DEVELOPMENT AND CHARACTERIZATION OF A HIGH ENERGY PHASE CONTRAST X-RAY IMAGING SYSTEM PROTOTYPE

The field of mammography receives constant research attention focused on improving the balance between the benefits of cancer screening and the risks of harmful radiation to the patient. As a result, numerous advancements have been made throughout the history of mammography, which have not only improved the ability to detect cancer at an earlier stage, but also to diagnose previously undetectable cancer. Numerous clinical trials have demonstrated the decrease in mortality rates. Due to the potential for saving lives, along with the recent public concerns regarding radiation dose, significant research attention remains focused on investigating methods for further improving the detection capabilities and reducing the radiation dose. However, the similar absorption characteristics of normal and malignant tissue present a challenge in differentiating between them using conventional x-ray imaging. The current method for providing higher image quality involves utilizing anti-scatter grids and operating at much lower x-ray energies than other radiography fields, both of which result in an increased radiation dose. An emerging technology called phase contrast imaging, which is based not only on absorption but also the effects produced by x-ray phase changes, holds the potential to increase the x-ray energy and remove the grid without compromising the image quality, which could reduce the patient dose and thus benefit the field of mammography. Preliminary studies in phase contrast imaging at the same energy as conventional imaging have indicated the ability to reduce the radiation dose without negatively impacting the diagnosis capabilities. However, existing challenges in clinical implementation have prevented the technology from further progress.The goal of the research presented in this dissertation comprises a thorough investigation of the potential of high energy phase contrast imaging to overcome these challenges and further reduce the radiation dose without decreasing the detection ability. Following an introductory chapter, Chapter 2 presents a detailed description of the necessary methods required to perform the dissertation research. The methods are separated into four categories: image quality, statistical methods, phase contrast imaging, and radiation dose. Chapters 3 through 6 encompass four preliminary studies accomplished to demonstrate a thorough understanding of the research methods, as well as to evaluate the feasibility of the research and corresponding motivation in the medical imaging field. The development and preliminary feasibility investigation of a high energy phase contrast imaging system prototype is presented in Chapter 7, followed by an image quality comparison to high and low energy conventional imaging with similar entrance exposures in Chapter 8. Chapter 9 presents a comprehensive image quality and dose comparison of high energy phase contrast and low energy conventional imaging. Finally, the summary and discussion of results are presented in Chapter 10, along with planned research direction for future studies.This dissertation encompasses numerous original contributions, perhaps the most significant of which were the demonstration of the ability of phase contrast imaging to deliver acceptable image quality for detection and diagnosis at higher x-ray energies than investigated previously, as well as the comprehensive comparison of high energy phase contrast imaging with low energy conventional imaging. These results clearly demonstrate the ability of phase contrast imaging to sustain the image quality improvement at high x-ray energies and for clinical thicknesses without an increase in the radiation dose. In addition, each of the preliminary studies involved the development of novel methods or techniques to improve existing procedures. First, the step-by-step optimization of the MTF algorithm presented in Chapter 4 was an original approach, which also included the application of new methods to several of the steps, resulting in an optimized algorithm with significantly improved accuracy. Next, Chapter 5 presented the development of a quantitative method to determine the error contributed to any calculated result by each of the represented components, as well as a new method for calculating the magnification factor that considerably reduces the error, especially for clinical systems. Chapter 6 presented the novel application of the existing method of beam hardening to reduce the radiation dose without affecting the detection capability, which holds the potential to greatly benefit mammography and related fields.The research presented in this dissertation is a strong indication of the potential of high energy phase contrast imaging to dramatically benefit x-ray imaging fields such as mammography by improving the ability to detect and diagnose diseases at earlier stages or when previously undetectable without increasing the radiation dose. The ability to improve the capability to diagnose disease without increasing the risk of harmful radiation to the patient would significantly improve the balance between the risks and benefits of cancer screening, which holds the potential to revolutionize the fields of x-ray imaging and lower mortality rates

