Ictal Magnetic Source Imaging in Presurgical Assessment

Area of Science:

• Neuroscience
• Medical Imaging
• Epileptology

Background:

• Ictal magnetoencephalography (MEG) recordings are infrequent but valuable for epilepsy research.
• Accurate localization of the epileptogenic zone (EZ) is crucial for surgical planning in epilepsy patients.

Purpose of the Study:

• To evaluate the effectiveness of ictal magnetic source localization (MSI) using two algorithms: linearly constrained minimum variance (LCMV) and equivalent current dipole (ECD).
• To validate MSI results against stereoelectroencephalography (SEEG) defined EZ and quantify concordance.

Main Methods:

• Six patients with epilepsy underwent ictal MEG recordings.
• Ictal MSI was performed using LCMV beamforming and ECD algorithms.
• Results were compared with SEEG-defined EZ, quantified by the epileptogenicity index (EI).

Main Results:

• Ictal MEG patterns showed rhythmic activities between 10 and 20 Hz in all patients.
• LCMV demonstrated superior concordance with SEEG-defined EZ compared to ECD methods.
• LCMV identified EZ in 4/6 cases, while ECD methods showed lower concordance rates.

Conclusions:

• Ictal MSI, particularly using the LCMV beamformer, can effectively localize the EZ in patients with epilepsy.
• LCMV offers better performance than ECD for ictal source localization, aiding in presurgical evaluation.
• Further investigation into LCMV's ability to reveal ictal dynamics, such as delayed propagation, is warranted.