Brain scans for dementia

Which brain scans are used to diagnose dementia?

Brain scans alone cannot diagnose dementia, rather they are used as a step in the process of diagnosing dementia. They can also be useful in diagnosing the type of disease that is causing the dementia. For more information on the other stages of the diagnostic process click here.

There are a number of brain scans which can be used to help to diagnose dementia, including:

Scans that show structural changes to brain tissue

  • CT (computerised tomography) also known as CAT (computerised axial tomography).

A CT scan uses x-rays to provide an image of your brain. A CT scan can show signs of brain shrinkage and can identify signs of a stroke or brain tumour, useful in identifying vascular dementia, which is often caused by strokes.

The scan can take up to 20 minutes and involves lying very still on a bed while the scanner passes over your head. The scanner is a ring so your whole body isn’t surrounded.

  • MRI (magnetic resonance imaging).

An MRI scan uses magnetic fields and radio waves to produce detailed images of the inside of the brain. An MRI scan is more detailed than a CT scan and shows signs of shrinkage in specific brain areas and provides information about blood vessel damage.

MRI scans can help to identify the type of disease causing the dementia. For example, blood vessel damage is the cause of vascular dementia whereas shrinkage of the frontal and temporal lobes is the cause of frontotemporal dementia.

The scan can take up to an hour to complete and involves lying very still on a bed while you are moved into the scanner, which can cause some people to feel claustrophobic. At certain times the machine makes loud tapping noises so you are given headphones to wear.

Scans that show changes in brain activity

  • SPECT (single photon emission computerised tomography)
  • PET (positron emission tomography)

These scans are often used if a CT scan or MRI scan has failed to identify the type of disease causing the dementia. They pick up on blood flow abnormalities and show which areas of the brain are more active than others.

They can take up to 30 minutes to complete and involves lying very still on a bed which is moved into the centre of a cylindrical scanner.

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