title: Subdural porous and notched mini-grid electrodes for wireless intracranial electroencephalographic recordings.
abstract: BACKGROUND
  Intracranial electroencephalography (EEG) studies are widely used in the presurgical evaluation of drug-refractory patients with partial epilepsy. Because chronic implantation of intracranial electrodes carries a risk of infection, hemorrhage, and edema, it is best to limit the number of electrodes used without compromising the ability to localize the epileptogenic zone (EZ). There is always a risk that an intracranial study may fail to identify the EZ because of suboptimal coverage. We present a new subdural electrode design that will allow better sampling of suspected areas of epileptogenicity with lower risk to patients.
  
  
  METHODS
  Impedance of the proposed electrodes was characterized in vitro using electrochemical impedance spectroscopy. The appearance of the novel electrodes on magnetic resonance imaging (MRI) was tested by placing the electrodes into a gel solution (0.9% NaCl with 14 g gelatin). In vivo neural recordings were performed in male Sprague Dawley rats. Performance comparisons were made using microelectrode recordings from rat cortex and subdural/depth recordings from epileptic patients. Histological examinations of rat brain after 3-week icEEG intracerebral electroencephalography (icEEG) recordings were performed.
  
  
  RESULTS
  The in vitro results showed minimum impedances for optimum choice of pure gold materials for electrode contacts and wire. Different attributes of the new electrodes were identified on MRI. The results of in vivo recordings demonstrated signal stability, 50% noise reduction, and up to 6 dB signal-to-noise ratio (SNR) improvement as compared to commercial electrodes. The wireless icEEG recording system demonstrated on average a 2% normalized root-mean-square (RMS) deviation. Following the long-term icEEG recording, brain histological results showed no abnormal tissue reaction in the underlying cortex.
  
  
  CONCLUSIONS
  The proposed subdural electrode system features attributes that could potentially translate into better icEEG recordings and allow sampling of large of areas of epileptogenicity at lower risk to patients. Further validation for use in humans is required.
authors.affiliation: Polystim Neurotechnologies Laboratory, Polytechnique Montréal, QC, Canada.
authors.forename: Muhammad Tariqus
authors.initials: MT
authors.lastname: Salam
authors.affiliation: Polystim Neurotechnologies Laboratory, Polytechnique Montréal, QC, Canada.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Gélinas
authors.affiliation: Research Center, Sainte-Justine University Hospital Center (CHU Sainte-Justine), Université de Montréal, QC, Canada.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Desgent
authors.affiliation: Research Center, Sainte-Justine University Hospital Center (CHU Sainte-Justine), Université de Montréal, QC, Canada.
authors.forename: Sandra
authors.initials: S
authors.lastname: Duss
authors.affiliation: Polystim Neurotechnologies Laboratory, Polytechnique Montréal, QC, Canada ; Neurology Service, Department of Medicine, Notre-Dame Hospital, Centre Hospitalier de l'Université de Montréal (CHUM), QC, Canada.
authors.forename: Félix
authors.initials: F
authors.lastname: Bernier Turmel
authors.affiliation: Research Center, Sainte-Justine University Hospital Center (CHU Sainte-Justine), Université de Montréal, QC, Canada.
authors.forename: Lionel
authors.initials: L
authors.lastname: Carmant
authors.affiliation: Polystim Neurotechnologies Laboratory, Polytechnique Montréal, QC, Canada.
authors.forename: Mohamad
authors.initials: M
authors.lastname: Sawan
authors.affiliation: Neurology Service, Department of Medicine, Notre-Dame Hospital, Centre Hospitalier de l'Université de Montréal (CHUM), QC, Canada.
authors.forename: Dang Khoa
authors.initials: DK
authors.lastname: Nguyen
keywords: electrodes; epilepsy; monitoring; seizure; surgery