Functional connectivity (FC) analysis, which measures the connection between different brain regions, has been widely used to study brain function and development. However, FC-based analysis breaks the local structure in MRI images, resulting in a challenge for applying advanced deep learning models, e.g., convolutional neural networks (CNN). To fit the data in a non-Euclidean domain, graph convolutional neural network (GCN) was proposed, which can work on graphs rather than raw images, making it a suitable model for brain FC study. The small sample size is another challenge. Compared with natural images, medical images are usually limited in data sample size. Moreover, labeling medical images requires laborious annotation and is time-consuming. These limitations result in low accuracy and overfitting problem when training a conventional deep learning model on medical images. To address this problem, we employed a semi-supervised GCN with a Laplacian regularization term. By exploiting the between-sample information, semi-supervised GCN can achieve better performance on data with limited sample size. We applied the semi-supervised GCN model to a brain imaging cohort to classify the groups with different Wide Range Achievement Test (WRAT) scores. Experimental results showed semi-supervised GCN can improve classification accuracy, demonstrating the superior power of semi-supervised GCN on small datasets.
KEYWORDS: Brain, Simulation of CCA and DLA aggregates, Neuroimaging, Canonical correlation analysis, Genetics, Functional magnetic resonance imaging, Brain imaging, Visualization, Alzheimer's disease, Neurons
Distance correlation is a measure that can detect both linear and nonlinear associations. However, applying distance correlation to imaging genetic studies often needs multiple testing correction due to the large number of multiple inferences. As a result, the sensitivity of its detection may be low. We propose a new model, distance canonical correlation analysis (DCCA), which overcomes this problem by searching a combination of features with the highest distance correlation. This is achieved by constructing a distance kernel function followed by solving a subsequent optimization problem. The ability to detect both linear and nonlinear associations makes DCCA suitable for analyzing complex multimodal and imaging-genetic associations. When applied to a brain imaging-genetic study from the Philadelphia Neurodevelopmental Cohort (PNC), DCCA detected several mental disorder-related gene pathways and brain networks. Experiments on brain connectivity found that the default mode network had strong nonlinear connections with other brain networks. When applied to the study of age effects, DCCA revealed that the connections of brain networks were relatively weak in younger groups but became stronger at older age stages. It indicates that adolescence is a vital stage for brain development. DCCA thus reveals a number of interesting findings and demonstrates a powerful new approach for analyzing multimodal brain imaging data.
Investigating the association between brain regions and genes continues to be a challenging topic in imaging genetics. Current brain region of interest (ROI)-gene association studies normally reduce data dimension by averaging the value of voxels in each ROI. This averaging may lead to a loss of information due to the existence of functional sub-regions. Pearson correlation is widely used for association analysis. However, it only detects linear correlation whereas nonlinear correlation may exist among ROIs. In this work, we introduced distance correlation to ROI-gene association analysis, which can detect both linear and nonlinear correlations and overcome the limitation of averaging operations by taking advantage of the information at each voxel. Nevertheless, distance correlation usually has a much lower value than Pearson correlation. To address this problem, we proposed a hybrid correlation analysis approach, by applying canonical correlation analysis (CCA) to the distance covariance matrix instead of directly computing distance correlation. Incorporating CCA into distance correlation approach may be more suitable for complex disease study because it can detect highly associated pairs of ROI and gene groups, and may improve the distance correlation level and statistical power. In addition, we developed a novel nonlinear CCA, called distance kernel CCA, which seeks the optimal combination of features with the most significant dependence. This approach was applied to imaging genetic data from the Philadelphia Neurodevelopmental Cohort (PNC). Experiments showed that our hybrid approach produced more consistent results than conventional CCA across resampling and both the correlation and statistical significance were increased compared to distance correlation analysis. Further gene enrichment analysis and region of interest (ROI) analysis confirmed the associations of the identified genes with brain ROIs. Therefore, our approach provides a powerful tool for finding the correlation between brain imaging and genomic data.
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