Magnetoencephalographic spikes not detected by conventional electroencephalography.

OBJECTIVE: To investigate some of the reasons why magnetoencephalographic (MEG) spikes are at times not apparent in conventional electroencephalograms (EEG) when the data are co-registered, and to explore to what extent modern EEG analysis methods can improve the yield. METHODS: Seventy seconds of MEG-EEG co-registration on a 122 channel Neuromag system were studied in a 10-year-old boy with Landau-Kleffner syndrome. Twenty-six EEG channels were originally recorded with a left ear reference. The EEG data were subsequently reformatted (BESA) to a variety of montages for the 10-20 and 10-10 electrode array. A 10 s data epoch was compared in detail for concordance between MEG and EEG spikes. To detect the characteristics of hidden low voltage EEG spikes, MEG spikes were averaged and compared with the concomitant averaged EEG spike. RESULTS: While there was an abundance of EEG as well as MEG spikes on the left; definite right-sided spikes were not visible in the EEG. Right hemispheric MEG spikes were, however, plentiful with an average strength of 757 fT. When the individual MEG spikes from the right hemisphere were compared with the corresponding EEG events their amplitude ranged between 24 and 31 microV and were, therefore, indistinguishable from background activity. The majority of them became visible, however, with further sophisticated data analysis. CONCLUSIONS: When the relative merits of MEG versus EEG recordings for the detection of epileptogenic spike are investigated the 10-20 system of electrode placement and conventional methods of EEG analysis do not provide optimal data assessment. The use of the 10-10 electrode array combined with modern methods of digital data analysis can provide better concordance with MEG data.     

MEG and EEG in epilepsy.

Both EEG and magnetoencephalogram (MEG), with a time resolution of 1 ms or less, provide unique neurophysiologic data not obtainable by other neuroimaging techniques. MEG has now emerged as a mature clinical technology. While both EEG and MEG can be performed with more than 100 channels, MEG recordings with 100 to 300 channels are more easily done because of the time needed to apply a large number of EEG electrodes. EEG has the advantage of the long-term video EEG recordings, which facilitates extensive temporal sampling across all periods of the sleep/wake cycle. MEG and EEG seem to complement each other for the detection of interictal epileptiform discharges, because some spikes can be recorded only on MEG but not on EEG and vice versa. Most studies indicate that MEG seems to be more sensitive for neocortical spike sources. Both EEG and MEG source localizations show excellent agreement with invasive electrical recordings, clarify the spatial relationship between the irritative zone and structural lesions, and finally, attribute epileptic activity to lobar subcompartments in temporal lobe and to a lesser extent in extratemporal epilepsies. In temporal lobe epilepsy, EEG and MEG can differentiate between patients with mesial, lateral, and diffuse seizure onsets. MEG selectively detects tangential sources. EEG measures both radial and tangential activity, although the radial components dominate the EEG signals at the scalp. Thus, while EEG provides more comprehensive information, it is more complicated to model due to considerable influences of the shape and conductivity of the volume conductor. Dipole localization techniques favor MEG due to the higher accuracy of MEG source localization compared to EEG when using the standard spherical head shape model. However, if special care is taken to address the above issues and enhance the EEG, the localization accuracy of EEG and MEG actually are comparable, although these surface EEG analytic techniques are not typically approved for clinical use in the United States. MEG dipole analysis is approved for clinical use and thus gives information that otherwise usually requires invasive intracranial EEG monitoring. There are only a few dozen whole head MEG units in operation in the world. While EEG is available in every hospital, specialized EEG laboratories capable of source localization techniques are nearly as scarce as MEG facilities. The combined use of whole-head MEG systems and multichannel EEG in conjunction with advanced source modeling techniques is an area of active development and will allow a better noninvasive characterization of the irritative zone in presurgical epilepsy evaluation. Finally, additional information on epilepsy may be gathered by either MEG or EEG analysis of data beyond the usual bandwidths used in clinical practice, namely by analysis of activity at high frequencies and near-DC activity.     

