Electrical Impedance Computed Tomography Based on a Finite Element Model
TL;DR: It is shown that the conductivity distribution in the field can be estimated from the impedance data obtained for the body surface leads and the finite element model must be chosen properly to provide the unique solution.
Abstract: A simulation study of electrical impedance computed tomography is presented. This is an inverse problem. A field is discretized by the finite element method and an iterative approach derived from the sensitivity theorem is examined for leads taken on the field surface. It is shown that the conductivity distribution in the field can be estimated from the impedance data obtained for the body surface leads. Simulation suggests the availability and the limitation for impedance plethysmography application. The finite element model must be chosen properly to provide the unique solution.
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TL;DR: A survey of the work in electrical impedance tomography can be found in this article, where the authors survey some of the most important works in the field. Butt.t.
Abstract: t. This paper surveys some of the work our group has done in electrical impedance tomography.
1,726 citations
TL;DR: An improved electrical impedance tomographic reconstruction algorithm is presented that is generally guaranteed to converge and provides significantly better reconstructions than any of the other methods.
Abstract: An improved electrical impedance tomographic reconstruction algorithm is presented that is generally guaranteed to converge. The algorithm is attractive for several reasons. A modified Newton?Raphson method varies a finite-element model of resistivities to fit a set of voltage measurements in a least-squared sense. Two procedures for calculating the Jacobian matrix are derived. One is standard, while the other is based on the compensation theorem. This second procedure is more efficient for computations, and just as accurate as the standard one. The inherent ill-conditioning in the approximate Hessian matrix of the linearized system is eliminated using the Marquardt method. Results from two-dimensional computer simulations are compared to four other reconstruction algorithms, which are based on methods proposed by other authors. The modified Newton?Raphson method provided significantly better reconstructions than any of the other methods. The algorithms compared are the perturbation, equipotential, iterative-equipotential, and the double-constraint methods. The modified Newton?Raphson method was found to be sensitive to measurement error, but future work in designing electrode-probing configurations is expected to reduce this sensitivity.
608 citations
TL;DR: Criteria for the distinguishability of two different conductivity distributions inside a body by electric current computed tomography (ECCT) systems with a specified precision are given.
Abstract: We give criteria for the distinguishability of two different conductivity distributions inside a body by electric current computed tomography (ECCT) systems with a specified precision. It is shown in a special case how these criteria can be used to determine the measurement precision needed to distinguish between two different conductivity distributions. It is also shown how to select the patterns of current to apply to the body in order to best distinguish given conductivity distributions with an ECCT system of finite precision.
443 citations
Cites background from "Electrical Impedance Computed Tomog..."
...T HEproblem ofreconstructing theconductivity inside a bodyfromlow-frequency measurements on the body's surface hasbeendiscussed in[1]-[ 10 ], [13]-[20]....
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...Descriptions ofattempts tosolve this inverse problem arein[1]-[ 10 ], [13]-[20]....
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28 Dec 2001
TL;DR: This article focuses on the type of EIT called adaptive current tomography (ACT) in which currents are applied simultaneously to all the electrodes, where a number of current patterns are applied, where each pattern defines the current for each electrode, and the subsequent electrode voltages are measured to generate the data required for image reconstruction.
Abstract: Methods and apparatus for obtaining a representation of the distribution of electrical impedance within a multiphase flow with an electrically continuous or discontinuous principle flow (3) contained within an electrically conductive solid ring electrode (1), comprising providing a plurality of mutually spaced electrical contacts (2) mounted at the outside wall of the ring and electrically contacted with the ring, applying currents or voltages (4) to the ring from the electrical contacts (2), generating a more homogeneous electric field distribution within the material (3), measuring voltage or current (5) distribution along the ring from other electrical contacts (2), relatively intensifying the imaging sensitivity at the central area of the sensing domain using a π/2 angle sensing strategy and reconstructing the representation of the impedance distribution using CG method with an error processing strategy.
227 citations
TL;DR: Findings suggest that widespread use of AEDs will require only modest training, and the difference between the groups is surprisingly small, considering the naïveté of the children as untutored first-time users.
