Tomoscan sr7000

We included 12 epilepsy patients (mean age 27, range 15-49; see Table 1) who were implanted with subdural
ECoG grids to localize the seizure focus. Two types of grids were used. Standard
ECoG grids had an inter-electrode distance center-to-center of 1 cm and 2.3 mm
exposed surface diameter, whereas high-density grids had either 32 or 64
channels, with 1.3 mm exposed surface diameter and an inter-electrode distance
of 3 mm center-to-center (all AdTech, Racine, USA). For the following analysis,
some electrodes were excluded because they showed flat or unstable signals, or
high power-line noise levels. From the remaining electrodes, only those located
over sensorimotor cortex (as determined by visual inspection, see Figure 1) were considered for further
analysis. For this, the electrodes were localized using co-registration between
a post-implantation Computerized Tomography (CT) scan (Philips Tomoscan SR7000,
Best, the Netherlands) and a pre-operative T1-weighted anatomical scan on a 3T
Magnetic Resonance system (Philips 3T Achieva, Best, the Netherlands), corrected
for brain shift (Hermes et al., 2009 (link);
Branco et al., 2017b ) and projected on
a cortex surface rendering (Figure 1). The
Medical Ethical Committee of the Utrecht University Medical Center approved the
study and all patients signed informed consent according to the Declaration of
Helsinki (2013).

Subjects (three males, one female) were epilepsy patients who underwent implantation of subdural electrode grids to determine the site of epileptic foci for the purpose of possible surgical removal of the epileptogenic tissue. Implanted grids extended to healthy tissue in the hMT+ area of the left (n=2) and right (n=2) hemisphere. Before the subdural electrode implantation, subjects underwent an fMRI scan and were presented with visual motion stimuli identical to the ones performed during ECoG measurements, except that the presentation timing was adjusted to match the timing of the hemodynamic (fMRI) responses. A high resolution (0.5×0.5×1mm) 3D computed tomography (CT, Philips TomoscanSR7000) scan was acquired after implantation to localize ECoG grid electrodes on each subjects brain. The study was approved by the medical ethical board of the Utrecht University Medical Center. All subjects gave their written informed consent to participate in the study in compliance with the Declaration of Helsinki 2013.

Data from 8 patients who underwent surgery for removal of their focus of epilepsy were used. Six subjects (S1-S6) were implanted with ECoG grids 5-7 days before resection (chronic grids) and two only underwent ECoG during surgery (acute grids). All patients were implanted with high-density (HD) ECoG grids (Table 1) and gave consent to participate in the study. For 5 subjects (S1-3 and S5-6), the electrode positions, as predicted with the new GridLoc method (detailed below), were compared with locations obtained with a standard localization method (Hermes et al. 2010 (link); Branco et al. 2017b (link)), where the clinical post-operative CT scan (Philips Tomoscan SR7000, Table 1) was co-registered with their structural MRI scan. For the other three subjects (S4, chronic grid; and S7 and S8, acute grids) the GridLoc electrode positions were compared with (visible) locations determined with intra-operative photographs (Hermes et al. 2010 (link)). The study was approved by the ethical committee of the University Medical Center Utrecht, in accordance with the Declaration of Helsinki (2013).

Electrode selection was based on the individual response to task 1. Electrodes with a significant response to task 1 were selected per run with a paired t-test (p < 0.05, Bonferroni corrected) between rest and active HFB mean values (rest period -2 to -1 s and active period -1 to 0 s, both relative to the peak of force; see also Figure 3). When a subject performed more than one run, the union of the significant channels of individual runs was used. Significant electrodes were grouped into four regions-of-interest (ROIs), depending on their cortical region (Figure 2, Table 3): all electrodes (in- and out-side the SMC), electrodes over M1, electrodes over central sulcus and electrodes over S1. For this purpose, the electrodes were localized by co-registering a pre-operative T1-weighted anatomical magnetic resonance imaging (MRI) scan (Philips 3T Achieva, Best, the Netherlands) with a post-implantation computerized tomography (CT) scan (Philips Tomoscan SR7000, Best, the Netherlands). The electrode locations were corrected for brain shift and projected on a cortex surface rendering (Branco et al., 2018 (link); Hermes et al., 2010 (link)). In total, four averaged signals were used in the following analysis, each representing the mean HFB signal across one of the four ROIs.