Considerations in Electrical Impedance Imaging

Nick Polydorides1, William R. Lionheart2 and Hugh McCann1

1Dept of Electrical Engineering and Electronics

2Dept of Mathematics, UMIST

UMIST, PO Box 88, Manchester M60 1QD, UK mchpinp2@stud.umist.ac.uk, bill.lionheart@umist.ac.uk, h.mccann@umist.ac.uk

ABSTRACT

The correctness of the two-dimensional reconstructed images obtained using Electrical Impedance Tomography has been a source of debate mainly due to the assumption that the electrostatic field is strictly confined within the electrodes' plane. In reality this is not correct because even if the electrodes are located in a plane arrangement, the electrostatic field they set up remains three-dimensional. Incorporating a 3D measurement volume, a realistic electrode model and a Newton based iterative technique we have investigated whether 3D images could be reconstructed when using plane electrode arrangements and 2D measurement protocols. After a series of simulated experiments we conclude that irrespectively of the number of parallel electrode rings mounted at the boundaries, unless 3D voltage measurements are captured no sensible images can be obtained. Exploring the significance of accurate modelling in EIT we also attempt to reconstruct some simulated 3D data using a simplistic 2D model aiming to validate the claim that 'no model conductivity consistent with measurement exists when the dimension is wrong' (Lionheart, 1999). At a further stage we look at some of the computational issues regarding 3D bulky reconstruction problems including the efficient computation of the forward solution and the Jacobian matrix.

Keywords: Electrical Impedance Tomography, plane electrodes, 3D measurements and computational efficiency.