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Magnetoencephalography in prospective clinical routine
375
Magnetoencephalography Routine
in Prospective
Clinical
C. Lefebre, D. Jam, and W. Christie
The principles of magnetoencephalography (MEG) are well known (Cohen, 1972; Erne et al., 1981). The method has been a very useful tool in experimental brain research for several years (Romani et al., 1982; Hari et al., 1983). It has been used to study both event related signals (Kaufman and Williamson, 1982; Hari et al., 1983) and spontaneous synchronous activity of many neurons in interictal epileptic spiking or during focal epileptic seizures to localize the focus (Barth et al., 1982; Sutherling et al., 1987). Here we briefly summarize the main theoretical differences and possible advantages of MEG in comparison to EEG: (I) The magnetic field passes the borders between the intracranial sources and the extracranial magnetometer, influenced only by the distance-related attenuation. The electrical signal is diminished and smeared by the conducting intracranial structures between source and electrode. (2) The magnetic field is generated by intracellular axial currents which are originated by the discharging region itself, whereas the generators of EEG are volume currents around the discharging region which are spread over a larger area. (3) Using the “sphere” model for the head, the MEG shows the tangential In the EEG radial and tangential components of the discharging neurons. components of the electrical field are mixed. (4) The electrical resistance of the scalp, which must be low for high quality EEG recordings, has no influence on the quality of MEG data because the recording can be performed without skin contact. Nevertheless, MEG still has to prove its necessity in clinical applications. The most promising application in neurology may be localizing epileptogenic foci in patients suffering from pharmacoresistent temporal lobe epilepsy who are candidates for brain surgery. Those patients currently have to undergo precise localization of the epileptogenic focus with EEG recordings from intracranial implanted electrodes before it is possible to remove the focus. Patients who are candidates for surgery undergo long-term EEG examinations for seizure recording, sleep EEG after sleep deprivation, regional cerebral blood flow measurement (rCBF by SPECT), CT, CCT, MRI, and neuropsychological examinations. Patients who are still candidates
Reprint FRG.
requests to: C. Lefebre,
01651781/89/$03.50
Dept. of Neurology,
@ 1989 Elsevier Scientific
Univ. of Berlin-Charlottenburg,
Publishers Ireland
Ltd.
D-1000
Berlin 19,
376
for surgery after the complete noninvasive presurgical evaluation will have 7-channel MEG in the “Physikalisch-Technische Bundesanstalt,” Berlin (PTB). After preparing and completing experimental measurements, we now continue with MEG recordings of selected patients in clinical routine in cooperation with the PTB, Berlin.
References Barth, D.S.; Sutherling, W.; and Engel, J. Neuromagnetic localization of epileptiform spike activity in the human brain. Science, 218:891, 1982. Cohen, D. Magnetoencephalography: Detection of the brain’s electrical activity with a superconducting magnetometer. Science, 175664, 1972. Erne, S.N.; Hahlbohm, H.D.; and Luebbig, H. Biomagnetism. Berlin: De Greyter, 1981. Hari, R., et al. Neuromagnetic responses from the second somatosensory cortex in man. Acta Neurologica Scandinavica. 68:207, 1983. Kaufman, L., and Williamson, S.J. Magnetic location of cortical activity. Annals of the New York Academy of Sciences, 388: 197, 1982. Romain, G.L.; Williamson, S.J.; and Kaufmann, L. Biomagnetic instrumentation. Review of Scientific Instrumentation, 53: I8 15, 1982. Sutherling, W., et al. The magnetic field of complex partial seizures agrees with intracranial localizations. Annals of Neurology, 21548, 1987.
Magnetoencephalography Routine
in Prospective
Clinical
C. Lefebre, D. Jam, and W. Christie
The principles of magnetoencephalography (MEG) are well known (Cohen, 1972; Erne et al., 1981). The method has been a very useful tool in experimental brain research for several years (Romani et al., 1982; Hari et al., 1983). It has been used to study both event related signals (Kaufman and Williamson, 1982; Hari et al., 1983) and spontaneous synchronous activity of many neurons in interictal epileptic spiking or during focal epileptic seizures to localize the focus (Barth et al., 1982; Sutherling et al., 1987). Here we briefly summarize the main theoretical differences and possible advantages of MEG in comparison to EEG: (I) The magnetic field passes the borders between the intracranial sources and the extracranial magnetometer, influenced only by the distance-related attenuation. The electrical signal is diminished and smeared by the conducting intracranial structures between source and electrode. (2) The magnetic field is generated by intracellular axial currents which are originated by the discharging region itself, whereas the generators of EEG are volume currents around the discharging region which are spread over a larger area. (3) Using the “sphere” model for the head, the MEG shows the tangential In the EEG radial and tangential components of the discharging neurons. components of the electrical field are mixed. (4) The electrical resistance of the scalp, which must be low for high quality EEG recordings, has no influence on the quality of MEG data because the recording can be performed without skin contact. Nevertheless, MEG still has to prove its necessity in clinical applications. The most promising application in neurology may be localizing epileptogenic foci in patients suffering from pharmacoresistent temporal lobe epilepsy who are candidates for brain surgery. Those patients currently have to undergo precise localization of the epileptogenic focus with EEG recordings from intracranial implanted electrodes before it is possible to remove the focus. Patients who are candidates for surgery undergo long-term EEG examinations for seizure recording, sleep EEG after sleep deprivation, regional cerebral blood flow measurement (rCBF by SPECT), CT, CCT, MRI, and neuropsychological examinations. Patients who are still candidates
Reprint FRG.
requests to: C. Lefebre,
01651781/89/$03.50
Dept. of Neurology,
@ 1989 Elsevier Scientific
Univ. of Berlin-Charlottenburg,
Publishers Ireland
Ltd.
D-1000
Berlin 19,
376
for surgery after the complete noninvasive presurgical evaluation will have 7-channel MEG in the “Physikalisch-Technische Bundesanstalt,” Berlin (PTB). After preparing and completing experimental measurements, we now continue with MEG recordings of selected patients in clinical routine in cooperation with the PTB, Berlin.
References Barth, D.S.; Sutherling, W.; and Engel, J. Neuromagnetic localization of epileptiform spike activity in the human brain. Science, 218:891, 1982. Cohen, D. Magnetoencephalography: Detection of the brain’s electrical activity with a superconducting magnetometer. Science, 175664, 1972. Erne, S.N.; Hahlbohm, H.D.; and Luebbig, H. Biomagnetism. Berlin: De Greyter, 1981. Hari, R., et al. Neuromagnetic responses from the second somatosensory cortex in man. Acta Neurologica Scandinavica. 68:207, 1983. Kaufman, L., and Williamson, S.J. Magnetic location of cortical activity. Annals of the New York Academy of Sciences, 388: 197, 1982. Romain, G.L.; Williamson, S.J.; and Kaufmann, L. Biomagnetic instrumentation. Review of Scientific Instrumentation, 53: I8 15, 1982. Sutherling, W., et al. The magnetic field of complex partial seizures agrees with intracranial localizations. Annals of Neurology, 21548, 1987.