Head CT / Computed Tomography

Computed Tomography (“tomo” meaning slice), also called CAT scan or CT for short, uses a special X-ray machine to take detailed pictures of the organs and tissues of the head. CT provide more details on head injuries, stroke, brain tumors, and other brain diseases than plain X-ray pictures. CT can also show bone, soft tissues, and blood vessels in the same pictures.

How does the scan work?

Unlike standard X-rays, which produce pictures of the shadows cast by body structures of varying thickness, CT scanning uses X-rays in a much different way. In Head CT, many X-ray beams are passed through the skull and brain at many angles, and special detectors measure the amount of radiation absorbed by different tissues. The X-ray tube revolves around you, and sends and records data from many angles of the head, forming cross-sectional pictures (slices) of the head and brain.

To imagine the slices through the brain, visualize the head as a loaf of bread and that you are looking at one end of the loaf (i.e., at the top of someone's head). As you remove each slice of bread, you can see the entire surface of that slice from the edge (bread crust) to the center.

How should I prepare for the CT Scan?

• If an intravenous (IV) injection of a contrast material is needed, you will be asked in advance about any allergies or serious reactions to any medicine in the past. Contrast materials contain iodine, which can cause a reaction if you are allergic. If you have known allergies to other medicine, there may be a chance that you could have a reaction to the contrast material. 
• Tell your doctor or CT technologist if there is a chance you might be pregnant.

How is the CT Scan performed?

You will be put in a special head-holder that uses soft straps to keep the head and neck in the proper place. In some cases, you will lie on your back, and in others, on your stomach. You will lie very still on a table that will be guided into the center of the scanner.

For the first few scans, the table will move quickly through the scanner to check the correct starting position. The rest of the scans are made as the table moves more slowly through the hole in the scanner.

If contrast material is needed for your scan, it will be given through your IV line.

CT exam of the head and brain can take between two and 20 minutes. When it is done you will be asked to wait until the technologist checks the pictures for quality. More scans will be done as needed.

What will I feel during the scan?

CT is painless, though you may feel some discomfort from staying still.
If contrast injection is needed, you may feel discomfort at the injection site. You may notice a warm, flushed sensation during the injection of contrast material. You may also notice a metallic taste in your mouth that lasts for about two minutes. These reactions are normal and go away within one to two minutes.

Once in a while, a patient will develop itching and hives for up to a few hours after the injection; this can be relieved with medication. Light-headedness or shortness of breath may be due to a more severe allergic reaction – a doctor or nurse will be nearby during the exam to help you, if needed.
Because CT uses X-rays, you may not have a family member or friend in the CT room during the exam.

Who interprets the results and how do I get them?

A radiologist skilled in CT scanning will review and interpret the CT findings. A detailed report will be sent to your doctor, who will give you the results. The radiologist will not discuss the results with you.