Dissertations / Theses on the topic 'X-ray imaging technique'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 45 dissertations / theses for your research on the topic 'X-ray imaging technique.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
MALALLA, NUHAD ABDULWAHED YOUNIS. "C-ARM TOMOGRAPHIC IMAGING TECHNIQUE FOR DETECTION OF KIDNEY STONES." OpenSIUC, 2016. https://opensiuc.lib.siu.edu/dissertations/1278.
Full textKsenia, Chechet. "Edge Illumination technique using direct conversion photon counting detectors for X-ray Phase Contrast imaging." Thesis, KTH, Fysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-170408.
Full textSetlur, Nagesh Swetadri Vasan. "Improved imaging for x-ray guided interventions| A high resolution detector system and patient dose reduction technique." Thesis, State University of New York at Buffalo, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3613101.
Full textOver the past couple of decades there has been tremendous advancements in the field of medicine and engineering technology. Increases in the level of integration between these two branches of science has led to better understanding of physiology and anatomy of a living organism, thus allowing for better understanding of diseases along with their cures and treatments. The work presented in this dissertation aims at improving the imaging aspects of x-ray image guided interventions with endovascular image guided intervention as the primary area of application.
Minimally invasive treatments for neurovascular conditions such as aneurysms, stenosis, etc involve guidance of catheters to the treatment area, and deployment of treatment devices such as stents, coils, balloons, etc, all under x-ray image guidance. The features in these device are in the order of a few 10 µm's to a few 100 µm's and hence demand higher resolution imaging than the current state of the art flat panel detector. To address this issue three high resolution x-ray cameras were developed. The Micro Angiography Fluoroscope (MAF) based on a Charge Coupled Device (MAF-CCD), the MAF based on Complementary Metal Oxide Semiconductors (MAF-CMOS) and the Solid State X-ray Image Intensifier based on Electron Multiplying CCDs. The construction details along with performance evaluations are presented. The MAF-CCD was successfully used in a few interventions on human patient to treat neurovascular conditions, primarily aneurysm. Images acquired by the MAF-CCD during these procedures are presented.
A software platform CAPIDS was previously developed to facilitate the use of the high resolution MAF-CCD in a clinical environment. In this work the platform was modified to be used with any camera. The upgrades to CAPIDS, along with parallel programming including both the Graphics Processing Unit (GPU) and Central Processing Unit (CPU) are presented.
With increasing use of x-ray guidance for minimally invasive interventions, a major cause of concern is that of prolonged exposure to x-ray radiation that can cause biological damage to the patient. Hence during x-ray guided procedures necessary steps must be taken to minimize the dose to the patient. In this work a novel dose reduction technique, using a combination of Region of Interest (ROI) fluoroscopy to reduce dose along with spatially different temporal filtering to restore image quality is presented.
Finally a novel ROI imaging technique for biplane imaging in interventional suites, combining the use of high resolution detector along with dose reduction technique using ROI fluoroscopy with spatially different temporal filtering is presented.
Sassi, Salem Ahmed. "Region of interest imaging technique : a novel approach to increase image contrast within the region of interest and reduce patient dose in fluoroscopy." Thesis, St George's, University of London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264975.
Full textSik, Ayhan Serkan. "X-ray Physics And Computerized Tomography Simulation Using Java And Flash." Master's thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/3/756239/index.pdf.
Full textPaziresh, Mahsa. "Development of energy selective techniques in x-ray computed tomography." Phd thesis, Canberra, ACT : The Australian National University, 2016. http://hdl.handle.net/1885/155541.
Full textYocky, David Alan. "Characterization and evaluation of a photostimulable phosphor x ray imaging system." Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184529.
Full textLee, Tiffany (Tiffany Ting). "Long range x-ray imaging utilizing coded aperture techniques and dynamic reconstruction." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/44837.
Full textIncludes bibliographical references (p. 50).
Improvised explosive devices (IED) pose a very serious threat to civilians and military forces around the world, and new technologies must be developed for the early detection of these objects. Because of the high concentrations of low atomic number material such as nitrogen and hydrogen present in these explosives, x-ray backscattering provides a viable method of collecting information about these targets by analyzing their shape. Furthermore, a coded aperture used in conjunction with dynamic reconstruction algorithms offers high sensitivity and resolution even while the target is moving towards the detector. This paper describes a lab-based system that simulated a source-target-detector arrangement to be utilized in a radiation detecting vehicle in order to test dynamic reconstruction methods. Using a 225 kVp x-ray tube as the source, a medical CT-system camera fitted with a drill mask of 50% fill factor as the detector, and both radioisotope sources and low Z backscatter targets, images were acquired and reconstructed. The geometry of the experimental setup was optimized to reduce background noise from air scatter and environmental sources, as well as to prevent incident photons from directly reaching the detector from the x-ray tube. Measurements of a Co-60 point source and Co-57 area source with high activity generated high contrast images for which the shapes of the sources were clearly resolved. Acquisitions with varying target-detector distance of low Z materials, including a filled water jug and a four inch thick polyethylene arrow, produced lower contrast images in which the shapes were not as easily distinguished. The radioisotope tests were a proof of principle for dynamic reconstruction and the backscatter targets provided much insight on methods for improving the lab system, including the addition of steel behind the target, the narrowing of the detector energy window, and reassessment of the x-ray cone-beam.
by Tiffany Lee.
