Sensitivity of EEG and MEG to conductivity perturbations

2003-09-21
Solution of the Electro-Magnetic Source Imaging (EMSI) problem requires an accurate representation of the head using a numerical model. Some of the errors in source estimation are due to the differences between this model and the actual head. This study investigates the effects of conductivity perturbations, that is, changing the conductivity of a small region by a small amount, on the EEG and MEG measurements. By computing the change in measurements for perturbations throughout the volume, it is possible to obtain a spatial distribution of sensitivity. Using this information, it is possible, for a given source configuration, to identify the regions to which a measurement is most sensitive. In this work, two mathematical expressions for efficient computation of the sensitivity distribution are presented. The formulation is implemented for a numerical head model using the finite element method (FEM). 3D sensitivity distributions are computed and analyzed for selected dipoles and sensors. It was observed that the voltage measurements are sensitive to the skull, the regions near the dipole and the electrodes. The magnetic field measurements are mostly sensitive to regions near the dipole. It could also be possible to use the computed sensitivity matrices to estimate or update the conductivity of the tissues from EEG and MEG measurements.

Suggestions

Use of the reciprocal problems in electro-magnetic source imaging of the human brain
Gençer, Nevzat Güneri (2003-09-21)
In this work, solution of the Electro-magnetic source imaging forward problem is formulated using the reciprocity theorem. Lead field solutions for electrode potentials and sensor magnetic fields are computed for a realistic head model using the Finite Element Method. Potentials and magnetic fields obtained using the lead fields are compared to analytical solutions and direct numerical solutions. It is found that the accuracy of lead field based solution is comparable to the accuracy of direct numerical sol...
Development of realistic head models for electromagnetic source imaging of the human brain
Akahn, Z.; Acar, C.E.; Gençer, Nevzat Güneri (Institute of Electrical and Electronics Engineers (IEEE); 2002-12-07)
In this work, a methodology is developed to solve the forward problem of electromagnetic source imaging using realistic head models. For this purpose, first segmentation of the 3 dimensional MR head images is performed. Then triangular, quadratic meshes are formed for the interfaces of the tissues. Thus, realistic meshes, representing scalp, skull, CSF, brain and eye tissues, are formed. At least 2000 nodes for the scalp and 5000 for the cortex are needed to obtain reasonable geometrical approximation. Solu...
ENHANCEMENT OF THE RESOLUTION OF A SEMICONDUCTOR PHOTOGRAPHIC SYSTEM IN A MAGNETIC-FIELD
SALAMOV, BG; Akınoğlu, Bülent Gültekin; ELLIATLIOGLU, S; ALLAKHVERDIEV, KR; LEBEDEVA, NN (1994-01-01)
A method is described for enhancing the resolution R of a semiconductor photographic system by subjecting it to a homogenous magnetic field. Bi has been chosen as the photographic plate, since it has a large value of the cathode sputtering coefficient which is important in the formation of image by charged particle flux. A considerable increase of the resolution is observed when the applied magnetic field is parallel to the electric field between the electrodes. Effect of the magnetic field on the I - V cha...
Investigation of effect of design and operating parameters on acoustophoretic particle separation via 3D device-level simulations
Sahin, Mehmet Akif; ÇETİN, BARBAROS; Özer, Mehmet Bülent (Springer Science and Business Media LLC, 2019-12-16)
In the present study, a 3D device-level numerical model is implemented via finite element method to assess the effects of design and operating parameters on the separation performance of a microscale acoustofluidic device. Elastodynamic equations together with electromechanical coupling at the piezoelectric actuators for the stress field within the solid parts, Helmholtz equation for the acoustic field within fluid, and Navier-Stokes equations for the fluid flow are coupled for the simulations. Once the zer...
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 ...
Citation Formats
C. Acar and N. G. Gençer, “Sensitivity of EEG and MEG to conductivity perturbations,” 2003, vol. 25, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/40588.