How do brain scans help with a dementia diagnosis?

There are several types of brain scans which might be used to diagnose dementia. Here's the key facts that are worth knowing

In a nutshell

When diagnosing dementia, brain scans are mainly used to rule out other conditions which may have similar symptoms to dementia, such as brain tumours and head injuries. Brain scans are sometimes recommended as part of a dementia diagnosis, but not always.

Three types of brain scans

Generally speaking brain scans (which are sometimes called brain imaging) don't hurt, but they can involve lying still for quite a while.

CT scan (computerised tomography)

This provides an image which is a detailed 'slice' of your brain. It can show if the brain has shrunk and reveal evidence of strokes, mini strokes and tumours. It can therefore be an effective way to diagnosis vascular dementia because vascular dementia is often linked to strokes.

What actually happens?
During a CT scan you lie on your side, on a table that slides into a small chamber whilst the machine scans your brain and takes images. It lasts around 20 minutes and is totally painless.

MRI scan (magnetic resonance imaging)

This provides more detailed images of your brain and gives even more detail than a CT scan about strokes, blood vessel abnormalities and tumours. MRI scans can be an effective way to reveal the damage caused to the brain by Alzheimer's.

What actually happens
During an MRI scan you lie on your side in a big tube-like machine which makes loud banging noises when it takes an image. An MRI scan is painless, however it can take an hour or more to complete. knowing what to expect (especially that the noisy machine sound is normal) can make the whole experience much easier to deal with.

SPECT scan or PET scan

A SPECT (single photon emission computerised tomography) or PET (positron emission tomography) scan is usually only used if the CT scan or MRI scan fail to reveal anything conclusive and are usually requested by a specialist. They both produce images that show how the organs actually work, revealing which areas of your brain are more or less active than others, and therefore which – if any – areas of the brain are being affected by dementia.

What actually happens
During a SPECT or PET scan you lie on a bed that moves into a doughnut shaped x-ray machine and produces 3D images of the brain. It takes around 30-40 minutes.

Did you know? A new brain scanning technique to rule out Alzheimer's is now available on the NHS. It involves giving the person a tiny amount of a radioactive chemical called Amyvid before scanning them. The chemical then shows up the plaques of Alzheimer's on the brain scan. However you will only be offered this sort of scan if your diagnosis of dementia is complex or unclear.

Brain scans: Your rights

Brain scans are not considered an essential part of a dementia diagnosis, so you aren't automatically entitled to receive one on the NHS. Dementia Guidelines by NICE (National Institute of Clinical Excellence) state that brain scans 'may not always be needed in those presenting with moderate to severe dementia, if the diagnosis is already clear.' The guidelines also say that if you want a brain scan your GP must provide 'detailed clinical information' suggesting why it is necessary.

In other words, those who are elderly, frail or already showing obvious signs of dementia you probably won't be offered a brain scan. But those who are young, or have symptoms which could also indicate other brain diseases such as tumours and cancers, should be referred to hospital for a scan, though the waiting times can vary from days to several weeks, depending on where you live.