EEG spike source localization before and after surgery for temporal lobe epilepsy: a BOLD EEG-fMRI and independent component analysis study

Simultaneous measurements of EEG-functional magnetic resonance imaging (fMRI) combine the high temporal resolution of EEG with the distinctive spatial resolution of fMRI. The purpose of this EEG-fMRI study was to search for hemodynamic responses (blood oxygen level-dependent - BOLD responses) associated with interictal activity in a case of right mesial temporal lobe epilepsy before and after a successful selective amygdalohippocampectomy. Therefore, the study found the epileptogenic source by this noninvasive imaging technique and compared the results after removing the atrophied hippocampus. Additionally, the present study investigated the effectiveness of two different ways of localizing epileptiform spike sources, i.e., BOLD contrast and independent component analysis dipole model, by comparing their respective outcomes to the resected epileptogenic region. Our findings suggested a right hippocampus induction of the large interictal activity in the left hemisphere. Although almost a quarter of the dipoles were found near the right hippocampus region, dipole modeling resulted in a widespread distribution, making EEG analysis too weak to precisely determine by itself the source localization even by a sophisticated method of analysis such as independent component analysis. On the other hand, the combined EEG-fMRI technique made it possible to highlight the epileptogenic foci quite efficiently.58258

The spatio-temporal mapping of epileptic networks: Combination of EEG–fMRI and EEG source imaging

Simultaneous EEG–fMRI acquisitions in patients with epilepsy often reveal distributed patterns of Blood Oxygen Level Dependant (BOLD) change correlated with epileptiform discharges. We investigated if electrical source imaging (ESI) performed on the interictal epileptiform discharges (IED) acquired during fMRI acquisition could be used to study the dynamics of the networks identified by the BOLD effect, thereby avoiding the limitations of combining results from separate recordings. Nine selected patients (13 IED types identified) with focal epilepsy underwent EEG–fMRI. Statistical analysis was performed using SPM5 to create BOLD maps. ESI was performed on the IED recorded during fMRI acquisition using a realistic head model (SMAC) and a distributed linear inverse solution (LAURA). ESI could not be performed in one case. In 10/12 remaining studies, ESI at IED onset (ESIo) was anatomically close to one BOLD cluster. Interestingly, ESIo was closest to the positive BOLD cluster with maximal statistical significance in only 4/12 cases and closest to negative BOLD responses in 4/12 cases. Very small BOLD clusters could also have clinical relevance in some cases. ESI at later time frame (ESIp) showed propagation to remote sources co-localised with other BOLD clusters in half of cases. In concordant cases, the distance between maxima of ESI and the closest EEG–fMRI cluster was less than 33 mm, in agreement with previous studies. We conclude that simultaneous ESI and EEG–fMRI analysis may be able to distinguish areas of BOLD response related to initiation of IED from propagation areas. This combination provides new opportunities for investigating epileptic networks

Combined EEG-fMRI and ESI improves localisation of paediatric focal epilepsy

OBJECTIVE: Surgical treatment in epilepsy is effective if the epileptogenic zone (EZ) can be correctly localized and characterized. Here we use simultaneous Electroencephalography-functional MRI (EEG-fMRI) data to derive EEG-fMRI and Electrical Source Imaging (ESI) maps. Their yield and their individual and combined ability to 1) localize the epileptogenic zone and 2) predict seizure outcome was then evaluated. METHODS: Fifty-three children with drug-resistant epilepsy underwent EEG-fMRI. Interictal discharges were mapped using both EEG-fMRI haemodynamic responses and Electrical Source Imaging (ESI). A single localization was derived from each individual test (EEG-fMRI global maxima (GM)/ESI maxima) and from the combination of both maps (EEG-fMRI/ESI spatial intersection). To determine the localisation accuracy and its predictive performance the individual and combined test localisations were compared to the presumed EZ and to the postsurgical outcome. RESULTS: Fifty-two/53 patients had significant maps; 47/53 for EEG-fMRI; 44/53 for ESI; 34/53 had both. The epileptogenic zone was well characterised in 29 patients; 26 had an EEG-fMRI GM localisation which was correct in 11; 22 patients had ESI localisation which was correct in 17; 12 patients had combined EEG-fMRI and ESI which was correct in 11. Seizure outcome following resection was correctly predicted by EEG-fMRI GM in 8/20 patients, by the ESI maxima in 13/16. The combined EEG-fMRI/ESI region entirely predicted outcome in 9/9 patients including 3 with no lesion visible on MRI. INTERPRETATION: EEG-fMRI combined with ESI provides a simple unbiased localisation that may predict surgery better than each individual test including in MRI-negative patients

