The purpose of this study is to develop and quantitatively assess whether fusion of EEG and MEG (... more The purpose of this study is to develop and quantitatively assess whether fusion of EEG and MEG (MEEG) data within the maximum entropy on the mean (MEM) framework increases the spatial accuracy of source localization, by yielding better recovery of the spatial ex-tent and propagation pathway of the underlying generators of inter-ictal epileptic discharges (IEDs). The key element in this study is the integration of the complementary in-formation from EEG and MEG data within the MEM framework. MEEG was compared with EEG and MEG when localizing single transient IEDs. The fusion approach was evaluated using realistic simulation models involving one or two spatially extended sources mimicking propagation patterns of IEDs. We also assessed the impact of the number of EEG electrodes required for an efficient EEG–MEG fusion. MEM was compared with minimum norm estimate, dynamic statistical parametric mapping, and standardized low-resolution electromagnetic tomogra-phy. The fusion approach wa...
We investigated two important means for improving source reconstruction in presurgical ep-ilepsy ... more We investigated two important means for improving source reconstruction in presurgical ep-ilepsy diagnosis. The first investigation is about the optimal choice of the number of epileptic spikes in averaging to (1) sufficiently reduce the noise bias for an accurate determination of the center of gravity of the epileptic activity and (2) still get an estimation of the extent of the irritative zone. The second study focuses on the differences in single modality EEG (80-electrodes) or MEG (275-gradiometers) and especially on the benefits of combined EEG/ MEG (EMEG) source analysis. Both investigations were validated with simultaneous ste-reo-EEG (sEEG) (167-contacts) and low-density EEG (ldEEG) (21-electrodes). To account for the different sensitivity profiles of EEG and MEG, we constructed a six-compartment fi-nite element head model with anisotropic white matter conductivity, and calibrated the skull conductivity via somatosensory evoked responses. Our results show that, unlike single...
ObjectivePharmacological activation of focal epileptic discharges is employed during presurgical ... more ObjectivePharmacological activation of focal epileptic discharges is employed during presurgical evaluation to increase the yield of epileptic activity. Administration of etomidate has been shown to increase focal epileptic activity recorded by foramen ovale electrodes and by magnetoencephalography (MEG). However, results from simultaneous MEG and electroencephalography (MEG/EEG) recordings suggest that sensitivity of surface EEG for epileptic spikes might be diminished due to generalized theta/delta activity caused by etomidate. This project aimed to show differences between epilepsy patients and a control group with respect to clinical and EEG changes after administration of etomidate.MethodsA total of 11 patients with focal epilepsy underwent activation with etomidate with simultaneous video EEG monitoring during presurgical evaluation. In addition activation with etomidate was performed in a control group of four patients without epilepsy under surveillance with simultaneous vid...
Purpose To evaluate a MRI postprocessing tool for the enhanced and rapid detection of focal corti... more Purpose To evaluate a MRI postprocessing tool for the enhanced and rapid detection of focal cortical dysplasia (FCD). Methods MP2RAGE sequences of 40 consecutive, so far MRI-negative patients and of 32 healthy controls were morphometrically analyzed to highlight typical FCD features. The resulting morphometric maps served as input for an artificial neural network generating a FCD probability map. The FCD probability map was inversely normalized, co-registered to the MPRAGE2 sequence, and re-transferred into the PACS system. Co-registered images were scrolled through “within a minute” to determine whether a FCD was present or not. Results Fifteen FCD, three subcortical band heterotopias (SBH), and one periventricular nodular heterotopia were identified. Of those, four FCD and one SBH were only detected by MRI postprocessing while one FCD and one focal polymicrogryia were missed, respectively. False-positive results occurred in 21 patients and 22 healthy controls. However, true positi...
