University of Twente Student Theses


Comparison of 2D and 3D realistic models of white matter microstructure

Licht, Christian (2019) Comparison of 2D and 3D realistic models of white matter microstructure.

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Abstract:Neurodegenerative diseases, for instance mutliple sclerosis (MS) or amyotrophic lateral sclerosis (ALS), are characterized by a progressive degradation of the myelin sheath. Myelin is an insulation around an axon and enhances signal transmission speed. The loss of myelin hinders the signal propagation and is therefore associated with many cognitive and physical impairments. Specific magnetic resonance imaging (MRI) techniques enable to image myelin in-vivo. By fitting a biophysical model to the measured signal, it is possible to relate properties of white matter to the observed MR signal. The magnetic susceptibility of myelin affects both the magnitude and phase of the Gradient Recalled Echo (GRE) signal. Therefore, studying the signal using realistic models of white matter (WM) microstructure could provide insights into some of its properties and eventually, support to study diseases that are characterized by degradation of myelin sheath. Multi-compartment (intra-axonal, extra-axonal, myelin sheath) 2D models of white matter based on electron microscopy (EM) data have been used in the past to, combined with magnetic susceptibility of the myelin and its orientation in respect to the static magnetic field, simulate the MR signal. Unfortunately, 2D models could have several limitations: they lack the ability to incorporate fibers’ orientation dispersion and the shape of axons might be unrealistically elongated and therefore, could not depict the real 3D case accurately. This thesis investigated how accurately the realistic 2D WM models, based on real axon shapes, simulate the GRE signal when compared to a more realistic 3D model. Therefore, a 3D model based on 3D electron microscopy data of white matter was developed. This model enables to simulate the GRE signal with respect to myelin’s microstructure in 3D. The comparison between the developed 3D model and the already available 2D model revealed that the 2D model accurately simulates the GRE signal. Furthermore, it was demonstrated that fibers’ orientation dispersion influence the simulated signal.
Item Type:Essay (Master)
Faculty:TNW: Science and Technology
Subject:44 medicine, 50 technical science in general
Programme:Biomedical Engineering MSc (66226)
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