833 research outputs found

    Computer-Aided Patient-Specific Coronary Artery Graft Design Improvements Using CFD Coupled Shape Optimizer

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    This study aims to (i) demonstrate the efficacy of a new surgical planning framework for complex cardiovascular reconstructions, (ii) develop a computational fluid dynamics (CFD) coupled multi-dimensional shape optimization method to aid patient-specific coronary artery by-pass graft (CABG) design and, (iii) compare the hemodynamic efficiency of the sequential CABG, i.e., raising a daughter parallel branch from the parent CABG in patient-specific 3D settings. Hemodynamic efficiency of patient-specific complete revascularization scenarios for right coronary artery (RCA), left anterior descending artery (LAD), and left circumflex artery (LCX) bypasses were investigated in comparison to the stenosis condition. Multivariate 2D constraint optimization was applied on the left internal mammary artery (LIMA) graft, which was parameterized based on actual surgical settings extracted from 2D CT slices. The objective function was set to minimize the local variation of wall shear stress (WSS) and other hemodynamic indices (energy dissipation, flow deviation angle, average WSS, and vorticity) that correlate with performance of the graft and risk of re-stenosis at the anastomosis zone. Once the optimized 2D graft shape was obtained, it was translated to 3D using an in-house “sketch-based” interactive anatomical editing tool. The final graft design was evaluated using an experimentally validated second-order non-Newtonian CFD solver incorporating resistance based outlet boundary conditions. 3D patient-specific simulations for the healthy coronary anatomy produced realistic coronary flows. All revascularization techniques restored coronary perfusions to the healthy baseline. Multi-scale evaluation of the optimized LIMA graft enabled significant wall shear stress gradient (WSSG) relief (~34%). In comparison to original LIMA graft, sequential graft also lowered the WSSG by 15% proximal to LAD and diagonal bifurcation. The proposed sketch-based surgical planning paradigm evaluated the selected coronary bypass surgery procedures based on acute hemodynamic readjustments of aorta-CA flow. This methodology may provide a rational to aid surgical decision making in time-critical, patient-specific CA bypass operations before in vivo execution

    An optical coherence tomography and endothelial shear stress study of a novel bioresorbable bypass graft

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    Endothelial shear stress (ESS) plays a key role in the clinical outcomes in native and stented segments; however, their implications in bypass grafts and especially in a synthetic biorestorative coronary artery bypass graft are yet unclear. This report aims to examine the interplay between ESS and the morphological alterations of a biorestorative coronary bypass graft in an animal model. Computational fluid dynamics (CFD) simulation derived from the fusion of angiography and optical coherence tomography (OCT) imaging was used to reconstruct data on the luminal anatomy of a bioresorbable coronary bypass graft with an endoluminal "flap" identified during OCT acquisition. The "flap" compromised the smooth lumen surface and considerably disturbed the local flow, leading to abnormally low ESS and high oscillatory shear stress (OSI) in the vicinity of the "flap". In the presence of the catheter, the flow is more stable (median OSI 0.02384 versus 0.02635, p < 0.0001; maximum OSI 0.4612 versus 0.4837). Conversely, OSI increased as the catheter was withdrawn which can potentially cause back-and-forth motions of the "flap", triggering tissue fatigue failure. CFD analysis in this report provided sophisticated physiological information that complements the anatomic assessment from imaging enabling a complete understanding of biorestorative graft pathophysiology

    Patient-specific design of the right ventricle to pulmonary artery conduit via computational analysis

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    Cardiovascular prostheses are routinely used in surgical procedures to address congenital malformations, for example establishing a pathway from the right ventricle to the pulmonary arteries (RV-PA) in pulmonary atresia and truncus arteriosus. Currently available options are fixed size and have limited durability. Hence, multiple re-operations are required to match the patients’ growth and address structural deterioration of the conduit. Moreover, the pre-set shape of these implants increases the complexity of operation to accommodate patient specific anatomy. The goal of the research group is to address these limitations by 3D printing geometrically customised implants with growth capacity. In this study, patient-specific geometrical models of the heart were constructed by segmenting MRI data of patients using Mimics inPrint 2.0. Computational Fluid Dynamics (CFD) analysis was performed, using ANSYS CFX, to design customised geometries with better haemodynamic performance. CFD simulations showed that customisation of a replacement RV-PA conduit can improve its performance. For instance, mechanical energy dissipation and wall shear stress can be significantly reduced. Finite Element modelling also allowed prediction of the suitable thickness of a synthetic material to replicate the behaviour of pulmonary artery wall under arterial pressures. Hence, eliminating costly and time-consuming experiments based on trial-and-error. In conclusion, it is shown that patient-specific design is feasible, and these designs are likely to improve the flow dynamics of the RV-PA connection. Modelling also provides information for optimisation of biomaterial. In time, 3D printing a customised implant may simplify replacement procedures and potentially reduce the number of operations required over a life time, bringing substantial improvements in quality of life to the patient

