Definition Computed tomography of the brain is a non-invasive imaging method that combines x-rays with computer technology. X-ray beams from a variety of angles are used to create a series of detailed cross-sectional images of the brain.
Who is a candidate for the test? Computed tomography is an excellent method for viewing the structures of the brain. It can provide detailed images of several types of tissue including bone, soft-tissue and blood vessels. For this reason, it can be used to:
provide information on brain and central nervous system diseases such as encephalitis and general paresis from syphilis
is allergic to shellfish, or foods with added iodine such as table salt
has experienced claustrophobia, or anxiety in enclosed spaces. If this is a problem, mild sedating medication may be given.
A woman will be asked if there is a possibility she might be pregnant. Frequently, a urine pregnancy test will be performed on females of child-bearing age before the CT scan.
The person having the test will first need to remove items that can interfere with the images, such as wigs, hairpins, clips and removable dental hardware. The person lies on a flat platform.
The individual's head is placed in a special pillow to allow for comfort and to limit movement during the scan. The table slowly moves into the donut-shaped machine. When the table is in the appropriate position, the device delivers x-ray beams through the person's brain and skull from a variety of angles.
Frequently a special substance called a contrast agent is used to enhance internal brain structures and improve image quality on the final images. Typically, the contrast agent is injected into a vein in the arm.A conventional CT test takes between 10 and 45 minutes. The scanning process is painless. To prevent distortion of the final images, the person must lie still for the duration of the examination.
The contrast agent may cause mild nausea in some people. Flushing, itching and a metallic taste in the mouth are frequently described in patients who receive an injected contrast agent. Most of these sensations disappear within a few minutes.
After the test, the person will be asked to wait until the pictures are examined to see if any more images are needed. The person will be observed for any delayed reactions to the contrast agent. Also, the individual will be encouraged to drink extra fluids to help rid the contrast from the body.
What is involved in preparation for the test? The person having a CT will need to refrain from eating or drinking for at least 4 hours prior to the test. The CT technologist will explain the procedure to the individual. People who are prone to claustrophobia will be given a calming medication before the examination.
What do the test results mean? A doctor specially trained in analysing CT images, called a radiologist, will examine the results of the test. The radiologist will forward a report of the findings to the individual's personal doctor.
Some of the conditions a head CT can reveal include:
Author: Stephanie Slon, BA Reviewer: HealthAnswers Australia Medical Review Panel Editor: Dr David Taylor, Chief Medical Officer HealthAnswers Australia Last Updated: 1/10/2001 Contributors Potential conflict of interest information for reviewers available on request