Giant molecular clouds in the non-grand design spiral galaxy NGC 6946

We present high spatial resolution observations of Giant Molecular Clouds (GMCs) in the eastern part of the nearby spiral galaxy NGC 6946 obtained with the Combined Array for Research in Millimeter-wave Astronomy (CARMA). We have observed 12CO(1-0), 12CO(2-1) and 13CO(1-0), achieving spatial resolutions of 5.4" x 5.0", 2.5" x 2.0" and 5.6" x 5.4" respectively over a region of 6 x 6 kpc. This region extends from 1.5 kpc to 8 kpc galactocentric radius, thus avoiding the intense star formation in the central kpc. We have recovered short-spacing u-v components by using single dish observations from the Nobeyama 45m and IRAM 30m telescopes. Using the automated CPROPS algorithm we identified 44 CO cloud complexes in the 12CO(1-0) map and 64 GMCs in the 12CO(2-1) maps. The sizes, line widths, and luminosities of the GMCs are similar to values found in other extragalactic studies. We have classified the clouds into on-arm and inter-arm clouds based on the stellar mass density traced by the 3.6 um map. On-arm clouds present in general higher star formation rates than clouds located on inter-arm regions. Although the star formation efficiency shows no systematic trend with galactocentric radius, some on-arm clouds -- which are more luminous and more massive compared to inter-arm GMCs -- are also forming stars more efficiently than the rest of the identified GMCs. These structures appear to be located on two specific regions in the spiral arms. One of them shows a strong gradient, suggesting that this region of high star formation efficiency may be the result of gas flow convergence.Comment: 23 pages, 21 figures, 3 tables. To be published in The Astrophysical Journa

A critical role for cystathionine-β-synthase in hydrogen sulfide-mediated hypoxic relaxation of the coronary artery

Hypoxia-induced coronary artery vasodilatation protects the heart by increasing blood flow under ischemic conditions, however its mechanism is not fully elucidated. Hydrogen sulfide (H2S) is reported to be an oxygen sensor/transducer in the vasculature. The present study aimed to identify and characterise the role of H2S in the hypoxic response of the coronary artery, and to define the H2S synthetic enzymes involved. Immunoblotting and immunohistochemistry showed expression of all three H2S-producing enzymes, cystathionine-β-synthase (CBS), cystathionine-γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (MPST), in porcine coronary artery. Artery segments were mounted for isometric tension recording; hypoxia caused a transient endothelium-dependent contraction followed by prolonged endothelium-independent relaxation. The CBS inhibitor amino-oxyacetate (AOAA) reduced both phases of the hypoxic response. The CSE inhibitor dl-propargylglycine (PPG) and aspartate (limits MPST) had no effect alone, but when applied together with AOAA the hypoxic relaxation response was further reduced. Exogenous H2S (Na2S and NaHS) produced concentration-dependent contraction followed by prolonged relaxation. Responses to both hypoxia and exogenous H2S were dependent on the endothelium, NO, cGMP, K+ channels and Cl−/HCO3 − exchange. H2S production in coronary arteries was blocked by CBS inhibition (AOAA), but not by CSE inhibition (PPG). These data show that H2S is an endogenous mediator of the hypoxic response in coronary arteries. Of the three H2S-producing enzymes, CBS, expressed in the vascular smooth muscle, appears to be the most important for H2S generated during hypoxic relaxation of the coronary artery. A contribution from other H2S-producing enzymes only becomes apparent when CBS activity is inhibited

Resolved Giant Molecular Clouds in Nearby Spiral Galaxies: Insights from the CANON CO (1-0) Survey

