Sensitivity distributions of EEG and MEG measurements

doi:10.1109/10.554766

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Sensitivity distributions of EEG and MEG measurements

Journal Article•DOI•

Sensitivity distributions of EEG and MEG measurements

Jaakko Malmivuo¹, V. Suihko¹, Hannu Eskola¹•Institutions (1)

Tampere University of Technology¹

01 Mar 1997-IEEE Transactions on Biomedical Engineering (IEEE)-Vol. 44, Iss: 3, pp 196-208

TL;DR: The localization of measurement sensitivity using these techniques was evaluated quantitatively in an inhomogeneous spherical head model using a new concept called half-sensitivity volume (HSV), and it is shown that the planar gradiometers has a far smaller HSV than the axial gradiometer.

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Abstract: It is generally believed that because the skull has low conductivity to electric current but is transparent to magnetic fields, the measurement sensitivity of the magnetoencephalography (MEG) in the brain region should be more concentrated than that of the electroencephalography (EEG). It is also believed that the information recorded by these techniques is very different. If this were indeed the case, it might be possible to justify the cost of MEG instrumentation which is at least 25 times higher than that of EEG instrumentation. The localization of measurement sensitivity using these techniques was evaluated quantitatively in an inhomogeneous spherical head model using a new concept called half-sensitivity volume (HSV). It is shown that the planar gradiometer has a far smaller HSV than the axial gradiometer. However, using the EEG it is possible to achieve even smaller HSVs than with whole-head planar gradiometer MEG devices. The micro-superconducting quantum interference device (SQUID) MEG device does have HSVs comparable to those of the EEG. The sensitivity distribution of planar gradiometers, however, closely resembles that of dipolar EEG leads and, therefore, the MEG and EEG record the electric activity of the brain in a very similar way.

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Journal Article•DOI•

EEG source imaging

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Christoph M. Michel, Micah M. Murray, Göran Lantz, Sara L. Gonzalez, Laurent Spinelli, Rolando Grave de Peralta - Show less +2 more

01 Oct 2004-Clinical Neurophysiology

TL;DR: It is shown that modern EEG source imaging simultaneously details the temporal and spatial dimensions of brain activity, making it an important and affordable tool to study the properties of cerebral, neural networks in cognitive and clinical neurosciences.

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1,600 citations

Cites background from "Sensitivity distributions of EEG an..."

...Similarities and differences between EEG and MEG have been discussed elsewhere (e.g. Anogianakis et al., 1992; Liu et al., 2002; Malmivuo et al., 1997; Wiskwo et al., 1993; see also discussion in Barkley and Baumgartner (2003))....
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Journal Article•DOI•

Monte Carlo simulation studies of EEG and MEG localization accuracy.

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Arthur K. Liu¹, Anders M. Dale¹, John W. Belliveau¹•Institutions (1)

Harvard University¹

01 May 2002-Human Brain Mapping

TL;DR: Results show that surprisingly, EEG localization is more accurate than MEG localization for the same number of sensors averaged over many source locations and orientations; as expected, combining EEG with MEG produces the best accuracy for the the same total number of sensor locations.

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Abstract: Both electroencephalography (EEG) and magnetoencephalography (MEG) are currently used to localize brain activity The accuracy of source localization depends on numerous factors, including the specific inverse approach and source model, fundamental differences in EEG and MEG data, and the accuracy of the volume conductor model of the head (ie, the forward model) Using Monte Carlo simulations, this study removes the effect of forward model errors and theoretically compares the use of EEG alone, MEG alone, and combined EEG/MEG data sets for source localization Here, we use a linear estimation inverse approach with a distributed source model and a realistic forward head model We evaluated its accuracy using the crosstalk and point spread metrics The crosstalk metric for a specified location on the cortex describes the amount of activity incorrectly localized onto that location from other locations The point spread metric provides the complementary measure: for that same location, the point spread describes the mis-localization of activity from that specified location to other locations in the brain We also propose and examine the utility of a "noise sensitivity normalized" inverse operator Given our particular forward and inverse models, our results show that 1) surprisingly, EEG localization is more accurate than MEG localization for the same number of sensors averaged over many source locations and orientations; 2) as expected, combining EEG with MEG produces the best accuracy for the same total number of sensors; 3) the noise sensitivity normalized inverse operator improves the spatial resolution relative to the standard linear estimation operator; and 4) use of an a priori fMRI constraint universally reduces both crosstalk and point spread

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341 citations

Cites methods from "Sensitivity distributions of EEG an..."

