目的:众所周知,阿尔茨海默病痴呆(ADD)可引起脑结构和功能连接的改变。然而,报告的连通性变化主要限于全球/本地网络功能,用于诊断目的的特异性差。随着机器学习的最新进展,深度神经网络,特别是基于图神经网络(GNN)的方法,在大脑研究中也有应用。GNN的大多数现有应用程序都采用单个网络(单模或结构/功能统一),尽管广泛接受的观点认为大脑的结构连接和神经活动模式之间存在着不平凡的相互依存关系,据推测在ADD中受到干扰。通过提出的“结构-功能差异学习网络”(sfDLN)将这种破坏量化为差异得分,并在临床认知能力下降的范围内研究其分布。测量的差异评分被用作诊断生物标志物,并与现有技术的诊断分类器进行比较。
方法:sfDLN是一种具有连体结构的GNN,其基础是结构和功能连接模式之间的不匹配在认知衰退范围内增加,从主观认知障碍(SCI)开始,通过中期轻度认知障碍(MCI),最后添加。使用基于扩散MRI的纤维束成像技术构建的结构性脑连接体(sNET),使用fMRI构建的稀疏(精益)功能性大脑连接体(NET)输入到sfDLN。对暹罗sfDLN进行训练,以提取符合所提出假设的连接体表示和差异(差异)得分,并在MCI组上进行盲目测试。
结果:sfDLN产生的结构-功能差异评分显示ADD和SCI受试者之间存在很大差异。在42名受试者的队列中,SCI-ADD分类的leave-one-out实验达到88%的准确率,在文献中超越了最先进的基于GNN的分类器。此外,一项由46名MCI受试者组成的队列的盲法评估证实了MCI组的中介特征.用于调查观察到的差异的解剖学决定因素的GNNExplainer模块证实了sfDLN在神经上与ADD相关的皮质区域。
结论:支持我们的假设,大脑的结构和功能组织之间的协调随着认知衰退的增加而退化。这种差异,显示根植于神经上与ADD相关的大脑区域,可以通过sfDLN进行量化,并且在用作生物标志物时优于最先进的基于GNN的ADD分类方法。
OBJECTIVE: Alzheimer\'s disease dementia (ADD) is well known to induce alterations in both structural and functional brain connectivity. However, reported changes in connectivity are mostly limited to global/local network features, which have poor specificity for diagnostic purposes. Following recent advances in machine learning, deep neural networks, particularly Graph Neural Network (GNN) based approaches, have found applications in brain research as well. The majority of existing applications of GNNs employ a single network (uni-modal or structure/function unified), despite the widely accepted view that there is a nontrivial interdependence between the brain\'s structural connectivity and the neural activity patterns, which is hypothesized to be disrupted in ADD. This disruption is quantified as a discrepancy score by the proposed \"structure-function discrepancy learning network\" (sfDLN) and its distribution is studied over the spectrum of clinical cognitive decline. The measured discrepancy score is utilized as a diagnostic biomarker and is compared with state-of-the-art diagnostic classifiers.
METHODS: sfDLN is a GNN with a siamese architecture built on the hypothesis that the mismatch between structural and functional connectivity patterns increases over the cognitive decline spectrum, starting from subjective cognitive impairment (SCI), passing through a mid-stage mild cognitive impairment (MCI), and ending up with ADD. The structural brain connectome (sNET) built using diffusion MRI-based tractography and the novel, sparse (lean) functional brain connectome (ℓNET) built using fMRI are input to sfDLN. The siamese sfDLN is trained to extract connectome representations and a discrepancy (dissimilarity) score that complies with the proposed hypothesis and is blindly tested on an MCI group.
RESULTS: The sfDLN generated structure-function discrepancy scores show high disparity between ADD and SCI subjects. Leave-one-out experiments of SCI-ADD classification over a cohort of 42 subjects reach 88% accuracy, surpassing state-of-the-art GNN-based classifiers in the literature. Furthermore, a blind assessment over a cohort of 46 MCI subjects confirmed that it captures the intermediary character of the MCI group. GNNExplainer module employed to investigate the anatomical determinants of the observed discrepancy confirms that sfDLN attends to cortical regions neurologically relevant to ADD.
CONCLUSIONS: In support of our hypothesis, the harmony between the structural and functional organization of the brain degrades with increasing cognitive decline. This discrepancy, shown to be rooted in brain regions neurologically relevant to ADD, can be quantified by sfDLN and outperforms state-of-the-art GNN-based ADD classification methods when used as a biomarker.