Abstracts

Rationale: The role of three-dimensional multi-modality imaging (3DMMI) is becoming increasingly important in focal epilepsy resective surgery. We discuss strategy and methods of using 3DMMI for intracranial electroencephalography (IC-EEG), including stereotactic-electroencephalography (SEEG), for implantation, monitoring and resection planning. In the past, common imaging tests have often been reviewed independently from other available frames of reference during epilepsy surgery evaluation. With the advancement of 3D imaging integration (co-registration) software it is advantageous to combine previously independent imaging tests into a 3D volume for consideration of concordant data during invasive EEG analysis and resection planning. Methods: At our hospital, we implemented 3D volume rendered models and labeling of delineated electrodes for image generation during invasive evaluations since 2010. Using standardized protocols, cortical reconstruction involving a preoperative (1.5T or 3T) 3D T1 MRI is segmented using FreeSurfer software (freesurfer.net) and converted to SPM (Analyze) format. Co-registration of the MRI and high-resolution post-implantation CT (0.5-1mm slices) is done in Neuroscan Curry version 6 (compumedicsneuroscan.com) using rigid-body co-registration of bone. Electrodes are individually delineated and labeled after locations are confirmed using platinum markers between the number 1 and 2 electrodes for grids or strips. Depth electrode locations are confirmed by anatomical landmark and unique numbers of contacts. Electrodes are colored according to the wire leading out of the skull. The composite images are then provided directly to the EEG monitoring unit, epileptologists, and primary surgeon for ease-of-use and consistency in communication. Depending on the individual patient's pre-surgical seizure localization, other imaging modalities may be co-registered including T2-weighted MRI (for mass lesions such as tubers), functional MRI (fMRI), magnetoencephalography (MEG), subtraction ictal SPECT (SISCOM). Results: The resulting images acquired from this methodology generate detailed resolution of each individual contact in both subdural grids and depth electrodes including SEEG implantation. Figure 1 shows a right posterior subdural grid implantation including lateral, mesial, and basal coverage. Figure 2 depicts an individual contact of an insular electrode with SEEG implantation. Conclusions: With 3DMMI, co-registration of structural and functional tests can produce unique and concordant data that is vital to the surgical planning process. This method allows for detailed visualization of electrodes not only on the lateral convexity, but also mesial and basal planes as illustrated in Figure 1. Not only are subdural electrodes visualized in detail, but this allows for high-resolution (1-2 millimeters) visualization of individual SEEG electrode contacts as in Figure 2. In SEEG implantations, 3D visualization of implanted electrodes are especially appreciated over traditional reconstructions. Consistent visualization with accurate and reproducible 3D reconstructed models improve communication, monitoring, and appreciation of 3D spatial arrangement of the electrodes. Such high quality images aid in delineation of the epileptogenic zone, and in precise resection planning. Funding: None