Individualized localization and cortical surface-based registration of intracranial electrodes

Abstract

In addition to its widespread clinical use, the intracranial electroencephalogram (iEEG) is increasingly being employed as a tool to map the neural correlates of normal cognitive function as well as for developing neuroprosthetics. Despite recent advances, and unlike other established brain mapping modalities (e.g. functional MRI, magneto- and electroencephalography), registering the iEEG with respect to neuroanatomy in individuals – and coregistering functional results across subjects – remains a significant challenge. Here we describe a method which coregisters high-resolution preoperative MRI with postoperative computerized tomography (CT) for the purpose of individualized functional mapping of both normal and pathological (e.g., interictal discharges and seizures) brain activity. Our method accurately (within 3mm, on average) localizes electrodes with respect to an individual’s neuroanatomy. Furthermore, we outline a principled procedure for either volumetric or surface-based group analyses. We demonstrate our method in five patients with medically-intractable epilepsy undergoing invasive monitoring of the seizure focus prior to its surgical removal. The straight-forward application of this procedure to all types of intracranial electrodes, robustness to deformations in both skull and brain, and the ability to compare electrode locations across groups of patients makes this procedure an important tool for basic scientists as well as clinicians.

Rotating waves during human sleep spindles organize global patterns of activity that repeat precisely through the night

“…Post-implantation electrode localization utilized coregistration of preoperative magnetic resonance imaging (MRI) with postoperative computed tomography (CT), as described by Dykstra et al (Dykstra et al, 2012). Cortical surfaces were computed with FreeSurfer Fischl et al, 1999).…”

“…Cortical surfaces were computed with FreeSurfer Fischl et al, 1999). To account for the misalignment between the MRI and CT due to the craniotomy, the locations of the grid electrodes were projected onto the cortical surface (Dykstra et al, 2012). Geodesic electrode distances, which take into account the folded geometry of the cortical surface and were used in some calculations (e.g.…”

Improved Localization of Implanted Subdural Electrode Contacts on Magnetic Resonance Imaging With an Elastic Image Fusion Algorithm in an Invasive Electroencephalography Recording

“…A photographic documentation of the electrode contact positions would have been preferable, as shown by Tao et al, 17 LaViolette et al, 18 and Pieters et al, 19 in cases in which a grid was implanted through a craniotomy. Dykstra et al 20 faced the same problem we do with localizing electrode contacts that are implanted through burr holes. Not being able to compare with intraoperative photographs, they simply shift the electrode contacts to the level of the pia.…”

“…With grid implantation through craniotomy, the brain surface can be photographed and images can be superimposed onto a cortical MRI reconstruction. [15][16][17][18][19][20] Combinations of photography and 2-dimensional radiography have been described, 10 as have linear superpositions using a 3-dimensional visualization system. 9 Contacts under the margins of the craniotomy or placed through burr holes cannot be documented photographically; these contacts are also subject to brain shift, which can be corrected mathematically.…”

“…9 Contacts under the margins of the craniotomy or placed through burr holes cannot be documented photographically; these contacts are also subject to brain shift, which can be corrected mathematically. 7,20 Using the anatomic information of the CT scan and combining this with the high spatial and contact soft-tissue resolution of MRI provide a potential new option to handle this situation. Modern computers allowing highly complex calculations, together with newly developed elastic fusion algorithms, can be used to compensate for brain shift effects in the future.…”