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ItemDevelopment of virtual mitral valve leaflet models from three-dimensional echocardiography(Georgia Institute of Technology, 2012-07-05) Icenogle, David A.Mitral valve (MV) disease is responsible for approximately 2,581 deaths and 41,000 hospital discharges each year in the US. Mitral regurgitation (MR), retrograde blood from through the MV, is often an indicator of MV disease. Surgical repair of MVs is preferred over replacement, as it is correlated with better patient quality of life. However, replacement rates are still near 40% because MV surgical repair expertise is not spread across all hospitals. In addition, 15-80% of surgical repair patients have recurrent MR within 10 years. Quantitative patient-specific models could aid these issues by providing less experienced surgeons with additional information before surgery and a quantitative map of patient valve changes after surgery. Real-time 3D echocardiography (RT3DE) can provide high quality 3D images of MVs and has been used to generate quantitative models previously. However, there is not currently an efficient, dynamic, and validated method that is fast enough to use in common practice. To fill this need, a tool to generate quantitative 3D models of mitral valve leaflets from RT3DE in an efficient manner was created. Then an in vitro echocardiography correction scheme was devised and a dynamic, in vitro validation of the tool was performed. The tool demonstrated that it could generate dynamic, complex MV geometry accurately and more efficiently than current methods available. In addition, the ability for mesh interpolation techniques to reduce segmentation time was demonstrated. The tool generated by this study provides a method to quickly and accurately generate MV geometry that could be applied to dynamic patient specific geometry to aid surgical decisions and track patient geometry changes after surgery.
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ItemEffects of Mechanical Forces on the Biological Properties of Porcine Aortic Valve Leaflets(Georgia Institute of Technology, 2005-01-12) Xing, YunCardiac valves are dynamic, sophisticated structures which interact closely with the surrounding hemodynamic environment. Altered mechanical stresses, including pressure, shear and bending stresses, are believed to cause changes in valve biology, but the cellular and molecular events involved in these processes are not well characterized. Therefore, the overall goal of this project is to determine the effects of pressure and shear stress on porcine aortic valve leaflets biology. Results from the pressure study showed that elevated constant pressure (140 and 170 mmHg) causes significant increases in collagen synthesis. The increases were 37.5% and 90% for 140 and 170 mmHg, respectively. No significant differences in DNA and sGAG synthesis were observed under constant pressure. In the cyclic pressure study, the effects of both pressure magnitude and pulse frequency were studied. With the frequency fixed at 1.167 Hz, collagen and sGAG synthesis increased proportionally with mean pressure level. At a fixed pressure level (80-120 mmHg), collagen and sGAG synthesis were slightly increased by 25% and 14% at 0.5 Hz, respectively. DNA synthesis was significantly increased by 72% at 2 Hz. An experiment combining high magnitude (150-190 mmHg) and high frequency (2 Hz) demonstrated significant increases in collagen and sGAG synthesis (collagen: 74%, sGAG: 56%), but no significant changes in cell proliferation. Shear levels ranging from 1 to 80 dyne/cm2 were studied. Scanning electron microscopy results indicated that 48 hrs exposure to shear stress did not alter the circumferential alignment of endothelial cells. Collagen synthesis was significantly enhanced at 9 and 25 dyne/cm2, but not different from static controls under other shear conditions. Leaflets denuded of the endothelium were exposed to identical shear stress and showed very different responses. Collagen synthesis was not affected at any shear levels, but sGAG content was increased at shear of 9, 25 and 40 dyne/cm2. Further studies showed that the increases in collagen synthesis under pressure or shear stress was concurrent with a decline in the expression and activities of cathepsins L and S. This converse relationship between collagen synthesis and cathepsin activity indicated that cathepsins might be involved in valvular ECM remodeling.
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ItemRenal Arterial Blood Flow Quantification by Breath-held Phase-velocity Encoded MRI(Georgia Institute of Technology, 2004-05-14) Wallin, Ashley KayAutosomal dominant polycystic disease (ADPKD) is the most common hereditary renal disease and is characterized by renal cyst growth and enlargement. Hypertension occurs early when renal function is normal and is characterized by decreased renal blood flow. Accordingly, the measurement of blood flow in the renal arteries can be a valuable tool in evaluating disease progression. In studies performed in conjunction with this work, blood flow was measured through the renal arteries using magnetic resonance imaging (MRI). In order to validate these in vivo measurements, a vascular phantom was created using polyvinyl alcohol (PVA) and also scanned using MRI under controlled steady flow conditions. Ranges of vessel diameters and flow velocities were used to simulate actual flow in a normal and diseased population of adults and children. With the vessel diameters studied in this experiment, minimization of field of view and an increase in spatial resolution is important in obtaining accurate data. However, a significant difference does not exist between the results when using the 160 or 200 mm FOV. An increase in the number of phase encodings provides improved results, although an increase in image acquisition time is observed. Velocity-encoding in all three orthogonal directions does not improve image data. This method of using MRI to measure flow through a vessel is shown to be both accurate and reproducible, and the protocol providing the most correct results is prescribed. Breath-hold phase-velocity encoded MRI proves to be an accurate and reproducible technique in capturing flow and has the potential to be used for the purpose of observing hemodynamic changes in the renal arteries with the progression of ADPKD.
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ItemStentless mitral valve fixation : impact on hemodynamic performance(Georgia Institute of Technology, 2000-05) Jensen, Morten Ølgaard Jegstrup
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ItemA fluid mechanic assessment of the total cavopulmonary connection(Georgia Institute of Technology, 2000-05) Ensley, Ann Elizabeth
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ItemVisualization and quanification of early diastolic function by magnetic resonance phase velocity mapping(Georgia Institute of Technology, 1998-08) Milet, Sylvain F.
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ItemVisualization and quantification of left heart blood flow by phase encoding magnetic resonance imaging(Georgia Institute of Technology, 1994-08) Milet, Sylvain F.