Combining Electrical and Magnetic Fields for Source Analysis: A(n) Attractive or Repelling Thought

Event Abstract Back to Event Localization of interictal spikes and high frequency oscillations (HFO) using magnetoencephalography (MEG) Vahe Poghosyan1* 1 King Fahad Medical City, Department of Neurophysiology, National Neuroscience Institute, Saudi Arabia Epidemiological data show that about 40% of the patients with epilepsy are refractory to pharmacological treatment. In many such patients with focal epilepsy, an alternative therapeutic option of choice is the surgical resection of the epileptogenic zone. At present, a variety of diagnostic tools (e.g. analysis of seizure semiology, electrophysiological and neuroimaging tools, functional testing etc.) are used to define the different epilepsy-related cortical zones (symptomatogenic, irritative, seizure onset and functional deficit zones, and epileptogenic lesion), each of which indexes to a certain extent the location and boundaries of the epileptogenic zone. Recently, high frequency oscillations (HFO, 80 – 500 Hz) have been proposed as accurate biomarkers of the epileptogenic zone in intracranial electroencephalography recordings (Jacobs et al. 2012). Magnetoencephalography (MEG) substantially contributes to the pre-surgical evaluation of patients with focal epilepsy. Currently, its primary application is to localize the cortical sources of interictal spikes (irritative zone) as an estimate for the epileptogenic zone. Recent studies have shown that MEG can also be used to identify and localize sources of HFOs (Papadelis et al., 2009; Rampp et al., 2010). Accurate identification and localization of MEG HFOs can provide an important non-invasive biomarker for epileptogenicity. We have used several source localization methods to estimate and compare the sources of MEG interictal spikes and HFOs, and correlate them with the clinical information and post-surgical outcome. In this presentation, I will describe the results of this analysis and provide relevant recommendations. References Jacobs J., Staba R., Asano E., Otsubo H., Wu J.Y., Zijlmans M., Mohamed I., Kahane P., Dubeau F., Navarro V., and Gotman J. (2012). High-frequency oscillations (HFOs) in clinical epilepsy. Progress in neurobiology, 98: 302–315 Papadelis C., Poghosyan V., Fenwick P.B.C., and Ioannides A.A. (2009). MEG’s ability to localize accurately weak transient neural sources. Clinical Neurophysiology, 120: 1958–1970 Rampp S., Kaltenhäuser M., Weigel D., Buchfelder M., Blümcke I., Dörfler A., and Stefan, H. (2010). MEG correlates of epileptic high gamma oscillations in invasive EEG. Epilepsia, 51: 1638–1642. Keywords: Epilepsy, interictal epileptiform discharges, interictal spikes, Magnetoencephalography (MEG), high frequency oscillation Conference: SAN2016 Meeting, Corfu, Greece, 6 Oct - 9 Oct, 2016. Presentation Type: Oral Presentation in the Symposium Epilepsy and Sleep Topic: Symposium Epilepsy and Sleep Citation: Poghosyan V (2016). Localization of interictal spikes and high frequency oscillations (HFO) using magnetoencephalography (MEG). Conference Abstract: SAN2016 Meeting. doi: 10.3389/conf.fnhum.2016.220.00122 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 01 Aug 2016; Published Online: 01 Aug 2016. * Correspondence: Dr. Vahe Poghosyan, King Fahad Medical City, Department of Neurophysiology, National Neuroscience Institute, Riyadh, Saudi Arabia, vpoghosyan@kfmc.med.sa Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Vahe Poghosyan Google Vahe Poghosyan Google Scholar Vahe Poghosyan PubMed Vahe Poghosyan Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Preoperative localization of seizure onset zones (SOZs) is an evolving field in the treatment of refractory epilepsy. Both magnetic source imaging (MSI), and the more recent EEG-correlated functional MRI (EEG-fMRI), have shown applicability in assisting surgical planning. The purpose of this study was to evaluate the capability of each method and their combination in localizing the seizure onset lobe (SL). The study included 14 patients who underwent both MSI and EEG-fMRI before undergoing implantation of intracranial EEG (icEEG) as part of the presurgical planning of the resection of an epileptogenic zone (EZ) during the years 2012-2018. The estimated location of the SL by each method was compared with the location determined by icEEG. Identification rates of the SL were compared between the different methods. MSI and EEG-fMRI showed similar identification rates of SL locations in relation to icEEG results (88% ± 31% and 73% ± 42%, respectively; p = 0.281). The additive use of the coverage lobes of both methods correctly identified 100% of the SL, significantly higher than EEG-fMRI alone (p = 0.039) and nonsignificantly higher than MSI (p = 0.180). False-identification rates of the additive coverage lobes were significantly higher than MSI (p = 0.026) and EEG-fMRI (p = 0.027). The intersecting lobes of both methods showed the lowest false identification rate (13% ± 6%, p = 0.01). Both MSI and EEG-fMRI can assist in the presurgical evaluation of patients with refractory epilepsy. The additive use of both tests confers a high identification rate in finding the SL. This combination can help in focusing implantation of icEEG electrodes targeting the SOZ.

