The Study Of Diffusion Tensor Imaging On Detecting White Matter Alteration Of Aging And Alzheimer's Disease

This study is to investigate the effects of aging (ON) and early stage Alzheimer's disease (AD) on white matter (WM) integrity using diffusion tensor imaging (DTI). The main contents and results including: (1) DTI acquisition techniques were studied and optimized. We investigated the two main acquisition parameters of number of diffusion-encoding gradient directions (NDGD) and diffusion sensitized factor b value on the effects of WM quantitative measurements. In results, at the regions of interest (ROI) level, no significant differences were found for mean diffusivity () and fractional anisotropy (FA) among protocols,however, not for eigenvalues of diffusion tensor. At the voxel level, the correlation coefficients between the protocols between 21- and 31-NDGD protocols were higher in most locations. Signal-to-noise ratio (SNR) reduced with b increased. Apparent diffusion coefficient (ADC) and its SD had different change at certain b value range. (2) Post-processing techniques including Pre-postprocess of DTI, calculating DTI indices, and techniques for analysis and comparison of WM were established. Susceptibility artifacts were corrected by fieldmap method; eddy current artifacts and motion artifacts were corrected by registration method. DTI indices were calculated and their corresponding maps were created using home-developed software. The method for quantitative analysis and comparison of WM based on ROI was established by home-built software. (3) Thirty-eight subjects were evaluated. Five DTI indice values were computed and compared on different ROIs between old (18-ON)and young (20-YN) sbjects to investigate the effects of aging on WM integrity. The simple correlation analyses between DTI measurements and age were performed to estimate the relationships between WM alterations and age. The effects of age on WM change were investigated while controlling for brain volume change. The Results showed that compared with YN, ON showed that ,λ₁,λ₂ andλ₃ significantly increased in all ROIs, FA, however, significant decreased only in genu and body of Corpus Callosum. Correlation studies showed that ,λ1,λ₂ andλ₃ positively correlated with age in most ROI, and FA negatively correlated with age in genu and body of Corpus Callosum. There was still a significant correlation between age and WM change even controlling for brain volume change as age increasing. (4) 14 mildly impaired patients and 18 elder controls (ON) were included in these studies. Five DTI indices were computed and compared for different ROIs to investigate effects of early stage AD on WM alteration. 8 standard neuropsychological tests were performed and compared between AD and ON to evaluate basic cognitive capacities of AD. Correlation analysis was applied between DTI measurements and scores of neuropsychological tests. The Results showed that FA significantly decreased in posterior Corpus Callosum (CCP) and posterior parietal-temporal region (S2), significantly increased in CCP,λ₁ significantly increased in CCM,λ₃ significantly increased in CCP in AD patients. AD patients showed lower scores compared with ON in all neuropsychological tests. FA positively correlated with several tests scores mainly in CCP, S2, posterior cinguluim and superior longitudinal fasciculus;,λ₁,λ₂ andλ₃ negatively correlated with several tests scores in multiple locations. In the earlier stages of AD neuropathology not only affect on functioning, but also on white matter structure, and they have strong relationship.