Magnetoencephalographic mapping of interictal spike propagation: a technical and clinical report.

MGH/MIT/HMS Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, USA.
American Journal of Neuroradiology (Impact Factor: 3.68). 10/2007; 28(8):1486-8. DOI: 10.3174/ajnr.A0596
Source: PubMed

ABSTRACT Distinguishing propagated epileptic activity from primary epileptic foci is of critical importance in presurgical evaluation of patients with medically intractable focal epilepsy. We studied an 11-year-old patient with complex partial epilepsy by using simultaneous magnetoencephalography (MEG) and electroencephalography (EEG). In EEG, bilateral interictal discharges appeared synchronous, whereas MEG source analysis suggested propagation of spikes from the right to the left frontal lobe.

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    ABSTRACT: To investigate whether interictal magnetoencephalography (MEG) concordant with other techniques can predict surgical outcome in patients with lesional and nonlesional refractory neocortical epilepsy (NE). 23 Patients with lesional NE and 20 patients with nonlesional NE were studied. MEG was recorded for all patients with a 275 channel whole-head system. Synthetic aperture magnetometry (SAM) with excess kurtosis (g2) and conventional Equivalent Current Dipole (ECD) were used for MEG data analysis. 27 Patients underwent long-term extraoperative intracranial video electroencephalography (iVEEG) monitoring. Surgical outcomes were assessed based on more than 1-year of post-surgical follow-up using Engel classification system. As we expected, both favorable outcomes (Engel class I or II) and seizure freedom outcomes (Engel class IA) were higher for the concordance condition (MEG findings are concordant with MRI or iVEEG findings) versus the discordance condition. Also the seizure free rate was significantly higher (χ2=5.24, P<0.05) for the patients with lesional NE than for the patients with nonlesional NE. In 30% of the patients with nonlesional NE, the MEG findings proved to be valuable for intracranial electrode implantation. This study demonstrates that a favorable post-surgical outcome can be obtained in most patients with concordant MEG and MRI results even without extraoperative iVEEG monitoring, which indicates that the concordance among different modalities could indicate a likelihood of better postsurgical outcomes. However, extraoperative iVEEG monitoring remains prerequisite to the patients with discordant MEG and MRI findings. For nonlesional cases, our results showed that MEG could provide critical information in the placement of intracranial electrodes.
    Seizure 07/2011; 20(9):692-700. DOI:10.1016/j.seizure.2011.06.021 · 2.06 Impact Factor
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    ABSTRACT: Magnetoencephalography (MEG), which acquires neuromagnetic fields in the brain, is a useful diagnostic tool in presurgical evaluation of epilepsy. Previous studies have shown that MEG affects the planning intracranial electroencephalography placement and correlates with surgical outcomes by using a single dipole model. Spatiotemporal source analysis using distributed source models is an advanced method for analyzing MEG, and has been recently introduced for analyzing epileptic spikes. It has advantages over the conventional single dipole analysis for obtaining accurate sources and understanding the propagation of epileptic spikes. In this article, we review the source analysis methods, describe the techniques of the distributed source analysis, interpretation of source distribution maps, and discuss the benefits and feasibility of this method in evaluation of epilepsy.
    Frontiers in Human Neuroscience 02/2014; 8:62. DOI:10.3389/fnhum.2014.00062 · 2.90 Impact Factor
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    ABSTRACT: A persistent problem in developing plausible neurophysiological models of perception, cognition, and action is the difficulty of characterizing the interactions between different neural systems. Previous studies have approached this problem by estimating causal influences across brain areas activated during cognitive processing using structural equation modeling (SEM) and, more recently, with Granger-Geweke causality. While SEM is complicated by the need for a priori directional connectivity information, the temporal resolution of dynamic Granger-Geweke estimates is limited because the underlying autoregressive (AR) models assume stationarity over the period of analysis. We have developed a novel optimal method for obtaining data-driven directional causality estimates with high temporal resolution in both time and frequency domains. This is achieved by simultaneously optimizing the length of the analysis window and the chosen AR model order using the SURE criterion. Dynamic Granger-Geweke causality in time and frequency domains is subsequently calculated within a moving analysis window. We tested our algorithm by calculating the Granger-Geweke causality of epileptic spike propagation from the right frontal lobe to the left frontal lobe. The results quantitatively suggested that the epileptic activity at the left frontal lobe was propagated from the right frontal lobe, in agreement with the clinical diagnosis. Our novel computational tool can be used to help elucidate complex directional interactions in the human brain.
    Human Brain Mapping 06/2009; 30(6):1877-86. DOI:10.1002/hbm.20772 · 6.92 Impact Factor

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