From early on we learnt that a dielectric is an insulator, and a practical way to measure it was to place it between two capacitor plates. The plates were dry and so was the dielectric – the resistance between the plates was very high. With living tissue it was quite different, the material was not dry and the capacitor plates had wet contact with the tissue. At the wet plates polarization impedance appeared constituting an important source of error. The discipline of bioimpedance had one problem more than the discipline of dielectrics. Even so it became more
Electrical impedance spectroscopy is a widely used tool for characterization the structure of tissues and cell cultures [ 1 ]. In the cases where the properties of objects are changing in time (e.g., heart muscle) or the objects are moving as cells in a microfluidic channel, the coverage of the frequency range of interest within a short timeframe demands to satisfy the criteria of the linear time-invariant (LTI) system. If the properties of a sample under test (SUT) are changing significantly during a measurement timeframe, the corresponding
Farhad Abtahi, Fernando Seoane and Kaj Lindecrantz
monitoring [ 5 , 6 ] and even the monitoring of cell growth [ 7 , 8 , 9 ].
In the assessment of tissue state or body composition, the EBIS signal is considered to be time-invariant and hence any dynamic changes are essentially ignored and instead treated as noise or interference. This interference can then be removed, or rather reduced, through the averaging, i.e. lowpass filtering, of the impedance signal. In many cases this works sufficiently well. However, there are situations when the frequency of the interference is higher than half the rate at which the impedance
Jakob Orschulik, Diana Pokee, Tobias Menden, Steffen Leonhardt and Marian Walter
not related to either human or animals use.
Focusing of Tetrapolar Impedance Measurements
In bioimpedance measurements, a tetrapolar electrode setup is typically used to measure an electrical impedance. In this setup, two electrodes are used to inject a small, alternating current into the body while two separate electrodes are measuring the resulting voltage drop across those electrodes. In contrast to impedance-based imaging techniques such as Electrical Impedance Tomography, where multiple measurements are performed at different electrode locations, single
pneumography (MIP). In MIP, the data are acquired by successively exciting each coil in order to induce an eddy-current density within the dorsal tissues and measuring the corresponding response magnetic field strength by the remaining coils. The recorded set of data is then used to reconstruct the internal conductivity distribution by means of algorithms that minimize the residual norm of the difference between the estimated and measured data [ 9 ]. Regularization methods are typically applied to stabilize the image reconstruction process [ 10 ].
To simulate the