Abstract
Objective: Magnetoencephalography source imaging (MSI) of interictal epileptiform discharges (IED) is a useful presurgical tool in the evaluation of drug-resistant frontal lobe epilepsy (FLE) patients. Yet, failures in MSI can arise related to artifacts and to interference of background activity. Independent component analysis (ICA) is a popular denoising procedure but its clinical application remains challenging, as the selection of multiple independent components (IC) is controversial, operator dependent, and time consuming. We evaluated whether selecting only one IC of interest based on its similarity with the average IED field improves MSI in FLE.Methods: MSI was performed with the equivalent current dipole (ECD) technique and two distributed magnetic source imaging (dMSI) approaches: minimum norm estimate (MNE) and coherent Maximum Entropy on the Mean (cMEM). MSI accuracy was evaluated under three conditions: (1) ICA of continuous data (Cont_ICA), (2) ICA at the time of IED (IED_ICA), and (3) without ICA (No_ICA). Localization performance was quantitatively measured as actual distance of the source maximum in relation to the focus (Dmin), and spatial dispersion (SD) for dMSI.Results: After ICA, ECD Dmin did not change significantly (p > 0.200). For both dMSI techniques, ICA application worsened the source localization accuracy. We observed a worsening of both MNE Dmin (p < 0.05, consistently) and MNE SD (p < 0.001, consistently) for both ICA approaches. A similar behaviour was observed for cMEM, for which, however, Cont_ICA seemed less detrimental.Conclusion: We demonstrated that a simplified ICA approach selecting one IC of interest in combination with distributed magnetic source imaging can be detrimental. More complex approaches may provide better results but would be rather difficult to apply in real-world clinical setting. In a broader perspective, caution should be taken in applying ICA for source localization of interictal activity. To ensure optimal and useful results, effort should focus on acquiring good quality data, minimizing artifacts, and determining optimal candidacy for MEG, rather than counting on data cleaning techniques.
Highlights
About 30% of patients affected by focal epilepsy are drug-resistant and may be considered for surgical candidacy
In this study we aimed to evaluate whether selecting only one independent components (IC) of interest based on its similarity with the average IED field improves source localization in patients with drug-resistant frontal lobe epilepsy (FLE)
We retrospectively studied a cohort of 17 patients with medically refractory FLE that underwent a MEG recording session
Summary
About 30% of patients affected by focal epilepsy are drug-resistant and may be considered for surgical candidacy. Epilepsy surgery success is conditional to the accurate identification and resection of the cortical region generating epileptiform activity. This is relatively easier to achieve in well-defined epileptic syndromes such as temporal lobe epilepsy with mesial temporal sclerosis, with up to 84% seizure freedom at one year post-surgery [1]. Identification of the focus is far more complex in patients with extratemporal epilepsy and especially frontal lobe epilepsy (FLE). The latter constitutes the second most frequent surgery group following mesial temporal lobe resections, but seizure freedom rates are still disappointing at ∼50% at one year postsurgery [2]. One crucial question is the accuracy we achieve in localizing the generator within the frontal lobes
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
