Voxel-Wise Brain Graphs From Diffusion MRI: Intrinsic Eigenspace Dimensionality and Application to Functional MRI

• Published in: IEEE open journal of engineering in medicine and biology Vol. 6; pp. 158 - 167
• Main Authors: Behjat, Hamid, Tarun, Anjali, Abramian, David, Larsson, Martin, Ville, Dimitri Van De
• Format: Journal Article
• Language: English
• Published: United States IEEE 01.01.2025; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Annan medicinteknik; Brain; Brain graph; diffusion MRI; Diffusion tensor imaging; Distribution functions; Eigenvalues and eigenfunctions; Engineering and Technology; Functional magnetic resonance imaging; functional MRI; Functionals; graph signal processing; Graph theory; Graphs; High resolution; Information processing; Laplace equations; Medical Engineering; Medicinteknik; Nodes; Other Medical Engineering; Signal processing; Spatial data; spectral graph theory; Structure-function relationships; Substantia alba; Substantia grisea; Task analysis; Teknik; Tensors; diffusion MRI; functional MRI; Brain graph; graph signal processing; spectral graph theory
• ISSN: 2644-1276; 2644-1276
• DOI: 10.1109/OJEMB.2023.3267726

Goal: Structural brain graphs are conventionally limited to defining nodes as gray matter regions from an atlas, with edges reflecting the density of axonal projections between pairs of nodes. Here we explicitly model the entire set of voxels within a brain mask as nodes of high-resolution, subject-specific graphs. Methods: We define the strength of local voxel-to-voxel connections using diffusion tensors and orientation distribution functions derived from diffusion MRI data. We study the graphs' Laplacian spectral properties on data from the Human Connectome Project. We then assess the extent of inter-subject variability of the Laplacian eigenmodes via a procrustes validation scheme. Finally, we demonstrate the extent to which functional MRI data are shaped by the underlying anatomical structure via graph signal processing. Results: The graph Laplacian eigenmodes manifest highly resolved spatial profiles, reflecting distributed patterns that correspond to major white matter pathways. We show that the intrinsic dimensionality of the eigenspace of such high-resolution graphs is only a mere fraction of the graph dimensions. By projecting task and resting-state data on low-frequency graph Laplacian eigenmodes, we show that brain activity can be well approximated by a small subset of low-frequency components. Conclusions: The proposed graphs open new avenues in studying the brain, be it, by exploring their organisational properties via graph or spectral graph theory, or by treating them as the scaffold on which brain function is observed at the individual level.