A portable, low-cost, and open-source electrical impedance tomography system with a modular analog front-end based on STM32 and AD5933.

Electrical impedance tomography (EIT) is a non-invasive, radiation-free medical imaging technique, but commercial devices remain costly and complex. This paper presents a portable, low-cost (95.3 USD) open-source 16-electrode time-difference EIT system based on the AD5933 impedance converter and an STM32F407VGT6 microcontroller. Its highly modular analog front-end enables switching between Load-in-the-Loop and Mirrored Howland Voltage-Controlled Current Source (VCCS) topologies, alongside AD620 module or INA118P instrumentation amplifiers. Utilizing an adjacent pattern, the computationally efficient system acquires 208 impedance data points in 2 s, which is highly suitable for static phantom imaging. Hardware validation at 50.68 kHz demonstrated exceptional measurement precision, yielding standard deviations between 0.54 and 6.33 , and a peak Signal-to-Noise Ratio (SNR) of 43.7 dB. Phantom experiments using a 3D-printed container filled with saline (966 mS/m) successfully evaluated the configurations using both conductive (stainless steel) and non-conductive (plastic) target anomalies across various positions. The 2D boundary voltages were reconstructed using the Back-Projection algorithm in the pyEIT library, achieving a maximum Structural Similarity Index Measure (SSIM) of 0.9242 and a minimum Root Mean Square Error (RMSE) of 28.29. This highly replicable, fully open-source platform offers a robust and accessible foundation for EIT research and education.