...Some modeling work found MEG to be more accurate than EEG [Murro et al., 1995; Stok, 1987], whereas others found EEG and MEG accuracy to be comparable [Malmivuo et al., 1997], or EEG accuracy better than MEG [Mosher et al., 1993; Pascual-Marqui and Biscay-Lirio, 1993]....
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Journal Article•DOI•

EEG source localization: Sensor density and head surface coverage.

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Jasmine Song, Colin Davey, Catherine Poulsen, Phan Luu¹, Sergei Turovets¹, Erik Anderson, Kai Li, Don M. Tucker¹ - Show less +4 more•Institutions (1)

University of Oregon¹

30 Dec 2015-Journal of Neuroscience Methods

TL;DR: The most accurate source localization is obtained when the voltage surface is densely sampled over both the superior and inferior surfaces, as well as across all sampling density and inverse methods.

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265 citations

Journal Article•DOI•

Electric source imaging of human brain functions

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Christoph M. Michel¹, Gregor Thut¹, Stéphanie Morand¹, Asaid Khateb¹, Alan J. Pegna¹, Rolando Grave de Peralta¹, Sara L. Gonzalez¹, Margitta Seeck¹, Theodor Landis¹ - Show less +5 more•Institutions (1)

Geneva College¹

01 Oct 2001-Brain Research Reviews

TL;DR: The presented data show rapid and parallel activation of different areas within complex neuronal networks, including early activity of brain regions remote from the primary sensory areas, and indicate information exchange between homologous areas of the two hemispheres in cases where unilateral stimulus presentation requires interhemispheric transfer.

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249 citations

Cites background from "Sensitivity distributions of EEG an..."

...Because the temporal amount of information they provide about the sources as resolution is in the one millisecond range or faster, these long as the same number of electrodes / sensors is used in techniques permit the determination of the sequence of the two techniques [37]....
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Journal Article•DOI•

Estimating the spatial Nyquist of the human EEG

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Ramesh Srinivasan¹, Don M. Tucker, Michael Andrew Murias²•Institutions (2)

University of Oregon¹, University of California, Irvine²

01 Mar 1998-Behavior Research Methods Instruments & Computers

TL;DR: Evidence is provided that adequately sampling the human electroencephalograph (EEG) across the full surface of the head requires a minimum of 128 sensors and that additional increases in sensor density beyond 128 channels will improve the spatial resolution of the scalp EEG.

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Abstract: The discrete sampling of the brain’s electrical field at the scalp surface with individual recording sensors is subject to the same sampling error as the discrete sampling of the time series at any one sensor with analog-to-digital conversion. Unlike temporal sampling, spatial sampling is intrinsically discrete, so that the post hoc application of analog anti-aliasing filters is not possible. However, the skull acts as a low-pass spatial filter of the brain’s electrical field, attenuating the high spatial frequency information. Because of the skull’s spatial filtering, a discrete sampling of the spatial field with a reasonable number of scalp electrodes is possible. In this paper, we provide theoretical and experimental evidence that adequately sampling the human electroencephalograph (EEG) across the full surface of the head requires a minimum of 128 sensors. Further studies with each of the major EEG and event-related potential phenomena are required in order to determine the spatial frequency of these phenomena and in order to determine whether additional increases in sensor density beyond 128 channels will improve the spatial resolution of the scalp EEG.

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241 citations

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References

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Book•

Static and dynamic electricity

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W. R. Smythe

01 Jan 1939

2,503 citations

Book•

Bioelectromagnetism: Principles and Applications of Bioelectric and Biomagnetic Fields

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Jaakko Malmivuo, Robert Plonsey

01 Jan 1995

1,613 citations

Journal Article•DOI•

Ueber einige Gesetze der Vertheilung elektrischer Ströme in körperlichen Leitern mit Anwendung auf die thierisch‐elektrischen Versuche

[...]

