Coupling Of Brain Structural And Functional Network In Alzheimer’s Disease Based On Multimodal MRI

Alzheimer’s disease(AD)is a neurodegenerative disease that is clinically characterized by progressive memory impairment and loss of cognitive functions,considered a syndrome of disconnectivity among brain regions.It’s helpful to explore its pathological mechanism and find its biomarker for reducing the impact of AD on society,patients and families.AD is a diffuse brain disease,and the method of constructing brain network is gradually applied to AD research.The brain network analysis is based on structural connectivity(SC)or functional connectivity(FC).A large number of studies have independently used diffusion-tensor imaging(DTI)to construct SC or rest-state functional magnetic resonance imaging(f MRI)to construct FC,to reflect the changes in the topological properties of functionally connected networks or structurally connected networks.In addition to studying the independent role of FC and SC in AD,the relationship between FC and SC also needs to consider.Recently,researchers have argued that the functional network connections of the human brain are limited by the potential anatomical white matter pathway and interact with each other.The association between SC and FC,called structural–functional(SC-FC)coupling,whichcan describe the functional dynamics of the brain from a structural topological perspective and may detect subtle brain changes more sensitively than any single imaging modality.The article proposes two methods of association analysis between SC and FC,detecting the structure and function network of AD and control brain networks from different angles.The main research contents are as follows:(1)Look for the Rich-club organization of the brain network,conduct the SC-FC coupling study of the Rich-club organization,and reveal the relationship between the SC-FC coupling,Rich-club organization,and cognitive decline in AD patients.The results show the connection between important nodes in the brain network,called Rich-club organizations,affects the entire network.In this study,we first look for the Rich-club node of the brain network of AD patients,dividing the network node into Rich-club node and non-Rich-club node,as well as the edge of the network into three connections,nameed Rich-club connection(between Rich-club nodes),Feeder connection(between Rich-club and non-Rich-club nodes),Local connection(between non-Rich-club nodes).Next,the correlation analysis among Rich-club organization,network topology attributes and SC-FC coupling research based on Rich-club organization are further carried out.The results show that the overall SC level of AD patients decrease,and the number of SC-FC coupling of AD patients increase,indicating that the hierarchical structure of the AD patient’s brain network may be destroyed,resulting in abnormal integrated information transmission networks and functional network reorganization.(2)From the perspective of module structure and node,conduct SC-FC coupling research on module structure and node.Nodes in the same module in the brain network are closely connected,while nodes in different modules are sparsely connected.The study of the SC-FC coupling of different modules helps to understand the neurophysiological mechanisms associated with AD.Similarly,node-based SC-FC coupling research can more accurately find related brain regions affected by AD disease.In this study,the module structure of the brain network of AD patients is divided firstly,and the edges of the network are divided into different intra-module connections and inter-module connections.On this basis,the SC-FC coupling research based on the module structure is carried out.After that,a node-based SC-FC coupling study is conducted.The results show that the SC-FC coupling of some intramodule connections and inter-module connections of AD patients is significantly increased,but not all SC-FC couplings of the patient brain network are showing an upward trend.In the SC-FC coupling results based on node connection,the nodes with significant anomalies are distributed in the prefrontal lobe and parietal lobe.The results show that AD may break the hierarchical structure of the brain network,leading to the abnormality of information transmission network integration and functional network reorganization.(3)From the perspective of a dynamic network,conduct a dynamic SC-FC coupling study over time to reveal the dynamic changes of SC-FC coupling over time under the influence of disease.It is now generally believed that even the resting state FC is dynamic over time,while the underlying SC is relatively stationary.The different network states of FC appearing at different times in the static state show different levels corresponding to SC.The study of dynamic SC-FC coupling over time will be well worth exploring.Researchers use a sliding time window method to construct a dynamic functional network,and then couple it with a static structural network to study the dynamic SC-FC coupling.In this study,it is thefirst time to use the sliding time window method to build a dynamic functional network,and then couple it with a static structure network.Based on the three network levels of global network,Rich-club organization and module organization,we study dynamic SC-FC coupling.The results show that: in the dynamic coupling research,even in the static state,the functional network connection changes with time.Therefore,the emergence of functional networks with different network states shows different levels of correspondence with structurally connected networks.Based on the AAL brain atlas and BN brain atlas,this paper discuss the association research of brain structure and function network based on whole network,Rich-club tissue,module tissue and node in alzheimer’s disease.Then,from the perspective of a dynamic network,a study of dynamic SC-FC coupling over time is conducted.In summary,the current findings enhance the understanding of the neurophysiological mechanisms associated with MCI and AD,promoting a mechanical understanding of the dynamics of clinical presentation,contributing to the search for potential biomarkers that can be used with high sensitivity to detect subtle damage to brain connections.