Development of a Miniaturized, Low-Cost Electrical Impedance Tomography System

This work focuses on the development of a miniaturized, wearable, and low-cost (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\$}$ </tex-math></inline-formula>25) electrical impedance tomography (EIT) system based on an ESP32 microcontroller unit (MCU) combined with microsize complex programmable logic device (CPLD). The voltage data are sent to a personal computer (PC) via Wi-Fi and the image is reconstructed with EIDORS in MATLAB. The hardware of the designed EIT system includes an acquisition board, a data processing board powered by a 1000-mAh Li-Po battery, a configurable electrode-sensor unit, and a PC. The system is developed to meet the EIT performance requirement with the smallest possible size, and its printed circuit boards (PCBs) are with a size of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$40\times 36$ </tex-math></inline-formula> mm. The system supports 2–16 electrodes and a configurable measuring pattern with self-adaptive gain control. It can provide voltage data frames at more than 30 fps. The amplitude of the excitation current can be adjusted from 0.3 mAp (mA peak) to 2.0 mAp (complies with the IEC standard 60601-1) when the excitation frequency is 97.65625 kHz. Results indicate that the highest signal-to-noise ratio (SNR) is 61.6 dB, the average impedance measurement accuracy (IMA) is 97.9%, and the average image correlation coefficient (ICC) is 71.2%. It is potential that the proposed EIT system can be developed into a beneficial, convenient for physicians and patients in various applications.