Signal Space Separation (SSS) method is a technique which exploits the possibility of expressing the magnetic field signals measured outside the brain as a sum of two separate and rapidly converging expansions in terms of spherical harmonic functions with one set of expansion terms for signals arising from sources localized inside a designated volume (signal of interest) and the other set of expansion terms for signals arising from sources outside the designated volume (noise). This expansion can be utilized to eliminate the contribution of unwanted signals due to external magnetic noise that inevitably get recorded along with the actual biomagnetic signal. In this paper, the SSS method has been implemented by regrouping the radial functions in the expansion. Our calculations show that it is possible to extract the true biomagnetic signal arising due to intracranial sources located inside the measurement volume from the measured magnetic signal which includes the contribution from an external magnetic dipole artifact which is about 50 times stronger compared to the intracranial sources but is positioned at a distance of 1.2m from the centre of the spherical shell. We observe that the root mean square deviation of the signal inferred from a truncated expansion is minimum when the truncation order is set at L_1 = 9 for signals of interest and L_2= 3 for external noise sources.
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