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Diagnosis of Alzheimer's Disease - Imaging Procedures and Psychological Evaluation

Rudolph C. Hatfield, PhD., edited by Kathryn Patricelli, MA

Imaging procedures

MRI scan of brain These are a group of tests that provide information about the shape, size, and health of brain structures, as well as how well the brain functions during activities. A CT scan (computerized tomography), and/or a MRI (magnetic resonance imaging) scan are used to look for:

  • brain tumors
  • blood clots
  • strokes
  • normal pressure hydrocephalus
  • other abnormalities that might account for Alzheimer's-like symptoms.

There are other scans, done in a clinic or hospital, that can show more detailed information and provide even clearer information. These include:

  • A PET scan (positron emission tomography)
  • a SPECT scan (single photon emission computed tomography)
  • a fMRI (functional magnetic resonance imaging test)

Here is a bit more information about each of these imaging procedures:

A CT scan produces a clear, two-dimensional image of the brain. It is used to detect brain tumors, blood clots, strokes, or damage due to head injury. CT scans are painless. However, they may be frightening to people who are claustrophobic (afraid of small, enclosed spaces). The procedure involves lying on a special table that is inserted into a chamber where the pictures are taken.

An MRI uses computer-generated radio waves and a strong magnetic field to produce a detailed image of the brain. MRIs are helpful in diagnosing tumors, infections, inflammation, and damage due to head injury. Like the CT procedure, an MRI requires the patient to lie on a table that is slid into a tube that holds the equipment which takes the images. Again, people who are uncomfortable in small, enclosed spaces, or who are obese, may be uneasy with this test. Also, because of the strong magnetic field involved, people with medical implants, such as pacemakers, should avoid having this test. MRIs take up to an hour to complete. They produce both two-dimensional and three-dimensional images of a far better quality than the images produced by a CT scan.

A PET scan provides both two- and three-dimensional pictures of brain activity by measuring radioactive isotopes. These are elements that attach to chemicals that flow through the brain that are injected into the bloodstream for the test. PET scans are used to detect tumors and damaged tissue, measure metabolism (chemical reactions that are the basis of brain function), and view blood flow in the brain. PET scans are often used as a follow-up to CT scans or MRIs to better understand what is happening in a certain part of the brain. After the isotope is injected into the bloodstream, the patient lies still while overhead sensors register the isotope's activity. The collected information is processed by a computer and displayed on a monitor or film. The length of time to complete a PET scan varies depending on the reason for the test (what conditions are being evaluated).

A SPECT scan integrates two technologies: CT scan and an injection of a radioactive material or tracer (similar to a PET scan procedure) to view how blood flows through arteries and veins in the brain. Two-dimensional or three-dimensional pictures can be produced that show areas of the brain that have reduced blood flow (areas of injury). The test is different from a PET scan because the chemical stays in your blood stream (rather than being absorbed by surrounding tissues). SPECT scans are cheaper and generally more easily available than PET scans.

An fMRI combines MRI and PET/SPECT technology. This produces a test that can measure brain activity by measuring changes associated with blood flow and areas of the brain while the person performs cognitive tasks. Increased blood flow to an area of the brain is taken to mean that that area is active during some activity. Decreased blood flow to an area of the brain that should be active during activity suggests that there may be brain damage or other issues associated with that area of the brain that lead to decreased cognition.

At the time of this writing there are other more advanced imaging techniques that are available to some doctors and may be used in some cases to assist in the diagnosis of dementia. However, the diagnosis of any form of dementia cannot be based solely on information provided by these scans alone. Moreover, PET, SPECT, and even fMRI scans are still more appropriate for research purposes than they are for formal diagnostic purposes.

Psychological/Psychiatric Evaluation

This is a collection of procedures that are used to obtain detailed information about past and current mood, thinking, or behavioral problems. The person with suspected Alzheimer's symptoms and the primary caregiver should be interviewed separately to gain a complete picture of what is going on. This "double interview" technique is particularly important when a person's memory for past and present information is impaired because he or she may accidentally provide inaccurate information during the interview. This evaluation should include an assessment for anxiety and depression. These conditions can create dementia-like symptoms in older people. They can also occur at the same time with Alzheimer's or another form of dementia. Depression can result in a reversible set of symptoms collectively known as pseudodementia (described in more detail later in this topic center).

People with depression often complain about memory problems and are upset about them, while people with dementia will often deny memory problems or minimize their importance. People with depression are less likely to exhibit large mood swings. They are more likely to remain "down in the dumps" most of the time. On the other hand, people with dementia usually show a range of emotions, and sometimes respond with an inappropriate emotion (laughing while others are sad). If a mood disorder such as depression is detected, it can be treated alongside other disorders, such as Alzheimer's.

Mental status exams assess memory, concentration, and other cognitive skills. This research-based set of questions results in a score representing a person's general level of cognitive functioning. This can assist in the diagnosis process and identify areas that may need further investigation.



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