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: 3.59). 10/2007; 28(8):1486-8. DOI: 10.3174/ajnr.A0596
Source: PubMed


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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    • "A cortical parcellation, provided by Freesurfer (Dale et al., 1999; Fischl et al., 1999), is helpful for understanding detailed anatomical location of activation (Figure 5). More importantly, spatial source distribution is considered representing to the cortical extent of spike involvement; activation in a small cortical area suggests that the spiking area is restricted (Hara et al., 2007; Tanaka et al., 2013b). Widespread cortical activation, extending over two lobes or bilaterally, may reflect a large abnormal neural network associated with epilepsy (Shiraishi et al., 2005a,b, 2011). "
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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.
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    • "The spatial accuracy of the MNE source modeling on the MEG data has been studied extensively. Based on our clinical experience and comparison with the ECD modeling results we chose our ROI by selecting a critical threshold of P value at 10 À6 [Hara et al., 2007]. The selection of the threshold may affect the size of ROI, and subsequently the available time courses within a ROI will be different. "
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