Method to reduce blur distortion from EEG's using a realistic head model

Abstract

A mathematical procedure, which we call "Deblurring," was developed to reduce spatial blur distortion of scalp-recorded brain potentials due to transmission through the skull and other tissues. Deblurring estimates potentials at the superficial cerebral cortical surface from EEG's recorded at the scalp using a finite element model of each subject's scalp, skull and cortical surface constructed from their magnetic resonance images (MRI's). Simulations indicate that Deblurring is numerically stable, while a comparison of deblurred data with a direct cortical recording from a neurosurgery patient suggests that the procedure is valid. Application of Deblurring to somatosensory evoked potential data recorded at 124 scalp sites suggests that the method produces a dramatic improvement in spatial detail, and merits further development.

The surface Laplacian technique in EEG: Theory and methods

“…Unfortunately, it was outside the scope of our work to discuss methods to make the scalp model more realistic and reduce error in electrode locations, as they require additional tools such as MRI that are often not readily available to most researchers. The interested reader is referred to the relevant references for this matter (Le and Gevins, 1993;Babiloni et al, 1996;Bortel and Sovka, 2013).…”

A cortical potential imaging study from simultaneous extra- and intracranial electrical recordings by means of the finite element method

“…Furthermore, the cortical potential distribution can be experimentally measured using ECoG grids (Le & Gevins, 1993;Gevins et al, 1994;Towle et al, 1995;Lantz et al, 1997;He et al, 2002;Tao et al, 2005). The dramatic improvement of spatial resolution achieved in the previous studies is promising and indicates that CPI may play an important role in lateralization and localization of epileptogenic foci in presurgical evaluation.…”

“…While the scalp electroencephalogram (EEG) has the advantage of unsurpassed millisecond temporal resolution necessary for resolving dynamic neural processes, its application to mapping spatial distribution of brain electrical activity is limited by its poor spatial resolution due to the blurring effect of the head volume conductor, especially the low-conductivity skull layer (Nunez, 1981;He, 2004He, , 2005. Tremendous effort has been made to enhance the spatial resolution of the conventional EEG by solving the so-called EEG inverse problem, which attempts to overcome the head volume conductor effect (Scherg & Von Cramon, 1985;He et al, 1987He et al, , 1996He et al, , 1999He et al, , 2001He et al, , 2002Cohen et al, 1990;Sidman et al, 1990;Dale & Sereno, 1993;Le & Gevins, 1993;Ebersole et al, 1994;Gevins et al, 1994;Nunez et al, 1994;Babiloni et al, 1997Babiloni et al, , 2003Fuchs et al, 1999;Michel et al, 1999;Ollikainen et al, 2001;Zhang et al, 2003).…”

“…The direct BEM-based CPI technique has been validated in somatosensory evoked potentials (SEP) (He et al, 2002) by comparing the CPI results estimated from pre-operative scalp SEP data with the post-operative electrocorticogram (ECoG) during somatosensory stimulation. Gevins and co-workers (Le & Gevins, 1993;Gevins et al, 1994) developed the first finite element method (FEM) based CPI, to estimate directly the cortical potentials from the scalp potentials. While it has the potential to incorporate local conductivity inhomogeneity by means of FEM, Gevins and co-workers only included skull inhomogeneity into their FEM algorithm and evaluated it by intracranial recordings in separated recordings from two neurosurgical patients (i.e.…”

Slow potential topography

“…Scanning the recent literature one finds all the relevant aspects already addressed and the groundwork accomplished-that is, spatial sampling (Coppola, 1990;Gevins, 1989Gevins, , 1990Lehmann, 1986;Srinivasan, Nunez, Tucker, Silberstein, & Cadusch, 1996;Srinivasan, Tucker, & Murias, 1998;Wang, Cohen, & Hallett, 1989), ways of reducing blur distortion due to volume conduction (Gevins, 1990;Law & Nunez, 1991;Le, Menon, & Gevins, 1994;Nunez, 1989Nunez, , 1990Srinivasan et al, 1996), and enhancement ofspatial resolution by using realistically shaped head models (Gevins, 1990;Gevins et al, 1990;Gevins et al, 1991;Gevins et al, 1994;Le & Gevins, 1993). In order to encourage the practical application of the suggested solutions in SPT, an overview will be given below.…”