Abstract
A new prototype of a multi-frequency electrical impedance tomography system is presented. The system uses a field-programmable gate array as a main controller and is configured to measure at different frequencies simultaneously through a composite waveform. Both real and imaginary components of the data are computed for each frequency and sent to the personal computer over an ethernet connection, where both time-difference imaging and frequency-difference imaging are reconstructed and visualized. The system has been tested for both time-difference and frequency-difference imaging for diverse sets of frequency pairs in a resistive/capacitive test unit and in self-experiments. To our knowledge, this is the first work that shows preliminary frequency-difference images of in-vivo experiments. Results of time-difference imaging were compared with simulation results and shown that the new prototype performs well at all frequencies in the tested range of 60 kHz–960 kHz. For frequency-difference images, further development of algorithms and an improved normalization process is required to correctly reconstruct and interpreted the resulting images.
Highlights
Electrical impedance tomography (EIT) is a method for imaging the impedance distribution of the human body in a cross-section of the thorax
The results the first measurements performed with the Multi-frequency EIT (mfEIT) prototype are presented
We have developed a novel 16-electrode multi-frequency EIT prototype, configured to measure impedance distribution in a cross-section of the body at different frequencies simultaneously by means of a composite waveform
Summary
Electrical impedance tomography (EIT) is a method for imaging the impedance distribution of the human body in a cross-section of the thorax It relies on the injection of small alternating currents and measurement of the resulting voltages at the thorax surface. Sensors 2016, 16, 1158 to take advantage of the frequency-dependance of the complex impedances of tissue In these systems, time-difference images at multiple frequencies have mainly been used [11,12,13], frequency-difference imaging is of increasing interest [14,15,16] as this may provide additional information on tissues and, extra diagnostic information; frequency-difference imaging does not need a reference in time [15]. We present the hardware/software co-design of a serial FPGA-based EIT system, including the signal generation for current injection, voltage measurement and demodulation, control of the measurement method and data transfer. Time-difference images and frequency-different images are reconstructed and presented for both measurement sets
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