Gradient magnetic-field topography for dynamic changes of epileptic discharges

We developed gradient magnetic-field topography (GMFT) for magnetoencephalography (MEG). We plotted the Euclidean norms of gradient magnetic fields occurring at the centers of 102 sensors onto 49-point grids and projected these norms onto the MRI brain surface of a 12-year-old boy who presented with neocortical epilepsy secondary to a left temporal tumor. The peak gradient magnetic field located posterior to the tumor and correlated to MEG dipoles. The gradient magnetic field propagated to the temporo-parietal region and corresponded with spike locations on electrocorticography. GMFT revealed the location and distribution of spikes while avoiding the inverse problem.