Numerical and experimental haemodynamic studies of stenotic coronary arteries

Dissertação de mestrado integrado em Engenharia Biomédica (área de especialização em Biomateriais, Reabilitação e Biomecânica)Cardiovascular diseases remain the most frequent cause of mortality worldwide and constitute a major healthcare challenge. Among them, coronary artery disease causes nearly half of the deaths and, thus it is of great interest to better understand its development and effects. This disease is characterized by the narrowing (stenosis) of coronary arteries due to plaque deposition at the arterial wall, a pathological process known as atherosclerosis. This dissertation aimed to study the hemodynamics in stenotic coronary arteries, in order to get a deeper understanding of the effects of this pathology on the blood flow behavior. For this purpose, both numerical and experimental studies were conducted using idealized models. The numerical research was carried out using Ansys® software by means of computational fluid dynamics which applies the finite volume method. The experimental approach was performed using a high-speed video microscopy system, to visualize and investigate the blood flow in the in vitro stenotic biomodels. Initially, the influence of roughness in flow visualizations was studied, and the best biomodel was the one printed with the lowest resolution having been, therefore, the selected to perform the hemodynamic studies. To compare those results with numerical data, the flow was set to be laminar and stationary and the fluid was considered Newtonian. In general, the numerical and experimental results were in good agreement, not only in the prediction of the flow behavior with the appearance of recirculation zones in the post-stenotic section, but also in the velocity profiles. In a posterior phase, a pulsatile inlet condition was applied to compare the use of laminar and turbulent assumptions, using the SST k- model. The results obtained allowed to conclude that the second one is more appropriate to simulate the blood flow. Subsequently, the main differences in hemodynamics were examined considering blood as a Newtonian and non-Newtonian fluid (Carreau model). For these models, the differences were very slight in terms of velocity fields, but more significant for the wall shear stress measurements, with the Newtonian model predicting lower values. The remaining simulations were performed using the Carreau model and a transient inlet flow, having observed an increase in the velocities and wall shear stress values with the degree of stenosis, which is associated with a greater risk of thrombosis.As doenças cardiovasculares continuam a ser a causa mais frequente de mortalidade em todo o mundo e constituem um grande desafio para a saúde. Entre elas, a doença arterial coronariana causa quase metade das mortes e, portanto, é de enorme interesse entender melhor o seu desenvolvimento e efeitos. Esta doença é caracterizada pelo estreitamento (estenose) das artérias coronárias devido à deposição de placas na parede arterial, um processo patológico conhecido como aterosclerose. Esta dissertação teve como objetivo estudar a hemodinâmica nas artérias coronárias estenóticas, a fim de obter uma compreensão mais profunda dos efeitos desta patologia no comportamento do fluxo sanguíneo. Para tal, foram realizados estudos numéricos e experimentais, utilizando modelos idealizados. A investigação numérica foi realizada no software Ansys®, através da dinâmica computacional dos fluidos, que aplica o método dos volumes finitos. A abordagem experimental foi realizada utilizando um sistema de microscopia de vídeo de alta velocidade, para visualizar e investigar o fluxo sanguíneo nos biomodelos estenóticos in vitro. Inicialmente, estudou-se a influência da rugosidade nas visualizações do escoamento, e o melhor biomodelo foi o impresso com menor resolução tendo sido, portanto, o selecionado para a realização dos estudos hemodinâmicos. Para comparar esses resultados com dados numéricos, o escoamento foi definido como laminar e estacionário e o fluído foi considerado Newtoniano. Em geral, os resultados numéricos e experimentais foram concordantes, não só na previsão do comportamento do fluxo com aparecimento de zonas de recirculação na zona pós-estenótica, mas também nos perfis de velocidade. Numa fase posterior, foi aplicada uma condição de entrada pulsátil para comparar o uso de simulações de natureza laminar e turbulenta, usando o modelo SST k-. Os resultados obtidos permitiram concluir que a segunda é mais apropriado para simular o fluxo sanguíneo. Posteriormente, foram examinadas as principais diferenças hemodinâmicas, considerando o sangue como fluído Newtoniano e não-Newtoniano (modelo de Carreau). Para estes modelos, as diferenças foram muito pequenas nos perfis de velocidade, mas mais significativas nas tensões de corte na parede medidas, com o modelo Newtoniano a prever valores mais baixos. As restantes simulações foram realizadas usando o modelo de Carreau e um escoamento de entrada transiente, tendo-se observado um aumento dos valores das velocidades e da tensão de corte na parede com o grau de estenose, o que está associado a um maior risco de trombose

