Development of an impedance spectrometer for tissue ischemia monitoring: instrument realization and performance

Ischemia induces a series of biochemical changes in a tissue. Some of these changes also cause variations in tissue resistivity. To non-invasively measure tissue ischemia, the correlation between ischemia levels and tissue resistivity is investigated. A specially designed impedance spectrometer is necessary for this project. The objective of this research is the realization of such an instrument which will work in a wide frequency range and with variable current and voltage amplitudes. The system uses the four electrode impedance measurement method, and is based on synchronous sampling demodulation with one analog channel. Preliminary testing of the instrument produced a voltage measurement accuracy of ⩽±0.4% for amplitude and ⩽±0.2° for phase