Detection of epileptiform activity by human interpreters: blinded comparison between electroencephalography and magnetoencephalography

PURPOSE: Objectively to evaluate whether independent spike detection by human interpreters is clinically valid in magnetoencephalography (MEG) and to characterize detection differences between MEG and scalp electroencephalography (EEG). METHODS: We simultaneously recorded scalp EEG and MEG data from 43 patients with intractable focal epilepsy. Raw EEG and MEG waveforms were reviewed independently by two experienced epileptologists, one for EEG and one for MEG, blinded to the other modality and to the clinical information. The number and localization of spikes detected by EEG and/or MEG were compared in relation to clinical diagnosis based on postoperative seizure freedom. RESULTS: Interictal spikes were captured in both EEG and MEG in 31, in MEG alone in eight, in EEG alone in one, and in neither modality in three patients. The number of detections ranged widely with no statistical difference between modalities. A median of 25.7% of total spikes was detectable by both modalities. Spike localization was similarly consistent with the epilepsy diagnosis in 85.2% (EEG) and 78.1% (MEG) of the patients. Inaccurate localization occurred only in those cases with very few spikes detected, especially when the detections were in one modality alone. CONCLUSIONS: Interictal epileptiform discharges are easily perceived in MEG. Independent spike identification in MEG can provide clinical results comparable, but not superior, to EEG. Many spikes were seen in only one modality or the other; therefore the use of both EEG and MEG may provide additional information.     

Simultaneous EEG and MEG source reconstruction in sparse electromagnetic source imaging

Electroencephalography (EEG) and magnetoencephalography (MEG) have different sensitivities to differently configured brain activations, making them complimentary in providing independent information for better detection and inverse reconstruction of brain sources. In the present study, we developed an integrative approach, which integrates a novel sparse electromagnetic source imaging method, i.e., variation‐based cortical current density (VB‐SCCD), together with the combined use of EEG and MEG data in reconstructing complex brain activity. To perform simultaneous analysis of multimodal data, we proposed to normalize EEG and MEG signals according to their individual noise levels to create unit‐free measures. Our Monte Carlo simulations demonstrated that this integrative approach is capable of reconstructing complex cortical brain activations (up to 10 simultaneously activated and randomly located sources). Results from experimental data showed that complex brain activations evoked in a face recognition task were successfully reconstructed using the integrative approach, which were consistent with other research findings and validated by independent data from functional magnetic resonance imaging using the same stimulus protocol. Reconstructed cortical brain activations from both simulations and experimental data provided precise source localizations as well as accurate spatial extents of localized sources. In comparison with studies using EEG or MEG alone, the performance of cortical source reconstructions using combined EEG and MEG was significantly improved. We demonstrated that this new sparse ESI methodology with integrated analysis of EEG and MEG data could accurately probe spatiotemporal processes of complex human brain activations. This is promising for noninvasively studying large‐scale brain networks of high clinical and scientific significance. Hum Brain Mapp, 2013. © 2010 Wiley Periodicals, Inc.     

Klinischer Stellenwert der Quellenanalyse epileptischer Aktivit?t

As a non-invasive tool MEG provides additional information for presurgical epilepsy diagnostics. Numerous studies have demonstrated its applicability and impact in comparison to invasive EEG and postsurgical outcome. As a shortcoming MEG is usually limited to the analysis of interictal activity. Although ictal EEG recording is mandatory for surgical decision-making, there are less data on EEG source analysis and its clinical implications; however, the results from EEG studies were promising. Therefore, MEG and EEG should be combined because the partially complementary information is an advantage compared to one analysis alone. This article summarizes the situation with respect to studies on preclinical diagnostics using source analysis in MEG and surface EEG combined and in particular discusses the clinical relevance of the methods.     

An automatic procedure for the analysis of electric and magnetic mismatch negativity based on anatomical brain mapping

Data processing techniques in electroencephalography (EEG) and magnetoencephalography (MEG) need user interactions. However, particularly in clinical applications, fast and objective data processing is important. Here we present an observer-independent method for EEG and MEG analysis of mismatch negativity (MMN) that allows reliable estimation of source activity based on objective anatomical references. The procedure integrates several steps including artifact rejection, source estimation and statistical analysis. It enables the evaluation of source activity in a fully automatic and unsupervised manner. To test its feasibility we obtained EEG and MEG responses in an auditory oddball paradigm in 12 healthy volunteers. The automatized method of EEG and MEG data analysis estimated source activity. The automatically detected MMN was closely comparable with the results obtained by a user-controlled method based on the dipole fitting. The presented workflow can be performed easily, rapidly, and reliably. This development may open new fields in research and clinical applications of source-based EEG and MEG.     

Controversies in neurophysiology. MEG is superior to EEG in localization of interictal epileptiform activity: Pro.

