Development of algorithms to image impedance changes inside the human head.

Bayford, Richard and Bagshaw, Andrew P. and Liston, Adam D. and Tizzard, Andrew and Holder, David S. (2002) Development of algorithms to image impedance changes inside the human head. In: The First Mummy Range Workshop on Electric Impedance Imaging, Colorado, US.

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Abstract

It is assumed that inclusion of head geometry in the forward model will improve the localisation accuracy of image reconstruction algorithms for imaging impedance changes inside the human head. Initially we developed an algorithm, which assumed that the human head could be modelled as a simple homogenous sphere or multiple shelled spheres. This is an assumption often used in localising dipoles in the human head from measurement of surface potentials (Electroencephalogram EEG). This did not always yield a solution with correct localisation. To test the idea that including geometric information will improve localisation we have developed a new difference reconstruction algorithm for Electrical Impedanc Tomography (EIT) that incorporates a forward model derived from a Finite Element model of the human head. The new algorithm uses a sensitivity approach. The linear sensitivity matrix is created from a geometrically accurate model of the human head obtain from segmented MRI data. Generating meshes of the human head is difficult due to the complex geometry and multiple shells, i.e. scalp, skull, CSF and brain. This can produce distorted elements, which impact of the quality on the reconstructed image. Also the number of elements in scalp and CSF are limited reducing the accuracy of the final solution. We examine the effect of the mesh quality on the reconstructed image. The inverse solution was obtained by normalising the sensitivity matrix then inverting it using truncated Singular Value Decomposition (SVD). We present the results of this new image reconstruction algorithm and compare its image quality and location accuracy against an algorithm which models the head as four concentric spheres.

Item Type:Conference or Workshop Item (Paper)
Additional Information:

ID: 204; RP: NOT IN FILE

Keywords (uncontrolled):Human
Research Areas:School of Science and Technology > Science & Technology
School of Science and Technology > Natural Sciences
ID Code:2914
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Deposited On:03 Nov 2009 09:26
Last Modified:06 Feb 2013 11:45

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