FPGA-Based Planar Sensor Electrical Impedance Tomography (FPGA-psEIT) System Characterized by Double Feedback Howland Constant- Current Pump and Programmable Front-End Measurement

The field-programmable gate array (FPGA)-based planar sensor electrical impedance tomography (FPGA-psEIT) system has been developed for skin sodium content imaging, which is characterized by double feedback Howland constant-current pump (DFHC) and programmable front-end measurement (PFM). In order to ensure the FPGA-psEIT suitability for medical application, DFHC maintains current stability across a broad frequency spectrum, while PFM reduces the measurement error over wide range of impedance level. The hardware performance of FPGA-psEIT system is assessed through the signal-to-noise ratio (SNR) evaluation, which is conducted at various load-impedance levels. Further to validate the system, experiments are undertaken by using calf skin of human subjects to investigate the level of sodium content
$\gamma ^{\text {Na}}$
in the dermis layer. As the result of the performance test of FPGA-psEIT, the SNR is achieved 89 dB at
$f_{0} =10$
–100 kHz. Lastly, in the human calf experiments, FPGA-psEIT exhibits a consistent tendency to yield higher
$\langle ^{\ast } \sigma \rangle $
as compared to the impedance analyzer (IA) with an average difference of 29%. The aforementioned results indicate that FPGA-psEIT system is capable to produce a high-quality image of the conductivity distribution of
$\gamma ^{\text {Na}}$
applied in human calf skin.