Abstracts

Rationale:
Magnetoencephalography is used to find epileptic foci in patients with refractory focal epilepsy by localizing interictal spikes. The equivalent current dipole is the most common metric in MEG spike localization. However, the technique requires an expert magnetoencephalographer and is time intensive. Beamforming methods such as SAMepi and SAMg2 have been developed as automated techniques for spike localization and yield similar results to the equivalent current dipole. We sought to compare the automated beamforming methods SAMEpi and SAMg2 to ECD in patients with medically refractory focal epilepsy. We further sought to compare spike localization with surgical outcomes in these patients using these techniques.
Method:
Synthetic aperture magnetometry (SAMg2), synthetic aperture magnetometry with g2 averaged over a sliding time window (SAMepi), and equivalent current dipole analysis (ECD) were performed retrospectively in patients with refractory focal epilepsy who underwent surgical resection and compared to Engel classification 12 months postoperatively.
Results:
We identified 46 patients who met our inclusion criteria of a MEG study of sufficient quality followed by resective epilepsy surgery and at least one year of post-op follow-up. Spiking locations were detected in 27 (59%) patients using SAMepi, 28 (61%) patients using SAMg2, and 25 (54%) patients using ECD. Complete concordance with surgical resection lobe occurred in 48% (13/27), 39% (11/28), and 52% (13/25) of the cases with a positive result using SAMepi, SAMg2, and ECD, respectively (p = 0.63). Of the cases in which each technique was in complete concordance with resection lobe, patients were postoperative Engel class 1 a total of 69% (9/13), 72% (8/11), and 62% (8/13) of the time at 12 months for SAMepi, SAMg2, and ECD, respectively (p = 0.90). Conversely, discordance with surgical resection lobe occurred in 33% (9/27), 25% (7/28), 28% (7/25) of the cases with a positive result, respectively (p = 0.70). Of the cases in which the respective techniques were discordant with the resection lobe, patients were postoperative Engel class >1 a total of 78% (7/9), 72% (5/7), and 57% (4/7) of the time at 12 months (p = 0.85).
Conclusion:
SAMepi, SAM(g2) and ECD may have similar sensitivities for detection of epileptiform activity, and their findings may be similarly correlated with surgical outcome. Beamforming techniques such as SAMEpi and SAMg2 therefore may have a clinical role in MEG spike localization.
Funding:
:N/A