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Modern Bioelectromagnetism Methods for Optimizing Diagnosis and Therapy in Epilepsy

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A special issue of Brain Sciences (ISSN 2076-3425). This special issue belongs to the section "Neurotechnology and Neuroimaging".

Deadline for manuscript submissions: closed (15 May 2022) | Viewed by 13932

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Special Issue Editors

Prof. Dr. Carsten Wolters

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Guest Editor

Institute for Biomagnetism and Biosignalanalysis, University of Münster, 48149 Münster, Germany
Interests: magnetoencephalography (MEG); electroencephalography(EEG); magnetic resonance imaging (MRI); diffusion MRI (dMRI); multimodal brain imaging; brain stimulation; neuronal networks; presurgical epilepsy diagnosis; schizophrenia

Dr. Stefan Rampp

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Guest Editor

1. Department of Neurosurgery, University Hospital Erlangen, Schwabachanlage 6, 91054 Erlangen, Germany;
2. Department of Neurosurgery, University Hospital Halle (Saale), Ernst-Grube-Straße 40, 06120 Halle (Saale), Germany
Interests: neuroscience; electroencephalography(EEG); electrophysiology; neurophysiology; brain; neuroimaging; cognitive neuroscience; functional neuroimaging; brain imaging; cognitive neuropsychology; magnetoencephalography (MEG); clinical neuroscience; epilepsy; intraoperative monitoring; functional mapping; MRI; functional MRI (fMRI)

Dr. Elaine Foley

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Guest Editor

Aston Brain Centre, Aston Neuroscience Institute, Aston University, B4 7ET Birmingham, UK
Interests: cognitive neuroscience; neuroimaging; magnetoencephalography (MEG); functional MRI (fMRI); paediatric epilepsy; functional mapping; epilepsy surgery; brain injury; language; memory; MRI; neurophysiology

Special Issue Information

Dear Colleagues,

Pediatric and adult epilepsy are among the most common neurological diseases. Therefore, new diagnosis and treatment methods have a high impact on society. Only in two-thirds of cases can seizures be adequately controlled with anticonvulsant drug treatment. For the remaining refractory patients with focal epilepsy, epilepsy surgery is currently the most effective treatment option. However, only 15-20% of those patients are eligible for epilepsy surgery. The main reasons are the insufficient localization of the epileptogenic zone with standard diagnostic means, and the overlap of the epileptogenic zone with eloquent cortical areas, so that it cannot be surgically removed without considerable neurological deficits.

Our Special Issue aims to highlight new approaches to improve this situation with a focus on personalized methods. On the diagnostic side, we welcome contributions for new multimodal electroencephalography (EEG), magnetoencephalography (MEG) and magnetic resonance imaging (MRI) neuroimaging methods to improve the localization of the epileptic cortex and eloquent cortex mapping. On the therapeutic side, our Special Issue will focus on modern approaches to epilepsy surgery as well as non-invasive brain stimulation methods such as targeted and optimized multi-channel transcranial electric (TES) and magnetic (TMS) stimulations to reduce seizure frequency and severity.

We welcome contributions to new methods and applications of forward and inverse modelling in EEG, MEG and especially combined EEG/MEG source analysis using realistic head volume conductor modelling as well as other modern approaches to the neuroimaging of the epileptic cortex (e.g., morphological investigations, Diffusion tensor imaging (DTI) and also functional MRI (fMRI)) and presurgical functional mapping. On the therapeutic side, besides modern methods of epilepsy surgery, new minimally invasive procedures such as laser ablation or radiofrequency thermo-coagulation are welcome, as well as non-invasive targeted TES and TMS brain stimulation approaches.

Prof. Dr. Carsten Wolters
Dr. Stefan Rampp
Dr. Elaine Foley
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Brain Sciences is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2200 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

EEG
MEG
functional mapping
epilepsy surgery
non-invasive brain stimulation
TMS
TES

Published Papers (5 papers)

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Research

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22 pages, 2309 KiB

Open AccessArticle

Validating EEG, MEG and Combined MEG and EEG Beamforming for an Estimation of the Epileptogenic Zone in Focal Cortical Dysplasia

by Frank Neugebauer, Marios Antonakakis, Kanjana Unnwongse, Yaroslav Parpaley, Jörg Wellmer, Stefan Rampp and Carsten H. Wolters

Brain Sci. 2022, 12(1), 114; https://0-doi-org.brum.beds.ac.uk/10.3390/brainsci12010114 - 14 Jan 2022

