Application Of DTI And Multi-Voxel MRS Reconstruction In Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of degenerative brain dementia. Early detection of AD is very important since the essential treatment is not available yet. Mild cognitive impairment (MCI) is known as a transitional state between normal aging and AD, which is associated with a significantly increased risk of developing AD compared to the normal eldly population without cognitive impairment. In this paper, we studied the application of magnetic resonance spectroscopy (MRS) and diffusion tensor imaging (DTI) technology in AD and MCI.Magnetic resonance spectroscopy (MRS) is a noninvasice neuroimaging techniques which can be used for qualitative and quantitative determination of in vivo brain metabolite concentrations in a variety of neurodegenerative diseases. Using multi-voxel MRS technique to observe changes in hippocampal tissue metabolite concentrations is an important tool for the differential diagnosis of AD and MCI. Decreased ratio of N-acetyl aspartate (NAA) and creatine complex (Cr), increased ratio of inositol (ml) and Cr, as well as increased ratio of ml and NAA have been reportd in many researchs of AD and MCI. In this paper, we studied the automatic identification method of AD and MCI based on multi-voxel MRS of hippocampus.32 patients with AD,30 patients with MCI and 42 normal cognition (NC) underwent multi-voxel MRS of hippocampus. NAA/Cr, ml/Cr and mI/NAA were extracted as input features to creat an automatic classification model by support vector machine (SVM). The results showed that the multi-classification model of SVM can effectively identify and distinguish patients with AD and MCI from subjects of NC. The accuracy of the model is 86.54% in this study. Therefore, the multi-voxel MRS of hippocampus can provide additional information for the early diagnosis of MCI and AD.Besides the gray matter atrophy, white matter damages and degeneration are also exist in patients with AD and MCI. Diffusion tensor imaging (DTI) is the only noninvasice neuroimaging techniques for studying cerebral white matter. DTI have reported anisotropic diffusion changes in different white matter regions in AD and MCI as measured by fractional anisotropy (FA) and mean diffusivity (MD).25 patients with AD,29 patients with MCI and 34 NC underwent DTI scanning by Achieva 3.0T TX MR in this study. The results of TBSS showed that, compared with NC, patients with AD demonstrated widespred decreased FA in most region of the FA skeleton, while patients with MCI showed regional decreased FA. The analysis of white matter tracts Atlas showed that patients with AD and MCI existed significant decreased FA and incresead MD in most of the tracts, while the white matter abnormalities are much heavier in AD. The results of automatic fiber quantification (AFQ) found that the white matter abnormalities are not widely distributed in the entire fiber tracts, but on a particular section of the bundle. The studies of DTI in AD and MCI showed the white matter abnormalities in AD and MCI. The change of FA and MC may reflect the severity of cognitive impairment, which can be used in the early diagnosis of AD.