A study of three dimensional effects in induced current impedance imaging.

Previous studies of the induced current impedance imaging technique have been unable
to reconstruct images of three dimensional (3-D) structures. In this study the cause of
the problem is identified and the reconstruction algorithm of Purvis is adapted to
facilitate the correct reconstruction of images of a limited class of structures which have
the form of a long cylinder. The images produced by the algorithm are improved by a
data filter based on that of Barber, Brown and Avis.
By consideration of the underlying field equations which govern 3-D induced current
Electrical Impedance Tomography (EIT) systems, the finite element method (FEM) is
used for the computation of the potential field for arbitrary conductivity distributions
excited by various coil configurations. A phantom system is built to test the results of
the FEM and particular attention is paid to the improvement of the instrumentation. A
statistical comparison of the results of measurement and simulation is unable to detect
any error in the FEM model. The FEM model is consequently used to develop the
reconstruction algorithm but physical measurements are also used to test the algorithm
in the presence of noise.
The behaviour of the 3-D algorithm is tested for its plane selectivity showing Similar
characteristics to those of injected current systems developed by other workers. A
possible approach which could both reduce the volume to which the system is sensitive
and generate extra measurements for the possible reconstruction of multi-layered
images is investigated.