<p>The accuracy and precision of measurements of pulsating flow obtained with phase contrast magnetic resonance imaging (PC MRI) was studied. Measurements were carried out using known flow rates through a phantom connected to a pump that created pulsation in the flow. Repeated measurements were made in both the negative and positive encoding direction, using both breath-hold and non breath hold sequences. The obtained data was analyzed using code written in MATLAB and also using the FLOW software that is offered by the manufacturer of the MRI system.</p><p>A range of different flow velocities was scanned, and results show that the overall accuracy of the measurements is relatively good, with an average error of between 1.2% to 5.7% using the clinically employed flow calculation software. There is however indication of a systematic phase offset in the data that influences the measurements. The effect of the offset on the results depends on the direction of flow and the sequence used. The results also show the importance of properly selecting the area over which the flow rate is calculated.</p>

The accuracy and precision of measurements of pulsating flow obtained with phase contrast magnetic resonance imaging (PC MRI) was studied. Measurements were carried out using known flow rates through a phantom connected to a pump that created pulsation in the flow. Repeated measurements were made in both the negative and positive encoding direction, using both breath-hold and non breath hold sequences. The obtained data was analyzed using code written in MATLAB and also using the FLOW software that is offered by the manufacturer of the MRI system. A range of different flow velocities was scanned, and results show that the overall accuracy of the measurements is relatively good, with an average error of between 1.2% to 5.7% using the clinically employed flow calculation software. There is however indication of a systematic phase offset in the data that influences the measurements. The effect of the offset on the results depends on the direction of flow and the sequence used. The results also show the importance of properly selecting the area over which the flow rate is calculated.

Das zentrale Thema dieser Dissertation ist die Anwendung illustrativer Methoden auf zwei bisher ungelöste Probleme der Strömungsvisualisierung. Das Ziel der Strömungsvisualisierung ist die Bereitstellung von Software, die Experten beim Auswerten ihrer Strömungsdaten und damit beim Erkenntnisgewinn unterstützt. Bei der illustrativen Visualisierung handelt es sich um einen Zweig der Visualisierung, der sich an der künstlerischen Arbeit von Illustratoren orientiert. Letztere sind darauf spezialisiert komplizierte Zusammenhänge verständlich und ansprechend zu vermitteln. Die angewendeten Techniken werden in der illustrativen Visualisierung auf reale Daten übertragen, um die Effektivität der Darstellung zu erhöhen. Das erste Problem, das im Rahmen dieser Dissertation bearbeitet wurde, ist die eingeschränkte Verständlichkeit von komplexen Stromflächen. Selbstverdeckungen oder Aufrollungen behindern die Form- und Strömungswahrnehmung und machen diese Flächen gerade in interessanten Strömungssituationen wenig nützlich. Auf Basis von handgezeichneten Strömungsdarstellungen haben wir ein Flächenrendering entwickelt, das Silhouetten, nicht-photorealistische Beleuchtung und illustrative Stromlinien verwendet. Interaktive Flächenschnitte erlauben die Exploration der Flächen und der Strömungen, die sie repräsentieren. Angewendet auf verschiedene Stromflächen ließ sich zeigen, dass die Methoden die Verständlichkeit erhöhen, v.a. in Bereichen komplexer Strömung mit Aufwicklungen oder Singularitäten. Das zweite Problem ist die Strömungsanalyse des Blutes aus 4D PC-MRI-Daten. An diese relativ neue Datenmodalität werden hohe Erwartungen für die Erforschung und Behandlung kardiovaskulärer Krankheiten geknüpft, da sie erstmals ein dreidimensionales, zeitlich aufgelöstes Abbild der Hämodynamik liefert. Bisher werden 4D PC-MRI-Daten meist mit Werkzeugen der klassischen Strömungsvisualisierung verarbeitet. Diese werden den besonderen Ansprüchen der medizinischen Anwender jedoch nicht gerecht, die in kurzer Zeit eine übersichtliche Darstellung der relevanten Strömungsaspekte erhalten möchten. Wir haben ein Werkzeug zur visuellen Analyse der Blutströmung entwickelt, welches eine einfache Detektion von markanten Strömungsmustern erlaubt, wie z.B. Jets, Wirbel oder Bereiche mit hoher Blutverweildauer. Die Grundidee ist hierbei aus vorberechneten Integrallinien mit Hilfe speziell definierter Linienprädikate die relevanten, d.h. am gefragten Strömungsmuster, beteiligten Linien ausgewählt werden. Um eine intuitive Darstellung der Resultate zu erreichen, haben wir uns von Blutflußillustrationen inspirieren lassen und präsentieren eine abstrakte Linienbündel- und Wirbeldarstellung. Die Linienprädikatmethode sowie die abstrakte Darstellung der Strömungsmuster wurden an 4D PC-MRI-Daten von gesunden und pathologischen Aorten- und Herzdaten erfolgreich getestet. Auch die Evaluierung durch Experten zeigt die Nützlichkeit der Methode und ihr Potential für den Einsatz in der Forschung und der Klinik. / This thesis’ central theme is