Spatiotemporal Examination of Interictal Discharges Using Equivalent Current Dipole in MEG
Abstract number :
3.136
Submission category :
3. Neurophysiology / 3D. MEG
Year :
2023
Submission ID :
1210
Source :
www.aesnet.org
Presentation date :
12/4/2023 12:00:00 AM
Published date :
Authors :
Presenting Author: Elena Hayday, BS – NINDS
Kaya Scheman, BS – Postbac IRTA, NINDS, National Institutes of Health; Price withers, BS – Postbac IRTA, NINDS, National Institutes of Health; Jeffrey Stout, PhD – Computer Systems Analyst, NIMH, National Institutes of Health; Ivano Antonio Triggiani, PhD – Staff Scientist, NINDS, National Institutes of Health; Sara Inati, MD – Principal Investigator, NINDS, National Institutes of Health
Rationale: Although epilepsy surgery is often an effective treatment for drug-resistant epilepsy (DRE), outcomes remain sub-optimal, at least in part due to inaccurate localization of seizure foci. Interictal discharges (IEDs) are often used for localization due to their high frequency of occurrence; however, large spatial areas of cortex must be involved to be seen in non-invasive recordings. The current clinical gold standard for IED localization in magnetoencephalography (MEG), the equivalent current dipole (ECD) method, rests on the assumption that IED sources can be effectively modeled as a single focal source and that the dipole with the best fit most closely approximates that source. This would be expected in patients with predominantly local radial spread, but this assumption may be violated in IEDs involving more distant or multifocal propagation, resulting in poor fits and/or erroneous localization. Here, we examine whether goodness of fit (GOF) differed between patients with stationary dipoles versus those with moving dipole source localizations in the pre-spiking period, hypothesizing that IEDs with moving dipoles may involve more distant propagation of activity and therefore be modeled less accurately as a single dipole.
Methods: We studied 18 DRE patients who underwent pre-surgical evaluation at NIH (10 male; 25±24 years). Forty-five minute resting state MEG was performed at a 600 Hz sampling rate. A multisphere head model was created from a T1w MRI and coregistered to the MEG using three fiducial points in AFNI. A single population of IEDs was identified using an automated spike detection algorithm then clinically validated. Dipoles were fitted in CTF software in 2ms time windows from 50ms before to the peak of the spike. GOF was obtained from CTF software at the earliest point in the window and at the point with the lowest error. Dipole movement was calculated as Euclidean distance between the dipole position at the first sampled point and the marked peak. Distance moved and GOF were averaged across all spikes in a single population for each patient.
Results: Patients were categorized into moving (n=8) and stationary dipole groups (n=10) by whether movement surpassed 1.0 cm in the 10ms preceding the peak (Fig. 1). Groups had similar proportions of temporal and extratemporal patients (>0.99). On average, the first GOF was 85.9% in the stationary group and 81.1% in the moving group (p=0.06), while the best goodness of fit was 86.2% in the stationary group and 81.4% in the moving group (p=0.04, Fig. 2).
Conclusions: Patients with moving dipoles display significantly lower best goodness of fit than those with stationary dipoles. This is consistent with the idea that IEDs in patients with moving dipoles may have non-radial spread patterns that are less accurately localized using the dipole method. This finding is significant because such patients may benefit from other modelling approaches such as distributed source imaging methods to more accurately localize IED sources during evaluation for surgical resection.
Funding: Intramural Research Program
Neurophysiology