Both EEG and magnetoencephalography (MEG), with a time resolution of 1 ms or less, provide unique neurophysiologic data not obtainable by other neuroimaging techniques. MEG and EEG have often been compared to each other now although the two are complementary. Now that MEG has emerged as a mature clinical technology, it is worthwhile to compare the relative strengths of each for the localization of interictal epileptiform activity and to describe the strengths of MEG relative to EEG in the localization of interictal epileptiform activity. The sources of MEG and EEG signals will first be reviewed. Issues relevant to solving the forward problem and the inverse problem in MEG and EEG will be addressed followed by a comparison of research concerning the detection and localization of interictal epileptiform activity by MEG and EEG. The emphasis will be upon techniques and software routinely used in clinical applications but some emerging areas of MEG research which are entering clinical practice will also be reviewed. SIGNIFICANCE: MEG is a new noninvasive neurophysiologic technique which provides unique information for the clinical evaluation of patients with epilepsy, revealing aspects of neuronal function that previously could only be obtained by invasive EEG monitoring, and giving a new window for research of neuronal activity.     

Magnetoencephalographic and electroencephalographic evaluation in patients with cryptogenetic partial epilepsy.

Magnetoencephalography (MEG) has been applied for more than 20 years to the localization of the epileptic focus in partial epilepsies, but correlation with electroencephalographic (EEG) data in homogeneous groups of patients is scarce. OBJECTIVE: The aim of our work was to use EEG and MEG for the study of a group of adults and children affected by cryptogenetic partial epilepsy. METHODS: We analyzed the traces obtained from electroencephalographic and magnetoencephalographic recordings of 10 patients of ages ranging from 7 to 38 years affected by cryptogenetic partial epilepsy. We evaluated the presence of commonly detected or uniquely detected spikes, and, whenever possible, we used MEG for localization of the epileptic focus. RESULTS: Three patients showed no epileptic activity during the EEG and MEG sessions. Overall agreement between EEG and MEG (presence of concordant spikes with the same localization shown by both techniques) was obtained in five patients. In one patient the spikes detected by EEG and MEG were different, and in another patient interictal activity was demonstrated exclusively by EEG. CONCLUSIONS: EEG in this series was not inferior to MEG in terms of spike detection. Combination of EEG and MEG is feasible, better than each technique alone, and may be useful for non-invasive diagnosis and monitoring of pediatric and adult patients with partial epilepsies.     

Human brain mapping: hemodynamic response and electrophysiology.

In view of the recent advance in functional neuroimaging, the current status of non-invasive techniques applied for human brain mapping was reviewed by integrating two principles: hemodynamic and electrophysiological, from the viewpoint of clinical neurophysiology. The currently available functional neuroimaging techniques based on hemodynamic principles are functional magnetic resonance imaging (fMRI), positron emission tomography (PET) or single-photon emission computed tomography (SPECT), and near-infrared spectroscopy (NIRS). Electrophysiological techniques include electroencephalography (EEG), magnetoencephalography (MEG), and transcranial magnetic stimulation (TMS). As for the coupling between hemodynamic response and neuronal activity (neurovascular coupling), experimental studies suggest that the hemodynamic response is significantly correlated to neuronal activity, especially local field potential (synaptic activity) rather than spiking activity, within a certain range. The hemodynamic response tends to be more widespread in space and lasts longer in time as compared with the neuronal activity. Since each technique has its own characteristic features especially in terms of spatial and temporal resolution, it is important to adopt the most appropriate technique for solving each specific question, and it is useful to combine two techniques either simultaneously or in separate sessions. As for the multi-modal approach, the combined use of EEG and MEG, EEG and PET, or EEG and fMRI is applied for the simultaneous studies, and for the separate use of two different techniques, the information obtained from fMRI is used for estimating the generator source from EEG or MEG data (fMRI-constrained source estimation). Functional connectivity among different brain areas can be studied by using a single technique such as the EEG coherence or the correlation analysis of fMRI or PET data, or by combining the stimulation technique such as TMS with neuroimaging. Further advance of each technology and improvement in the analysis method will promote the understanding of precise functional specialization and inter-areal coupling, and will contribute to the increased efficacy of rapidly developing physiological treatments of neurological and psychiatric disorders.     

