An evaluation of kurtosis beamforming in magnetoencephalography to localize the epileptogenic zone in drug resistant epilepsy patients (original) (raw)
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Towards source volume estimation of interictal spikes in focal epilepsy using magnetoencephalography
NeuroImage, 2012
Interictal spikes are a hallmark of cortical epileptogenicity; their spatial distribution in the cortex defines the so-called 'irritative' zone or spiking volume (SV). Delineating the SV precisely is a challenge during the presurgical evaluation of patients with epilepsy. Magnetoencephalography (MEG) recordings enable determination of the brain sources of epileptic spikes using source localization procedures. Most previous clinical MEG studies have relied on dipole modeling of epileptic spikes, which does not permit a volumetric estimation of the spiking cortex. In the present study, we propose a new source modeling procedure, Volumetric Imaging of Epileptic Spikes (VIES). In VIES, the SV is identified as the 3D region where sources of the high frequency activities (> 20 Hz) associated with epileptic spikes are distributed. We localized these sources using a beamforming approach (DICS, Dynamic Imaging of Coherent Neural Sources). To determine the optimal parameters and accuracy of the method, we compared the SV obtained by VIES with the SV defined by the invasive gold standard, intracranial stereotactic EEG recordings (SEEG), in 21 patients with focal epilepsy. Using rigorous validation criteria based on the exact anatomical location of SEEG contacts, we found that the overall sensitivity of VIES for detecting spiking SEEG contacts was 76% and its specificity for correctly identifying nonspiking SEEG contacts was 67%, indicating a good agreement between VIES and SEEG. Moreover, we found that classical dipole clustering was not informative in 9/21 patients, while VIES enable to delineate the SV in all patients. For the 12 patients having a SV delineated both with VIES and dipole clustering, VIES method had higher sensitivity and lower specificity. This proof-of-concept study shows that VIES is a promising approach to non-invasive estimation of the SV in focal epilepsy.
Magnetoencephalography in partial epilepsy: Clinical yield and localization accuracy
Annals of Neurology, 1997
The goals of this study were to determine (1) the yield of magnetoencephalography (MEG) according to epilepsy type, (2) if MEG spike sources colocalize with focal epileptogenic pathology, and (3) if MEG can identify the epileptogenic zone when scalp ictal electroencephalogram (EEG) or magnetic resonance imaging (MRI) fail to localize it. Twenty-two patients with mesial temporal (10 patients), neocortical temporal (3 patients), and extratemporal lobe epilepsy (9 patients) were studied. A 37-channel biomagnetometer was used for simultaneously recording MEG with EEG. During the typical 2-3-hour MEG recording session, interictal epileptiform activity was observed in 16 of 22 patients. MEG localization yield was greater in patients with neocortical epilepsy (92%) than in those with mesial temporal lobe epilepsy (50%). In 5 of 6 patients with focal epileptogenic pathology, MEG spike sources were colocalized with the lesions. In 11 of 12 patients with nonlocalizing (ambiguous abnormalities or normal) MRI, MEG spike sources were localized in the region of the epileptogenic zone as ultimately defined by all clinical and EEG information (including intracranial EEG).
Clinical Neurophysiology Practice, 2020
Objective: To evaluate a novel analysis method (SAMepi) in the localization of interictal epileptiform magnetoencephalographic (MEG) activity in parietal lobe epilepsy (PLE) patients in comparison with equivalent current dipole (ECD) analysis. Methods: We analyzed the preoperative interictal MEG of 17 operated PLE patients utilizing visual analysis and: (1) ECD with a spherical conductor model; (2) ECD with a boundary element method (BEM) conductor model; and (3) SAMepi-a kurtosis beamformer method. Localization results were compared between the three methods, to the location of the resection and to the clinical outcome. Results: Fourteen patients had an epileptiform finding in the visual analysis; SAMepi detected spikes in 11 of them. A unifocal finding in both the ECD and in the SAMepi analysis was associated with a better chance of seizure-freedom (p = 0.02). There was no significant difference in the distances from the unifocal MEG localizations to the nearest border of the resection between the different analysis methods. Conclusions: Localizations of unifocal interictal spikes detected by SAMepi did not significantly differ from the conventional ECD localizations. Significance: SAMepi-a novel semiautomatic analysis method-is useful in localizing interictal epileptiform MEG activity in the presurgical evaluation of parietal lobe epilepsy patients.
