Abstracts

Rationale: Data from multiple imaging modalities contribute to the successful localization of the epileptogenic zone in patients with treatment-resistant epilepsy. Each imaging modality has inherent strengths and weaknesses with regards to spatial and temporal resolution. Multimodal coregistration of pre-surgical imaging modalities may overcome the weaknesses of individual imaging datasets, and is generally accepted to improve outcome after surgical therapy. In order to maximize the utility of multimodal neuroimaging for surgical planning, it is important to be able to present any combination of modalities in a 3-dimensional model. We present a standardized process for coregistration of magneto-encephalography (MEG) data for presentation in a three-dimensional model concurrently with other neuroimaging modalities. Methods: MEG source estimates for epileptiform and functional localization are coregistered to a T1 thin-sliced 3T MRI to create the magnetic source images. This MRI serves as the anatomic basis for coregistration of all other pre-surgical imaging modalities (eg PET, Ictal SPECT subtraction). MEG source estimate representations are extracted using a histogram analysis to produce a dataset which may be overlaid with additional coregistered imaging modalities. A 3-dimensional anatomic brain model is created from the MRI using MeVisLab. Isocontours of the MEG dipoles and other coregistered modalities can then be overlaid in varying combinations and manipulated to provide a more complete picture of the anatomical structure, function, and epileptogenic localization in relation to each other. Results: The process was developed and applied to 6 cases in which epileptiform MEG dipoles and either Ictal SPECT Subtraction or PET data were available. The resultant 3-dimensional models were then compared with the original 2-dimensional studies to confirm that they are accurate representations. The model (Figure 1) can be oriented and clipped in all 3 orthogonal planes to maximize appreciation for the epileptogenic zone localization as identified by MEG and its relationship to functional cortex. This model can be expanded to include epileptogenic localization based on other modalities and functional response MEG dipoles. The typical 2-dimensional presentation of the data is shown in Figure 1 for comparison. Conclusions: This standardized protocol for displaying MEG data in 3-dimensions provides improved visual presentation. The overall relationship between modalities is more readily apparent and can be easily manipulated between the axial, coronal, and sagittal planes. In addition, this protocol allows assessment of congruence amongst complementary anatomic and functional imaging studies with regards to epileptogenic zone localization and the proximity to functional cortex, potentially contributing to improved subdural grid placement and surgical outcomes. Subsequent research validating the value of 3-dimensional multimodal modeling in regards to surgical planning and outcome is planned.