S.B.
Walker, David. "Investigation of RbTiOASOâ‚„ and related ferroelectrics using X-ray imaging and dielectric techniques." Thesis, University of Warwick, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.429803.
Full textMcRae, Reagan. "Investigating metal homeostasis in mammalian cells using high resolution imaging techniques." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/41197.
Full textLatti, Emari (Emarencia Martha). "Development of a digital X-ray-imaging system at the National Accelerator Centre." Thesis, Stellenbosch : Stellenbosch University, 2000. http://hdl.handle.net/10019.1/51685.
Full textENGLISH ABSTRACT: A digital portal X-ray imaging system was developed to replace the radiographic X-ray films currently used for patient position verification at the National Accelerator Centre (NAC) proton therapy facility. The main advantage of a digital system is the short time in which the image can be obtained. Other advantages include optimisation of the image display, effective archiving of the digital images, access from various locations through data networks, and lower operational costs. The digital system described in this thesis consists of a Gd202S:Tb scintillator screen for converting X-rays to visible light, a protected aluminum front silvered mirror to direct the light to a Charge Coupled Device (CCD) camera for capture and a personal computer for data acquisition, processing and display. Compared with other digital imaging systems, this is a simple, compact and affordable system. The properties of the various components were investigated. The Rarex G-130 (Gd202S:Tb) scintillation screen was chosen for its good spatial resolution, high emission efficiency and good matching between the spectral emission wavelength peak and the quantum efficiency of the CCD camera. The spatial resolution measured for the system with a field of view (FOV) of 290 x 190 mnr' is 1.3 lp/mm, which can be improved by increasing the CCD chip resolution or decreasing the field of view, since the CCD camera limits the spatial resolution. Intrinsic detector noise determines the lower limit of the dynamic range of the detector and is reduced by cooling the CCD camera. A dark current exposure is subtracted from the image to remove the bias signal and background signal level mainly caused by thermal noise. Photon noise, beam in-homogeneity and efficiency variations across the CCD chip are removed by a flat field correction. The digital images obtained with this system compare very well with the currently used radiographic film images and they are satisfactory for the purpose of patient position verification. Using the digital system it is possible to reduce the patient dose by 19 % and still obtain satisfactory image quality.
AFRIKAANSE OPSOMMING: 'n Digitale X-straalafbeeldingstelsel is ontwikkel om die radiografiese X-straalfilm wat tans gebruik word vir die kontrolering van die pasientposisionering voor die toediening van protonterapie by die Nasionale Versnellersentrum, te vervang. Die voordeel van die digitale sisteem is dat die beelde feitlik onmiddellik beskikbaar is. Verdere voordele sluit die optimisering van die vertoon van beeldkontras, effektiewe liassering, vinnige bereik deur datanetwerke en lae lopende kostes in. Die digitale sisteem beskryf in die tesis bestaan uit 'n gadolinium oksi-sulfied (Gd202S:Tb) sintillasieskerm wat X-strale omskakel na sigbare lig, 'n eerste-oppervlak aluminiumspieël wat die lig na 'n digitale kamera (CCD kamera) weerkaats en In persoonlike rekenaar vir dataverwerwing, verwerking en vertoon. Vergeleke met ander digitale stelsels is hierdie digitale beeldingstelsel eenvoudig, kompak en bekostigbaar. Die eienskappe van die verskillende komponente van die stelsel is ondersoek. Die Rarex G- 130 (Gd202S:Tb) sintillasieskerm IS gekies vanweë goeie resolusie, hoë emissiedoeltreffendheid en die hoë omsettingsdoeltreffendheid van die digitale kamera by die spektrale emissiegolflengte van dié sintillasieskerm. Die ruimtelike oplosvermoë van die stelsel is bepaal met In veldgrootte van 290 x 190 mnr' as 1.3 lynpare per millimeter. Die ruimtelike oplosvermoë kan verhoog word deur die kameraresolusie te verhoog of die veldgrootte te verklein, omdat die resolusie van die kamera tans die oplosvermoë van die stelsel beperk. Intrinsieke ruis van die detektor beperk die onderste grens van die dinamiese reikwydte van die detektor en kan verminder word deur die kamera te verkoel. 'n Donkerstroom-beeld word van die X-straalbeelde afgetrek om die voorspanningsein en die agtergrondsein, wat hoofsaaklik veroorsaak word deur termiese ruis, te verwyder. Ruis wat ontstaan as gevolg van fluktuasies in die aantal fotone, nie-homogeniteite in die bundel of variasie van die sensitiwiteit in die skerm word verwyder met behulp van 'n plat vlak beeld. Die digitale beelde verkry met die stelsel vergelyk goed met die beelde wat tans op film geneem word en die beeldkwalitiet is voldoende vir die kontrolering van die pasientopstelling. Dit is moontlik om die pasiëntdosis met 19 % te verminder en steeds voldoende beeldkwaliteit te verkry.