ABSTRACT Main objective(s) The aim of this prospective study is to examine the potential contribu... more ABSTRACT Main objective(s) The aim of this prospective study is to examine the potential contribution of SWDD localisation in clinical preoperative epilepsy focus localisation. Methods Preoperative MEG-SWDD localisations are calculated and overlaid on MR-images of pharmaco-resistant epilepsy patients undergoing presurgical focus localisation evaluation. For all 10 patients who have been operated within at least 6 months, postsurgical outcomes available up to now, are discussed. SWDD localisation results are compared to other preoperative findings and to MEG-spike results and are correlated to postoperative outcome (Engel) after 6 months or 12 months. Results 7 of 10 patients showed significant local increase of SWDD. In these SWDD localisation results were always concordant with preoperative findings. All 7 patients were postoperatively seizure-free or had a worthwhile improvement of seizure situation. 3 of 10 patients showed no significant local increase of SWDD and, therefore, were without SWDD result. Comparison to MEG spike results: Among these 7 patients, 6 showed MEG-spike concordant localisations, one had no spikes in the MEG. Conclusions SWDD is able to localise brain areas exhibiting pathological slow wave activity and might become a useful tool for preoperative epilepsy diagnosis. KeywordsMagnetoencephalography-slow wave-slow wave dipole density-epilepsy-postoperative outcome
We investigated two important means for improving source reconstruction in presurgical epilepsy d... more We investigated two important means for improving source reconstruction in presurgical epilepsy diagnosis. The first investigation is about the optimal choice of the number of epileptic spikes in averaging to (1) sufficiently reduce the noise bias for an accurate determination of the center of gravity of the epileptic activity and (2) still get an estimation of the extent of the irritative zone. The second study focuses on the differences in single modality EEG (80-electrodes) or MEG (275-gradiometers) and especially on the benefits of combined EEG/MEG (EMEG) source analysis. Both investigations were validated with simultaneous stereo-EEG (sEEG) (167-contacts) and low-density EEG (ldEEG) (21-electrodes). To account for the different sensitivity profiles of EEG and MEG, we constructed a six-compartment finite element head model with anisotropic white matter conductivity, and calibrated the skull conductivity via somatosensory evoked responses. Our results show that, unlike single mod...
Zusammenfassung Hintergrund Die pharmakologische Aktivierung wird genutzt, um in der prächirurgi... more Zusammenfassung Hintergrund Die pharmakologische Aktivierung wird genutzt, um in der prächirurgischen Evaluation von Patienten mit Epilepsie das Auftreten der epileptischen Aktivität zu erhöhen. Bisher konnte gezeigt werden, dass nach der Verabreichung von Etomidat vermehrt fokale epileptische Aktivität mithilfe von Foramen-ovale-Elektroden und Magnetenzephalographie (MEG) aufgezeichnet wurde. Jedoch ergaben simultane MEG-/EEG-Aufzeichnungen, dass die Sensitivität des Oberflächen-EEG durch eine generalisierte θ-/δ-Aktivität, die durch Etomidat
Spike-based magnetoencephalography (MEG) source localization is an established method in the pres... more Spike-based magnetoencephalography (MEG) source localization is an established method in the presurgical evaluation of epilepsy patients. Focal cortical dysplasias (FCDs) are associated with focal epileptic discharges of variable morphologies in the beta frequency band in addition to single epileptic spikes. Therefore, we investigated the potential diagnostic value of MEG-based localization of spike-independent beta band (12-30Hz) activity generated by epileptogenic lesions. Five patients with FCD IIB underwent MEG. In one patient, invasive EEG (iEEG) was recorded simultaneously with MEG. In two patients, iEEG succeeded MEG, and two patients had MEG only. MEG and iEEG were evaluated for epileptic spikes. Two minutes of iEEG data and MEG epochs with no spikes as well as MEG epochs with epileptic spikes were analyzed in the frequency domain. MEG oscillatory beta band activity was localized using Dynamic Imaging of Coherent Sources. Intralesional beta band activity was coherent between simultaneous MEG and iEEG recordings. Continuous 14Hz beta band power correlated with the rate of interictal epileptic discharges detected in iEEG. In cases where visual MEG evaluation revealed epileptic spikes, the sources of beta band activity localized within <2cm of the epileptogenic lesion as shown on magnetic resonance imaging. This result held even when visually marked epileptic spikes were deselected. When epileptic spikes were detectable in iEEG but not MEG, MEG beta band activity source localization failed. Source localization of beta band activity has the potential to contribute to the identification of epileptic foci in addition to source localization of visually marked epileptic spikes. Thus, this technique may assist in the localization of epileptic foci in patients with suspected FCD.
