E-Book Content
Electrical Impedance Tomography
By Waleed A. AlWalaie Supervised By Dr. Saleh AlShebeili
January, 2003
Abstract In electrical impedance tomography (EIT) images of the object are formed based on passive electrical properties of the interior structures. In EIT an array of electrodes is attached around the object and small alternating currents are injected via these electrodes and the resulting voltages are measured. Using different current injections and voltage measurements, an approximation for the spatial distribution of impedance (or resistivity) within the object can be reconstructed. EIT is a relatively new technique with most of the development having occurred over the past ten years. Technical developments are still taking place but people have begun to explore areas of possible applications. The spatial resolution of EIT images so far obtained is only about 10% of the diameter of the image field. However, the sensitivity of the images to changes in impedance is good with changes of 1% seen relatively easily. It is also possible to collect images at 25 frames per second using relatively low cost equipment and with no hazard to the object. In the first part of this project, we will give an overview of the EIT including its applications, advantages over other imaging techniques, data collection strategies, and the mathematical model. Then, in the second part of the project, we’ll give an overview to the reconstruction algorithms currently available and we will implement one of them and evaluate its performance using actual measured data.
Contents
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Introduction to Electrical Tomography
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1.0 Introduction ………………………………………….
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1.1 Electrical Capacitance Tomography (ECT) …………………
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1.2 Electromagnetic Tomography (EMT) ……………………...
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1.2 Electrical Impedance Tomography (EIT) …………………...
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Electrical Impedance Tomography (EIT)
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2.1 Introduction ………………………………………….
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2.2 Applications of EIT ……………………………………
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2.3 Advantages of EIT …………………………………….
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2.4 Data Collection in EIT ………………………………….
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2.4.1 Electric Measurement of Impedance …………………
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Neighboring Method ……………………………..
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Cross Method …………………………………..
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Opposite Method ………………………………..
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Adaptive Method ………………………………..
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The Mathematical Model
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3.1 Introduction ………………………………………….
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3.2 Mathematical Model …………………………………...
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3.2.1 The Equation Inside The Body ……………………..
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3.2.2 Boundary Conditions …………………………….
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Continuum Model ……………………………….
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Gap Model ……………………………………..
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Shunt Model ……………………………………
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Complete Electrode Model ………………………...
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Future Work …………………………………………...
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References ……………………………………………………
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CHAPTER1
Introduction to Electrical Tomography
Contents: 1.0 1.1 1.2 1.3
Introduction Electrical Capacitance Tomography (ECT) Electromagnetic Tomography (EMT) Electrical Impedance Tomography (EIT)
1.0
Introduction
The term tomography derives from the Greek tomos (cutting) and grapho (to write). Originally the term was applied to sectional radiography achieved by a synchronous motion of the x-ray source and detector in order to blur undesired data while creating a sharp image of the selected plane [1]. Electrical Tomography (ET) is an imaging method which tries to reconstruct different electrical properties of materials within a volume given only “boundary measurements” resulting from an injected current. These mea