Electrical impedance imaging at multiple frequencies in phantoms

We have recently built and tested a 32 channel, multi-frequency (1 kHz to 1 MHz) voltage mode system to investigate electrical impedance spectroscopy (EIS) imaging. We completed a series of phantom experiments to define the b aseline imaging performance of our system. Our phantom consisted of a plast ic circular rank (20 cm diameter) filled with 0.9% aqueous NaCl solution. C onductors and nonconductors of decreasing width (W5: 3.4 cm, W4: 2.54 cm, W 3: 0.95 cm, W2: 0.64 cm and W1: 0.32 cm) were positioned at various distanc es from the tank edge (1 cm, 2 cm, 4 cm and 8 cm). The results suggest that the detection of objects less than 1 cm in width is limited to the first 1 to 2 cm from the tank edge for absolute images, but this depth can extend to 8 cm in difference images. Larger 3.4 cm wide objects can be detected in absolute images at depths up to 8 cm from the tank edge. Generally, conduc tor images were clearer than their nonconductor counterparts. Not only did electrode artefacts lessen as the frequency increased, but the system's max imum resolution was attained at the highest operating frequencies. Although the system recovered the value of the electrical conductivity at the corre ct order of magnitude, it tended to smooth our large property discontinuiti es. The calculated electrical permittivity in these phantom studies was inc onclusive due to the presence of electrode artefacts.