1 Clinical Neurophysiology Section, Clínica Universidad de Navarra, Pamplona, Spain; IdiSNA, Instituto de Investigación Sanitaria de Navarra, Pamplona, Spain; Analytical Neurophysiology Lab, Montreal Neurological Institute and Hospital, McGill University, Montreal, Quebec, Canada; Montreal Neurological Institute and Hospital, McGill University, Montreal, Quebec, Canada.
2 Analytical Neurophysiology Lab, Montreal Neurological Institute and Hospital, McGill University, Montreal, Quebec, Canada; Multimodal Functional Imaging Lab, Biomedical Engineering Department, McGill University, Canada. Electronic address: tamir.avigdor@mail.mcgill.ca.
3 Analytical Neurophysiology Lab, Montreal Neurological Institute and Hospital, McGill University, Montreal, Quebec, Canada; Multimodal Functional Imaging Lab, Biomedical Engineering Department, McGill University, Canada. Electronic address: chifaou.abdallah@mail.mcgill.ca.
4 Analytical Neurophysiology Lab, Montreal Neurological Institute and Hospital, McGill University, Montreal, Quebec, Canada. Electronic address: daniel.mansilla@mail.mcgill.ca.
5 Analytical Neurophysiology Lab, Montreal Neurological Institute and Hospital, McGill University, Montreal, Quebec, Canada; Montreal Neurological Institute and Hospital, McGill University, Montreal, Quebec, Canada. Electronic address: john.thomas3@mail.mcgill.ca.
6 Montreal Neurological Institute and Hospital, McGill University, Montreal, Quebec, Canada. Electronic address: nicolas.vonellenrieder@mcgill.ca.
7 Analytical Neurophysiology Lab, Montreal Neurological Institute and Hospital, McGill University, Montreal, Quebec, Canada; Multimodal Imaging and Connectome Analysis Laboratory, Montreal Neurological Institute and Hospital, McGill University, Montreal, Quebec, Canada. Electronic address: jessica.royer@mail.mcgill.ca.
8 Montreal Neurological Institute and Hospital, McGill University, Montreal, Quebec, Canada; Multimodal Imaging and Connectome Analysis Laboratory, Montreal Neurological Institute and Hospital, McGill University, Montreal, Quebec, Canada. Electronic address: boris.bernhardt@mcgill.ca.
9 Montreal Neurological Institute and Hospital, McGill University, Montreal, Quebec, Canada; Multimodal Functional Imaging Lab, Biomedical Engineering Department, McGill University, Canada; Multimodal Functional Imaging Lab, PERFORM Center, Department of Physics, Concordia University, Montreal, QC, Canada. Electronic address: christophe.grova@mcgill.ca.
10 Montreal Neurological Institute and Hospital, McGill University, Montreal, Quebec, Canada. Electronic address: jean.gotman@mcgill.ca.
11 Analytical Neurophysiology Lab, Montreal Neurological Institute and Hospital, McGill University, Montreal, Quebec, Canada; Montreal Neurological Institute and Hospital, McGill University, Montreal, Quebec, Canada; Department of Neurology, Duke University Medical Center, Durham, NC, United States; Department of Biomedical Engineering, Duke Pratt School of Engineering, Durham, NC, United States. Electronic address: birgit.frauscher@duke.edu.

Objective: High-density (HD) electroencephalography (EEG) is increasingly used in presurgical epilepsy evaluation, but it is demanding in time and resources. To overcome these issues, we compared EEG source imaging (ESI) solutions with a targeted density and HD-EEG montage.

Methods: HD-EEGs from patients undergoing presurgical evaluation were analyzed. A low-density recording was created by selecting the 25 electrodes of a standard montage from the 83 electrodes of the HD-EEG and adding 8-11 electrodes around the electrode with the highest amplitude interictal epileptiform discharges. The ESI solution from this "targeted" montage was compared to that from the HD-EEG using the distance between peak vertices, sublobar concordance and a qualitative similarity measure.

Results: Fifty-eight foci of forty-three patients were included. The median distance between the peak vertices of the two montages was 13.2 mm, irrespective of focus' location. Tangential generators (n = 5/58) showed a higher distance than radial generators (p = 0.04). We found sublobar concordance in 54/58 of the foci (93%). Map similarity, assessed by an epileptologist, had a median score of 4/5.

Conclusions: ESI solutions obtained from a targeted density montage show high concordance with those calculated from HD-EEG.

Significance: Requiring significantly fewer electrodes, targeted density EEG allows obtaining similar ESI solutions as traditional HD-EEG montage.