Mclean, Ivan Hugh. "An adaptive discrete cosine transform coding scheme for digital x-ray images." Thesis, Rhodes University, 1989. http://hdl.handle.net/10962/d1002032.
Full textNam, Cheolhee. "Quantitative investigation of solidification in Ni-based superalloys by in-situ X-ray imaging techniques." Kyoto University, 2019. http://hdl.handle.net/2433/245322.
Full textNervo, Laura. "Characterisation of the deformation mechanisms in HCP metals by combined use of X-ray imaging and diffraction techniques." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/characterisation-of-the-deformation-mechanisms-in-hcp-metals-by-combined-use-of-xray-imaging-and-diffraction-techniques(50fe7be6-4fbf-48e3-86de-942589bb000d).html.
Full textDamato, Antonio Leonardo. "Capabilities and limitations of Phase Contrast Imaging techniques with X-rays and neutrons." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/53263.
Full textCataloged from PDF version of thesis.
Includes bibliographical references.
Phase Contrast Imaging (PCI) was studied with the goal of understanding its relevance and its requirements. Current literature does not provide insight on the effect of a relaxation in coherence requirements on the PCI capabilities of an imaging system. This problem is all the more important since coherent X-ray and Neutron sources are mostly unavailable. We develop a model for PCI contribution to imaging for partially incoherent systems, and develop a methodology to identify a minimum and an optimum coherence length 4min and opt. We propose a figure-of-merit KPcI that quantifies the PCI capabilities of an imaging system. Our calculations show that X-ray PCI systems based on free space propagation using microfocus X-ray tubes have little PCI capabilities. We develop a model to explain the edge enhancement observed with those systems; our results suggest that scatter reduction is the process responsible for the observed edge enhancement. We performed experiments that show good agreement with the model. Coded Source Imaging (CSI) is proposed as a tool to produce highly coherent sources. The general theory of CSI is developed. We propose two possible systems: Fluorescent Coded Sources (FCS) and the AEB Encoded X-ray tube.
by Antonio Leonardo Damato.
Ph.D.
Shaheen, Islam. "Study of the most effective analysis procedures using multispectral imaging techniques on ancient egyptian painted objects." Master's thesis, Universidade de Évora, 2020. http://hdl.handle.net/10174/29337.
Full textLeal, Michael J. "Effect of pixel size and scintillator on image quality of a CCD-based digital x-ray imaging system." Link to electronic thesis, 2001. http://www.wpi.edu/Pubs/ETD/Available/etd-0502101-123456.
Full textBacilieri, Ginevra. "Teos-based consolidants for stone conservation: evaluation of the effects and testing by x-ray imaging." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amslaurea.unibo.it/6416/.
Full textBougeant, Olivier. "Alternative techniques of backscatter radiography Snapshot Aperture Backscatter Radiography and Collimated Segmented Detector Scatter X-ray Imaging /." [Gainesville, Fla.] : University of Florida, 2009. http://purl.fcla.edu/fcla/etd/UFE0025092.
Full textParks, Daniel. "X-ray Scattering Techniques for Coherent Imaging in Reflection Geometry, Measurement of Mutual Intensity, and Symmetry Determination in Disordered Materials." Thesis, University of Oregon, 2013. http://hdl.handle.net/1794/13221.
Full textMittone, Alberto [Verfasser], and Paola [Akademischer Betreuer] Coan. "Development of X-ray phase-contrast imaging techniques for medical diagnostics : towards clinical application / Alberto Mittone. Betreuer: Paola Coan." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2015. http://d-nb.info/1076242901/34.
Full textYang, Weibing. "Probing electronic, magnetic and structural heterogeneity in advanced materials and Nanostructures with x-ray imaging, scattering and spectroscopic techniques." Diss., Temple University Libraries, 2018. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/588064.
Full textPh.D.
