Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item APPLYING OPERATIONS RESEARCH MODELS TO PROBLEMS IN HEALTH CARE(2015) Price, Stuart Patrick; Golden, Bruce; Business and Management: Decision & Information Technologies; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Intensity- modulated radiation therapy is a form of cancer treatment that directs high energy x-rays to irradiate a tumor volume. In order to minimize the damage to surround-ing tissue the radiation is delivered from multiple angles. The selection of angles is an NP-hard problem and is currently done manually in most hospitals. We use previously evaluated treatment plans to train a machine learning model to sort potential treatment plans. By sorting potential treatment plans we can find better solutions while only evalu-ating a fifth as many plans. We then construct a genetic algorithm and use our machine learning models to search the space of all potential treatment plans to suggest a potential best plan. Using the genetic algorithm we are able to find plans 2% better on average than the previously best known plans. Proton therapy is a new form of radiation therapy. We simulated a proton therapy treatment center in order to optimize patient throughput and minimize patient wait time. We are able to schedule patients reducing wait times between 20% and 35% depending on patient tardiness and absenteeism. Finally, we analyzed the impact of operations research on the treatment of pros-tate cancer. We reviewed the work that has been published in both operations research and medical journals, seeing how it has impacted policy and doctor recommendations.Item OPTIMIZATION OF DEDICATED BREAST COMPUTED TOMOGRAPHY: BOWTIE FILTER DESIGN AND OPTIMAL SPECTRUM ANALYSIS(2014) Kontson, Kimberly; Chen, Yu; Jennings, Robert J; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Recently, researchers have been investigating the use of a new imaging modality called dedicated breast CT as a means of alleviating the problem of tissue superposition that comes from acquiring a two-dimensional image of a three-dimensional object in conventional mammography. Several groups have investigated the optimal spectrum for this new imaging modality using the dose efficiency as the FOM, but results are inconsistent. None of these groups have employed the use of bowtie filtration in their optimal spectrum studies. Given the right design, the inclusion of bowtie filtration will lead to improved dose efficiency as well as consistency in the metric independent of position in a given phantom. Bowtie filters can improve performance in several ways, including DR reduction, scatter reduction, patient dose reduction, and reduction of beam-hardening effects. In this dissertation, three different filter types with different choices for the tradeoffs between the performance improvements listed above are described. Examples of each type of bowtie filter are created for computational and Monte Carlo analyses, and two designs were fabricated for experimental analysis. Studies analyzing the material selection for each bowtie filter design and characterizing the scatter were also completed. Verification of the performance of the designs was done by calculating/measuring the HVL, intensity, and µeff behind the phantom as a function of fan-angle. The performance of the designs depended only weakly on incident spectrum and tissue composition. With various breast diameters, the calculated parameters varied the most, but the variation was substantially less than the no-bowtie filter case. For all designs, the DR requirement on the detector was reduced compared to the no-bowtie filter case. Simulation and experimental data showed that the use of our bowtie filters can reduce the peripheral dose to the breast by 61%, and provide uniform noise and CNR distributions. The best performing bowtie filter design was implemented in simulation studies analyzing the optimal spectrum through calculation of the dose efficiency metric. The results from this study show the improvement and consistency that can be obtained with the inclusion of the proper bowtie filter, and provide the research community with a methodology that will help lead to more consistent optimal spectrum results.Item Visual Computing Tools for Studying Micro-scale Diffusion(2014) Bista, Sujal; Varshney, Amitabh; Computer Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this dissertation, we present novel visual computing tools and techniques to facilitate the exploration, simulation, and visualization of micro-scale diffusion. Our research builds upon the latest advances in visualization, high-performance computing, medical imaging, and human perception. We validate our research using the driving applications of nano-assembly and diffusion kurtosis imaging (DKI). In both of these applications, diffusion plays a central role. In the former it mediates the process of transporting micron-sized particles through moving lasers, and in the latter it conveys brain micro-geometry. Nanocomponent-based devices, such as bio-sensors, electronic components, photonic devices, solar cells, and batteries, are expected to revolutionize health care, energy, communications, and the computing industry. However, in order to build such useful devices, nanoscale components need to be properly assembled together. We have developed a hybrid CPU/GPU-based computing tool to understand complex interactions between lasers, optical beads, and the suspension medium. We demonstrate how a high-performance visual computing tool can be used to accelerate an optical tweezers simulation to compute the force applied by a laser onto micro particles and study shadowing (refraction) behavior. This represents the first steps