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


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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    • "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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    ABSTRACT: A number of diffusion tensor imaging (DTI) studies have reported substantial white matter (WM) abnormalities in alcohol-dependent patients. These studies were usually performed in recovering alcohol-dependent patients who had been abstinent for days to several weeks. The current study was designed to examine WM microstructure and decision-making in a sample of long-term abstinent alcohol-dependent patients. The study included 12 subjects with alcohol dependence who had been abstinent for at least 6 months before testing and scanning and 13 healthy control subjects. The Iowa Gambling Task (IGT) was used to measure decision-making. We found that the long-term abstinent alcohol-dependent group had significantly higher radial and axial diffusivity (RD and AD, respectively) values in frontal, temporal and parietal WM than was found in the healthy control group despite showing no difference in fractional anisotropy (FA) values in comparison to controls. In conclusion, we found widespread WM changes in long-term abstinent alcohol-dependent patients compared with healthy controls. Our findings suggested that AD and RD should be included in analyses of DTI data in addition to the more commonly studied FA. In the current study, FA values of the detoxified alcoholics had recovered and were comparable to those of the controls, whereas significant changes in AD and RD were still observed in some clusters in the frontal, parietal and temporal lobes of detoxified alcoholics even after 27.8 months.
    Psychiatry Research: Neuroimaging 10/2014; 224(1). DOI:10.1016/j.pscychresns.2014.07.006 · 2.42 Impact Factor
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    • "In the thalamotomy group, mean FA was significantly decreased in the right SCP (leading to the operated thalamus) compared to the left SCP (leading to the non-operated thalamus) (t[5] "
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    ABSTRACT: Background This study set out to determine whether structural changes are present outside the thalamus after thalamotomy in patients with essential tremor (ET), specifically in the cerebellorubrothalamic tracts. We hypothesized that diffusion tensor imaging (DTI) would detect these changes. Methods We collected DTI scans and analysed differences in Fractional Anisotropy (FA) and Mean Diffusivity (MD) between the left and right superior and middle cerebellar peduncle in ET patients that have undergone unilateral, left, thalamotomy and ET patients that did not undergo thalamotomy (control group). We used classical ROI-based statistics to determine whether changes are present. Results We found decreased FA and increased MD values in the right superior cerebellar peduncle leading to the left, lesioned thalamus, only in the thalamotomy group. Conclusions Our study suggests long-term structural changes in the cerebellorubrothalamic tract after thalamotomy. This contributes to further understanding of the biological mechanism following surgical lesions in the basal ganglia.
    Parkinsonism & Related Disorders 05/2014; 20(5). DOI:10.1016/j.parkreldis.2014.02.020 · 3.97 Impact Factor
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    • "When considering studies analyzing DA, less consistent results make findings in this DTI metric more difficult to interpret (Agosta et al., 2011; O'Dwyer et al., 2011b; Huang et al., 2012). Although low DA has been related to axonal degeneration in rodent models (Song et al., 2003), a human histology study showed that DA follows a complex, non-monotonous trajectory of change after axonal injury (Concha et al., 2006), and DA has also been reported to increase with age (Madden et al., 2012). Thus, changes in DA seem more complex to interpret than the other metrics. "
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    ABSTRACT: Alzheimer's Disease has traditionally been regarded as a disease of the gray matter (GM). However, the advent of diffusion tensor imaging (DTI) has contributed to new knowledge about how changes in white matter (WM) microstructure in vivo may be directly related to the pathophysiology of AD. It is now evident that WM is heavily affected in AD, even at early stages. Still, our knowledge about WM degeneration in AD is poor compared to what we know about GM atrophy. For instance, it has not been clear if WM can be directly affected in AD independently of GM degeneration, or whether WM changes mainly represent secondary effects of GM atrophy, e.g. through Wallerian degeneration. In this paper, we review recent studies using DTI to study WM alterations in AD. These studies suggest that microstructural WM affection at pre-AD stages cannot completely be accounted for by concomitant GM atrophy. Further, recent research has demonstrated relationships between increased cerebrospinal fluid levels of Tau proteins and changes in WM microstructure indexed by DTI, which could indicate that WM degeneration in pre-AD stages is related to ongoing axonal damage. We conclude that DTI is a promising biomarker for AD, with the potential also to identify subgroups of patients with especially high degree of WM affection, thereby contributing to more differentiated pre-AD diagnoses. However, more research and validation studies are needed before it is realistic to use this information in clinical practice with individual patients. This article is part of a Special Issue entitled: The CNS White Matter.
    Neuroscience 02/2014; 276. DOI:10.1016/j.neuroscience.2014.02.017 · 3.36 Impact Factor
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