In this dissertation, we have used a combination of synchrotron-based x-ray spectroscopic, scattering and imaging techniques to investigate the electronic, magnetic and structural properties of materials and material systems which exhibit natural as well as engineered nanoscale structural distortions. In order to investigate the interplay between the above-mentioned degrees of freedom with spatial and depth resolution, we have utilized non-destructive techniques, such as x-ray absorption spectroscopy (XAS), polarization-dependent photoemission electron microscopy (PEEM), nanoscale scanning x-ray diffraction microscopy (nano-SXDM) and standing-wave x-ray photoemission spectroscopy (SW-XPS). The results were compared to several types of state-of-the-art first-principles theoretical calculations. In the first part of the dissertation, we have investigated the nanoscale magneto-elastic structure of the Fe3Ga magnetic alloy, which was recently reported to exhibit non-volume conserving magnetostriction. As the result of our combined PEEM and nano-SXDM study, we have discovered the structural basis for this phenomenon – periodic long-wavelength (~269 nm) elastic domain walls, with domains (regions of zero-strain) existing as narrow transition regions. Atto-scale elastic gradients and self-strain across the elastic domain walls were quantitatively measured and imaged by nano-SXDM. Our measurements revealed that the gradients inside the elastic walls are accommodated by gradually increasing/decreasing inter-planar spacing resembling a longitudinal wave. Our element-specific polarization-dependent PEEM measurements revealed that the magnetic structure of the crystal modulates with similar periodicity (~255 nm), and the resulting magneto-elastic coupling produces a ‘giant’ field-induced bulk deformation, which is equal to the measured self-strain of the elastic domain wall. In the second part of this dissertation, we utilized a combination of soft x-ray standing-wave photoemission spectroscopy (SW-XPS), hard x-ray photoemission spectroscopy (HAXPES) and scanning transmission electron microscopy (STEM) to probe the depth-dependent and single-unit-cell resolved electronic structure of isovalent manganite superlattices (Eu0.7Sr0.3MnO3/La0.7Sr0.3MnO3)15 wherein the electronic and magnetic properties are intentionally modulated with depth via engineered O octahedral rotations and A-site displacements. Standing-wave-excited spectroscopy of the Mn 2p and O 1s core-levels confirmed the isovalent nature of the Mn ions in the superlattice and revealed significant depth-dependent variations in the local chemical and electronic environment around the O atoms, consistent with the state-of-the-art theoretical calculations. Furthermore, it was shown that a surface relaxation and orbital reconstruction in the several top Eu0.7Sr0.3MnO3 atomic layers produces substantial changes in the observed electronic structure, which, according to the first-principles theoretical calculations, occur due to the establishment of orbital stripe order in the top unit cell. In summary, we have used synchrotron-based x-ray spectroscopic and microscopic techniques, in conjunction with high-resolution electron microscopy, to study the electronic, magnetic and structural properties of advanced functional materials exhibiting strong nanoscale heterogeneity. We discovered a strong coupling between the nanoscale structural and magnetic properties in the non-conventional magnetostrictive Fe3Ga single crystal. Our results suggest that this coupling provides the fundamental basis for the non-conventional magnetostriction phenomenon in this material. We have also discovered that the electronic properties of the Eu0.7Sr0.3MnO3/La0.7Sr0.3MnO3 superlattices can be epitaxially tuned via engineered A-site cation displacement, which is a result of the strong interfacial coupling between the Eu0.7Sr0.3MnO3 and La0.7Sr0.3MnO3 layers. This suggests a new way of tailoring and spatially-confining electronic and ferroic behavior in complex oxide heterostructures and creating novel ordered surface-reconstruction effects.
Temple University--Theses
Parks, Daniel H. "X-ray scattering techniques for coherent imaging in reflection geometry, measurement of mutual intensity, and symmetry determination in disordered materials." Thesis, University of Oregon, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3589544.
Full textThe advent of highly-coherent x-ray light sources, such as those now available world-wide in modern third-generation synchrotrons and increasingly available in free-electron lasers, is driving the need for improved analytical and experimental techniques which exploit the coherency of the generated light. As the light illuminating a sample approaches full coherence, a simple Fourier transform describes the diffraction pattern generated by the scattered light in the far field; because the Fourier transform of an object is unique, coherent scattering can directly probe local structure in the scattering object instead of bulk properties.
In this dissertation, we exploit the coherence of Advanced Light Source beamline 12.0.2 to build three types of novel coherent scattering microscopes. First, we extend the techniques of coherent diffractive imaging and Fourier transform holography, which uses iterative computational methods to invert oversampled coherent speckle patterns, into reflection geometry. This proof-of-principle experiment demonstrates a method by which reflection Bragg peaks, such as those from the orbitally-ordered phase of complex metal oxides, might eventually be imaged. Second, we apply a similar imaging method to the x-ray beam itself to directly image the mutual coherence function with only a single diffraction pattern.
This technique supersedes the double-slit experiments commonly seen in the scattering literature to measure the mutual intensity function by using a set of apertures which effectively contains all possible double slit geometries. Third, we show how to evaluate the speckle patterns taken from a labyrinthine domain pattern for "hidden" rotational symmetries. For this measurement, we modify the iterative algorithms used to invert speckle patterns to generate a large number of domain configurations with the same incoherent scattering profile as the candidate pattern and then use these simulations as the basis for a statistical inference of the degree of ordering in the domain configuration. We propose extending this measurement to position-resolved speckle patterns, creating a symmetry-sensitive microscope. The three new techniques described herein may be employed at current and future light sources.
Baimpas, Nikolaos. "'Hybrid' non-destructive imaging techniques for engineering materials applications." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:1aa00fed-34e6-4a5e-951b-c710e21ac23c.
Full textDong, Kang [Verfasser], John [Akademischer Betreuer] Banhart, John [Gutachter] Banhart, Yan [Gutachter] Lu, and Julia [Gutachter] Kowal. "Characterization of battery anode materials by X-ray and electron-based imaging techniques / Kang Dong ; Gutachter: John Banhart, Yan Lu, Julia Kowal ; Betreuer: John Banhart." Berlin : Technische Universität Berlin, 2020. http://d-nb.info/1204995486/34.
Full textJones, Bernard Lee. "Development of dosimetry and imaging techniques for pre-clinical studies of gold nanoparticle-aided radiation therapy." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/43727.
