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MEG and EEG dipole clusters from extended cortical sources

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Abstract

Data from magnetoencephalography (MEG) and electroencephalography (EEG) suffer from a rather limited signal-to-noise-ratio (SNR) due to cortical background activities and other artifacts. In order to study the effect of the SNR on the size and distribution of dipole clusters reconstructed from interictal epileptic spikes, we performed simulations using realistically shaped volume conductor models and extended cortical sources with different sensor configurations. Head models and cortical surfaces were derived from an averaged magnetic resonance image dataset (Montreal Neurological Institute). Extended sources were simulated by spherical patches with Gaussian current distributions on the folded cortical surface. Different patch sizes were used to investigate cancellation effects from opposing walls of sulcal foldings and to estimate corresponding changes in MEG and EEG sensitivity distributions. Finally, white noise was added to the simulated fields and equivalent current dipole reconstructions were performed to determine size and shape of the resulting dipole clusters. Neuronal currents are oriented perpendicular to the local cortical surface and show cancellation effects of source components on opposing sulcal walls. Since these mostly tangential aspects from large cortical patches cancel out, large extended sources exhibit more radial components in the head geometry. This effect has a larger impact on MEG data as compared to EEG, because in a spherical head model radial currents do not yield any magnetic field. Confidence volumes of single reconstructed dipoles from simulated data at different SNRs show a good correlation with the extension of clusters from repeated dipole reconstructions. Size and shape of dipole clusters reconstructed from extended cortical sources do not only depend on spike and timepoint selection, but also strongly on the SNR of the measured interictal MEG or EEG data. In a linear approximation the size of the clusters is proportional to the inverse SNR.

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References

  1. Knowlton RC, Razdan SN, Limdi N, Elgavish RA, Killen J, Blount J, et al. Effect of epilepsy magnetic source imaging on intracranial electrode placement. Ann Neurol. 2009;65:716–23.

    Article  Google Scholar 

  2. Murakami H, Wang ZI, Marashly A, Krishnan B, Prayson RA, Kakisaka Y, Mosher JC, Bulacio J, Gonzalez-Martinez JA, Bingaman WE, Najm IM, Richard C, Burgess RC, Alexopoulos AV. Correlating magneto-encephalography to stereo-electroencephalography in patients undergoing epilepsy surgery. Brain. 2016;139:2935–47.

  3. El Tahry R, Wang ZI, Kakisaka Y, Murakami H, Shibata S, Krishnan B, Kotagal P, Alexopoulos A, Burgess RC. A single tight MEG cluster may only represent a fragment of type I FCD. Clin Neurophysiol. 2016;127:2570–2.

    Article  Google Scholar 

  4. Iwasaki M, Nakasato N, Shamoto H, Nagamatsu K, Kanno A, Hatanaka K, et al. Surgical implications of neuromagnetic spike localization in temporal lobe epilepsy. Epilepsia. 2002;43:415–24.

    Article  Google Scholar 

  5. Cooper R, Winter AL, Crow HJ, et al. Comparison of subcortical, cortical and scalp activity using chronically indwelling electrodes in man. Electroencephalogr Clin Neurophysiol. 1965;18:217–28.

    Article  Google Scholar 

  6. Baumgartner C, Barth DS, Levesque MF, Sutherling WW. Detection of epileptiform discharges on magnetoencephalography in comparison to invasive measurements. In: Hoke M, Erne SN, Okada YC, Romani GL, editors. Biomagnetism: clinical aspects. Amsterdam: Elsevier; 1992. p. 67–71.

    Google Scholar 

  7. Mikuni N, Nagamine T, Ikeda A, et al. Simultaneous recording of epileptiform discharges by MEG and subdural electrodes in temporal lobe epilepsy. Neuroimage. 1997;5:298–306.

    Article  Google Scholar 

  8. Oishi M, Otsubo H, Kameyama S, et al. Epileptic spikes: magnetoencephalography versus simultaneous electrocorticography. Epilepsia. 2002;43:1390–5.

