ELECTRICAL IMPEDANCE TOMOGRAPHY

ELECTRICAL IMPEDANCE TOMOGRAPHY

ABSTRACT:

Imbalances in regional lung ventilation, with gravity-dependent collapse and over distention of nondependent zones, are likely associated to ventilator-induced lung injury. Electric impedance tomography is a new imaging technique that is potentially capable of monitoring those imbalances. The aim of this study was to validate electrical impedance tomography measurements of ventilation distribution, by comparison with dynamic computerized tomography in a heterogeneous population of critically ill patients under mechanical ventilation.

This thesis is concerned with Electrical Impedance Tomography (EIT), a medical imaging technique in which pictures of the electrical conductivity distribution of the body are formed from current and voltage data taken on the body surface. The focus of the thesis is on the mathematical aspects of reconstructing the conductivity image from the measured data.

Electrical impedance tomography (EIT) is to reconstruct an impedance distribution in an object of interest from electrical measurement on the boundary of the object. Because of its non-invasiveness, portability and practical utilities, EIT has been actively studied since 1970s and led to many useful and inspiring results.

The primary focus of this work is the visualization of multiphase flows (specifically suspensions of neutral buoyant and buoyant particles at low Reynolds number) using EIT. This imaging technique can lead to a better understanding of the nature of these multiphase flows. Therefore, electrical impedance tomography helps in determining the optimal mechanical ventilation in a patient with acute lung injury.

INTRODUCTION:

Electrical Impedance Tomography (EIT) is a non-invasive imaging technique that has applications in the medical field and industrial processes. EIT has been used to image lung functions. Additionally EIT has been used to determine pulp consistency, which can be integrated into a process control loop in the paper manufacturing process.

Electrical impedance tomography (also called applied potential tomography) is a novel imaging technique with applications in medicine and process control. Compared with techniques like computerized x-ray tomography and positron emission tomography, EIT is about a thousand times cheaper, a thousand times smaller and requires no ionizing radiation. Further, EIT can in principle produce thousands of images per second. Its major limitations are its low spatial resolution, and in the medical field - large variability of images between subjects. Recordings are typically made by applying current to the body or system under test using a set of electrodes, and measuring the voltage developed between other electrodes. To obtain reasonable images, at least one hundred, and preferably several thousand, such measurements must be made.

In the medical field, the most studied applications for EIT are measurement of gastric emptying and lung function. In the industrial field typical applications are imaging the distribution of oil and water in a pipeline and imaging the flow of substances in a mixing vessel. In some ways industrial applications are more favorable for EIT because it is usually possible to use a rigid, fixed array of electrodes. The fixing of electrodes on the human body is one of the residual problems facing medical EIT.


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