H. Jain et al., ELECTRICAL-IMPEDANCE TOMOGRAPHY OF COMPLEX CONDUCTIVITY DISTRIBUTIONSWITH NONCIRCULAR BOUNDARY, IEEE transactions on biomedical engineering, 44(11), 1997, pp. 1051-1060
Electrical impedance tomography (EIT) uses low-frequency current and v
oltage measurements made on the boundary of a body to compute the cond
uctivity distribution within the body. Since the permittivity distribu
tion inside the body also contributes significantly to the measured vo
ltages, the present reconstruction algorithm images complex conductivi
ty distributions. A finite element model (FEM) is used to solve the fo
rward problem, using a 6017-node mesh for a piecewise-linear potential
distribution. The finite element solution using this mesh is compared
with the analytical solution for a homogeneous field and a maximum er
ror of 0.05% is observed in the voltage distribution. The boundary ele
ment method (BEM) is also used to generate the voltage data for inhomo
geneous conductivity distributions inside regions with noncircular bou
ndaries. An iterative reconstruction algorithm is described for approx
imating both the conductivity and permittivity distributions from this
data. The results for an off-centered inhomogeneity showed a 35% impr
ovement in contrast from that seen with only one iteration, for both t
he conductivity and the permittivity values. It is also shown that a s
ignificant improvement in images results from accurately modeling a no
ncircular boundary. Both static and difference images are distorted by
assuming a circular boundary and the amount of distortion increases s
ignificantly as the boundary shape becomes more elliptical. For a homo
geneous field in an elliptical body with axis ratio of 0.73, an image
reconstructed assuming the boundary to be circular has an artifact at
the center of the image with an error of 20%. This error increased to
37% when the axis ratio was 0.64. A reconstruction algorithm which use
d a mesh with the same axis ratio as the elliptical boundary reduced t
he error in the conductivity values to within 0.5% of the actual value
s.