Four electrode measurement (4EM) systems have been used to measure conductivity in tissue where electrode polarization would cause unacceptable inaccuracy in measurement results and where directional measurement of conductivity is required Less polarization than a two-electrode measurement system where the current is applied by the same electrodes that measures the potential and directional measurement as opposed to a coaxial measurement system that measures bulk conductivity but gives no information about direction. ( 1 , 2 , 3) . The system
Martina Sammer, Bob Laarhoven, Ernest Mejias, Doekle Yntema, Elmar C. Fuchs, Gert Holler, Georg Brasseur and Ernst Lankmayr
as a static capacitor. The dielectric properties of biological cells and their different components (cell wall, membranes and cytoplasm) were summarized by Markx and Davey [ 4 ]. Over the last couple of decades a lot of research was done on the impedance of cell suspensions, in which a relationship between capacitance and viable cell number was reported [ 5 , 6 , 7 , 8 ]. Fehrenbach et al. [ 5 ] used online capacitive measurements for biomass estimation of Saccaromyces cerevisiae , Pitchia pastoris and Streptomyces virginiae in suspension culture. In their
the tissue engineered constructs. However, these methods such as histology staining, are destructive and time-consuming and require fixing and cutting the tissue cultures ( 6 ).
Therefore, there is a need for real-time and noninvasive monitoring techniques to evaluate the quality of the tissue engineered constructs before implanting them in the body, without the need to use fluorescents or radioactive labels or destructive methods. This in addition, would reduce the number of animals required for this purpose ( 5 , 6 ).
Piotr Ulkowski, Wojciech Bulski and Barbara Gwiazdowska
Reports Series, Vienna, 2000; No TRS 398.
IAEA. Calibration of reference dosimeters for external beam radiotherapy. Technical Reports Series, Vienna, 2009; No TRS 469.
IAEA. Dosimetry in diagnostic radiology. An international code of practice. Technical Reports Series, Vienna, 2007; No TRS 457.
ISO/IEC/OIML/BIPM, Guide to the expression of uncertainty in measurements. 1995.
Ørjan G.Martinsen, Oliver Pabst, Christian Tronstad and Sverre Grimnes
Skin conductance measurements have been used in psychophysiology for more than a century. Measurements of galvanic skin response (GSR) (also referred to by the more general term electrodermal activity (EDA)) have been reported as early as the last part of the nineteenth century (see [ 1 ] for an overview). Through many decades, the method of using direct current (DC) measurements of skin conductance with a constant applied voltage has dominated the EDA literature [ 2 ].
However, there are potential complications with the DC method, such as
The stray capacitance between the human body and earth ground can play a significant role in bioimpedance measurement systems where it may yield, for example, apparent inductive components not associated to any magnetic phenomena [ 1 , 2 ]. It is also an intervening factor in the assessment of human body impedance for risk analysis in case of electric contacts [ 3 ] or electromagnetic radiation [ 4 ] and in electrostatic discharge studies [ 5 ], and has strong influence in power-line interference in biopotential measurements [ 6 , 7 , 8
Impedance spectroscopy measurements of electrolytes are frequently difficult to perform due to a thin charged layer (double layer) that forms between the electrode and the media [ 1 , 2 ]. The double layer is a result of charge redistribution close to the electrode that results in a very thin layer of high capacitance disturbing the impedance measurements of the media (particularly at low frequencies). We have investigated the possibility of eliminating the double layer effect by constructing a measurement cell capable of varying the distance
Ørjan G. Martinsen, Håvard Kalvøy, Dindar S. Bari and Christian Tronstad
Electrodermal activity (EDA) has been studied for many decades and is typically measured as either skin conductance (at DC or low frequency AC) or skin potential [ 1 , 2 ]. Both parameters are sometimes measured and compared, but this has usually been done simultaneously contra-lateral ( 3 ) or in sequence ( 4 ).
In 2011, we described a set-up for simultaneous measurements of the two parameters with a constant current source and a two-electrode system where one of the electrodes were very large to enable quasi-monopolar measurements on the
 Verdun FR, Racine D, Ott JG, et al. Image quality in CT: From physical measurements to model observers. Phys Med. 2015;31(8):823-843.
 International Atomic Energy Agency. Status of computed tomography: Dosimetry for wide cone beam scanners. IAEA-Human Health Reports No 5. 2011.
 Kalender WA, Seissler W, Klotz E, Vock P. Spiral volumetric CT with single-breath-hold technique, continuous transport, and continuous scanner rotation. Radiology. 1990;176(1):181-183.
 McCollough CH, Zink FE. Performance evaluation of a
Martina F. Callaghan, Torben Lund, Ivan M. Roitt and Richard H. Bayford
Accuracy and precision are paramount in bioimpedance measurements ( 1 ). Electrode polarisation effects arise at electrode surfaces due to the transition between electronic and ionic current flow. In the case of a two-electrode impedance measurement, these effects are superimposed on the actual impedance of the material being investigated. Schwan proposed the tetrapolar approach as a means of removing electrode polarisation effects ( 2 ). However, this approach is not devoid of measurement error. Residual electrode polarisation effects are one