Understanding diagnostic tests
CT / CAT Scan
A computed tomography scan uses X-rays and a computer to create detailed images. A head CT can help the healthcare team investigate structural problems, particularly when a rapid assessment is needed.
About this information
This webpage is subject to continuous review by Epilepsy Ontario to help keep the information current. This material is for informational purposes only and should not be used for self-diagnosis or as a substitute for professional medical advice, diagnosis, or treatment. Consult your healthcare provider about your own health and care.
Why might a CT scan be used?
A CT scan shows the brain’s structure. It can help identify concerns such as bleeding, injury, or a mass that may be relevant to a person’s symptoms.
CT is often useful in urgent assessment because images can be obtained quickly. MRI may be recommended later when more detailed imaging is needed.
CT looks at structure
It produces images of the brain and skull. It does not record the brain’s electrical activity.
EEG records electrical activity
An EEG answers different questions. The healthcare team may use both tests as part of an assessment.
A normal CT does not rule out epilepsy. Some causes are not visible on CT, and epilepsy can occur without a visible structural abnormality.
Before your scan
- Follow your centre’s instructions about eating, drinking, and medication.
- Tell the team if you are pregnant or might be pregnant.
- Report kidney problems and any previous reaction to contrast.
- Bring a medication list and explain any accessibility or communication needs.
- Remove jewellery and other items as directed.
Will I receive contrast?
Some CT examinations use an injected iodinated contrast agent to make particular structures easier to assess. Many head CT scans are performed without it.
If contrast is planned, the team will review relevant medical information. Report any breathing difficulty, swelling, or other concerning symptoms immediately.
Breastfeeding: Routine interruption is generally not required after standard intravenous iodinated contrast. Discuss your circumstances with the radiology team rather than following an automatic “stop for 24 hours” rule.
During the scan
You lie on a table that moves through the scanner’s short opening. You will be asked to remain still while images are collected.
The technologist monitors you and can communicate with you. The image collection is usually brief, although the full appointment may take longer.
Radiation and pregnancy
CT uses ionizing radiation. The team weighs the expected benefit against the radiation risk and adjusts the examination appropriately, including for children.
Pregnancy is not an automatic ban on a medically necessary head CT. Tell the team so they can assess the examination and explain the risks and benefits.
After your scan
Follow any instructions related to contrast or sedation. A radiologist reviews the images and sends a report to the referring healthcare provider.
Questions to ask
- What is the scan intended to investigate?
- Will contrast or sedation be used?
- Do I need to change anything before the appointment?
- Who will explain the results?
- Could an MRI or another test be needed afterward?
