Multimodal Magnetic Resonance Imaging-based Investigation Of The Mechanism Of Cerebral Small Vessel Disease Patients With Gait Disorder

Background:Cerebral small vessel disease（CSVD）is one of the most common types of cerebrovascular diseases,which may result in a series of clinical symptoms,such as cognitive impairment,emotional,urinary and fecal disorders and gait disturbance.In recent years,the motor symptoms caused by CSVD have attracted more and more attention.Gait disorder is the second most common clinical features of CSVD,only after cognitive impairment,which significantly increases the risk of falls and disability,and seriously affects the quality of life of patients.Therefore,it is of great significance to explore the occurrence and development mechanism of gait disorder in CSVD.At present,the neural network mechanism of gait disorder in patients with CSVD remains unclear.Previous studies have established the relationship between brain structural changes and gait disorders in patients with CSVD.However,little is known about the pattern of brain function changes in CSVD patients with gait disorders.The development of functional magnetic resonance imaging（f MRI）,especially the application of resting state functional magnetic resonance imaging（rs-f MRI）,provides us an important direction to study the neuropsychiatric diseases.Rs-f MRI explores the changes of brain activity at low frequency through a variety of analysis methods,such as brain local functional activity,functional connectivity and brain network attributes.Degree centrality（DC）is the most common research method based on graph theory in brain network analysis,while functional connectivity has been widely used to explore the functional correlation between brain regions,especially in neuropsychiatric diseases.In addition to resting state functional connectivity,in recent years,more and more studies have found that resting state functional connectivity is not absolutely ‘static’,but varies with time.Therefore,apart from analyzing resting state functional connectivity,exploration of the temporal variability of functional connectivity is conducive to a more comprehensive interpretation of the changes of brain function and possible pathophysiological mechanism in CSVD patients with gait disorders.Moreover,when the brain functional activity changes,the cerebral blood flow（CBF）will be regulated according to the energy demand and neuronal activity to maintain cell homeostasis and function,that is,neurovascular coupling.If the CBF does not match with nerve activity,the brain function will be destroyed.At present,the brain static and dynamic functional activities and neurovascular coupling mechanism of CSVD with gait disorder are still unclear.Objectives: Based on the above research status and previous research background,this study intends to apply multimodal magnetic resonance technology to explore the neural network mechanism of gait disorder of CSVD.（1）Study 1: To investigate the alteration of network node attributes and brain static functional connectivity in CSVD patients with gait disorder by DC and functional connectivity analysis.（2）Study 2: To explore the dynamic functional connectivity（DFC）patterns in CSVD patients with gait disorders by sliding time window method and cluster analysis.（3）Study 3: To explore the characteristics of neurovascular coupling in CSVD patients with gait disorders using CBF and mean fractional amplitude of low-frequency fluctuation（mf ALFF）,based on arterial spin labeling（ASL）and rs-f MRI.Methods:（1）Study 1: Seventy-five CSVD patients were enrolled from the Neurology department of the First Affiliated Hospital of Anhui Medical University.Thirty-two healthy people matched with gender,age and education were also collected as normal controls（HC）.Gait was assessed by Time up and go test（TUG test）and Intelligent Device for Energy Expenditure and Activity（IDEEA）.According to the gait examination results（TUG test）,CSVD patients were divided into CSVD with gait disorder group（CSVD-GD,n=31,TUG≥15s）and CSVD-non gait disorder group（CSVD-NGD,n=44,TUG<15s）.Rsf MRI was used to obtain blood oxygen level dependent signal（BOLD）parameters for DC analysis,and then functional connectivity analysis was performed based on DC results to detect the changes of functional connection between local brain region and remote brain region in CSVD patients with gait disorder.（2）Study 2: Based on the rs-f MRI data,the dynamic functional connection matrix of each subject was constructed by sliding window method,and k-means cluster analysis was performed to estimate the DFC states and parameters,and to explore the inter-group differences of functional connectivity of local brain regions in different states.Validated analysis was performed using different window widths and k values.Finally,the correlation between clinical scales and DFC parameters was investigated.