Distributed inverse solutions aim to realistically
reconstruct the origin of interictal epileptic... more Distributed inverse solutions aim to realistically reconstruct the origin of interictal epileptic discharges (IEDs) from noninvasively recorded electroencephalography (EEG) and magnetoencephalography (MEG) signals. Our aim was to compare the performance of different distributed inverse solutions in localizing IEDs: coherent maximum entropy on the mean (cMEM), hierarchical Bayesian implementations of independent identically distributed sources (IID, minimum norm prior) and spatially coherent sources (COH, spatial smoothness prior). Source maxima (i.e., the vertex with the maximum source amplitude) of IEDs in 14 EEG and 19 MEG studies from 15 patients with focal epilepsy were analyzed. We visually compared their concordance with intracranial EEG (iEEG) based on 17 cortical regions of interest and their spatialdispersion around source maxima. Magnetic source imaging (MSI) maxima from cMEM were most often confirmed by iEEG (cMEM: 14/19, COH: 9/19, IID: 8/19 studies). COH electric source imaging (ESI) maxima co-localized best with iEEG (cMEM: 8/14, COH: 11/14, IID: 10/14 studies). In addition, cMEM was less spatially spread than COH and IID for ESI and MSI (p\0.001 Bonferronicorrected post hoc t test). Highest positive predictive values for cortical regions with IEDs in iEEG could be obtained with cMEM for MSI and with COH for ESI. Additional realistic EEG/MEG simulations confirmed our findings. Accurate spatially extended sources, as found in cMEM (ESI and MSI) and COH (ESI) are desirable for source imaging of IEDs because this might influence surgical decision. Our simulations suggest that COH and IID overestimate the spatial extent of the generators compared to cMEM.
Primate models are commonly used in Parkinson&amp... more Primate models are commonly used in Parkinson's disease research to study stereotaxic strategies that demand accurate localization of the structures in basal ganglia. We demonstrate a method to construct an extensive tabular database of 3D stereotaxic co-ordinates of various basal ganglia structures from high-quality magnetic resonance (MR) images of 47 adult female 3-5 kg rhesus monkeys. For each animal, the structures in the basal ganglia were traced as they appeared on the axial MR images. Their maximal outlines were projected in the axial plane to create a stack of images and X, Y, Z co-ordinates were calculated for margins of each structure. These co-ordinates and the outlines of the individual nuclei help delineate a "common area," which was further narrowed down to a point that represents the 'most reliable target point' (MRTP) in subthalamic nucleus, globus pallidum, caudate and putamen on both sides. Common area and MRTP represent the region that can most definitely be associated with a structure and hence the most definite target for a given structure. The goal of this study is to demonstrate the method of construction, discuss the feasibility and usefulness of such a tabular database that could potentially add to accuracy of localization while using atlas-based stereotaxy. Though use of MRI remains a standard practice and advances in imaging have made targeting for functional surgery more accurate, in developing countries that implies prohibitive costs per procedure. Population based human databases similar to the monkey database described here, when used along with less expensive imaging modalities can reduce the costs considerably as well as add to the accuracy of targeting.
Blood oxygenation level-dependent (BOLD) signal changes at the time of interictal epileptic disch... more Blood oxygenation level-dependent (BOLD) signal changes at the time of interictal epileptic discharges (IEDs) identify their associated vascular/hemodynamic responses. BOLD activations and deactivations can be found within the epileptogenic zone but also at a distance. Source imaging identifies electric (ESI) and magnetic (MSI) sources of IEDs, with the advantage of a higher temporal resolution. Therefore, the objective of our study was to evaluate the spatial concordance between ESI/MSI and BOLD responses for similar IEDs. Twenty-one patients with similar IEDs in simultaneous electroencephalogram/functional magnetic resonance imaging (EEG/fMRI) and in simultaneous EEG/magnetoencephalogram (MEG) recordings were studied. IEDs in EEG/fMRI acquisition were analyzed in an event-related paradigm within a general linear model (GLM). ESI/MSI of averaged IEDs was performed using the Maximum Entropy on the Mean. We assessed the spatial concordance between ESI/MSI and clusters of BOLD activations/deactivations with surface-based metrics. ESI/MSI were concordant with one BOLD cluster for 20/21 patients (concordance with activation: 14/21 patients, deactivation: 6/21 patients, no concordance: 1/21 patients; concordance with MSI only: 3/21, ESI only: 2/21). These BOLD clusters exhibited in 19/20 cases the most significant voxel. BOLD clusters that were spatially concordant with ESI/MSI were concordant with IEDs from invasive recordings in 8/11 patients (activations: 5/8, deactivations: 3/8). As the results of BOLD, ESI and MSI are often concordant, they reinforce our confidence in all of them. ESI and MSI confirm the most significant BOLD cluster within BOLD maps, emphasizing the importance of these clusters for the definition of the epileptic focus.
