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Estimating $c$-level partial correlation graphs with application to brain imaging
摘要： Alzheimer’s disease (AD) is a chronic neurodegenerative disease that changes the functional connectivity of the brain. The alteration of the strong connections between different brain regions is of particular interest to researchers. In this article, we use partial correlations to model the brain connectivity network and propose a data-driven procedure to recover a c-level partial correlation graph based on PET data, which is the graph of the absolute partial correlations larger than a pre-speci?ed constant c. The proposed procedure is adaptive to the “large p, small n” scenario commonly seen in whole brain studies, and it incorporates the variation of the estimated partial correlations, which results in higher power compared to the existing methods. A case study on the FDG-PET images from AD and normal control (NC) subjects discovers new brain regions, Sup Frontal and Mid Frontal in the frontal lobe, which have different brain functional connectivity between AD and NC.
关键词： Partial correlation,High dimensionality,Alzheimer’s Disease,Brain connectivity
更新于2025-09-23 15:23:52
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Mouse optical imaging for understanding resting-state functional connectivity in human fMRI
摘要： Resting-state functional connectivity (FC), which measures the temporal correlation of spontaneous hemodynamic activity between distant brain areas, is a widely accepted method in functional magnetic resonance imaging (fMRI) to assess the connectome of healthy and diseased human brains. A common assumption underlying FC is that it reflects the temporal structure of large-scale neuronal activity that is converted into large-scale hemodynamic activity. However, direct observation of such relationship has been difficult. In this commentary, we describe our recent progress regarding this topic. Recently, transgenic mice that express a genetically encoded calcium indicator (GCaMP) in neocortical neurons are enabling the optical recording of neuronal activity in large-scale with high spatiotemporal resolution. Using these mice, we devised a method to simultaneously monitor neuronal and hemodynamic activity and addressed some key issues related to the neuronal basis of FC. We propose that many important questions about human resting-state fMRI can be answered using GCaMP expressing transgenic mice as a model system.
关键词： mouse,calcium imaging,functional connectivity,fMRI,resting-state
更新于2025-09-23 15:23:52
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Perspective: Prospects of non-invasive sensing of the human brain with diffuse optical imaging
摘要： Since the initial demonstration of near-infrared spectroscopy (NIRS) for noninvasive measurements of brain perfusion and metabolism in the 1970s, and its application to functional brain studies (fNIRS) in the 1990s, the field of noninvasive optical studies of the brain has been continuously growing. Technological developments, data analysis advances, and novel areas of application keep advancing the field. In this article, we provide a view of the state of the field of cerebral NIRS, starting with a brief historical introduction and a description of the information content of the NIRS signal. We argue that NIRS and fNIRS studies should always report data of both oxy- and deoxyhemoglobin concentrations in brain tissue, as they complement each other to provide more complete functional and physiological information, and may help identify different types of confounds. One significant challenge is the assessment of absolute tissue properties, be them optical or physiological, so that relative measurements account for the vast majority of NIRS and fNIRS applications. However, even relative measurements of hemodynamics or metabolic changes face the major problem of a potential contamination from extracerebral tissue layers. Accounting for extracerebral contributions to fNIRS signals is one of the most critical barriers in the field. We present some of the approaches that were proposed to tackle this challenge in the study of cerebral hemodynamics and functional connectivity. Finally, we critically compare fNIRS and functional magnetic resonance imaging by relating their measurements in terms of signal and noise, and by commenting on their complementarity.
关键词： hemodynamics,functional connectivity,functional magnetic resonance imaging,human brain,near-infrared spectroscopy,diffuse optical imaging,non-invasive sensing,functional near-infrared spectroscopy
更新于2025-09-23 15:21:21
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Edge Computing Enabled Unmanned Module Defect Detection and Diagnosis System for Large-scale Photovoltaic Plants
摘要： The network connectivity of sel?sh wireless networks (SeWNs) constituted by sel?sh nodes (SeNs) is investigated. The SeN’s degree of node-sel?shness (DeNS) is used for characterizing the effects of its energy resources and the bene?ts of the incentives provided for enhancing its transmission willingness. Furthermore, the SeNs’ signal to interference plus noise ratios are de?ned in terms of both their DeNSs and their interference factors. We then continue by quantifying the effect of node-sel?shness on the grade of network connectivity and derive both the upper and lower bounds of the critical DeNS. Explicitly, the network is deemed to be connected when the DeNS is below the lower bound and unconnected for a DeNS above the upper bound. This allows us to quantify the asymptotic critical DeNSs for our SeWNs. In addition, we develop an energy-conscious node-sel?shness model for characterizing the relationship between the SeN’s residual energy and its DeNS. Based on this model and on the asymptotic critical DeNS derived, the critical amount of residual energy required for maintaining a speci?c grade of network connectivity is determined, which is veri?ed by our simulation results.
