Browsing by Subject "PET"
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Item Automated Determination of Arterial Input Function Areas in Perfusion Analysis(2013-04-04) Liu, QunPerfusion in biological system refers to capillary-level blood flow in tissues, and is a critical parameter used for detecting physiological changes. Medical imaging provides an effective way to measure tissue perfusion. Quantitative analysis of perfusion studies requires the accurate determination of the arterial input function (AIF), which describes the delivery of intravascular tracers to tissues. Automating the process of finding the AIF can save operating time, remove the inter-operator variability, and correct the errors in the presence of the dispersion of the arterial system. Even though several methods are currently developed for automatically extracting an AIF, they are specific to a single modality and particular to a certain tissue. In this thesis, we developed an algorithm to automatically determine an AIF by classifying the characteristic parameters of image pixels' dynamic evaluation curves between blood feeding areas and tissues. This automated AIF determination can be used to facilitate the generation of parametric maps for perfusion studies based on various imaging modalities and covering a variety of tissues. Automatic AIF determination was accomplished by extracting characteristic parameters such as maximum slope, maximum enhancement, time to peak, time to wash-out, and wash-out slope. Multi-dimensional data containing the characteristic parameters were converted and reduced into two-dimensional (2-D) representations, which were presented as a plurality of 2-D plots. Then physiological phases were localized within the simplified representations. Automated segmentation of non-AIF tissues and determination of AIF areas were accomplished by automatically finding peaks and valleys of each physiological phase on the plurality of 2-D plots. The algorithm was tested in CT myocardial perfusion studies, in which a pig was used as a model of myocardial ischemia and perfusion. PET gastrointestinal (GI) perfusion studies were performed using this algorithm, in which GI perfusion was evaluated when cardiac outputs were controlled with four modes. This automated AIF determination study was compared with manual selection of AIF in PET imaging and microsphere studies to assess the effectiveness of this algorithm. In the CT myocardial perfusion study, the perfusion of infarcted myocardium was significantly lower than that of non-infarcted areas and lower than that when it was normal. In the PET abdominal perfusion study, PET imaging data gives lower value of standard deviation relative to the mean than that in microsphere results. In the manual AIF selection study, a slight change in selecting the AIF region caused a big influence on the result. On the contrary, the automated AIF selection remains consistent in the entire study and reduces inter-operator variation. A conclusion was made that this technique is applicable to several imaging modalities, such as PET, CT and MRI, and is effective on many tissues. In addition, this algorithm is straightforward and provides consistent results. More importantly, this automated AIF determination technique replaces the conventional spatial classification method with the functional classification method, taking more physiological considerations and explanations involved.Item Modeling of material response during fiber drawing of semicrystalline pet(Texas A&M University, 2007-09-17) Yadav, SeemantAccurate constitutive modeling of polymeric fibers presents a difficult and distinct challenge. While significant progress has been made in constructing models applicable for small strains and limited strain-rate and temperature regimes, much less has been made for more general conditions. This is due in part to the complexity of polymeric behavior. In this work, experimental results of uniaxial extension tests on Polyethylene terephthalate (PET) were obtained from Dr. S.Bechtel, were analyzed, and were formulated into a new model which explains the behavior of PET at different temperatures and strains. The biggest impediment in the determining the behavior of polymeric was the difference in the behavior of PET above and below its glass transition temperature. Consequently, well established (from microstructural considerations) constitutive models and concepts for rubber elasticity and plasticity were not directly transferable to modeling PET fibers. In the model, the PET fibers were assumed to be constituted by amorphous and crystallization segments and the response of the material during stretching was the combined response of simultaneous stretching of the amorphous and the crystalline segments. The strengthening mechanism is due to orientation of the amorphous segments during stretching. The model involves a friction element which took account of the plastic behavior below the glass transition temperature. The model was used to predict the response of PET at different temperatures and the results from the model showed good agreement with the experimental data. The results from the research will be further used to increase the overall efficiency of the fiber drawing process.Item PET/CT shielding design comparisons(Texas A&M University, 2007-09-17) Coker, Audra LeeThe objective of this project was to compare two different methods of calculating dose through lead-shielded walls in the PET/CT suite at Scott & White Hospital in Temple, Texas. The ultimate goal was to see which of the two methods agreed with the actual physical measurements. Minimizing shielding needed in future suite designs would result in a possible reduction of structural as well as financial burden. Formulas and attenuation coefficients following the basic January 2006 AAPM guidelines were used to calculate unattenuated radiation through existing lead walls. The computer code MCNPX was used to simulate the leaded walls of the PET/CT suite and provide another set of results. These two sets of results were compared to doses gathered from OSL badges placed around the suite for a period of two months. For this type of problem, MCNPX proved to provide results that were inconsistent and unreliable. It was concluded that the traditional computational methods are the most reliable for designing shielding in a PET/CT suite.Item Using Advanced Imaging to Study Fish(2013-05-31) Browning, Zoe SwezyAlthough mammals are the most commonly utilized laboratory animal, laboratory animal medicine continually seeks to replace them with animals of lower phylogenic classification. Fish are becoming increasingly important as investigators seek alternative animal models for research. Fish can provide an economical and feasible alternative to typical mammalian models; moreover, many fish, which have comparatively short life spans, can easily reproduce in the laboratory. One key area of animal health research in which fish have been underutilized is the field of advanced imaging. Although many images of fish have been captured through the use of computed tomography (CT), radiography, and ultrasonography, these images have been primarily utilized for anatomical study. In addition, fish have never before been studied with positron emission tomography/ computed tomography (PET/CT). My objectives were to determine if these imaging techniques can be used to obtain physiological information from fish, therefore making it more likely that fish can be utilized as replacement animals using these new imaging techniques (CT, PET/CT). I performed two different types of studies to assess the potential application of advanced imaging techniques to fish. In the first experiment, microCT was used to characterize otolith deformity in vitamin C deficient captive-raised red drum and relate the deformity to behavioral and physiological changes. I found that the normal and abnormal fish had statistically significant differences in behavior, cortisol levels, and otolith volume and density. MicroCT assessment of abnormal fish revealed operculum abnormalities, malocclusions, and several types of otolith malformations. Therefore, the affected fish had not only an abnormal skeletal appearance but also significantly abnormal behavior and cortisol responses. In the second experiment, fluorodeoxyglucose-positron emission tomography/ computed tomography (FDG-PET/CT) was used to quantify glucose uptake in select organs prior to carcinogenesis studies in fish. The quantified glucose uptake was compared to published data on humans, mice, and dogs. Rapid, quantifiable glucose uptake was demonstrated, particularly in brain, kidneys, and liver in all imaged fish species. Glucose uptake in the major organ systems of fish was closer to that in humans than uptake in mice or dogs, indicating that fish may serve as an effective alternative animal model for tumor studies using this technology. Other applications for this technique in fish may include metabolism studies and screening for environmental carcinogenesis. I found that both microCT and PET/CT imaging provided useful and meaningful results. In addition, the use of non-invasive scanning allows for re-use of fish, thus reducing the number of animal models used in experiments. These experiments suggest that fish will be good replacement models for mammals using these advanced imaging techniques.