the use of illustrative methods to solve flow visualization problems. The goal of flow visualization is to provide users with software tools supporting them analyzing and extracting knowledge from their fluid dynamics data. This fluid dynamics data is produced in large amounts by simulations or measurements to answer diverse questions in application fields like engineering or medicine. This thesis deals with two unsolved problems in flow visualization and tackles them with methods of illustrative visualization. The latter is a subbranch of visualization whose methods are inspired by the art work of professional illustrators. They are specialized in the comprehensible and esthetic representation of complex knowledge. With illustrative visualization, their techniques are applied to real data to enhance their representation. The first problem dealt with in this thesis is the limited shape and flow perception of complex stream surfaces. Self-occlusion and wrap-ups hinder their effective use in the most interesting flow situations. On the basis of hand-drawn flow illustrations, a surface rendering method was designed that uses silhouettes, non-photorealistic shading, and illustrative surface stream lines. Additionally, geometrical and flow-based surface cuts allow the user an interactive exploration of the surface and the flow it represents. By applying this illustrative technique to various stream surfaces and collecting expert feedback, we could show that the comprehensibility of the stream surfaces was enhanced – especially in complex areas with surface wrap-ups and singularities. The second problem tackled in this thesis is the analysis of blood flow from 4D PC-MRI data. From this rather young data modality, medical experts expect many advances in the research of cardiovascular diseases because it delivers a three-dimensional and time-resolved image of the hemodynamics. However, 4D PC-MRI data are mainly processed with standard flow visualizaton tools, which do not fulfill the requirements of medical users. They need a quick and easy-to-understand display of the relevant blood flow aspects. We developed a tool for the visual analysis of blood flow that allows a fast detection of distinctive flow patterns, such as high-velocity jets, vortices, or areas with high residence times. The basic idea is to precalculate integral lines and use specifically designed line predicates to select and display only lines involved in the pattern of interest. Traditional blood flow illustrations inspired us to an abstract and comprehensible depiction of the resulting line bundles and vortices. The line predicate method and the illustrative flow pattern representation were successfully tested with 4D PC-MRI data of healthy and pathological aortae and hearts. Also, the feedback of several medical experts confirmed the usefulness of our methods and their capabilities for a future application in the clinical research and routine.

abstract: Magnetic resonance flow imaging techniques provide quantitative and qualitative information that can be attributed to flow related clinical pathologies. Clinical use of MR flow quantification requires fast acquisition and reconstruction schemes, and minimization of post processing errors. The purpose of this work is to provide improvements to the post processing of volumetric phase contrast MRI (PCMRI) data, identify a source of flow bias for cine PCMRI that has not been previously reported in the literature, and investigate a dynamic approach to image bulk cerebrospinal fluid (CSF) drainage in ventricular shunts. The proposed improvements are implemented as three research projects. In the first project, the improvements to post processing are made by proposing a new approach to estimating noise statistics for a single spiral acquisition, and using the estimated noise statistics to generate a mask distinguishing flow regions from background noise and static tissue in an image volume. The mask is applied towards reducing the computation time of phase unwrapping. The proposed noise estimation is shown to have comparable noise statistics as that of a vendor specific noise dynamic scan, with the added advantage of reduced scan time. The sparse flow region subset of the image volume is shown to speed up phase unwrapping for multidirectional velocity encoded 3D PCMRI scans. The second research project explores the extent of bias in cine PCMRI based flow estimates is investigated for CSF flow in the cerebral aqueduct. The dependance of the bias on spatial and temporal velocity gradient components is described. A critical velocity threshold is presented to prospectively determine the extent of bias as a function of scan acquisition parameters. Phase contrast MR imaging is not sensitive to measure bulk CSF drainage. A dynamic approach using a CSF label is investigated in the third project to detect bulk flow in a ventricular shunt. The proposed approach uses a preparatory pulse to label CSF signal and a variable delay between the preparatory pulse and data acquisition enables tracking of the CSF bulk flow. / Dissertation/Thesis / Doctoral Dissertation Biomedical Engineering 2017

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No description available.