The purpose of this study is to develop and quantitatively assess whether fusion of EEG and MEG (... more The purpose of this study is to develop and quantitatively assess whether fusion of EEG and MEG (MEEG) data within the maximum entropy on the mean (MEM) framework increases the spatial accuracy of source localization, by yielding better recovery of the spatial ex-tent and propagation pathway of the underlying generators of inter-ictal epileptic discharges (IEDs). The key element in this study is the integration of the complementary in-formation from EEG and MEG data within the MEM framework. MEEG was compared with EEG and MEG when localizing single transient IEDs. The fusion approach was evaluated using realistic simulation models involving one or two spatially extended sources mimicking propagation patterns of IEDs. We also assessed the impact of the number of EEG electrodes required for an efficient EEG–MEG fusion. MEM was compared with minimum norm estimate, dynamic statistical parametric mapping, and standardized low-resolution electromagnetic tomogra-phy. The fusion approach wa...
We investigated two important means for improving source reconstruction in presurgical ep-ilepsy ... more We investigated two important means for improving source reconstruction in presurgical ep-ilepsy diagnosis. The first investigation is about the optimal choice of the number of epileptic spikes in averaging to (1) sufficiently reduce the noise bias for an accurate determination of the center of gravity of the epileptic activity and (2) still get an estimation of the extent of the irritative zone. The second study focuses on the differences in single modality EEG (80-electrodes) or MEG (275-gradiometers) and especially on the benefits of combined EEG/ MEG (EMEG) source analysis. Both investigations were validated with simultaneous ste-reo-EEG (sEEG) (167-contacts) and low-density EEG (ldEEG) (21-electrodes). To account for the different sensitivity profiles of EEG and MEG, we constructed a six-compartment fi-nite element head model with anisotropic white matter conductivity, and calibrated the skull conductivity via somatosensory evoked responses. Our results show that, unlike single...
ObjectivePharmacological activation of focal epileptic discharges is employed during presurgical ... more ObjectivePharmacological activation of focal epileptic discharges is employed during presurgical evaluation to increase the yield of epileptic activity. Administration of etomidate has been shown to increase focal epileptic activity recorded by foramen ovale electrodes and by magnetoencephalography (MEG). However, results from simultaneous MEG and electroencephalography (MEG/EEG) recordings suggest that sensitivity of surface EEG for epileptic spikes might be diminished due to generalized theta/delta activity caused by etomidate. This project aimed to show differences between epilepsy patients and a control group with respect to clinical and EEG changes after administration of etomidate.MethodsA total of 11 patients with focal epilepsy underwent activation with etomidate with simultaneous video EEG monitoring during presurgical evaluation. In addition activation with etomidate was performed in a control group of four patients without epilepsy under surveillance with simultaneous vid...
Purpose To evaluate a MRI postprocessing tool for the enhanced and rapid detection of focal corti... more Purpose To evaluate a MRI postprocessing tool for the enhanced and rapid detection of focal cortical dysplasia (FCD). Methods MP2RAGE sequences of 40 consecutive, so far MRI-negative patients and of 32 healthy controls were morphometrically analyzed to highlight typical FCD features. The resulting morphometric maps served as input for an artificial neural network generating a FCD probability map. The FCD probability map was inversely normalized, co-registered to the MPRAGE2 sequence, and re-transferred into the PACS system. Co-registered images were scrolled through “within a minute” to determine whether a FCD was present or not. Results Fifteen FCD, three subcortical band heterotopias (SBH), and one periventricular nodular heterotopia were identified. Of those, four FCD and one SBH were only detected by MRI postprocessing while one FCD and one focal polymicrogryia were missed, respectively. False-positive results occurred in 21 patients and 22 healthy controls. However, true positi...
