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Electrical Bioimpedance Measurement

Related products: MFIA, MFLI, MF-IA, MF-MD, HF2LI, HF2TA, HF2LI-MF

Application Description

The measurement of electrical bioimpedance is a non-invasive detection approach similar to microfluidic cell detection, although it focuses on tissue rather than on individual cells. The technique is widely used for medical purposes, and is complementary to physicochemical and biochemical methods. Applications include bioelectrical impedance analysis (BIA), electrocardiography (ECG), electrical impedance tomography (EIT), and electrical impedance myography (EIM). In these applications, a weak AC voltage or current signal is applied to the body tissue, which comprises resistive body water and capacitive cell membrane. The resulting current or voltage signal is measured with a phase-sensitive technique to quantify the complex electrical impedance of the tissue.

Measurement Strategies

An LCR meter is often used to measure bioimpedance at one or several fixed frequencies typically ranging between 10 Hz and 100 kHz, but no equivalent circuit model can be confirmed based on such a limited dataset. This range of frequencies is also insufficient to capture the full picture of the tissue's impedance, and it is neither suitable for penetrating the cell membrane (which requires frequencies above 1 MHz) nor to distinguish low-frequency signals from heartbeats or breathing (on the order of 1 Hz or below).

The MFIA Impedance Analyzer and the HF2LI Lock-in Amplifier give access to broad frequency ranges going from 1 mHz to 5 MHz and 50 MHz, respectively, and offer both 2-terminal and 4-terminal configurations (also known as 2-wire or 4-wire configurations). In particular, the advantage of the 4-terminal arrangement (see Figure 1) is to mitigate the effect of the contact resistance between the electrodes and the tissue. If the contact resistance itself is the parameter of interest, it can be determined by measuring in 2-terminal and 4-terminal configurations sequentially. In addition to frequency-domain sweeps of impedance and related parameters (see Figure 2), time-domain measurements make it possible to study the time evolution of impedance, as in the case of a fast change in a neuron network or a small change due to a subtle muscle movement (as shown in Figure 3).

Electrical bioimpedance measurement setup with the Zurich Instruments MFIA

Figure 1. Sketch showing a 4-wire impedance measurement on a tissue sample using the MFIA Impedance Analyzer. The high-frequency, high-capacitive path is represented in orange, whereas the low-frequency resistive path is shown in blue.

Frequency-dependent impedance measurement with the MFIA

Figure 2. LabOne Sweeper module showing the frequency-dependent impedance measured on a human forearm. The impedance amplitude (red), phase (blue) and RMS current (green) are plotted over a logarithmic frequency axis. The vertical axis displays the phase.

Small impedance and phase changes captured with the LabOne Plotter module

Figure 3. LabOne Plotter module showing small impedance and phase changes (1.5 Ohm and 1.5 deg) caused by a fist clench movement, which recovers after releasing to the resting state.

The Benefits of Choosing Zurich Instruments

  • Determine your equivalent circuit model thanks to impedance sweeps over a wide frequency range including the low-frequency regime.
  • Tracking fast impedance and phase changes with high precision and at high speed only requires the LabOne Plotter or Data Acquisition modules – no external digitizer card is needed.
  • Save time by performing more measurements in parallel: probing the frequency-dependent impedance at multiple frequencies simultaneously is possible with the MF-MD or HF2LI-MF options.
  • Workflow automation becomes straightforward thanks to the included LabOne APIs for Python, C, MATLAB®, LabVIEW™ and .NET.

 

Please note: The MFIA is suitable for laboratory research use only and should not be used for diagnostic procedures.

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Videos

MFIA Impedance Analyzer Overview
What makes a great Impedance Analyzer?

Publications

Chen, L. et al.

Textile-Based Capacitive Sensor for Physical Rehabilitation via Surface Topological Modification

ACS Nano 14, 8191–8201 (2020)

Schuelke, C. et al.

Bioimpedance and Electrochemistry for Neural Stem Cell Characterization and Detection of Dopamine Release

41st Annual International Conference of the IEEE Engineering in Medicine and Biology Society (2019)

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