Design and Implementation of an Electrical Impedance Tomography System
Christos Dimas
Abstract
In this diploma thesis, an electrical impedance tomography system is designed and implemented (in Printed Circuit Board). This method constitutes a non surgery way of human internal tissues imaging, by detecting their impedance between adjacent nodes. Purpose of this thesis is the implementation of an experimental setup with relatively high precision, improved response, relatively low cost, small size and weight, so that it becomes portable. Specifically in this treatise a system is designed in such a way that a low intensity alternating current is diffused into the human tissue under examination, and through a series of lots of electrodes, a voltage is measured. That voltage indicates the resistance that this current flows and through this resistance it is possible to deduce about the tissue types being flowed. Then, with appropriate algorithms we are able to image the tissue interior. In order to design such a system, a proper and extensive study of the electrical properties of human tissue as well as the requirements of the device so as to determine its specifications and therefore its components and the connections between them, should be preceded. The total circuit drives correctly the current to the electrodes and receives the voltage that is about to be measured through them. The basic parts of the circuit designed is a current source, an appropriate system of multiplexers for current injection and voltages switching, the appropriate microcontroller system to program the integrated circuits and receive the measurements, and the differential exit stage. In this thesis, we specifically use 64 electrodes, something which makes the circuit design quite complicated.The present printed matter, firstly refers to the method of electrical impedance tomography and its advantages, then the requirements of the system are analyzed and the components to be used are selected. Subsequently, simulation and measurement results are presented and in final, some possible future extensions and capabilities of the system to allow full utilization are referred.