TORONTO - Using an MRI technique known as quantitative susceptibility mapping (QSM), Canadian researchers have found evidence of a biomarker that could help differentiate between normal aging and early cognitive decline, according to a study presented on Tuesday at the International Society for Magnetic Resonance in Medicine (ISMRM) annual meeting.
Despite a relatively small cohort of patients, the researchers believe the study offers promising evidence that QSM may show a correlation between the level of iron in certain brain regions and poor cognitive performance.
Lead investigator Dr. Armin Eilaghi and colleagues found evidence of significantly higher concentrations of iron in multiple areas of the brain in subjects who were considered normal but who scored low on a cognitive assessment, compared with subjects whose cognitive tests were rated as normal.
Dr. Armin Eilaghi from the University of Calgary.The results highlight "the potential value of the quantitative susceptibility mapping technique as an imaging-based technique to identify cognitive decline in its earlier stage," Eilaghi, a postdoctoral fellow at the University of Calgary, told AuntMinnie.com. The information "will be useful because treatment strategies for the disease are believed to be maximal, in terms of success and outcome, only when the disease is detected and we can manage it at its earliest possible time."
Magnetic susceptibility is an inherent property of brain tissue, and quantitative susceptibility mapping is used to quantify the amount of magnetic susceptibility within an MR image.
"There is also evidence in previous literature that the amount of magnetic susceptibility in deep gray matter is highly correlated with iron concentration in different areas of the brain," Eilaghi explained.
The ability to measure changes in regional iron concentrations in vivo could help researchers understand the specific events that lead to cognitive impairment, as well as provide a biomarker to detect such impairment early, he and his colleagues noted.
Therefore, the rationale behind this study, Eilaghi said, was to investigate mild cognitive impairment or early cognitive decline -- which is the presymptomatic phase of Alzheimer's disease -- using QSM as a potential imaging-based biomarker to determine the amount of iron-related susceptibility in deep gray matter.
The researchers imaged 49 presumed normal individuals (22 males, 27 females; mean age, 51 years ± 15) on a 3-tesla MRI scanner (Discovery 750, GE Healthcare). Subjects were excluded if they had a history of neurological disorders, had contraindications for MRI, or were claustrophobic.
Prior to the scans, subjects were given the Montreal Cognitive Assessment (MoCA) test to determine which individuals were considered normal or cognitively impaired. Forty participants had a score of 26 or greater and were considered cognitively normal, whereas nine had a score of less than 26 and were deemed cognitively impaired.
The researchers then used a custom software program (Cerebra-QSM, Calgary Image Processing and Analysis Centre) to create QSM images of the external and internal globus pallidus, putamen, caudate nucleus, red nucleus, and thalamus regions of the brain, which change with natural aging and are associated with cognitive impairment and Alzheimer's disease.
"We selected those regions because they were shown to change first with normal healthy aging and also with Alzheimer's disease," Eilaghi said
QSM findings
In comparing the two subject groups, the researchers found that magnetic susceptibility was significantly higher in the cognitively impaired individuals in four brain regions (the putamen, external and internal globus pallidus, and caudate nucleus), and the results trended toward a significant difference in the thalamus. After controlling for age, magnetic susceptibility was still significantly greater in the same four brain regions.
There also was a "significant correlation" between regional iron susceptibility and MoCA score in the putamen and external and internal globus pallidus.
"The take-home message is the amount of magnetic susceptibility or iron concentration in deep gray matter was significantly higher in multiple areas of the brain in the cognitively impaired group, compared to the normal group," Eilaghi said. "That highlights the potential value of the quantitative susceptibility mapping technique as an imaging-based technique to identify cognitive decline in its earlier stage."
"We can apply the same technique to different MRI machines," he added. "It has been used on 1.5-tesla, 4.7-tesla, and 7-tesla systems."
Eilaghi cited a few limitations of the study, including the need for evidence beyond failing the Montreal assessment test to determine whether a person is cognitively impaired.