Assessing the localization accuracy and clinical utility of electric and magnetic source imaging in children with epilepsy

ObjectiveFocal cortical dysplasia (FCD) is a leading cause of drug‐resistant epilepsy and is associated with sleep‐related seizures, yet the underlying electrophysiological mechanisms during different brain states remain poorly understood. We investigated whether fast oscillations (FOs) within the seizure onset zone (SOZ) and irritative zone (IZ) change significantly during sleep compared with wake in FCD patients. We analyzed multiple frequency bands—beta (14–20 Hz), gamma (40–80 Hz), ripple (80–250 Hz), and broadband BGR (14–250 Hz) to provide comprehensive information about sleep‐related changes. We hypothesized that sleep‐related FO changes would be associated with sleep‐related epilepsy, frontal location, or FCD type II.MethodsWe examined intracranial EEG (iEEG) recordings from 22 FCD patients undergoing presurgical evaluation between 2010 and 2023, with a mean age of 25.3 ± 12.8 years and a disease duration of 17.7 ± 12.3 years. Using semiautomated detection, we compared FO rates between wake and sleep epochs, focusing on contacts within IZ and SOZ. Distance‐based multivariate analysis of variance (MANOVA) was employed for patient‐level analysis, accounting for spatial organization and enabling multiband evaluation.ResultsAnalysis of 67 ± 28 bipolar iEEG contact pairs per patient revealed distinct sleep‐related patterns. In SOZ, gamma oscillations showed significant increases in 10/22 patients (45%), followed by BGR in 7/22 patients (32%). IZ exhibited stronger changes, with BGR and gamma showing significance in 13/22 patients each (59%) with high concordance. Gamma oscillation rates in SOZ increased in patients with confirmed sleep‐related epilepsy (p < 0.05), while no associations were found with frontal location or FCD type II.SignificanceGamma oscillations showed robust sleep‐related increases in SOZ, while gamma and BGR frequencies demonstrated strong changes in IZ, often occurring simultaneously. These findings suggest gamma oscillations, complemented by BGR analysis, may qualify as markers for characterizing sleep‐related changes in FCD patients, potentially advancing understanding of mechanisms underlying sleep‐related seizures.Plain Language SummaryFocal cortical dysplasia (FCD) is a brain malformation that causes difficult‐to‐treat epilepsy, with patients experiencing seizures mainly during sleep. We studied electrical brain waves in 22 FCD patients using electrodes placed directly within or on the brain during pre‐surgery evaluation. We compared brain wave activity between wake and sleep, focusing on fast brain waves. We found that fast brain waves, especially gamma waves, increased significantly during sleep in brain areas where seizures start, particularly in patients whose seizures occur mainly during sleep. These findings potentially help us better understand why seizures happen more often during sleep in FCD patients.