关键词： node-sel?shness,Network connectivity,energy resource,percolation theory,sel?sh wireless network
更新于2025-09-23 15:21:01
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Effects of HD-tDCS on Resting-State Functional Connectivity in the Prefrontal Cortex: An fNIRS Study
摘要： Functional connectivity is linked to several degenerative brain diseases prevalent in our aging society. Electrical stimulation is used for the clinical treatment and rehabilitation of patients with many cognitive disorders. In this study, the effects of high-definition transcranial direct current stimulation (HD-tDCS) on resting-state brain networks in the human prefrontal cortex were investigated by using functional near-infrared spectroscopy (fNIRS). The intrahemispheric as well as interhemispheric connectivity changes induced by 1 mA HD-tDCS were examined in 15 healthy subjects. Pearson correlation coefficient-based correlation matrices were generated from filtered time series oxyhemoglobin (ΔHbO) signals and converted into binary matrices. Common graph theory metrics were computed to evaluate the network changes. Systematic interhemispheric, intrahemispheric, and intraregional connectivity analyses demonstrated that the stimulation positively affected the resting-state connectivity in the prefrontal cortex. The poststimulation connectivity was increased throughout the prefrontal region, while focal HD-tDCS effects induced an increased rate of connectivity in the stimulated hemisphere. The graph theory metrics clearly distinguished the prestimulation and poststimulation networks for a range of thresholds. The results of this study suggest that HD-tDCS can be used to increase functional connectivity in the prefrontal cortex. The increase in functional connectivity can be explored clinically for neurorehabilitation of patients with degenerative brain diseases.
关键词： HD-tDCS,neurorehabilitation,fNIRS,graph theory,functional connectivity,prefrontal cortex
更新于2025-09-23 15:21:01
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Comparison of the Optical Connectivity Method to X-Ray spray measurements in the near field of a diesel injector
摘要： For diesel sprays, the primary breakup processes are only rarely understood due to the high optical density and the resulting difficulties to measure them with extremely high spatial and sufficient temporal resolution. The Optical Connectivity Method (OCM) has been proposed in the last years to allow the determination of the breakup length of the connected liquid core, thus giving a measurement quantity of the primary breakup. In this work, an improved optical setup of the OCM is applied to a three-hole test injector nozzle where several measurement techniques are compared currently under well-defined conditions up to 100 MPa injection pressure. In this work, the direct comparison with X-Ray measurements done at the Advanced Photon Source of the Argonne National Laboratory will be described. This allows an evaluation of the OCM technique and a comparison of the different measurement quantities in the first 500 μm range of the spray. The structure of the spray is measured by X-Ray phase contrast imaging and the fuel mass distribution is measured by X-Ray absorption imaging. A detailed comparison of the two X-Ray techniques and the OCM technique has been possible for the first time. It is found that the measurement data of the spray near field are very congruent with all three methods. Due to this comparison, the measurement of the non-perturbed length, which describes the distance from the nozzle orifice up to the point where the formation of surface disturbances is starting, by the OCM is validated for the first time. Within this non-perturbed length of the spray, the OCM signal is weak before it starts to illuminate from the scattering of the perturbed surface. Thus, the OCM technique can deliver two characteristic length scales, the non-perturbed length and the breakup length , characterizing the primary spray breakup.
关键词： X-Ray diagnostics,Non-perturbed length,Breakup length,Primary breakup,Optical Connectivity Method
更新于2025-09-23 15:21:01
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[IEEE 2019 IEEE Industry Applications Society Annual Meeting - Baltimore, MD, USA (2019.9.29-2019.10.3)] 2019 IEEE Industry Applications Society Annual Meeting - High-Efficient High-Power-Factor Off-Line LED Driver based on Integrated Buck and Boost Converter
摘要： The network connectivity of sel?sh wireless networks (SeWNs) constituted by sel?sh nodes (SeNs) is investigated. The SeN’s degree of node-sel?shness (DeNS) is used for characterizing the effects of its energy resources and the bene?ts of the incentives provided for enhancing its transmission willingness. Furthermore, the SeNs’ signal to interference plus noise ratios are de?ned in terms of both their DeNSs and their interference factors. We then continue by quantifying the effect of node-sel?shness on the grade of network connectivity and derive both the upper and lower bounds of the critical DeNS. Explicitly, the network is deemed to be connected when the DeNS is below the lower bound and unconnected for a DeNS above the upper bound. This allows us to quantify the asymptotic critical DeNSs for our SeWNs. In addition, we develop an energy-conscious node-sel?shness model for characterizing the relationship between the SeN’s residual energy and its DeNS. Based on this model and on the asymptotic critical DeNS derived, the critical amount of residual energy required for maintaining a speci?c grade of network connectivity is determined, which is veri?ed by our simulation results.
