Diffusion tensor imaging in chronic head injury survivors: correlations with learning and memory indices.
ABSTRACT Diffusion tensor imaging (DTI) provides a unique insight into the cellular integrity of the brain. While conventional magnetic resonance imaging underestimates the extent of pathology following closed head injury, diffusion-weighted imaging has been shown to more accurately delineate the extent of cerebral damage. There have only been a few case studies of DTI in chronic head injury survivors. This study used DTI to investigate changes in anisotropy and diffusivity in survivors of head injury at least 6 months after their injury. The relationship between cognition and diffusion abnormality was also investigated. The voxel-based analysis revealed significant bilateral decreases in anisotropy, in major white matter tracts and association fibers in the temporal, frontal, parietal and occipital lobes. Statistically significant increases in diffusivity were also found in widespread areas of the cortex. A significant positive correlation was found between diffusivity and impairment of learning and memory in the left posterior cingulate, left hippocampal formation and left temporal, frontal and occipital cortex. The common pattern of abnormality despite heterogeneous injury mechanism and lesion location in the group suggests that these cellular changes reflect secondary insults. The importance of diffusion abnormalities in head injury outcome is emphasized by the significant correlation between a learning and memory index and diffusivity in areas known to subserve this cognitive function.
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ABSTRACT: Deficits in working memory are a common consequence of pediatric traumatic brain injury (TBI), and are believed to contribute to difficulties in a range of cognitive and academic domains. Reduced integrity of the corpus callosum (CC) following TBI may disrupt connectivity between bilateral frontoparietal neural networks underlying working memory. In the present investigation, diffusion tensor imaging (DTI) tractography of eight callosal subregions (CC1-CC8) was examined in relation to measures of verbal and visuospatial working memory in 74 children sustaining TBI and 49 typically developing (TD) comparison children. Relative to the comparison group, children with TBI demonstrated poorer visuospatial working memory, but comparable verbal working memory. Microstructure of the CC was significantly compromised in brain-injured children, with lower FA and higher axial and radial diffusivity metrics in all callosal subregions. In both groups of children, lower FA and/or higher radial diffusivity in callosal subregions connecting anterior and posterior parietal cortical regions predicted poorer verbal working memory; higher radial diffusivity in callosal subregions connecting anterior and posterior parietal, as well as temporal, cortical regions predicted poorer visuospatial working memory. DTI metrics, especially radial diffusivity, in predictive callosal subregions accounted for significant variance in working memory over and above remaining callosal subregions. Reduced microstructural integrity of the CC, particularly in subregions connecting parietal and temporal cortices, may act as a neuropathological mechanism contributing to long-term working memory deficits. The future clinical use of neuroanatomical biomarkers may allow for the early identification of children at highest risk for working memory deficits and earlier provision of interventions for these children.Journal of neurotrauma 04/2013; · 4.25 Impact Factor
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ABSTRACT: Abstract Objectives: To examine structural integrity loss in the fornix from 5-30 months after moderate and severe traumatic brain injury (TBI) using diffusion tensor imaging. Methods: MRIs were prospectively undertaken in 29 adults with moderate and severe TBI at two time points. Fractional anisotropy (FA) was calculated for the fornix (column/body, right crux and left crux) at 5 and 30 months post-injury. Results: Paired t-tests revealed significant FA reductions with large effect sizes across time in the column/body, p < 0.001, right crux, p < 0.001 and left crux, p < 0.001. Conclusions: These data contribute to the growing body of evidence that loss of white matter continues in moderate and severe TBI even after the acute neurological effects of TBI have resolved. As the fornix plays a critical role in memory, this may be a contributing factor to the poor clinical outcomes observed in these patients.Brain Injury 10/2013; · 1.51 Impact Factor