H. Helmholtz

01 Jan 1853-Annalen der Physik

866 citations

"Sensitivity distributions of EEG an..." refers background in this paper

...) According to the reciprocity theorem of Helmholtz [9], the current field produced in this manner in the volume conductor is identical to the distribution of the sensitivity of the lead....
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...What the Helmholtz Theorem expresses is not the independence of electric and magnetic signals, but the independence of thesensitivity distributionsof the recordings of the flow and vortex sources, i.e., the electric and magnetic lead fields....
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...It is now possible to resolve the paradox involving Helmholtz’s Theorem....
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...In the beginning of biomagnetic research it was believed that because of the Helmholtz Theorem, these two fields are independent and that as much new information can be obtained from magnetic recordings as is already present in electric recordings....
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...[9] H. L. F. Helmholtz, “Ueber einige Gesetze der Vertheilung elektrischer Ströme in körperlichen Leitern mit Anwendung auf die thierischelektrischen Versuche,”Ann....
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Journal Article•DOI•

EEG Electrode Sensitivity-An Application of Reciprocity

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Stanley Rush¹, Daniel A. Driscoll¹•Institutions (1)

University of Vermont¹

01 Jan 1969-IEEE Transactions on Biomedical Engineering

TL;DR: The reciprocity theorem is used to determine the sensitivity of EEG leads to the location and orientation of sources in the brain and the following conclusions are drawn.

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Abstract: In this paper, the reciprocity theorem is used to determine the sensitivity of EEG leads to the location and orientation of sources in the brain. Quantitative information used in determining the sensitivity is derived from constant potential plots of a three-concentric-sphere mathematical model of the head with current applied through surface leads (the reciprocal problem), and from an electrolytic tank employing a human skull. Advantages of the reciprocal or lead field approach are outlined and the following conclusions are drawn. 1) Leads placed at the end of a diameter through the center of the brain have a range of sensitivity due to source location of only 3 to 1. 2) For the same electrode placement, sensitivity is maximum to sources oriented parallel to the line of the electrodes regardless of source location. 3) Electrodes spaced 5 cm apart are about ten times more sensitive to proximal cortical sources (by virtue of position) than to sources near the center of the brain.

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457 citations

"Sensitivity distributions of EEG an..." refers background or methods in this paper

...Assuming solution of the form the general solution can be shown to be [17]...
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...Though the absolute values of the conductivities in those works differ from those of the original paper of Rush and Driscoll [17], the conductivity ratios are the same....
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...Lead fields for the EEG and MEG leads were calculated in the spherical head model introduced by Rush and Driscoll [17], Fig....
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...The equations for calculating the electric lead fields and HSV’s can be found from [16], [17], [21], and [22]....
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...from those of the original paper of Rush and Driscoll [17],...
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Journal Article•DOI•

MEG versus EEG localization test using implanted sources in the human brain

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David Cohen¹, B N Cuffin¹, K Yunokuchi², Maniewski R³, C. Purcell¹, G. R. Cosgrove⁴, John R. Ives⁴, J G Kennedy⁵, Donald L. Schomer⁴ - Show less +5 more•Institutions (5)

Massachusetts Institute of Technology¹, Kagoshima University², Polish Academy of Sciences³, Beth Israel Deaconess Medical Center⁴, Dartmouth–Hitchcock Medical Center⁵

01 Dec 1990-Annals of Neurology

TL;DR: The results suggest that the MEG offers no significant advantage over the EEG in localizing a focal source, however, this does not diminish other uses of the M EG.

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Abstract: It is believed that the magnetoencephalogram (MEG) localizes an electrical source in the brain to within several millimeters and is therefore more accurate than electroencephalogram (EEG) localization, reported as 20 mm. To test this belief, the localization accuracy of the MEG and EEG were directly compared. The signal source was a dipole at a known location in the brain; this was made by passing a weak current pulse simulating a neural signal through depth electrodes already implanted in patients for seizure monitoring. First, MEGs and EEGs from this dipole were measured at 16 places on the head. Then, computations were performed on the MEG and EEG data separately to determine the apparent MEG and EEG source locations. Finally, these were compared with the actual source location to determine the MEG and EEG localization errors. Measurements were made of four dipoles in each of three patients. After MEGs with weak signals were discounted, the MEG average error of localization was found to be 8 mm, which was worse than expected. The average EEG error was 10 mm, which was better than expected. These results suggest that the MEG offers no significant advantage over the EEG in localizing a focal source. However, this does not diminish other uses of the MEG.

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288 citations

"Sensitivity distributions of EEG an..." refers background in this paper

...The relative merits of the EEG and magnetoencephalography (MEG) have been a subject of very controversial discussion including articles on scientific experiments [2], [4], [6], scientific discussions [24], and editorial articles [5]....
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