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Title: Dielectric relaxation time spectroscopy for tissue characterisation
Author: Jouravleva, Svetlana
ISNI:       0000 0001 3593 2615
Awarding Body: Oxford Brookes University
Current Institution: Oxford Brookes University
Date of Award: 2001
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This thesis is concerned with Electrical Impedance Spectroscopy (EIS), a noninvasive technique for characterising biological tissue and distinguishing pathology. The thesis is focused on the development of an improved method for extracting physiologically related parameters from the measured impedance data in vivo and instrumentation for spectroscopic measurements. In EIS, the electrical properties of physiological tissues, defined by their composition and structure, are measured as functions of frequency. Experimental observations of the existence of dielectric dispersions caused by distributions of dielectric relaxation time (DRT) constants were made on different types of biological material. It is postulated that widely used approaches for modelling these electrical properties are fundamentally flawed. The research work concentrates on the reconstruction of DRT spectra directly from the measured frequency response. The reconstruction problem involves inversion of a linear operator and like many inverse problems, is complicated by the ill-posed nature of the problem. In this thesis an inversion algorithm - Galerkin Regularised Inverse Method (GRIM) - based on standard mathematical methods is developed. The DRT spectrum establishes a link between the raw impedance data and the physiological structure and function of biological tissues. The GRIM yields a large number of independent parameters each related to process on a different scale. Special care was taken in testing the method on simulated data and improving its resolution. The thesis is also concerned with the design and practical implementation of EIS systems. Two approaches are considered: systems based on commercially available Impedance Analysers and systems designed specially for studies in vivo. To evaluate the GRIM, an Impedance Analyser, benefitting from a higher accuracy and a wider frequency range, is used. To meet the more rigorous specification demanded for studies on living human tissues, an electrical impedance spectrometer is developed. The suitability of different current sources is investigated. This research work includes studies of animal tissue in vitro and in vivo. Optimal experiments are defined in terms of the measurement frequency range and the entire experimental protocol for dielectric spectroscopy is established. These biological data are used to evaluate the GRIM. A comparison between different tissue classes in vivo is made. From studying ischemic tissues, it is postulated and verified that physiological differences and changes can be measured using the technique of DRT spectroscopy.
Supervisor: McLeod, Chris Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Electrical impedance; Physiology