脑磁图和脑电图在癫痫诊治中的应用

目的:观察脑磁图、脑电图和磁共振检查在癫痫诊治中的应用,探讨脑磁图和脑电图的相关性。方法:选择38例经临床诊断的癫痫患者,已进行磁共振检查,并经脑磁图和脑电图发现异常放电。观察三种检查方法的定位符合率,比较影像检查与电生理检查的关系。结果:MEG与EEG定位完全一致的有18例(47．4％),定位基本一致(致少有1个叶定位一致)的有8例(21．1％)。EEG发现双侧放电的13例中,5例与MEG定位基本一致,而EEG单侧局灶放电的25例中,20例与MEG基本一致,EEG与MEG定位符合率在单侧局灶放电患者中高(P＜0．05)。MRI发现结构异常15例,与MEG和EEG定位均一致的有6例。结论:脑磁图和脑电图定位符合率约为68．5％。在单侧局灶放电中, MEG与EEG相结合可使致痫灶定位更加准确。     

脑磁图对颞叶以外癫痫颅内电极置入的指导价值

目的研究在颞叶以外癫痫的诊疗中,脑磁图对颅内电极置入方案的指导价值。方法自2011年3月至2013年9月,对将行颅内电极置入的顽固性癫痫患者评估,先在电-临床症状学、影像学、脑电图等结果的基础上设计出初步的颅内电极埋置方案,然后添加MEG定位信息,并根据MEG调整电极埋置方案,得出最终颅内电极置入计划。继而行颅内脑电图监测并行手术治疗。最后分析颞叶以外癫痫中,脑磁图对颅内电极置入方案的指导价值。结果成功定位癫痫发作起始区并完成手术治疗、且经颅内电极证实为颞叶以外癫痫（NTLE）者有22例。9例（40.1%）患者MEG对iEEG电极置入方案产生额外于其它常规评估手段的指导作用（因MEG而增加电极覆盖）,其中7例（31.8%）经iEEG证实这些增加的定位信息与发作起始区一致。术后平均随访33.3个月：EngelⅠ级14例（63.6%）,EngelⅡ级3例（13.6%）,EngelⅢ级3例（13.6%）,EngelⅣ级2例（9.1%）。结论区别于视频脑电图、MRI等其它的无创检查,MEG能够对有创的iEEG电极埋置方案起到额外指导作用,能使电极埋置更合理精确、有针对性,并可能提高癫痫手术的疗效。     

Combined EEG and MEG analysis of early somatosensory evoked activity in children and adolescents with focal epilepsies.

OBJECTIVE: The study aimed to evaluate differences between EEG and MEG analysis of early somatosensory evoked activity in patients with focal epilepsies in localizing eloquent areas of the somatosensory cortex. METHODS: Twenty-five patients (12 male, 13 female; age 4-25 years, mean 11.7 years) were included. Syndromes were classified as symptomatic in 17, idiopathic in 2 and cryptogenic in 6 cases. 10 patients presented with malformations of cortical development (MCD). 122 channel MEG and simultaneous 33-channel EEG were recorded during tactile stimulation of the thumb (sampling rate 769 Hz, band-pass 0.3-260 Hz). Forty-four hemispheres were analyzed. Hemispheres were classified as type I: normal (15), II: central structural lesion (16), III: no lesion, but central epileptic discharges (ED, 8), IV: lesion or ED outside the central region (5). Analysis of both sides including one normal and one type II or III hemisphere was possible in 15 patients. Recordings were repeated in 18 hemispheres overall. Averaged data segments were filtered (10-250 Hz) and analyzed off-line with BESA. Latencies and amplitudes of N20 and P30 were analyzed. A regional source was fitted for localizing S1 by MRI co-registration. Orientation of EEG N20 was calculated from a single dipole model. RESULTS: EEG and MEG lead to comparable good results in all normal hemispheres. Only EEG detected N20/P30 in 3 hemispheres of types II/III while MEG showed no signal. N20 dipoles had a more radial orientation in these cases. MEG added information in one hemisphere, when EEG source analysis of a clear N20 was not possible because of a low signal-to-noise ratio. Overall N20 dipoles had a more radial orientation in type II when compared to type I hemispheres (p=0.01). Further N20/P30 parameters (amplitudes, latencies, localization related to central sulcus) showed no significant differences between affected and normal hemispheres. Early somatosensory evoked activity was preserved within the visible lesion in 5 of the 10 patients with MCD. CONCLUSIONS: MEG should be combined with EEG when analyzing tactile evoked activities in hemispheres with a central structural lesion or ED focus. SIGNIFICANCE: At time, MEG analysis is frequently applied without simultaneous EEG. Our results clearly show that EEG may be superior under specific circumstances and combination is necessary when analyzing activity from anatomically altered cortex.     