    Article  Google Scholar 

  9. Tao JX, Ray A, Hawes-Ebersole S, Ebersole JS. Intracranial EEG substrates of scalp EEG interictal spikes. Epilepsia. 2005;46:669–76.

    Article  Google Scholar 

  10. Vadera S, Jehi L, Burgess RC, Shea K, Alexopoulos AV, Mosher J, Gonzalez-Martinez J, Bingaman W. Correlation between magnetoencephalography-based “clusterectomy” and postoperative seizure freedom. Neurosurg Focus. 2013;34:E9.

    Article  Google Scholar 

  11. Lantz G, Spinelli L, Seeck M, de Peralta Menendez RG, Sottas CC, Michel CM. Propagation of interictal epileptiform activity can lead to erroneous source localizations: a 128-channel EEG mapping study. J Clin Neurophysiol. 2003;20:311–9.

    Article  Google Scholar 

  12. Ray A, Tao JX, Hawes-Ebersole SM, Ebersole JS. Localizing value of scalp EEG spikes: a simultaneous scalp and intracranial study. Clin Neurophysiol. 2007;118:69–79.

    Article  Google Scholar 

  13. Fuchs M, Kastner J, Wagner M, Hawes S, Ebersole JS. A standardized boundary element method volume conductor model. Clin Neurophysiol. 2002;113:702–12.

    Article  Google Scholar 

  14. Fonov VS, Evans AC, McKinstry RC, Almli CR, Collins DL. Unbiased nonlinear average age-appropriate brain templates from birth to adulthood. Neuroimage. 2009;47:S102.

    Article  Google Scholar 

  15. Wagner M, Kohler T, Fuchs M, Kastner J. An extended source model for current density reconstructions. In: Nenonen J, Ilmoniemi RJ, Katila T, editors. Biomag 2000: proceedings of the 12th international conference on biomagnetism. Finland: Helsinki University of Technology; 2001. p. 749–52.

    Google Scholar 

  16. Fuchs M, Wagner M, Kastner J. Development of volume conductor and source models to localize epileptic foci. J Clin Neurophysiol. 2007;24:101–19.

    Article  Google Scholar 

  17. Ahlfors SP, Han J, Lin FH, Witzel T, Belliveau JW, Hämäläinen MS, Halgren E. Cancellation of EEG and MEG signals generated by extended and distributed sources. Hum Brain Mapp. 2010;31(1):140–9.

    Google Scholar 

  18. Fuchs M, Wagner M, Kastner J. Confidence limits of dipole source reconstruction results. Clin Neurophysiol. 2004;115:1442–51.

    Article  Google Scholar 

  19. Ebersole JS, Ebersole SM. Combining MEG and EEG source modeling in epilepsy evaluations. J Clin Neurophysiol. 2010;27:360–71.

    Article  Google Scholar 

  20. Ebersole JS. Equivalent dipole modeling: a new EEG method for epileptogenic focus localization. In: Pedley TA, Meldrum BS, editors. Recent advances in epilepsy. 5th ed. Edinburgh: Churchill Livingstone; 1991. p. 51–72.

    Google Scholar 

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Authors and Affiliations

  1. Compumedics Neuroscan GmbH, Heussweg 25, 20255, Hamburg, Germany

    Manfred Fuchs, Jörn Kastner, Reyko Tech, Michael Wagner & Fernando Gasca

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  1. Manfred Fuchs
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  2. Jörn Kastner
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  3. Reyko Tech
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  4. Michael Wagner
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  5. Fernando Gasca
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Correspondence to Manfred Fuchs.

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The CURRY software used in this submission is a commercial product of Compumedics USA, Charlotte, NC, USA. The authors of this paper are employees of Compumedics Germany GmbH, Hamburg, Germany. Both Compumedics Germany GmbH and Compumedics USA are subsidiaries of Compumedics Ltd., Melbourne, Australia.

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Fuchs, M., Kastner, J., Tech, R. et al. MEG and EEG dipole clusters from extended cortical sources. Biomed. Eng. Lett. 7, 185–191 (2017). https://doi.org/10.1007/s13534-017-0019-2

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  • DOI: https://doi.org/10.1007/s13534-017-0019-2

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