Source reconstruction of mesial-temporal epileptiform activity: comparison of inverse techniques

To evaluate whether advanced source reconstruction such as current density reconstruction (CDR) provides additional hints for clinical presurgical evaluation, different source reconstruction techniques with idealized spherical as well as realistically shaped head models (boundary element method, BEM) were applied on interictal and ictal epileptiform activity in presurgical evaluated patients with temporal lobe epilepsy. It is discussed whether CDR and BEM give additional information for presurgical evaluation compared to "conventional" strategies, such as single moving, and spatio-temporal dipole modeling with spherical head models.

A variety of source reconstruction procedures were applied to the data of five patients with pharmacoresistent temporal lobe epilepsy with probable mesial origin: (1) single-moving dipole in a spherical head model and (2) in BEM, (3) spatio-temporal dipole modeling in a spherical head model and (4) in BEM; and (5) deconvolution with fixed locations and orientations and (6) with cortically constrained L1-norm CDR in BEM. In addition, simulated sources of temporal lobe origin were calculated in each subject with CDR to prove the basic feasibility of this technique in the particular application.

Source activity was correctly localized within the affected temporal lobe by all source reconstruction techniques used. Neither single moving dipole, spatio-temporal modeling, nor CDR was able to localize sources at a sublobar level. In the case of two sources, single moving dipole solutions showed changes in dipole orientation in time and spatio-temporal modeling separated two sources, whereas CDR at the peak latency failed to distinguish among different origins. BEM enhanced localization accuracy.

There was no advantage of using CDR. Single moving dipole as well as spatio-temporal dipole modeling in BEM leads to more precise localization within the individual anatomy and provides a simple algorithm, which is capable of indicating both the time course and the number of sources.