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 10Hz to 1MHz. Many electrodes are available on the market for clinical applications, ranging from ECG to TENs electrodes. However, 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 "off the shelf" non-invasive electrodes throughout the frequency range of interest. The most important parameter 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 "off the shelf" non-invasive electrodes can be identified that can be utilized for clinical measurements of tissue impedance throughout a range of frequencies, while maintaining good signal to noise ratio. We conducted experiments on two human subjects using nine different types of electrodes and determined the average percent noise for each electrode for thirty frequencies ranging from 10Hz to 1MHz. We then determined the average percent noise in the range of 1KHz to 100KHz, to establish a baseline noise level for each electrode, and the bandwidth for each electrode, defined as the range of frequencies where the average noise was less than 5 percent. Based on this analysis we were able to determine that the Blue Sensor Q-00-A electrode is the optimal electrode for use in clinical studies.
Worcester Polytechnic Institute
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