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

Shallow foundation analysis by smoothed particle hydrodynamics method

This paper illustrates the use of Smoothed Particle Hydrodynamics (SPH) technique to compute the bearingcapacity of shallow foundations and establish their failure mechanism. SPH is a numerical method based on aLagrangian formulation to solve partial differential equations by discretizing the computational domain with a setof particles that have field variables such as mass, and density. SPH is a meshless method and is not affected bythe particles’ arbitrariness due to its adaptive nature, and it can naturally handle problems that are caused by largedeformations. Non-associated Drucker-Prager model is implemented into the model to simulate the soil behavior.The computed values are then compared with PLAXIS 2D finite element results. Agreements of the results ofthese two methods show that SPH is potentially a promising method for geotechnical problems experiencing largedeformations and mesh distortions

Astronomical Site Selection for Turkey Using GIS Techniques

A site selection of potential observatory locations in Turkey have been carried out by using Multi-Criteria Decision Analysis (MCDA) coupled with Geographical Information Systems (GIS) and satellite imagery which in turn reduced cost and time and increased the accuracy of the final outcome. The layers of cloud cover, digital elevation model, artificial lights, precipitable water vapor, aerosol optical thickness and wind speed were studied in the GIS system. In conclusion of MCDA, the most suitable regions were found to be located in a strip crossing from southwest to northeast including also a diverted region in southeast of Turkey. These regions are thus our prime candidate locations for future on-site testing. In addition to this major outcome, this study has also been applied to locations of major observatories sites. Since no goal is set for \textit{the best}, the results of this study is limited with a list of positions. Therefore, the list has to be further confirmed with on-site tests. A national funding has been awarded to produce a prototype of an on-site test unit (to measure both astronomical and meteorological parameters) which might be used in this list of locations.Comment: 17 pages, 10 figures, accepted by Experimental Astronom

Система управління оборотним капіталом підприємства: елементна структура та ефектівність

Метою дослідження є створення комплексної сістеми менеджменту оборотним капіталом та забезпечення її ефективного функціонування. В цьому зв’язку необхідно управляти не лише окремими елементами оборотного капіталу, але і всіма бізнес – процесами підприємства з інтегруванням у стратегічне управління. Це зумовлено тим, що систему управління оборотним капіталом не доцільно розглядати відокремлено від всього підприємства, а її варто досліджувати у комплексі з іншими підсистемами

Assessment of Dynamic Change of Coronary Artery Geometry and Its Relationship to Coronary Artery Disease, Based on Coronary CT Angiography

To investigate the relationship between dynamic changes of coronary artery geometry and coronary artery disease (CAD) using computed tomography (CT). Seventy-one patients underwent coronary CT angiography with retrospective electrocardiographic gating. End-systolic (ES) and end-diastolic (ED) phases were automatically determined by dedicated software. Centerlines were extracted for the right and left coronary artery. Differences between ES and ED curvature and tortuosity were determined. Associations of change in geometrical parameters with plaque types and degree of stenosis were investigated using linear mixed models. The differences in number of inflection points were analyzed using Wilcoxon signed-rank tests. Tests were done on artery and segment level. One hundred thirty-seven arteries (64.3%) and 456 (71.4%) segments were included. Curvature was significantly higher in ES than in ED phase for arteries (p = 0.002) and segments (p < 0.001). The difference was significant only at segment level for tortuosity (p = 0.005). Number of inflection points was significantly higher in ES phase on both artery and segment level (p < 0.001). No significant relationships were found between degree of stenosis and plaque types and dynamic change in geometrical parameters. Non-invasive imaging by cardiac CT can quantify change in geometrical parameters of the coronary arteries during the cardiac cycle. Dynamic change of vessel geometry through the cardiac cycle was not found to be related to the presence of CAD

Three-Dimensional Finite Element Modeling for Spudcan Penetration into a Clayey Seabed

In this study the penetration of spudcan foundation for "jack-up rig" type offshore oil platform into a uniform clayey seabed is investigated with three-dimensional finite element modeling (Abaqus 6.14) using Coupled Eulerian Lagrangian method that can handle large deformation problems. One of the goals of this study is to compare the penetration-bearing resistance behavior of spudcan obtained by numerical study with the method suggested in InSafeJIP design guideline. For the spudcan geometry and soil properties used in this study, based on the three dimensional finite element analyses, the required penetration depth for a target bearing capacity of spudcan is less than that required by analytical method in InSafeJIP guideline. The second goal of the study is to explore the effects of some geometrical and soil variables on spudcan bearing resistance-penetration behavior. The variables in this study are spudcan diameter (7.5 to 15 m), the surface roughness of spudcan (roughness coefficient of 0 to 1.0) and undrained shear strength of clay (20 to 80 kPa). Understanding the relations between the factors and penetration behavior may help in future studies on enhanced and economical design of spudcans

Three dimensional finite element modelling for offshore platform foundation penetration into clayey seabed

In this study the penetration of spudcan foundation for “jack-up rig” type offshore oil platform into a uniform clayey seabed is investigated with three-dimensional finite element modeling (Abaqus 6.14) using coupled Eulerian-Lagrangian method that can handle large strain problems. One of the goals of this study is to compare the penetration-bearing resistance behavior of spudcan obtained by numerical study with the method suggested in InSafeJIP design guideline. For the spudcan geometry and soil properties used in this study, based on the three dimensional finite element analyses, the required penetration depth for a target bearing capacity of spudcan is less than that required by analytical method in InSafeJIP guideline. The second goal of the study is to explore the effects of some geometrical and soil variables on spudcan bearing resistance-penetration behavior. The variables in this study are spudcan diameter (7.5 to 15.0 m), the surface roughness of spudcan (roughness coefficient of 0 to 1.0) and undrained shear strength of clay (20 to 80 kPa). Understanding the relations between these factors and penetration behavior may help in future studies on enhanced and economical design of spudcans.Bu çalışmada, jack-up tipi açık deniz platform temellerinin (spudcan) uniform killi deniz tabanına penetrasyonu, üç boyutlu sonlu elemanlar modeli (Abaqus 6.14) ile bağlı EulerLagranj metodu kullanılarak ele alınmıştır. Bu çalışmanın amaçlarından biri üç boyutlu numerik çalışmalarla elde edilen penetrasyon – taşıma kapasitesi davranışını mevcut dizayn kılavuzundaki (InSafeJIP) sonuçlarla karşılaştırmaktır. Bu çalışmada kullanılan spudcan geometrisi ve zemin özellikleri için, üç boyutlu sonlu elemanları metodu ile elde edilen hedef spudcan taşıma kapasitesi için gerekli penetrasyon derinliği, InsafeJIP yöntemi ile elde edilenden daha azdır. Çalışmanın ikinci amacı, spudcan temellerin bazı geometrik özellikleri ile zemine ait değişkenlerin taşıma kapasitesi ve penetrasyon derinliği ilişkisine etkilerini araştırmaktır. Çalışmadaki değişkenler spudcan çapı (7.5 – 15.0 m), spudcan yüzey pürüzlülüğü (pürüzlülük katsayısı 0 – 1.0 m) ve kilin drenajsız kayma dayanımıdır (20 – 80 kPa)’dır. Bu faktörler ve penetrasyon davranışı arasındaki ilişkileri anlamak, daha gelişmiş ve daha ekonomik spudcan temel tasarımlarında faydalı olabilecektir