http://www.biosciencetechnology.com/news/2014/12/imaging-shows-connection-breakdown-early-alzheimer%E2%80%99s-brains?
Changes in brain connections visible on MRI could represent an imaging biomarker of Alzheimer's disease, according to a new study presented at the annual meeting of the Radiological Society of North America (RSNA).
Alzheimer's disease is the most common form of dementia. As many as
5 million Americans are affected, a number expected to grow to 14
million by 2050, according to the Centers for Disease Control and
Prevention. Preventive treatments may be most effective before
Alzheimer's disease is diagnosed, such as when a person is suffering
from mild cognitive impairment (MCI), a decline in cognitive skills that
is noticeable but not severe enough to affect independent function.
Previous efforts at early detection have focused on beta amyloid, a
protein found in abnormally high amounts in the brains of people with
Alzheimer's disease.
For the new study, researchers looked at the brain's structural
connectome, a map of white matter tracts that carry signals between
different areas of the brain.
"The structural connectome provides us with a way to characterize
and measure these connections and how they change through disease or
age," said study co-author Jeffrey Prescott, radiology resident at Duke
University Medical Center in Durham, N.C.
Prescott and colleagues analyzed results from 102 patients enrolled
in a national study called the Alzheimer's Disease Neuroimaging
Initiative (ADNI) 2. The patients had undergone diffusion tensor imaging
(DTI), an MRI method that assesses the integrity of white matter tracts
in the brain by measuring how easy it is for water to move along them.
"It is known that water prefers moving along the defined physical
connections between regions in the brain, which makes DTI a great tool
for evaluating the structural connectome," Prescott said.
The researchers correlated changes in the structural connectome
with results from florbetapir positron emission tomography (PET)
imaging, a technique that measures the amount of beta amyloid plaque in
the brain. Increased florbetapir uptake corresponds with greater amounts
of the protein.
The results showed a strong association between florbetapir uptake
and decreases in strength of the structural connectome in each of the
five areas of the brain studied.
"This study ties together two of the major changes in the
Alzheimer's brain— structural tissue changes and pathological amyloid
plaque deposition— and suggests a promising role for DTI as a possible
diagnostic adjunct," Prescott said.
Based on these findings, DTI may offer a role in assessing brain
damage in early Alzheimer's disease and monitoring the effect of new
therapies.
"Traditionally, Alzheimer's disease is believed to exert its
effects on thinking via damage to the brain's gray matter, where most of
the nerve cells are concentrated," said Jeffrey Petrella, professor of
radiology at Duke and senior author on the study. "This study suggests
that amyloid deposition in the gray matter affects the associated white
matter connections, which are essential for conducting messages across
the billions of nerve cells in the brain, allowing for all aspects of
mental function."
"We suspect that as amyloid plaque load in the gray matter
increases, the brain's white matter starts to break down or malfunction
and lose its ability to move water and neurochemicals efficiently,"
added Prescott.
The researchers plan to continue studying this cohort of patients
over time to gain a better understanding of how the disease evolves in
individual patients. They also intend to incorporate functional imaging
into their research to learn about how the relationship between function
and structure is affected with increasing amyloid burden.
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