Can Magnetoencephalography Aid Epilepsy Surgery?

Magnetoencephalography (MEG) has a long history of development for the application of epilepsy. Technical and clinical validation of spike source estimation has been demonstrated in most partial epilepsies. The question that needs to be clarified concerns clinical value: Do identification and localization of epileptiform discharges play an important role in the determination of epilepsy localization for surgery? EEG is the mainstay in the investigation of seizure disorders and will remain so because it alone possesses the attribute of long-term recordings that can capture seizures. In contrast, MEG has the unique capability of nearly instantaneous high-resolution recording, with detection sensitivity and spike localization precision beyond that of EEG. Do these distinctions matter from a clinical standpoint?The magnetoencephalogram (MEG) is a remarkable technological accomplishment. In a superconducting environment with induction coils submerged in liquid helium at near absolute zero temperature, whole-head arrays of detectors record the incredibly small magnetic fields (10⁻¹² T) generated by intraneuronal currents of the human brain in vivo. Although analogous to the EEG in that both measure and record signal reflecting neuronal activity, fundamental differences exist (1). Today''s MEG systems allow rapid high-resolution (100–300 channels) recordings of cortical function and dysfunction that are neither attenuated nor distorted by the skull or other variable intervening tissue layers between the scalp and brain. These technical attributes created the tendency, at least historically, to use MEG rather than EEG for source analysis. High-resolution EEG recording combined with real-head modeling (i.e., using the subject''s own anatomy from their MRI or CT) may overcome some of the source localization challenges of EEG; however to date, this approach still has not been used or validated to any appreciable extent in the clinical arena.MEG, in contrast, has been studied and used extensively for clinical application since the inception of multidetector array systems became available in the early 1990s. In fact, in the United States, MEG-based source localization, called magnetic source imaging (MSI) when combined with structural imaging, received Food and Drug Administration approval for clinical use in 1997 and was given Current Procedural Terminology (CPT) codes for epilepsy localization and presurgical brain mapping in 2003. Yet, in spite of nearly two decades of MEG clinical investigation, controversy and questions remain as to what contribution MEG adds to EEG and the role that it plays among other established epilepsy localization tests, particularly multimodality imaging and intracranial EEG (ICEEG). MEG presurgical brain mapping is well established for primary sensory and motor modalities; more complex cognitive mapping is probably best served by MEG or its combination with fMRI, thus providing high spatial and temporal resolution to resolve networked areas of brain processing that are likely to overlap. Although brain mapping is often an integral component of the presurgical evaluation, this review is limited to MEG and epilepsy localization.     

Establishing correlations of scalp field maps with other experimental variables using covariance analysis and resampling methods.

OBJECTIVE: In EEG/MEG experiments, increasing the number of sensors improves the spatial resolution of the results. However, the standard statistical methods are inappropriate for these multivariate, highly correlated datasets. We introduce a procedure to identify spatially extended scalp fields that correlate with some external, continuous measure (reaction-time, performance, clinical status) and to test their significance. METHODS: We formally deduce that the channel-wise covariance of some experimental variable with scalp field data directly represents intracerebral sources associated with that variable. We furthermore show how the significance of such a representation can be tested with resampling techniques. RESULTS: Simulations showed that depending on the number of channels and subjects, effects can be detected already at low signal to noise ratios. In a sample analysis of real data, we found that foreign-language evoked ERP data were significantly associated with foreign-language proficiency. Inverse solutions of the extracted covariances pointed to sources in language-related areas. CONCLUSIONS: Covariance mapping combined with bootstrapping methods has high statistical power and yields unique and directly interpretable results. SIGNIFICANCE: The introduced methodology overcomes some of the 'traditional' statistical problems in EEG/MEG scalp data analysis. Its application can improve the reproducibility of results in the field of EEG/MEG.     

