Automated voxel classification used with atlas-guided diffuse optical tomography for assessment of functional brain networks in young and older adults

Abstract

Abstract. Atlas-guided diffuse optical tomography (atlas-DOT) is a computational means to image changes in cortical hemodynamic signals during human brain activities. Graph theory analysis (GTA) is a network analysis tool commonly used in functional neuroimaging to study brain networks. Atlas-DOT has not been analyzed with GTA to derive large-scale brain connectivity/networks based on near-infrared spectroscopy (NIRS) measurements. We introduced an automated voxel classification (AVC) method that facilitated the use of GTA with atlas-DOT images by grouping unequal-sized finite element voxels into anatomically meaningful regions of interest within the human brain. The overall approach included volume segmentation, AVC, and cross-correlation. To demonstrate the usefulness of AVC, we applied reproducibility analysis to resting-state functional connectivity measurements conducted from 15 young adults in a two-week period. We also quantified and compared changes in several brain network metrics between young and older adults, which were in agreement with those reported by a previous positron emission tomography study. Overall, this study demonstrated that AVC is a useful means for facilitating integration or combination of atlas-DOT with GTA and thus for quantifying NIRS-based, voxel-wise resting-state functional brain networks.

Graph theoretical approach to functional connectivity in prefrontal cortex via fNIRS

“…Since PFC is usually considered to have been one large network, it would seem only reasonable to treat it as one network and so we focused on a metric that would provide the connectivity of the whole network. 82,83 Intrinsic functional networks of the human brain have been generated by EEG, fMRI, or MEG modalities and they all demonstrate a converging and highly conserved topological organization over different scales, such as small-world and modular structures. 21,33,55,57,65,66,70 More importantly, some of these features exhibit specific changes associated with normal development, aging, and various pathological attacks, which indicates the potential value of these approaches in capturing and monitoring the brain organization under different mental states.…”

Whole-cortical graphical networks at wakeful rest in young and older adults revealed by functional near-infrared spectroscopy

“…reported distinct small-world features in the frontal cortical areas when the participants undertook deceptive actions with respect to their wakeful rest. Li et al 18 . utilized GTA to reveal age-related changes in the anterior cortical regions.…”

“…However, all the reported fNIRS-based GTA studies had a common deficiency: limited measurement channels (source–detector pairs) resulted in partial coverage of the brain networks on a human head. For example, 24 channels were used to investigate only the middle frontal and sensorimotor (SM) cortex, 17 and 70 channels were able to cover only prefrontal, SM, and part of frontal-parietal (FP) cortical regions 18 . While a total of 46 channels were employed to cover the entire human cortex, the placement or distribution of the channels was very sparse 15 .…”

Comparing diffuse optical tomography and functional magnetic resonance imaging signals during a cognitive task: pilot study

“…44 The measured activation patterns can only be projected onto structural MRI, which is performed on the individual subject, when external landmarks are required for cranio-cerebral correlations with the 10 − 10∕10 − 20 electrode placement system. 45 An approach would be to create a finite element for a standard brain template [46][47][48] or subject-specific MR scans, 49,50 which forward model considering different optical properties for each brain layer, which could minimize the reconstruction errors and improve spatial accuracy.…”