Patients who are treated in an intensive care unit need continuous monitoring in orderfor clinicians to be prepared to intervene should a secondary event occur. For patientstreated at the neurointensive care unit (NICU) who have suffered a subarachnoid hemorrhage (SAH) this secondary event could be ischemia, resulting in a lack of blood flow.Blood flow can be measured using magnetic resonance imaging (MRI). The process is facilitated with a software called NOVA. Repeated measurements can therefore be performedas a way to monitor the patients, which in this context would be referred to as longitudinalmeasurements. As more data can be collected ways of analyzing and visualizing the datain a comprehensible way is needed. The aim of this thesis was therefore to develop and implement a method for analyzing and visualizing the longitudinal MR measurement data.With this aim in mind two research questions were relevant. The first one was how NOVAflow longitudinal measurements can be visualized to simplify interpretation by cliniciansand the second one was in what ways the longitudinal data can be analyzed. A graphicaluser interface (GUI) was created to present the developed analysis and visualization tool.Development of the tool progressed using feedback from supervisors and neurosurgeons.Visualization and analysis was done through plots of blood velocity and blood flow as themain component as well as a 2D vessel map. The final implementation showed multipleexamples of how the longitudinal data could be both visualized and analyzed. The resultstherefore provided a tool to analyze and visualize NOVA flow longitudinal measurementsin a way which was easily interpreted. Further improvements of the tool is possible andan area of improvement could involve increasing the adaptability of the tool.

yes / Purpose To characterize the intracranial volumetric changes that influence the cerebrospinal fluid (CSF) pulse in the Aqueduct of Sylvius (AoS). Materials and methods Neck MRI data were acquired from 12 healthy adults (8 female and 4 males; mean age = 30.9 years), using a 1.5 T scanner. The intracranial arterial, venous and CSF volumes changes, together with the aqueductal CSF (aCSF) volume, were estimated from flow rate data acquired at C2/C3 level and in the AoS. The correlations and temporal relationships among these volumes were computed. Results The aCSF volumetric changes were strongly correlated (r = 0.967, p < 0.001) with the changes in intracranial venous volume, whose peak occurred 7.0% of cardiac cycle (p = 0.023) before peak aCSF volume, but less correlated with the intracranial arterial and CSF volume changes (r = −0.664 and 0.676 respectively, p < 0.001). The intracranial CSF volume change was correlated with the intracranial venous volume change (r = 0.820, p < 0.001), whose peak occurred slightly before (4.2% of CC, p = 0.059). Conclusion The aCSF pulse is strongly correlated with intracranial venous volume, with expansion of the cortical veins occurring prior to aCSF flow towards the third ventricle. Both caudal-cranial aCSF flow and venous blood retention occur when arterial blood volume is at a minimum.

