Modeling Skull Electrical Properties |
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Authors: | R J Sadleir A Argibay |
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Institution: | (1) The J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Box 116131, Gainesville, FL 32611-6131, USA;(2) Present address: Gaumard Scientific, 14700 SW 136 St, Miami, FL 33196, USA |
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Abstract: | Accurate representations and measurements of skull electrical conductivity are essential in developing appropriate forward
models for applications such as inverse EEG or Electrical Impedance Tomography of the head. Because of its layered structure,
it is often assumed that skull is anisotropic, with an anisotropy ratio around 10. However, no detailed investigation of skull
anisotropy has been performed. In this paper we investigate four-electrode measurements of conductivities and their relation
to tissue anisotropy ratio (ratio of tangential to radial conductivity) in layered or anisotropic biological samples similar
to bone. It is shown here that typical values for the thicknesses and radial conductivities of individual skull layers produce
tissue with much smaller anisotropy ratios than 10. Moreover, we show that there are very significant differences between
the field patterns formed in a three-layered isotropic structure plausible for bone, and those formed assuming that bone is
homogeneous and anisotropic. We performed a measurement of conductivity using an electrode configuration sensitive to the
distinction between three-layered and homogeneous anisotropic composition and found results consistent with the sample being
three-layered. We recommend that the skull be more appropriately represented as three isotropic layers than as homogeneous
and anisotropic. |
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Keywords: | Skull conductivity Anisotropy Finite element model Head model |
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