USE OF POLYACRYLAMIDE GELS IN A SALINE-FILLED TANK TO DETERMINE THE LINEARITY OF THE SHEFFIELD MARK-1 ELECTRICAL-IMPEDANCE TOMOGRAPHY (EIT) SYSTEM IN MEASURING IMPEDANCE DISTURBANCES

Polyacrylamide gels have been assessed as a means of producing reliable small impedance changes for EIT studies in saline-filled tanks. Test rods could be made in about 10 min from a stock solution of acrylamide monomer and bis-acrylamide, ammonium persulphate and tetramethylethylaminediamine, completed with saline. Impedance increases of about 10%-200% were produced by varying the gel concentration. The method appears to be easy to use, inexpensive and is stable over time. Its use was illustrated by acquiring EIT images with a Sheffield Mark 1 system and a tank filled with 0.2% saline. Polythene or polyacrylamide rods of varying resistivities, 10% of the tank diameter wide, were placed in one of three positions. The magnitude of the impedance increase in Err images varied linearly with the actual impedance change in the rods for increases up to 20%, but the blurring in images was similar when polythene rods were used. This suggests that the use of highly resistive test objects gives a reasonable indication of the blurring in Err images acquired with the system used, but measurement of the magnitude of the impedance change is more likely to be accurate for changes of a few tens of per cent.