We resolve 182 individual giant molecular clouds (GMCs) larger than 2.5 × 10^5 M ☉ in the inner disks of 5 large nearby spiral galaxies (NGC 2403, NGC 3031, NGC 4736, NGC 4826, and NGC 6946) to create the largest such sample of extragalactic GMCs within galaxies analogous to the Milky Way. Using a conservatively chosen sample of GMCs most likely to adhere to the virial assumption, we measure cloud sizes, velocity dispersions, and ^(12)CO (J = 1-0) luminosities and calculate cloud virial masses. The average conversion factor from CO flux to H_2 mass (or X_(CO)) for each galaxy is 1-2 × 10^(20) cm^(–2) (K km s^(–1))^(–1), all within a factor of two of the Milky Way disk value (~2 × 10^(20) cm^(–2) (K km s^(–1))^(–1)). We find GMCs to be generally consistent within our errors between the galaxies and with Milky Way disk GMCs; the intrinsic scatter between clouds is of order a factor of two. Consistent with previous studies in the Local Group, we find a linear relationship between cloud virial mass and CO luminosity, supporting the assumption that the clouds in this GMC sample are gravitationally bound. We do not detect a significant population of GMCs with elevated velocity dispersions for their sizes, as has been detected in the Galactic center. Though the range of metallicities probed in this study is narrow, the average conversion factors of these galaxies will serve to anchor the high metallicity end of metallicity-X_(CO) trends measured using conversion factors in resolved clouds; this has been previously possible primarily with Milky Way measurements

Really Underage Drinkers: Alcohol Use Among Elementary Students

Despite the current societal concern with underage drinking, little attention has been paid to alcohol use within the preadolescent population. This article presents the proceedings of a symposium held at the 2003 Research Society on Alcoholism meeting in Fort Lauderdale, Florida, that was organized and chaired by John E. Donovan. The intent of the symposium was to kick start research on alcohol use among elementary school children by reviewing what is known regarding drinking in childhood. Presentations included (1) The Epidemiology of Children's Alcohol Use, by John E. Donovan; (2) The Validity of Children's Self-Reports of Alcohol Use, by Sharon L. Leech; (3) Predicting Onset of Drinking From Behavior at Three Years of Age: Influence of Early Child Expectancies and Parental Alcohol Involvement Upon Early First Use, by Robert A. Zucker; and (4) Parent, Peer, and Child Risk Factors for Alcohol Use in Two Cohorts of Elementary School Children, by Carol J. Loveland-Cherry. Presentations indicated the need for better nationwide surveillance of children's experience with alcohol; suggested that children's reports of their use of alcohol tend to be reliable and valid; supported children's alcohol use schemas and parental drinking and alcoholism at child age three as independent predictors of early onset drinking; and showed that onset of drinking before fourth or fifth grade, peer pressure, and parental norms and monitoring predict elementary student alcohol use and misuse.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65944/1/01.ALC.0000113922.77569.4E.pd

UGC 4599: A Photometric Study of the Nearest Hoag-Type Ring Galaxy

We present a photometric study of UGC 4599, a low-luminosity galaxy superficially resembling Hoag's Object in that on sky survey images it appears to be a complete ring surrounding a roundish core. The nature of the outer ring of Hoag-type galaxies is still debated and may be related either to slow secular evolution or to environmental processes, such as galaxy-galaxy interactions. we show that in UGC 4599 (a) the nearly round central body follows well an r^1/4 light profile almost all the way to the centre, (b) the isophotes are strongly twisted with a sharp 45 deg transition at a radius of r~6 arcsec, (c) the blue ring seems to have reached near-equilibrium configuration with the central body, (d) the ring is actually composed of a one-and-a-half turn spiral feature, and (e) one side of the spiral shows conspicuous star formation in the form of at least nine HII regions, revealed by their H_alpha emission. Based on the photometric data, together with HI information from the literature, we characterize UGC 4599 as an elliptical-like object surrounded by a luminous ring and a massive, extremely extended HI disc. Given its observed properties, we rule out UGC 4599 as representing a late phase in barred early-type galaxies evolution. We discuss the origin of UGC 4599 and conclude that this galaxy could be the result of a major interaction between two gas-rich spiral galaxies that took place at least 5 Gyr ago. However, deep optical imaging and a detailed stellar population analysis are required to determine whether the large gas reservoir could have been accreted directly from the intergalactic medium onto a pre-existing elliptical galaxy in the early Universe. A detailed kinematical study will shed light on the exact nature of the central body and the ring of UGC 4599.Comment: 14 pages, 6 figures and 5 tables. Accepted for publication in MNRAS. The abstract is abridged compared to the published versio