title: Head model and electrical source imaging: a study of 38 epileptic patients.
abstract: Electrical source imaging (ESI) aims at reconstructing the electrical brain activity from scalp EEG. When applied to interictal epileptiform discharges (IEDs), this technique is of great use for identifying the irritative zone in focal epilepsies. Inaccuracies in the modeling of electro-magnetic field propagation in the head (forward model) may strongly influence ESI and lead to mislocalization of IED generators. However, a systematic study on the influence of the selected head model on the localization precision of IED in a large number of patients with known focus localization has not yet been performed. We here present such a performance evaluation of different head models in a dataset of 38 epileptic patients who have undergone high-density scalp EEG, intracranial EEG and, for the majority, subsequent surgery. We compared ESI accuracy resulting from three head models: a Locally Spherical Model with Anatomical Constraints (LSMAC), a Boundary Element Model (BEM) and a Finite Element Model (FEM). All of them were computed from the individual MRI of the patient and ESI was performed on averaged IED. We found that all head models provided very similar source locations. In patients having a positive post-operative outcome, at least 74% of the source maxima were within the resection. The median distance from the source maximum to the nearest intracranial electrode showing IED was 13.2, 15.6 and 15.6 mm for LSMAC, BEM and FEM, respectively. The study demonstrates that in clinical applications, the use of highly sophisticated and difficult to implement head models is not a crucial factor for an accurate ESI.
authors.affiliation: Department of Fundamental and Clinical Neurosciences, University of Geneva, Rue Michel Servet 1, 1211 Genève, Switzerland.
authors.forename: Gwénael
authors.initials: G
authors.lastname: Birot
authors.affiliation: EEG and Epilepsy Unit, Department of Neurology, University Hospital of Geneva, Rue Gabrielle-Perret-Gentil 4, 1205 Genève, Switzerland.
authors.forename: Laurent
authors.initials: L
authors.lastname: Spinelli
authors.affiliation: EEG and Epilepsy Unit, Department of Neurology, University Hospital of Geneva, Rue Gabrielle-Perret-Gentil 4, 1205 Genève, Switzerland.
authors.forename: Serge
authors.initials: S
authors.lastname: Vulliémoz
authors.affiliation: EEG and Epilepsy Unit, Department of Neurology, University Hospital of Geneva, Rue Gabrielle-Perret-Gentil 4, 1205 Genève, Switzerland ; Department of Neurosurgery, Hofstra North Shore-LIJ School of Medicine, Feinstein Institute for Medical Research, Manhasset, NY 11030, USA.
authors.forename: Pierre
authors.initials: P
authors.lastname: Mégevand
authors.affiliation: Department of Fundamental and Clinical Neurosciences, University of Geneva, Rue Michel Servet 1, 1211 Genève, Switzerland.
authors.forename: Denis
authors.initials: D
authors.lastname: Brunet
authors.affiliation: EEG and Epilepsy Unit, Department of Neurology, University Hospital of Geneva, Rue Gabrielle-Perret-Gentil 4, 1205 Genève, Switzerland.
authors.forename: Margitta
authors.initials: M
authors.lastname: Seeck
authors.affiliation: Department of Fundamental and Clinical Neurosciences, University of Geneva, Rue Michel Servet 1, 1211 Genève, Switzerland.
authors.forename: Christoph M
authors.initials: CM
authors.lastname: Michel
mesh_terms: D000293:Adolescent; D000328:Adult; D001931:Brain Mapping / Q000379:methods*; D002540:Cerebral Cortex / Q000503:physiopathology*; D002648:Child; D002675:Child, Preschool; D003198:Computer Simulation; D004569:Electroencephalography; D004827:Epilepsy / Q000503:physiopathology*; D005260:Female; D006257:Head; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D008959:Models, Neurological; D055815:Young Adult
keywords: BEM; Electrical source imaging; Epilepsy; FEM; Head model; High-density EEG