Automated long-term EEG analysis to localize the epileptogenic zone (original) (raw)
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Brain topography, 2014
In patients diagnosed with pharmaco-resistant epilepsy, cerebral areas responsible for seizure generation can be defined by performing implantation of intracranial electrodes. The identification of the epileptogenic zone (EZ) is based on visual inspection of the intracranial electroencephalogram (IEEG) performed by highly qualified neurophysiologists. New computer-based quantitative EEG analyses have been developed in collaboration with the signal analysis community to expedite EZ detection. The aim of the present report is to compare different signal analysis approaches developed in four different European laboratories working in close collaboration with four European Epilepsy Centers. Computer-based signal analysis methods were retrospectively applied to IEEG recordings performed in four patients undergoing pre-surgical exploration of pharmaco-resistant epilepsy. The four methods elaborated by the different teams to identify the EZ are based either on frequency analysis, on nonlin...
Temporal stability of intracranial EEG abnormality maps for localising epileptogenic tissue
arXiv (Cornell University), 2023
Objective Identifying abnormalities in interictal intracranial EEG, by comparing patient data to a normative map, has shown promise for the localisation of epileptogenic tissue and prediction of outcome. The approach typically uses short interictal segments of around one minute. However, the temporal stability of findings has not been established. Methods Here, we generated a normative map of iEEG in non-pathological brain tissue from 249 patients. We computed regional band power abnormalities in a separate cohort of 39 patients for the duration of their monitoring period (0.92-8.62 days of iEEG data, mean 4.58 days per patient, over 4,800 hours recording). To assess the localising value of band power abnormality, we computed &'-a measure of how different the surgically resected and spared tissue were in terms of band power abnormalities-over time. Results In each patient, band power abnormality was relatively consistent over time. The median &' of the entire recording period separated seizure free (ILAE = 1) and not seizure free (ILAE > 1) patients well (AUC = 0.69). This effect was similar interictally (AUC = 0.69) and peri-ictally (AUC = 0.71). Significance Our results suggest that band power abnormality &' , as a predictor of outcomes from epilepsy surgery, is a relatively robust metric over time. These findings add further support for abnormality mapping of neurophysiology data during presurgical evaluation.
Human Brain Mapping, 2014
Presurgical monitoring with intracerebral electrodes in patients with drug-resistant focal epilepsy represents a standard invasive procedure to localize the sites of seizures origin, defined as the epileptogenic zone (EZ). During presurgical evaluation, intracerebral single-pulse electrical stimulation (SPES) is performed to define the boundaries of eloquent areas and to evoke seizureassociated symptoms. Extensive intracranial exploration and stimulation generate a large dataset on brain connectivity that can be used to improve EZ detection and to understand the organization of the human epileptic brain. We developed a protocol to analyse field responses evoked by intracranial stimulation. Intracerebral recordings were performed with 105-162 recording sites positioned in fronto-temporal regions in 12 patients with pharmacoresistant focal epilepsy. Recording sites were used for bipolar SPES at 1 Hz. Reproducible early and late phases (<60 ms and 60-500 ms from stimulus artefact, respectively) were identified on averaged evoked responses. Phase 1 and 2 responses recorded at all and each recording sites were plotted on a 3D brain reconstructions. Based on connectivity properties, electrode contacts were primarily identified as receivers, mainly activators or bidirectional. We used connectivity patterns to construct networks and applied cluster partitioning to study the proprieties between potentials evoked/stimulated in different regions. We demonstrate that bidirectional connectivity during phase 1 is a prevalent feature that characterize contacts included in the EZ. This study shows that the application of an analytical protocol on intracerebral stimulus-evoked recordings provides useful information that may contribute to EZ detection and to the management of surgical-remediable epilepsies.
Rapid identification of epileptogenic sites in the intracranial EEG
2011
The paper presents a novel computationally simple, easy-to-interpret compressed EEG display for multichannel intracranial EEG recordings. The compressed display is based on the level of sharp activity (relative sharpness index (RSI)) in the EEG, which profoundly increases during paroxysmal activities. RSI is graphically presented as a color-intensity plot that allows compressing several hours of EEG into a single display page. RSI display is a bird's-eye-view of the EEG that may reveal seizure evolution ('build-up'), seizure precursors, or sites associated with the seizures. We present examples from two patients to illustrate the method's ability to identify epileptogenic sites that may be difficult to observe in the conventional review process. RSI is compared with the color density spectral array (CDSA) and amplitude integrated EEG (aEEG) display. Examples demonstrate the RSI display to be simple, easy to interpret, computationally light and fast enough for online application.
Automatic localisation of epileptic foci in long-term continuous EEG
International Journal of Medical Engineering and Informatics, 2008
We describe a new algorithm for identifying the signal epochs that contain the epileptiform transients in the long-term continuous EEG and automatic localisation of exact epileptic foci in the human epileptic brain using two-level multi-resolution analysis. Our system consists of three stages: detection of epileptic events using two-level multi-resolution analysis, extraction of spike portion of signal from raw EEG data and localisation of epileptic foci. The key points are: the computation of an appropriate adaptive threshold, the localisation of epileptic foci and computation of number of spikes per second. The results suggest that epileptic foci could be quantitatively identified and accurately localised using two-level multi-resolution analysis. In comparison to visual identification of spike, the new approach is sensitive and provides the possibility of classifying epilepsies into generalised and focal epilepsies. The proposed algorithm has been implemented in MATLAB.