Full textWang, Lejing Verfasser], Nassir [Akademischer Betreuer] [Navab, Russel H. [Akademischer Betreuer] Taylor, and Ekkehard [Akademischer Betreuer] Euler. "Novel techniques for integrating video augmented X-ray imaging into orthopedic and trauma surgery / Lejing Wang. Gutachter: Nassir Navab ; Russel H. Taylor ; Ekkehard Euler. Betreuer: Nassir Navab." München : Universitätsbibliothek der TU München, 2012. http://d-nb.info/1031550534/34.
Full textSeyyedi, Saeed [Verfasser], Tobias [Akademischer Betreuer] Lasser, Tobias [Gutachter] Lasser, J. Webster [Gutachter] Stayman, and Franz [Gutachter] Pfeiffer. "Advanced Reconstruction and Noise Reduction Techniques in Four- and Six-Dimensional X-ray Imaging Modalities / Saeed Seyyedi ; Gutachter: Tobias Lasser, J. Webster Stayman, Franz Pfeiffer ; Betreuer: Tobias Lasser." München : Universitätsbibliothek der TU München, 2018. http://d-nb.info/116577318X/34.
Full textHerzog, Charlotte. "imagerie plénoptique : de la lumière visible aux rayons X." Thesis, Bordeaux, 2020. http://www.theses.fr/2020BORD0116.
Full textPlenoptic imaging is a technique that acquires spatial and angular information of the light rays incoming from a scene. After a single acquisition, numerical data treatment allows image manipulation such as synthetic aperture, changing viewpoint, refocusing at different depths, and consequently 3D reconstruction of the scene. Visible plenoptic has been widely studied. However, transposition from visible to X-rays has never been done and remains challenging. X-ray plenoptic would be beneficial to the X-ray imaging panorama. A single acquisition should be sufficient to reconstruct a volume, against 1000’s for X-ray tomography that is the today reference in 3D X-ray imaging.In this thesis, we consider plenoptic camera composed of a main lens, a microlens array and a detector. So far, two different configurations have been developed: the traditional and the focused plenoptic setups. Although these configurations are usually studied separately, they only differ by the distances between the optical elements. These two configurations were studied in detail to choose the most suitable for X-ray imaging, considering the constraints of X-ray optics. We observed a full continuity between the two systems. Therefore, we extended the previous work to more general formulas about optical configuration and theoretical resolutions. Theory about resolution along the depth axis was refined, as depth reconstruction and extraction are the main interest of X-ray plenoptic. Specific study was done on the evolution of contrast along depth as being a key parameter for depth reconstruction. We realized that contrast decreases when moving away from a privileged depth. This is important to consider as it can affect image reconstruction and quality of depth extraction.We also worked on refocusing algorithms. The refocusing algorithms are usually developed for each configuration separately. We worked to go beyond this separation. We developed a new algorithm valid for any configurations. Moreover, our algorithm is based on real distances between the optical elements, allowing generating images at any distances from the plenoptic camera. We defined a new parameterization between object and image spaces. Using geometrical optics, we calculated the matrix transformation between the two spaces. This allows back-projecting data from the acquired raw image to the object space, and reconstructing the pixels one by one, until the whole object. With this algorithm, we were able to simulate the process of image acquisition, and create synthetic plenoptic data. Reconstruction of these data was used to quantify the accuracy of the novel algorithm and prove its consistency.The refocusing algorithm allows reconstructing the depth planes one by one. Each refocused plane contains information about the whole 3D scene that has to be disentangled. The elements physically present at the refocused depth are intrinsically sharp, whereas the ones located at other depths are blurred. We used this contrast property to extract depth from the refocused images. We tested several existing methods derived from the field of depth from focus and studied their efficiency when applied to our images.In collaboration with European teams, we realized the first X-ray plenoptic camera that was tested at P05 beamline of PETRA III synchrotron. Based on the theoretical work developed in this thesis, we defined the best optical configuration, mounted the plenoptic camera, acquired X-ray plenoptic images, numerically refocused them using the new algorithm and verified the experimental resolutions and contrasts. Depth from focus techniques applied on the refocused stack allow to retrieve the expected depth plane. These are the first images acquired with an X-ray plenoptic camera
Drumond, Gisele Russo Canato. "Avaliação de exposição ocupacional em radiologia digital veterinária portátil." Universidade Tecnológica Federal do Paraná, 2012. http://repositorio.utfpr.edu.br/jspui/handle/1/447.
Full textThis study evaluates the distribution of the dose received by work-people involved in portable digital veterinary radiology procedures and checks the dose reduction obtained with the use of individual protection equipments. For this evaluation measurements were made using TLD-100 thermoluminescent dosimeters,positioned at seven different spots on the body of the assistants: hands, chest (outside the apron), thyroid (inside the apron), left and right eye corners and at the forehead, and in five different spots in the veterinarian: chest (outside the apron), thyroid (inside the apron), left and right eye corners and the center of the eyes. The dosage was evaluated through the 63 procedures performed with 49 assistants and a veterinarian in the metropolitan region of Curitiba, PR. The results show the importance of using thyroid protection and lead aprons to reduce the dosage received by the veterinarian and assistants. The dosages of the assistants who held the animals were higher in the areas of the hands. This study shows the need for additional protective measurements and the implementation of training mechanisms in radiation protection for physicians and assistants who work with portable digital radiology.