toward building a real-time nano-assembly planning system. A challenge in building such a system, however, is that optical tweezers systems typically lack stereo depth cues. We have developed a visual tool to provide an enhanced perception of a scene's 3D structure using the kinetic depth effect. The design of our tool has been informed by user studies of stereo perception using the kinetic-depth effect on monocular displays. Diffusion kurtosis imaging is gaining rapid adoption in the medical imaging community due to its ability to measure the non-Gaussian property of water diffusion in biological tissues. Compared with the traditional diffusion tensor imaging (DTI), DKI can provide additional details about the underlying microstructural characteristics of neural tissues. It has shown promising results in studies on changes in gray matter and mild traumatic brain injuries, where DTI is often found to be inadequate. However, the highly detailed spatio-angular fields in DKI datasets present a special challenge for visualization. Traditional techniques that use glyphs are often inadequate for expressing subtle changes in the DKI fields. In this dissertation, we outline a systematic way to manage, analyze, and visualize spatio-angular fields using spherical harmonics lighting functions to facilitate insights into the micro-structural properties of the brain.Item TASK SPECIFIC EVALUATION METHODOLOGY FOR CLINICAL FULL FIELD DIGITAL MAMMOGRAPHY(2012) Liu, Haimo; Kyprianou, Iacovos S; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Purpose: The purpose of this dissertation is to evaluate the image quality of clinical Full Field Digital Mammography (FFDM) systems. This is done by evaluating image acquisition performance of clinical FFDM in a comprehensive way that accounts for scatter, focal spot un-sharpness, detector blur and anti-scatter grid performance using an anthropomorphic phantom. Additionally we intend to provide a limited evaluation of the effects that image processing in clinical FFDM has in signal detectability. Methodology: We explored different strategies and a variety of mathematical model observers in order to evaluate the performance of clinical FFDM systems under different conditions. To evaluate image acquisition performance, we tested a system-model-based Hotelling observer (SMHO) model on a bench-top system using a uniform anthropomorphic phantom for an signal known exactly background known exactly (SKE/BKE) task. We then applied this concept on two clinical FFDM systems to compare their performance. In a limited study to evaluate the effects of image processing in the detectability of FFDM, we implemented the channelized Hotelling observer (CHO) model on clinically realistic images of an anatomical phantom for an SKE/BKE task. Results: Even though the two systems use different detection technologies, there was no significant difference between their image acquisition performances quantified by the Contrast-Detail (CD) curves. We applied the CHO model to investigate the image processing algorithms used in GE Senographe DS FFDM system. For the particular SKE/BKE task with rotationally symmetric signals, the image processing tends to contribute to a non-significant reduction of system detectability. Conclusion: We provided a complete description of FFDM system performance including the image acquisition chain and post-acquisition image processing. We demonstrated the simplicity and effectiveness of both the MFHO and CHO methods in a clinical setting.Item Estimation of Ultrasound Induced Heat Generationfor Therapeutic Applications(2012) Echeverria, Esteban; Thamire, Chandrasekhar; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The use of ultrasound for therapeutic applications has been increasingly examined mostly because of its noninvasive nature. Though many experimental studies have been conducted to verify the feasibility of the method, no correlations predicting the ultrasonic parameters required to generate prescribed volumetric heat generation rates. In this study, heat generated due to propagation of ultrasound, in soft tissue mimicking material, is examined. Using numerical methods, pressure fields are first computed for different source geometries, signal frequencies, and signal waveforms. Volumetric heat generation rates are then calculated from the computed pressures. The Klinger and Pennes bioheat transfer models are used to compute the temperature distributions. Results from this study will be useful in estimating the volumetric heat generation fields from prescribed ultrasound parameters, which in turn can be used to design ultrasound devices as well as treatment protocols for a variety of therapeutic applications.Item Dose and image quality considerations in computed tomography(2011) Abboud, Samir; Kyprianou, Iacovos; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The increased use of Computed Tomography as an imaging modality is of concern because of the growing body of evidence linking radiation exposure to cancer incidence. However, a framework does not yet exist for balancing the immediate needs of the clinical task (image quality) with future risks due to the imaging procedure (dose). We developed a method to estimate the shape and thickness of materials yielding attenuation equivalent to that of bow-tie-shaped filters in clinical scanners. The results are especially useful for accurate modeling in Monte Carlo simulations of radiation transport. We then investigated measures of dose and image quality using both simulation and laboratory experimentation. We found that current measures of dose are robust under current clinical conditions. We also found that measures of image quality are object and task specific.