Optimal reference electrode selection for electric source imaging

1996-01-01
Gençer, Nevzat Güneri
GUEZİEC, ANDREİ
HUMMEL, ROBERT
Show full item record
Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.
124
views
0
downloads
One goal of recording voltages on the scalp is to form images of electrical sources across the cerebral cortex (electric source imaging). In this study, an objective criterion is introduced for selecting the optimal location for the reference electrode to attain the maximum spatial resolution of the source image, for example as provided here by the truncated singular value decomposition pseudo-inverse solution. The head model features a realistic cortex within a 3-shell conductive sphere, and pyramidal cell activity is represented by 9104 normal current elements distributed across the cortical area. On the scalp, 234 electrodes provide the measurements with respect to a chosen reference electrode. The effects of the reference electrode when located at the mastoid, occipital pole, vertex or center of the head are analyzed by a singular value decomposition of the lead field matrices. Sensitivity to noise, and hence the spatial resolution, is found to depend on characteristics of the lead field matrix are determined by the choice of the image source surface, electrode array and location of the reference electrode. Using a reference close to a source surface increases the sensitivity of the measurement system in identifying the nearby activity of low spatial frequency content. However, this feature is compromised by a reduction in spatial resolution for distant cortical areas due to noise in the measurement. A new performance measure, the image sensitivity map, is introduced to identify the cortical regions that provide peak image sensitivity. This measure may be exploited in designing the geometry of an electrode array and selecting the location of the reference electrode to follow the activity on a specific area of the cortical surface.
Electroencephalography, Singular value decomposition, Truncated pseudoinverse, Reference electrode selection
https://hdl.handle.net/11511/41436
Electroencephalography and Clinical Neurophysiology
Department of Electrical and Electronics Engineering, Article

Suggestions

Forward problem solution of electromagnetic source imaging using a new BEM formulation with high-order elements
Gençer, Nevzat Güneri (IOP Publishing, 1999-09-01)
Representations of the active cell populations on the cortical surface via electric and magnetic measurements are known as electromagnetic source images (EMSIs) of the human brain. Numerical solution of the potential and magnetic fields for a given electrical source distribution in the human brain is an essential part of electromagnetic source imaging. In this study, the performance of the boundary element method (BEM) is explored with different surface element types. A new BEM formulation is derived that m...
Differential characterization of neural sources with the bimodal truncated SVD pseudo-inverse for EEG and MEG measurements
Gençer, Nevzat Güneri (1998-07-01)
A method for obtaining a practical inverse for the distribution of neural activity in the human cerebral cortex is developed for electric, magnetic, and bimodal data to exploit their complementary aspects. Intracellular current is represented by current dipoles uniformly distributed on two parallel sulci joined by a gyrus, Linear systems of equations relate electric, magnetic, and binodal data to unknown dipole moments. The corresponding lead-field matrices are characterized by singular value decomposition ...
Design and realization of a hybrid medical imaging system: harmonic motion microwave doppler imaging
Tafreshi, Azadeh Kamali; Gençer, Nevzat Güneri; Department of Electrical and Electronics Engineering (2016)
Harmonic Motion Microwave Doppler Imaging (HMMDI) is a novel imaging modality to image electrical and mechanical properties of body tissues. This modality is recently proposed by the researchers in the METU EEE department for early-stage diagnosis of cancerous tissues. The main goal of this thesis study is to contribute various stages of the HMMDI's development processes. Speci cally, phantom development, dielectric and elastic characterization of the phantoms, experimental system realization, phantom exper...
Sensitivity of EEG and MEG measurements to tissue conductivity
Gençer, Nevzat Güneri (IOP Publishing, 2004-03-07)
Monitoring the electrical activity inside the human brain using electrical and magnetic field measurements requires a mathematical head model. Using this model the potential distribution in the head and magnetic fields outside the head are computed for a given source distribution. This is called the forward problem of the electro-magnetic source imaging. Accurate representation of the source distribution requires a realistic geometry and an accurate conductivity model. Deviation from the actual head is one ...
Solving the forward problem of electrical source imaging by applying the reciprocal approach and the finite difference method
Ahi, Sercan Taha; Gençer, Nevzat Güneri; Department of Electrical and Electronics Engineering (2007)
One of the goals of Electroencephalography (EEG) is to correctly localize brain activities by the help of voltage measurements taken on scalp. However, due to computational difficulties of the problem and technological limitations, the accuracy level of the activity localization is not perfect and should be improved. To increase accuracy level of the solution, realistic, i.e. patient dependent, head models should be created. Such head models are created via assigning realistic conductivity values of head ti...
Citation Formats
N. G. Gençer, A. GUEZİEC, and R. HUMMEL, “Optimal reference electrode selection for electric source imaging,” Electroencephalography and Clinical Neurophysiology, pp. 163–173, 1996, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/41436.
METU IIS - Integrated Information Service open@metu.edu.tr