Anisotropic conductivity tensor imaging using magnetic induction tomography

Capacitively Coupled Phase-based Dielectric Spectroscopy Tomography

Impedance imaging is an effective approach for non-intrusively reconstruct the distribution of dielectric parameters inside the region of interest. Most common form of impedance imaging is electrical impedance tomography (EIT), which requires direct contact with the medium via electrodes. In this work we present a novel impedance imaging using capacitive coupling which provides a contactless method, totally non-invasive and non-intrusive, by measuring the phase. There are less attentions in many prior works to the phase information of the voltage/current measurements. This work studies for the first time the capacitively coupled electrical phase spectroscopy for contactless dielectric parameter imaging. A 12-electrode capacitively coupled test phantom and a measurement system were used to obtain the phase measurements within a wideband frequency range from 200 kHz to 15 MHz. Background data with different conductivity levels were investigated in the experiments to show a broad application possibility. The forward modelling was implemented by simulation and the image reconstruction based on phase measurements was implemented with the total variation algorithm. The potentials, possibilities and challenges of such capacitively coupled dielectric spectroscopy tomography with phase data are discussed in this work.

Magnetic Induction Spectroscopy for Permeability Imaging

The structural health monitoring of ferromagnetic materials is essential for controlling product quality. This paper presents the first known characterisation, utilising magnetic induction spectroscopy, of the magnetic permeability of ferromagnetic materials, a property that can facilitate such monitoring. Magnetic induction coils are interrogated by a sweep of excitation frequencies in the range of 1–100 kHz, with amplitudes of induced voltages collected from both non-magnetic and ferromagnetic specimens, and their associated spectral permeability imaged. The reconstructed images show that magnetic permeability can be reconstructed using frequency difference imaging in the investigated frequency range. As such, the relative magnetic permeability of a ferromagnetic specimen can be reconstructed without needing a time difference measurement. This provides a robust imaging approach for the material characterisation of ferromagnetic specimens.

Advancements in transmitters and sensors for biological tissue imaging in magnetic induction tomography

Magnetic Induction Tomography (MIT), which is also known as Electromagnetic Tomography (EMT) or Mutual Inductance Tomography, is among the imaging modalities of interest to many researchers around the world. This noninvasive modality applies an electromagnetic field and is sensitive to all three passive electromagnetic properties of a material that are conductivity, permittivity and permeability. MIT is categorized under the passive imaging family with an electrodeless technique through the use of excitation coils to induce an electromagnetic field in the material, which is then measured at the receiving side by sensors. The aim of this review is to discuss the challenges of the MIT technique and summarize the recent advancements in the transmitters and sensors, with a focus on applications in biological tissue imaging. It is hoped that this review will provide some valuable information on the MIT for those who have interest in this modality. The need of this knowledge may speed up the process of adopted of MIT as a medical imaging technology.

Fourier analysis in Magnetic Induction Tomography: Mapping of anisotropic, inhomogeneous resistivity

Magnetic Induction Tomography is an electromagnetic-based technique for mapping the passive electromagnetic properties of conductors and has the potential for applications in biomedical imaging. In a previous analysis we approached the inverse problem of determining isotropic resistivity with a Fourier-based analysis. Here, we extend that analysis to anisotropic media. The proposed Fourier-based solution method, when properly filtered, robustly handles noise to accurately map the inhomogeneous terms of the resistivity tensor. We observe a random variation in the measure of accuracy (mean deviation) that is resolved with independent spatial frequencies in the x- and y-directions in the applied field. Further, the formation of improper images we noted in our previous analysis is addressed through this use of independent spatial frequencies and through the use of additional applied fields. We conclude with a discussion of computation time for the large system of linear equations this method requires and propose methods for limiting memory usage.