Chemical differences of atherosclerotic plaques in native and bypass human coronary arteries and diseased and non-diseased human aortas

ABSTRACT Cardiovascular disease, primarily atherosclerosis involves a number of distinct processes that are associated with plaque development. The use of differential gel electrophoresis to determine differences between proteins produced in native and bypass coronary arteries from the same heart has been studied. The analytical techniques presented in this study to characterize plaque samples include two dimensional gel electrophoresis, sodium dodecylsulfate polyacrylamide gel electrophoresis, mass spectrometry, differential gel electrophoresis, and high performance liquid chromatography. An overview of the stages involved in atherosclerosis and the theories implicated in the manifestation of atherosclerosis was presented. A design study using the Box Behnken method was used to optimize the components in lysis buffer to solubilize the membrane proteins present in the intima in atherosclerotic plaques. The number of proteins located as spots in the gel were optimized in this study. The isolation and characterization of proteins in intima and media extracts of diseased aortas were separated using two dimensional gel electrophoresis followed by excision of gel spots and tryptic digestion to peptides. Mass analysis (MS and MS/MS) of the digested peptides with a linear quadrupole trap Fourier transform ion cyclotron resonance mass spectrometer was used to determine the amino acid sequences. Protein extracts of normal and diseased aortas and native and bypass arteries were analyzed using differential gel electrophoresis system. Cydye 3 (1-(5-carboxypentyl)-1`-propylindocarbocyanine halide N-hydroxy-succinimidyl ester) and Cydye 5 (1-(5-carboxypentyl)-1´-methylindodicarbocyanine halide N-hydroxy-succinimidyl ester) are fluorescent dyes used in our study to identify differentially expressed proteins of interest in the same gel using matrix assisted laser desorption ionization time-of-flight mass spectrometry. Several proteins in normal and diseased tissues were identified A study of the separation and quantification of cholesterol and cholesteryl esters was performed using reverse phase high performance liquid chromatograph interfaced with atmospheric pressure chemical ionization probe that was introduced into a quadrupole mass analyzer. Thirty-five samples were analyzed by principal component analysis that produced two distinct age groups based on age. In addition, a disease severity index was generated from the data. This study concluded that age and low disease severity index were indicators of the atherogenic states of the extracts analyzed

Bioengineering Stents for Proactive Biocompatibility: From Biomaterials to Stents

The thesis describes methods to characterize modified biomaterial surfaces in vitro, and investigate its short term implications at the artery interface in vivo. Plasma activated coating (PAC) technology has been previously deposited on a stainless steel biomaterial (316LSS), investigated in the stent form in vivo. Initial histopathology characterizations conducted with resin-artery-stents evaluate artery-stent interface interactions in vivo. The 7 day pilot study was followed by detailed material characterization and biofunctionalization on a modified cobalt chromium metal alloy L605, for the first time herein. The outcome of this study, is to transfer optimized plasma technology to new generation cobalt chromium stents (Multi Link 8, Abbott Vascular); currently in use to treat coronary artery disease (CAD). Plasma technology is unique for its ability to not delaminate from a biomaterial, while providing surface hemocompatibility, cytocompatibility, and controlled covalent attachment of protein tropoelastin (TE), in its native conformation. The present study addressed three key questions: 1. Do PAC 316LSS stents engineered with TE improve in vivo biocompatibility at 7 days? 2. How does PAC adhere to cobalt chromium alloy L605 (novel biomaterial) to prevent delamination under stress? 3. How does PAC-L605 maintain superior hemocompatibility and promote homogenous cell culture compared to alloy L605

