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Overview
Computed Tomography (CT) is a medical imaging test that uses X-rays and computer technology to create detailed pictures of the inside of your body.
At The Ottawa Hospital, CT scans (also known as CAT scans) are performed by trained medical imaging professionals using advanced equipment. The scan is painless and usually takes only a few minutes. You may be asked to lie still on a table while the scanner rotates around you to capture images from different angles.
These images help your care team diagnose and monitor a wide range of health conditions.
Uses
A CT (computed tomography) uses many X-ray images from different angles and computer to produce cross sectional images.
This allows the radiologist (a physician specialized in radiology) to see inside the body. It is useful to view bone and soft tissues, which may not be well seen on a regular X-ray.
The X-rays are captured to show up as a picture on the computer monitor, usually in different shades of grey, although some scans are processed with colored images. A picture of your body is then created by the computer using the thin slices (cross-section).
A radiologist can see bone, muscle, organs, brain tissue, blood vessels and nerves with a CT scan.
Preparing for your CT scan
You may take your regular medication. Bring a list of everything you’re currently taking.
Take insulin as directed. You can eat a light meal after taking it.
Tell staff if you have any allergies, especially to iodine or contrast agents used in previous imaging tests.
Let staff know if you are pregnant or think you might be.
If you expect to receive an IV contrast injection, drink eight glasses of water in the 24 hours before your scan. You’ll be asked to drink more water after the test to help flush it out.
You do not need a full bladder. You may urinate before the exam. If you’re on fluid restrictions, call the CT Booking Office at 613-761-4831, option 1 (weekdays, 8 a.m. to 8 p.m.).
For abdomen or pelvis scans, you may need to arrive early to drink oral contrast. This can take up to two hours.
Please let staff know if you have an ostomy.
You may bring a flavour enhancer (like Crystal Light®) to improve the taste of the oral contrast. Avoid red-coloured drinks.
Fast for six hours before your test.
Wear clothes without metal zippers or studs. You may be asked to change into a hospital gown. Avoid bringing valuables.
Be ready to remove any pumps or devices that shouldn’t be exposed to radiation (e.g. insulin pumps).
Remove hair clips, glasses and removable dentures before the scan.
During your CT scan
A technologist will ask you to lie down on a narrow table. You may be asked to hold your breath briefly to help get clear images.
The table will slowly move into the CT scanner, which looks like a large ring. Inside, an X-ray tube rotates to take detailed pictures. You may hear clicking or whirring sounds during the scan.
The technologist will operate the scanner from a separate control room behind a leaded glass window. They can see and hear you at all times and will speak with you through an intercom. The scan can be stopped at any time if needed.
No one will be able to stay with you during the exam. This is because CT scans use X-rays, and others should not be in the room during the test.
Understanding contrast in CT scans
Contrast agents are used during some CT scans to help highlight specific areas of the body and improve the clarity of the images.
Breastfeeding and contrast agents
If you are breastfeeding and receive an IV contrast agent or gadolinium-based contrast for your scan, you can choose whether to continue breastfeeding or pause for a short time afterward.
Only a very small amount (1 per cent) of contrast passes into breast milk, and even less than 1 per cent is absorbed by your baby. Research shows it is safe to keep breastfeeding after the injection.
If you’re concerned, you may choose to stop breastfeeding for 24 hours. During that time, you can express and discard your milk. You may also want to pump and store milk before your scan to feed your baby during the break.
If you have questions, speak with your doctor or a lactation consultant at The Ottawa Hospital.
After your CT scan
If you received a contrast agent during your procedure, you’ll be asked to stay for 15 minutes so we can monitor you for any side effects. After that, the needle will be removed and you’ll be free to leave. If you were given a sedative to help with anxiety, you’ll need someone to take you home. You should not drive until the sedative wears off.
If you did not receive a contrast agent, you may leave right after your procedure.
You are welcome to ask the CT technologist how long it will take for your report to be ready.
Recovering at home
Your body will naturally remove the contrast agent through your kidneys. It will be stored in your bladder and passed when you urinate. Your urine will look the same as usual.
You can eat and drink normally after your scan. We recommend drinking a few extra glasses of water over the next 24 hours to help your body clear the contrast agent.
Keep an eye on the injection site. If it stays dry, you can remove the bandage or dressing after two hours, unless you were told otherwise.
The iodine in the contrast agent may affect some blood and urine test results. If you have tests scheduled within 48 hours of your scan, let your doctor know. If you have hyperthyroidism, your TSH levels may stay elevated for a month or longer after receiving contrast.
When to call your doctor
If you cannot reach your doctor, go to the nearest emergency department.
- You notice significant swelling or bleeding at the injection site.
- You develop hives or itching.
- You have trouble swallowing or breathing.