Surgical treatment of drug-resistant epilepsy relies on the identification of the seizure onset zone (SOZ) and often requires intracranial EEG (iEEG). We have developed a new approach for non-invasive magnetic and electric source imaging of the SOZ (MSI-SOZ and ESI-SOZ) from ictal magnetoencephalography (MEG) and EEG recordings, using wavelet-based Maximum Entropy on the Mean (wMEM) method. We compared the performance of MSI-SOZ and ESI-SOZ with interictal spike source localization (MSI-spikes and ESI-spikes) and clinical localization of the SOZ (i.e., based on iEEG or lesion topography, denoted as clinical-SOZ). A total of 46 MEG or EEG seizures from 13 patients were analyzed. wMEM was applied around seizure onset, centered on the frequency band showing the strongest power change. Principal component analysis applied to spatiotemporal reconstructed wMEM sources (0.4-1 s around seizure onset) identified the main spatial pattern of ictal oscillations. Qualitative sublobar concordance and quantitative measures of distance and spatial overlaps were estimated to compare MSI/ESI-SOZ with MSI/ESI-Spikes and clinical-SOZ. MSI/ESI-SOZ were concordant with clinical-SOZ in 81% of seizures (MSI 90%, ESI 64%). MSI-SOZ was more accurate and identified sources closer to the clinical-SOZ (P = 0.012) and to MSI-Spikes (P = 0.040) as compared with ESI-SOZ. MSI/ESI-SOZ and MSI/ESI-Spikes did not differ in terms of concordance and distance from the clinical-SOZ. wMEM allows non-invasive localization of the SOZ from ictal MEG and EEG. MSI-SOZ performs better than ESI-SOZ. MSI/ESI-SOZ can provide important additional information to MSI/ESI-Spikes during presurgical evaluation. Hum Brain Mapp 37:2528-2546, 2016. © 2016 Wiley Periodicals, Inc.

The object of this study was to determine the concordance of the anatomical location of interictal magnetoencephalographic (MEG) spike foci with the location of ictal onset zones identified by invasive ictal intracranial electroencephalographic recordings in children undergoing evaluation for epilepsy surgery. MEG was performed in 11 children with intractable, nonlesional, extratemporal, localization-related epilepsy. Subsequently, chronic invasive intracranial electroencephalographic monitoring was performed by using subdural electrodes to localize the ictal onset zone and eloquent cortex. Based on the invasive monitoring data, all children had excision of, or multiple subpial transections through, ictal onset cortex and surrounding irritative zones. In 10 of 11 patients, the anatomical location of the epileptiform discharges as determined by MEG corresponded to the ictal onset zone established by ictal intracranial recordings. In all children, the anatomical location of the somatosensory hand area, determined by functional mapping through the subdural electrode array, was the same as that delineated by MEG. Nine of 11 patients became either seizure-free or had a greater than 90% reduction in seizures after surgery, with a mean follow-up of 24 months. MEG is a powerful and accurate tool in the presurgical evaluation of children with refractory nonlesional extratemporal epilepsy.

Magnetoencephalography (MEG) records the magnetic field generated by electrical activity of cortical neurons. The signal is not distorted or attenuated, and it is contactless recording that can be performed comfortably even for longer than an hour. It has excellent and decent temporal resolution, especially when it is combined with the patient's own brain magnetic resonance imaging (magnetic source imaging). Data of MEG and electroencephalography are not mutually exclusive and it is recorded simultaneously and interpreted together. MEG has been shown to be useful in detecting the irritative zone in both lesional and nonlesional epilepsy surgery. It has provided valuable and additive information regarding the lesion that should be resected in epilepsy surgery. Better outcomes in epilepsy surgery were related to the localization of the irritative zone with MEG. The value of MEG in epilepsy surgery is recruiting more patients to epilepsy surgery and providing critical information for surgical planning. MEG cortical mapping is helpful in younger pediatric patients, especially when the epileptogenic zone is close to the eloquent cortex. MEG is also used in both basic and clinical research of epilepsy other than surgery. MEG is a valuable diagnostic modality for diagnosis and treatment, as well as research in epilepsy.

