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Biomedical Functional Imaging and Neuroengineering Laboratory

College of Science & Engineering > Dept. of Biomedical Engineering

Electrophysiological Neuroimaging

Cortical Imaging

The aim of this project is to develop novel techniques which can noninvasively image cortical potentials from the scalp electroencephalogram (EEG). Currently, electrocorticogram (ECoG) is widely used in a clinical setting to aid surgical planning in epilepsy patients. We have developed a novel cortical imaging technique in our laboratory to estimate noninvasively cortical potentials in a realistic geometry inhomogeneous head model by means of the boundary element method (He et al. 1999, IEEE-TBME, pdf), and rigorously validated the technique in a group of epilepsy patients (He et al. 2002, NeuroImage, Abstract). Recently, we have further advanced the cortical imaging technique with the use of finite element method (FEM), incorporating highly inhomogeneous media during intracranial recordings into the head model. Using this FEM-based technique, we have successfully conducted a pilot study to validate cortical imaging technique with simultaneously recorded EEG and ECoG data (Zhang et al., NeuroImage, 2006, Abstract) during interictal spikes in epilepsy patient, and to estimate the accurate effective skull conductivity (in reference to brain conductivity) in a living human (Zhang et al., Applied Physics Letters, 2006, pdf).

Fig. 1 Schematic diagram of electrophysiological cortical imaging.

Fig. 2 Left: Scalp-recorded SEP (EEG). Middle: Invasively recorded cortical potentials. Right: Noninvasive cortical imaging results in the same patient. Note the substantially enhanced spatial resolution of the cortical potentials as compared with the scalp potentials, and the correspondence between the recorded and imaged cortical potentials in the same patient (from B. He, X. Zhang, J. Lian, H. Sasaki, D. Wu and V. L. Towle,"Boundary Element Method-Based Cortical Potential Imaging of Somatosensory Evoked Potentials Using Subjects' Magnetic Resonance Images", NeuroImage 2002(16), 564-576, with permission from Elsevier)

3D Current Source Imaging and Connectivity Imaging

The aim of this project is to develop source imaging techniques which can image brain activity and connectivity from noninvasive EEG. We have been developing a novel subspace source localization algorithm - FINE, for localizing brain electrical current sources in 3D brain space with high spatial resolution (Xu et al. Physics Med. & Biol., 2004, Abstract), and further advanced the approach by considering the realistic geometry inhomogeneous head model (Ding & He, IEEE-TBME, 2006, pdf). We have initially demonstrated the applicability of this novel source localization approach in aiding epilepsy source localization (Ding et al., Physics Med. & Biol., 2006, Abstract). Furthermore, we have been developing connectivity imaging techniques to image the "primary" seizure sources from EEG. Our pilot study demonstrates the high accuracy of this novel seizure source imaging approach in a group of 5 epilepsy patients with 100% success rate (Ding et al., NeuroImage, 2007, Abstract).

Fig. 1 An example of FINE and MUSIC imaging in localizing neural sources of interictal spike from an epilepsy patient. (a) The consecutive scalp EEG maps during the interictal spike. (b) Neural sources identified by FINE. (c) Neural sources identified by MUSIC. Note that multiple closely-spaced sources distinguished by FINE, but not by MUSIC. (from Ding et al., Phy. Med & Biol., 2006)

Fig. 2 An example of seizure source-connectivity imaging. Locations (pseudo-colors on MRI images), waveforms (green curves), and connectivity patterns (big arrows) for these sources. The connectivity analysis revealed the "red" and "blue" sources are "primary" sources which are well correlated with MRI visible lesions. (from Ding L, Worrell GA, Lagerlund TD, He B: "Ictal Source Analysis: Localization and Imaging of Causal Interactions in Humans," NeuroImage, Nov 15 [Epub], 2006, with permission from Elsevier)