Abstracts

MEG and MR Spectroscopy

Abstract number : 1.201
Submission category :
Year : 2000
Submission ID : 3184
Source : www.aesnet.org
Presentation date : 12/2/2000 12:00:00 AM
Published date : Dec 1, 2000, 06:00 AM

Authors :
C Hummel, I Schaefer, R Hopfengaetner, C Tilz, H Stefan, Univ OF ERLANGEN-NUERNBERG, Erlangen, Germany; Univ OF ERLANGEN, Erlangen, Germany.

RATIONALE:Magnetoencephalography (MEG) and Magnetic Resonance Spectroscopy (MRS) are relatively new methods recently introduced to presurgical evaluation of epilepsy surgery candidates, both representing different approaches to identify certain sites in the brain possibly involved in epileptogenicity. The aim of this preliminary retrospective study was to compare results of both approaches in patients with pharmacologically refractory epilepsy of the temporal lobe. METHODS:40 candidates for epilpesy surgery with temporal lobe epilpesy (TLE) had MEG and MRS scans during the course of preoperative focus evaluation. Bihemispheric MEG recordings were performed with a dual unit, 74 channel biomagnetic system (BTI, San Diego, USA). Localization of specific epileptic signals was based upon the model of an equivalent current dipole in a homogenously conducting sphere. Dipole locations were displayed in co-registered MRI slices. Proton MR-Spectroscopy was performed on a 1.5T MAGNETOM Vision (Siemens, Erlangen, Germany). Two-diemensional Chemical Shift Imaging-technique (CSI) was used for the determination of NAA (N-acetyl-aspartate) and Choline (Cho) in the right and left temporal lobes. A group of six coherent voxels was placed in each temporal lobe, three of them included the hippocampus and three included neighboring cortical gray and white matter. The size of each voxel was 12?12?15mm. RESULTS:Approximately three quarters of the patients showed significant deviations of the NAA/Cho quotient in at least one voxel. MEG sensitivity was in the same range; 11 patients had no epilpetic discharges during the recording. Only in 2 cases both methods failed to produce results. Lateralization from MEG and MRS disagreed in 2 patients. Examples will be given to illustrate congruent MEG and MRS findings in mesial as well as lateral temporal structures. CONCLUSIONS:Both MEG and MRS contribute significantly to presurgical diagnostics in epilepsy. Although primarily emphasizing different aspects of temporal lobe focus identification-mesial sources tending to escape MEG recordings wherease MRS mainly focuses on these-the chances and limits of both mutual complementarity and compatibility need to be further evaluated.