Quantitative imaging in cardiovascular CT angiography

In de afgelopen decennia is computertomografie (CT) een prominente niet-invasieve modaliteit om hart- en vaatziekten te evalueren geworden. Dit proefschrift heeft als doel de rol van CT in de therapeutische behandeling van coronaire hartziekte (CAD) en klepaandoeningen te onderzoeken.De relatie tussen kransslagadergeometrie (statisch en dynamisch) en aanwezigheid en omvang van CAD met CT werd onderzocht. De resultaten suggereren dat de statische geometrie van de kransslagader significant gerelateerd is aan de aanwezigheid van plaque en stenose. Er was echter geen verband tussen dynamische verandering van de coronaire arterie-geometrie en de ernst van CAD. Een algoritme om de invloed van intraluminair contrastmiddel op niet-verkalkte atherosclerotische plaque Hounsfield-Unit-waarden te corrigeren werd gepresenteerd en gevalideerd met behulp van fantomen.Diagnose en operatieplanning kunnen cruciale gevolgen hebben voor de klinische uitkomst van chirurgische ingrepen. In dit proefschrift wordt beschreven dat halfautomatische softwareprogramma’s het kwantificeren van het aortaklepgebied betere reproduceerbare resultaten toonden in vergelijking met handmatige metingen, en vergelijkbare resultaten met de huidige gouden standaard, de echocardiografie. Een systematische review over het dynamische gedrag van de aorta-annulus toont aan dat de vorm van de aorta-annulus tijdens de hartcyclus verandert, wat impliceert dat er bij het bepalen van een prothese rekening moet worden gehouden met meerdere fasen. Een andere review beschrijft het gebruik van 3D-printen in de chirurgische planning samen met andere toepassingen voor de behandeling van hartklepaandoeningen.CT is de belangrijkste beeldvormingsmodaliteit in deze onderzoeken, die gericht waren op de therapeutische behandeling van hart- en vaatziekten, van vroege risicobepaling tot diagnose en chirurgische planning.In the recent decades computed tomography (CT) has emerged as a dominant non-invasive modality to evaluate cardiovascular diseases. This thesis aimed to explore the role of CT in the therapeutic management of coronary artery disease (CAD) and valvular diseases.The relationship between both static and dynamic coronary artery geometry and presence and extent of CAD using CT was investigated. The results suggest that the static coronary artery geometry is significantly related to presence of plaque and significant stenosis. However, there were no such relationship between dynamic change of coronary artery geometry and severity of CAD. As part of this thesis an algorithm to correct the influence of lumen contrast enhancement on non-calcified atherosclerotic plaque Hounsfield-Unit values was presented. The algorithm was validated using phantoms. The diagnosis and surgical planning may have crucial impact on clinical outcome. Semi-automatic software for aortic valve area quantification presented in this thesis was proven to be more repeatable and similar to gold standard echocardiography in comparison to manual measurements. The systematic review regarding the dynamic behavior of aortic annulus revealed that aortic annulus geometry changes throughout the cardiac cycle which implies that multiple phases should be taken into account for prosthesis sizing. Another review in this thesis discusses the use of 3D printing in the surgical planning along with other applications for the treatment of valvular diseases.CT is the main imaging modality in these studies which were focused on the therapeutic management of cardiovascular diseases from early risk determination to diagnosis and surgical planning

Scanning protocol optimisation for dual-energy computed tomography angiography in peripheral artery stenting

In this thesis, a novel approach has been proposed to evaluate the optimal scanning protocol for dual energy computed tomography angiography in peripheral arterial stents. This new approach includes evaluation of different protocols and image reconstructions at different energy level, development of the optimal protocol based on lowest radiation dose and acceptable image quality. Furthermore, an optimal contrast medium protocol has been identified in imaging peripheral arterial disease

