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- Lätt, Jimmy
(författare)
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Investigation of Water Mobility using Diffusion-Sensitive MRI: The Role of q-Space Imaging, High b-Values and Diffusion Time
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nuclear magnetic resonance (NMR) diffusometry provides important information about molecular motion on a microscopic scale. The advantage of NMR diffusometry is its ability to characterise microstructures non-invasively. This has made the method important not only in chemistry, biochemistry and materials science, but also in medicine. Diffusion-weighted magnetic resonance imaging (DW-MRI) has been used for about 20 years at specialised radiology departments worldwide. One of the most important clinical features of DW-MRI is its ability to reveal ischaemic lesions within minutes of the onset of an infarct. Surprisingly, the mechanism behind the observed image contrast has not yet been completely explained. As the performance of clinical MRI scanner hardware improves, methods originally developed for experimental NMR spectrometers can be applied to studies of human tissue in vivo. This will benefit patients by improving the diagnostic capability of MRI. The aim of the studies described in this doctoral thesis was to use DW-MRI measurements to develop and evaluate methods for studies of the microstructural environment of diffusing water molecules in vivo. The experiments were primarily performed using a 3T clinical head scanner, but additional phantom measurements were carried out using an NMR spectrometer. In one of the studies, multiple sclerosis (MS) patients were examined and q-space-related parameters were evaluated with respect to image contrast. A closer examination of the limitations of the q-space method using both phantom measurements and extensive Monte Carlo simulations was performed in an additional project. The knowledge obtained was applied to investigations of a biological phantom in which compartments sizes restricting the diffusion of water were quantified using a clinical scanner. Based on the understanding gained from the simulations and phantom measurements, a slightly different approach, based on the use of different diffusion times, was used in a volunteer study to investigate the possible effects of restricted diffusion in nerve tissue in vivo. This approach was pursued in a preliminary study of patients with ischaemic lesions, and the results revealed water exchange between different water pools within the lesions.
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- Mårtensson, Johanna
(författare)
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Diffusion tensor magnetic resonance imaging of the brain : Tractography analysis with application in healthy individuals and patients
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In study 1, thirty-eight healthy controls were used for optimization of the method. Fifteen patients with progressive supranuclear palsy and an equal number of age-matched healthy controls underwent diffusion tensor MRI and were then investigated and compared groupwise.It was shown that tractography analyses may preferably be performed regionally, such as along the tracts or in different segments of the tracts. Normalization of white matter tracts can be performed using anatomical landmarks.In study 2, 104 males and 153 females in the age interval 13 to 84 years of age participated as healthy individuals in order to investigate age-related changes with diffusion tensor MRI.It was shown that spatially differences in age-related changes exist between subdivided segments within white matter tracts. The aging processes within the CB and the IFO vary regionally.In study 3, 38 human brains were used for investigation of the white matter tract inferior longitudinal fasciculus (ILF) and its subcomponents. Of these, white matter anatomical dissection was performed in 14 post-mortem normal human brains. The remaining 24 brains were investigated in vivo with diffusion tensor MRI in healthy individuals.It was validated that fibers of the ILF in the occipito-temporal region have a clear, constant and detailed organisation. The anatomical connectivity pattern, and quantitative differences between the ILF subcomponents, confirmed a pivotal role of the ILF.In study 4, 12 patients with iNPH were included in the study and examined with diffusion tensor at three time points. For comparison, 12 healthy controls, matched by gender and age were also included. Controls were examined with MRI only once.It was shown that DTI measures differ significantly between patients with iNPH and healthy controls. DTI measures of the CC, the CST and the SLF, correlated to changes in clinical symptoms after shunt surgery.Deeper knowledge about functions of the brain increases possibilities to take advantages from DTI analyses with tractography.
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