What is a CT scan of the brain?

A CT scan can be used to diagnose a stroke and other brain problems, as Professor Joanna Wardlaw explains to Senior Cardiac Nurse Emily McGrath.

CT scan showing damage from a haemorrhagic stroke

CT scan shows damage from a haemorrhagic stroke (caused by a burst artery) in different layers of this patient’s brain

Why would I have a CT scan of my brain?

A CT scan of the brain is one of the first tests to diagnose a stroke or transient ischaemic attack (also called a TIA or mini-stroke). It’s used if you’ve had a knock to the head, or a suspected brain tumour, or to diagnose a leaking or burst aneurysm, which is causing bleeding on the brain. It can also be used to see what is causing frequent headaches.

It could also diagnose a previous stroke, so may be used during tests for dementia. This is because vascular dementia (the second most common type of dementia) is closely linked to stroke.

What will a CT scan tell my doctor?

A CT scan can also show whether a stroke is caused by a blood vessel that’s blocked by a clot, or by a blood vessel bursting. If the blood vessel is blocked, you will be given treatment to thin the blood or to dissolve the clot. But if a blood vessel has burst, you don’t want to do that, as it would make the bleeding worse.

A CT scan can also show whether a stroke is caused by a blood vessel that’s blocked by a clot, or by a blood vessel bursting

As well as diagnosis, a scan can be used to guide treatments. For example, if someone has just had a stroke, they could have a CT angiogram, where a CT scan is used to show the layout of the blood vessel and location of the clot, then the clot is removed with a tube (similar to an angioplasty you would have for a heart attack).

What does a CT scan involve?

CT scans are very straightforward. The scanner (pictured below) is like a big doughnut with a hole in the middle. The part of you that is being scanned will stay within the hole of the doughnut and the scanner will move up and down and make some whirring noises while you lie still. You might be asked to hold your breath a couple of times while the image is being taken.

In some cases, you will be given contrast dye beforehand, either as an injection or as a drink. This contains iodine and makes your body tissues show up more clearly on the scan.

How long will a CT scan take?

The actual scan is usually just a few minutes, though it can be longer in more complex cases.

Do I need to do anything to prepare for a CT scan?

Only if a contrast dye is needed, in which case you may be asked not to eat for a couple of hours beforehand to avoid nausea.

A CT scanner

Will a CT scan hurt?

No. If you need an injection of contrast dye you will feel a funny warm sensation as the dye is injected in. The warm feeling can be strongest around your groin, so you may feel like you are passing urine, but this won’t be the case and it only lasts for a few seconds. You might get a metallic taste in your mouth due to the iodine in the contrast dye.

What are the risks of CT brain scans?

In recent years, CT scanning has got faster (meaning patients don’t have to lie still for so long) and the radiation dose is lower

Regular CT scans expose you to a very small amount of radiation (a brain scan is a year’s worth of normal background radiation in the UK, which is a very small amount). More complex CT scans involve a higher level of radiation, but this is still considered safe. Some people could have an allergic reaction to the contrast dye, but this is very rare.

Is there anyone who shouldn’t have a CT scan of the brain?

Tell the doctor if you’re pregnant, as a different test could be considered. If you absolutely need the scan, your stomach can be screened off with a lead cover. The dye should not be used if you have kidney problems (your kidney function may be tested beforehand). If you are taking metformin for diabetes, it will need to be stopped 24 hours before having the dye.

What are the latest developments in CT scanning?

In recent years, CT scanning has got faster (meaning patients don’t have to lie still for so long) and the radiation dose is lower. Modern CT scanning can also create complex 3D images.

Professor Joanna WardlawProfessor Joanna Wardlaw

  • Professor of Applied Neuroimaging, Head of Division of Neuroimaging Sciences and Director of the Brain Research Imaging Centre, University of Edinburgh
  • Honorary Consultant Neuroradiologist at NHS Lothian
  • Author of more than 400 publications
  • Recipient of University of Edinburgh Chancellor’s award for research and the British Society of Neuroradiologists President’s medal
  • Her groundbreaking studies have changed how patients with stroke are treated all over the world

Discover Professor Wardlaw's research into lacunar stroke and dementia.

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