Abstract: Background—Survival after out-of-hospital cardiac arrest (OHCA) is strongly influenced by time to defibrillation. Wider availability of automated external defibrillators (AEDs) may decrease response times but only with increased lay use. Consequently, this study endeavored to improve our understanding of AED use in naive users by measuring times to shock and appropriateness of pad location. We chose sixth-grade students to simulate an extreme circumstance of unfamiliarity with the problem of OHCA and defibrillation. The children’s AED use was then compared with that of professionals. Methods and Results—With the use of a mock cardiac arrest scenario, AED use by 15 children was compared with that of 22 emergency medical technicians (EMTs) or paramedics. The primary end point was time from entry onto the cardiac arrest scene to delivery of the shock into simulated ventricular fibrillation. The secondary end point was appropriateness of pad placement. All subject performances were videotaped to assess safety...
225 citations
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TL;DR: In this article, a new estimate minimum information theoretical criterion estimate (MAICE) is introduced for the purpose of statistical identification, which is free from the ambiguities inherent in the application of conventional hypothesis testing procedure.
Abstract: The history of the development of statistical hypothesis testing in time series analysis is reviewed briefly and it is pointed out that the hypothesis testing procedure is not adequately defined as the procedure for statistical model identification. The classical maximum likelihood estimation procedure is reviewed and a new estimate minimum information theoretical criterion (AIC) estimate (MAICE) which is designed for the purpose of statistical identification is introduced. When there are several competing models the MAICE is defined by the model and the maximum likelihood estimates of the parameters which give the minimum of AIC defined by AIC = (-2)log-(maximum likelihood) + 2(number of independently adjusted parameters within the model). MAICE provides a versatile procedure for statistical model identification which is free from the ambiguities inherent in the application of conventional hypothesis testing procedure. The practical utility of MAICE in time series analysis is demonstrated with some numerical examples.
47,133 citations
TL;DR: The change in mutual impedance ?
Abstract: The change in mutual impedance ?Z resulting from a change ?g in the conductivity of a particular region of a volume conductor is shown to be given by ?Z = - ?g?Lt?·L? dv. L? and L? are the lead fields associated with the two ports used to measure ?Z. The integration is over the region where the conductivity has changed. The superscript t indicates that the lead field is to be evaluated following the change in conductivity. An example involving a spherical conductor is provided.
500 citations
TL;DR: A vector relationship similar to Green's theorem incorporating simplifications which can be made for impedance plethysmography is derived and Geselowitz's lead theory result is rederived.
Abstract: A vector relationship similar to Green's theorem incorporating simplifications which can be made for impedance plethysmography is derived. The mathematics involved are simplified by the use of current density instead of electric field. Geselowitz's lead theory result [1] is rederived and a limitation of such proofs is discussed.
111 citations
TL;DR: In this paper, the results of the initial studies of CT imaging are presented, and preliminary computer simulations are described and discussed, with the following advantages: (1) reduced biological hazard, (2) less expensive hardware, (3) easily extended to full 3D image, (4) very high data rates, and ability to make unique physiological measurements.
Abstract: The results of our initial studies of a new method of CT imaging are presented. The technique does not use x rays, but rather employs a weak electrical current to map out the electrical properties of the tissues in a tomographic slice. Results of preliminary computer simulations are described and discussed. Compared to x-ray CT, we expect ICT to have the following advantages: (1) reduced biological hazard, (2) less expensive hardware, (3) easily extended to full 3-D image, (4) very high data rates, (5) ability to make unique physiological measurements.
57 citations
TL;DR: The problem of reconstructing a two-dimensional distribution of electrical conductivity from impedance measurements made on the circumference of a circle enclosing the distribution is studied and it is indicated how ambiguities might be resolved by making extensive sets of measurements.
Abstract: The problem of reconstructing a two-dimensional distribution of electrical conductivity from impedance measurements made on the circumference of a circle enclosing the distribution is studied. It is shown to be, in general, impossible to uniquely reconstruct such conductivity distributions when employing certain recently proposed approaches based on the concept of computed tomography which is so successful when X-rays are used. The trouble is that the current stream-lines cannot usually be forced to be straight and paralel. It is indicated how ambiguities might be resolved by making moe extensive sets of measurements.
37 citations