Combined EEG-fMRI and ESI improves localisation of paediatric focal epilepsy

OBJECTIVE: Surgical treatment in epilepsy is effective if the epileptogenic zone (EZ) can be correctly localized and characterized. Here we use simultaneous Electroencephalography-functional MRI (EEG-fMRI) data to derive EEG-fMRI and Electrical Source Imaging (ESI) maps. Their yield and their individual and combined ability to 1) localize the epileptogenic zone and 2) predict seizure outcome was then evaluated. METHODS: Fifty-three children with drug-resistant epilepsy underwent EEG-fMRI. Interictal discharges were mapped using both EEG-fMRI haemodynamic responses and Electrical Source Imaging (ESI). A single localization was derived from each individual test (EEG-fMRI global maxima (GM)/ESI maxima) and from the combination of both maps (EEG-fMRI/ESI spatial intersection). To determine the localisation accuracy and its predictive performance the individual and combined test localisations were compared to the presumed EZ and to the postsurgical outcome. RESULTS: Fifty-two/53 patients had significant maps; 47/53 for EEG-fMRI; 44/53 for ESI; 34/53 had both. The epileptogenic zone was well characterised in 29 patients; 26 had an EEG-fMRI GM localisation which was correct in 11; 22 patients had ESI localisation which was correct in 17; 12 patients had combined EEG-fMRI and ESI which was correct in 11. Seizure outcome following resection was correctly predicted by EEG-fMRI GM in 8/20 patients, by the ESI maxima in 13/16. The combined EEG-fMRI/ESI region entirely predicted outcome in 9/9 patients including 3 with no lesion visible on MRI. INTERPRETATION: EEG-fMRI combined with ESI provides a simple unbiased localisation that may predict surgery better than each individual test including in MRI-negative patients

Multimodale Bildgebung in der prächirurgischenEpilepsiediagnostik bei Kindern und Jugendlichen

