Electrical impedance tomography of complex conductivity distributions with noncircular boundary

• Published in: IEEE transactions on biomedical engineering Vol. 44; no. 11; pp. 1051 - 1060
• Main Authors: Jain, H., Isaacson, D., Edic, P.M., Newell, J.C.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.11.1997; Institute of Electrical and Electronics Engineers
• Subjects: Algorithms; Biological and medical sciences; Boundary element method; Boundary element methods; Conductivity measurement; Distributed computing; Electric Conductivity; Electric Impedance; Finite element method; Finite element methods; Fourier Analysis; Humans; Image Processing, Computer-Assisted - methods; Image reconstruction; Impedance; Investigative techniques, diagnostic techniques (general aspects); Iterative methods; Mathematical models; Medical sciences; Miscellaneous. Technology; Models, Theoretical; Pathology. Cytology. Biochemistry. Spectrometry. Miscellaneous investigative techniques; Permittivity; Permittivity measurement; Piecewise linear techniques; Reconstruction algorithms; Tomography; Tomography - methods; Voltage measurement; Electrical conductivity; Electrical properties; Potential distribution; Iterative method; Boundary condition; Image reconstruction; Finite element method; Algorithm performance; Tomography; Technique; Permittivity; Comparative study; Boundary element method; Electrical impedance
• DOI: 10.1109/10.641332
• ISSN: 0018-9294

Electrical impedance tomography (EIT) uses low-frequency current and voltage measurements made on the boundary of a body to compute the conductivity distribution within the body. Since the permittivity distribution inside the body also contributes significantly to the measured voltages, the present reconstruction algorithm images complex conductivity distributions. A finite element model (FEM) is used to solve the forward 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 error of 0.05% is observed in the voltage distribution. The boundary element method (BEM) is also used to generate the voltage data for inhomogeneous conductivity distributions inside regions with noncircular boundaries. An iterative reconstruction algorithm is described for approximating both the conductivity and permittivity distributions from this data. The results for an off-centered inhomogeneity showed a 35% improvement in contrast from that seen with only one iteration, for both the conductivity and the permittivity values. It is also shown that a significant improvement in images results from accurately modeling a noncircular boundary. Both static and difference images are distorted by assuming a circular boundary and the amount of distortion increases significantly as the boundary shape becomes more elliptical. For a homogeneous 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 used a mesh with the same axis ratio as the elliptical boundary reduced the error in the conductivity values to within 0.5% of the actual values.