（3）Study 3: The data of ASL and rs-f MRI were collected,and the parameters of CBF and mf ALFF were analyzed respectively.The CBF-mf ALFF coupling coefficient was then calculated in both whole brain and local brain level.Additionally,the CBF/mf ALFF coupling coefficients of CSVD patients in regions with inter group differences were extracted and used for further relationship analysis with gait parameters.Results:（1）Study 1: Compared with CSVD-NGD group,CSVD-GD patients presented significantly decreased DC in the left hemisphere,such as the left cuneus（CUN.L）,the left precentral gyrus（Pre CG.L）and the left inferior parietal lobule（IPL.L）,while the DC value was significantly increased in the right cerebral hemisphere,such as the right hippocampus（HIP.R）,the right angular gyrus（ANG.R）and the right thalamus（THA.R）.Compared with HC group,the DC value of CSVD-GD group was decreased significantly in multiple brain regions,such as Pre CG.L,CUN.L,THA.R,ANG.R,the right parahippocampal gyrus（PHG.R）and the left postcentral gyrus（Po CG.L）.Secondary seed-based functional connectivity analysis showed that compared with CSVD-NGD group,patients with CSVD-GD showed remarkably decreased functional connectivity in the Pre CG.L with regions in visual network,such as the left lingual gyrus（LING.L）,the left superior temporal gyrus（STG.L）,and in the attentional network,such as the left middle frontal gyrus（MFG.L）as well as in the motor network,such as the left middle cingulate cortex（MCC.L）.Reduced functional connectivity was also found in the CUN.L with region in visual network,such as the left superior occipital gyrus（SOG.L）,and the MCC.L as well as cerebellum.Further correlation analysis found that the abnormal DC value and functional connectivity in Pre CG.L and CUN.L were positively correlated with walking speed.（2）Study 2: DFC analysis showed two different connected states（State I: sparse connected state and State II: strong connected state）in all subjects.Compared with HC group,the proportion of State I in CSVD patients was increased,and the incidence was decreased in State II.In terms of temporal properties of DFC,CSVD patients showed significantly longer mean dwelled time（MDT）in sparse connected State I than HC group after adjusting gender,age,education and frame displacement（FD）values,but no significant difference of MDT was found in strong connected State II.CSVD subgroups analysis showed that the frequency of sparse connection State I in CSVD-GD patients was higher than that in CSVD-NGD group（65.44% vs.54.13%）,while the frequency of strong connected State II was lower than that in CSVD-NGD group（34.56% vs.45.87%）,but the difference was not statistically significant.The strength of connections analysis showed that compared with HC group,CSVD patients showed decreased strength of functional connectivity in temporal-occipital lobe in State I,especially in occipital lobe,while decreased in temporal lobe in State II.In the comparison of CSVD subgroups,it was found that compared with CSVD-NGD patients,the decreased internetwork and intra-network functional activities strength in CSVD-GD patients was mainly distributed in the frontal-temporal lobe and occipital lobe.In addition,the fractional windows of State I were negatively correlated with gait parameters（such as TUG,speed）.The correlation between the fractional windows and the clinical scales in the State II was opposite to that in the State I.（3）Study 3: At the whole brain level,the CBF-mf ALFF coupling coefficient in CSVDGD group（0.954 ± 0.012）was significantly lower than that in CSVD-NGD group（0.959± 0.009）and HC group（0.960 ± 0.006）（p=0.048;p=0.017）.At the regional level,compared with HC group,the CBF/mf ALFF ratio in the right precuneus（Pcu.R）and left middle occipital gyrus（MOG.L）were significantly lower in CSVD group,but significantly higher in the left caudate nucleus（CAU.L）,the right putamen（PUT.R）,the right anterior cingulate cortex（ACC.R）and the right supplementary motor area（SMA.R）.In the comparison of CSVD subgroups and HC group,it was found that CBF/mf ALFF ratio were decreased in CSVD-GD patients compared with HC group,which was mainly located in occipital brain regions,such as the right middle occipital gyrus（MOG.R）,the right cuneus（CUN.R）and Pcu.R,while increased in the left hippocampus（HIP.L）,PUT.R and CAU.L.Compared with HC group,CSVD-NGD patients showed increased CBF/mf ALFF ratio in the PUT.R and CAU.L,but decreased CBF/mf ALFF ratio in the Pcu.R.In the comparison of CSVD-GD and CSVD-NGD patients,no significant difference was found in CBF/mf ALFF ratio.Correlation analysis exhibited that the CBF/mf ALFF ratio in the Pcu.R,CAU.L and PUT.R was significantly correlated with speed;and in the Pcu.R,CAU.L and MOG.L was correlated with the step length.The CBF/mf ALFF ratio in the SMA.R was correlated with the variability of both gait speed and cadence.Conclusions:（1）Study 1: Our main findings presented the altered attributes of network nodes in multiple brain regions,and abnormal functional connections with attention network,motor network,especially visual network,which reflects the important role of attention and visuospatial integration function on motor controls in CSVD-GD patients.（2）Study 2: Our study showed that the frequency and MDT in sparse state were significantly increased in CSVD patients,especially in the CSVD-GD subgroup.The DFC alteration was closely associated with gait disorder in CSVD patients.（3）Study 3: CSVD-GD patients showed decreased CBF-mf ALFF at the whole brain level,and disrupted CBF/mf ALFF coupling in multiple local brain regions.The decreased CBF/mf ALFF coupling are mainly located in the occipital lobe,while the increased CBF/mf ALFF coupling are mainly located in the basal ganglia.