Portable 8-electrode EIT measurement system

To make electrical impedance tomography (EIT) measurements, we inject currents into a volume through electrodes, then measure the voltages at the electrodes. In this paper we introduce an 8-electrode EIT measurement system which is completely portable and is based on a PDA instead of a PC. The system is composed of a data acquisition board (E-Pack), a current source, a PDA and software, which was developed in eVC 4.0. The E-pack collects data through a pre-amplifier. The signal is then sampled and demodulated with an AD9240 ADC with 14-bit resolution and 10msps speed, and finally completed through 32 point sampling in the digital signal processor (DSP). For the DSP, we have chosen an Analog Devices ADSP-2181. Custom designed protocol between the PDA and E-Pack enables selection of any current drive and measurement electrode pairs. Images can be reconstructed and displayed on the PDA. We present experimental results for a cylindrical phantom that demonstrate the performance and applicability of our system. Measurements on a 50Ω resistor network show that the precision of our system is better than 0.2%.