This prospective study was approved by the Ningde Hospital Medical Ethics Committee affiliated with Ningde Normal University.A total of 30 patients with Alzheimer’s disease who were hospitalized and clinically diagnosed in our hospital from January 2018 to December 2019 were included as the AD group; 30 patients with mild cognitive impairment and 30 healthy individuals without any neurological disease were selected as the MCI and control groups. Three groups of patients with sex, age, education time and other clinical data were not statistically significant (p > 0.05). Specific inclusion criteria were as follows: patients in the AD group met the diagnostic criteria of Alzheimer’s disease revised in the fourth edition of the American Manual of Mental Disease Diagnosis and Statistics, and the MMSE score was less than 24 points. Patients with MCI met the following criteria: 1) awareness of subjective cognitive decline in one year; 2) MMSE score greater than 24 points; 3) Montreal cognitive assessment less than 26 points; and 4) daily life ability scale less than 26 points. The informed consent was obtained from all subjects and from a parent and/or legal guardian as Vulnerable population in the studya, all methods were performed in accordance with the principles of the 1983 Declaration of Helsinki.
All MR images were obtained from a 3.0-T MR scanner (General Electric, Milwaukee, WI, USA) . The imaging protocol included axial three-dimensional brain volume imaging (3D T1WI), axial fast spin-echo (FSE) T2-weighted imaging (T2WI), axial T2 fluid attenuation inversion recovery (T2 FLAIR), and two SE echo-planar DWI sequences (TR msec/TE msec/excitations, 3,000/96/1; 23 sections; bandwidth, 250 kHz; section thickness, 3.0 mm; intersection gap, 0.3 mm; field of view, 240 mm×240 mm; matrix, 128×128; voxel resolution, 0.938×0.938×3.0 mm) applied in three or thogonal directions[16, 29]. The first DWI sequence was performed with standard b-values (0, 1,000 s/mm2), while the second DWI sequence was performed with 15 different b-values (0, 30, 50, 100, 200, 300, 500, 800, 1,000, 1, 500, 2,000, 3,000, 3,500, 4,000, and 5,000 s/mm2) [16, 30]. Eddy current correction was applied with real-time field adjustment and real-time correction of motion-induced phase error to obtain high-quality diffusion images. Spatial coverage for both DWI sequences was identical, from the lower margin of the pons to the upper margin of basal ganglia. The scan times for the sequence with standard b-values and the sequence with 15 b-values were 0.37 min and 6.85 min, respectively. The total scan time of the whole examination was approximately 14 min. Head pads were used to constrain head movement in both PD patients and control subjects.
WMH volume calculation
WMH volume was calculated using the AccuBrainTM analysis system (Shenzhen Bonao Medical Technology Co., Ltd., Hong Kong, China). AccuBrainTM is a new automatic quantitative measurement tool for brain structure. The DICOM format data of 3D T1 and T2 FLAIR of all patients were compressed into Zip format files and uploaded to the AccuBrainTM cloud system for image analysis. The template is then registered with the patient image in a nonrigid manner. After registration, the predefined tags in the map are transformed and fused to generate the segmentation tags of the patient, and the volume of each tag area is recorded. After approximately 25 minutes of processing, the system will automatically generate a PDF report containing patient information, brain volume and WMH volume information. This study included the absolute volume of WMHs and the relative volume of WMHs in the PDF report (the percentage of absolute volume of WMHs in total intracranial volume) for analyses.
Grading of WMH on MRI
On the basis of the Fazekas scale, WMHs were visually scored using FLAIR images in the periventricular and deep subcortical areas by one of the authors, who was blinded to the patient’s cognitive status. The intrarater reliability was represented with ICCs of 0.972 and 0.964 in the periventricular and deep subcortical areas, respectively. The severity of WMH in the periventricular area (PVWMH) was graded as follows: 0, no lesion; 1, cap or pencil-thin lining; 2, small halo; 3, irregular periventricular WMH extending into deep white matter. The severity of WMH in the deep subcortical area (DWMH) was graded as follows: 0, no lesion; 1, punctate lesion; 2, beginning confluence of lesion; 3, large confluence of lesion. Figure 2E demonstrates different grades of WMH in the periventricular and deep subcortical areas. Patients were defined as having WMH if there were any identifiable WMH regardless of severity or location (either grade of PVWMH≥1 or grade of DWMH≥1). Patients were defined to have PVWMH and DWMH if graded with any nonzero grade on the region-specific Fazekas scale (PVWMH or DWMH) regardless of severity.
Quantitative image analysis
All DWI data were transferred to a GE Advanced Workstation 4.4. UHBV-DWI software in GE Functool 9.4.05a was used to perform UHBV-DWI analysis.
The ADC map was calculated from the DWI sequence using the monoexponential model by fitting b values (0, 1000 s mm–2) to equation (1)
UHBV-ADC is calculated by fitting the five UHBVs (2000, 2500, 3000, 3500, 4000 and 4500 s/mm2) to equation (2)
T2 FLAIR was used to show the basic features of white matter hyperintensities, which were used to determine the ROI. ROIs were manually drawn on white matter hyperintensities with supporting workstation processing software, avoiding necrotic, cystic, or hemorrhagic components and adjacent normal brain tissue. The ROIs were drawn on one conventional image and automatically marked on UHBV-DWI (ADCuh) and DWI (ADC) images by UHBV-DWI software in GE Functool 9.4.05a in GE Advanced Workstation 4.4, and the corresponding area of the opposite side was drawn through the mirror image. The final ADCuh value represented the ROI of the overloading side/the ROI of the opposite side mirror (%).
Two experienced independent radiologists, who were blinded to the AQP results, performed ROI selection and measured each parameter value three times based on the criterion for the selection of ROIs, followed by calculating the total mean standard deviation.
Establishment and Test of Multiple Linear Regression Analysis Model
Through tidyverse, lattice, ggplot2 and caret package statistical analysis and drawing pictures. According to the independent variable to have a linear relationship with the dependent variable, the residuals are basically normally distributed. The residual variance is basically unchanged (homogeneity of variance). The residuals (samples) are independently correlated to test the model .
SPSS 22.0 statistical software was used for analysis. Continuous variables with a normal distribution are expressed as the mean ± standard deviation, and one-way analysis of variance was used. The classification variables are represented by percentages and tested by the χ2 test. The correlation of MRI results with AD was analyzed by Pearson correlation analysis. P < 0.05 was considered statistically significant.