A narrowband multiple frequency simultaneous drive EIT system applied to a linear array.

A high speed, injected current, Electrical Impedance Tomography (EIT) system for producing images of electrical conductivity distributions is described. The measurements required to produce an image are acquired in a time of 2ms, allowing rapidly changing distributions to be imaged. To achieve this speed, the drive currents of different frequencies are applied simultaneously to the medium of interest. The system is applied to a linear array, although other electrode configurations could be used. An introduction to the topic of Electrical Impedance Tomography (EIT) is presented detailing present applications of EIT and giving some theoretical background to the technique. Reasons for reducing the measurement time and applying the system to a linear array are given. The general specification for the system is derived and the parallel drive and measurement circuitry is described in detail. The filtering process used to determine the components of the measured data at each of the drive frequencies is described. The algorithm used to form images is explained and image filters are applied to images generated from analytic data in order to improve the image quality. Measurements made on conductivity distributions set up in a phantom and images generated from these measurements are presented including images o f single and multiple objects of higher and lower conductivity than the background medium. Images of moving objects, including a sequence o f images generated from measurements taken in consecutive 2ms intervals, are presented. Conclusions from the work are drawn and suggestions for further work are given.