An instrumentation amplifier as a front-end for a four-electrode bioimpedance measurement

Abstract

The performance of a monolithic instrumentation amplifier used as an interface for a four-electrode bioimpedance measurement is examined with a commercially available impedance meter based on an auto-balancing bridge. The errors due to particularities in the input stage of the impedance meter, when used without a front-end, were several orders of magnitude higher than the measured quantity. The analysis was performed on an electrical circuit model of the skin and electrodes over a frequency range of 20 Hz to 1 MHz. The achieved accuracy with balanced electrode impedances for the frequencies up to 100 kHz can be below 0.2% for impedance magnitude and 0.1 degrees for impedance phase, which is within the specified basic accuracy range of the LCR-meter used for the measurements. At frequencies above 100 kHz the errors are increasing and are higher than the LCR-meter's basic accuracy. This study indicates that use of an instrumentation amplifier as a front-end with the particular LCR-meter can significantly improve the measurement accuracy of the four-electrode bioimpedance measurement at low frequencies.

The application of bioimpedance in the detection and evaluation of gastric motility for erosive gastritis patients

“…In the extraction of gastric motility parameter, we are interested in the key parameters of gastric motility mainly from the rhythm of the signal analysis instead of signal amplitude as in [9]- [10].…”

“…For the peak power lower than 2 CPM, we call it gastric bradygastria, if the peak power is higher than 4 CPM, we call it gastric tachygastria. The power instability coefficient SD Freq and the frequency instability coefficient IC Freq in fact reflect frequency stability of signal and its stable degree of dominant frequency per minute as in [9]. The formula is as in.…”

Circuit Architecture for Electrical Impedance Spectroscopy Instrumentation to Address Electrode Impedance Mismatch in Clinical Devices

“…A simplified Cole-Cole circuit, as illustrated in Figure 1.b, is commonly used [14] to model the system element behaviour and we have used it for both electrodes and Zx. Many researchers [6][10] [27] analyse the effect of the electrode impedances; however, their modelling assumes that the electrode impedances are balanced, i.e. are the same for all electrodes and this paper will concentrate on the effects of mismatch in electrode impedances.…”

“…4 R2 and R5)  Buffered electrode potentials are available for other physiological measurements such as EEG, EMG, ECG etc. Tozer [29] described active electrodes to increase the electrode input impedance for magnetic induced impedance imaging systems and they have also been employed for EIT systems [27] [31]. For current driven systems the current source is usually implemented centrally and hence the current source output will be shunted by the cabling capacitance.…”

A Comparison of Front-End Amplifiers for Tetrapolar Bioimpedance Measurements

“…1(b) by the addition of the four Z e impedances at the terminals of Z x , assuming for simplicity that all four are equal. If the H cur and L cur terminals are used to connect to the current injection electrodes and H pot and L pot are used to connect to the voltage measurement electrodes of a tetrapolar electrode system to measure the potential across Z x , then L cur and L pot terminals will no longer be at the same potential due to the large Z e s. This leads to large measurement errors [4], [11], [18], [22]. In addition, the open/short/load compensation procedure typically performed applies only to bipolar measurements.…”