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Proceedings ArticleDOI

Bipolar current injection methods for electrical impedance tomography: a comparative study

13 Mar 2017-Proceedings of SPIE (International Society for Optics and Photonics)-Vol. 10137, pp 1013718

TL;DR: Based on the simulation studies and experimental validations, cross method is found to be the optimal current injection method to attain better data acquisition and image reconstruction.
Abstract: A comparative study of different bipolar current injection methods viz. Adjacent method, Cross method and Opposite method used in Electrical Impedance Tomography(EIT) is reported in this paper. Different electrode configurations are considered for current injection and voltage measurement to identify the one which yields better signal strength. Sensitivity of different current injection methods to inhomogeneity at different locations is examined. The effect of conductivity contrast on boundary voltages is studied by varying the conductivity of the inhomogeneity from 0.01mS/cm to 9.1mS/cm. Ill-posedness of the inverse problem is analyzed in terms of condition number for the aforementioned methods. Reconstruction of two closely placed inhomogeneities is done using Levenberg Marquardt method for different current injection methods to compare the resolution and corresponding error voltage is determined. Experiments are conducted using agar phantoms to validate some of the results obtained from the simulations. Based on the simulation studies and experimental validations, cross method is found to be the optimal current injection method to attain better data acquisition and image reconstruction.
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Book ChapterDOI
28 Dec 1999-

27 citations


Journal ArticleDOI
Lin Yang1, Chao Zhang, Wenbo Liu1, Hang Wang1  +6 moreInstitutions (1)
TL;DR: Electrical impedance tomography (EIT) was able to sensitively detect hemothorax as small as 10 ml in volume, as well as its location, and demonstrated that EIT has a unique potential for early diagnosis and continuous monitoring of hemothsorax in clinical practice.
Abstract: Hemothorax is a serious medical condition that can be life-threatening if left untreated. Early diagnosis and timely treatment are of great importance to produce favorable outcome. Although currently available diagnostic techniques, e.g., chest radiography, ultrasonography, and CT, can accurately detect hemothorax, delayed hemothorax cannot be identified early because these examinations are often performed on patients until noticeable symptoms manifest. Therefore, for early detection of delayed hemothorax, real-time monitoring by means of a portable and noninvasive imaging technique is needed. In this study, we employed electrical impedance tomography (EIT) to detect the onset of hemothorax in real time on eight piglet hemothorax models. The models were established by injection of 60 ml fresh autologous blood into the pleural cavity, and the subsequent development of hemothorax was monitored continuously. The results showed that EIT was able to sensitively detect hemothorax as small as 10 ml in volume, as well as its location. Also, the development of hemothorax over a range of 10 ml up to 60 ml was well monitored in real time, with a favorable linear relationship between the impedance change in EIT images and the volume of blood injected. These findings demonstrated that EIT has a unique potential for early diagnosis and continuous monitoring of hemothorax in clinical practice, providing medical staff valuable information for prompt identification and treatment of delayed hemothorax.

3 citations


Cites methods from "Bipolar current injection methods f..."

  • ...To increase the sensitivity to changes in impedance caused by central lung regions and maintain a good signal-to-noise ratio, the protocol of opposite excitation-adjacent measurement protocol was adopted in EIT data acquisition [38]....

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References
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Book ChapterDOI

[...]

01 Jan 2012-

123,310 citations


"Bipolar current injection methods f..." refers background in this paper

  • ...Table 2: Independent measurements for different current injection and voltage measurement methods (3,4), (4,5), (5,6), (6,7), (7,8), (8,10), (10,11)....

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  • ...Voltages are measured across electrode pairs in the order (3,4), (4,5),..(8,9), (9,11), (11,12)....

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  • ...If electrode pair (1,9) are the current electrodes, electrode 10 is chosen as fixed voltage measurement electrode and voltages are measured across (10,2), (10,3)...(10,8), (10,11),....

