An accessible electrical impedance tomograph for 3D imaging
Abstract
A new electrical tomograph that is designed specifically for low-cost and accessibility is described. It offers a unique environment for three-dimensional (3D) electrical impedance imaging. Using a cross-bar switch, the hardware can support ad hoc measurement strategies and is linked to control software, which integrates the complete process from 3D finite element modelling through to image reconstruction and generation of movie files. Digital signal processing algorithms are used to derive measurements of complex impedance from the measurement of amplitude and phase difference between the driven and received signals. This is achieved by rapid sampling of sinusoidal signals having frequencies between 1.0 Hz and 1.0 MHz. The instrument can deliver about 100 measurements per second, corresponding to a typical 16-electrode tomography frame, and is targeted at processes with modest dynamics or for laboratory development of tomographic applications and algorithms. The latest version (LCT2) is described here and uses a USB2 link to provide data transfer rates up to 20 MBytes per second. Sinusoidal excitation signals are derived using a direct digital synthesis chip. Voltage measurements are digitized to 16-bit accuracy and the standard system can accommodate 64 electrodes. The software embraces the EIDORS-3D soft-field reconstruction algorithms and the resulting impedance imaging capability of the device and characterization of the signals are described.