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Michelle Mellenthin
Hardware Improvements to Reduce Interference and Improve Electrode-Skin
Modeling in Electrical Impedance Tomography
Electrical Impedance Tomography (EIT) is a low-cost, portable, and radiation-free
functional imaging modality that can be used to create low spatial resolution images
which reflect differences in ion concentration or electrical properties of biological tissues.
One of the main research interests of the EIT laboratories at both Colorado State
University (CSU) and the University of Sao Paulo (USP) is creating cross-sectional
images of the human chest to allow for better diagnosis of different lung pathologies.
The quality of EIT images depends greatly upon both the reconstruction algorithm and
hardware. Improved image quality, or better spatial resolution and accuracy of
reconstructed values in EIT images, is essential for better distinguishability between
tissues and anomalies. To aid in upcoming experiments involving electrode-skin
modeling and reconstruction algorithms, the hardware system needed to be modified to
accurately acquire complex voltages. The important changes implemented were: (1) an
active electrode to allow for accurate acquisition of complex voltages, (2) a novel bipolar
current source, and (3) analog Butterworth anti-aliasing filters to further reduce noise.
One of the difficulties encountered during this work was that the detailed design of the
data acquisition system and the large number of improvements needed was not fully
divulged until arrival. In addition, the project timeline had to be altered because all
expensive hardware purchases needed to be made through the accountants of the
university. The data acquisition boards that were supposed to arrive before the start of the
fellowship did not arrive until the end.
Despite challenges, the outcomes of this work are of considerable importance to both
laboratories. Most significantly, this work resulted in an upgraded EIT system, which is
less sensitive to interference. We also investigated novel designs for current sources,
which could be adopted by other groups. The use of the new tomographer will allow for
better versatility during testing, and the complex voltage measurements it acquires are
crucial for my doctoral project involving skin modeling.