Dokument: Advances in Whole-Brain Diffusion MRI at High and Ultra-High Field
| Titel: | Advances in Whole-Brain Diffusion MRI at High and Ultra-High Field | |||||||
| URL für Lesezeichen: | https://docserv.uni-duesseldorf.de/servlets/DocumentServlet?id=68827 | |||||||
| URN (NBN): | urn:nbn:de:hbz:061-20250305-125158-2 | |||||||
| Kollektion: | Dissertationen | |||||||
| Sprache: | Englisch | |||||||
| Dokumententyp: | Wissenschaftliche Abschlussarbeiten » Dissertation | |||||||
| Medientyp: | Text | |||||||
| Autor: | Veldmann, Marten [Autor] | |||||||
| Dateien: |
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| Beitragende: | Prof. Dr. Stöcker, Tony [Gutachter] Prof. Dr. Heinzel, Thomas [Gutachter] | |||||||
| Dewey Dezimal-Klassifikation: | 500 Naturwissenschaften und Mathematik » 530 Physik | |||||||
| Beschreibung: | This thesis addresses the development of fast MRI sequences for whole-brain diffusion-weighted imaging (DWI), focusing on high (3T) and ultra-high (7T) field strengths. DWI allows the assessment of tissue microstructure, particularly white matter pathways, by measuring water diffusion. The work involves both sequence design for DWI using spiral k-space trajectories and methods for correcting field inhomogeneity of the main magnetic field B0 and the radiofrequency field B1 to improve imaging accuracy.
In the first part, a framework for open-source sequence development and image reconstruction is introduced. This framework integrates different open-source tools for sequence design, reconstruction, and analysis, enabling rapid prototyping and sharing among researchers without dependence on proprietary software. It supports both Cartesian and non-Cartesian imaging techniques, validated through various applications, such as accelerated 3D imaging, field mapping, and non-Cartesian spiral trajectories. Additional integration of the workflow in an MRI simulation framework allows comparison of experimental and simulated results. The proposed framework was extensively used for sequence design und image reconstruction in the subsequent parts. The second part focuses on improving axon radius estimation in human white matter using a multiband spiral sequence for DWI at a 3T scanner with a high-performance gradient system. Magnetic field monitoring was employed to reduce artifacts, particularly those caused by eddy currents due to strong magnetic field gradients. Axon radii were estimated by applying strong diffusion weighting to suppress extra-axonal signals, and test-retest experiments assessed the reliability of these measurements. The spiral sequence outperformed the current gold standard, multiband echo-planar imaging (EPI), by providing a higher signal-to-noise ratio in DWI images and reduced test-retest variability. In the third part, a novel variant of the 3D dual refocusing echo acquisition mode (3DREAM) sequence is proposed for B1 field mapping at a 7T scanner. B1 mapping is a prerequisite for parallel transmit (pTx) techniques. A 3D stack-of-spirals readout scheme, which replaces the standard Cartesian scheme, was employed to reduce image blurring caused by fast decay of the stimulated echo signal. The spiral approach enabled improved quality of B1 maps by reducing image blurring and ventricular contrast and showed excellent agreement with established B1 mapping techniques at significantly lower acquisition time. The final part examines whole-brain DWI at 7T, addressing challenges posed by B1 and B0 field inhomogeneities. Parallel transmit (pTx) pulses were employed to mitigate signal dropouts in brain areas like the cerebellum caused by B1 inhomogeneity. These pulses were integrated into both EPI and spiral DWI sequences. Additionally, field monitoring and static field mapping were used to correct inhomogeneities of the B0 field. It was found that deteriorating effects of B1 inhomogeneities in DWI images were largely resolved by using pTx pulses. However, at a field strength of 7T, static B0 inhomogeneity posed a more severe problem in image reconstruction compared to 3T, as artifacts such as geometric distortions and blurring could not be fully resolved. In accordance with part two, the SNR of spiral DWI was increased compared to EPI DWI. | |||||||
| Lizenz: |  Dieses Werk ist lizenziert unter einer Creative Commons Namensnennung 4.0 International Lizenz | |||||||
| Fachbereich / Einrichtung: | Mathematisch- Naturwissenschaftliche Fakultät » WE Physik | |||||||
| Dokument erstellt am: | 05.03.2025 | |||||||
| Dateien geändert am: | 05.03.2025 | |||||||
| Promotionsantrag am: | 22.10.2024 | |||||||
| Datum der Promotion: | 21.02.2025 |
