A Multimodal MRI-based Study Of Brain Abnormalities In Mild Cognitive Impairment

Mild cognitive impairment is defined as a syndrome with objective memory deficits.Patients with mild cognitive impairment largely retain general cognitive function and complete physical functional activity.It is a pathological transition stage between normal aging and Alzheimer’s disease,one of the most predominant neurological disorders with symptoms such as loss of memory,thinking and language skills.Although changes in whole-brain structural and functional information have been previously studied in mild cognitive impairment,structural-functional coupling abnormalities in whole-brain impairment are in urgent need of investigation.Previous studies have focused only on individual structural or functional indicators,and there are few studies on multimodal nuclear magnetic imaging abnormalities in structural and functional coupling parameters and magnetic resonance imaging signal complexity.In this paper,we used the OASIS-3 dataset,which included 53 subjects with mild cognitive impairment,90 subjects with very mild cognitive impairment,and 100 age-,sex-,and education-matched normal controls.Ratio analysis of low-frequency fluctuation amplitude to fractional low-frequency fluctuation amplitude,voxel-based morphometry and low-frequency fluctuation amplitude/voxel-based morphometry values and multiple brain entropies(scatter entropy,differential entropy,approximate entropy,fuzzy entropy,sample entropy,alignment entropy and Range entropy)were used to assess whole-brain abnormalities in structural,functional aspects of mild cognitive impairment.We derived the following experimental results:The amplitude of low-frequency fluctuations in these regions,distributed within the cerebellum and the gray matter of the nucleus accumbens,tended to increase progressively with increasing disease symptoms.Similar results were found in the frontal globus pallidus,the nucleus accumbens,and the paracentric lobule within the white matter.At the same time,the functional coupling between the parahippocampal gyrus and hippocampal structures in the gray matter gradually decreased with increasing disease symptoms,as well as in the cuneus and frontal lobes in the white matter.And it was also found that hippocampal parabrachial gyrus and hippocampal structural-functional coupling values were positively correlated with the severity of cognitive impairment,indicating the validity of structural-functional coupling indexes for the analysis of abnormalities in brain dysfunction as well.In the analysis of abnormal regions in early Alzheimer’s disease using the seven BENs,sample entropy performed the best,where sample entropy had an accuracy of 0.7in the classification between normal and diseased subjects(ACC=0.7864,SP=0.7497,SE=0.7298,AUC=0.6937).In the results of the two-sample t-test of sample entropy versus differential entropy for the normal versus disease group,the disease group showed significant differences in brain entropy in the hypothalamus,hippocampus,and right precuneus,right insula,right supramarginal gyrus,and right precentral gyrus compared to the normal group of subjects,and these brain regions also accounted for a greater weight in the SVM’s dichotomous classification task.In our study,these brain regions showed similar differences in low-frequency fluctuation amplitude and structural like metrics,as well as in multiple brain entropy analyses,further demonstrating that these brain regions are altered in the early stages of Alzheimer’s disease.These findings provide new information to study the pathophysiological mechanisms of Alzheimer’s disease and suggest the validity of structure-function coupling within whole brain regions with brain entropy in the medical diagnosis of cognitive decline in Alzheimer’s patients.The amplitude of low-frequency fluctuations in these regions,distributed within the cerebellum and the gray matter of the nucleus accumbens,tended to increase progressively with increasing disease symptoms.Similar results were found in the frontal globus pallidus,the nucleus accumbens,and the paracentric lobule within the white matter.At the same time,the functional coupling between the parahippocampal gyrus and hippocampal structures in the gray matter gradually diminished with increasing disease symptoms,as did the cuneus and frontal lobes in the white matter.In addition,hippocampal parabrachial gyrus and hippocampus structure-function coupling values were positively correlated with the severity of cognitive impairment,indicating the validity of the structure-function coupling index for the analysis of abnormalities in brain dysfunction as well.