    Histological evaluation of surgical experiments in animal models

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    Introduction: The dissertation is based on six studies that focus on the application of quantitative histology in animal model experiments. It includes a presentation of virtual microscopy procedures and image field sampling strategies, mapping changes in the microscopic structure of ovine and porcine carotid segments and their comparison with human coronary arteries and internal thoracic arteries, vascularization assessment in a mouse model of lymphoma xenografts (PDX), the effect of hyperbaric oxygen therapy on type III collagen production and on vascularization in a skin wound in a Zucker Diabetic Fatty rat. Methods: The review article about virtual microscopy was focused on an example of sampling images from various areas of quantitative histology. In other studies, histologically processed sections were stained with a variety of methods for vascular wall construction, cell infiltration (orcein, picrosirius red, Verhoeff's hematoxylin and green trichrome, Gill's hematoxylin, alcian blue) and immunohistochemical antigen detection (α-smooth muscle actin, neurofilament protein, CD-31, von Willebrand factor). Using unbiased sampling and stereological methods, we quantified the area fraction of components (elastin, collagen, smooth muscle actin and chondroitin sulfate) using a stereological grid...Úvod: Dizertační práce je založena na šesti studiích, které se zaměřují na uplatnění kvantitativní histologie v hodnocení experimentů u zvířecích modelů. Zahrnuje představení postupů virtuální mikroskopie a strategií vzorkování obrazových polí, mapování změn mikroskopické struktury segmentů ovčích a prasečích krkavic a jejich porovnání s lidskými koronárními cévami a arteria thoracica interna, hodnocení vaskularizace u myšího modelu s xenografty lymfomů (PDX), vliv hyperbarické oxygenoterapie na tvorbu kolagenu typu III a na vaskularizaci v kožní ráně u Zucker Diabetic Fatty potkana. Metody: Přehledový článek o virtuální mikroskopii byl zaměřen na ukázku příkladu vzorkování snímků z různých oblastí kvantitativní histologie. V ostatních studiích byly histologicky zpracované řezy barvené škálou metod zaměřených na stavbu cévní stěny, a buněčné osídlení (orcein, pikrosiriová červeň, Verhoeffův hematoxylin a zelený trichrom, Gillův hematoxylin, alcianová modř) a imunohistochemickým průkazem antigenů (α-hladký svalový aktin, neurofilamentový protein, CD-31, von Willebrandův faktor). Pomocí nevychýleného vzorkování a stereologických metod jsme kvantifikovali plošné podíly složek (elastin, kolagen, hladkosvalový aktin a chondroitinsulfát) použitím stereologické bodové mřížky; dvourozměrnou hustotu...Ústav histologie a embryologieLékařská fakulta v PlzniFaculty of Medicine in Pilse

    Experimental and Computational simulation of strain in medium sized arteries at macro- and micro-level.

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    Cardiovascular disease remains the leading cause of mortality in Western world. Current treatments for vascular disease include vascular grafting and stenting. Owing to the limitations of current treatments, over the past few years a significant research effort has been directed towards the development of tissue engineered blood vessels (TEBV). However, a TEBV that matches the biological and biomechanical functionality of natural blood vessels has yet to be developed. One of the strategies employed in the development of TEBVs involves the use of decellularised or synthetic scaffolds, which are seeded with the patient’s own cells and physically conditioned in bioreactors, with a view to developing blood-vessel-equivalent functionality prior to implantation. Along this line, the physical conditioning in bioreactors needs to replicate the in vivo haemodynamic stimulation, in order to guide normal cellular function and appropriate graft remodelling and regeneration. However, the in vitro set up, with the cells seeded on to a decellularised or synthetic scaffold and subjected to pulsatile flow in a bioreactor, does not represent a physiological scenario. Even if the bioreactor is able to simulate physiological haemodynamic conditions at the macroscale, the stimulus that would be transferred to the microscale and sensed by the cells to regulate their function is likely to be different from the micro-stimulus sensed by the cells in vivo in a native blood vessel. Therefore, in order to appropriately guide cellular function in vitro it would be necessary to assess the level of micro-stimulus sensed by the native cells in the native blood vessel in vivo, with a view to simulating this micro-stimulus in artificial bioreactor environments for conditioning the cells that are seeded onto scaffolds with non-native histoarhitectures. However, this micro-stimulus that vascular cells are exposed to in vivo cannot be assessed experimentally. The advances in computing and software resources have enabled the use of computational modelling for conducting such assessments. The aim of this project was to develop computational models for assessing the stress and strain fields on the vascular tissue and cells at the macro- and micro-scales, which will assist the bioreactor conditioning towards the development of tissue engineered vascular grafts. The 3D macro-scale simulations involved fluid-structure interaction (FSI) analysis with main focus on the strain on the vascular wall, while the 2D micro-scale simulation involved finite element analysis (FEA), focused on the local strain variation. All simulations were based on relatively physiological structures after experimental assessment. The simulations were also compared against experimental findings for strain. Macro strain resulted in approximately 11% for FSI against 19% for experimental pressure test. However, the limitations of the experimental procedure overestimated the performed dilation. Moreover, the 2D FEA simulations performed under different material properties, as an attempt to approach more physiological conditions, and under uniaxial strain only. The variation in material properties indicated inhomogeneicity, as expected, and also seemed to replicate the local strain spread when compared to experimental findings. However, further investigation is needed, which will involve the development of 3D FEA models, more physiological material properties and biaxial stretching. Under these circumstances, more information may be extracted and eventually applied to the bioreactor conditioning. Nevertheless, the novel methodology developed in this project for the study of the strain at the micro-level allows the further investigation on the tissue micro-environment
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