The answer to this question will not be a simple 'yes' or 'no'.
Dementia involves loss of cells in the brain. This means certain parts of the brain are reduced in volume. And this can be identified with MRI.
MRI scan can also help differentiate between different types of Dementia, such as Alzheimer's Disease, Vascular Dementia, etc.
On the other hand, there are instances where the MRI may not show any abnormality while the person has symptoms of probable dementia. This may happen in the early stages of Dementia.
I hope I could throw some light on this.
Regarding your other question ("how is dementia diagnosed") in the same forum -
All the symptoms that a person may have are taken into account. The treating physician ( or a Neurologist/Psychiatrist/other specialist) tries to find out if the symptoms fit into any specific category/type of dementia. Accordingly, certain signs of dementia are looked for. This involves assessment of the functioning of brain (memory tests, etc.).
Once this initial information is gathered, the physician may order for scans (MRI / PET / etc.) of the brain and some other tests including laboratory tests. All the results are evaluated and a diagnosis is given.
I have found a good and simple article for you to read about dementia. It should be enough to get you started on the topic.
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