Fusion of MRI and CT with Subdural Grid Electrodes

Abstract

In patients with drug-resistant focal epilepsies subdural grid electrodes may be implanted to determine the seizure onset zone and eloquent cortex areas. Since the spatial relationship of the grid to the underlying brain is poorly visualized on MRI, we co-registered MRI before and CT after implantation of subdural grid electrodes. In this study we sought an appropriate algorithm to combine both imaging modalities. We compared six different co-registration algorithms including surface-oriented, mutual information-based and landmark-based methods. The resulting overlay matrices were analyzed by calculating rotational and translational shifts and by judging co-registered MRI and CT scans visually. A brain surface oriented method had the lowest rotational (axial 0.7 +/- 0.6 degrees; coronal 1.7 +/- 1.1 degrees; sagittal 1.9 +/- 1.8 degrees) and translational shifts (3.7 +/- 1.3 mm). It was judged visually to be the best, had a low intra- and inter-observer variability, and lasted approximately 15 minutes. This algorithm is recommended when co-registering MRI before and CT after implantation of subdural grid electrodes. Skin-, voxel-, and landmark-based algorithms are less accurate, which is most likely due to postsurgical deformation of extra- and intracranial soft tissue.

3D visualization of subdural electrode shift as measured at craniotomy reopening

“…Several techniques have been employed to visualize electrode placement in vivo including artifact localization (Bootsveld et al, 1993; Silberbusch et al, 1998), three-dimensional reconstruction and X-ray derived location projection (Dalal et al, 2008; Winkler et al, 2000), automated template MRI transformation and projection (Kovalev et al, 2005), X-ray co-registration (Dalal et al, 2008; Miller et al, 2007; Winkler et al, 2000), curvilinear reformation (Schulze-Bonhage et al, 2002), CT/MRI co-registration (Grzeszczuk et al, 1992; Nelles et al, 2004; Tao et al, 2009), computer aided stereo-tactic model creation (Morris et al, 2004; Wagner et al, 2009) as well as digital 2D photography co-registered to 3D reconstructed MRI (Mahvash et al, 2007; Wellmer et al, 2002). …”

An integrated tool for automated visualization of subdural electrodes in epilepsy surgery evaluation

“…Co-registration errors were evaluated by determining anatomical landmarks proposed by Nelles et al [9]. The To determine the total mismatch between the calculated position and the true position of the electrode grid due to registration errors and cortical displacement, the intraoperative photograph was manually co-registered with the 3D-reconstructed cortical surface of the MRI dataset (Fig.…”

A head phantom prototype to verify subdural electrode localization tools in epilepsy surgery

“…from the Internet Brain Segmentation Repository, www.cma.mgh.harvard.edu/ibsr/) are used as reference data. Quantification of registration accuracy in patient data sets is done by comparing the automatically registered data with manually registered data using anatomical landmarks (Nelles et al, 2004). Alternatively, registration accuracy can be determined by using homogeneous phantoms with reference points inside a head contour (Isambert et al, 2008;Zhang et al, 2009).…”