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Analysis of Selected Artefacts in Diffusion-Based Magnetic Resonance Measurements
Marcoň, Petr ; Král, Bohumil (referee) ; Frollo, Ivan (referee) ; Bartušek, Karel (advisor)
The presented dissertation thesis analyses artefacts in diffusion-weighted images. In medical practice, the artefacts can impede the diagnostics of pathological tissues and, therefore, need to be eliminated. As the first step within the thesis, an analysis of the most frequent artefacts in diffusion-weighted images is performed, and the hitherto known approaches to artefact elimination are described. In order to facilitate the reduction of artefacts caused by the inhomogeneity of the static magnetic field and induced by eddy currents, a novel three-measurement method is shown. This technique will find application especially in measuring the diffusion coefficient of isotropic materials. At this point, it is important to note that a significant and commonly found problem is the magnetic susceptibility artefact; different magnetic susceptibility values at the boundary between two materials can cause magnetic field inhomogeneities and even complete loss of the signal. Therefore, we designed a novel method for the measurement of magnetic susceptibility in various samples of magnetically incompatible materials, which do not produce any MR signal. The technique was experimentally verified using a set of differently shaped diamagnetic and paramagnetic samples. In addition to the magnetic susceptibility problem, the thesis presents artefacts such as noise, motion-induced items, hardware limitations, chemical shift, and the dependence of the diffusion coefficient on the temperature. To enable precise measurement of the diffusion coefficient, we proposed a thermal system; in the experiment, it was determined that when the measurement error does not exceed 5%, the temperature change should not be higher than 0,1 °C. In the final sections of the thesis, practical application examples involving the designed methods are shown.
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Application of Diffusion Tensor Imaging to Brain Gray and White Marker
Rulseh, Aaron Michael ; Vymazal, Josef (advisor) ; Hluštík, Petr (referee) ; Hájek, Milan (referee)
Application of Diffusion Tensor Imaging to Brain Gray and White Ma er A In the present work we explore the gray and white ma er applicability of diffusion tensor imaging (DTI). To evaluate effect of ferritin-bound iron on gray ma er contrast in DTI, we created an in vitro model consisting of agarose gel phantoms doped with ferritin, and validated our results in vivo on healthy volunteer subjects - years of age in the basal ganglia. We further explored the application of DTI to amyotrophic lateral sclerosis (ALS) and multiple system atrophy (MSA); neurodegenerative diseases with gray and white ma er pathophysiological components. In the ALS study, patients and age- and sex-matched controls were recruited, while the MSA study included probable MSA subjects ( MSA-P, MSA-C) and age- and sex-matched controls. We found that ferritin-bound iron may make a signi cant contribution to DTI scalars in gray ma er regions of the brain, mediated by eigenvalue repulsion. is has important implications for DTI studies targeting gray ma er regions, especially in adolescence and in diseases associated with altered brain-iron load. In ALS, we found altered diffusion in the corona radiata and callosal body, and changes in R in the caudate nucleus and frontal white ma er. In MSA, we observed widespread white ma er changes associated...
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Application of Diffusion Tensor Imaging to Brain Gray and White Marker
Rulseh, Aaron Michael ; Vymazal, Josef (advisor) ; Hluštík, Petr (referee) ; Hájek, Milan (referee)
Application of Diffusion Tensor Imaging to Brain Gray and White Ma er A In the present work we explore the gray and white ma er applicability of diffusion tensor imaging (DTI). To evaluate effect of ferritin-bound iron on gray ma er contrast in DTI, we created an in vitro model consisting of agarose gel phantoms doped with ferritin, and validated our results in vivo on healthy volunteer subjects - years of age in the basal ganglia. We further explored the application of DTI to amyotrophic lateral sclerosis (ALS) and multiple system atrophy (MSA); neurodegenerative diseases with gray and white ma er pathophysiological components. In the ALS study, patients and age- and sex-matched controls were recruited, while the MSA study included probable MSA subjects ( MSA-P, MSA-C) and age- and sex-matched controls. We found that ferritin-bound iron may make a signi cant contribution to DTI scalars in gray ma er regions of the brain, mediated by eigenvalue repulsion. is has important implications for DTI studies targeting gray ma er regions, especially in adolescence and in diseases associated with altered brain-iron load. In ALS, we found altered diffusion in the corona radiata and callosal body, and changes in R in the caudate nucleus and frontal white ma er. In MSA, we observed widespread white ma er changes associated...
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Analysis of Selected Artefacts in Diffusion-Based Magnetic Resonance Measurements
Marcoň, Petr ; Král, Bohumil (referee) ; Frollo, Ivan (referee) ; Bartušek, Karel (advisor)
The presented dissertation thesis analyses artefacts in diffusion-weighted images. In medical practice, the artefacts can impede the diagnostics of pathological tissues and, therefore, need to be eliminated. As the first step within the thesis, an analysis of the most frequent artefacts in diffusion-weighted images is performed, and the hitherto known approaches to artefact elimination are described. In order to facilitate the reduction of artefacts caused by the inhomogeneity of the static magnetic field and induced by eddy currents, a novel three-measurement method is shown. This technique will find application especially in measuring the diffusion coefficient of isotropic materials. At this point, it is important to note that a significant and commonly found problem is the magnetic susceptibility artefact; different magnetic susceptibility values at the boundary between two materials can cause magnetic field inhomogeneities and even complete loss of the signal. Therefore, we designed a novel method for the measurement of magnetic susceptibility in various samples of magnetically incompatible materials, which do not produce any MR signal. The technique was experimentally verified using a set of differently shaped diamagnetic and paramagnetic samples. In addition to the magnetic susceptibility problem, the thesis presents artefacts such as noise, motion-induced items, hardware limitations, chemical shift, and the dependence of the diffusion coefficient on the temperature. To enable precise measurement of the diffusion coefficient, we proposed a thermal system; in the experiment, it was determined that when the measurement error does not exceed 5%, the temperature change should not be higher than 0,1 °C. In the final sections of the thesis, practical application examples involving the designed methods are shown.
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