CT or CAT Scan [Computerized (Axial) Tomographic Scan]

August 8, 2011

The CAT scan, also known as CT (Computed Tomography) imaging, is a safe and non-invasive procedure which uses low radiation X-rays to create a computer-generated, three-dimensional image of the brain. It provides detailed information about the structure of the brain.

The CT scan uses a narrow beam of X-rays, which pass through the head and hit a detector on the opposite side. The beam moves around the head and the detector moves with it. Since different brain tissues have different densities, each will block the X rays from reaching the detector to different degrees. These may reveal abnormalities (blood clots, cysts, tumours, scar tissue, etc.) in the skull or brain which may be related to seizures.

This allows physicians to examine this structure, section by section, as the test is being conducted. The CAT scan helps point to where a person’s seizures originate. The CT scan only shows what the brain looks like, not how it works. The scanning period is brief, safe and painless.

Before a CAT Scan

  • Dress your child in comfortable, loose-fitting clothing.
  • Remove any metal objects such as jewellery, belts, hairpins, hearing aids or glasses before going to the test centre. These objects  may degrade the clarity of the images.
  • If a contrast medium is going to be used, your child should not eat or drink anything four to eight hours before the test.
    • A contrast medium is a dye that may be given to your child orally or injected into his/her hand or arm. This fluid goes up to the brain and makes the scan easier to read.
    • Some people are allergic to particular contrast mediums. It is important to inform your doctor if your child has any allergies, especially to iodine.
      • You should also inform the doctor if your child has diabetes, asthma, a heart condition, kidney problems, or thyroid condition. These conditions may indicate a higher risk of iodine reactions.
    • Ensure your child knows to inform the technician if they feel any itching or shortness of breath after the administration of the contrast medium.
      • After the injection your child may feel flushed, have a metallic taste in his/her mouth, or feel nauseated.
      • Another mild reaction that can occur following the administration of iodine is itching over various parts of the body. This lasts from several minutes to several hours and is usually treated with medication.
      • More serious but less common reactions may include shortness of breath, swelling of the throat or other parts of the body. If your child has these reactions, they require immediate treatment.
    • A CAT scan still provides valuable information without administering a contrast agent. If your child is at risk of reaction to the contrast agent, the physician may decide not to administer it during a CAT scan.

During a CAT Scan

  • After the administration of the contrast agent, your child will be asked to lie down on a scanning table.
  • The technician will move to another room and then proceed to move your child into the scanner machine.
  • A series of X-rays will be taken by a camera, which will rotate around your child’s head.
  • It is important that your child lies completely still until the entire examination is complete.
    • Any movement will blur the image.
    • Your child may be asked to hold his/her breath during the scanning procedure to help to eliminate blurring of the images caused by the movements of breathing.
  • During the examination, your child will hear some noise from the machine and the CT table may move slightly. This will not cause any discomfort.
  • If your child has any questions or concerns throughout the examination, s/he can speak with the technologist via intercom.
  • You cannot accompany your child during the scanning process because the CT scanner uses X-rays. Only your child should be in the CT scanner room during the procedure.
  • The scan should be complete in about 15 to 20 minutes.

After a CAT Scan

  • Your child can return to his/her usual daily activities and resume his/her regular diet immediately after the scan unless instructed otherwise by the doctor.
  • If your child was given an injection and the injection site remains sore, you are encouraged to call your child’s physician.
  • You may need to monitor your child while returning from the test centre as the effects of the sedative may not have worn off yet.
  • A radiologist will interpret the images and send them to your child’s doctor who will review the results with you at a follow-up appointment. Additional tests or a treatment plan will be designed accordingly.

Important Considerations

  • If your child has allergies or has experienced discomfort because of any contrast agent previously, inform the technologist and the doctor before the examination.


  • Radiologists
    • interpret the CT images
    • send a report to the referring physician
    • administer or observe the contrast injection
  • CT technologists
    • operate computerized tomography scanner to produce cross sectional views of the body section being scanned
    • perform the examination under the supervision of the radiologist
    • may also administer the contrast injection


The CAT Scan is covered by the Ontario Health Insurance Plan (OHIP).

Click here to learn about other types of diagnostic tests.

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