MRI TECHNIQUE DETECTS EVIDENCE OF COGNITIVE DECLINE BEFORE SYMPTOMS APPEAR
A magnetic resonance
imaging (MRI) technique can detect signs of cognitive decline in the brain even
before symptoms appear, according to a new study published online in the
journal Radiology. The
technique has the potential to serve as a biomarker in very early diagnosis of
preclinical dementia.
The World Health
Organization estimates that dementia affects more than 35 million people
worldwide, a number expected to more than double by 2030. Problems in the brain
related to dementia, such as reduced blood flow, might be present for years but
are not evident because of cognitive reserve, a phenomenon where other parts of
the brain compensate for deficits in one area. Early detection of cognitive
decline is critical, because treatments for Alzheimer's disease, the most
common type of dementia, are most effective in this early phase.
Researchers recently
studied arterial spin labeling (ASL), a promising MRI technique that doesn't
require injection of a contrast agent. ASL measures brain perfusion, or
penetration of blood into the tissue.
"ASL MRI is
simple to perform, doesn't require special equipment and only adds a few
minutes to the exam," said study author Sven Haller, M.D., from the
University of Geneva in Geneva, Switzerland.
The study group
included 148 healthy elderly participants and 65 people with mild cognitive
impairment (MCI). The participants underwent brain MRI and a neuropsychological
assessment, a common battery of tests used to determine cognitive ability.
Of the 148 healthy
individuals, 75 remained stable, while 73 deteriorated cognitively at 18 months
clinical follow-up. Those who deteriorated had shown reduced perfusion at their
baseline ASL MRI exams, particularly in the posterior cingulate cortex, an area
in the middle of the brain that is associated with the default mode network,
the neural network that is active when the brain is not concentrating on a
specific task. Declines in this network are seen in MCI patients and are more
pronounced in those with Alzheimer's disease.
The pattern of reduced
perfusion in the brains of healthy individuals who went on to develop cognitive
deficits was similar to that of patients with MCI.
"There is a known
close link between neural activity and brain perfusion in the posterior
cingulate cortex," Dr. Haller said. "Less perfusion indicates
decreased neural activity."
The results suggest
that individuals with decreased perfusion detected with ASL MRI may temporarily
maintain their cognitive status through the mobilization of their cognitive
reserve, but will eventually develop subtle cognitive deficits.
Previous research done
with positron emission tomography (PET), the current gold standard for brain
metabolism imaging, found that patients with Alzheimer's disease had reduced
metabolism in the same area of the brain where the perfusion abnormalities were
found using ASL MRI. This points to a close link between brain metabolism and
perfusion, according to Dr. Haller.
ASL MRI has potential
as a standalone test or as an adjunct to PET for dementia screening, Dr. Haller
said. While PET can identify markers of Alzheimer's disease in the brain and
cerebrospinal fluid, it exposes the patient to radiation. ASL does not expose
the patient to radiation and is easy to perform in routine clinical settings.
"ASL might
replace the classic yet unspecific fluordesoxyglucose PET that measures brain
metabolism. Instead, PET could be done with the new and specific amyloid PET
tracers," Dr. Haller said.
The results also
support a role for ASL MRI as an alternative to neuropsychological testing.
The researchers plan
to perform follow-up studies on the patient group to learn more about ASL and
long-term cognitive changes.
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