Maschio, Célio. "Tomografia computadorizada de raios-X como tecnica de ensaios não destrutivos de materiais." [s.n.], 1997. http://repositorio.unicamp.br/jspui/handle/REPOSIP/263266.
Full textDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
Made available in DSpace on 2018-07-22T16:25:26Z (GMT). No. of bitstreams: 1 Maschio_Celio_M.pdf: 7517102 bytes, checksum: b541bb4f611106b935e681d6189f03a7 (MD5) Previous issue date: 1997
Resumo: A tomografia computadorizada de raios-x tem extrapolado a área médica e ganhado campo em inúmeras aplicações onde se faz necessária a interpretação (qualitativa e quantitativa) da estrutura interna de um material opaco, sem destruí-lo. O presente trabalho demonstra a aplicação desta técnica em ensaios não destrutivos, utilizando-se amostras de materiais e componentes de diferentes densidades e geometrias, com defeitos simulados e reais, ensaiados em tomógrafos médicos. Demonstra-se, também, o uso da técnica na caracterização de filtros eletroquímicos usados para remoção de agentes contaminantes (no caso, zinco) de efluentes industriais. Foram usadas técnicas de processamento digital de imagens (sistema Khoros) para a caracterização dos defeitos encontrados, através da medida do coeficiente de atenuação do material em regiões de interesse, e por meio do cálculo de parâmetros dimensionais tais como área e perímetro. Foram aplicadas operações de filtragem matemática para a correção do efeito de endurecimento de feixe, verificado nas imagens de materiais metálicos, sobretudo no alumínio. Devido à sua natureza qualitativa e quantitativa, a tomografia computadorizada de raios-x demonstrou ser uma ferramenta promissora em ensaios não destrutivos de materiais. Este trabalho demonstra e reforça sua aplicabilidade através do uso de processamento digital de imagens
Abstract: X-ray computed tomography (XCT), originally developed for medical purposes is becoming increasingly applied to several applications where it is necessary the interpretation of the internal structure of an object nondestructively. The present work shows the application of this technique to nondestructive testing using materiaIs and components of different density and geometry, with simulated and real defects tested in a medical scanner. Characterization of electrochemical filters used to remove contamination agents (in this case, zinc) in industrial effluents, by XCT technique is also described. Digital image processing have been used (software Khoros) for defects characterization, determining the attenuation coefficient in regions of interest and measuring parameters like area and perimeter. Digital filtering operations have been applied for beam hardening correction in metallic materiaIs images, mainly aluminum. Due its qualitative and quantitative nature, XCT technique established to be a promising tool of nondestructive materiaIs evaluation and this work emphasizes its applicability through digital image processing
Mestrado
Materiais e Processos de Fabricação
Mestre em Engenharia Mecânica
Maschio, Célio. "Desenvolvimento de metodos para avaliação de processos de filtração por meio de simulação por meio de simulação numerica e tomografia de raios-x." [s.n.], 2001. http://repositorio.unicamp.br/jspui/handle/REPOSIP/262896.
Full textTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
Made available in DSpace on 2018-07-31T14:51:24Z (GMT). No. of bitstreams: 1 Maschio_Celio_D.pdf: 13410400 bytes, checksum: bcad1a44963fabb3c498533b4663302a (MD5) Previous issue date: 2001
Resumo: O objetivo deste trabalho foi o desenvolvimento de metodologias para o estudo de filtros e processos de filtração, utilizando a tomografia de raios-X, técnicas de processamento digital de imagens e simulação numérica. Os ensaios convencionais utilizados pelos fabricantes são realizados através da medida de parâmetros, tais como pressão e vazão, em pontos localizados a montante e a jusante do filtro. Estes ensaios não são eficientes na caracterização de defeitos e não revelam como ocorre o processo de saturação no interior do filtro. Neste trabalho, a tomografia de raios-X foi utilizada para duas finalidades básicas: estudar a distribuição de contaminantes e analisar defeitos no interior de elementos filtrantes. Os modelos de filtração encontrados na literatura não levam em conta o efeito do acúmulo de contaminantes no desempenho do filtro ao longo do processo de filtração. Neste trabalho, foi desenvolvido um modelo acoplando-se as equações de filtração com as equações fenomenológicas (lei de Darcy e equação da continuidade), de tal forma que o acúmulo de partículas no meio poroso (filtro) fosse considerado na simulação do processo de filtração. Os resultados demonstraram que o processo de saturação no interior dos elementos analisados não ocorre de forma homogênea, ou seja, o acúmulo de partículas é predominante em determinadas regiões. Em geral, há formação de canais preferenciais e o espaço interno do filtro não é totalmente utilizado na captura de partículas. Demonstrou-se também que, em alguns casos, o comportamento do filtro não é coerente com a especificação do fabricante. Foi possível, por fim, a utilização dos dados experimentais, obtidos via tomografia, para a validação do modelo teórico desenvolvido
