title: Non-harmonicity in high-frequency components of the intra-operative corticogram to delineate epileptogenic tissue during surgery.
abstract: OBJECTIVE
  We aimed to test the potential of auto-regressive model residual modulation (ARRm), an artefact-insensitive method based on non-harmonicity of the high-frequency signal, to identify epileptogenic tissue during surgery.
  
  
  METHODS
  Intra-operative electrocorticography (ECoG) of 54 patients with refractory focal epilepsy were recorded pre- and post-resection at 2048Hz. The ARRm was calculated in one-minute epochs in which high-frequency oscillations (HFOs; fast ripples, 250-500Hz; ripples, 80-250Hz) and spikes were marked. We investigated the pre-resection fraction of HFOs and spikes explained by the ARRm (h2-index). A general ARRm threshold was set and used to compare the ARRm to surgical outcome in post-resection ECoG (Pearson X2).
  
  
  RESULTS
  ARRm was associated strongest with the number of fast ripples in pre-resection ECoG (h2=0.80, P<0.01), but also with ripples and spikes. An ARRm threshold of 0.47 yielded high specificity (95%) with 52% sensitivity for channels with fast ripples. ARRm values >0.47 were associated with poor outcome at channel and patient level (both P<0.01) in post-resection ECoG.
  
  
  CONCLUSIONS
  The ARRm algorithm might enable intra-operative delineation of epileptogenic tissue.
  
  
  CONCLUSIONS
  ARRm is the first unsupervised real-time analysis that could provide an intra-operative, 'on demand' interpretation per electrode about the need to remove underlying tissue to optimize the chance of seizure freedom.
authors.affiliation: Stichting Epilepsie Instellingen Nederland (SEIN), The Netherlands.
authors.forename: Evelien E
authors.initials: EE
authors.lastname: Geertsema
authors.affiliation: Brain Center Rudolf Magnus, Dept. of Neurology & Neurosurgery, University Medical Center Utrecht, The Netherlands.
authors.forename: Maryse A
authors.initials: MA
authors.lastname: van 't Klooster
authors.affiliation: Brain Center Rudolf Magnus, Dept. of Neurology & Neurosurgery, University Medical Center Utrecht, The Netherlands.
authors.forename: Nicole E C
authors.initials: NEC
authors.lastname: van Klink
authors.affiliation: Brain Center Rudolf Magnus, Dept. of Neurology & Neurosurgery, University Medical Center Utrecht, The Netherlands.
authors.forename: Frans S S
authors.initials: FSS
authors.lastname: Leijten
authors.affiliation: Brain Center Rudolf Magnus, Dept. of Neurology & Neurosurgery, University Medical Center Utrecht, The Netherlands.
authors.forename: Peter C
authors.initials: PC
authors.lastname: van Rijen
authors.affiliation: Stichting Epilepsie Instellingen Nederland (SEIN), The Netherlands.
authors.forename: Gerhard H
authors.initials: GH
authors.lastname: Visser
authors.affiliation: Stichting Epilepsie Instellingen Nederland (SEIN), The Netherlands.
authors.forename: Stiliyan N
authors.initials: SN
authors.lastname: Kalitzin
authors.affiliation: Stichting Epilepsie Instellingen Nederland (SEIN), The Netherlands; Brain Center Rudolf Magnus, Dept. of Neurology & Neurosurgery, University Medical Center Utrecht, The Netherlands. Electronic address: mzijlmans@sein.nl.
authors.forename: Maeike
authors.initials: M
authors.lastname: Zijlmans
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000293:Adolescent; D000069280:Electrocorticography / Q000379:methods*; D004569:Electroencephalography / Q000379:methods; D004827:Epilepsy / Q000175:diagnosis / Q000503:physiopathology* / Q000601:surgery*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D064795:Intraoperative Neurophysiological Monitoring / Q000379:methods*; D008297:Male; D012189:Retrospective Studies
keywords: Automatic localisation; Epilepsy surgery; High-frequency oscillations; Non-harmonicity; Post-surgical outcome