Estimating scalp MEG from whole-head MEG measurements

Studies based on whole-head MEG recordings are providing more and more impr essive results. In such recordings, the MEG sensors are several centimeters away from the scalp and the positions of the MEG sensors with respect to t he head differ from subject to subject, and from session to session for the same subject. In this paper, a method is presented and tested to estimate the scalp MEG distributions from whole-head MEG measurements. The goal is t o remove the discrepancy of MEG measurements caused by the various sensor p ositions with respect to the head, as well as to reduce the smearing effect caused by the distance of the MEG sensors from the scalp. The MEG measurem ent was first projected to a hypothetical dipole layer within the head volu me conductor model using the inverse solution. The scalp MEG estimation was then obtained from the resultant dipole layer by the forward solution. The results from simulation studies, phantom experiments, and the auditory evo ked field analysis demonstrated that, with reasonable signal to noise ratio s, this method is a feasible way to achieve our goals.