Abstract: The development of methods for analysis of filters and filtration process, using X-ray computerized tomography, digital image processing and numerical simulation, was the objective of this work. Tests conventionally used by filter manufacturers are made through the measurement ofparameters, such as flow and pressure, at upstream and downstream ofthe filter. These tests are not efficient in the characterization of defects and do not reveal how the saturation process occurs within the filter. In this work, X-ray computerized tomography was used for two basic purposes: to evaluate contaminant distribution and to detect defects within the interior of the filter elements. The filtration models found in the literature do not consider the effect of contaminant concentration on the filter efficiency during the filtration processo In this work, filtration equations and phenomenological equations (Darcy's law and continuity equation) were coupled and a model that takes into account the contaminant accumulation on the filter performance was developed. The results demonstrated that the saturation process within the analyzed filters is not homogeneous, that is, the accumulation of partic1es is predominant in some regions. Generally, there are preferential channels and the interior of the filter elements is not totally utilized. In some cases, it was also demonstrated that the filter behavior does not agree with the manufacturer specifications. Finally, it was possible to use the experimental data obtained with X-ray computerized tomography, in order to validate the theoretical developed model
Doutorado
Materiais e Processos de Fabricação
Doutor em Engenharia Mecânica
Valerija, Munteanu. "Утврђивање морфолошких типова пинеалне жлезде хистолошком и методом компјутеризоване томографије." Phd thesis, Univerzitet u Novom Sadu, Medicinski fakultet u Novom Sadu, 2016. http://www.cris.uns.ac.rs/record.jsf?recordId=101507&source=NDLTD&language=en.
Full textUvod: Pinealna žlezda je neuroendokrini, cirkumventrikularni organ filogenetski poreklom organa vida. Kalcifikacije pinealne žlezde su čest nalaz prilikom radioloških pretraga, bez još uvek dovoljno dokaza da li su one normalan nalaz. Magnetna rezonanca opisuje tri morfološka tipa pinealne žlezde. Ciljevi: Utvrditi stepen korelacije morfoloških tipova pinealne žlezde utvrđenih patohistološkim nalazom sa nalazom kompjuterizovane tomografije, kao i stepen korelacije prisustva kalcifikacija u pinealnoj žlezdi utvrđenih patohistološkim nalazom i nalazom kompjuterizovane tomografije. Utvrditi stepen kalcifikacije pinealne žlezde patohistološkim nalazom u zavisnosti od starosti. Materijal i metode: Makroskopskom morfološkom i mikroskopskom, histološkom analizom obuhvaćeno je 111 izolovanih pinealnih žlezdi osoba oba pola, ne mlađih od 18 godina od kojih je 27 snimljeno aparatom Somatom Sensation 64 sa debljinama rekonstruisanih preseka 5 i 1mm, a još 9 aparatom Somatom Emotion 16. Rezultati: Postoji statistički značajna razlika u određivanju sva tri dijametra epifize petomilimetarskim rekonstrukcijama, i pri utvrđivanju dva dijametra jednomilimetarskim rekonstrukcijama. Postoji statistički značajna razlika u utvrđivanju morfoloških tipova histološkom i metodom kompjuterizovane tomografije. Prisutna je pozitivna korelacija kalcifikovanosti žlezde određene merenjem njene gustine u Haunsfildovim jedinicama i utvrđene mikroskopski. Kalcifikovanost pinealnog parenhima ne korelira starosti. Zaključak: Naša studija je pokazala da su jednomilimetarske rekonstrukcije tačnije u određivanju dijametara žlezde. Makroskopskim i mikroskopskim merenjem utvrđena su sva tri tipa pinealne žlezde opisana magnetnorezonantnim oslikavanjem. Utvrđena je statistički značajna povezanost gustine pinealne žlezde izmerene u Haunsfildovim jedinicama na jednomilimetarskim rekonstrukcijama i stepena kalcifikovanosti izraženog u procentima. Nije utvrđena povezanost kalcifikovanosti epifize merene mikroskopski i starosti.
Introduction: Pineal gland is a small neuroendocrine, circumventricular organ wich evolved from the eye. Calcifications were incidentally discovered and frequently without a proof whether they were normal or abnormal. Magnetic resonance imaging describes three morphological types. Aim: To determine if there is a correlation between pineal gland morphology types and calcifications established with histology and with computed tomography (CT) and if there is the correlation between calcifications and age. Method of work and material: Macroscopic and mycroscopic analysis encounted 111 isolated pineal glands of both sexes, no younger than 18, from wich 27 was examed with Somatom Sensation 64 and 9 with Somatom Emotion 16 with 5mm and 1mm reformated pictures. Results: All three diameters measured on 5mm reformated pictures and two measured on 1mm reformated pictures differed statistically compared to diameters measured macroscopically. There was siginificant difference between morphological types established on computed tomography and macroscopically. Pineal gland calcifications measured microscopically and with CT correlated positivelly. Pineal gland calcifications were not dependant on the patients age. Conclusion: Allthough 1mm reformated pictures are more accurate than 5mm, the pineal gland morpholgy types determined macroscopically and with CT are not correlated. However, calcification measurement with CT correlates with the microscopic measurement. Calcifications measured microscopically are not correlated with age.
