Alzheimer's Disease and Molecular Imaging: Get the Facts

Alzheimer’s Disease and Molecular Imaging: Get the Facts
About Alzheimer’s disease
What MI technologies currently are available for
Alzheimer’s disease is the most common form of dementia—a general Alzheimer’s patients?
term that describes memory loss or other mental impairments serious The MI technology most commonly used in diagnosing and guiding treatment
enough to interfere with daily life. More than 5 million people are currently of Alzheimer’s patients is PET scanning. [See also “PET/CT scanning: Get The
living with Alzheimer’s—and experts predict this number could triple by Facts.”]
2050. Alzheimer’s usually sets in after age 60 and involves a progression
of symptoms, beginning with impairments in learning and memory and PET Scanning
later extending to every aspect of thinking, judgment and behavior. New
developments in molecular imaging technologies are contributing to our
understanding of Alzheimer’s disease and improving the ways in which How can PET scanning help Alzheimer’s patients?
Alzheimer’s disease (AD) is diagnosed. Early detection of AD through Specifically, PET scanning is a powerful tool for:
molecular imaging techniques will assist the development and evaluation
• Diagnosing Alzheimer’s earlier;
of medications to slow the progression of the disease and optimize patient
care.
• Differentiating Alzheimer’s disease from other types of dementia;
and
What are molecular imaging procedures, and how
• Monitoring the progression of the disease and the effectiveness
can they help Alzheimer’s patients?
of new therapies in clinical trials.
Molecular imaging (MI) procedures are highly effective, safe and painless
diagnostic imaging and treatment tools that present physicians with a How does PET scanning work?
detailed view of what’s going on inside an individual’s body at the cellular PET scanning is a molecular imaging procedure that allows physicians to
level. Most nuclear medicine procedures are molecular imaging procedures obtain three-dimensional images of what is happening in a patient’s body
using radioactive substances.
at the molecular and cellular level. For a PET scan, a patient is injected
with a very small amount of a radiotracer such as fluorodeoxyglucose (FDG),
The most commonly used molecular imaging procedure for diagnosing or which contains a sugar with a radioactive tag attached. The radiotracer is
guiding treatment of Alzheimer’s disease is positron emission tomography absorbed by the brain and will show the amount of sugar consumption in
(PET) scanning. Conventionally, the confirmation of Alzheimer’s is a long different regions of the brain. The brains of people with dementia consume
process of elimination that may take two to three years of diagnostic and less energy and therefore less sugar, and in patterns specific to the different
cognitive testing. However, MI technologies are now available that help types of dementia. In addition, radiotracers for amyloid plaques have been
physicians safely and painlessly identify abnormalities in the brain that developed recently that show the presence and extent of plaques in the brain.
indicate the presence of Alzheimer’s disease. [For more information on PET/
This allows for early detection of Alzheimer’s disease. Though still in clinical
CT scanning, please read SNM’s fact sheet “PET/CT Scans: Get the Facts” on trial, new PET tracers for amyloid plaque are expected to be available for
SNM’s Web site at http://interactive.snm.org/index.cfm?PageID=7988.]
patient care within a few years.

June 2009

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After the radiotracer is injected, the patient lies down on a table, and his or Does PET show promise for identifying those at risk
her head is moved to the center of a PET or PET/CT scanner. The PET scanner for developing Alzheimer’s disease?
is composed of an array of detectors that receive signals emitted by the Postmortem studies suggest that the amyloid plaques of Alzheimer’s are
radiotracer. Using these signals, the PET scanner detects the amount of present for as long as a decade before dementia sets in. The results of
metabolic activity while a computer reassembles the signals into images. several clinical trials indicate that PET imaging of amyloid plaques can
[For more information on PET/CT scans and how they work, visit “PET/CT identify patients destined to develop Alzheimer’s disease several years before
Scanning: Get the Facts.”]
the development of dementia. For example, researchers at the University of
Pittsburgh conducted a study of PET scanning with a radiotracer for amyloid
How accurate are PET scans in detecting Alzheimer’s plaques known as Pittsburgh Compound-B (PiB) in patients who had mild
disease?
cognitive impairment, a condition that often—but not always—precedes
Studies indicate that PET is very accurate at diagnosing Alzheimer’s disease Alzheimer’s disease. Using PET with PiB, the researchers tracked patients
and differentiating it from other types of dementia. In one recent study that with mild cognitive impairment for four years and found that only patients
included seven centers in the United States and Europe, investigators at with brain plaques developed Alzheimer’s. Other tracers are also being
the New York University (NYU) School of Medicine used optimized FDG-PET tested for this purpose.
analysis techniques to measure glucose metabolism in different regions of
the brain.1 More than 90 percent of the time, researchers were successfully Where can I get more information about Alzheimer’s
able to distinguish patients with Alzheimer’s disease from healthy subjects disease and molecular imaging?
and patients with other dementias such as frontotemporal dementia—an To learn more about Alzheimer’s disease, visit www.snm.org/facts. To learn
umbrella term for a diverse group of rare disorders that primarily affect the more about PET/CT scanning or other nuclear medicine procedures, visit the
frontal and temporal lobes of the brain—the areas generally associated SNM Molecular Imaging Center of Excellence (www.molecularimagingcenter.
with personality and behavior.
org).
How can PET scanning help in the long-term (Endnotes)
management of Alzheimer’s disease?
1 Journal of Nuclear Medicine, “Multicenter Standardized 18F-FDG PET
PET scanning can help physicians gain a clear understanding of the Diagnosis of Mild Cognitive Impairment, Alzheimer’s Disease, and Other
existence, progression and aggressiveness of the disease. Researchers Dementias,” Vol. 49, No. 3, 390–398, http://jnm.snmjournals.org/cgi/
are experimenting with several new treatments for Alzheimer’s disease. content/abstract/49/3/390.
Molecular imaging tools such as PET can help determine whether treatments
are working as intended. Molecular imaging may also help researchers learn
more about the causes of Alzheimer’s and how the disease progresses.
How long does it take to get PET scan results?
A trained radiologist or nuclear medicine physician will interpret the results
and write a report for the physician who ordered the tests. A verbal report is
available the day of the PET scan, and the written report is usually delivered
to the physician within two or three days.
Will insurance reimburse for PET scans?
Insurance companies will cover the cost of most FDG PET scans. Because
of the mounting evidence of the effectiveness of FDG PET/CT scanning for
the diagnosis and treatment of a wide range of cancers, coverage levels
continue to expand. Coverage for PET scans that measure brain amyloid
plaques is not yet available. For the most updated figures, check with your
insurance carrier or physician, as the levels at which Medicare reimburses
for PET are under review with CMS and subject to change.
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