Design, Development and Comparison of two Different Measurements Devices for Time-Resolved Determination of Phase Shifts of Bioimpedances

Abstract: Bioimpedance measurements are a non-invasive method to determine the composition of organic tissue. For measuring the complex bioimpedance between two electrodes, an alternating current with a constant amplitude is injected into the tissue. The developed voltage drop is used to calculate the real and imaginary part of the impedance under test. Measurements in the past indicated that it could be possible that the beating of the heart has an effect on the measured phase shift of the impedance under test. In this work a hardware system is developed, capable of measuring changes of the bioimpedance phase shift with high resolution. Two different measurement methods are used. The first method is an analog circuit, which has been developed in a previous project. The other method uses the integrated circuit AFE4300 (Texas Instruments) [1]. The results of both methods are transmitted with a microcontroller (Xmega256A3BU from Atmel Corp.) via the USB interface to a host PC. On the host PC the visualization of the measurements and the control of the embedded system is achieved with a developed LabView program. The work includes the development of the hardware and software, as well as a comparison of the accuracy of the two measurement methods. The result of a verification of the systems is that both measurement methods have an effective resolution of about 0.3{\deg}.