep the X-ray equipment at a constant temperature.

Some people feel discomfort or anxiety (claustrophobia) when placed inside the CT scanner. If this keeps you from lying still in the scanner, you may be given a medication (sedative) to help you relax.

If contrast material is injected into your arm, you may feel warm and flushed and get a metallic taste in your mouth. In rare cases, the contrast material may cause nausea, vomiting, or a headache. If you develop these symptoms, tell the technologist or your doctor.

Risks
A CT scan of the head has a small risk of causing a problem:

• There is a slight risk of developing an allergic reaction to the iodine contrast material. The reaction can be mild (itching, rash) or severe (difficulty breathing or sudden shock). Death resulting from an allergic reaction is rare. Most reactions can be controlled using medication. Be sure to tell your doctor if you have allergies of any kind (such as hay fever, iodine allergy, asthma, hives, or food allergies).
• The contrast material can cause water loss or direct damage to the kidneys that may lead to kidney failure. This is a special concern for people who have kidney problems, diabetes, or dehydration. Special precautions are taken during the test to prevent problems for people with these conditions.
• There is always a slight risk of damage from being exposed to any radiation, including the low levels of X-rays used for a CT scan. However, if this test is really needed, the risk of damage from the X-rays is usually very low compared with the potential benefits of the test.

Results
The radiologist may discuss preliminary results of the CT scan with you right after the test. However, complete results usually take 1 to 2 days after all of the images have been reviewed.