Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 100-103).

Thesis (Ph. D.)--University of Hong Kong, 1987.

Thesis (M. Phil.)--University of Hong Kong, 2001. / Includes bibliographical references.

published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

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

Reliability and repeatability are fundamental concepts in ultrasonic nondestructive testing. An inspection technique must be able to accurately detect, characterize, position and size any defect indication. In manual ultrasonic inspection, however, the operator can be a frequent source of error. Mistakes often arise due to the volume of information the operator must memorize and process. Existing solutions require mechanical probe manipulators that restrict the operator's movements and often require changes to trusted methods and procedures. The aim of this research programme was to investigate the potential of a computer system that assists the operator in the analysis of echodynamic patterns. The system allows the operator to record A-scan sequences, store them to disk, and recall them for review. The system's flexible user interface gives the operator freedom to retain existing inspection practices, in addition to the benefits of computer recording. A novel feature of the system was a speech recognition system to provide hands-free control, which minimizes disruption to the flow of the inspection. Trials were conducted to assess the recognizer's reliability under various conditions. The trials showed that focusing upon echodynamic pattern analysis is a valid and useful approach. Only a limited trial was conducted, however, so the research program was not able to conclusively show that the system will reduce operator errors or improve inspection reliability. In user testing sessions, operators agreed that such a system would be helpful during a manual inspection and there were few objections to the imposition of new hardware. Users quickly became used to the speech recognizer, and the speed of interaction and 'flow' of inspection were greatly enhanced. The author suggests that a computerized assistant is worthy of further development, and has the potential to be a valuable tool in manual ultrasonic inspection.

The research represents a first approach to measure the utilization potential of ultrasonic pretreatment on six different substrates: fat, oil and grease (FOG), paper sludge, ground switch grass, ground hay, ground wheat straw, and cut wheat straw. Several laboratories techniques were applied to determine the influence of ultrasonication on biogas production and yield, biogas quality, and digestibility ratio. With the data, mathematical definitions of Net Energy Balance and Net Economy Balance were computed to draw a first justification or rejection of the use of this pretreatment technology for the specific substrates. Ultrasonic pretreatment has a significant effect on biogas production and yield as well as digestibility ratio (p-value < 0.0001) from the early stages of digestion until as far as 50 days of digestion. Ultrasonication and macro particle size management did not influence significantly the methane (CH4) content in the biogas (p-value = 0.1793). Also, the impact of ultrasonication on the substrate varies between all studied feedstock. Most of the ultrasonicated digestion cases studied provided a negative Net Energy and Economic Balance except for FOG where a certain window of utilization was found. In the context of an ultrasonication process retrofit upgrade, the technology looks to be more useful for substrates that are hard to digest when the retention time is, unfortunately, longer than common retention time. In the context of a new facility, a design that includes an understood ultrasonication technology has yet a small potential success depending on several variables. The ultrasonication technology for anaerobic digestion is hard to recommend due to its energy consumption that, in many cases, overshadows the energy surplus derived from its use. / MITACS

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