Subdural porous and notched mini-grid electrodes for wireless intracranial electroencephalographic recordings

Abstract

BackgroundIntracranial 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.MethodImpedance 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.ResultsThe 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.ConclusionThe 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.

Minimal Tissue Reaction after Chronic Subdural Electrode Implantation for Fully Implantable Brain–Machine Interfaces

“…Several animal models have been established in preclinical research because of their relatively suitable skull sizes for implanted devices [ 23 , 24 , 26 , 39 , 40 , 41 , 42 ]. Minipigs and sheep have been used in studies of cuff electrodes and the WIMAGINE epidural ECoG system [ 25 , 43 ] to mimic the implantation of clinical devices.…”

Investigating the Feasibility of Epicranial Cortical Stimulation Using Concentric-Ring Electrodes: A Novel Minimally Invasive Neuromodulation Method

“…ECS concentric-ring was modeled as an inner disc electrode and an outer ring electrode both embedded in an insulating silicon material (polydimethylsiloxane or PDMS, typically used for invasive electrode designs) (Meacham et al, 2008; Guo et al, 2013; Ochoa et al, 2013; Salam et al, 2014). The electrode was placed in contact with the skull with the disc and ring electrodes facing the skull and the silicon layer in contact with the skin.…”