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Functional brain mapping by high resolution electroencephalography with deblurring and realistic 3-D head models Au Young, Simon Man Wai

Abstract

This thesis discusses the application of high resolution electroencephalography (HREEG) in human functional brain mapping. Clinically, mapping of brain function is important for epilepsy surgery. Routine electroencephalography (EEG) has been an important assessment tool for epileptic events and abnormal brain activity, whereas electrocorticography (ECoG) is the definitive clinical mapping tool to localize the epileptic focus. HR-EEG, with Deblurring™ and realistic head models, is a non-invasive method, and it may be able to provide more information during the pre-surgical evaluation than routine EEG. Deblurring™ is a signal enhancement technique to correct blur distortion of the scalp-recorded EEG signals. Realistic head models are constructed from subjects' high resolution anatomic 3-D MRIs. This thesis examines the clinical potentials, benefits, and the validity of this method through a series of mapping studies on adult volunteers and two pediatric patients. The results of the visual evoked potential (VEP) and functional magnetic resonance imaging (fMRI) study on adult volunteers showed that the deblurred results localized the brain region involved better than the scalp data. The deblurred topography did not match with the fMRI data in some subjects, which may be explained by the difference between surface mapping and 3-D activity mapping, and the volume conduction properties of EEG signals. The results of the SEP study on a adult volunteer showed that Deblurring™ improved the SEP peaks to become more focal and less variable than routine EEG or scalp HR-EEG. Patient studies allowed direct comparison of the deblurred results with the ECoG results. There was concordance between the deblurred and ECoG results in both SEP and seizure onset mapping. The present HR-EEG with Deblurring™ technique has its shortcomings and limitations such that it is premature to conclude on the validity of Deblurring™ based on a small sample of subjects. However, the improvement of spatial resolution of the EEG data by higher density of electrodes and Deblurring™, plus the co-registration of the functional data on a realistic head model, may be able to provide extra information for placement of subdural grid before ECoG recording than clinical EEG data alone.

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