Journal of Clinical Neurophysiology, 2007
It is desirable to estimate both location and extent information of epileptogenic zones from noninvasive EEG. In the present study, we use a subspace source localization method, i.e. FINE, combined with a local thresholding technique to achieve such tasks. We have evaluated the performance of this method in interictal spikes from three pediatric patients with medically intractable partial epilepsy. The present results suggest that the thresholded subspace correlation, which is obtained from FINE scanning, is a favorable marker, which implies the extents of current sources associated with epileptic activities. Our findings were validated through comparison to invasive ECoG recordings during interictal spikes. The surgical resections in these three patients are well correlated with the epileptogenic zones identified from both EEG sources and ECoG potential distributions. The value of the proposed noninvasive technique for estimating epileptiform activity was supported by satisfactory surgery outcomes.
Detection of focal epileptiform events in the EEG by spatio-temporal dipole clustering
Clinical Neurophysiology, 2008
Objective: Methods for the detection of epileptiform events can be broadly divided into two main categories: temporal detection methods that exploit the EEG's temporal characteristics, and spatial detection methods that base detection on the results of an implicit or explicit source analysis. We describe how the framework of a spatial detection method was extended to improve its performance by including temporal information. This results in a method that provides (i) automated localization of an epileptogenic focus and (ii) detection of focal epileptiform events in an EEG recording. For the detection, only one threshold value needs to be set. Methods: The method comprises five consecutive steps: (1) dipole source analysis in a moving window, (2) automatic selection of focal brain activity, (3) dipole clustering to arrive at the identification of the epileptiform cluster, (4) derivation of a spatio-temporal template of the epileptiform activity, and (5) template matching. Routine EEG recordings from eight paediatric patients with focal epilepsy were labelled independently by two experts. The method was evaluated in terms of (i) ability to identify the epileptic focus, (ii) validity of the derived template, and (iii) detection performance. The clustering performance was evaluated using a leave-one-out cross validation. Detection performance was evaluated using Precision-Recall curves and compared to the performance of two temporal (mimetic and wavelet based) and one spatial (dipole analysis based) detection methods. Results: The method succeeded in identifying the epileptogenic focus in seven of the eight recordings. For these recordings, the mean distance between the epileptic focus estimated by the method and the region indicated by the labelling of the experts was 8 mm. Except for two EEG recordings where the dipole clustering step failed, the derived template corresponded to the epileptiform activity marked by the experts. Over the eight EEGs, the method showed a mean sensitivity and selectivity of 92 and 77%, respectively. Conclusions: The method allows automated localization of the epileptogenic focus and shows good agreement with the region indicated by the labelling of the experts. If the dipole clustering step is successful, the method allows a detection of the focal epileptiform events, and gave a detection performance comparable or better to that of the other methods. Significance: The identification and quantification of epileptiform events is of considerable importance in the diagnosis of epilepsy. Our method allows the automatic identification of the epileptic focus, which is of value in epilepsy surgery. The method can also be used as an offline exploration tool for focal EEG activity, displaying the dipole clusters and corresponding time series.
EEG Source Localization of Interictal and Ictal Spikes Acquired During Video-EEG Monitoring
ejnpn.org
Objective: We investigated the feasibility of electroencephalography (EEG) dipole source localization of interictal and ictal epileptiform discharges from data acquired during routine clinical video-EEG monitoring (VEM) that utilizes a 25channel 'routine montage' with an additional inferior temporal electrodes 'surgical montage'. Methods: Twenty five consecutive patients who had VEM for the presurgical evaluation of medically refractory partial epilepsy were screened. EEG data was acquired with 25 electrodes including an inferior temporal row (surgical montage). For comparison, the 10 additional electrodes were excluded from analysis (routine montage). Using ASA 2 software, a computed dipole source localization of averaged spikes was performed utilizing a magnetic resonance imaging-based finite element model. Dipole localization was compared with that of the comprehensive epilepsy program evaluation. Results: Dipole source localization using ASA was highly complementary to the four landmarks of the epileptogenic zone, the ictal symptomatic zone, irritative zone, pace maker zone and epileptogenic lesion. The concordance between these zones was 32% but with ASA it reached 96% with highly significant difference. The lateralizing ability of data without ASA was not statistically significantly different after the use of ASA (P=0.247). As regards the localization ability before ASA only 4 cases could be localized and 14 cased had regional localization, after ASA all cases could be localized with highly significant difference (P=.000002). Conclusions: EEG source localization has a significant diagnostic yield in localization of epileptogenic zone in preoperative settings, however this yield needs to be validated by invasive EEG.
SOLO: An EEG Processing Software Framework for Localising Epileptogenic Zones
2013
The paper describes an EEG signal processing software framework designed for performing validation tests in the ENIAC-CSI FP7 project for wireless EEG measurement sensors. The project aims at improving imaging devices and processing methods used in the localisation of epileptogenic zones in epileptic patients. The developed software allows specialist to view multi-channel EEG signals, identify epileptic features and perform source localisation operations based on realistic head models, and generate equivalent dipole data that can be used in localisation accuracy and reproducibility error analysis. Epilepsy is a devastating disease affecting about 1% of the population. About 60% of all epilepsy patients have symptomatic focal epilepsies (1). In these cases, one particular portion of the brain is affected by the disease. This region, referred to as focus, is responsible for the epileptic seizures. The focal concept of the epilepsies can be formed by overlapping epileptic zones represe...