Advanced MRI technique confirms dementia risk

U.K. researchers have developed a unique diffusion-tensor MR imaging (DTI-MRI) algorithm to identify which patients with stroke-related small-vessel disease could progress to cognitive decline and possible dementia, according to a study published online September 12 in Stroke.

Called diffusion-tensor image segmentation (DSEG), the algorithm is designed to separate isotropic and anisotropic diffusion space into 16 distinct segments. The result is a DSEG map of microstructural tissue properties that detail areas of brain damage from small vessel disease after just one DTI scan.

Researchers believe that DSEG so far has proved to be an accurate marker of the severity of small-vessel disease, pinpointing individuals who will develop dementia within five years.

"Our study shows that DTI data can be used to generate a whole-cerebrum-based marker of small-vessel disease severity without the use of any other imaging modality or spatial averaging across individuals," wrote the authors, led by Owen Williams, PhD, from St George's University of London. "Consequently, DSEG provides a fast and reliable alternative to conventional makers of small vessel disease severity that may be used in a clinical setting without the use of advanced preprocessing."

DTI-MRI has been used to detect a number of biomarkers for small-vessel disease, such as white-matter hyperintensities and microstructural damage, gray-matter atrophy, and cerebral microbleeds and infarcts. In previous studies, Williams and colleagues summarized these abnormalities with a DESG score -- DSEG-θ -- that describes the microstructure of the whole cerebrum. They also determined that changes in DSEG-θ were related to the aforementioned small-vessel disease biomarkers but had not explored how DESG results might foretell future cognitive performance and dementia risk.

"Here, we test the hypothesis that baseline DSEG-θ scores and three-year change in DSEG-θ obtained from a cohort of patients with small-vessel disease will be significantly related to decline in executive function and information processing speed over a five-year period," they added. "We also assess the hypothesis that differences in baseline DSEG-θ parameters are associated with an elevated risk of developing dementia over time."

The researchers performed annual 1.5-tesla DTI-MRI scans (Signa HDxt, GE Healthcare) for three years and annual neuropsychological tests on 99 patients with small-vessel disease (mean age, 68.4 ± 10 years; range, 43-88 years) for five years. None of the subjects showed signs of dementia at baseline.

During follow-up, 18 participants (18%) developed dementia, with an average time to onset of approximately three years and four months. A review of DSEG-θ values show that both baseline DSEG-θ (hazard ratio, 3.331) and changes in DSEG-θ (hazard ratio, 3.905) over five years were associated with significant increases in the risk of dementia (p < 0.001).

Baseline DSEG-θ also correlated with declines in executive function and global cognition due to brain damage from small-vessel disease, all three of which were significantly greater in patients who developed dementia, compared with patients who did not progress to dementia.

"DSEG offers a highly accurate and sensitive marker of small-vessel disease severity in a single measure that can be used to distinguish between individuals who will and will not go on the develop dementia in a five-year period," Williams and colleagues wrote. "Furthermore, DSEG was highly related to small-vessel disease-related cognitive decline, even in individuals who did not convert to dementia. Taken together, these findings suggest that DSEG may be used as a clinical tool to monitor small-vessel disease progression in patients and predict risk of developing dementia."

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