Alzheimer's disease (AD) classically presents with gray matter atrophy, as well as feature significant white matter abnormalities. Previous evidence indicates the overall burden of these pathological changes continues to advance as the disease progresses. The aim of this study was to investigate whether pathological alterations of white matter tracts correlate with the course of AD disease progression. 35 AD patients and 29 normal controls were recruited to the study and administered baseline magnetic resonance diffusion tensor imaging (DTI) acquisition and a cognitive function assessment at the time of initial evaluation. Subjects were re-evaluated with secondary DTI scan and cognitive function assessment at intervals of about 1.5 years on average. For the DTI acquired scans, we calculated diffusion tensor parameters, fractional anisotropy (FA), apparent diffusion coefficient (ADC), radial diffusivity (DR), and axial diffusivity (DA) along with the uncinate fasciculus (UNC), the inferior longitudinal fasciculus (ILF), and the inferior occipitofrontal fasciculus (IOFF). Compared to baseline, a significant mean FA reduction of the bilateral UNC, as well as a significant mean DR increase of the left UNC, was evident in AD patients at follow-up. Compared with normal controls, AD patients exhibited significant diffusion parameter abnormalities in their UNC, ILF, and IOFF. Taken together, these results indicate that progressive pathological white matter alterations can be quantified using the DTI parameters utilized here and may prove to be a useful biological marker for monitoring the pathophysiological course of AD.
Background: Neuroimaging studies show increased diffusivity and decreased anisotropy in Alzheimer's disease (AD) patients by diffusion tensor imaging (DTI). Previous reports have analyzed a correlation with cognitive function and DTI parameters, but their results are inconsistent. A reason for this might be a region of interest (ROI) method, used to calculate parameters for DTI, because this method has various usages of how to place a ROI and includes summations of values for various neuronal fiber tracts, resulting in contamination of unintended fibers. To improve the instability with ROI placement, a tractography-based method might be useful. Our coworker reported decreased fractional anisotropy (FA) and increased apparent diffusion coefficient (ADC) of uncinate fasciculus (UF) in patients with AD by tractography. To confirm whether DTI parameter values are related to severity of cognitive function in patients with AD, we measured mean diffusion anisotropy and diffusivity of coregistered voxels along the tracking lines (i.e. tract of interest) of UF. Methods: The subjects were 30 patients with probable AD (NINCDS-ADRDA criteria). Assessment of cognitive function was carried out according to the Mini-Mental State Examination (MMSE) and the Alzheimer's Disease Assessment Scale-cognitive component-Japanese version (ADAS-Jcog). A 1.5-T clinical magnetic resonance unit was used to obtain diffusion tensor images. Diffusion tensors were computed and fiber-tract maps were created using 'dTV II' DTI software developed by Masutani et al. We measured mean FA and ADC values along the bilateral UF. Results: FA values were positively correlated with MMSE score (r = 0.67) and were negatively correlated with ADAS-Jcog score (r = -0.62), while ADC values were negatively correlated with MMSE score (r = -0.58) and were positively correlated with ADAS-Jcog score (r = 0.59). Conclusion: FA and ADC values might reflect the severity of cognitive dysfunction. The tract-of-interest method might be a useful tool for objectively evaluating DTI parameters in AD.
BACKGROUND AND PURPOSE:Tract-based analysis can be used to investigate required tracts extracted from other fiber tracts. However, the fractional anisotropy (FA) threshold influences tractography analysis. The current study evaluated the influence of the FA threshold in measuring diffusion tensor parameters for tract-based analysis of the uncinate fasciculus in subjects with Alzheimer disease (AD).
Subjective cognitive impairment may be a very early at-risk period of the continuum of dementia. However, it is difficult to discriminate at-risk states from normal aging. Thus, detection of the early pathological changes in the subjective cognitive impairment period is needed. To elucidate these changes, we employed diffusion tensor imaging and volumetry analysis, and compared subjective cognitive impairment with normal, mild cognitive impairment and Alzheimer's disease. The subjects in this study were 39 Alzheimer's disease, 43 mild cognitive impairment, 28 subjective cognitive impairment and 41 normal controls. There were no statistically significant differences between the normal control and subjective cognitive impairment groups in all measures. Alzheimer's disease and mild cognitive impairment had the same extent of brain atrophy and diffusion changes. These results are consistent with the hypothetical model of the dynamic biomarkers of Alzheimer's disease.
The present study revealed that patients with bipolar disorder have microstructural abnormalities in the corpus callosum during depressed or euthymic states, which may deteriorate the exchange of emotional information between the cerebral hemispheres, resulting in emotional dysregulation. Our results indicate the possible use of diffusion tensor imaging as a differential diagnostic tool.
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