Epilepsia, 2007
Purpose: The diagnosis of frontal lobe epilepsy may be compounded by poor electroclinical localization, due to distributed or rapidly propagating epileptiform activity. This study aimed at developing optimal procedures for localizing interictal epileptiform discharges (IEDs) of patients with localization related epilepsy in the frontal lobe. To this end the localization results obtained for magnetoencephalography (MEG) and electroencephalography (EEG) were compared systematically using automated analysis procedures. Methods: Simultaneous recording of interictal EEG and MEG was successful for 18 out of the 24 patients studied. Visual inspection of these recordings revealed IEDs with varying morphology and topography. Cluster analysis was used to classify these discharges on the basis of their spatial distribution followed by equivalent dipole analysis of the cluster averages. The locations of the equivalent dipoles were compared with the location of the epileptogenic lesions of the patient or, if these were not visible at MRI with the location of the interictal onset zones identified by subdural electroencephalography. Results: Generally IEDs were more abundantly in MEG than in the EEG recordings. Furthermore, the duration of the MEG spikes, measured from the onset till the spike maximum, was in most patients shorter than the EEG spikes. In most patients, distinct spike subpopulations were found with clearly different topographical field maps. Cluster analysis of MEG spikes followed by dipole localization was successful (n = 14) for twice as many patients as for EEG source analysis (n = 7), indicating that the localizability of interictal MEG is much better than of interictal EEG. Conclusions: The automated procedures developed in this study provide a fast screening method for identifying the distinct categories of spikes and the brain areas responsible for these spikes. The results show that MEG spike yield and localization is superior compared with EEG. This finding is of importance for the diagnosis and preoperative evaluation of patients with frontal lobe epilepsy. KEY WORDS: Frontal lobe epilepsy-Interictal epileptiform discharges-Cluster analysis-Equivalent dipole localization. Patients with frontal lobe epilepsy (FLE) comprise about 20% of the group of patients with localization related epilepsy. For mesiotemporal lobe epilepsy, it has been reported (e.g., by Boon and D'Havé, 1995; Gilliam et al.,
Magnetoencephalography in Focal Epilepsy
Epilepsia, 2000
The introduction of whole-head magnetoencephalographic (MEG) systems facilitating simultaneous recording from the entire brain surface has led to a major breakthrough in the MEG evaluation of epilepsy patients. MEG localizations estimates of the interictal spike zone showed excellent agreement with invasive electrical recordings and were useful to clarify the spatial relationship of the irritative zone and structural lesions. MEG appears to be especially useful for study of patients with neocortical epilepsy, and helped to guide the placement of subdural grid electrodes in patients with nonlesional epilepsies. MEG could differentiate between patients with mesial and lateral temporal seizure onset. Spike propagation in the temporal lobe and the spatio-temporal organization of the interictal spike complex could be studied noninvasively. MEG was useful to delineate essential brain regions before surgical procedures adjacent to the central fissure. MEG appears to be more sensitive than scalp EEG for detection of epileptic discharges arising from the lateral neocortex, whereas only highly synchronized discharges arising from mesial temporal structures could be recorded. A major limitation of MEG has been the recording of seizures because long-term recordings cannot be performed on a routine basis with the available technology. Because MEG and EEG yield both complementary and confirmatory information, combined MEG-EEG recordings in conjunction with advanced source modeling techniques should improve the noninvasive evaluation of epilepsy patients and further reduce the need for invasive procedures.
