UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

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 given thesis/dissertation in DRUM.

More information is available at Theses and Dissertations at University of Maryland Libraries.

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2007 - 20102

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    A dual modality, DCE-MRI and x-ray, physical phantom for quantitative evaluation of breast imaging protocols
    (2010) Freed, Melanie; Badano, Aldo; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The current clinical standard for breast cancer screening is mammography. However, this technique has a low sensitivity which results in missed cancers. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) has recently emerged as a promising technique for breast cancer diagnosis and has been reported as being superior to mammography for screening of high-risk women and evaluation of extent of disease. At the same time, low and variable specificity has been documented in the literature as well as a rising number of mastectomies possibly due to the increasing use of DCE-MRI. In this study, we developed and characterized a dual-modality, x-ray and DCE-MRI, anthropomorphic breast phantom for the quantitative assessment of breast imaging protocols. X-ray properties of the phantom were quantitatively compared with patient data, including attenuation coefficients, which matched human values to within the measurement error, and tissue structure using spatial covariance matrices of image data, which were found to be similar in size to patient data. Simulations of the phantom scatter-to-primary ratio (SPR) were produced and experimentally validated then compared with published SPR predictions for homogeneous phantoms. SPR values were as high as 85% in some areas and were heavily influenced by the heterogeneous tissue structure. MRI properties of the phantom, T1 and T2 relaxation values and tissue structure, were also quantitatively compared with patient data and found to match within two error bars. Finally, a dynamic lesion that mimics lesion border shape and washout curve shape was included in the phantom. High spatial and temporal resolution x-ray measurements of the washout curve shape were performed to determine the true contrast agent concentration as a function of time. DCE-MRI phantom measurements using a clinical imaging protocol were compared against the x-ray truth measurements. MRI signal intensity curves were shown to be less specific to lesion type than the x-ray derived contrast agent concentration curves. This phantom allows, for the first time, for quantitative evaluation of and direct comparisons between x-ray and MRI breast imaging modalities in the context of lesion detection and characterization.
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    Design of an Anthropomorphic Robotic Hand for Space Operations
    (2007-08-02) Tai, Emily; Akin, David; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Robotic end-effectors provide the link between machines and the environment. The evolution of end-effector design has traded off between simplistic single-taskers and highly complex multi-function grippers. For future space operations, launch payload weight and the wide range of desired tasks necessitate a highly dexterous design with strength and manipulation capabilities matching those of the suited astronaut using EVA tools. The human hand provides the ideal parallel for a dexterous end-effector design. This thesis discusses efforts to design an anthropomorphic robotic hand, focusing on the detailed design, fabrication, and testing of an individual modular finger with considerations into overall hand configuration. The research first aims to define requirements for anthropomorphism and compare the geometry and motion of the design to that of the human hand. Active and passive ranges of motion are studied along with coupled joint behavior and grasp types. The second objective is to study the benefits and drawbacks of an active versus passive actuation systems. Tradeoffs between controllability and packaging of actuator assemblies are considered. Finally, a kinematic model is developed to predict tendon tensions and tip forces in different configurations. The esults show that the measured forces are consistent with the predictive model. In addition, the coupled joint motion shows similar behavior to that of the human hand.