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Contribution to the development of a novel method of Spectroscopic Electrical Impedance tomography (EIT) with application to the assessment of hidden caries: Final report project "Contribution to the development of a novel method of Spectroscopic Electrical Impedance tomography (EIT) with application to the assessment of hidden caries" Authors: B. Truyen Publication Date: Jan. 2004
Abstract: The significant decline in the incidence of dental caries that is observed in the last two decades [Sawle et al., 1988] [Kalsbeek et al., 1998], also seems to be accompanied by a distinctive change in the lesion morphology. In particular, the phenomenon of slowly progressing dentinal lesions, obscured by apparently intact enamel [Kidd et al., 1992] [Poorterman et al., 1999], renders the established diagnostic procedures of visual examination and intra-oral radiography, largely ineffective [Poorterman et al., 2000]. However, reliable detection at an early stage of the carious progression remains crucial to allow for an appropriate preventive or minimal invasive treatment.
Although electrical conductivity measurements have been demonstrated to exhibit superior detection sensitivity under experimental conditions, clinical application seems to be severely complicated by a lack of reproducibility. This variation in the measurement outcomes makes it very difficult to define a generally applicable diagnostic threshold for discriminating among carious involvement. It may be hypothesized, that this problem is related to the very nature of the 2-point measurement configuration, which is underlying all of the experimental methods described in the literature as today. This study aims to develop and evaluate a new method of spectroscopic Electrical Impedance Tomography (EIT), capable of reconstructing cross-sectional maps of site-specific electrical impedance spectra. The resulting method promises to improve upon existing electrical caries detection methods, both in terms of its improved cross-sectional sampling strategy, dispensing with the need to rely on visual surface indications to determine appropriate measurement sites, and its immunity with regard to the variability in electrical conductance between individual teeth. The tomographic representation of the measurement results will allow diagnostic interpretation to proceed on the basis of relative changes in tissue impedance among different spatial locations, instead of being dependent on a single quantitative reading.
To acquire a more fundamental understanding of the electrical conduction phenomena in dental structures, a first, morphological accurate, numerical simulation model of a whole tooth will be constructed. The detailed anatomical input data for this model will be derived from micro-CT scans, acquired with a microfocal desktop system. Intrinsic electrical parameters of the constituent dental tissues are found in the existing literature, and will be reevaluated against new data acquired using a state-of-the-art measurement setup with superior accuracy specifications.
Finally, in order to appreciate to full extent the potential of this unreleased method of spectroscopic Electrical Impedance Tomography, it may assist to recognize the parallel that can be drawn with some of the recent developments that also have been observed in nuclear magnetic resonance (NMR or MR) imaging. Originally devised as an analytical tool to probe the physico-chemical composition of small samples, some crucial insights in the encoding of spatial information led to the development of MR as an anatomical imaging method capable of generating detailed cross-sectional images of the human body. Not until more recently, however, it was realized that essentially the same measurement equipment used for anatomical imaging, could also be exploited to obtain site-specific spectroscopic information. In this way, it became possible to synthesize cross-sectional maps of metabolic body composition. Today, MR-spectroscopy, which already finds widespread application in many research studies, starts to make its first appearances also in the clinical applications. Surprisingly enough, a completely analogous evolutionary development process, but instead for the case of electrical material characterization, lead us to the basic ideas underlying the proposed research.
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