3D Imaging for Planning of Minimally Invasive Surgical Procedures

Novel minimally invasive surgeries are used for treating cardiovascular diseases and are performed under 2D fluoroscopic guidance with a C-arm system. 3D multidetector row computed tomography (MDCT) images are routinely used for preprocedural planning and postprocedural follow-up. For preprocedural planning, the ability to integrate the MDCT with fluoroscopic images for intraprocedural guidance is of clinical interest. Registration may be facilitated by rotating the C-arm to acquire 3D C-arm CT images. This dissertation describes the development of optimal scan and contrast parameters for C-arm CT in 6 swine. A 5-s ungated C-arm CT acquisition during rapid ventricular pacing with aortic root injection using minimal contrast (36 mL), producing high attenuation (1226), few artifacts (2.0), and measurements similar to those from MDCT (p\u3e0.05) was determined optimal. 3D MDCT and C-arm CT images were registered to overlay the aortic structures from MDCT onto fluoroscopic images for guidance in placing the prosthesis. This work also describes the development of a methodology to develop power equation (R2\u3e0.998) for estimating dose with C-arm CT based on applied tube voltage. Application in 10 patients yielded 5.48┬▒177 2.02 mGy indicating minimal radiation burden. For postprocedural follow-up, combinations of non-contrast, arterial, venous single energy CT (SECT) scans are used to monitor patients at multiple time intervals resulting in high cumulative radiation dose. Employing a single dual-energy CT (DECT) scan to replace two SECT scans can reduce dose. This work focuses on evaluating the feasibility of DECT imaging in the arterial phase. The replacement of non-contrast and arterial SECT acquisitions with one arterial DECT acquisition in 30 patients allowed generation of virtual non-contrast (VNC) images with 31 dose savings. Aortic luminal attenuation in VNC (32┬▒177 2 HU) was similar to true non-contrast images (35┬▒177 4 HU) indicating presence of unattenuated blood. To improve discrimination between c

3D Imaging for Planning of Minimally Invasive Surgical Procedures

Novel minimally invasive surgeries are used for treating cardiovascular diseases and are performed under 2D fluoroscopic guidance with a C-arm system. 3D multidetector row computed tomography (MDCT) images are routinely used for preprocedural planning and postprocedural follow-up. For preprocedural planning, the ability to integrate the MDCT with fluoroscopic images for intraprocedural guidance is of clinical interest. Registration may be facilitated by rotating the C-arm to acquire 3D C-arm CT images. This dissertation describes the development of optimal scan and contrast parameters for C-arm CT in 6 swine. A 5-s ungated C-arm CT acquisition during rapid ventricular pacing with aortic root injection using minimal contrast (36 mL), producing high attenuation (1226), few artifacts (2.0), and measurements similar to those from MDCT (p\u3e0.05) was determined optimal. 3D MDCT and C-arm CT images were registered to overlay the aortic structures from MDCT onto fluoroscopic images for guidance in placing the prosthesis. This work also describes the development of a methodology to develop power equation (R2\u3e0.998) for estimating dose with C-arm CT based on applied tube voltage. Application in 10 patients yielded 5.48┬▒177 2.02 mGy indicating minimal radiation burden. For postprocedural follow-up, combinations of non-contrast, arterial, venous single energy CT (SECT) scans are used to monitor patients at multiple time intervals resulting in high cumulative radiation dose. Employing a single dual-energy CT (DECT) scan to replace two SECT scans can reduce dose. This work focuses on evaluating the feasibility of DECT imaging in the arterial phase. The replacement of non-contrast and arterial SECT acquisitions with one arterial DECT acquisition in 30 patients allowed generation of virtual non-contrast (VNC) images with 31 dose savings. Aortic luminal attenuation in VNC (32┬▒177 2 HU) was similar to true non-contrast images (35┬▒177 4 HU) indicating presence of unattenuated blood. To improve discrimination between c

NOVEL STRATEGIES FOR THE MORPHOLOGICAL AND BIOMECHANICAL ANALYSIS OF THE CARDIAC VALVES BASED ON VOLUMETRIC CLINICAL IMAGES