Functional endothelium on tissue engineered small diameter vascular grafts

Er zijn veel mensen die beschadigde of verstopte kransslagaderen of perifere vaten hebben. Bij deze patiënten is het noodzakelijk om de bloeddoorstroming te herstellen. Het uitvoeren van een bypass operatie is de voornaamste behandeling hiervoor. Een andere groep patiënten die ook afhankelijk kunnen zijn van vasculaire grafts zijn patiënten met een nierziekte die afhankelijk zijn van dialyse. Tegenwoordig worden voor bypass operaties vaak patiënt-eigen (slag)aders of synthetische grafts gebruikt. Sommige van deze grafts hebben een beperkte levensduur en functioneren niet optimaal. Wanneer bijvoorbeeld een ader uit het onderbeen wordt gebruikt om een kransslagader te vervangen zit na 10 jaar ongeveer 57% van deze bypasses dicht. Tevens is het zo dat voor vaatvervangingen grafts steeds vaker nodig zijn, aangezien een toenemend aantal patiënten een heroperatie moet ondergaan en geen geschikte vaten meer over heeft. Het kweken van bloedvaten in het laboratorium (tissueengineering) zou een goed alternatief kunnen zijn om de beperkingen van de huidige grafts te verhelpen. Zulke bloedvaten bestaan uit levend patiënt-eigen weefsel en hebben daardoor de eigenschap om zich te herstellen en te remodelleren. Recentelijk zijn er grote vooruitgangen geboekt in de ontwikkeling van sterke humane getissue-engineerde grafts met een kleine diameter. Er is echter minder onderzoek gedaan aan de ontwikkeling van een functionele endotheelcel (EC) laag op die grafts. De EC laag is een zeer actieve cellaag die betrokken is bij weefsel homeostase en de regulering van vaatwandspanning. Verder is deze cellaag ook betrokken bij de regulering van groei van andere celtypen. Daarnaast wordt trombose, wat een belangrijke oorzaak is van het falen van grafts, actief voorkomen door de aanwezigheid van een intacte EC laag. Daarom was het doel van dit proefschrift om een functionele EC laag te creëren op humane getissue-engineerde grafts. Deze grafts zijn gebaseerd op een scaffold van polyglycolic acid met een poly-4-hydroxybutyrate coating, die gezaaid wordt met humane myofibroblasten (MF) afkomstig van de vena saphena. Om een getissue-engineerde graft te endothelialiseren is het noodzakelijk de twee celtypen (ECs en MFs) samen te kweken. Dit is niet triviaal, aangezien de twee celtypen normaal verschillende kweekomstandigheden vereisen. In dit proefschrift is een 3D co-cultuur ontwikkeld, waarin de omstandigheden om de MFs en ECs samen te kweken konden worden geoptimaliseerd. Er is aangetoond dat ECs niet overleven in standaard kweekmedium (DMEM), maar dat deze cellen een speciaal EC medium nodig hebben. Wanneer dit medium gebruikt wordt en de ECs pas na 3 of 4 weken kweken op de vasculaire constructen gezaaid worden, resulteert dit in mooie volle EC laag. Het is bekend dat ECs het fenotype van de cellen in hun omgeving kunnen beïnvloeden wanneer deze cellen samen gekweekt worden. Het is in dit proefschrift aangetoond dat zowel de groei als de expressie van een gladde spiercel marker van MFs beïnvloed wordt door het samen kweken met ECs. Het is ook aangetoond dat een laag ECs de weefselcompositie van de vasculaire constructen beïnvloedt. Een functionele EC laag dient ook niet trombogeen te zijn. Om dit te onderzoeken zijn de vasculaire constructen blootgesteld aan een bloedstroming en hiermee is aangetoond dat ECs inderdaad de trombogeniciteit van de constructen verlaagd. Als laatste is er een bioreactor ontwikkeld om getissue-engineerde bloedvaten met een kleine diameter te kweken en waarmee ook een EC laag aangebracht kan worden. Eén dag na het zaaien van de ECs is de cellaag bijna vol en hebben de cellen een ronde vorm. De gezaaide ECs worden vervolgens geconditioneerd door kweekmedium door de grafts te laten stromen, wat een afschuifspannig op de cellen veroorzaakt. De viscositeit van het kweekmedium is verhoogd tot de waarde van bloed door middel van xanthaan gom. Xanthaan gom is een stabiel verdikkingsmiddel en zorgt al bij lage concentraties voor hoge viscositeiten. Het gebruik van xanthaan gom zorgt ervoor dat, wanneer we een fysiologische stroming aanbrengen in het vat, ook een fysiologische afschuifspanning ontstaat. Het is in dit proefschrift aangetoond dat xantaan gom geen invloed heeft op de groei van ECs, hun oriëntatie in de richting van de vloeistofstroming en hun bloedvatverwijdende eigenschappen. De afschuifspanning op de ECs van de getissue-engineerde vaten zorgt ervoor dat de ECs wel een volle laag vormen. Tevens oriënteren de ECs zich in de richting van de stroming en krijgen ze een langgerekte vorm, in tegenstelling tot de ongeconditioneerde ECs, die geen volle cellaag vormen. Samenvattend kan gesteld worden dat in dit proefschrift verschillende EC functies zijn onderzocht met behulp van verschillende modelsystemen. Er is tevens een bioreactor systeem ontwikkeld waarmee bloedvaten met een kleine diameter gekweekt zijn. Na optimalisatie van de kweekomstandigheden is op deze vaten een functionele EC laag gecreëerd, die fysiologische afschuifspanningen kan weerstaan. Deze functionele EC laag is een belangrijke stap voor de klinische toepasbaarheid van deze vaten