ABSTRACT Main objective(s) The aim of this prospective study is to examine the potential contribu... more ABSTRACT Main objective(s) The aim of this prospective study is to examine the potential contribution of SWDD localisation in clinical preoperative epilepsy focus localisation. Methods Preoperative MEG-SWDD localisations are calculated and overlaid on MR-images of pharmaco-resistant epilepsy patients undergoing presurgical focus localisation evaluation. For all 10 patients who have been operated within at least 6 months, postsurgical outcomes available up to now, are discussed. SWDD localisation results are compared to other preoperative findings and to MEG-spike results and are correlated to postoperative outcome (Engel) after 6 months or 12 months. Results 7 of 10 patients showed significant local increase of SWDD. In these SWDD localisation results were always concordant with preoperative findings. All 7 patients were postoperatively seizure-free or had a worthwhile improvement of seizure situation. 3 of 10 patients showed no significant local increase of SWDD and, therefore, were without SWDD result. Comparison to MEG spike results: Among these 7 patients, 6 showed MEG-spike concordant localisations, one had no spikes in the MEG. Conclusions SWDD is able to localise brain areas exhibiting pathological slow wave activity and might become a useful tool for preoperative epilepsy diagnosis. KeywordsMagnetoencephalography-slow wave-slow wave dipole density-epilepsy-postoperative outcome
We investigated two important means for improving source reconstruction in presurgical epilepsy d... more We investigated two important means for improving source reconstruction in presurgical epilepsy diagnosis. The first investigation is about the optimal choice of the number of epileptic spikes in averaging to (1) sufficiently reduce the noise bias for an accurate determination of the center of gravity of the epileptic activity and (2) still get an estimation of the extent of the irritative zone. The second study focuses on the differences in single modality EEG (80-electrodes) or MEG (275-gradiometers) and especially on the benefits of combined EEG/MEG (EMEG) source analysis. Both investigations were validated with simultaneous stereo-EEG (sEEG) (167-contacts) and low-density EEG (ldEEG) (21-electrodes). To account for the different sensitivity profiles of EEG and MEG, we constructed a six-compartment finite element head model with anisotropic white matter conductivity, and calibrated the skull conductivity via somatosensory evoked responses. Our results show that, unlike single mod...
Zusammenfassung Hintergrund Die pharmakologische Aktivierung wird genutzt, um in der prächirurgi... more Zusammenfassung Hintergrund Die pharmakologische Aktivierung wird genutzt, um in der prächirurgischen Evaluation von Patienten mit Epilepsie das Auftreten der epileptischen Aktivität zu erhöhen. Bisher konnte gezeigt werden, dass nach der Verabreichung von Etomidat vermehrt fokale epileptische Aktivität mithilfe von Foramen-ovale-Elektroden und Magnetenzephalographie (MEG) aufgezeichnet wurde. Jedoch ergaben simultane MEG-/EEG-Aufzeichnungen, dass die Sensitivität des Oberflächen-EEG durch eine generalisierte θ-/δ-Aktivität, die durch Etomidat
Spike-based magnetoencephalography (MEG) source localization is an established method in the pres... more Spike-based magnetoencephalography (MEG) source localization is an established method in the presurgical evaluation of epilepsy patients. Focal cortical dysplasias (FCDs) are associated with focal epileptic discharges of variable morphologies in the beta frequency band in addition to single epileptic spikes. Therefore, we investigated the potential diagnostic value of MEG-based localization of spike-independent beta band (12-30Hz) activity generated by epileptogenic lesions. Five patients with FCD IIB underwent MEG. In one patient, invasive EEG (iEEG) was recorded simultaneously with MEG. In two patients, iEEG succeeded MEG, and two patients had MEG only. MEG and iEEG were evaluated for epileptic spikes. Two minutes of iEEG data and MEG epochs with no spikes as well as MEG epochs with epileptic spikes were analyzed in the frequency domain. MEG oscillatory beta band activity was localized using Dynamic Imaging of Coherent Sources. Intralesional beta band activity was coherent between simultaneous MEG and iEEG recordings. Continuous 14Hz beta band power correlated with the rate of interictal epileptic discharges detected in iEEG. In cases where visual MEG evaluation revealed epileptic spikes, the sources of beta band activity localized within <2cm of the epileptogenic lesion as shown on magnetic resonance imaging. This result held even when visually marked epileptic spikes were deselected. When epileptic spikes were detectable in iEEG but not MEG, MEG beta band activity source localization failed. Source localization of beta band activity has the potential to contribute to the identification of epileptic foci in addition to source localization of visually marked epileptic spikes. Thus, this technique may assist in the localization of epileptic foci in patients with suspected FCD.
