ABSTRACT
The objective of magnetic detection electrical impedance tomography (MD-EIT) is to reconstruct in vivo images of conductivity from magnetic field measurements taken around the body. MD-EIT is performed by applying an alternating current, at one of a range of frequencies, to a conducting object through a pair of electrodes fixed to the surface of the object. Magnetic field measurements recorded by search coils at a number of positions around the object are used to determine the current distribution that is generating the magnetic field. From this distribution, a conductivity map of a cross-section of the object can be reconstructed. This paper describes the development of an MD-EIT data acquisition system and discusses the related image reconstruction issues. The ill-conditioned nature of the inverse problem is examined and a number of image reconstruction methods are compared. The technical feasibility of MD-EIT data collection and image reconstruction is demonstrated with example images of current density from both phantom and human data.
Subject(s)
Algorithms , Electric Impedance , Image Interpretation, Computer-Assisted/methods , Magnetics , Thorax/anatomy & histology , Thorax/physiology , Tomography/methods , Equipment Design , Equipment Failure Analysis , Feasibility Studies , Humans , Information Storage and Retrieval/methods , Magnetics/instrumentation , SoftwareABSTRACT
Tissue can be characterized by its electrical impedance, especially if measurement can be extended over a range of frequencies. Recently, there has been a great deal of interest in imaging the distribution of electrical impedance through the technique of electrical impedance tomography (EIT). However, EIT has a number of practical problems relating to the placement of electrodes on the body. Such contacts are not required to collect magnetic field data around an object through which current is flowing and thus this approach may be more practical than EIT in the clinical environment. This paper describes the technique of magnetic impedance tomography (MIT), which allows reconstruction of the current distribution from magnetic field measurements. The reconstruction techniques used to generate the images and the prototype data collection system are described. Images produced using data collected from discrete and distributed current phantoms and the thorax during human respiration are presented.