Localization of Epileptic Foci Based on Simultaneous EEG–fMRI Data

Sadjadi, Seyyed Mostafa; Ebrahimzadeh, Elias; Shams, Mohammad; Seraji, Masoud; Soltanian‐Zadeh, Hamid

doi:10.3389/fneur.2021.645594

Cited by 24 publications

(23 citation statements)

References 163 publications

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“…First, the locations of the single voxel with maximal z-score of the maximum BOLD cluster and the extracted dipole from ICA algorithm were determined. Next, the distance between the locations was measured and classified into three levels of spatial concordance: (i) concordant (C) for the distance <25 mm; (ii) partially concordant (PC) for the distance between 25 and 50 mm; and (iii) discordant (D) for the distance more than 50 mm ( 36 , 40 ). To evaluate the distance between dipole and maximum BOLD, the spherical head model has been co-registered to the MNI brain.…”

Section: Methodsmentioning

confidence: 99%

Localizing Epileptic Foci Using Simultaneous EEG-fMRI Recording: Template Component Cross-Correlation

et al. 2021

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Conventional EEG-fMRI methods have been proven to be of limited use in the sense that they cannot reveal the information existing in between the spikes. To resolve this issue, the current study obtains the epileptic components time series detected on EEG and uses them to fit the Generalized Linear Model (GLM), as a substitution for classical regressors. This approach allows for a more precise localization, and equally importantly, the prediction of the future behavior of the epileptic generators. The proposed method approaches the localization process in the component domain, rather than the electrode domain (EEG), and localizes the generators through investigating the spatial correlation between the candidate components and the spike template, as well as the medical records of the patient. To evaluate the contribution of EEG-fMRI and concordance between fMRI and EEG, this method was applied on the data of 30 patients with refractory epilepsy. The results demonstrated the significant numbers of 29 and 24 for concordance and contribution, respectively, which mark improvement as compared to the existing literature. This study also shows that while conventional methods often fail to properly localize the epileptogenic zones in deep brain structures, the proposed method can be of particular use. For further evaluation, the concordance level between IED-related BOLD clusters and Seizure Onset Zone (SOZ) has been quantitatively investigated by measuring the distance between IED/SOZ locations and the BOLD clusters in all patients. The results showed the superiority of the proposed method in delineating the spike-generating network compared to conventional EEG-fMRI approaches. In all, the proposed method goes beyond the conventional methods by breaking the dependency on spikes and using the outside-the-scanner spike templates and the selected components, achieving an accuracy of 97%. Doing so, this method contributes to improving the yield of EEG-fMRI and creates a more realistic perception of the neural behavior of epileptic generators which is almost without precedent in the literature.

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Section: Methodsmentioning

confidence: 99%

Localizing Epileptic Foci Using Simultaneous EEG-fMRI Recording: Template Component Cross-Correlation

et al. 2021

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“…We applied standard preprocessing procedures in EEGLAB (version 2021) to reduce noise and artifacts from the EEG signals [ 26 ]. Based on manual, trial-by-trial visual inspection of the data, the entire data sets of three patients were rejected due to excessive motion artifacts.…”

Section: Methodsmentioning

confidence: 99%

Multiple sclerosis reduces synchrony of the magnocellular pathway

et al. 2021

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Multiple Sclerosis (MS) is an autoimmune demyelinating disease that damages the insulation of nerve cell fibers in the brain and spinal cord. In the visual system, this demyelination results in a robust delay of visually evoked potentials (VEPs), even in the absence of overt clinical symptoms such as blurred vision. VEPs, therefore, offer an avenue for early diagnosis, monitoring disease progression, and, potentially, insight into the differential impairment of specific pathways. A primary hypothesis has been that visual stimuli driving the magno-, parvo-, and konio-cellular pathways should lead to differential effects because these pathways differ considerably in terms of myelination. Experimental tests of this hypothesis, however, have led to conflicting results. Some groups reported larger latency effects for chromatic stimuli, while others found equivalent effects across stimulus types. We reasoned that this lack of pathway specificity could, at least in part, be attributed to the relatively coarse measure of pathway impairment afforded by the latency of a VEP. We hypothesized that network synchrony could offer a more sensitive test of pathway impairments. To test this hypothesis, we analyzed the synchrony of occipital electroencephalography (EEG) signals during the presentation of visual stimuli designed to bias activity to one of the three pathways. Specifically, we quantified synchrony in the occipital EEG using two graph-theoretic measures of functional connectivity: the characteristic path length (L; a measure of long-range connectivity) and the clustering coefficient (CC; a measure of short-range connectivity). Our main finding was that L and CC were both smaller in the MS group than in controls. Notably, this change in functional connectivity was limited to the magnocellular pathway. The effect sizes (Hedge’s g) were 0.89 (L) and 1.26 (CC) measured with magno stimuli. Together, L and CC define the small-world nature of a network, and our finding can be summarized as a reduction in the small-worldness of the magnocellular network. We speculate that the reduced efficiency of information transfer associated with a reduction in small-worldness could underlie visual deficits in MS. Relating these measures to differential diagnoses and disease progression is an important avenue for future work.

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“…Indeed, the origins of simultaneous EEG-fMRI are in epilepsy research and this field has contributed to the development of the technique and analysis strategies [ 102 , 103 , 104 , 105 ]. Localisation of epileptic generators is a critical topic for the understanding and treatment of epilepsy; however, localising the precise region of epileptic foci is challenging, but simultaneous EEG-fMRI can be used to meet this challenge [ 106 ]. Electrical brain activity associated with epilepsy can be measured as interictal epileptiform discharges (IEDs/spikes) or seizures using scalp EEG [ 107 ].…”

Section: Applications Of Eeg-fmrimentioning

confidence: 99%

Section: Figurementioning

confidence: 99%

Simultaneous EEG-fMRI: What Have We Learned and What Does the Future Hold?

Warbrick

2022

Sensors

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Simultaneous EEG-fMRI has developed into a mature measurement technique in the past 25 years. During this time considerable technical and analytical advances have been made, enabling valuable scientific contributions to a range of research fields. This review will begin with an introduction to the measurement principles involved in EEG and fMRI and the advantages of combining these methods. The challenges faced when combining the two techniques will then be considered. An overview of the leading application fields where EEG-fMRI has made a significant contribution to the scientific literature and emerging applications in EEG-fMRI research trends is then presented.

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Localization of Epileptic Foci Based on Simultaneous EEG–fMRI Data

Cited by 24 publications

References 163 publications

Localizing Epileptic Foci Using Simultaneous EEG-fMRI Recording: Template Component Cross-Correlation

Localizing Epileptic Foci Using Simultaneous EEG-fMRI Recording: Template Component Cross-Correlation

Multiple sclerosis reduces synchrony of the magnocellular pathway

Simultaneous EEG-fMRI: What Have We Learned and What Does the Future Hold?

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