关键词： node-sel?shness,Network connectivity,energy resource,percolation theory,sel?sh wireless network
更新于2025-09-23 15:19:57
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Cross density of states and mode connectivity: Probing wave localization in complex media
摘要： We introduce the mode connectivity as a measure of the number of eigenmodes of a wave equation connecting two points at a given frequency. Based on numerical simulations of scattering of electromagnetic waves in disordered media, we show that the connectivity discriminates between the diffusive and the Anderson localized regimes. For practical measurements, the connectivity is encoded in the second-order coherence function characterizing the intensity emitted by two incoherent classical or quantum dipole sources. The analysis applies to all processes in which spatially localized modes build up, and to all kinds of waves.
关键词： Anderson localization,disordered media,cross density of states,wave localization,electromagnetic waves,mode connectivity
更新于2025-09-19 17:15:36
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Identification of the Pain Process by Cold Stimulation: Using Dynamic Causal Modeling of Effective Connectivity in Functional Near-Infrared Spectroscopy (fNIRS)
摘要： Background: Pain is an unpleasant sensory and emotional experience followed by anxiety, depression, and frustration. Functional Near-Infrared Spectroscopy (fNIRS) as an optical technique identifies the brain functional networks by investigating connectivity between functionally linked of different anatomical regions in response to pain stimulation. Methods: In this research, fNIRS was performed in order to study the difference in effective functional connectivity of the brain prefrontal cortex between the two modes of pain and rest based on the dynamic causal modeling (DCM) method. Effective functional connectivity changes in the prefrontal cortex between pain and rest states were calculated using DCM approach to investigate (1) areas known for pain sensation and (2) to analyze inter-network functional connectivity strength (FCS) by selecting several brain functional networks based on the analysis findings. All analyses were performed using toolboxes SPM-fNIRS and SPM8, Matlab software. Results: Regional hemodynamics changes caused deoxyhemoglobin concentration to decrease in the prefrontal cortex of both hemispheres, particularly on the right side. We found a simultaneous increase in the concentration of oxyhemoglobin in the prefrontal cortex of the left hemisphere in comparison to the right hemisphere, that there was a trend toward reduction in oxyhemoglobin concentration. The results indicate that during the cold pain stimulation, the connectivities between prefrontal cortex regions were significantly changed. Specifically, a significantly consistent increase in the RPFC to MPFC connectivity was found while a significant consistent decrease was observed in the both MPFC to LPFC and LPFC to MPFC connectivities. Conclusion: This study contributes to the pain research field to identify the directionality and causality of neuronal connections in the prefrontal cortex by applying DCM to fNIRS data. The results suggest that the proposed method infers directional interactions between hidden neuronal states in the brain under neuronal dynamic conditions based on optical density changes measurement.
关键词： Diagnosing pain,Neurology,Effective connectivity,Brain mapping,Dynamic causal modeling,fNIRS,Pain
更新于2025-09-19 17:15:36
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[IEEE 2019 International Conference on Microwave and Millimeter Wave Technology (ICMMT) - Guangzhou, China (2019.5.19-2019.5.22)] 2019 International Conference on Microwave and Millimeter Wave Technology (ICMMT) - Research on High Directional Waveguide Directional Coupler
摘要： In this paper, we developed a model-based and a data-driven estimator for directed information (DI) to infer the causal connectivity graph between electrocorticographic (ECoG) signals recorded from brain and to identify the seizure onset zone (SOZ) in epileptic patients. DI, an information theoretic quantity, is a general metric to infer causal connectivity between time series and is not restricted to a particular class of models unlike the popular metrics based on Granger causality or transfer entropy. The proposed estimators are shown to be almost surely convergent. Causal connectivity between ECoG electrodes in five epileptic patients is inferred using the proposed DI estimators, after validating their performance on simulated data. We then proposed a model-based and a data-driven SOZ identification algorithm to identify SOZ from the causal connectivity inferred using the model-based and data-driven DI estimators, respectively. The data-driven SOZ identification outperforms the model-based SOZ identification algorithm when benchmarked against the visual analysis by neurologist, the current clinical gold standard. The causal connectivity analysis presented here is the first step toward developing novel nonsurgical treatments for epilepsy.
关键词： ECoG,seizure onset zone,epilepsy,directed information,Causal connectivity
更新于2025-09-19 17:13:59