Characterization of native and bypass human coronary artery plaque deposits from the same heart: investigation of the chemical form of calcium in human coronary artery plaque deposits

Gradual deposits of lipids, proteins, and calcium on the coronary arterial walls cause atherosclerosis, leading to blockage of the blood flow and possible heart attack. Despite many studies, the mechanism underlying these processes remains unclear. In this research, differences between native and bypass plaque deposits from the same heart were examined. In addition, the crystalline and the amorphous plaques within these native and bypass vessels were characterized. The techniques used to characterize the deposits included inductively coupled plasma mass spectrometry (ICPMS), solid-state nuclear magnetic resonance (NMR), high performance liquid chromatography (HPLC), etc. The results from the ICPMS technique showed that the concentrations of Ca and P varied widely in the bypass arteries. In contrast, the concentrations of Ca and P were higher in the native deposits. The molar ratios of Ca/P indicated that these elements probably exist as hydroxyapatite in the calcified tissues. However, the molar ratio of Ca/P in the soft tissue suggests that the phosphorus does not only exist as hydroxyapatite but that at least half of it may also be organic. The 13C and 31P solid-states NMR spectra of the native and bypass coronary plaques from the same heart indicated that the concentrations of carbonyl groups, typical of cholesterol esters, were similar between the native and bypass arteries. Significant signals of carbonyl groups in the crystalline and amorphous plaques were due to amino acids and proteins deposited in the plaques. Studies of 31P showed that the phosphorus exists mostly as hydroxyapatite in the crystalline native plaque, but a large proportion exists as organic phosphorus. To study the interactions of calcium with homocysteine and cholesterol, 13C solid-state NMR of homocysteine, Ca-homocysteine, Ca-homocysteine-cholesterol, Ca-cholesterol were performed. Significant spectral changes were also noted when calcium was added to homocysteine and cholesterol. The chemical forms and the distribution of calcium were studied using x-ray absorption and light microscopy with silver staining. Finally, chromatographic methods (CEC and APCI-MS) showed that only 40 % or less of the plaque in native or bypass arteries consisted of cholesterol and its esters and the remaining, 60% were composed of proteins, fatty acids, and phospholipids

CARDIAC RECONSTRUCTION WITH ORGAN SPECIFIC EXTRACELLULAR MATRIX

Surgical reconstruction of congenital heart defects is often limited by the non-resorbable material used to approximate normal anatomy. In contrast, non-crosslinked extracellular matrix (ECM) biologic scaffold materials have been used for tissue reconstruction of multiple organs and are replaced by host tissue. Preparation of whole organ ECM by vascular perfusion can maintain much of the native three-dimensional (3D) structure, strength, and tissue specific composition. A 3D Cardiac-ECM (C-ECM) biologic scaffold material would logically have structural and functional advantages over materials such as Dacron™ for myocardial repair, but the in vivo remodeling characteristics of C-ECM have not been investigated to date. Intact porcine and rat hearts were decellularized through retrograde aortic perfusion to create a 3D C-ECM biologic scaffold material. C-ECM biochemical and structural composition were evaluated. C-ECM was not different in cell survival assays from a standard ECM material, urinary bladder matrix (UBM), and supported cardiomyocytes in both 2D and 3D culture. Finally, a porcine C-ECM or Dacron™ patch was used to reconstruct a full thickness right ventricular outflow tract (RVOT) defect in a rat model with a primary endpoint of 16 wk The Dacron patch was encapsulated by dense fibrous tissue and showed little cellular infiltration. Echocardiographic analysis showed that the Dacron patched heart had dilated right ventricular minimum and maximum dimensions at 16 wk compared to pre-surgery baseline values. The C-ECM patch remodeled into dense, cellular connective tissue including: collagen, endothelium, smooth muscle, and small islands of cardiomyocytes. The C-ECM patch showed no ventricular dimensional or functional differences to baseline values at either the 4 or 16 wk time point. The porcine and rat heart can be efficiently decellularized using perfusion in less than 10 hours. The potential benefit of the 2D and 3D C-ECM was shown to support cardiomyocytes with an organized sarcomere structure. The C-ECM patch was associated with better function and histomorphology compared to the Dacron™ patch in this rat model of RVOT reconstruction. While there is much work to be done, the methodology described herein provides a useful step to fully realizing a functional cardiac patch

