CURRENT DIPOLE LOCALIZATION WITH AN IDEAL MAGNETOMETER SYSTEM

The goal of the study was to explore the most fundamental aspects of a magnetoencephalography (MEG)-based dipole source analysis, For that p urpose, a MEG measurement with an ideal magnetometer system (providing the radial component of the magnetic held as a continuous function) i s considered, The analytical formulas derived for the variances and co variances of the parameter estimation errors, validated by means of Mo nte Carlo simulations, allow quantitative predictions in terms of dipo le depth, radius and span of the magnetometer system, signal-to-noise (SNR) ratio, and other parameters, A negative correlation exists betwe en radial coordinate and longitudinal component of the moment (perpend icular to radial direction, same plane as actual dipole moment and cen ter of sphere), whereas the other parameters are independent, The stan dard deviations of the five dipole parameters show fundamental differe nces with respect to their asymptotic behavior for deep dipoles: If th e root mean square (rms) value of the magnetic field is kept constant (moment with depth-dependent amplitude), the error for the transverse coordinate (perpendicular to radial and longitudinal coordinate) is pr oportional to the distance R between dipole and center of sphere, the errors for the other dipole coordinates, and the relative error for th e transverse component of the dipole moment are constant, and the rela tive error for the longitudinal component of the dipole moment follows a 1/R law.