Quantitative tractography metrics of white matter integrity in diffusion-tensor MRI

Abstract

We present new quantitative diffusion-tensor imaging (DTI) tractography-based metrics for assessing cerebral white matter integrity. These metrics extend prior work in this area. Tractography models of cerebral white matter were produced from each subject's DTI data. The models are a set of curves (e.g., "streamtubes") derived from DTI data that represent the underlying topography of the cerebral white matter. Nine metrics were calculated in whole brain tractography models and in three "tracts-of-interest" (TOI): transcallosal fibers, and the left and right cingulum bundles. The metrics included the number of streamtubes and several metrics based on the summed length of streamtubes in including some that were weighted by scalar anisotropy metrics and normalized for estimated intracranial volume. We then tested whether patients with subcortical ischemic vascular disease (i.e., vascular cognitive impairment or VCI) vs. healthy controls (HC) differed on the metrics. The metrics were significantly lower in the VCI group in whole brain and in transcallosal TOI but not in the left or right cingulum bundles. The metrics correlated significantly with cognitive functions known to be impacted by white matter abnormalities (e.g., processing speed) but not with those more impacted by cortical disease (e.g., naming). These new metrics help bridge the gap between DTI tractography and scalar analytical methods and provide a potential means for examining group differences in white matter integrity in specific tracts-of-interest.

A General Factor of Brain White Matter Integrity Predicts Information Processing Speed in Healthy Older People

“…While this does not mean that all tracts across the brain will show exactly the same degree of white matter integrity, thereby permitting some regional differences as in the well established age-related anteriorposterior gradient (Sullivan and Pfefferbaum, 2006), these results do suggest that individual differences in white matter integrity are to a substantial degree common to different tracts, not just a phenomenon that primarily affects specific individual tracts. Furthermore, while it has been shown in some studies that information processing speed relates to white matter integrity of the whole brain (Vernooij et al, 2009), broad regions of interest (Deary et al, 2006), and individual tracts (Correia et al, 2008;Turken et al, 2008), our study adds the novel result that it is shared integrity across tracts that is associated with speed rather than the integrity of specific tracts. Global tract integrity was exclusively associated with processing speed, but not with higher cognitive abilities like general intelligence and memory, perhaps because speed tends to be affected earlier in life by age-related decline (Salthouse and Ferrer-Caja, 2003;Finkel et al, 2007), whereas higher abilities are more likely to be maintained by compensatory processes (Park and Reuter-Lorenz, 2009).…”

Multimodal imaging of the self-regulating developing brain

“…Furthermore, forceps major is not assumed to be especially important for cognitive control. This assumption does not exclude the possibility that maturation of specific WM tracts can be related to more specific cognitive functions (57)(58)(59)(60), but it will likely also have general beneficial effects on major cognitive functions through facilitation of processing speed (61)(62)(63)(64)(65)(66)(67)(68)(69)(70)(71).…”

White matter changes with age utilizing quantitative diffusion MRI

“…6 This method is sensitive to white matter changes within entire tracts and thus may be more beneficial than methods that involve placing ROIs on 2-dimensional scalar DTI parameter maps. 6 In the present study, we utilized qtDTI tractography methods to examine the impact of aging on the white matter integrity in the brains among healthy older adults. All selected tracts have been previously associated with various factors related to age.…”