Imaging, Electrical Impedance Tomography

See also an application of electrical impedance tomography (EIT) in Section 10.7. 

A mapping of the immittance distribution in a tissue layer (tomography) is possible with an electrode system of multiple skin surface electrodes. In EIT, a current (about 1 mA) is typically injected in one electrode pair and the voltages between other electrodes are recorded (Resell et al., 1988b Bayford and Tizzard, 2012). Current injection is then successively shifted so that all electrode pairs are used. The reciprocal theorem can serve as a control of system linearity. A frequency on the order of 50 kHz is conunonly used, so a complete set of measurements with, for example, around 50 electrodes can be performed in less than 0.1 s. The images obtained have a resolution of about 1 cm at 10 cm tissue depth. 

In principle, the method of mapping tissue immittance distribution is not limited to a slice. By increasing the number of electrodes, volume acquisition is equally possible. One of the potential benefits from 3D BIT is that it could take into account that the current spreads out of the imaging plane of 2D BIT. However, the complexity of both the BIT hardware and software will increase considerably by introducing this third dimension. Some important achievements in the pursuit of 3D BIT were, for example, presented in Nature in 1996 (Metherall et al., 1996). 

As explained in Section 6.4.5, the sensitivity of the measurement to a given local change in admittivity is given by the dot product of the current density vectors resulting from injecting current through the two pairs of current and potential electrodes, respectively. 

The sensitivity may be highest close to the current injecting or potential PU electrodes and lowest toward the center of the medium, depending on the size of the electrodes and the distance between them. 

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Abdullah, M. Z., Electrical impedance tomography for imaging conducting mixtures in hydrocyclone separators. PhD Thesis, UMIST (1993). 

Because of the changes in the cell membrane resistance during electroporation, the technique can be controlled and monitored with electrical impedance tomography, a realtime imaging method that maps the electrical impedance distribution inside the tissue (Davalos et al., 2004). Ivorra et al. concluded in (Ivorra and Rubinsky, 2(X)7) that... 

Davalos, R.V., Otten, D.M., Mir, L.M., Rubinsky, B., 2004. Electrical impedance tomography for imaging tissue electroporation. IEEE Trans. Biomed. Eng. 51, 761—767. 

Holder, D.S., 1992. Detection of cortical spreading depression in anesthetised rat by impedance measurement with scalp electrodes — implications for noninvasive imaging in the brain with electrical impedance tomography. Clin. Phys. Physiol. Meas. 13 (1), 77—86. 

Oh, T., Gilad, O., Ghosh, A., Schuettler, M., Holder, D.S., 2011. A novel method for recording neuronal depolarization with recording at 125—825 Hz implications for imaging fast neural activity in the brain with electrical impedance tomography. Med. Biol. Eng. Comput. 49, 593—604. 

Riu, R, RoseU, J., Lozano, A., PaUas-Areny, R., 1995. Multifiequency static imaging in electrical impedance tomography. Part 1 Instrumentation Requirements. Med. Biol. Eng. Comput. 33, 784—792. 

Scaife, J.M., Tozer, R.C., Freestone, I.L., 1994. Conductivity and permittivity images from an induced current electrical impedance tomography system. lEE Proc. Sci. Meas. Technol. 141 (5), 356—362. 

Advanced measuring techniques With the advent of sophisticated imaging and velocimetry techniques, better understanding of the flow behavior and consequently a better prediction of regime transition is possible. The techniques used in the literature are listed below with the corresponding references. Readers interested in a specific technique may refer to these references Electrical capacitance tomography (ECT) (Bennett et al. 1999 Tapp et al. 2003) Electrical impedance tomography (EIT) (Tapp et al. 2003)... 

Bera T. K. and Nagaraju J., Resistivity imaging of a reconfigurable phantom with circular inhomogeneities in 2D-electrical impedance tomography. Measurement, vol. 44, no. 3, pp. 518-526, doi 10.1016/j.measurement.2010.11.015, March 2011. 

Breckon W. R., Image Reconstruction in Electrical Impedance Tomography, PhD Thesis, Oxford Polytechnic, 1990. 

Bera T. K., Biswas S. K., Rajan K., and Nagaraju J., Improving image quality in electrical impedance tomography (EIT) using projection error propagation-based regularization (PEPR) technique A simulation study,. Elec. Bioimpedance, vol. 2, pp. 2-12, doi 10.5617/jeb.l58, 2011. 

Thomas D. C., Siddall-Allum J. N., Sutherland I. A., and Beard R. W., Correction of the non-uniform spatial sensitivity of electrical impedance tomography images. Physiol. Meas., vol. 15, pp. A147-A152, 1994. 

Bera T. K. and Nagaraju J., A gold sensors array for imaging the real tissue phantom in electrical impedance tomography. International Conference on Materials Science and Engineering 2012 (ICMST 2012), Kerala, India, 2012. 

Tarleton E.S. and Hancock D.L., 1996. The imaging of filter cakes through electrical impedance tomography, Filtr. Sep., 33, 491-494. 

Electrical Impedance Tomography (EIT) techniques elaborate two dimension images from average spatial distribution of resistivity within a three-dimensional structure. 

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