This work was focused on the morphological and biomechanical analysis of the heart valves exploiting the volumetric data. Novel methods were implemented to perform cardiac valve structure and sub-structure segmentation by defining long axis planes evenly rotated around the long axis of the valve. These methods were exploited to successfully reconstruct the 3D geometry of the mitral, tricuspid and aortic valve structures. Firstly, the reconstructed models were used for the morphological analysis providing a detailed description of the geometry of the valve structures, also computing novel indexes that could improve the description of the valvular apparatus and help their clinical assessment. Additionally, the models obtained for the mitral valve complex were adopted for the development of a novel biomechanical approach to simulate the systolic closure of the valve, relying on highly-efficient mass-spring models thus obtaining a good trade-off between the accuracy and the computational cost of the numerical simulations. In specific: \u2022 First, an innovative and semi-automated method was implemented to generate the 3D model of the aortic valve and of its calcifications, to quantitively describe its 3D morphology and to compute the anatomical aortic valve area (AVA) based on multi-detector computed tomography images. The comparison of the obtained results vs. effective AVA measurements showed a good correlation. Additionally, these methods accounted for asymmetries or anatomical derangements, which would be difficult to correctly capture through either effective AVA or planimetric AVA. \u2022 Second, a tool to quantitively assess the geometry of the tricuspid valve during the cardiac cycle using multidetector CT was developed, in particular focusing on the 3D spatial relationship between the tricuspid annulus and the right coronary artery. The morphological analysis of the annulus and leaflets confirmed data reported in literature. The qualitative and quantitative analysis of the spatial relationship could standardize the analysis protocol and be pivotal in the procedure planning of the percutaneous device implantation that interact with the tricuspid annulus. \u2022 Third, we simulated the systolic closure of three patient specific mitral valve models, derived from CMR datasets, by means of the mass spring model approach. The comparison of the obtained results vs. finite element analyses (considered as the gold-standard) was performed tuning the parameters of the mass spring model, so to obtain the best trade-off between computational expense and accuracy of the results. A configuration mismatch between the two models lower than two times the in-plane resolution of starting imaging data was yielded using a mass spring model set-up that requires, on average, only ten minutes to simulate the valve closure. \u2022 Finally, in the last chapter, we performed a comprehensive analysis which aimed at exploring the morphological and mechanical changes induced by the myxomatous pathologies in the mitral valve tissue. The analysis of mitral valve thickness confirmed the data and patterns reported in literature, while the mechanical test accurately described the behavior of the pathological tissue. A preliminary implementation of this data into finite element simulations suggested that the use of more reliable patient-specific and pathology-specific characterization of the model could improve the realism and the accuracy of the biomechanical simulations

Towards an Efficient Gas Exchange Monitoring with Electrical Impedance Tomography - Optimization and validation of methods to investigate and understand pulmonary blood flow with indicator dilution

