What brain scans help identify dementia type?
While a clinical diagnosis of dementia is primarily based on a person’s history and cognitive testing, brain imaging plays a vital role in identifying the specific underlying cause. In a clinical context, scans are used to look for structural changes, such as brain shrinkage or blood vessel damage, and in some cases, functional changes like reduced glucose metabolism. These physical markers help clinicians distinguish between Alzheimer disease, vascular dementia, frontotemporal dementia, and other rarer forms.
In the United Kingdom, the diagnostic pathway typically follows a structured approach, starting with more common structural scans before moving to advanced functional imaging if the subtype remains uncertain. This guide explores the different types of scans used in 2026, what they reveal about the brain, and how they contribute to an accurate diagnosis.
What we will discuss in this article
- The role of MRI and CT in identifying structural brain changes
- How specific patterns of atrophy point toward different dementia types
- The use of SPECT and PET scans for assessing brain function
- Identifying vascular damage and small vessel disease
- Advanced PET scans for detecting amyloid and tau proteins
- When specialist scans like DaTscans are required
- emergency guidance for identifying signs of health deterioration
Structural imaging: MRI and CT scans
Structural scans are the most common imaging tools used to rule out other conditions and identify patterns characteristic of specific dementias.
Magnetic Resonance Imaging (MRI)
MRI is generally the preferred scan for identifying dementia types because it provides high-resolution images of the brain structure. It is particularly effective at showing shrinkage in specific areas, such as the hippocampus in early Alzheimer disease. It can also detect subtle white matter changes and microinfarcts that are essential for diagnosing vascular dementia.
Computed Tomography (CT)
CT scans use X rays to create cross sectional images of the brain. While they offer less detail than an MRI regarding soft tissue shrinkage, they are faster and more widely available. In a clinical setting, a CT scan is often used to rule out other potential causes of cognitive decline, such as brain tumours, subdural haematomas, or large strokes.
Functional imaging: SPECT and PET scans
If structural scans do not provide a clear answer, specialists may request functional imaging to see how well different parts of the brain are working.
FDG PET and SPECT
These scans measure blood flow (SPECT) or glucose metabolism (PET) in the brain. Each type of dementia tends to have a specific functional signature:
- Alzheimer Disease: Often shows reduced activity in the parietal and temporal lobes.
- Frontotemporal Dementia: Characterised by reduced activity in the frontal and temporal lobes.
- Vascular Dementia: Shows a patchy, irregular pattern of activity corresponding to areas of poor blood flow.
Amyloid and Tau PET
In 2026, specialised PET scans can detect the buildup of amyloid plaques and tau tangles, the biological hallmarks of Alzheimer disease. While these are not yet standard for every patient, they are increasingly used in specialist research centres to confirm a biological diagnosis of Alzheimer disease.
Identifying specific dementia patterns
Clinicians look for focal areas of damage that are disproportionately affected early in the disease process.
| Dementia Type | Primary Scan Findings | Key Brain Regions Affected |
| Alzheimer Disease | Disproportionate atrophy | Hippocampus and parietal lobes |
| Vascular Dementia | White matter disease / strokes | Subcortical areas and white matter |
| Frontotemporal | Focal frontal/temporal atrophy | Frontal and temporal lobes |
| Lewy Body | Often minimal structural change | Generalised mild atrophy |
| Normal Pressure Hydrocephalus | Enlarged ventricles | Fluid filled spaces in the brain |
Specialist scans for movement disorders
If a doctor suspects dementia with Lewy bodies or Parkinson disease dementia, they may request a DaTscan. This specialized imaging test looks at the dopamine system in the brain. A reduction in dopamine transporter levels helps confirm these specific types of dementia and distinguishes them from Alzheimer disease.
To summarise
Brain scans are a cornerstone of the modern diagnostic process, helping clinicians move from a general diagnosis of dementia to identifying a specific subtype. From the structural detail of an MRI to the functional insights of PET and SPECT scans, imaging allows for the visualisation of the physical damage causing cognitive decline. While no scan can be used in isolation, combining these images with clinical history and cognitive tests ensures that patients receive the most accurate diagnosis possible, which is essential for accessing the correct treatments and support.
emergency guidance
While brain scans for dementia are typically scheduled appointments, certain sudden neurological changes require emergency action. Call 999 or seek immediate clinical help if a person experiences a sudden onset of extreme confusion, a total loss of speech, or weakness on one side of the body. These symptoms are often signs of an acute stroke or a brain haemorrhage, which require an emergency CT or MRI scan to determine the cause and start life saving treatment. Any rapid and severe drop in a person cognitive or physical ability is a medical emergency and must be assessed by an emergency medical team.
Will I definitely need a brain scan?
Not necessarily. If the clinical history and memory tests already provide a clear diagnosis, a scan may not be required, especially for very frail individuals.
Can a brain scan be normal if I have dementia?
Yes. In the very early stages of some dementias, such as Lewy body dementia, structural changes can be so subtle that they do not appear on a standard scan.
Are there any risks with these scans?
MRI and CT are generally very safe. PET and SPECT scans involve a small amount of radiation from a tracer injection, but the levels are low and the tracer leaves your body quickly.
How long does it take to get the results?
After the scan is performed, a radiologist must interpret the images and send a report to your specialist. This process can take anywhere from a few days to a couple of weeks.
Why did I get a CT instead of an MRI?
CT scans are often used if someone has a pacemaker or other metal implants that make an MRI unsafe, or if a fast result is needed to rule out an acute problem like a bleed.
Can scans tell how fast the dementia will progress?
While a single scan cannot predict the exact speed of decline, the extent of the damage shown can sometimes give clinicians an idea of the disease stage.
Authority Snapshot
Dr. Rebecca Fernandez is a UK trained physician with an MBBS and experience in general surgery, cardiology, internal medicine, gynecology, intensive care, and emergency medicine. She has managed critically ill patients, stabilised acute trauma cases, and provided comprehensive inpatient and outpatient care. In psychiatry, Dr. Fernandez has worked with psychotic, mood, anxiety, and substance use disorders, applying evidence based approaches such as CBT, ACT, and mindfulness based therapies. Her skills span patient assessment, treatment planning, and the integration of digital health solutions to support mental well being in 2026.
