Date of Award

8-1-2022

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College/School/Department

Department of Electrical and Computer Engineering

Content Description

1 online resource (xix, 149 pages) : illustrations (some color)

Dissertation/Thesis Chair

Gary Saulnier

Committee Members

James Moulic, Daphney-Stavroula Zois, Jonathan Newell

Keywords

EIT, Electrical Impedance Tomography, Electrical impedance tomography

Subject Categories

Computer Engineering | Electrical and Electronics

Abstract

This dissertation describes the design and implementation of Adaptive Current Tomograph 5 (ACT5) with a focus on the digital processing and data ow in the instrument. ACT5 is an electrical impedance tomography (EIT) instrument that produces images of the complex impedivity distribution within the body by injecting currents through and measuring voltages on electrodes applied to the skin. ACT5 is a parallel-drive EIT system with a dedicated current source for each electrode, capable of driving all electrodes simultaneously and measuring the induced voltages on them. It can support up to 48 electrodes with a frequency range of 5 kHz to 1MHz with fully programmable current drive patterns. ACT5 can acquire data at a frame rate of ~ 30 frames per second when using 32 electrodes. For each electrode channel, a dedicated field-programmable gate array (FPGA) generates a sinusoidal burst with the help of a digital-to-analog converter (DAC) and a Howland current pump, and measures the phase and the amplitude of the induced voltage by using an analog-to-digital converter (DAC) and a matched filter. The low-level setup and synchronization of the channels is done by a controller that manages the ow of information in the system and controls the execution timings of operation. The high-level control of the system is in the hands of an operator through a graphical user interface (GUI) on a PC that communicates with the controller via a serial communication link. The last major hardware component of ACT5 is the calibration unit that is responsible for calibrating the channels so that the injected currents and the measured voltages on one channel are accurate and in agreement with the rest of the channels. ACT5 incorporates multiple novel design ideas compared to other EIT systems. Analog circuits and processing are minimized in ACT5, and the functions are moved to the digital domain. ACT5 also can calibrate itself while it is attached to patients, making it suitable for long-term monitoring of patients. Simultaneous monitoring of heart activity through measuring and recording electrocardiogram (ECG) signals is another feature of ACT5. Lastly, one of the major benefits of ACT5 is its ability to apply optimal current patterns to provide the maximum amount of information for an arbitrary shape and distribution. This dissertation provides an overview of fundamentals of EIT systems with an extensive literature review. It then discusses various aspects of the design of ACT5, such as the hardware, communication links, modes of operation, calibration process, and safety features in detail. Additionally, a wide variety of experimental results including image reconstructions of objects in a saline tank, three-dimensional image reconstructions of the thorax region of human subjects, ECG recordings from human subjects are presented. Additionally, the ability of ACT5 to detect small changes in the impedance network seen by the electrodes and the ability to apply optimal current patterns are presented to show the performance of ACT5.

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Available for download on Thursday, August 08, 2024

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