Effect of conductor geometry on source localization: Implications for epilepsy studies
We shall discuss the effects of conductor geometry on source localization for applications in epilepsy studies. The most popular conductor model for clinical MEG studies is a homogeneous sphere. However, several studies have indicated that a sphere is a poor model for the head when the sources are deep, as is the case for epileptic foci in the mesial temporal lobe. We believe that replacing the spherical model with a more realistic one in the inverse fitting procedure will improve the accuracy of localizing epileptic sources. In order to include a realistic head model in the inverse problem, we must first solve the forward problem for the realistic conductor geometry. We create a conductor geometry model from MR images, and then solve the forward problem via a boundary integral equation for the electric potential due to a specified primary source. One the electric potential is known, the magnetic field can be calculated directly. The most time-intensive part of the problem is generating the conductor model; fortunately, this needs to be done only once for each patient. It takes little time to change the primary current and calculate a new magnetic field for use in the inverse fitting procedure. We present the results of a series of computer simulations in which we investigate the localization accuracy due to replacing the spherical model with the realistic head model in the inverse fitting procedure. The data to be fit consist of a computer generated magnetic field due to a known current dipole in a realistic head model, with added noise. We compare the localization errors when this field is fit using a spherical model to the fit using a realistic head model. Using a spherical model is comparable to what is usually done when localizing epileptic sources in humans, where the conductor model used in the inverse fitting procedure does not correspond to the actual head.
- Research Organization:
- Los Alamos National Lab., NM (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- W-7405-ENG-36
- OSTI ID:
- 10163541
- Report Number(s):
- LA-UR-94-1446; CONF-9404183-1; ON: DE94014718; TRN: 94:007483
- Resource Relation:
- Conference: NABMAG 2: North American Biiomagnetism Action Group conference,Detroit, MI (United States),15-17 Apr 1994; Other Information: PBD: [1994]
- Country of Publication:
- United States
- Language:
- English
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99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE
EPILEPSY
DIAGNOSTIC TECHNIQUES
HEAD
NMR IMAGING
STRUCTURAL MODELS
ACCURACY
COMPUTERIZED SIMULATION
ELECTRIC POTENTIAL
GEOMETRY
ELECTROENCEPHALOGRAPHY
MORPHOLOGY
LEAST SQUARE FIT
550602
990200
EXTERNAL RADIATION IN DIAGNOSTICS
MATHEMATICS AND COMPUTERS