Doctors can use MRI or CT scans to help diagnose dementia or even detect signs of dementia before symptoms appear. But they’re not enough to diagnose dementia on their own.

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Brain scans are one of several diagnostic tests doctors can use to detect dementia. Some common types of brain scans include:

In general, imaging scans provide a visual of the brain that doctors can analyze for signs consistent with dementia.

This article explores what dementia looks like on a brain scan. We’ll also review the pros, cons, and steps involved in different types of imaging scans for dementia.

Dementia vs. Alzheimer’s

Dementia isn’t a specific condition. It refers to a group of symptoms that damage a person’s ability to remember, think, problem-solve, and communicate. It can also cause mood and personality changes.

Alzheimer’s is the leading cause of dementia. According to the National Institute on Aging, more than 6 million people live with Alzheimer’s in the United States alone.

Other types of dementia include vascular dementia and Lewy body dementia.

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The symptoms of dementia are linked to changes in brain structures and functions that doctors can see using imaging techniques such as MRI, CT, and PET. But the changes vary slightly from one type of dementia to the next.

Brain atrophy (shrinking) is widespread in most types of dementia. A doctor may be able to identify the type of dementia by looking for a specific pattern of atrophy. For example, frontotemporal dementia typically causes atrophy of the frontal and temporal areas of the brain.

Alzheimer’s disease may be due to changes in the hippocampus, a part of your brain involved in memory and learning. The hippocampus of a person with Alzheimer’s typically appears shrunken (atrophied) on a brain scan.

Vascular dementia, on the other hand, results from long-term disease of the blood vessels in your brain. This can cause multiple strokes that lead to a buildup of damage and a decline in cognitive function. Doctors might use MRI or CT scans during the diagnostic process to look for evidence of a stroke.

Finally, dementia with Lewy bodies often occurs alongside Parkinson’s disease. In this case, imaging studies from PET scans can reveal changes to your brain’s dopamine-producing areas.

Doctors use MRI and CT scans to detect changes that may help during the diagnosis of dementia. Each method has its advantages and disadvantages. Here are a few key differences:

  • Risks: MRIs use radio waves to detect brain structures. Radio waves are not known to have any risks. CT scans use X-rays, so they involve exposure to a small dose of radiation.
  • Duration: MRIs take longer to administer than CT scans. They aren’t usually the best option for people who can’t stay still for a long time and are medically unstable.
  • Image: MRIs capture more detailed brain images than CT scans. MRI might be the better option when brain changes are less obvious, such as during early-stage dementia or after a minor stroke.
  • Contraindications: MRI scans aren’t necessarily suitable for people with certain medical implants, such as artificial joints and pacemakers.
  • Cost: MRIs are costlier than CTs. A CT scan might be the better choice if cost is an issue.

It’s also possible your doctor will recommend another type of scan to help in dementia diagnosis.

PET scans are slightly different from MRIs and CTs. They help doctors visualize brain functions as opposed to structures. They might observe changes in brain function that might develop during the early stages of dementia.

Doctors can adjust PET scans to the machine detects different aspects of brain function. Sometimes, they can inject a substance so the scan shows the function in a specific brain area.

Can brain scans diagnose dementia early?

Brain changes linked to dementia may be visible on imaging scans in the early stages of the disease. In some cases, they might even be noticeable before symptoms appear.

Doctors can use amyloid PET scans to diagnose early dementia. These detect amyloid plaques in the brain, a key component of Alzheimer’s disease. Doctors use this technique to confirm an Alzheimer’s diagnosis in someone experiencing early symptoms.

But other tests are necessary to detect Alzheimer’s in someone with amyloid plaques but no symptoms. This is because some people with amyloid plaques never develop symptoms at all. Some people also have a clinical diagnosis of Alzheimer’s but don’t have these changes on a PET scan.

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Brain scans are noninvasive procedures. Healthcare professionals usually perform them on an outpatient basis in hospitals or radiology clinics.

Before the brain scan, medical staff might ask you to wear a hospital gown. If contrast dye is required, a healthcare professional will insert it through an IV line.

For most scans, you’ll lie on a long table that slides forward so the scanner is above your head. The machine or a technician will then take the required images of your brain while you remain still.

Most CT scans are over in a matter of minutes. Brain MRIs take between 30 and 60 minutes.

A brain scan typically isn’t enough to diagnose dementia on its own. Doctors use brain scans and other tests to verify a dementia diagnosis.

Some other sources of information used to detect and diagnose dementia include:

  • Symptoms and history: A doctor will ask you or a loved one to describe your symptoms and how they affect you daily. They’ll also ask about your medical and family history.
  • Physical examination: The doctor will examine your body to rule out other potential causes of your symptoms.
  • Mental ability tests: The doctor might administer tests that measure your ability to problem-solve, pay attention, or remember. These tests can help reveal dementia-related changes in cognition.
  • Laboratory tests: The doctor may use other standard lab tests, such as blood or urine samples, to look for the cause of your symptoms. Cerebrospinal fluid (CSF) testing can help rule out dementia by detecting changes consistent with other diseases, such as meningitis or encephalitis.

Early indications of dementia

Dementia can take many forms. Although memory loss is a well-known symptom, it’s not always the first sign of dementia. And most people experience lapses in memory from time to time.

Some other early signs of dementia include:

  • apathy
  • confusion
  • difficulty communicating
  • frustration
  • incomplete tasks
  • mood or personality changes
  • poor attention span
  • poor judgment
  • poor sense of direction

If you or a loved one is experiencing one or more of the symptoms listed above, consult a doctor.

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Brain scans are a helpful tool for detecting dementia, with CT and MRI scans among the most frequently used techniques.

Both types of scans can provide an image of the brain, which allows your doctor to spot areas of atrophy, stroke, or other damage.

PET scans look at brain activity. They are less common in clinical practice but may help diagnose early-stage dementia.

A neurologist can recommend the best scan for you or your loved one.