Cited by 8 | Viewed by 3128

Abstract

MEG and EEG source analysis is frequently used for the presurgical evaluation of pharmacoresistant epilepsy patients. The source localization of the epileptogenic zone depends, among other aspects, on the selected inverse and forward approaches and their respective parameter choices. In this validation study, we compare the standard dipole scanning method with two beamformer approaches for the inverse problem, and we investigate the influence of the covariance estimation method and the strength of regularization on the localization performance for EEG, MEG, and combined EEG and MEG. For forward modelling, we investigate the difference between calibrated six-compartment and standard three-compartment head modelling. In a retrospective study, two patients with focal epilepsy due to focal cortical dysplasia type IIb and seizure freedom following lesionectomy or radiofrequency-guided thermocoagulation (RFTC) used the distance of the localization of interictal epileptic spikes to the resection cavity resp. RFTC lesion as reference for good localization. We found that beamformer localization can be sensitive to the choice of the regularization parameter, which has to be individually optimized. Estimation of the covariance matrix with averaged spike data yielded more robust results across the modalities. MEG was the dominant modality and provided a good localization in one case, while it was EEG for the other. When combining the modalities, the good results of the dominant modality were mostly not spoiled by the weaker modality. For appropriate regularization parameter choices, the beamformer localized better than the standard dipole scan. Compared to the importance of an appropriate regularization, the sensitivity of the localization to the head modelling was smaller, due to similar skull conductivity modelling and the fixed source space without orientation constraint. Full article

(This article belongs to the Special Issue Modern Bioelectromagnetism Methods for Optimizing Diagnosis and Therapy in Epilepsy)

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Figure 1

14 pages, 5241 KiB

Open AccessArticle

Sensitivity of a 29-Channel MEG Source Montage

by Jukka Nenonen, Liisa Helle, Amit Jaiswal, Elizabeth Bock, Nicole Ille and Harald Bornfleth

Brain Sci. 2022, 12(1), 105; https://0-doi-org.brum.beds.ac.uk/10.3390/brainsci12010105 - 13 Jan 2022

Cited by 1 | Viewed by 1947

Abstract

In this paper, we study the performance of a source montage corresponding to 29 brain regions reconstructed from whole-head magnetoencephalographic (MEG) recordings, with the aim of facilitating the review of MEG data containing epileptiform discharges. Test data were obtained by superposing simulated signals from 100-nAm dipolar sources to a resting state MEG recording from a healthy subject. Simulated sources were placed systematically to different cortical locations for defining the optimal regularization for the source montage reconstruction and for assessing the detectability of the source activity from the 29-channel MEG source montage. The signal-to-noise ratio (SNR), computed for each source from the sensor-level and source-montage signals, was used as the evaluation parameter. Without regularization, the SNR from the simulated sources was larger in the sensor-level signals than in the source montage reconstructions. Setting the regularization to 2% increased the source montage SNR to the same level as the sensor-level SNR, improving the detectability of the simulated events from the source montage reconstruction. Sources producing a SNR of at least 15 dB were visually detectable from the source-montage signals. Such sources are located closer than about 75 mm from the MEG sensors, in practice covering all areas in the grey matter. The 29-channel source montage creates more focal signals compared to the sensor space and can significantly shorten the detection time of epileptiform MEG discharges for focus localization. Full article

(This article belongs to the Special Issue Modern Bioelectromagnetism Methods for Optimizing Diagnosis and Therapy in Epilepsy)

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Figure 1

16 pages, 779 KiB

Open AccessArticle

MEG Node Degree Differences in Patients with Focal Epilepsy vs. Controls—Influence of Experimental Conditions

by Stephan Vogel, Martin Kaltenhäuser, Cora Kim, Nadia Müller-Voggel, Karl Rössler, Arnd Dörfler, Stefan Schwab, Hajo Hamer, Michael Buchfelder and Stefan Rampp

Brain Sci. 2021, 11(12), 1590; https://0-doi-org.brum.beds.ac.uk/10.3390/brainsci11121590 - 30 Nov 2021