Distributed inverse solutions aim to realistically
reconstruct the origin of interictal epileptic... more Distributed inverse solutions aim to realistically reconstruct the origin of interictal epileptic discharges (IEDs) from noninvasively recorded electroencephalography (EEG) and magnetoencephalography (MEG) signals. Our aim was to compare the performance of different distributed inverse solutions in localizing IEDs: coherent maximum entropy on the mean (cMEM), hierarchical Bayesian implementations of independent identically distributed sources (IID, minimum norm prior) and spatially coherent sources (COH, spatial smoothness prior). Source maxima (i.e., the vertex with the maximum source amplitude) of IEDs in 14 EEG and 19 MEG studies from 15 patients with focal epilepsy were analyzed. We visually compared their concordance with intracranial EEG (iEEG) based on 17 cortical regions of interest and their spatialdispersion around source maxima. Magnetic source imaging (MSI) maxima from cMEM were most often confirmed by iEEG (cMEM: 14/19, COH: 9/19, IID: 8/19 studies). COH electric source imaging (ESI) maxima co-localized best with iEEG (cMEM: 8/14, COH: 11/14, IID: 10/14 studies). In addition, cMEM was less spatially spread than COH and IID for ESI and MSI (p\0.001 Bonferronicorrected post hoc t test). Highest positive predictive values for cortical regions with IEDs in iEEG could be obtained with cMEM for MSI and with COH for ESI. Additional realistic EEG/MEG simulations confirmed our findings. Accurate spatially extended sources, as found in cMEM (ESI and MSI) and COH (ESI) are desirable for source imaging of IEDs because this might influence surgical decision. Our simulations suggest that COH and IID overestimate the spatial extent of the generators compared to cMEM.
Primate models are commonly used in Parkinson&amp... more Primate models are commonly used in Parkinson's disease research to study stereotaxic strategies that demand accurate localization of the structures in basal ganglia. We demonstrate a method to construct an extensive tabular database of 3D stereotaxic co-ordinates of various basal ganglia structures from high-quality magnetic resonance (MR) images of 47 adult female 3-5 kg rhesus monkeys. For each animal, the structures in the basal ganglia were traced as they appeared on the axial MR images. Their maximal outlines were projected in the axial plane to create a stack of images and X, Y, Z co-ordinates were calculated for margins of each structure. These co-ordinates and the outlines of the individual nuclei help delineate a "common area," which was further narrowed down to a point that represents the 'most reliable target point' (MRTP) in subthalamic nucleus, globus pallidum, caudate and putamen on both sides. Common area and MRTP represent the region that can most definitely be associated with a structure and hence the most definite target for a given structure. The goal of this study is to demonstrate the method of construction, discuss the feasibility and usefulness of such a tabular database that could potentially add to accuracy of localization while using atlas-based stereotaxy. Though use of MRI remains a standard practice and advances in imaging have made targeting for functional surgery more accurate, in developing countries that implies prohibitive costs per procedure. Population based human databases similar to the monkey database described here, when used along with less expensive imaging modalities can reduce the costs considerably as well as add to the accuracy of targeting.
