t. This paper surveys some of the work our group has done in electrical impedance tomography.

Electrical Impedance Tomography

We review developments, issues and challenges in electrical impedance tomography (EIT) for the 4th Conference on Biomedical Applications of Electrical Impedance Tomography, held at Manchester in 2003. We focus on the necessity for three-dimensional data collection and reconstruction, efficient solution of the forward problem, and both present and future reconstruction algorithms. We also suggest common pitfalls or 'inverse crimes' to avoid.

https://iopscience.iop.org/article/10.1088/0967-3334/25/1/021/pdf

EIT reconstruction algorithms: pitfalls, challenges and recent developments

Measurement of electrical resistivity via four probes is widely used in a variety of applications ranging from geophysical prospecting to silicon wafer manufacture. Electrical resistivity tomography is an extension of this approach and is performed via an array of equi-spaced electrodes mounted into the periphery of a process vessel to map non-intrusively the spatial distribution of resistivities within. The digitized boundary data are 'inverted' by an image reconstruction algorithm to produce a map of the internal resistivity distribution. This paper focuses on the design and operation of flexible electrical resistivity tomography instrumentation for use on laboratory- and plant-scale process equipment.

https://iopscience.iop.org/article/10.1088/0957-0233/7/3/005/pdf

Electrical resistance tomography for process applications

The paper surveys the status of electrical tomography for industrial applications. For the present purposes this is considered to include “low” excitation frequencies, up to about 1 MHz, comprising Resistance (ERT), Capacitance (ECT), Inductance (EMT) and Impedance (EIT) modalities. Introductory background material is followed by comparisons between the instruments that have emerged. Data processing is considered with emphasis on the trade-offs that are necessary in implementing algorithms for reconstructing images. Recent applications are tabulated and case studies are presented for six contrasting areas that illustrate significant progress towards industrial benefit. Some comparison is made with applications to medical tomography and a number of issues are identified for future research.

Status of electrical tomography in industrial applications

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.

Electrical impedance tomography

Following the successful development of a multiple-drive electrical impedance tomography system OXPACT-II featuring a voltage-driven current method for in vitro studies, research work currently being undertaken at the EIT research group in Oxford is aimed at developing a real-time multiple-drive adaptive system, called the Oxford Brookes Adaptive Current Tomograph Mark-III (OXBACT-III) which will operate at several frequencies in between 10-160 kHz. The objective of this system development is to enable EIT clinical studies to be undertaken based on the adaptive current method. One of the most important issues addressed in the new system design is to achieve high data acquisition speed while maintaining sufficient system accuracy. This paper will describe the overall data acquisition system structure and relevant system performance specifications.

https://iopscience.iop.org/article/10.1088/0967-3334/15/2A/005/pdf

Development of a real-time adaptive current tomograph

The accuracy requirements for adaptive current electrical impedance tomography (EIT) measurements exceed the capability of available current sources. A new architecture for an EIT system is described in which the electrode current is set indirectly from a voltage-drive structure. A numerically inverted admittance matrix, obtained from current measurements and driving voltages, has been used to achieve the desired current pattern from programmable voltage sources.

Electrode current determination from programmable voltage sources

A high output impedance current source was required for electrical impedance tomography applications capable of operating up to 200 kHz. The architecture is based on operational-amplifier power-supply current sensing and produces a predominantly capacitive output impedance, which for the design presented is approximately 1.2 pF.

https://iopscience.iop.org/article/10.1088/0967-3334/15/2A/011/pdf

A high output impedance current source.

An adaptive electric current tomography system that contains a novel front-end analog architecture was developed. Programmable voltage sources were used to deliver currents into the study object and to avoid the difficulties of obtaining high-quality current sources. Through inverting an admittance matrix, the system is capable of achieving a desired current drive pattern by applying a computed voltage pattern. The tomograph, operating at 9.6 kHz, comprises 32 driving electrodes and 32 voltage measurement electrodes. The study of system noise performance shows high SNR in the data acquisition which is enhanced by a digital demodulation scheme. In vitro reconstruction images have been obtained with the data collected by the tomograph. >

Q.S. Zhu

Papers

Development of a real-time adaptive current tomograph

Electrode current determination from programmable voltage sources

A high output impedance current source.

An adaptive current tomograph using voltage sources

High output impedance voltage controlled current source for bio-impedance instrumentation