Kinder mit einer Epilepsie, die nicht auf Medikamente ansprechen, können durch einen operativen Eingriff geheilt werden. In der prächirurgischen Diagnostik dieser Kinder ist es notwendig die epileptogene Zone eindeutig zu bestimmen: dazu bedarf es Hypothesen. Verschiedene Verfahren (Elektroenzephalographie, Magnetresonanztomographie, Positron-Emissions-Tomographie, Single-Photon-Emissionscom-putertomographie) werden aktuell angewandt. Doch keine der genannten Methoden kann die epileptogene Zone mit der erforderlichen Sicherheit eingrenzen, jede hat Limitationen, so dass es auf die Zusammenschau der Verfahren ankommt. Deshalb wurde in dieser Studie erstmalig bei Kindern mit symptomatischen und kryptogenen fokalen Epilepsien die Kombination aus der simultanen Ableitung von Elektroenzephalographie und der Aufzeichnung von funktioneller Magnetresonanztomographie in Kombination mit einer Quellenanlyse untersucht. Die Kombination von Elektroenzephalographie und funktioneller Magnetresonanztomographie ist eine nicht invasive Methode, die hämodynamische Veränderungen im gesamten Gehirn während interiktaler epileptischer Aktivität detektieren kann. Dabei werden bei 540 Magnetresonanz-Aufnahmen mit schnellen Sequenzen die Unterschiede dargestellt, die einerseits zwischen den Aufnahmen bestehen, bei denen eine interiktale epileptische Aktivität im Elektroenzephalogramm zu sehen war und andererseits zwischen den Aufnahmen, bei denen dies nicht der Fall war. In früheren Studien bei Kindern mit verschiedenen Epilepsieformen zeigte sich je-doch, dass die Ergebnisse selten lokalisiert, sondern meist ausgedehnt zur Darstel-lung kamen. Daher untersuchten wir, ob eine Kombination mit einer Quellenanalyse, die auf verteilten Quellen basiert, diese ausgedehnten Aktivierungsareale zeitlich differenzieren kann. Wir wählten von 26 Patienten, die an einem epilepsiechirurgischen Programm teil-nahmen, sechs Patienten aus, die einen klaren erwarteten epileptogenen Fokus durch Übereinstimmung von Positron-Emissions-Tomographie, iktaler Single-Photon-Emissionscomputertomographie und Video-Elektroenzephalographie zeigten. Bei allen Patienten fanden wir eine signifikante Signaländerung in der Elektroenzephalographie und funktioneller Magnetresonanztomographie sowie eine Übereinstimmung mit der erwarteten epileptogenen Zone bei fünf Patienten. Bei fünf Patienten sahen wir zusätzlich ausgedehnte Aktivierungsareale. Die Quel-lenanalyse zeigte, dass der Beginn der interiktalen epileptischen Aktivität bei allen Patienten in der erwarteten epileptogenen Zone lag und bei fünf Patienten eine Verlagerung in nahe Gehirnregionen erfolgte. Diese Ausbreitungen der Quellen korrespondierten mit Arealen der Signaländerungen im funktionellen MRT. Die Kombination von Elektroenzephalographie und funktioneller Magnetresonanztomographie ist eine Methode, die signifikante Aktivierungen im Bereich der epileptogenen Zone zeigen kann, jedoch sind diese Aktivierungen meist darüber hinaus ausgebreitet, so dass es zusätzlicher Methoden bedarf, diese ausgedehnten Bereiche zu erklären. Die Quellenanalyse, die auf verteilte Quellen basiert, ist in der Lage, die Ergebnisse der funktionellen Magnetresonanztomographie durch die hohe zeitliche Auflösung zu interpretieren und für die prächirurgische Diagnostik zu verbessern

Conectividade efectiva em epilepsia

A epilepsia é uma das mais comuns patologias que afectam o cérebro humano e caracteriza-se por uma actividade cerebral oscilatória desordenada e excessiva que prejudica gravemente a qualidade de vida do doente. Com o objectivo de detectar o percurso da actividade cerebral anormal a ressonância magnética, em conjunto com a técnica de electroencefalografia (EEG) têm evoluído no sentido de tornar a identificação do foco epiléptico e respectivas vias de propagação mais clara e fácil para o neurocirurgião. Esta detecção pode recorrer ao efeito BOLD (do inglês “Blood Oxygenation Level Dependent”) para, de forma indirecta, obter um mapa de activação neuronal da zona em estudo contribuindo para uma possível intervenção cirúrgica à área epiléptica. No entanto, para chegar a uma conclusão definitiva sobre este mapa neuronal é necessário ter em conta que diferentes regiões podem apresentar HRFs (do inglês “Hemodynamic Response Functions”) diferentes, influenciando o resultado de qualquer análise se este facto não for tido em conta. Na presente dissertação foi aplicado um método de cálculo de influência causal entre regiões do cérebro humano a dados de epilepsia obtidos através da técnica EEG+fMRI. Foram utilizadas técnicas de conectividade efectiva (causalidade de Granger) usando um pacote de software (PyHRF) para estimar com precisão a HRF da região em estudo e permitir a desconvolução do sinal antes do cálculo de conectividade. Foi demonstrada a utilidade desta contribuição metodológica para a caracterização topográfica e dinâmica de uma crise epiléptica