Inter-subject variability of the electrical conductivity of brain, skull and skin strongly limits the accuracy by which current sources underlying electro-encephalography (EEG) can be localized in the brain using accurate head models. We estimated conductivity parameters of different tissues (e.g. skin, bone, corticospinal fluid, brain tissue) in vivo by analyzing the potentials generated by known electric currents, injected into different pairs of EEG electrodes. To optimize estimates of, in particular, scalp and skull geometry we employed MRI-UTE (Ultrashort Echo Time) scanning sequences and adjusted tissue segmentation accordingly. Here, a Woodbury update algorithm provided a fast conductivity update scheme for the corresponding boundary element modeling. We applied this approach for tailoring head models for forward and inverse modeling of EEG responses in primary somatosensory areas after median nerve stimulation. As expected, the inter-subject variability of the resulting somatosensory-evoked potentials appeared reduced though a full statistical evaluation is still pending.
