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Orientation of Sticks and Spheres - Estimating Tensor Shape and Orientation Distribution using Diffusion NMR

Leveau Novén, Mikael LU (2015) KFK920 20151
Biophysical Chemistry
Abstract
The diffusion characteristics of water can be measured by using NMR methods. Specifically, the diffusion profiles in samples containing domains of water barriers are of major importance to be able to describe in applications such as diffusion tensor imaging or diffusion MRI-sequences. These sequences can be used to study the internal structure of samples of complex diffusion profiles. The diffusion characteristics can be described by a diffusion tensor matrix which can be parameterised by the isotropic diffusion coefficient and the level of anisotropy. This thesis work aims to measure diffusion weighted NMR signals from a triple-stimulated spin-echo pulse sequence to simultaneously determine both the diffusion tensor characteristics and... (More)
The diffusion characteristics of water can be measured by using NMR methods. Specifically, the diffusion profiles in samples containing domains of water barriers are of major importance to be able to describe in applications such as diffusion tensor imaging or diffusion MRI-sequences. These sequences can be used to study the internal structure of samples of complex diffusion profiles. The diffusion characteristics can be described by a diffusion tensor matrix which can be parameterised by the isotropic diffusion coefficient and the level of anisotropy. This thesis work aims to measure diffusion weighted NMR signals from a triple-stimulated spin-echo pulse sequence to simultaneously determine both the diffusion tensor characteristics and the orientation density function, ODF. Traditionally, obtaining the ODF is based on assuming a fixed diffusion tensor in a diffusion-weighted NMR experiment to describe the different signal attenuations along different directions as differences in the shape of the microscopic water domains. By the work presented in this report, it is proven by measurements on lyotropic liquid crystal systems that the shape of the diffusion tensor and the ODF indeed can be extracted from the same measurement. This is shown for samples having either prolate or oblate diffusion tensors. (Less)
Popular Abstract
Mapping the inside: Study of water diffusion using NMR experiment

This work shows how the internal structures of samples, which for instance could be cells or crystals, containing microscopic water channels and other structures where the water molecules can move in some directions but not in others can be determined in detail by looking at the magnetic properties of atomic nuclei. In order to see the structures in which the water molecules can move, two kinds of information about how the molecules move around are needed. First, the way in which the water molecules can move inside of the channels, i.e. the diffusion of water, must be known. Second, the difference in how the water molecules can move around depending on the direction... (More)
Mapping the inside: Study of water diffusion using NMR experiment

This work shows how the internal structures of samples, which for instance could be cells or crystals, containing microscopic water channels and other structures where the water molecules can move in some directions but not in others can be determined in detail by looking at the magnetic properties of atomic nuclei. In order to see the structures in which the water molecules can move, two kinds of information about how the molecules move around are needed. First, the way in which the water molecules can move inside of the channels, i.e. the diffusion of water, must be known. Second, the difference in how the water molecules can move around depending on the direction within the sample must be known. Older ways of finding out the latter depends on guessing the former. The technique described in this work shows a way to determine both in the same measurement.

When you measure temperature with a thermometer it is the motion of molecules that is measured. Every molecule in a liquid moves around freely and randomly while still bumping into other molecules. This motion of molecules is called diffusion. Nuclear magnetic resonance (NMR) spectroscopy is the study of how the magnetic properties of atomic nuclei change from the influences of magnetic fields. As all nuclei are found within molecules and the molecules move around, it is understandable that the NMR signal can change if the molecules move around. In my work, I have shown that a NMR method can be used to map the diffusion of water molecules inside samples that have thin channels or corridors that the water molecules can move around in. Similar methods are used to map diffusion of water in the neurons in the brain, which among other things can show how the neurons are connected. The new thing that I showcase in my report, is that it is possible to determine two important features of the sample; both how much the water diffusion only can occur in one direction and also which directions the channels and corridors are oriented in. Previously, it has not been possible to determine both based on the same measurement. This improvement is important as it helps to make the map of the channel orientations more reliable. In the future, this might be used to study samples which is has a complex microscopical environment where the water molecules move around in wide or narrow corridors, big halls, and across planes. One very important application of this could be to gain more understanding of both the types, conditions, and structure of cells and tissues of the brain if the experiment could be performed in a clinical MRI scanner. (Less)
Please use this url to cite or link to this publication:
author
Leveau Novén, Mikael LU
supervisor
organization
course
KFK920 20151
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Diffusion NMR, ODF, NMR, Diffusion, biophysical chemistry, biofysikalisk kemi
language
English
id
7516536
date added to LUP
2015-10-08 16:27:22
date last changed
2015-10-08 16:27:22
@misc{7516536,
  abstract     = {The diffusion characteristics of water can be measured by using NMR methods. Specifically, the diffusion profiles in samples containing domains of water barriers are of major importance to be able to describe in applications such as diffusion tensor imaging or diffusion MRI-sequences. These sequences can be used to study the internal structure of samples of complex diffusion profiles. The diffusion characteristics can be described by a diffusion tensor matrix which can be parameterised by the isotropic diffusion coefficient and the level of anisotropy. This thesis work aims to measure diffusion weighted NMR signals from a triple-stimulated spin-echo pulse sequence to simultaneously determine both the diffusion tensor characteristics and the orientation density function, ODF. Traditionally, obtaining the ODF is based on assuming a fixed diffusion tensor in a diffusion-weighted NMR experiment to describe the different signal attenuations along different directions as differences in the shape of the microscopic water domains. By the work presented in this report, it is proven by measurements on lyotropic liquid crystal systems that the shape of the diffusion tensor and the ODF indeed can be extracted from the same measurement. This is shown for samples having either prolate or oblate diffusion tensors.},
  author       = {Leveau Novén, Mikael},
  keyword      = {Diffusion NMR,ODF,NMR,Diffusion,biophysical chemistry,biofysikalisk kemi},
  language     = {eng},
  note         = {Student Paper},
  title        = {Orientation of Sticks and Spheres - Estimating Tensor Shape and Orientation Distribution using Diffusion NMR},
  year         = {2015},
}