Thesis (M.S.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains v, 43 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 27).

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (M. Phil.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 194-209). Also available in print.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references (leaves 112-122). Available also in a digital version from Dissertation Abstracts.

Thesis--Ph. D., University of Hong Kong. / Typewritten.

published_or_final_version / Public Health / Master / Doctor of Medicine

Cardiovascular diseases is a leading cause of death worldwide and improvement of the corresponding screening tool is the best way to deal with this clinical problem. In this thesis we attempted to develop a framework of ultrasound high frame rate vector flow imaging (VFI) by emphasizing on the design of corresponding flow detector and flow estimator. We believe that the high temporal resolution and the complex blood flow visualization ability of high frame rate VFI enables it to be further developed as a reliable flow imaging modality for cardiological examination. In order to achieve high temporal resolution, fast data acquisition algorithm was applied in the framework. Doppler signals acquired using this acquisition algorithm have two unique characteristics comparing with conventional data acquisition algorithm: (1) widen spectral bandwidth and (2) greater clutter to blood signal ratio. These signal characteristics give rise to unique signal processing. In addition, complex blood flow pattern, which is common in cardiological examination, induces extra challenges in implementing high frame rate VFI. In this thesis, flow detector which is adaptive to different flow scenarios and high dynamic range 2D flow estimator were presented. The proposed flow detector employes K-means++ clustering algorithm to classify clutter components from acquired Doppler signals. As a performance analysis, Field II simulation studies were performed by a parabolic flow phantom (flow velocity: 10mm/s to 200mm/s; tissue motion: 10mm/s; beam-flow angle: 60?). The post-filtered Doppler power map and BCR were used as qualitative and quantitativemeasures of detectors performance. Analyzed result has indicated that, as compared with clutter downmixing detector and eigen-based detector, the proposed flow detector could classify and suppress clutter component more effectively. Results also suggested that the proposed flow detector is more adaptive to slow flow scenarios where existing flow detectors failed to distinguish between blood and clutter components. For the proposed flow estimator, it was characterized by the interpolation of speckle tracking results in Lagrangian reference frame. The estimation bias and RMS error were calculated for different flow scenarios (flow velocity: 100mm/s to 500mm/s; beam-flow angle: 15? to 60?). It was found that the proposed flow estimator provides higher dynamic range than conventional speckle tracking-based flow estimator. Nonetheless, it is also observed that the estimation variances and errors increases in slow flow scenarios. In order to demonstrate the medical potential of the proposed high frame rate VFI framework. A carotid bifurcation simulation model with realistic blood flow pattern calculated using computational fluid dynamic software was applied in the performance evaluation study. In the VFI image obtained, complex blood flow pattern was readily visualized. In contrast, conventional ultrasound flow imaging was only able to estimate axial velocity map and thus lead to many ambiguities in analyzing the complex blood flow pattern. It proved that ultrasound high frame rate VFI has the potential to be further developed into a new cardiological examination technique. / published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

Ischemic heart disease (IHD) is the most common cause of death around the world. The underlying cause of IHD is myocardial ischemia as a result of progressive narrowing of coronary arteries due to atherosclerosis with potential thrombotic complications mediated by platelets. In addition to the role in hemostasis, platelets are increasingly recognized as an important mediator in this atherothrombotic disease. Basic management of IHD lies on medical therapy and coronary revascularization procedures. Percutaneous coronary intervention (PCI) is a commonly used revascularization procedure in the treatment of IHD especially for relief and reduction of symptoms. On the other hand, antiplatelet therapy is often administrated to patients undergoing PCI in an attempt to prevent major adverse cardiac events (MACE) following the procedures. However not all patients respond to the same degree of the antiplatelet therapy and some still develop MACE or stent thrombosis in the presence of the treatment with antiplatelet drugs. Recently a flow cytometric-based assay has been developed to monitor the effect of the antiplatelet drug, particularly the P2Y12 receptor antagonist, in patients treated with this kind of drug. This assay measures the activity of platelets as platelet reactivity index (PRI) based on the phosphorylation state of an intracellular platelet protein called vasodilator stimulated phosphoprotein (VASP). The measured value of PRI is inversely related to the response of patient to the antiplatelet drug. In this study, the response of patients to the P2Y12 receptor antagonist Clopidogrel was investigated following PCI. The PRI of patients was found to be significantly lower than normal subjects without taking this drug, indicating the therapeutic effect of this drug on the patients. However nearly one-third of patients (17 out of 59) studied were found to be non-responsive to clopidogrel treatment based on a cut-off established in this study for classifying patients into responders or non-responders. Furthermore, significant difference between the two types of stents used in PCI procedure, namely bare metal stent (BMS) and drug eluting stent (DES), was observed in the study. Patients receiving DES had nearly three times higher percentage of being non-responsive to clopidogrel than the BMS counterpart (45% vs. 16%, p<0.028). This study provides evidence that DES may be implicated in the non-responsiveness or drug resistance of clopidogrel in patient undergoing PCI. / published_or_final_version / Pathology / Master / Master of Medical Sciences

Cardiovascular disease (CVD) is the leading cause of mortality and morbidity worldwide. In Sub-Saharan Africa, rates of CVD are increasing rapidly, but there is little evidence about the potential determinants of CVD risk in this population. This thesis investigated CVD risk factors in Gaborone, capital city of Botswana, by (i) documenting CVD risk factors in this population, (ii) investigating the association between diet and CVD risk factors and (iii) assessing the association between diet and risk of CVD. 787 adults were recruited. Of these 566 were generally “healthy” with no history of CVD, while 221 (“diseased”) had at least one reported CVD condition, hypertension or diabetes. The median (interquartile range) age was 27 (23, 32) and 52 (42, 62) years for healthy and diseased participants respectively. All participants completed an interview administered questionnaire, including a food frequency questionnaire. Height, weight, waist circumference and blood pressure were measured, and a non-fasting blood sample was obtained for analysis of lipids, lipoproteins and glucose. A high prevalence of overweight and obesity (36.8%), particularly in women (50.0%), and low HDL cholesterol (<1.0 mmol/L men and <1.3 mmol/L women) (62.6%) was found. High levels of triglycerides, LDL cholesterol, glucose and high blood pressure were also found in this population of young adults in Gaborone. Total fat and/or saturated fat intake (as percentage energy) was significantly linearly associated with increased LDL cholesterol (p=0.017), triglycerides (p=0.048), glucose (p=0.044) and with decreased HDL cholesterol (p=0.021). However, fibre, polyunsaturated fatty acids and dietary patterns were not independently associated with CVD risk factors. Carbohydrates intake was significantly associated with increased risk of disease. Unexpectedly, saturated fat intake was associated with reduced disease risk, but weakened after nutrients adjustment. CVD risk factors are relatively high in this population. These results suggest a need for further research on CVD in Botswana.

University of Macau / Faculty of Science and Technology / Department of Electrical and Computer Engineering