In cardiovascular medicine, the assessment of blood flow is fundamental to the understanding and detection of disease. Many pharmaceutical, interventional, and surgical treatments impact the flow. The primary purpose of the cardiovascular system is to drive, control and maintain blood flow to all parts of the body. In the normal cardiovascular system, fluid transport is maintained at high efficiency and the blood flow is essentially laminar. Disturbed and turbulent blood flow, on the other hand, appears to be present in many cardiovascular diseases and may contribute to their initiation and progression. Despite strong indications of an important interrelationship between flow and cardiovascular disease, medical imaging has lacked a non-invasive tool for the in vivo assessment of disturbed and turbulent flow. As a result, the extent and role of turbulence in the blood flow of humans have not yet been fully investigated. Magnetic resonance imaging (MRI) is a versatile tool for the non-invasive assessment of flow and has several important clinical and research applications, but might not yet have reached its full potential. Conventional MRI techniques for the assessment of flow are based on measurements of the mean velocity within an image voxel. The mean velocity corresponds to the first raw moment of the distribution of velocities within a voxel. An MRI framework for the quantification of any moment (mean, standard deviation, skew, etc.) of arbitrary velocity distributions is presented in this thesis. Disturbed and turbulent flows are characterized by velocity fluctuations that are superimposed on the mean velocity. The intensity of these velocity fluctuations can be quantified by their standard deviation, which is a commonly used measure of turbulence intensity. This thesis focuses on the development of a novel MRI method for the quantification of turbulence intensity. This method is mathematically derived and experimentally validated. Limitations and sources of error are investigated and guidelines for adequate application of MRI measurements of turbulence intensity are outlined. Furthermore, the method is adapted to the quantification of turbulence intensity in the pulsatile blood flow of humans and applied to a wide range of cardiovascular diseases. In these applications, elevated turbulence intensity was consistently detected in regions where highly disturbed flow was anticipated, and the effects of potential sources of errors were small. Diseased heart valves are often replaced with prosthetic heart valves, which, in spite of improved benefits and durability, continue to fall short of matching native flow patterns. In an in vitro setting, MRI was used to visualize and quantify turbulence intensity in the flow downstream from four common designs of prosthetic heart valves. Marked differences in the extent and degree of turbulence intensity were detected between the different valves. Mitral valve regurgitation is a common valve lesion associated with progressive left atrial and left ventricular remodelling, which may often require surgical correction to avoid irreversible ventricular dysfunction. The spatiotemporal dynamics of flow disturbances in mitral regurgitation were assessed based on measurements of flow patterns and turbulence intensity in a group of patients with significant regurgitation arising from similar valve lesions. Peak turbulence intensity occurred at the same time in all patients and the total turbulence intensity in the left atrium appeared closely related to the severity of regurgitation. MRI quantification of turbulence intensity has the potential to become a valuable tool in investigating the extent, timing and role of disturbed blood flow in the human cardiovascular system, as well as in the assessment of the effects of different therapeutic options in patients with vascular or valvular disorders.

Das zentrale Thema dieser Dissertation ist die Anwendung illustrativer Methoden auf zwei bisher ungelöste Probleme der Strömungsvisualisierung. Das Ziel der Strömungsvisualisierung ist die Bereitstellung von Software, die Experten beim Auswerten ihrer Strömungsdaten und damit beim Erkenntnisgewinn unterstützt. Bei der illustrativen Visualisierung handelt es sich um einen Zweig der Visualisierung, der sich an der künstlerischen Arbeit von Illustratoren orientiert. Letztere sind darauf spezialisiert komplizierte Zusammenhänge verständlich und ansprechend zu vermitteln. Die angewendeten Techniken werden in der illustrativen Visualisierung auf reale Daten übertragen, um die Effektivität der Darstellung zu erhöhen. Das erste Problem, das im Rahmen dieser Dissertation bearbeitet wurde, ist die eingeschränkte Verständlichkeit von komplexen Stromflächen. Selbstverdeckungen oder Aufrollungen behindern die Form- und Strömungswahrnehmung und machen diese Flächen gerade in interessanten Strömungssituationen wenig nützlich. Auf Basis von handgezeichneten