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Concha, L., Gross, D. W., Wheatley, B. M. & Beaulieu, C. Diffusion tensor imaging of time-dependent axonal and myelin degradation after corpus callosotomy in epilepsy patients. Neuroimage 32, 1090-1099

Department of Biomedical Engineering, University of Alberta, Edmonton, Alberta, Canada
NeuroImage (Impact Factor: 6.36). 10/2006; 32(3):1090-9. DOI: 10.1016/j.neuroimage.2006.04.187
Source: PubMed

ABSTRACT

Axonal degeneration of white matter fibers is a key consequence of neuronal or axonal injury. It is characterized by a series of time-related events with initial axonal membrane collapse followed by myelin degradation being its major hallmarks. Standard imaging cannot differentiate these phenomena, which would be useful for clinical investigations of degeneration, regeneration and plasticity. Animal models suggest that diffusion tensor magnetic resonance imaging (DTI) is capable of making such distinction. The applicability of this technique in humans would permit inferences on white matter microanatomy using a non-invasive technique. The surgical bisection of the anterior 2/3 of the corpus callosum for the palliative treatment of certain types of epilepsy serves as a unique opportunity to assess this method in humans. DTI was performed on three epilepsy patients before corpus callosotomy and at two time points (1 week and 2-4 months) after surgery. Tractography was used to define voxels of interest for analysis of mean diffusivity, fractional anisotropy and eigenvalues. Diffusion anisotropy was reduced in a spatially dependent manner in the genu and body of the corpus callosum at 1 week and remained low 2-4 months after the surgery. Decreased anisotropy at 1 week was due to a reduction in parallel diffusivity (consistent with axonal fragmentation), whereas at 2-4 months, it was due to an increase in perpendicular diffusivity (consistent with myelin degradation). DTI is capable of non-invasively detecting, staging and following the microstructural degradation of white matter following axonal injury.

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    • "Age-related modifications for AD were less consistent (Bennett et al., 2010; Burzynska et al., 2010). The pattern of FA decrease/RD increase, also observed in pathological conditions such as multiple sclerosis (Roosendaal et al., 2009; Liu et al., 2012), certainly reflects demyelination process, whereas the pattern of FA decrease/AD decrease reflects axonal degeneration as observed in callosotomy condition (Concha et al., 2006). The aging brain is also characterized by the presence of White Matter Hyperintensities (WMH) observed on T2-weighted sequences. "
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    Full-text · Article · Feb 2016 · Frontiers in Aging Neuroscience
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    • "Under this assumption, RD increases reflect demyelination [68], while changes in AD are more complex and time-dependent. Decreases in AD are thought to occur in response to acute axonal damage and inflammation [69]; conversely AD increases reflect expanded extra-cellular spaces resulting from Wallerian degeneration and other more gross atrophic processes [70] [71]. However, we would caution against the over-interpretation of instances where, for example , AD was significant and RD was not. "
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    • "brain . Moreover , myelin abnormalities seem to be partially persistent in long - term abstinent alcohol - dependent patients . For example , Estilaei et al . ( 2001 ) showed a persistent phospholipid abnormality in the WM of alcoholics abstinent for 31 months . A decrease in AD is thought to reflect potential axonal injury ( Song et al . , 2003 ; Concha et al . , 2006 ) . Interestingly , we found that AD was also significantly higher in long - term abstinent alcohol - dependent patients than in healthy controls in the frontal , temporal and parietal WM . Changes in AD values are difficult to interpret because they depend in a complex way on the underlying tissue structure . One plausible explanation "
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