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- 저자 : GUO XIAOYI (검색결과 1 건)
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GUO XIAOYI 경희대학교 대학원 2022 국내석사
Background: Universal brain template like the International Consortium of Brain Mapping (ICBM) was not suited for application on high brain volume variability diseases, such as Alzheimer’s disease (AD) and mild cognitive impairment (MCI). Using imprecise templates may affect subsequent registration, segmentation, and normalization of obtained images. According to previous reports, AD patients have alteration not only in the brain volume but also in microvascular morphology and structure. Unfortunately, conventional imaging techniques do not demonstrate the microvascular alterations in AD, so that the diagnosis of microvascular pathology commonly relies on postmortem. It was difficult to study the changes of blood vessels in the early stage of the disease. Animal studies were currently demonstrating microvascular structural alterations using 9.4 Tesla MRI with ultra-small superparamagnetic iron oxide as a contrast agent that the contrast agent was not suitable for humans. Objectives: The entire purpose of this work has two folds. In the first part, I develop an AD-specific three-dimensional (3D) T1 brain tissue template, and then evaluate the characteristics of AD, MCI, and cognitively normal (CN) populations by using the created template. In the second part, using the created AD-specific template, I evaluate the alteration of the microvascular structure in AD patients using a 3T clinical MRI system with a commercially available contrast agent. Methods: For the first part of my work, 3D T1-weighted (3D T1W) images were obtained from 294 individuals, including 101 AD, 96 amnestic MCI, and 97 CN individuals. The 3D T1W image was segmented again into different brain tissues to generate AD-specific brain tissue templates. I performed voxel-based analyses and regions-of-interest (ROI)-based analyses to compare the gray matter volume (GMV) and white matter volume (WMV) among the three participant groups and to evaluate the relationship of GMV and WMV loss with age, years of education, and Mini-Mental State Examination (MMSE) scores. For the second part of my work, multi-echo turbo spin-echo (ME TSE) and multi-echo gradient-echo (ME GRE) images were obtained from 11 AD patients and 11 non-AD controls before and after Gd-based contrast agent injection to calculate R2 and R2* relaxation rate changes (∆R2 and ∆R2*). Using ∆R2 and ∆R2*, the following microvessel index maps were calculated: blood volume fraction (BVf), mean vessel diameter (mVD), mean vessel density (Q), vessel size index (VSI), and microvessel-weighted imaging (MvWI). The voxel-based two-sample t-test was used to compare those maps between the two groups, and the voxel-based multiple regression analysis was performed to evaluate the relationship between those maps and age or MMSE score. In addition, ROI-based analyses were also performed. Results: In the first part of my work, I created a high-resolution AD-specific tissue probability maps (TPM) and a template. I found that in the AD and MCI groups, both GMV and WMV were lost compared with CN group. Both GMV and WMV were lower with increasing age in CN, MCI, and AD groups. GMV was positively correlated with years of education in the CN groups. In MCI and AD groups, GMV of the hippocampus was significantly correlated with MMSE scores (left, r=0.710 and P<0.001; right, r=0.680 and P<0.001), while WMV of the corpus callosum showed a weak correlation (left, r=0.142 and P=0.015; right, r=0.123 and P=0.035). In the second part of my work, compared with the non-AD group, BVf and MvWI were significantly increased in the AD group. Both mVD and VSI were significantly decreased in the AD group. Q was increased, but not statistically significant. The results of the correlation analysis showed that ADC, BVf, and MvWI were significantly positively correlated with ages at some ROIs. Furthermore, VSI was significantly positively correlated with MMSE scores at the caudate (rho= 0.475/ P=0.030) and corpus callosum (rho= 0.435/ P=0.049). Conclusions: I created a 3D T1 brain tissue template using imaging data from CN, MCI, and AD participants considering the participants’ age, sex, and years of education. This disease-specific template can help evaluate brains to promote the early diagnosis of MCI individuals and promote future voxel-based research on AD. My work suggests that the microvascular index may be a useful non-invasive method to evaluate a microvascular morphology alteration. The microvascular morphology of AD was manifested as the vessel constriction and increasing the blood volume fraction, and was associated with MMSE scores.
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