Correlation between Live and Post Mortem Skull Conductivity Measurements

Wendel, Katrina; Malmivuo, Jaakko

doi:10.1109/iembs.2006.259434

Cited by 19 publications

(22 citation statements)

References 17 publications

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“…Tissue properties and the CSF ion and protein concentration change in post-mortem subjects, for example as result of cell degeneration, disruption of brain barrier function, dehydration, or temperature (Li et al, 1968, Wendel and Malmivuo, 2006). Although the flow velocity of the ions in the CSF at the applied current intensity, is very low, it cannot be ruled out that the application of tDCS during functional imaging induces some physical movement of CSF, which could in turn produce changes in EPI signal magnitude.…”

Section: Discussionmentioning

confidence: 99%

Imaging artifacts induced by electrical stimulation during conventional fMRI of the brain

et al. 2014

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Functional magnetic resonance imaging (fMRI) of brain activation during transcranial electrical stimulation is used to provide insight into the mechanisms of neuromodulation and targeting of particular brain structures. However, the passage of current through the body may interfere with the concurrent detection of blood oxygen level dependent (BOLD) signal, which is sensitive to local magnetic fields. To test whether these currents can affect concurrent fMRI recordings we performed conventional gradient echo-planar imaging (EPI) during transcranial direct current (tDCS) and alternating current stimulation (tACS) on two post-mortem subjects. TDCS induced signals in both superficial and deep structures. The signal was specific to the electrode montage, with the strongest signal near cerebrospinal fluid (CSF) and scalp. The direction of change relative to non-stimulation reversed with tDCS stimulation polarity. For tACS there was no net effect of the MRI signal. High-resolution individualized modeling of current flow and induced static magnetic fields suggested a strong coincidence of the change EPI signal with regions of large current density and magnetic fields. These initial results indicate that: 1) fMRI studies of tDCS must consider this potentially confounding interference from current flow and 2) conventional MRI imaging protocols can be potentially used to measure current flow during transcranial electrical stimulation. The optimization of current measurement and artifact correction techniques, including consideration of the underlying physics, remains to be addressed.

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Section: Discussionmentioning

confidence: 99%

Imaging artifacts induced by electrical stimulation during conventional fMRI of the brain

et al. 2014

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“…The inner surface of the model was tessellated in 10240 triangular elements, and the other two surfaces in 5120 triangular elements. The adopted tissue electric conductivity values were 0.3 S/m for the brain and scalp, and 0.02 S/m for the skull [21,28,33]. We solved the forward problem for 120 electrodes on the scalp, placed according to an extension of the 10-20 system [14], and 160 magnetometers on a helmet, with approximately radial orientation and about 2 cm away from the scalp surface.…”

Section: Problem Setupmentioning

confidence: 99%

On the EEG/MEG forward problem solution for distributed cortical sources

Ellenrieder

Valdés-Hernández

Muravchik

2009

Med Biol Eng Comput

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In studies of EEG/MEG problems involving cortical sources, the cortex may be modeled by a 2-D manifold inside the brain. In such cases the primary or impressed current density over this manifold is usually approximated by a set of dipolar sources located at the vertices of the cortical surface tessellation. In this study, we analyze the different errors induced by this approximation on the EEG/MEG forward problem. Our results show that in order to obtain more accurate solutions of the forward problems with the multiple dipoles approximation, the moments of the dipoles should be weighted by the area of the surrounding triangles, or using an alternative approximation of the primary current as a constant or linearly varying current density over plane triangular elements of the cortical surface tessellation. This should be taken into account when computing the lead field matrix for solving the EEG/MEG inverse problem in brain imaging methods.

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“…Anthropometric data currently exists detailing deformations in craniometric landmarks (Department of Defense, 1997;Donelson & Gordon, 1991;Farkas et al, 2005;Howells, 1973); however, a database of landmark sizes coupled with age (Wendel & Malmivuo, 2006;Wendel, Väisänen, Seemann, Hyttinen & Malmivuo, 2010), gender (Wendel, Osadebey & Malmivuo, 2009;Wendel, Väisänen, Seemann, Hyttinen & Malmivuo, 2010), ethnic origin (Wendel, Osadebey & Malmivuo, 2009), and head shape (Wendel, Osadebey & Malmivuo, 2009) would improve the accuracy beyond the overly used fixed-geometry of highly complex models such as from the Visible Human Project (Ackerman, 1991;National Institutes of Health (NIH), 1995). Future studies that will advance the field of source imaging will save time and money.…”

Section: Complex Generic Modelsmentioning

confidence: 99%