수치 모델과 그래프 이론을 이용한 향상된 영상 분할 연구 -폐 영상에 응용-

학위논문 (박사)-- 서울대학교 대학원 : 공과대학 협동과정 바이오엔지니어링전공, 2016. 2. 김희찬.This dissertation presents a thoracic cavity segmentation algorithm and a method of pulmonary artery and vein decomposition from volumetric chest CT, and evaluates their performances. The main contribution of this research is to develop an automated algorithm for segmentation of the clinically meaningful organ. Although there are several methods to improve the organ segmentation accuracy such as the morphological method based on threshold algorithm or the object selection method based on the connectivity information our novel algorithm uses numerical algorithms and graph theory which came from the computer engineering field. This dissertation presents a new method through the following two examples and evaluates the results of the method. The first study aimed at the thoracic cavity segmentation. The thoracic cavity is the organ enclosed by the thoracic wall and the diaphragm surface. The thoracic wall has no clear boundary. Moreover since the diaphragm is the thin surface, this organ might have lost parts of its surface in the chest CT. As the previous researches, a method which found the mediastinum on the 2D axial view was reported, and a thoracic wall extraction method and several diaphragm segmentation methods were also informed independently. But the thoracic cavity volume segmentation method was proposed in this thesis for the first time. In terms of thoracic cavity volumetry, the mean±SD volumetric overlap ratio (VOR), false positive ratio on VOR (FPRV), and false negative ratio on VOR (FNRV) of the proposed method were 98.17±0.84%, 0.49±0.23%, and 1.34±0.83%, respectively. The proposed semi-automatic thoracic cavity segmentation method, which extracts multiple organs (namely, the rib, thoracic wall, diaphragm, and heart), performed with high accuracy and may be useful for clinical purposes. The second study proposed a method to decompose the pulmonary vessel into vessel subtrees for separation of the artery and vein. The volume images of the separated artery and vein could be used for a simulation support data in the lung cancer. Although a clinician could perform the separation in his imagination, and separate the vessel into the artery and vein in the manual, an automatic separation method is the better method than other methods. In the previous semi-automatic method, root marking of 30 to 40 points was needed while tracing vessels under 2D slice view, and this procedure needed approximately an hour and a half. After optimization of the feature value set, the accuracy of the arterial and venous decomposition was 89.71 ± 3.76% in comparison with the gold standard. This framework could be clinically useful for studies on the effects of the pulmonary arteries and veins on lung diseases.Chapter 1 General Introduction 2 1.1 Image Informatics using Open Source 3 1.2 History of the segmentation algorithm 5 1.3 Goal of Thesis Work 8 Chapter 2 Thoracic cavity segmentation algorithm using multi-organ extraction and surface fitting in volumetric CT 10 2.1 Introduction 11 2.2 Related Studies 13 2.3 The Proposed Thoracic Cavity Segmentation Method 16 2.4 Experimental Results 35 2.5 Discussion 41 2.6 Conclusion 45 Chapter 3 Semi-automatic decomposition method of pulmonary artery and vein using two level minimum spanning tree constructions for non-enhanced volumetric CT 46 3.1 Introduction 47 3.2 Related Studies 51 3.3 Artery and Vein Decomposition 55 3.4 An Efficient Decomposition Method 70 3.5 Evaluation 75 3.6 Discussion and Conclusion 85 References 88 Abstract in Korean 95Docto

Magnetic Resonance Imaging of Coronary Arteries: Latest Technical Innovations and Clinical Experiences

Cardiovascular disease (CVD) is the leading cause of death and a major health care challenge globally. Coronary artery disease (CAD) is a primary underlying pathological process in the majority of cardiovascular disease cases. Magnetic resonance imaging (MRI) can play a potentially important role in the management of CAD as a noninvasive imaging modality without ionizing radiation, although its early promise has not been delivered because of several crucial technical limitations. However, recent innovations in MRI have reopened the door, with tremendous opportunities for multiparametric assessment of CAD including luminal stenosis, plaque burden and composition, and disease activities such as inflammation and hemorrhage. Novel MRI acquisition and reconstruction strategies now offer much increased spatial resolution and image quality and shortened examination times compared with conventional approaches. Recent clinical experiences of coronary MRI indicated the potential to improve the current management of coronary atherosclerosis, such as identifying the patients at the highest risk and evaluating therapeutic responses. In this review we discuss the latest technical advances and clinical insights in coronary MRI