Powered By
There are five main types of dementia — Alzheimer’s disease, Lewy body dementia (LBD), vascular dementia, frontotemporal dementia, and mixed dementia. Each affects the brain in different ways. Doctors often use imaging tests and other tools to help determine what type is causing cognitive dysfunction.
Like memory and blood tests, brain scans play an important role in the diagnosis of dementia. Imaging tests allow doctors to see which areas of the brain are affected. This crucial information supports an accurate diagnosis and helps ensure you get the right care.
This article explains how brain scans help doctors diagnose different types of dementia and what these scans might mean.
Neuroimaging lets doctors see the central nervous system — the brain and spinal cord. These tests help healthcare providers evaluate both the health of these vital body parts and how they’re working. Brain scans are neuroimaging tests that focus on the brain.
The most common brain scans used to help diagnose dementia are computed tomography (CT) and magnetic resonance imaging (MRI).
CT scans use X-rays to take many pictures of the brain from different angles. These images are combined to show detailed views of the brain structure. CT scans can detect brain atrophy (shrinking), changes in blood vessels, damage from strokes, tumors, or a buildup of blood or fluid.
MRI scans use magnets and radio waves to construct images of the brain. MRI can show the same details as a CT scan but it may be more helpful for spotting atrophy, stroke damage, blood flow abnormalities, and inflammation.
To aid in diagnosis, doctors may also use scans that assess brain function, such as:
Most of these scans tend to be used more often for research than in routine diagnosis.
If you have seizures, your provider may recommend an electroencephalogram (EEG). This test records the brain’s electrical activity, which is also linked to cognition.
Brain scans can help doctors determine the cause of cognitive decline. They’re also helpful for distinguishing between different types of dementia. Here’s how brain scan results can point the way to a dementia diagnosis.
Affecting nearly 7 million adults 65 and older in the U.S., Alzheimer’s disease is the most common form of dementia. Like other types, Alzheimer’s dementia is progressive — symptoms get worse over time.
Alzheimer’s disease is linked to two proteins that build up within the brain — amyloid and tau. Amyloid plaques and tau tangles damage and kill brain cells, causing the brain to shrink. Brain atrophy due to cell death can be detected by both CT and MRI. Compared to a healthy brain, a brain with Alzheimer’s dementia will appear smaller in areas where cell death has occurred. This usually happens first in the hippocampus.
PET scans can also reveal any amyloid plaques or tau tangles. Amyloid plaques appear red on a PET scan. A brain with Alzheimer’s may show more red areas than a healthy brain would. However, amyloid buildup can also be a part of the normal aging process, so amyloid plaques alone aren’t used to diagnose Alzheimer’s.
FDG PET scans look at how the brain uses glucose for energy. How well glucose is metabolized (processed) can affect cognitive function. In these scans, healthy brain metabolism appears blue and black, while impaired metabolism, such as in Alzheimer’s dementia, shows up as yellow, green, or red.
Lewy body dementia is another common cause of dementia. In this type, proteins called Lewy bodies build up in nerve cells within the brain, often in parts that help with memory, thinking, and movement. Someone with LBD may gradually appear less alert and attentive and even hallucinate (see things that aren’t actually there).
MRI and CT scans are typically used to rule out other causes of symptoms. Functional imaging is more helpful for diagnosing LBD. These tests include PET and dopamine transporter SPECT (DaT SPECT) scans.
In DaT SPECT scans, a tracer (special dye) is used to measure dopamine activity in the brain. Compared to a healthy brain, a brain with LBD usually shows less dye sticking to dopamine transporters. This reduced activity displays darker on the scan, while regular dopamine uptake looks bright. FDG PET scans can also show poor energy use in certain areas of a brain with LBD.
It’s important to know that imaging alone can’t diagnose LBD. Doctors consider scan results along with symptoms and other evaluations.
Vascular dementia is the sole cause of dementia in about 5 percent to 10 percent of older adults in North America and Europe. However, it often develops in people who also have Alzheimer’s disease. This type of dementia results from reduced blood flow to the brain and can be due to a number of reasons, such as stroke.
When the brain can’t get enough nutrients and oxygen from the blood, brain tissues can be damaged. MRI and CT can detect changes in the brain’s blood vessels and look for signs of stroke. Because vascular dementia often occurs with Alzheimer’s, a PET scan may also be used to check for amyloid plaques.
MRI or CT results vary depending on why and where damage occurred. One stroke may damage a single part of the brain, and a series of strokes can affect multiple areas. Strokes can affect the gray matter (outer brain tissues) or the white matter (inner tissues). Small vessel disease — the constricting of blood vessels, which impairs blood flow — may also damage the white matter. The symptoms of vascular dementia and what shows up on brain scans depend on which brain regions are affected.
Frontotemporal dementia causes 10 percent to 20 percent of dementia cases. This type is linked to conditions that affect the frontal and temporal brain lobes. These areas control behavior, language, and personality, so frontotemporal dementia can lead to symptoms such as impulsive behavior and personality changes.
Frontotemporal dementia causes the temporal and frontal lobes to shrink. MRI scans may be used to see the size and shape of these lobes. In frontotemporal dementia, these areas may look smaller or differently shaped than those in a healthy brain. Doctors may also use FDG PET scans to assess how the brain uses glucose and help pinpoint damaged areas.
As with other dementias, frontotemporal dementia can’t be diagnosed using only imaging.
Mixed dementia — having more than one type at the same time — is thought to occur in 10 percent or more of all dementia cases. The most common combination is Alzheimer’s disease and vascular dementia.
Brain scan findings in mixed dementia depend on which types are involved. For example, when Alzheimer’s and vascular dementias appear together, imaging may show amyloid or tau protein deposits along with blood vessel damage, poor blood flow, or other signs of chronic brain injury. In some cases, Alzheimer’s disease protein buildups may appear alongside Lewy bodies. Though rarer, it’s also possible to have Alzheimer’s, vascular, and Lewy body dementias all at the same time.
If your doctor suspects mixed dementia, the types of brain scans they recommend will depend on your symptoms, medical history, and other evaluations.
On myALZteam, people share their experiences with Alzheimer’s disease, get advice, and find support from others who understand.
What kind of imaging did your doctor use to diagnose your dementia? Let others know in the comments below.
Get updates directly to your inbox.
Continue with Facebook
Sign up with your email
Become a member to get even more
Join
We'd love to hear from you! Please share your name and email to post and read comments.
You'll also get the latest articles directly to your inbox.