<p>Understanding the structure of the brain has been a major goal of neuroscience research over the past century, driven in part by the understanding that brain structure closely follows function. Normative brain maps, or atlases, can be used to understand normal brain structure, and to identify structural differences resulting from disease. Recently, diffusion tensor magnetic resonance imaging has emerged as a powerful tool for brain atlasing; however, its utility is hindered by image resolution and signal limitations. These limitations can be overcome by imaging fixed ex-vivo specimens stained with MRI contrast agents, a technique known as diffusion tensor magnetic resonance histology (DT-MRH). DT-MRH represents a unique, quantitative tool for mapping the brain with unprecedented structural detail. This technique has engendered a new generation of 3D, digital brain atlases, capable of representing complex dynamic processes such as neurodevelopment. This dissertation explores the use of DT-MRH for quantitative brain atlasing in an animal model and initial work in the human brain. </p><p>Chapter 1 describes the advantages of the DT-MRH technique, and the motivations for generating a quantitative atlas of rat postnatal neurodevelopment. The second chapter covers optimization of the DT-MRH hardware and pulse sequence design for imaging the developing rat brain. Chapter 3 details the acquisition and curation of rat neurodevelopmental atlas data. Chapter 4 describes the creation and implementation of an ontology-based segmentation scheme for tracking changes in the developing brain. Chapters 5 and 6 pertain to analyses of volumetric changes and diffusion tensor parameter changes throughout rat postnatal neurodevelopment, respectively. Together, the first six chapters demonstrate many of the unique and scientifically valuable features of DT-MRH brain atlases in a popular animal model.</p><p>The final two chapters are concerned with translating the DT-MRH technique for use in human and non-human primate brain atlasing. Chapter 7 explores the validity of assumptions imposed by DT-MRH in the primate brain. Specifically, it analyzes computer models and experimental data to determine the extent to which intravoxel diffusion complexity exists in the rhesus macaque brain, a close model for the human brain. Finally, Chapter 8 presents conclusions and future directions for DT-MRH brain atlasing, and includes initial work in creating DT-MRH atlases of the human brain. In conclusion, this work demonstrates the utility of a DT-MRH brain atlasing with an atlas of rat postnatal neurodevelopment, and lays the foundation for creating a DT-MRH atlas of the human brain.</p> / Dissertation

The goal of this study was to quantify the impact of dose uncertainty on radio-biological treatment plan evaluation. A formalism was developed for assessing the impact of dose uncertainty on survival fraction (SF). To distinguish between spatial and probabilistic dose variations, we define equivalent stochastic dose (ESD) as the voxel dose that gives an expected survival fraction for the randomly deposited dose. In the case where the probabilistic voxel dose follows a Gaussian distribution, we de-rive an analytic expression for SF(ESD). We show the analytic expression can account for multi-voxel dose distributions that incorporate both probabilistic and spatial dose heterogeneities. In addition, we incorporate dose uncertainty in the calculation of tu¬mour control probability (TCP) using the ESD formalism. We verify the derivation and implementation of the derived expression using the Monte Carlo method for cases of 60 Gy and 70 Gy at 2 Gy per fraction. The results show that the derived formalism is an effective method for evaluating the radiobiological impact of dose uncertainties on treatment plan evaluation.

A number of interventional procedures such as cardiac catheterization, angiography and the deployment of endovascular devices are routinely performed using x-ray fluoroscopy. To minimize the patient’s exposure to ionizing radiation, each fluoroscopic image is acquired using a very low x-ray exposure (~ 1 uR at the detector). At such an exposure, most semiconductor-based digital flat panel detectors (FPD) are not x-ray quantum noise limited (QNL) due to the presence of electronic noise which substantially degrades their imaging performance. The goal of this thesis was to investigate how a FPD based on amorphous selenium (a-Se) with internal avalanche multiplication gain could be used for QNL fluoroscopic imaging at the lowest clinical exposures while satisfying all of the requirements of a FPD for interventional radiology. Towards this end, it was first determined whether a-Se can reliably provide avalanche multiplication gain in the solid-state. An experimental method was developed which enabled the application of sufficiently large electric field strengths across the a-Se. This method resulted in avalanche gains as high as 10000 at an applied field of 105 V/um using optical excitation. This was the first time such high avalanche gains have been reported in a solid-state detector based on an amorphous material. Secondly, it was investigated how the solid-state a-Se avalanche detector could be used to image X-rays at diagnostic radiographic energies (~ 75 kVp). A dual-layered direct-conversion FPD architecture was proposed. It consisted of an x-ray drift region and a charge avalanche multiplication region and was found to eliminate depth-dependent gain fluctuation noise. It was shown that electric field strength non-uniformities in the a-Se do not degrade the detective quantum efficiency (DQE). Lastly, it was determined whether the solid-state a-Se avalanche detector satisfies all of the requirements of interventional radiology. Experimental results have shown that the total noise produced by the detector is negligible and that QNL operation at the lowest fluoroscopic exposures is indeed possible without any adverse effects occurring at much larger radiographic exposures. In conclusion, no fundamental obstacles were found preventing the use of avalanche a-Se in next-generation solid-state QNL FPDs for use in interventional radiology.

No description available.

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Assaying internal contamination due to inhalation is a primary concern in developing emergency procedures related to Radioactive Dispersal Devices (RDD). One method of determining internal contamination makes use of a common medical instrument, a Thyroid Uptake System (TUS). The TUS used in this research has two collimators a thyroid uptake collimator and a bioassay collimator. Both collimators were considered and modeled in MCNP to be used in conjunction with six MIRD-type (Medical Internal Radiation Dose) phantoms. The collimators were placed in four positions on the phantoms the front right lung, the back right lung, the neck, and the thigh. Unit sources of Cs-137, Co-60, I-131, Ir-192, Am-241, and Sr/Y-90 were placed in the organs of the phantoms. MCNP particle tallies were performed over the detector crystal volume to determine the count-rate contributions from the unit source in each organ. Biokinetic modeling was performed using DCAL (Dose and Risk Calculation System) to generate coefficients to describe activity as a function of time in various organs. By folding the count-rate results with the organ concentrations, the detector response as a function of time after intake has been determined. This work was performed under funding provided by the Radiation Studies Branch of the Centers for Disease Control and Prevention.

Thesis (Ph.D.)--University of Wollongong, 2006. / Typescript. Includes bibliographical references: p. 161-174.

Thesis (Ph.D. (Health))--University of Western Sydney, 2007. / A thesis presented to the University of Western Sydney, College of Health and Science, School of Biomedical and Health Sciences, in fulfilment of the requirements for the degree of Doctor of Philosophy (Health). Includes bibliographies.

Thesis (M. Sc.)--Carleton University, 2001. / Includes bibliographical references (p. 86-96). Also available in electronic format on the Internet.

Thesis (M.A.) -- University of Texas Southwestern Medical Center at Dallas, 2005. / Vita. Bibliography: 159.