ObjectiveSurgical treatment of focal epilepsy in patients with focal cortical dysplasia (FCD) is most successful if all epileptogenic tissue is resected. This may not be evident on structural magnetic resonance imaging (MRI), so intracranial electroencephalography (icEEG) is needed to delineate the seizure onset zone (SOZ). EEG-functional MRI (fMRI) can reveal interictal discharge (IED)-related hemodynamic changes in the irritative zone (IZ). We assessed the value of EEG-fMRI in patients with FCD-associated focal epilepsy by examining the relationship between IED-related hemodynamic changes, icEEG findings, and postoperative outcome.MethodsTwenty-three patients with FCD-associated focal epilepsy undergoing presurgical evaluation including icEEG underwent simultaneous EEG-fMRI at 3T. IED-related hemodynamic changes were modeled, and results were overlaid on coregistered T1-weighted MRI scans fused with computed tomography scans showing the intracranial electrodes. IED-related hemodynamic changes were compared with the SOZ on icEEG and postoperative outcome at 1 year.ResultsTwelve of 23 patients had IEDs during recording, and 11 of 12 had significant IED-related hemodynamic changes. The fMRI results were concordant with the SOZ in 5 of 11 patients, all of whom had a solitary SOZ on icEEG. Four of 5 had >50% reduction in seizure frequency following resective surgery. The remaining 6 of 11 patients had widespread or discordant regions of IED-related fMRI signal change. Five of 6 had either a poor surgical outcome (<50% reduction in seizure frequency) or widespread SOZ precluding surgery.InterpretationComparison of EEG-fMRI with icEEG suggests that EEG-fMRI may provide useful additional information about the SOZ in FCD. Widely distributed discordant regions of IED-related hemodynamic change appear to be associated with a widespread SOZ and poor postsurgical outcome. ANN NEUROL 2011

28 - Perfusion Imaging and Magnetoencephalography

In this paper the authors demonstrate the concordance between magnetic source (MS) imaging and direct cortical stimulation for mapping receptive language cortex. In 13 consecutive surgical patients, cortex specialized for receptive language functions was identified noninvasively by obtaining activation maps aided by MS imaging in the context of visual and auditory word-recognition tasks. Surgery was then performed for treatment of medically intractable seizure disorder (eight patients), and for resection of tumor (four), or angioma (one). Mapping of language areas with cortical stimulation was performed intraoperatively in 10 patients and extraoperatively in three. Cortical stimulation mapping verified the accuracy of the MS imaging-based localization in all cases. Information provided by MS imaging can be especially helpful in cases of atypical language representation, including bihemispheric representation, and location of language in areas other than those expected within the dominant hemisphere, such as the anterior portion of the superior temporal gyrus, the posteroinferior portion of the middle temporal gyrus, the basal temporal cortex, and the lateral temporooccipital cortex.

Localizing the Epileptogenic Zone with Novel Biomarkers

The prevalence of epilepsy is about 1% and one-third of cases do not respond to medical treatment. In an eligible subset of patients with drug-resistant epilepsy, surgical resection of the epileptogenic zone is the only treatment that can possibly cure the disease. Non-invasive techniques provide information for the localization of the epileptic focus in the majority of cases, whereas in others invasive procedures are required. In the last years, non-invasive neuroimaging techniques, such as simultaneous recording of functional magnetic resonance imaging and electroencephalogram (EEG-fMRI), positron emission tomography (PET), single photon emission computed tomography (SPECT), electric and magnetic source imaging (MSI, ESI), spectroscopy (MRS), have proved their usefulness in defining the epileptic focus. The combination of these functional techniques can yield complementary information and their concordance is crucial for guiding clinical decision, namely the planning of invasive EEG recordings or respective surgery. The aim of this review is to present these non-invasive neuroimaging techniques, their potential combination, and their role in the pre-surgical evaluation of patients with pharmaco-resistant epilepsy.

Successful epilepsy surgery relies on localization and removal of the brain area responsible for initializing the seizures called the epileptogenic zone (EZ). Intracranial EEG (icEEG) is gold standard of this localization but has several limitations like invasiveness and limited covered area. A noninvasive method with accurate localization precision is therefore desirable. The aim of this article is to investigate the following hypotheses: (1) Ictal onset zone as localized by magnetic source imaging (iMSI) can reliably localize the EZ in focal epilepsy and (2) this localization is as good as that of icEEG. Six original studies and a total of 59 unique patients were included in a meta-analysis. Sensitivity and specificity of iMSI based on surgery outcome were 77% (95% CI 60%-90%) and 75% (95% CI 53%-90%), respectively. Specificity of iMSI was statistically higher than that of icEEG. There was no significant difference between sensitivity of iMSI and icEEG. The meta-analysis supports that iMSI is an accurate method, achieving similar sensitivity and higher specificity than icEEG. However, at present the use of the method is limited by short recording times. A limitation that might be overcome in the future using technical advances.

ID 168 – Source localization of ictal epileptic activity based on high density scalp EEG data

Clinical Neurophysiology: EEG–Video Monitoring