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Identifier	000398257
Title	Diffusion magnetic resonance imaging techniques. : applications in brain and human body
Alternative Title	Εφαρμογές των τεχνικών απεικόνισης διάχυσης μαγνητικού συντονισμού στον εγκέφαλο και το ανθρώπινο σώμα
Author	Ιωαννίδης, Γεώργιος
Thesis advisor	Καμπάνης, Νίκος
Reviewer	Μαριάς, Κώστας Τσόγκα, Χρυσούλα
Abstract	Medical imaging is the process of creating visual representations of the interior of our body for clinical analysis and medical intervention. Medical imaging reveals the internal structures hidden by the skin and it is a powerful tool for population screening and efficient patient management. Thirty years ago, Magnetic Resonance Imaging (MRI) was introduced in clinical practice and was progressively established among the most frequently used medical imaging modalities. Apart from conventional MR imaging, more advanced techniques were arisen such as spectroscopy, diffusion and perfusion MRI. The main subject of this work is Diffusion Weighted Imaging (DWI) and is focused on obtaining diffusion parameters from the Intravoxel Incoherent Motion (IVIM) model which gives information about water diffusivity and tissue vascularity. In order to extract the aforementioned parameters from the IVIM model, non-linear least squares are used. As an iterative process, non-linear least squares need a starting point (initial guess), a lower and an upper bound. The initial point is of crucial significance for the convergence of the algorithm. Due to the complexity of the IVIM function (many local minima), standard non-linear least squares fail to produce clinically reliable results inside the natural bounds. To this end, we present a novel mathematical framework which exploits the characteristics of the Diffusion Weighted (DW) signal curve in order to find the appropriate initial starting points and bounds for the non-linear least squares. Comparisons between results obtained by the proposed and those of the standard initialization, for the non-linear least squares, results in clinically relevant and reliable results with our method, in contrast to the standard initialization which suffers from reproducibility of the results.
Language	English
Issue date	2015-11-20
Collection	School/Department--School of Sciences and Engineering--Department of Mathematics and Applied Mathematics--Post-graduate theses
	Type of Work--Post-graduate theses
Permanent Link	https://elocus.lib.uoc.gr//dlib/a/2/9/metadata-dlib-1452668040-595361-10781.tkl
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