Magnetic Induction Tomography (MIT)

Introduction

Magnetic Induction Tomography (MIT) which is also known with the name of Mutual Inductance Tomography or Electromagnetic Tomography (EMT) is among the technology ventured in early 90’s with first report appeared in 1992-1993. Same to other modalities, the research has both involved process industry and also in biomedical tissue imaging. MIT modality is categorized as passive imaging modality together with Electrical Impedance Tomography (EIT), Electrical Capacitance Tomography (ECT) and Magnetostatic Permeability Tomography (MPT). All these modalities are sensitive to all three passive electromagnetic properties (PEPs) which are conductivity, permittivity and permeability of material.

Several studies based on magnetic induction application on biological tissues had been reported in 1968 by Tarjan and McFee followed by Netz et al. (1993) (Netz et al. 1993) and Al-Zeibak and Saunders (1993). Their works have been further continued by the new researchers whose have made MIT being the interest of many researchers in the world with the new innovations and discoveries. Among the applications that have been involved are lung monitoring and imaging, brain imaging and stroke related problem, liver tissue monitoring, physiological measurement and several others.

Through the contribution by Gabriel (1996) who had mapped out the range of suitable frequencies on the biological tissues based on the experiment done by several previous researchers, the interest in MIT research had gain some positive sides. One motivation to the researchers who involved in these passive electrical properties is their characteristic dependence on the state of the hydration of biological tissue. This may provides opportunity and alternative in studying human body based on passive imaging modalities

MIT Theoretical Concept

MIT is a low resolution imaging modality which aims at reconstruction of the electrical conductivity, permittivity and permeability in the objects which is similar to the more established technique of Electrical Impedance Tomography (EIT). However in biological tissue, conductivity component is always be dominant compare to permittivity and permeability. The permittivity term for biological tissues is much smaller than the conductivity, especially at frequencies in the β-dispersion range (10 kHz–10 MHz). In term of device used, MIT is different from EIT since it does not require galvanic coupling between the device and the object, hence avoiding the ill defined electrode-skin interface. MIT consist of several components which are sensors (excitation coils, detection coils, and screen), interface electronics and host computer as in Figure 1. This contactless technique applies the interaction concept of an oscillating primary, generated from excitation coils with the conductive medium (object under investigation). This interaction is accompanied by the induced of eddy currents in the medium itself as primary field propagates and penetrates the medium. The field due to these generated eddy currents is known as secondary field, and also known with the name of magnetic perturbations field. This secondary field is the only interest in MIT since it carries the information of the PEPs distribution of the interested material. All these fields (primary and secondary) will be sense by the sensors at the receiver side. The concept of MIT is shown in Figure 2.

Figure 1. Block diagram of a typical MIT system (R. Binns et al. 2001)

Figure 2. Principle of an MIT system (Gürsoy et al. 2011)