title: A Comparison of Independent Component Analysis (ICA) of fMRI and Electrical Source Imaging (ESI) in Focal Epilepsy Reveals Misclassification Using a Classifier.
abstract: Interictal epileptiform discharges (IEDs) can produce haemodynamic responses that can be detected by electroencephalography-functional magnetic resonance imaging (EEG-fMRI) using different analysis methods such as the general linear model (GLM) of IEDs or independent component analysis (ICA). The IEDs can also be mapped by electrical source imaging (ESI) which has been demonstrated to be useful in presurgical evaluation in a high proportion of cases with focal IEDs. ICA advantageously does not require IEDs or a model of haemodynamic responses but its use in EEG-fMRI of epilepsy has been limited by its ability to separate and select epileptic components. Here, we evaluated the performance of a classifier that aims to filter all non-BOLD responses and we compared the spatial and temporal features of the selected independent components (ICs). The components selected by the classifier were compared to those components selected by a strong spatial correlation with ESI maps of IED sources. Both sets of ICs were subsequently compared to a temporal model derived from the convolution of the IEDs (derived from the simultaneously acquired EEG) with a standard haemodynamic response. Selected ICs were compared to the patients' clinical information in 13 patients with focal epilepsy. We found that the misclassified ICs clearly related to IED in 16/25 cases. We also found that the classifier failed predominantly due to the increased spectral range of fMRIs temporal responses to IEDs. In conclusion, we show that ICA can be an efficient approach to separate responses related to epilepsy but that contemporary classifiers need to be retrained for epilepsy data. Our findings indicate that, for ICA to contribute to the analysis of data without IEDs to improve its sensitivity, classification strategies based on data features other than IC time course frequency is required.
authors.affiliation: InBrain Lab, Department of Physics, FFLCRP, University of São Paulo, Av. Bandeirantes, 3900, Bairro Monte Alegre, Ribeirão Preto, SP, 14040-901, Brazil. danibeen@hotmail.com.|Developmental Imaging and Biophysics Section, UCL Institute of Child Health, 30 Guilford Street, London, WC1N 1EH, UK. danibeen@hotmail.com.
authors.forename: Danilo
authors.initials: D
authors.lastname: Maziero
authors.affiliation: InBrain Lab, Department of Physics, FFLCRP, University of São Paulo, Av. Bandeirantes, 3900, Bairro Monte Alegre, Ribeirão Preto, SP, 14040-901, Brazil. mjsturz@gmail.com.
authors.forename: Marcio
authors.initials: M
authors.lastname: Sturzbecher
authors.affiliation: Department of Neuroscience, Faculty of Medicine, Epilepsy Surgery Center, University of São Paulo, Av. Bandeirantes, 3900, Bairro Monte Alegre, Ribeirão Preto, SP, 14040-901, Brazil. tvelasco@fmrp.usp.br.
authors.forename: Tonicarlo Rodrigues
authors.initials: TR
authors.lastname: Velasco
authors.affiliation: InBrain Lab, Department of Physics, FFLCRP, University of São Paulo, Av. Bandeirantes, 3900, Bairro Monte Alegre, Ribeirão Preto, SP, 14040-901, Brazil. crondi2001@yahoo.com.br.
authors.forename: Carlo
authors.initials: C
authors.lastname: Rondinoni
authors.affiliation: Cuban Neuroscience Center, P.O. Box 6412/6414, Ave. 25, Esq.158, No. 15202, Cubanacan, Playa, Havana, Cuba. mlsttin@gmail.com.
authors.forename: Agustin Lage
authors.initials: AL
authors.lastname: Castellanos
authors.affiliation: Developmental Imaging and Biophysics Section, UCL Institute of Child Health, 30 Guilford Street, London, WC1N 1EH, UK. d.carmichael@ucl.ac.uk.
authors.forename: David William
authors.initials: DW
authors.lastname: Carmichael
authors.affiliation: InBrain Lab, Department of Physics, FFLCRP, University of São Paulo, Av. Bandeirantes, 3900, Bairro Monte Alegre, Ribeirão Preto, SP, 14040-901, Brazil. garrido@ffclrp.usp.br.
authors.forename: Carlos Ernesto Garrido
authors.initials: CE
authors.lastname: Salmon
mesh_terms: D001921:Brain / Q000098:blood supply* / Q000503:physiopathology; D001931:Brain Mapping; D004569:Electroencephalography; D004828:Epilepsies, Partial / Q000473:pathology* / Q000503:physiopathology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D010100:Oxygen / Q000097:blood; D025341:Principal Component Analysis; D012815:Signal Processing, Computer-Assisted
chemical_list: D010100:Oxygen
keywords: EEG-fMRI; Epilepsy; ICA and ESI