Magnetic determination of the spatial extent of a single cortical current source: a theoretical analysis.

In this paper a model, originally developed for calculating the magnetic field produced by a single nerve fiber, is used to compare the ability of two magnetometers with different spatial resolutions to map the magnetic field distribution from a highly localized current source in the cerebral cortex. It is concluded that whenever the source-to-coil distance is much larger than the dimensions of the source it will be difficult, if not impossible, to use an inverse calculation to determine the spatial extent of the source from the magnetic field. When the source-to-coil distance is comparable to the extent of the source, an inverse calculation can provide information regarding the axial length of a localized dipolar current source.