Electrode Circuits for Frequency- and Code-Division Multiplexed Impedance Tomography

Traditional impedance tomography measurement systems make sequential four-terminal impedance measurements. Potentially faster frequency- and code-division multiplexed impedance measurement systems require that simultaneous current injection and voltage measurement take place at all terminals, making four-terminal measurements difficult. We describe an electrode interface circuit that simultaneously implements balanced current injection, and current and potential measurement, allowing four-terminal measurements on sets of multiple electrodes using these faster techniques. Circuit results show that accurate simultaneous four-terminal measurements are possible, thereby enabling faster impedance tomography systems.