Contrast media in CT

What is contrast media?

CT contrast media is sometimes called “X-ray dye”. It is a colourless liquid that shows up very clearly on CT scans. The dye does not stain your body and is passed out in your wee.

Not all CT scans need contrast media. Please visit our resource about what a CT scan is for more information.

Why do I need contrast media?

The CT scanner is excellent at providing information on your bones and lungs, but some areas of the body do not show up very clearly on the scan. By giving you the contrast media, we can make some areas of your body show up in much more detail. This will help the doctors see the CT images and helps them understand what is going on in your body.

Am I okay to have contrast media?

A member of the x-ray staff called a radiographer will go through a checklist with you and your parents of carers to check if:

• you have had any problems with contrast media before
• you have asthma or any allergies, including hay fever
• you have a history of diabetes
• you have issues with your kidneys
• there is any chance you could be pregnant

If you do not have any of the above conditions, you should be ok to be given contrast. If you do have any of the above conditions, the radiographer will have to double check with a doctor that it is ok for the scan to go ahead.

How is the contrast media given to me?

The contrast media is usually injected into your veins through a cannula. Different types of scans need specific sizes of cannulas. Depending on the scan, contrast can also sometimes be injected into a central line, if you have one. If a cannula is needed for your test, you will be told when the appointment for the scan is made.

A doctor or radiographer will check that your cannula is working by passing a little bit of water through it. If the cannula is working correctly, then they will either inject the contrast through the cannula by hand, or attach your cannula to an automatic syringe pump.

Sometimes, you may be need to drink the contrast media instead of having it injected. If this is the case, the contrast will be mixed with water and given to you before the scan. The radiographer will explain how much you need to drink and over what period of time. You can add some squash to the mixture to give it a nicer flavour.

Will I feel anything?

Most children do not feel anything as the contrast is being injected.

Some people get a slight metallic taste in their mouth. It can make you feel warm over your body, and it can make you feel like you are weeing. These effects can last for around 20 seconds during and after the injection.

These effects are fairly common and pass quickly.

How long will the exam take?

CT scans are relatively quick and simple. They usually take 5 to 15 minutes, but can sometimes take a little longer.

You may be asked to attend early for your appointment so that a cannula can be put in place. The actual injection of contrast can take 10 seconds to 1 minute.

Once your injection finishes, you will need to be supervised for the next 30 minutes. The rest of the examination will be done during this time.

Once the scan is over, the radiographer will contact the ward to ask if a member of staff can take you back to your bed. If no one is available to escort you back, you will have to remain in the X-ray waiting area until the 30 minutes are up.

Are there any risks?

Like all medicine, there is a slight risk of side effects, but they are very rare.

The contrast may leak out of the blood vessel. Mild leakages can be treated with ice and compression, and will go away on their own.

Allergic reactions to contrast are very rare with the most serious reactions occurring within the 15 minutes following your injection. This is why you must remain supervised following your scan.

Your kidneys may struggle to cope with the contrast. This is why the doctors that request the scan and the radiographers will always check if you have any issues with your kidneys. You can help your kidneys process the contrast by drinking lots of water after the scan.