Theses and Dissertations from UMD
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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 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.Item Development of an Evidence Based Referral Protocol for Early Diagnosis of Vestibular Schwannomas(2008-09-03) Barrett, Jessica Ann; Gordon-Salant, Sandra; Hearing and Speech Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The purpose of this investigation was to identify the presenting symptoms and testing outcomes that were most suggestive of a potential vestibular schwannoma and to propose an audiological referral protocol for MRIs. To that end, a retrospective chart review was conducted to examine radiologic, audiometric, and case history information from patients at Walter Reed Army Medical Center who were referred to the Department of Radiology to rule out retrocochlear pathology. Charts of 628 patients were reviewed from their electronic medical records, although the final patient sample was 328 patients who had complete audiologic data. Analyses were conducted to compare the unaffected and affected ears of the positive MRI group to the better and poorer ears of the negative MRI group. Results were significant between the affected ear of the positive group and the poorer ear of the negative group for pure tone thresholds, speech discrimination scores, and acoustic reflex thresholds. Significant differences between the groups were not generally seen for the comparison of the unaffected ear to the better ear, with the exception of acoustic reflex thresholds. The interaural difference between ears was significant between the two groups for pure tone thresholds and speech discrimination scores; however, the difference was not significant for acoustic reflex thresholds. For all significant differences between the groups, the positive MRI group evidenced poorer audiological results. Additionally, three symptoms/outcomes that led to the patients' referral were significantly different between the two groups: unilateral tinnitus, asymmetrical word recognition, and positive rollover in speech recognition scores. Logistic regression was applied to the audiological tests and symptoms to determine the most predictive set of variables that differentiated between the patients with a positive and negative MRI. The most predictive model yielded a sensitivity of 81.25% and a specificity of 82.59% when applied to the current patient sample. The audiological profile identified may be useful for clinicians in deciding whether their patient should be referred for an MRI to rule out the presence of a vestibular schwannoma.Item Analysis of Drug Delivery in the Eye Using Magnetic Resonance Imaging(2007-11-19) Kim, Heekyong Stephanie; Wang, Nam S; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With the rapid increase in the elderly population, the number of Americans afflicted with vision impairment due to ocular disease is projected to rise substantially by the year 2020. Ocular disorders are becoming a major public health problem, and efforts have increased in recent years to develop methods of efficient drug delivery. Currently, the most effective method for treating serious ocular disorders is to inject drug solutions directly into the vitreous. However, injecting in this manner carries a high risk of severe side effects. As a safer alternative, researchers in recent years have been investigating transscleral drug delivery, in which the drug is administered to the outer coat of the eye. Various methods of transscleral drug delivery have been proposed, but it is still clinically not as effective as intravitreal drug delivery. In order to design improved transscleral drug delivery systems, the ocular barriers to drug transport must be accurately understood. While various barrier types have been identified in the eye, the significance and contribution of individual barriers have not been investigated and are still widely unknown. A reason for this lack of understanding is due to the inability to acquire concentration measurements in the eye in vivo. In this study, magnetic resonance imaging (MRI) was employed to obtain drug concentration measurements in vivo after transscleral drug delivery. To address the current needs of the ocular drug delivery community, several goals have been achieved in this work: (1) to evaluate transscleral drug delivery in vivo using MRI, (2) to assess MRI as a technique for evaluating drug delivery in the eye, and (3) to better understand the significance of individual barriers in the eye by quantitatively analyzing experimental (MRI) data and by pharmacokinetic modeling. While encompassing many advantages, it is found that MRI has limitations in spatial and temporal resolution that may restrict its use in measuring parameters with low sensitivity. However, the MRI results in parallel with analysis from the pharmacokinetic model give new insight into the barriers to drug transport in the eye.