Get access

Mapping the signal-to-noise-ratios of cortical sources in magnetoencephalography and electroencephalography

Authors

  • Daniel M. Goldenholz,

    Corresponding author
    1. Athinoula A. Martinos Center For Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts
    2. Biomedical Engineering Department, Boston University, Boston, Massachusetts
    • MGH-Martinos Center, Building 149, 13th St., Charlestown, MA 02129
    Search for more papers by this author
  • Seppo P. Ahlfors,

    1. Athinoula A. Martinos Center For Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts
    2. Harvard-MIT Division of Health Science and Technology, Massachusetts Institute of Technology, Cambridge, Massachusetts
    Search for more papers by this author
  • Matti S. Hämäläinen,

    1. Athinoula A. Martinos Center For Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts
    2. Harvard-MIT Division of Health Science and Technology, Massachusetts Institute of Technology, Cambridge, Massachusetts
    Search for more papers by this author
  • Dahlia Sharon,

    1. Athinoula A. Martinos Center For Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts
    Search for more papers by this author
  • Mamiko Ishitobi,

    1. Athinoula A. Martinos Center For Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts
    Search for more papers by this author
  • Lucia M. Vaina,

    1. Athinoula A. Martinos Center For Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts
    2. Biomedical Engineering Department, Boston University, Boston, Massachusetts
    3. Department of Neurology, Harvard Medical School, Boston, Massachusetts
    Search for more papers by this author
  • Steven M. Stufflebeam

    1. Athinoula A. Martinos Center For Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts
    2. Harvard-MIT Division of Health Science and Technology, Massachusetts Institute of Technology, Cambridge, Massachusetts
    Search for more papers by this author

Abstract

Although magnetoencephalography (MEG) and electroencephalography (EEG) have been available for decades, their relative merits are still debated. We examined regional differences in signal-to-noise-ratios (SNRs) of cortical sources in MEG and EEG. Data from four subjects were used to simulate focal and extended sources located on the cortical surface reconstructed from high-resolution magnetic resonance images. The SNR maps for MEG and EEG were found to be complementary. The SNR of deep sources was larger in EEG than in MEG, whereas the opposite was typically the case for superficial sources. Overall, the SNR maps were more uniform for EEG than for MEG. When using a noise model based on uniformly distributed random sources on the cortex, the SNR in MEG was found to be underestimated, compared with the maps obtained with noise estimated from actual recorded MEG and EEG data. With extended sources, the total area of cortex in which the SNR was higher in EEG than in MEG was larger than with focal sources. Clinically, SNR maps in a patient explained differential sensitivity of MEG and EEG in detecting epileptic activity. Our results emphasize the benefits of recording MEG and EEG simultaneously. Hum Brain Mapp 2009. © 2008 Wiley-Liss, Inc.

Ancillary