Abstract
The aim of the study is to investigate the diffusion characteristics of Alzheimer’s disease (AD) patients using an ultra-high b-values apparent diffusion coefficient (ADC_uh) and diffusion kurtosis imaging (DKI). A total of 31 AD patients and 20 healthy controls (HC) who underwent both MRI examination and clinical assessment were included in this study. Diffusion weighted imaging (DWI) was acquired with 14 b-values in the range of 0 and 5000 s/mm2. Diffusivity was analyzed in selected regions, including the amygdala (AMY), hippocampus (HIP), thalamus (THA), caudate (CAU), globus pallidus (GPA), lateral ventricles (LVe), white matter (WM) of the frontal lobe (FL), WM of the temporal lobe (TL), WM of the parietal lobe (PL) and centrum semiovale (CS). The mean, median, skewness and kurtosis of the conventional apparent diffusion coefficient (ADC), DKI (including two variables, Dapp and Kapp) and ADC_uh values were calculated for these selected regions. Compared to the HC group, the ADC values of AD group were significantly higher in the right HIP and right PL (WM), while the ADC_uh values of the AD group increased significantly in the WM of the bilateral TL and right CS. In the AD group, the Kapp values in the bilateral LVe, bilateral PL/left TL (WM) and right CS were lower than those in the HC group, while the Dapp value of the right PL (WM) increased. The ADC_uh value of the right TL was negatively correlated with MMSE (mean, r=-0.420, p=0.019). The ADC value and Dapp value have the same regions correlated with MMSE. Compared with the ADC_uh, combining ADC_uh and ADC parameters will result in a higher AUC (0.894, 95%CI=0.803-0.984, p=0.022). Comparing to ADC or DKI, ADC_uh has no significant difference in the detectability of AD, but ADC_uh can better reflect characteristic alternation in unconventional brain regions of AD patients.
Highlights
Alzheimer’s disease (AD) is a progressive neurodegenerative disease
Correlations between the diffusion characteristics and Mini-Mental State Examination (MMSE) were evaluated using the Spearman’s rank correlation, and this step was performed in SPSS (IBM Corp, version 25.0)
In the BlandAltman analysis, there is no significant difference between the parameters of the two tests except for the Kapp kurtosis (Fig. 3). It was originally found in our study that the ADC_uh values of deep white matter (WM) in the bilateral temporal lobe (TL) of AD patients were higher than that of the healthy controls (HC) group. This is inspired by an earlier study where the apparent diffusion coefficient (ADC) value of averaged bilateral temporal stems of AD patients was reported to be higher than in healthy people [35]
Summary
Alzheimer’s disease (AD) is a progressive neurodegenerative disease. As reported by the World Health Organization (WHO), the prevalence of dementia in the world is estimated to be 50 million, and there are nearly 10 million new cases every year, with AD potentially contributing to 60–70% of these cases [1, 2]. It was reported that the herpesvirus may be the original reason for AD [14]. In this study, they found a high level of human herpesvirus (HHV-6A and HHV-7) in the brain regions that present AD neuropathological changes. Aβ in the brain can be cleaned by water transport, and a lack of AQP4 can decrease the clearance of soluble Aβ [9, 21]. Some scholars believe that ADC_uh reflects the transport of water via aquaporins, which might be linked to the expression of AQP4 [26, 27]. Compared to ADC, ADC_uh showed a relatively higher sensitivity to WM degeneration in AD [28]
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