The tetrapolar electrode configuration used in bioimpedance suffers from negative sensitivity and is confounded by anisotropic tissue such as blood vessels or muscle and nerve fibres. Proposed is a circular array of electrodes to focus current directly underneath the probe and provide anisotropy information. It is shown that an implementation using 16 miniature electrodes is able to outperform the tetrapolar method in sensitivity and impedance estimation. The proposed method can also recover anisotropic conductivity tensors from experiments for the first time.

This paper reviews governing theorems in electrical impedance sensing for analysing the relationships of boundary voltages obtained from different sensing strategies. It reports that both the boundary voltage values and the associated sensitivity matrix of an alternative sensing strategy can be derived from a set of full independent measurements and sensitivity matrix obtained from other sensing strategy. A new sensing method for regional imaging with limited measurements is reported. It also proves that the sensitivity coefficient back-projection algorithm does not always work for all sensing strategies, unless the diagonal elements of the transformed matrix, ATA, have significant values and can be approximate to a diagonal matrix. Imaging capabilities of few sensing strategies were verified with static set-ups, which suggest the adjacent electrode pair sensing strategy displays better performance compared with the diametrically opposite protocol, with both the back-projection and multi-step image reconstruction methods. An application of electrical impedance tomography for sensing gas in water two-phase flows is demonstrated.This article is part of the themed issue ‘Supersensing through industrial process tomography’.

This paper presents bioimpedance spectroscopy measurements of anisotropic tissues using a 16 electrode probe and reconstruction method of estimating the anisotropic impedance spectrum in a local region just underneath the center of the probe. This may enable in-vivo surface bioimpedance measurements with similar performance to the ex-vivo gold standard that requires excising and placing the entire tissue sample in a unit measurement cell with uniform electric field. The multiple surface electrodes enable us to create a focused current pattern so that the resulting measured voltage is more sensitive to a local region and less sensitive to other areas. This is exploited in a reconstruction method to provide improved bioimpedance and anisotropy measurements. In this paper, we describe the current pattern for localized electrical energy concentration, performance with the spring loaded pin electrodes, data calibration and experimental results on anisotropic agar phantoms and different tissue types. The anisotropic conductivity spectra are able to differentiate insulating films of different thickness and detect their orientation. Bioimpedance spectra of biological tissues are in agreement with published data and reference instruments. The anisotropy expressed as the ratio of eigenvalues and the orientation of eigenfunctions were reconstructed at 45° intervals. This information is used to predict the underlying anisotropy of the region under the probe. Tissue measurements clearly demonstrate the expected higher anisotropy of muscle tissue compared to liver tissue and spectral changes.

Gas-oil-water three phase flow is of practical significance in oil and gas industries. An insight into the dynamics of such multiphase flows is significantly valuable to obtain optimal design parameters and operational conditions. Since flow patterns are sensitive to pipe geometry, flow conditions and thermophysicalfluid properties, it is extremely challenging to provide a universal solution for visualisation of three phase horizontal flows. This study deals with a fully developed turbulent three phase flow with no phase changing, and presents the outcomes of tomographic imaging techniques to visualise gas-oil-water flows in a horizontal pipeline.

Non-destructive label-free continuous monitoring of in vitro tissue culture is an unmet demand in tissue engineering. Noting that different compositions of cartilage lead to different electrical tissue properties, we propose a new method to measure the electrical conductivity and its anisotropy during in vitro chondrogenesis. We used a conductivity tensor probe with 17 electrodes and a bio-impedance spectroscopy (BIS) device to measure the conductivity values and the anisotropy ratios at the bottom and top surfaces of the tissue samples during the culture period of 6 weeks. Clearly distinguishing glycosaminoglycans (GAGs), collagen, and also various mixtures of them, the measured conductivity value and the estimated tissue anisotropy provide diagnostic information of the depth-dependent tissue structure and compositions. Continuously monitoring the individual tissue during the entire chondrogenesis process without any adverse effect, the proposed method may significantly increase the productivity of cartilage tissue engineering.