A computer simulation is used to investigate the relationship between skin impedance and image artefacts in electrical impedance tomography. Sets of electrode impedance are generated with a pseudo-random distribution and used to introduce errors in boundary voltage measurements. To simplify the analysis, the non-idealities in the current injection circuit are replaced by a fixed common-mode error term. The boundary voltages are reconstructed into images and inspected. Where the simulated skin impedance remains constant between measurements, large impedances (> 2k omega) do not cause significant degradation of the image. Where the skin impedances 'drift' between measurements, a drift of 5% from a starting impedance of 100 omega is sufficient to cause significant image distortion. If the skin impedances vary randomly between measurements, they have to be less than 10 omega to allow satisfactory images. Skin impedances are typically 100-200 omega at 50 kHz on unprepared skin. These values are sufficient to cause image distortion if they drift over time. It is concluded that the patient's skin should be abraded to reduce impedance, and measurements should be avoided in the first 10 min after electrode placement.

Effect of skin impedance on image quality and variability in electrical impedance tomography: a model study

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

Electrical Impedance Tomography

The purpose of this study was to develop and cross-validate predictive equations for estimating skeletal muscle (SM) mass using bioelectrical impedance analysis (BIA). Whole body SM mass, determine...

Estimation of skeletal muscle mass by bioelectrical impedance analysis.

A new method for the ablation of undesirable tissue such as cells of a cancerous or non-cancerous tumor is disclosed. It involves the placement of electrodes into or near the vicinity of the undesirable tissue through the application of electrical pulses causing irreversible electroporation of the cells throughout the entire area of the undesirable tissue. The electric pulses irreversibly permeate the cell membranes, thereby invoking cell death. The irreversibly permeabilized cells are left in situ and are removed by the body immune system. The amount of tissue ablation achievable through the use of irreversible electroporation without inducing thermal damage is considerable.

Tissue ablation with irreversible electroporation

As electronic devices become smaller, lower in power requirements, and less expensive, we have begun to adorn our bodies with personal information and communication appliances. Such devices include cellular phones, personal digital assistants (PDAs), pocket video games, and pagers. Currently there is no method for these devices to share data. Networking these devices can reduce functional I/O redundancies and allow new conveniences and services. The concept of Personal Area Networks (PANs) is presented to demonstrate how electronic devices on and near the human body can exchange digital information by capacitively coupling picoamp currents through the body. A low-frequency carrier (less than 1 megahertz) is used so no energy is propagated, minimizing remote eavesdropping and interference by neighboring PANs. A prototype pan system allows users to exchange electronic business cards by shaking hands.

/pdf/personal-area-networks-near-field-intrabody-communication-5em1iaxpz6.pdf

Personal area networks: near-field intrabody communication

In an APT method, the surface-contact electrodes are located in a closed loop or rosette array on one planar, or nominally planar, skin surface of a body to be investigated, and electrically connected to data acquisition and processing equipment. The invention also includes apparatus for carrying out this method, comprising an array of surface-contact electrodes (8), adapted to be applied to the skin of a body to be investigated, the electrodes (8) being arranged on a flexible carrier (10) in a closed loop, or rosette formation on one common plane, or nominal plane.

https://iopscience.iop.org/article/10.1088/0022-3735/17/9/002/pdf

Applied potential tomography

Electrical impedance tomography (EIT) has been the subject of quite intensive research for about 20 years but has yet to become established as a routine tool in healthcare. None the less the volume of published research work in this area is still rising. This review takes a broad look at what has been achieved and attempts to give the reader sufficient information to form an opinion as to the likely future for this interesting area of research.

Electrical impedance tomography (EIT): a review

Electrical impedance tomography (EIT) is an attractive method for clinically monitoring patients during mechanical ventilation, because it can provide a non-invasive continuous image of pulmonary impedance which indicates the distribution of ventilation. However, most clinical and physiological research in lung EIT is done using older and proprietary algorithms; this is an obstacle to interpretation of EIT images because the reconstructed images are not well characterized. To address this issue, we develop a consensus linear reconstruction algorithm for lung EIT, called GREIT (Graz consensus Reconstruction algorithm for EIT). This paper describes the unified approach to linear image reconstruction developed for GREIT. The framework for the linear reconstruction algorithm consists of (1) detailed finite element models of a representative adult and neonatal thorax, (2) consensus on the performance figures of merit for EIT image reconstruction and (3) a systematic approach to optimize a linear reconstruction matrix to desired performance measures. Consensus figures of merit, in order of importance, are (a) uniform amplitude response, (b) small and uniform position error, (c) small ringing artefacts, (d) uniform resolution, (e) limited shape deformation and (f) high resolution. Such figures of merit must be attained while maintaining small noise amplification and small sensitivity to electrode and boundary movement. This approach represents the consensus of a large and representative group of experts in EIT algorithm design and clinical applications for pulmonary monitoring. All software and data to implement and test the algorithm have been made available under an open source license which allows free research and commercial use.

/pdf/greit-a-unified-approach-to-2d-linear-eit-reconstruction-of-4p57gff6ds.pdf

GREIT: a unified approach to 2D linear EIT reconstruction of lung images.

Applied Potential Tomography (APT) is a new method of imaging changes in the distribution of electrical resistivity within the human body. Such changes occur during respiration and, because of the movement of blood within the chest, during the cardiac cycle. Changes can also be observed due to redistribution of fluid within the body during simulated weightlessness. As very low electric currents are used to take measurements the method is safe. The equipment is simple and compact and ideal for use in space based measurement of physiological changes in the human body.

Applied potential tomography.

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.

Brian H. Brown

Papers

Applied potential tomography

Electrical impedance tomography (EIT): a review

GREIT: a unified approach to 2D linear EIT reconstruction of lung images.

Applied potential tomography.

The Sheffield data collection system.