Effects of alcohol on spontaneous neuronal oscillations: a combined magnetoencephalography and electroencephalography study

Electroencephalography (EEG) and magnetoencephalography (MEG) can detect different aspects of alcohol effects on auditory processing measured with event-related potentials and magnetic fields. The present study aimed to detect alcohol-induced changes in spontaneous neuronal oscillations with combined EEG and MEG techniques. The effects of alcohol on spontaneous neuronal rhythms were studied in 12 healthy subjects after 0.8 g/kg alcohol or juice in a double-blind, placebo-controlled, cross-over design using simultaneous high-resolution MEG and EEG in eyes-open and eyes-closed conditions. The data were analyzed with a power spectral density analysis. MEG recording showed that alcohol significantly increased the relative power of alpha rhythm (8-10 Hz) and reduced the relative power of beta activity (17-25 Hz) in both left and right hemispheres, but only in the eyes-closed condition. These effects did not depend on gender. No analogous statistically significant changes were observed in EEG rhythms. However, the power of alpha and beta rhythms was positively correlated in MEG and EEG recordings, indicating that MEG and EEG reflect similar processes. A distinct sensitivity of MEG and EEG to the sources of cortical oscillations, a better signal-to-noise ratio of MEG, as well as strong spatial blurring of potentials in EEG are most likely the reasons for the observed differences in the effects of alcohol on spontaneous oscillations as detected with two methods.     

Modality-specific spike identification in simultaneous magnetoencephalography/electroencephalography: a methodological approach.

Epileptiform spikes may have a different morphology and signal-to-noise ratio in simultaneously recorded EEGs and magnetoencephalograms (MEGs) that may lead to differences in the identification of spikes if both the modalities are presented separately. Moreover, there are no criteria for MEG spikes. It is unknown to which extent the visual assessment of MEG data yields consistent and meaningful results. Nineteen patients were selected with mesial temporal lobe epilepsy who underwent whole-head simultaneous MEG/EEG. These data were split into MEG and EEG files and were assessed independently by three observers for the occurrence of spikes. Interobserver kappa values were calculated. A mean kappa value greater than 0.5 was taken as a criterion for the presence of unequivocal spikes. Index cases from the resulting four subgroups were studied further. One patient had unequivocal spikes in both modalities, one in EEG only, one in MEG only, and one did not show any unequivocal spike. Spikes on which at least two observers agreed were then subjected to a template match algorithm to test for equal morphology and distribution. Equal spikes were averaged and electrical and magnetic field maps were plotted. Unequivocal spikes were found in both MEG and EEG in one patient, in MEG only in two patients, in EEG only in two patients, and no spikes in either modality were seen in 14 patients. In the four index patients, MEG showed 50 to 80% more spikes than EEG. After averaging identical consensus spikes, MEG spikes revealed a concomitant spike in the EEG, but the reverse was not always true. Even in the patient with MEG and EEG spikes that met all selection criteria, simultaneous field maps showed unexpected inconsistencies. In most patients with mesial temporal lobe epilepsy, there are no unequivocal spikes during MEG/EEG. In some cases, however, experienced electroencephalographers can identify MEG spikes reliably. Because of a better signal-to-noise ratio, more spikes could be identified in MEG than in EEG. Simultaneous MEG/EEG recordings do not simply ensure the best of both, but one modality may improve the identification of spikes in the other. In addition, different aspects of a complex source can be revealed. Our three-step approach to combined data ensures a reproducible selection of spikes for source modeling.     

Controversies in clinical neurophysiology. MEG is superior to EEG in the localization of interictal epileptiform activity: Con.

OBJECTIVE: To assess whether MEG is superior to scalp-EEG in the localization of interictal epileptiform activity and to stress the 'con' part in this controversy. METHODS: Advantages and disadvantages of the two techniques were systematically reviewed. RESULTS: While MEG and EEG complement each other for the detection of interictal epileptiform discharges, EEG offers the advantage of long-term recording significantly increasing its diagnostic yield which is not feasible with MEG. Localization accuracies of EEG and MEG are comparable once inaccuracies for the solution of the forward problem are eliminated. MEG may be more sensitive for the detection of neocortical spike sources. EEG and MEG source localizations show comparable agreement with invasive electrical recordings, can clarify the spatial relationship between the irritative zone and structural lesions, guide the placement of invasive electrodes and attribute epileptic activity to lobar subcompartments in temporal lobe epilepsy and to a lesser extent in extratemporal epilepsy. CONCLUSIONS: A clear superiority of MEG over EEG for the localization of interictal epileptiform activity cannot be derived from the studies presently available. SIGNIFICANCE: The combination of EEG and MEG provides information for the localization of interictal epileptiform activity which cannot be obtained with either technique alone.     

