Data acquisition system for Lorentz force electrical impedance tomography using magnetic field measurements

Kaboutari, Keivan
Lorentz Force Electrical Impedance Tomography (LFEIT) is a novel imaging modality to image electrical conductivity properties of biological tissues. This modality is recently proposed for early stage diagnosis of cancerous tissues. The main aim of this thesis study is to develop a data acquisition system for LFEIT. Design of contactless receiver sensor, static magnetic field generation (0.56 T is generated by permanent neodymium magnets), amplification of received signals and experimental studies using various phantoms are in the scope of this thesis. Measurement of the AC magnetic fields generated by the induced Lorentz currents using coil sensors at the resonance frequency is the aim of this thesis. In this study, disk multiple layer receiver coil sensors are used in both numerical simulations and experiments. Physical and electrical characteristics of the sensors are evaluated. A design tool is developed using MATLAB, where the physical properties of the coil sensors are defined as inputs of the design tool. The electrical properties such as DC and AC resistance, resonance frequency and quality factor of the coil sensors are obtained as outputs. One of the coil sensors designed by this tool is used in the experimental studies. Sensitivity, signal to noise ratio, thermal noise and quality factor of the realized coil are about 392.72 nmV/HzA, 39.32 dB, 33.83 nV and 29, respectively. Minimum detectable AC magnetic field by the realized coil is about 0.17 pT. A custom made two stage amplifier is designed and utilized in the receiving system. The gain and upper 3dB frequency of the cascaded amplifiers are 100 dB and 1.02 MHz frequency, respectively. Pre-stage amplifier's gain, input RMS voltage noise and minimum RMS detectable signal are 52 dB, 5.09 and 7.19 uV. By connecting the realized coil to the pre-stage amplifier, input RMS voltage noise and minimum RMS detectable signal are increased to 6.28 and 8.87 uV. Then, pre-stage amplifier output is about 3.55 mV. Second stage amplifier's gain and minimum RMS detectable signal are 48 dB and 0.84 uV (-121.52 dB), respectively. Note that, the pre-stage amplifier output is greater than the minimum RMS detectable signal of the second stage. For experimental studies, four phantoms with inhomogeneities in electrical conductivity are developed (70, 800-3000 and 8times 10^6 S/m). The prepared phantoms are utilized in the LFEIT experimental system and generated signals are measured by the designed coil sensor. Signals originating from conductivity inhomogeneities reveal the location of inhomogeneities. Acquired signals are also used in order to generate fast LFEIT images of the phantoms. 


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In Lorentz Field Electrical Impedance Tomography (LFEIT), ultrasound waves are transmitted to a tissue under static magnetic field. Magnetic fields of currents generated in boundaries where conductivity difference exists because of vibrations are measured with coils. In this study, a static magnetic field is created with permanent magnets and magnetic core for LFEIT. The contribution of magnetic core to the created magnetic flux density is demonstrated. Based on these simulation studies magnetic core is des...
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Citation Formats
K. Kaboutari, “Data acquisition system for Lorentz force electrical impedance tomography using magnetic field measurements,” M.S. - Master of Science, Middle East Technical University, 2017.