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Journal ArticleDOI
TL;DR: Any improvement in spatial resolution can only be made at the expense of speed and sensitivity which may well be the more important factors in determining the clinical utility of APT.
Abstract: Because of the intrinsically low sensitivity of any surface potential measurement to resistivity changes within a volume conductor, any data collection system for impedance imaging must be sensitive to changes in the peripheral potential profile of the order of 0.1%. For example, whilst the resistivity changes associated with lung ventilation and the movement of blood during the cardiac cycle range from 3 to 100% the changes recorded at the surface are very much less than this. The Sheffield data collection system uses 16 electrodes which are addressed through 4 multiplexers. Overall system accuracy is largely determined by the front-end equivalent circuit which is considered in some detail. This equivalent circuit must take into account wiring and multiplexer capacitances. A current drive of 5 mA p-p at 5 kHz is multiplexed to adjacent pairs of electrodes and peripheral potential profiles are recorded by serially stepping around adjacent electrode pairs. The existing Sheffield system collects the 208 data points for one image in 79 ms and offers 10 image data sets per second to the microprocessor. For a homogeneous circular conductor the ratio of the maximum to minimum signals within each peripheral potential profile is 45:1. The temptation to increase the number of electrodes in order to improve resolution is great and an achievable performance for 128 electrodes is given. However, any improvement in spatial resolution can only be made at the expense of speed and sensitivity which may well be the more important factors in determining the clinical utility of APT.

380 citations


Reference EntryDOI
14 Apr 2006-
Abstract: 1. INTRODUCTIONThe electrical properties of biological tissues and cell sus-pensions have been of interest for over a century for manyreasons. They determine the pathways of current flowthrough the body and, thus, are very important in theanalysis of a wide range of biomedical applications such asfunctional electrical stimulation and the diagnosis andtreatment of various physiological conditions with weakelectric currents, radio-frequency hyperthermia, electro-cardiography, and body composition. On a more funda-mental level, knowledge of these electrical properties canlead to an understanding of the underlying basic biologicalprocesses. Indeed, biological impedance studies have longbeen important in electrophysiology and biophysics; one ofthe first demonstrations of the existence of the cell mem-brane was based on dielectric studies on cell suspensions(1).To analyze the response of a tissue to electric stimula-tion, we need data on the specific conductivities and rel-ative permittivities of the tissues or organs. A microscopicdescription of the response is complicated by the variety ofcell shapes and their distribution inside the tissue as wellas the different properties of the extracellular media.Therefore, a macroscopic approach is most often used tocharacterize field distributions in biological systems.Moreover, even on a macroscopic level, the electrical prop-erties are complicated. They can depend on the tissue ori-entation relative to the applied field (directionalanisotropy), the frequency of the applied field (the tissueis neither a perfect dielectric nor a perfect conductor), orthey can be time- and space-dependent (e.g., changes intissue conductivity during electropermeabilization).2. BIOLOGICAL MATERIALS IN AN ELECTRIC FIELDThe electrical properties of any material, including bio-logical tissue, can be broadly separated into two catego-ries: conducting and insulating. In a conductor, theelectric charges move freely in response to the applicationof an electric field, whereas in an insulator (dielectric), thecharges are fixed and not free to move. A more detaileddiscussion of the fundamental processes underlying theelectrical properties of tissue can be found in Foster andSchwan (2).If a conductor is placed in an electric field, charges willmove within the conductor until the interior field is zero.In the case of an insulator, no free charges exist, so netmigration of charge does not occur. In polar materials,however, the positive and negative charge centers in themolecules do not coincide. An electric dipole moment, p,issaid to exist. An applied field, E

310 citations


Journal ArticleDOI
Abstract: Biomedical applications of electrical impedance tomography: a critical review, D.S. Holder and B.H. Brown review of EIT systems available for medical use, Brian Brown an overview of image reconstruction, D.C. Barber in-vivo impedance images using sinusoidal current patterns, J.C. Newell, D. Isaacson, M. Cheney.

92 citations


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No. of citations received by the Paper in previous years
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20201
20181
19991