Strömungsdarstellungen haben wir ein Flächenrendering entwickelt, das Silhouetten, nicht-photorealistische Beleuchtung und illustrative Stromlinien verwendet. Interaktive Flächenschnitte erlauben die Exploration der Flächen und der Strömungen, die sie repräsentieren. Angewendet auf verschiedene Stromflächen ließ sich zeigen, dass die Methoden die Verständlichkeit erhöhen, v.a. in Bereichen komplexer Strömung mit Aufwicklungen oder Singularitäten. Das zweite Problem ist die Strömungsanalyse des Blutes aus 4D PC-MRI-Daten. An diese relativ neue Datenmodalität werden hohe Erwartungen für die Erforschung und Behandlung kardiovaskulärer Krankheiten geknüpft, da sie erstmals ein dreidimensionales, zeitlich aufgelöstes Abbild der Hämodynamik liefert. Bisher werden 4D PC-MRI-Daten meist mit Werkzeugen der klassischen Strömungsvisualisierung verarbeitet. Diese werden den besonderen Ansprüchen der medizinischen Anwender jedoch nicht gerecht, die in kurzer Zeit eine übersichtliche Darstellung der relevanten Strömungsaspekte erhalten möchten. Wir haben ein Werkzeug zur visuellen Analyse der Blutströmung entwickelt, welches eine einfache Detektion von markanten Strömungsmustern erlaubt, wie z.B. Jets, Wirbel oder Bereiche mit hoher Blutverweildauer. Die Grundidee ist hierbei aus vorberechneten Integrallinien mit Hilfe speziell definierter Linienprädikate die relevanten, d.h. am gefragten Strömungsmuster, beteiligten Linien ausgewählt werden. Um eine intuitive Darstellung der Resultate zu erreichen, haben wir uns von Blutflußillustrationen inspirieren lassen und präsentieren eine abstrakte Linienbündel- und Wirbeldarstellung. Die Linienprädikatmethode sowie die abstrakte Darstellung der Strömungsmuster wurden an 4D PC-MRI-Daten von gesunden und pathologischen Aorten- und Herzdaten erfolgreich getestet. Auch die Evaluierung durch Experten zeigt die Nützlichkeit der Methode und ihr Potential für den Einsatz in der Forschung und der Klinik. / This thesis’ central theme is the use of illustrative methods to solve flow visualization problems. The goal of flow visualization is to provide users with software tools supporting them analyzing and extracting knowledge from their fluid dynamics data. This fluid dynamics data is produced in large amounts by simulations or measurements to answer diverse questions in application fields like engineering or medicine. This thesis deals with two unsolved problems in flow visualization and tackles them with methods of illustrative visualization. The latter is a subbranch of visualization whose methods are inspired by the art work of professional illustrators. They are specialized in the comprehensible and esthetic representation of complex knowledge. With illustrative visualization, their techniques are applied to real data to enhance their representation. The first problem dealt with in this thesis is the limited shape and flow perception of complex stream surfaces. Self-occlusion and wrap-ups hinder their effective use in the most interesting flow situations. On the basis of hand-drawn flow illustrations, a surface rendering method was designed that uses silhouettes, non-photorealistic shading, and illustrative surface stream lines. Additionally, geometrical and flow-based surface cuts allow the user an interactive exploration of the surface and the flow it represents. By applying this illustrative technique to various stream surfaces and collecting expert feedback, we could show that the comprehensibility of the stream surfaces was enhanced – especially in complex areas with surface wrap-ups and singularities. The second problem tackled in this thesis is the analysis of blood flow from 4D PC-MRI data. From this rather young data modality, medical experts expect many advances in the research of cardiovascular diseases because it delivers a three-dimensional and time-resolved image of the hemodynamics. However, 4D PC-MRI data are mainly processed with standard flow visualizaton tools, which do not fulfill the requirements of medical users. They need a quick and easy-to-understand display of the relevant blood flow aspects. We developed a tool for the visual analysis of blood flow that allows a fast detection of distinctive flow patterns, such as high-velocity jets, vortices, or areas with high residence times. The basic idea is to precalculate integral lines and use specifically designed line predicates to select and display only lines involved in the pattern of interest. Traditional blood flow illustrations inspired us to an abstract and comprehensible depiction of the resulting line bundles and vortices. The line predicate method and the illustrative flow pattern representation were successfully tested with 4D PC-MRI data of healthy and pathological aortae and hearts. Also, the feedback of several medical experts confirmed the usefulness of our methods and their capabilities for a future application in the clinical research and routine.