Tissue ischemia monitoring using impedance spectroscopy: selection of optimal electrodes for clinical studies

The objective of this research is to develop a methodology and means for testing and identifying the optimal non-invasive electrodes for clinical impedance spectroscopic measurements from human subjects in a frequency range from 10 Hz to 1 MHz. Many electrodes are available on the market for clinical applications, ranging from ECG to TENS electrodes. These electrodes must function only within specific, relatively narrow frequency ranges. When used for wide-band impedance spectroscopic measurements, they significantly reduce the usable bandwidth of the system. Unfortunately, most manufacturers do not test their electrodes to determine their performances over a wide range of frequencies such as would be required for impedance spectroscopy. Due to the lack of data about electrode performance, we had to develop a testing protocol to determine the characteristics of various non-invasive electrodes throughout the frequency range of interest. The most important measurement characteristics is the recording accuracy of the electrodes. The instrument that we used to conduct the research is a custom-made impedance spectrometer that interfaces to a laptop computer. The main hypotheses of the project are that a testing protocol can be developed and optimal non-invasive electrodes can be identified for use in clinical measurements of tissue impedance throughout a range of frequencies, while maintaining good signal-to-noise ratio. Preliminary results support the principal hypotheses