2Dimensional inverse imaging (2DII) of epileptic seizure

It is difficult to perform ictal vs. interictal MEG localization studies. MEG recordings of epileptic seizures are rare and are often accompanied by patient movements. However, during routine MEG recordings of a presurgical patient with epilepsy, a complex partial seizure was recorded with a whole head neuromagnetometer (4D Neuroimaging Magnes WHS2500). During seizure, the patient opened his eyes and stared without body movement [1]. The MEG data during seizure consisted of 15 Hz rhythmic activity that changed to 5 Hz spike and wave discharges of increasing amplitude during the first 700 milliseconds. The largest magnetic field amplitudes were from MEG sensors adjacent to the left temporal scalp. Single equivalent current dipole (ECD) imaging indicated epileptic spike data peaks corresponded to focal source activity near the margin of a previous resection of the left temporal lobe [2]. However, these results are derived from a discontinuous series of single time slices in which the epileptic activity is dominated by a compact source that can be modeled as a single point current dipole. Thus, the ECD results do not adequately describe the full extent of the cortex involved. However, with the 2DII MEG imaging technique a complete sequence of whole brain images of the seizure event was produced [3,4]. These 2DII images included both focal and extended epileptic source activity as well as the ongoing background activity. Thus, it was possible to determine if the change from rhythmic to spike and wave activity involved the recruitment of other cortical regions or involved dynamic changes in a single regional structure. In addition, the analysis is enhanced when 2DII results are displayed as 3-dimensional false color images that can be rotated to any orientation. The focal cortical activity initiating the onset seizure event was imaged with the 2DII technique and the subsequent spread of activity was assessed. Also, prior focal activity at this seizure initiation site was observed in 2DII images even though it was not detected by the single ECD technique [2].