Image: Novel MRI approach identifies damage early in Alzheimer’s (Photo courtesy of Washington University School of Medicine in St. Louis)
An MRI scan of the hippocampus, the brain’s memory center, in an older person with no signs of cognitive decline and a person of similar age with mild Alzheimer’s has been analyzed with a new technique that shows where healthy brain cells have been lost. This novel MRI approach can identify brain cell damage in people at early stages of Alzheimer’s, before tissue shrinkage is visible on traditional MRI scans.
New research from Washington University School of Medicine in St. Louis (St. Louis, MO, USA) shows that a mathematical analysis of data obtained with a novel MRI approach can identify brain cell damage in people at early stages of Alzheimer’s, before tissue shrinkage is visible on traditional MRI scans and before cognitive symptoms arise. Alzheimer’s disease usually is diagnosed based on symptoms, such as when a person shows signs of memory loss and difficulty thinking. Up until now, MRI brain scans haven’t proven useful for early diagnosis in clinical practice. Such scans can reveal signs of brain shrinkage due to Alzheimer’s, but the signs only become unmistakable late in the course of the disease, long after the brain is significantly damaged and most people have been diagnosed via other means.
Alzheimer’s disease develops slowly over the course of two decades or more before symptoms arise. First the brain protein amyloid beta accumulates into plaques in the brain, then another brain protein - tau - coalesces into tangles and neurons begin to die. Finally, tissue atrophy becomes visible on MRI brain scans, and cognitive symptoms arise. People at early stages of the disease can be identified via amyloid-PET brain scans or by testing for amyloid in the blood or the cerebrospinal fluid that surrounds the brain and spinal cord, but such tests do not provide information on neuronal damage.
The new study relies on a new quantitative Gradient Echo (qGRE) MRI technique to show brain areas that are no longer functioning due to a loss of healthy neurons. While traditional MRI is capable of showing where damaged areas of the brain have decreased in volume, the qGRE technique goes a step further, detecting the loss of neurons that precedes brain shrinkage and cognitive decline. The study involved 70 people ages 60 to 90 who had completed extensive clinical and cognitive testing to assess their level of cognitive impairment. The participant group included people with no cognitive impairment as well as those with very mild, mild or moderate impairments. Each participant underwent either a PET brain scan or a spinal tap to gauge the amount of amyloid plaques in his or her brain. They also underwent MRI brain scans.
Researchers applied the qGRE MRI technique to scan the hippocampus, the brain’s memory center and one of the earliest affected brain regions in Alzheimer’s. Results showed the hippocampus often contained a viable tissue section with relatively preserved neurons and a dark matter dead zone virtually devoid of healthy neurons. These dark matter areas were present in people who tested positive for amyloid but were not yet experiencing symptoms, and they grew larger as the disease progressed. Compared with traditional MRI measures of brain atrophy, biomarkers for dark matter correlated much better with individual cognitive scores for very mild to moderate dementia.
Thus, the researchers documented the relationship between neuronal loss and Alzheimer’s symptoms using the non-invasive qGRE MRI technique in living patients. The research team also confirmed this relationship under the microscope by examining brain tissues that were donated after the death of a study participant. The postmortem examination showed that the neuronal loss in the hippocampus actually exceeds loss of tissue volume and that these changes are well reflected in MRI measures of dark matter.
PET brain scans are still the gold standard for detecting signs of Alzheimer’s, but the machines are expensive and seldom available for routine patient diagnosis, much less widespread clinical screening. PET scans also require the injection of a radioactive tracer for brain imaging. The qGRE MRI technique may be poised for early adoption since it is based on MRI technology that is widely available worldwide, is noninvasive and can be carried out without the use of radioactive tracers.
“This could be a new way to use MRI to diagnose people with Alzheimer’s before they develop symptoms,” said senior author Dmitriy Yablonskiy, PhD, a professor of radiology at the university’s Mallinckrodt Institute of Radiology. “The technique takes only six minutes to acquire data and can be implemented on MRI scanners that are already used worldwide for patient diagnostics and clinical trials.”
“Our qGRE test offers great potential as an early diagnostic tool for the preclinical stage of Alzheimer’s disease, thus providing a large window for therapeutic intervention,” Yablonskiy added. “It also has great potential as a noninvasive MRI technique available in a conventional clinical setting for the widespread screening that is necessary to get people with early Alzheimer’s into clinical drug trials.”
Washington University School of Medicine in St. Louis