Cited by 3 | Viewed by 2158

Abstract

Drug-resistant epilepsy can be most limiting for patients, and surgery represents a viable therapy option. With the growing research on the human connectome and the evidence of epilepsy being a network disorder, connectivity analysis may be able to contribute to our understanding of epilepsy and may be potentially developed into clinical applications. In this magnetoencephalographic study, we determined the whole-brain node degree of connectivity levels in patients and controls. Resting-state activity was measured at five frequency bands in 15 healthy controls and 15 patients with focal epilepsy of different etiologies. The whole-brain all-to-all imaginary part of coherence in source space was then calculated. Node degree was determined and parcellated and was used for further statistical evaluation. In comparison to controls, we found a significantly higher overall node degree in patients with lesional and non-lesional epilepsy. Furthermore, we examined the conditions of high/reduced vigilance and open/closed eyes in controls, to analyze whether patient node degree levels can be achieved. We evaluated intraclass-correlation statistics (ICC) to evaluate the reproducibility. Connectivity and specifically node degree analysis could present new tools for one of the most common neurological diseases, with potential applications in epilepsy diagnostics. Full article

(This article belongs to the Special Issue Modern Bioelectromagnetism Methods for Optimizing Diagnosis and Therapy in Epilepsy)

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22 pages, 18507 KiB

Open AccessArticle

Parametrizing the Conditionally Gaussian Prior Model for Source Localization with Reference to the P20/N20 Component of Median Nerve SEP/SEF

by Atena Rezaei, Marios Antonakakis, MariaCarla Piastra, Carsten H. Wolters and Sampsa Pursiainen

Brain Sci. 2020, 10(12), 934; https://0-doi-org.brum.beds.ac.uk/10.3390/brainsci10120934 - 03 Dec 2020

Cited by 9 | Viewed by 2799

Abstract

In this article, we focused on developing the conditionally Gaussian hierarchical Bayesian model (CG-HBM), which forms a superclass of several inversion methods for source localization of brain activity using somatosensory evoked potential (SEP) and field (SEF) measurements. The goal of this proof-of-concept study was to improve the applicability of the CG-HBM as a superclass by proposing a robust approach for the parametrization of focal source scenarios. We aimed at a parametrization that is invariant with respect to altering the noise level and the source space size. The posterior difference between the gamma and inverse gamma hyperprior was minimized by optimizing the shape parameter, while a suitable range for the scale parameter can be obtained via the prior-over-measurement signal-to-noise ratio, which we introduce as a new concept in this study. In the source localization experiments, the primary generator of the P20/N20 component was detected in the Brodmann area 3b using the CG-HBM approach and a parameter range derived from the existing knowledge of the Tikhonov-regularized minimum norm estimate, i.e., the classical Gaussian prior model. Moreover, it seems that the detection of deep thalamic activity simultaneously with the P20/N20 component with the gamma hyperprior can be enhanced while using a close-to-optimal shape parameter value. Full article

(This article belongs to the Special Issue Modern Bioelectromagnetism Methods for Optimizing Diagnosis and Therapy in Epilepsy)

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Review

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21 pages, 2603 KiB

Open AccessReview

Personalized tDCS for Focal Epilepsy—A Narrative Review: A Data-Driven Workflow Based on Imaging and EEG Data

by Steven Beumer, Paul Boon, Debby C. W. Klooster, Raymond van Ee, Evelien Carrette, Maarten M. Paulides and Rob M. C. Mestrom

Brain Sci. 2022, 12(5), 610; https://0-doi-org.brum.beds.ac.uk/10.3390/brainsci12050610 - 07 May 2022

Cited by 2 | Viewed by 2561

Abstract

Conventional transcranial electric stimulation(tES) using standard anatomical positions for the electrodes and standard stimulation currents is frequently not sufficiently selective in targeting and reaching specific brain locations, leading to suboptimal application of electric fields. Recent advancements in in vivo electric field characterization may enable clinical researchers to derive better relationships between the electric field strength and the clinical results. Subject-specific electric field simulations could lead to improved electrode placement and more efficient treatments. Through this narrative review, we present a processing workflow to personalize tES for focal epilepsy, for which there is a clear cortical target to stimulate. The workflow utilizes clinical imaging and electroencephalography data and enables us to relate the simulated fields to clinical outcomes. We review and analyze the relevant literature for the processing steps in the workflow, which are the following: tissue segmentation, source localization, and stimulation optimization. In addition, we identify shortcomings and ongoing trends with regard to, for example, segmentation quality and tissue conductivity measurements. The presented processing steps result in personalized tES based on metrics like focality and field strength, which allow for correlation with clinical outcomes. Full article

(This article belongs to the Special Issue Modern Bioelectromagnetism Methods for Optimizing Diagnosis and Therapy in Epilepsy)

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