Magnetoencephalography and New Imaging Modalities in Epilepsy
Neurotherapeutics, 2017
The success of epilepsy surgery is highly dependent on correctly identifying the entire epileptogenic region. Current state-of-the-art for localizing the extent of surgically amenable areas involves combining high resolution three-dimensional magnetic resonance imaging (MRI) with electroencephalography (EEG) and magnetoencephalography (MEG) source modeling of interictal epileptiform activity. Coupling these techniques with newer quantitative structural MRI techniques, such as cortical thickness measurements, however, may improve the extent to which the abnormal epileptogenic region can be visualized. In this review we assess the utility of EEG, MEG and quantitative structural MRI methods for the evaluation of patients with epilepsy and introduce a novel method for the colocalization of a structural MRI measurement to MEG and EEG source modeling. When combined, these techniques may better identify the extent of abnormal structural and functional areas in patients with medically intractable epilepsy.
Seizure, 2017
In addition to visual analysis digital computerized recording of electrical and magnetic fields by using EEG and MEG opened a new window for research concerning improved understanding of pathophysiology, diagnosis and treatment of epilepsies. In the last 25 years MEG was used more and more in clinical studies concerning localization of focal epileptic activity, functional cortex and network analysis. Simultaneous MEG/EEG recording and analysis offer the use of complimentary information increasing the sensitivity for tracing primary epileptic activity. Combined MEG/Stereo-EEG recordings showed that MEG noninvasively identified regional interictal networks. The current role of MEG for presurgical evaluation with regard to noninvasive localization in MRI normal patients, guiding of invasive electrode implantation and correlation to postoperative outcome after epilepsy surgery is stressed. Challenges and future opportunities for MEG in clinical epileptology are discussed.
Localization of Interictal Epileptic Spikes With MEG
Journal of Clinical Neurophysiology, 2016
OBJECTIVE-To describe and optimize an automated beamforming technique followed by identification of locations with excess kurtosis (g2) for efficient detection and localization of interictal spikes in medically refractory epilepsy patients. METHODS-Synthetic Aperture Magnetometry with g2 averaged over a sliding time window (SAMepi) was performed in 7 focal epilepsy patients and 5 healthy volunteers. The effect of varied window lengths on detection of spiking activity was evaluated. RESULTS-Sliding window lengths of 0.5-10 seconds performed similarly, with 0.5 and 1 second windows detecting spiking activity in one of the 3 virtual sensor locations with highest kurtosis. These locations were concordant with the region of eventual surgical resection in these 7 patients who remained seizure free at one year. Average g2 values increased with increasing sliding window length in all subjects. In healthy volunteers kurtosis values stabilized in datasets longer than two minutes. CONCLUSIONS-SAMepi using g2 averaged over 1 second sliding time windows in datasets of at least 2 minutes duration reliably identified interictal spiking and the presumed seizure focus in these 7 patients. Screening the 5 locations with highest kurtosis values for spiking activity is an efficient and accurate technique for localizing interictal activity using MEG. SIGNIFICANCE-SAMepi should be applied using the parameter values and procedure described for optimal detection and localization of interictal spikes. Use of this screening procedure could significantly improve the efficiency of MEG analysis if clinically validated.
Epilepsy Research, 2008
Epilepsy; Focal cortical dysplasia (FCD); Electrocorticography (ECoG); Magnetoencephalography (MEG); Synthetic Aperture Magnetometrykurtosis (SAM(g 2 )) Summary This study was carried out to evaluate Synthetic Aperture Magnetometry-kurtosis (SAM(g 2 )), a spatially filtered source localization technique in magnetoencephalography (MEG), for identification of epileptogenic areas of focal cortical dysplasia (FCD). Three children with FCD were investigated to localize the ictal onset zone (IOZ). All patients subsequently had extraoperative electrocorticography (ECoG) for intractable epilepsy and surgical resection. SAM(g 2 ) analysis showed overlapping of interictal MEG spike sources with the IOZ on ECoG in all children. We recommend MEG-SAM(g 2 ) and MEG interictal spike source localization in patients with epileptogenic FCD.