Abstract
Studies based on whole-head MEG recordings are providing more and more impressive results. In such recordings, the MEG sensors are several centimeters away from the scalp and the positions of the MEG sensors with respect to the 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 to remove the discrepancy of MEG measurements caused by the various sensor positions 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 measurement was first projected to a hypothetical dipole layer within the head volume 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 evoked field analysis demonstrated that, with reasonable signal to noise ratios, this method is a feasible way to achieve our goals.
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Babiloni, F., Babiloni, C., Carducci, F., Fattorini, L., Anello, C., Onorati, P. and Urbano, A. High resolution EEG: a new model-dependent spatial deblurring method using a realistically-shaped MR-constructed subject's head model. Electroencephalogr. Clin. Neurophysiol., 1997, 102:69-80.
Barth, D.S. and Sutherling, W. Current source-density and neuromagnetic analysis of the direct cortical response in rat cortex. Brain Res., 1988, 450: 280-294.
Cohen, D. Magnetoencephalography: Evidence of magnetic fields produced by alpha-rhythm currents. Science, 1968, 161: 784-786.
Cohen, D. Magnetoencephalography: Detection of the brain's electrical activity with a superconductivity magnetometer. Science, 1972, 175: 664-666.
Gallen, C.C., Tecoma, E., Iragui, V., Sobel, D.F., Schwartz, B.J. and Bloom, F.E. Magnetic source imaging of abnormal low-frequency magnetic activity in presurgical evaluations of epilepsy. Epilepsia, 1997, 38: 452-460.
Gorodnitsky, I.F., George, J.S. and Rao, B.D. Neuromagnetic source imaging with FOCUSS: a recursive weighted minimum norm algorithm. Electroenceph. and Clin. Neurophysiol., 1995, 95: 231-251.
Gutschalk, A., Mase, R., Roth, R., Ille, N., Rupp, A, Hahnel, S., Picton, T.W. and Scherg, M. Deconvolution of 40 Hz steady-state fields reveals two overlapping source activities of the human auditory cortex. Electroencephalogr. Clin. Neurophysiol., 1999, 110: 856-868.
Hamalainen, M. and Sarvas, J. Realistic conductivity geometry model of the human head for interpretation of neuromagnetic fields. IEEE Trans. Biomed. Eng., 1989, 36: 165-171.
Hari, R. MEG in the study of human cortical functions. Electroencephalogr. Clin. Neurophysiol. Suppl., 1996, 470: 47-54.
Kaufman, L., Okada, Y.C., Brenner, D. and Williammson, S.J. On the relationship between somatic evoked fields and potentials. Int. J. Neurosci., 1981, 15: 223-239.
Kearfott, R., Sidman, R., Major, D. and Hill, C. Numerical test of a method for calculating electrical potential on the cortical surface. IEEE Trans. Biomed. Eng., 1991, 38: 294-299.
Knosche, T.R., Maess, B. and Friederici, A.D. Processing of syntactic information monitored by brain surface current density mapping based on MEG. Brain Topography, 1999 (in press).
Koles, Z.J. Trends in EEG source localization. Electroencephalogr. Clin. Neurophysiol., 1998, 106: 127-137.
Le, J. and Gevins, A. Method to reduce blur distortion from EEG's using a realistic head model. IEEE Trans. Biomed. Eng., 1993, 40: 294-299.
Lopez, L., Chan, C.Y., Okada, Y.C. and Nicholson, C. Multimodal characterization of population responses evoked by applied electric field in vitro: Extracellular potential, magnetic evoked field, transmembrane potential and current-source density analysis. J. Neurosci., 1991, 11: 1998-2010.
Okada, Y.C., Lahteenmaki, A. and Xu, C. Comparison of MEG and EEG on the basis of somatic evoked responses elicited by stimulation of the snout in the juvenile swine. Electroencephalogr. Clin. Neurophysiol., 1999, 110: 214-219.
Pantev, C., Ross, B., Berg, P., Elbert, T. and Rockstroh, B. Study of the human auditory cortices using a whole-head magnetometer: left vs. right hemisphere and ipsilateral vs. contralateral. Audiol. Neurootol., 1998, 3: 183-190.
Pasqual-Marqui, R.D., Michel, C.M. and Lehmann, D. Low resolution electromagnetic tomography: a new method for localizing electrical activity in the brain. Int. J. Psychophysiol., 1994, 18:49-65.
Romani, G.L. and Rossini, P. Neuromagnetic functional localization: principles, state of the art, and perspectives. Brain Topography, 1988, 1: 5-21.
Sarvas, J. Basic mathematical and electromagnetic concepts of biomagnetic inverse problem. Phys. Med. Biol., 1987, 32:11-22.
Sekihara, K. and Scholz, B. Generalized wiener estimation of three-dimensional current distribution from biomagnetic measurements. IEEE Trans. Biomed. Eng., 1996, 43:281-291.
Sidman, R., Vincent, D., Smith, D. and Lee, L. Experimental tests of the cortical imaging technique-Applications to the responses of median nerve stimulation and the localization of epileptiform discharges. IEEE Trans. Biomed. Eng., 1992, 39: 437-444.
Tervaniemi, M., Kujala, A., Alho, K., Virtanen, J., Ilmoniemi, R.J. and Naatanen, R. Functional specialization of the human auditory cortex in processing phonetic and musical sounds: A magnetoencephalographic (MEG) study. NeuroImage, 1999, 9: 330-336.
Wang, J.Z., Williamson, S.J. and Kaufman, L. Magnetic source images determined by a lead field analysis: The minimum-norm least-square estimation. IEEE Trans. Biomed. Eng., 1992, 39: 665-675.
Wang, Y. and He, B. A computer simulation study of cortical imaging from scalp potentials. IEEE Trans. Biomed. Eng., 1998, 45: 724-735.
Wikswo, J.P. and Roth, B.J. Magnetic determination of the spatial extent of a single cortical current source: A theoretical analysis. Electroencephalogr. Clin. Neurophysiol., 1988, 69: 266-276.
Yamashita, Y. Theoretical studies on the inverse problem in electrocardiography and the uniqueness of the solution. IEEE Trans. Biomed. Eng., 1982, 29: 719-725.
Zouridakis, G., Simos, P.G., Breier, J.I. and Papanicolaou, A.C. Functional hemispheric asymmetry assessment in a visual language task using MEG. Brain Topography, 1998, 11: 57-65.
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Wang, Y., Oertel, U. Estimating Scalp MEG from Whole-Head MEG Measurements. Brain Topogr 12, 219–227 (2000). https://doi.org/10.1023/A:1023493908085
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DOI: https://doi.org/10.1023/A:1023493908085