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Eignung und Unsicherheiten geometrischer und fluiddynamischer Parameter zur Rupturrisikoabschätzung zerebraler Aneurysmen
Citation Link: https://doi.org/10.15480/882.2910
Publikationstyp
Doctoral Thesis
Publikationsdatum
2020
Sprache
German
Author
Advisor
Referee
Title Granting Institution
Technische Universität Hamburg
Place of Title Granting Institution
Hamburg
Examination Date
2020-09-15
Institut
TORE-URI
Citation
Technische Universität Hamburg (2020)
Cerebral aneurysms are abnormal bulges of blood vessels in the brain that, if ruptured, can cause severe damage - from motor and cognitive failure to death. The choice of a suitable therapy for a diagnosed aneurysm is currently largely dependent on the size and location of the aneurysm. In contrast, hemodynamic and mechanical properties of the vascular system are not currently used in clinical practice for the risk assessment of aneurysms, but could be of great diagnostic value, especially for the assessment of small aneurysms with regard to the assessment of formation, growth and ultimately rupture. Furthermore, a major problem in understanding aneurysms with regard to the exact mechanisms leading to rupture is that only a few image data sets of individual aneurysm structures exist at different points in time. The different developmental stages of a single aneurysm are therefore difficult to analyze, making it difficult to formulate and verify propositions regarding the factors that determine development and rupture. This problem was the motivation for this work, which is why we worked on the exact calculation of geometric deformation of aneurysms, the reliable calculation of fluid-mechanical parameters and a extrapolated temporal development of aneurysm structures. Typically, only limited ground-truth data sets are available in this field of research. Therefore, the goal for this work was to base the analysis on verifiable datasets as much as possible, which motivated the development of a hardware phantom.
The phantom simulates the fluid-mechanical characteristics of an aneurysm and material properties of the vessel wall and serves as a ground truth data set for all studies presented. The flow phantom was measured with different imaging modalities (MRI, CT, DSA), so that medical image data (which are common in this research field) are available, which represent the geometry and temporal geometric deformation. First, these data were used to develop a reliable method for the calculation of volumes and deformation of aneurysm geometries.
Although previous studies have tried to quantify aneurysm pulsation based on temporally resolved image data, artifacts of the used imaging modalities have not been addressed, so it is not clear to what extent the measured values correspond to a true deformation. In addition, in previous studies no ground-truth data sets were used to verify the generated results, which leaves the reliability regarding the quantified values open. In order to approach the reliable calculation of fluid mechanical parameters, a fluid mechanical calculation setup was set up using the Ground-Truth data set, which enables a reliable simulation and calculation of fluid mechanical parameters. The previously acquired knowledge of exact phantom geometry, deformation and fluid mechanical boundary conditions (inflow velocity, etc.) was used to verify the calculated results. Based on this calculation setup, patient-specific geometries, which were collected at the University Medical Center Hamburg-Eppendorf (Clinic and Polyclinic for Neuroradiological Diagnostics and Intervention), could be simulated and parameters, which correlated with an increased risk of rupture in previous studies, could be evaluated. This was carried out in the sense of a parameter study with the aim of identifying boundary conditions that could have a falsifying influence on the produced results, which could explain the partial contradiction of currently published studies.
In addition, different developmental stages of aneurysms were constructed and the geometric shape was simulated so that the fluid mechanical properties that change over the development process could be analysed.
The phantom simulates the fluid-mechanical characteristics of an aneurysm and material properties of the vessel wall and serves as a ground truth data set for all studies presented. The flow phantom was measured with different imaging modalities (MRI, CT, DSA), so that medical image data (which are common in this research field) are available, which represent the geometry and temporal geometric deformation. First, these data were used to develop a reliable method for the calculation of volumes and deformation of aneurysm geometries.
Although previous studies have tried to quantify aneurysm pulsation based on temporally resolved image data, artifacts of the used imaging modalities have not been addressed, so it is not clear to what extent the measured values correspond to a true deformation. In addition, in previous studies no ground-truth data sets were used to verify the generated results, which leaves the reliability regarding the quantified values open. In order to approach the reliable calculation of fluid mechanical parameters, a fluid mechanical calculation setup was set up using the Ground-Truth data set, which enables a reliable simulation and calculation of fluid mechanical parameters. The previously acquired knowledge of exact phantom geometry, deformation and fluid mechanical boundary conditions (inflow velocity, etc.) was used to verify the calculated results. Based on this calculation setup, patient-specific geometries, which were collected at the University Medical Center Hamburg-Eppendorf (Clinic and Polyclinic for Neuroradiological Diagnostics and Intervention), could be simulated and parameters, which correlated with an increased risk of rupture in previous studies, could be evaluated. This was carried out in the sense of a parameter study with the aim of identifying boundary conditions that could have a falsifying influence on the produced results, which could explain the partial contradiction of currently published studies.
In addition, different developmental stages of aneurysms were constructed and the geometric shape was simulated so that the fluid mechanical properties that change over the development process could be analysed.
Schlagworte
Aneurysm
Image processing
IMAGE REGISTRATION
Phantoms, Imaging
image analysis
DDC Class
570: Biowissenschaften, Biologie
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dissertation.pdf
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