脑磁图在癫外科灶定位中的作用(附47例分析)

目的探讨脑磁图(MEG)在癫外科灶定位中的临床价值。方法回顾性分析47例行MEG及头皮视频脑电图(V-EEG)检查的难治性癫病人的病例资料。其中39例接受手术治疗;10例开颅行皮质脑电(ECoG)监测。将MEG的结果与发作期及发作间期V-EEG及ECoG结果进行对比分析。结果MEG显示灶位置与发作间期和发作期V-EEG结果吻合率分别达76.6%和80.9%,与发作间期和发作期ECoG的吻合率均为80.0%。39例手术病人中,术后EngelⅠ级21例,Ⅱ级10例,Ⅲ级8例;其中29例拟切除的区域涉及到解剖学意义上的功能区,术中根据MEG显示的功能区位置进行了适当的处理,术后神经系统功能障碍未加重。结论MEG为无创性检查,对高频放电检出率较高,弥补了脑电在介质衰减方面的不足;同时也有利于癫外科治疗中对功能区的保护。     

Sensitivity of magnetoencephalography as a diagnostic tool for epilepsy: a prospective study

Aim. The diagnostic process for epilepsy can be lengthy and stressful, which may delay the start of treatment. The objective of this study was to determine the benefit of routine magnetoencephalography (MEG) with regard to diagnostic gain, compared to routine electroencephalography (EEG), EEG following sleep deprivation (EEGsd), and 24‐hour EEG. Methods. In this prospective study, patients were included from two centres (Academic Centre for Epileptology Kempenhaeghe, Heeze and Elisabeth‐Twee Steden Hospital, Tilburg) and MEG recording took place at a single centre (Amsterdam University Medical Centre, Vrije Universiteit Amsterdam) in The Netherlands. Consecutively referred patients from peripheral hospitals were included between August 2013 and March 2016. Patients were offered routine MEG in addition to EEG examination and MRI for the diagnosis of epilepsy. The final clinical diagnosis was based on all available clinical data and test results at the end of the diagnostic process. Sensitivity, specificity, and positive and negative predictive values were calculated for routine EEG, routine EEG plus additional EEG and MEG. In addition, diagnostic gain associated with MEG, relative to the other modalities, was calculated. Secondary outcome was congruence of localization of epileptiform discharges between MEG and MRI or final clinical diagnosis. Results. Based on a cohort of 138 patients, sensitivity and specificity was shown to be 31.6% and 78.4% for routine MEG, 31.6% and 100% for routine EEG, and 52.6% and 97.3% for routine EEG plus additional EEG, respectively. Routine MEG demonstrated a diagnostic gain of 16.8% compared to routine EEG and 9.5% compared to routine EEG plus additional EEG. In 35.7% of patients with a lesion on MRI that was consistent with the final clinical diagnosis, MEG showed epileptiform discharges in the same area. Conclusion. Routine MEG may provide additional value during the initial diagnosis of epilepsy.     

Benefit of simultaneous recording of EEG and MEG in dipole localization

PURPOSE: In this study, we tried to show that EEG and magnetoencephalography (MEG) are clinically complementary to each other and that a combination of both technologies is useful for the precise diagnosis of epileptic focus. METHODS: We recorded EEGs and MEGs simultaneously and analyzed dipoles in seven patients with intractable localization-related epilepsy. MEG dipoles were analyzed by using a BTI Magnes 148-channel magnetometer. EEG dipoles were analyzed by using a realistically shaped four-layered head model (scalp-skull-fluid-brain) built from 2.0-mm slice magnetic resonance imaging (MRI) images. RESULTS: (a) In two of seven patients, MEG could not detect any epileptiform discharges, whereas EEG showed clear spikes. However, dipoles estimated from the MEG data corresponding to the early phase of EEG spikes clustered at a location close to that of the EEG-detected dipole. (b) In two of seven patients, EEG showed only intermittent high-voltage slow waves (HVSs) without definite spikes. However, MEG showed clear epileptiform discharges preceding these EEG-detected HVSs. Dipoles estimated for these EEG-detected HVSs were located at a location close to that of the MEG-detected dipoles. (c) Based on the agreement of the results of these two techniques, surgical resection was performed in one patient with good results. CONCLUSIONS: Dipole modeling of epileptiform activity by MEG and EEG sometimes provides information not obtainable with either modality used alone.