Head model and electrical source imaging: a study of 38 epileptic patients

Area of Science:

• Neuroscience
• Biomedical Engineering
• Medical Imaging

Background:

• Electrical Source Imaging (ESI) reconstructs brain activity from scalp EEG.
• ESI aids in identifying the irritative zone for focal epilepsies using interictal epileptiform discharges (IEDs).
• Inaccurate head models in ESI can mislocalize IED generators.

Purpose of the Study:

• To systematically evaluate the influence of different head models on IED source localization precision.
• To compare the performance of Locally Spherical Model with Anatomical Constraints (LSMAC), Boundary Element Model (BEM), and Finite Element Model (FEM) in ESI.

Main Methods:

• ESI was applied to averaged IEDs from 38 epilepsy patients with high-density scalp EEG and intracranial EEG.
• Three head models (LSMAC, BEM, FEM) were computed from individual patient MRIs.
• Localization accuracy was assessed by comparing ESI results with post-operative outcomes and intracranial EEG data.

Main Results:

• All tested head models yielded highly similar IED source locations.
• In patients with positive surgical outcomes, 74% of source maxima were within the resected area.
• Median distances from source maxima to nearest ictal electrodes were comparable across models (13.2 mm for LSMAC, 15.6 mm for BEM and FEM).

Conclusions:

• The choice of head model complexity is not a critical factor for accurate ESI in clinical epilepsy applications.
• Simpler head models can achieve comparable localization precision to more complex ones.
• ESI is a valuable tool for identifying the epileptogenic zone in focal epilepsy.