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 reliabl e small impedance changes for EIT studies in saline-filled tanks. Test rods could be made in about 10 min from a stock solution of acrylamid e monomer and bis-acrylamide, ammonium persulphate and tetramethylethy laminediamine, completed with saline. Impedance increases of about 10% -200% were produced by varying the gel concentration. The method appea rs 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 an d a tank filled with 0.2% saline. Polythene or polyacrylamide rods of varying resistivities, 10% of the tank diameter wide, were placed in o ne of three positions. The magnitude of the impedance increase in Err images varied linearly with the actual impedance change in the rods fo r increases up to 20%, but the blurring in images was similar when pol ythene rods were used. This suggests that the use of highly resistive test objects gives a reasonable indication of the blurring in Err imag es acquired with the system used, but measurement of the magnitude of the impedance change is more likely to be accurate for changes of a fe w tens of per cent.