In vielen Fällen sind bei Patienten, die unter stark gestörtem Gasaustausch der Lunge leiden, die regionale Lungenventilation und die Perfusion nicht aufeinander abgestimmt. Besonders bei Patienten mit akutem Lungenversagen sind sehr heterogene räumliche Verteilungen von Belüftung und Perfusion der Lunge zu beobachten. Diese Patienten müssen auf der Intensivstation künstlich beatmet und überwacht werden, um einen ausreichenden Gasaustausch sicherzustellen. Bei schweren Lungenverletzungen ist es schwierig, durch die Anwendung hoher Beatmungsdrücke und -volumina eine optimale Balance zwischen dem Rekrutieren kollabierter Regionen zu finden, und gleichzeitig die Lunge vor weiterem Schaden durch die von außen angelegten Drücke zu schützen. Das Interesse für eine bettseitige Messung und Darstellung der regionalen Belüftungs- und Perfusionsverteilung für den Einsatz auf der Intensivstation ist in den letzten Jahren stark gestiegen, um eine lungenprotektive Beatmung zu ermöglichen und klinische Diagnosen zu vereinfachen. Die Elektrische-Impedanztomographie (EIT) ist ein nicht-invasives, strahlungsfreies und sehr mobil einsetzbares System. Es bietet eine hohe zeitliche Abtastung und eine funktionelle räumliche Auflösung, die es ermöglicht, dynamische (patho-) physiologische Prozesse zu visualisieren und zu überwachen. Die medizinische Forschung an EIT hat sich dabei hauptsächlich auf die Schätzung der räumlichen Belüftung konzentriert. Kommerziell erhältliche Systeme haben gezeigt, dass die EIT eine wertvolle Entscheidungshilfe während der mechanischen Beatmung darstellt. Allerdings ist die Abschätzung der pulmonalen Perfusion mit EIT noch nicht etabliert. Dies könnte das fehlende Glied sein, um die Analyse des pulmonalen Gasaustauschs am Krankenbett zu ermöglichen. Obwohl einige Publikationen die prinzipielle Machbarkeit der indikatorgestützten EIT zur Schätzung der räumlichen Verteilung des pulmonalen Blutflusses gezeigt haben, müssen diese Methoden optimiert und durch Vergleich mit dem Goldstandard des Lungenperfusions-Monitorings validiert werden. Darüber hinaus ist weitere Forschung notwendig, um zu verstehen welche physiologischen Informationen der EIT-Perfusionsschätzung zugrunde liegen. Mit der vorliegenden Arbeit soll die Frage beantwortet werden, ob bei der klinischen Anwendung von EIT neben der regionalen Belüftung auch räumliche Informationen des pulmonalen Blutflusses geschätzt werden können, um damit potenziell den pulmonalen Gasaustausch am Krankenbett beurteilen zu können. Die räumliche Verteilung der Perfusion wurde durch Bolusinjektion einer leitfähigen Kochsalzlösung als Indikator geschätzt, um die Verteilung des Indikators während seines Durchgangs durch das Gefäßsystem der Lunge zu verfolgen. Verschiedene dynamische EIT-Rekonstruktionsmethoden und Perfusionsparameter Schätzmethoden wurden entwickelt und verglichen, um den pulmonalen Blutfluss robust beurteilen zu können. Die geschätzten regionalen EIT-Perfusionsverteilungen wurden gegen Goldstandard Messverfahren der Lungenperfusion validiert. Eine erste Validierung wurde anhand von Daten einer tierexperimentellen Studie durchgeführt, bei der die Multidetektor-Computertomographie als vergleichende Lungenperfusionsmessung verwendet wurde. Darüber hinaus wurde im Rahmen dieser Arbeit eine umfassende präklinische Tierstudie durchgeführt, um die Lungenperfusion mit indikatorverstärkter EIT und Positronen-Emissions-Tomographie während mehrerer verschiedener experimenteller Zustände zu untersuchen. Neben einem gründlichen Methodenvergleich sollte die klinische Anwendbarkeit der indikatorgestützten EIT-Perfusionsmessung untersucht werden, indem wir vor allem die minimale Indikatorkonzentration analysierten, die eine robuste Perfusionsschätzung erlaubte und den geringsten Einfluss für den Patienten darstellt. Neben den experimentellen Validierungsstudien wurden zwei in-silico-Untersuchungen durchgeführt, um erstens die Sensitivität von EIT gegenüber des Durchgangs eines leitfähigen Indikators durch die Lunge vor stark heterogenem pulmonalen Hintergrund zu bewerten. Zweitens untersuchten wir die physiologischen Einflüsse, die zu den rekonstruierten EITPerfusionsbildern beitragen, um die Limitationen der Methode besser zu verstehen. Die Analysen zeigten, dass die Schätzung der Lungenperfusion auf der Basis der indikatorverstärkten EIT ein großes Potenzial für die Anwendung in der klinischen Praxis aufweist, da wir sie mit zwei Goldstandard-Perfusionsmesstechniken validieren konnten. Zudem konnten wertvolle Schlüsse über die physiologischen Einflüsse auf die geschätzten EIT Perfusionsverteilungen gezogen werden

Quantitative image analysis for the detection of motion artefacts in coronary artery computed tomography

Multi detector-row CT (MDCT), the current preferred method for coronary artery disease assessment, is still affected by motion artefacts. To rule out motion artefacts, qualitative image analysis is usually performed. Our study aimed to develop a quantitative image analysis for motion artefacts detection as an added value to the qualitative analysis. An anthropomorphic moving heart phantom with adjustable heart-rate was scanned on 64-MDCT and dual-source-CT. A new software technique was developed which detected motion artefacts in the coronaries and also in the myocardium, where motion artefacts are more apparent; with direct association to the qualitative analysis. The new quantitative analysis managed to detect motion artefacts in phantom scans and relate them to artefact-induced vessel stenoses. Quantifying these artefacts at corresponding locations in the myocardium, artefact-induced vessel stenosis findings could be avoided. In conclusion, the quantitative analysis together with the qualitative analysis rules out artefact-induced stenosis