MRI-Compatible and Conformal Electrocorticography Grids for Translational Research.

Florian Fallegger,Adrien May,Elvira Pirondini,Paul Constanthin,Jocelyne Bloch,Gregory Zegarek,Stéphanie P Lacour,Ludovic Serex,Blaise Yvert,Nicolas Vachicouras,Marie Palma,Dirk Van Roost,Giuseppe Schiavone,Karl Schaller,Fabien B Wagner,Grégoire Courtine,Mehrdad Khoshnevis

doi:10.1002/advs.202003761

Abstract

Intraoperative electrocorticography (ECoG) captures neural information from the surface of the cerebral cortex during surgeries such as resections for intractable epilepsy and tumors. Current clinical ECoG grids come in evenly spaced, millimeter‐sized electrodes embedded in silicone rubber. Their mechanical rigidity and fixed electrode spatial resolution are common shortcomings reported by the surgical teams. Here, advances in soft neurotechnology are leveraged to manufacture conformable subdural, thin‐film ECoG grids, and evaluate their suitability for translational research. Soft grids with 0.2 to 10 mm electrode pitch and diameter are embedded in 150 µm silicone membranes. The soft grids are compatible with surgical handling and can be folded to safely interface hidden cerebral surface such as the Sylvian fold in human cadaveric models. It is found that the thin‐film conductor grids do not generate diagnostic‐impeding imaging artefacts (<1 mm) nor adverse local heating within a standard 3T clinical magnetic resonance imaging scanner. Next, the ability of the soft grids to record subdural neural activity in minipigs acutely and two weeks postimplantation is validated. Taken together, these results suggest a promising future alternative to current stiff electrodes and may enable the future adoption of soft ECoG grids in translational research and ultimately in clinical settings.

Highlights

Functional neurosurgeons today routinely employ implantable electrodes to help assessing and treating neurological and traumatic disorders.[1,2,3,4,5,6,7] Epidural or subdural cortical grids, here referred as electrocorticography grids (ECoGs), are a class of such electrodes that are mainly used to collect intra- or extraoperatively functional maps of cortical activity with high spatiotemporal resolution, ahead of resection of brain tumors or epileptic foci
We tested the hypothesis that the soft ECoG embedded in silicone and engineered with a thin-film conductor technology would offer the inherent advantage of poorly interacting with external oscillating electromagnetic fields such as those used for magnetic resonance imaging (MRI)
We report a fully customizable silicone technology platform enabling the fabrication of MRI-compatible, multichannel, and soft electrode grids that facilitate the interfacing of large and convoluted brain areas

Summary

Introduction

Functional neurosurgeons today routinely employ implantable electrodes to help assessing and treating neurological and traumatic disorders.[1,2,3,4,5,6,7] Epidural or subdural cortical grids, here referred as electrocorticography grids (ECoGs), are a class of such electrodes that are mainly used to collect intra- or extraoperatively (up to 30 days, the patient staying at the hospital) functional maps of cortical activity with high spatiotemporal resolution, ahead of resection of brain tumors or epileptic foci. D. Van Roost Department of Neurosurgery Ghent University Ghent 9000, Belgium the relatively large Young’s modulus (1–5 GPa) of thermoplastic polymers dictates thicknesses of a few micrometers only to enable sufficiently low bending stiffness and capillary forces high enough to conform to the convoluted surface of the brain.[33] At this thickness scale, devices are harder to manipulate due to wrinkling and may be more prone to tear in some cases.[34] Micro-ECoGs on flexible foil technology are often limited to be used over small surface areas, e.g.,

Conformability and Manufacturability of Soft Electrode Grids

Clinical Usability and MRI Compatibility

Subdural Surface Recordings in Minipig Models

Conclusion

Data Availability Statement