Blood oxygenation level-dependent (BOLD) signal changes at the time of interictal epileptic disch... more Blood oxygenation level-dependent (BOLD) signal changes at the time of interictal epileptic discharges (IEDs) identify their associated vascular/hemodynamic responses. BOLD activations and deactivations can be found within the epileptogenic zone but also at a distance. Source imaging identifies electric (ESI) and magnetic (MSI) sources of IEDs, with the advantage of a higher temporal resolution. Therefore, the objective of our study was to evaluate the spatial concordance between ESI/MSI and BOLD responses for similar IEDs. Twenty-one patients with similar IEDs in simultaneous electroencephalogram/functional magnetic resonance imaging (EEG/fMRI) and in simultaneous EEG/magnetoencephalogram (MEG) recordings were studied. IEDs in EEG/fMRI acquisition were analyzed in an event-related paradigm within a general linear model (GLM). ESI/MSI of averaged IEDs was performed using the Maximum Entropy on the Mean. We assessed the spatial concordance between ESI/MSI and clusters of BOLD activations/deactivations with surface-based metrics. ESI/MSI were concordant with one BOLD cluster for 20/21 patients (concordance with activation: 14/21 patients, deactivation: 6/21 patients, no concordance: 1/21 patients; concordance with MSI only: 3/21, ESI only: 2/21). These BOLD clusters exhibited in 19/20 cases the most significant voxel. BOLD clusters that were spatially concordant with ESI/MSI were concordant with IEDs from invasive recordings in 8/11 patients (activations: 5/8, deactivations: 3/8). As the results of BOLD, ESI and MSI are often concordant, they reinforce our confidence in all of them. ESI and MSI confirm the most significant BOLD cluster within BOLD maps, emphasizing the importance of these clusters for the definition of the epileptic focus.
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reconstruct the origin of interictal epileptic discharges
(IEDs) from noninvasively recorded electroencephalography
(EEG) and magnetoencephalography (MEG) signals.
Our aim was to compare the performance of different
distributed inverse solutions in localizing IEDs: coherent
maximum entropy on the mean (cMEM), hierarchical
Bayesian implementations of independent identically distributed
sources (IID, minimum norm prior) and spatially
coherent sources (COH, spatial smoothness prior). Source
maxima (i.e., the vertex with the maximum source amplitude)
of IEDs in 14 EEG and 19 MEG studies from 15
patients with focal epilepsy were analyzed. We visually
compared their concordance with intracranial EEG (iEEG)
based on 17 cortical regions of interest and their spatialdispersion around source maxima. Magnetic source imaging
(MSI) maxima from cMEM were most often confirmed
by iEEG (cMEM: 14/19, COH: 9/19, IID: 8/19 studies).
COH electric source imaging (ESI) maxima co-localized
best with iEEG (cMEM: 8/14, COH: 11/14, IID: 10/14
studies). In addition, cMEM was less spatially spread than
COH and IID for ESI and MSI (p\0.001 Bonferronicorrected
post hoc t test). Highest positive predictive values
for cortical regions with IEDs in iEEG could be obtained
with cMEM for MSI and with COH for ESI. Additional
realistic EEG/MEG simulations confirmed our findings.
Accurate spatially extended sources, as found in cMEM
(ESI and MSI) and COH (ESI) are desirable for source
imaging of IEDs because this might influence surgical
decision. Our simulations suggest that COH and IID
overestimate the spatial extent of the generators compared
to cMEM.
reconstruct the origin of interictal epileptic discharges
(IEDs) from noninvasively recorded electroencephalography
(EEG) and magnetoencephalography (MEG) signals.
Our aim was to compare the performance of different
distributed inverse solutions in localizing IEDs: coherent
maximum entropy on the mean (cMEM), hierarchical
Bayesian implementations of independent identically distributed
sources (IID, minimum norm prior) and spatially
coherent sources (COH, spatial smoothness prior). Source
maxima (i.e., the vertex with the maximum source amplitude)
of IEDs in 14 EEG and 19 MEG studies from 15
patients with focal epilepsy were analyzed. We visually
compared their concordance with intracranial EEG (iEEG)
based on 17 cortical regions of interest and their spatialdispersion around source maxima. Magnetic source imaging
(MSI) maxima from cMEM were most often confirmed
by iEEG (cMEM: 14/19, COH: 9/19, IID: 8/19 studies).
COH electric source imaging (ESI) maxima co-localized
best with iEEG (cMEM: 8/14, COH: 11/14, IID: 10/14
studies). In addition, cMEM was less spatially spread than
COH and IID for ESI and MSI (p\0.001 Bonferronicorrected
post hoc t test). Highest positive predictive values
for cortical regions with IEDs in iEEG could be obtained
with cMEM for MSI and with COH for ESI. Additional
realistic EEG/MEG simulations confirmed our findings.
Accurate spatially extended sources, as found in cMEM
(ESI and MSI) and COH (ESI) are desirable for source
imaging of IEDs because this might influence surgical
decision. Our simulations suggest that COH and IID
overestimate the spatial extent of the generators compared
to cMEM.