Ibrahim, Mohamed Asim Yousif. "Co-processing of drugs and co-crystal formers and its effect on pharmaceutical dosage-form performance : co-crystallization of urea/2-methoxybenzamide, caffeine/malonic acid, caffeine/oxalic acid and theophylline/malonic acid systems : solid-state characterization including imaging, thermal, X-ray and Raman spectroscopic techniques with subsequent evaluation of tableting behaviour." Thesis, University of Bradford, 2008. http://hdl.handle.net/10454/12760.
Full textIbrahim, Mohamed Asim Y. "Co-processing of drugs and co-crystal formers and its effect on pharmaceutical dosage-form performance. Co-crystallization of urea/ 2-methoxybenzamide, caffeine/ malonic acid, caffeine/ oxalic acid and theophylline/ malonic acid systems: Solid-state characterization including imaging, thermal, X-ray and Raman spectroscopic techniques with subsequent evaluation of tableting behaviour." Thesis, University of Bradford, 2008. http://hdl.handle.net/10454/12760.
Full textIslamic University of Omdurman and the Ministry of Higher Education in Sudan
Cowan, Nigel Christopher. "The development of CT urography for investigating haematuria." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:284084de-2a71-4e35-8342-41f039b03df1.
Full textFeuillâtre, Hélène. "Détermination automatique de l'incidence optimale pour l'observation des lésions coronaires en imagerie rotationnelle R-X." Thesis, Rennes 1, 2016. http://www.theses.fr/2016REN1S039/document.
Full textThe thesis work deals with the planning of minimally invasive surgery of coronary artery lesions. The physician performs a coronarography following by a percutaneous transluminal angioplasty. The X-ray rotational angiography permits to visualize the lumen artery under different projection angles in several cardiac cycles. From these 2D projections, a 3D+T reconstruction of coronary arteries can be obtained. Our goal is to determine automatically from this 3D+T sequence, the optimal angiographic viewing angle of the stenotic segment. Several steps are proposed to compute the optimal angular position of the C-arm. Firstly, a mosaic-based tree matching algorithm of the 3D+T sequence is proposed to follow the stenotic lesion in the whole cardiac cycle. A pair-wise inexact tree matching is performed to build a tree union between successive trees. Next, these union trees are merged to obtain the mosaic tree which represents the most complete tree of the sequence. To take into account the non-rigid movement of coronary arteries during the cardiac cycle and their topology variations due to the 3D reconstruction or segmentation, similarity measures based on hierarchical and geometrical features are used. Artificial nodes are also inserted. With this global tree sequence matching, we propose secondly a new method to determine the optimal viewing angle of the stenotic lesion throughout the cardiac cycle. This 2D angiographic view which is proposed for three regions of interest (single segment, multiple segment or bifurcation) is computed from four criteria: the foreshortening, the external and internal overlap and the bifurcation opening angle rates. The optimal view shows the segment in its most extended and unobstructed dimension. This 2D view can be optimal either for the deployment of the stent or for the catheter guidance (from the root to the lesion). Our different algorithms are evaluated on real sequence (CT segmentation) and 41 simulated sequences
Chantziantoniou, Konstantinos. "An X-ray tube focal spot size measurement technique using a digital imaging computer method." 1991. http://hdl.handle.net/1993/17336.
Full textChien, Lin Yung, and 林永健. "The Developments of Infection-Control Procedure and Dual-Energy X-ray Imaging Technique for Acute Infectious Diseases." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/w4n3ma.
Full text元培科學技術學院
影像醫學研究所
94
Abstract We are presently faced with the threat of an avian flu outbreak in Taiwan. In response to this threat each unit in the hospital must develop a protocol for handling infected patients to protect the medical personnel and the patients being treated in the hospital. This abstract will discuss two issues the radiology department will have to deal with the possibility of an outbreak of avian flu. The first topic is suggestions for updating infectious control procedures in the radiology department. The second topic is a description of the dual energy X-ray image technique for acute respiratory diseases. Patients with an acute infectious disease will have symptoms of upper respiratory infection on their way to the hospital. It is often necessary to order a chest X ray based on the patient’s symptoms. Avian Flu and SARS have similar symptoms therefore proper precautions must be taken. We learned during the SARS outbreak the physicians and medical personnel did not take enough precautions. They did not have a clear idea of how easily the disease could spread, that strong measures of protection that were needed or they neglected using the type of protection recommended. Some medical personnel got infected and some sacrificed their lives as a result of the lack of proper precautions against the spread of SARS. There needs to be new protocol for examining patients in order to prevent the spread of the disease. Even so, X- ray technicians must be careful to use precautions while performing the X-Rays. Before putting on the outer protection equipment, they must spray themselves with phosphor from head to foot. Only after being sprayed can the technician wear the protective covering. After the work is completed, the protective clothing will be taken off and should be wrapped tightly in a bundle inside out. The protective clothes and the technician will be exposed to ultraviolet to check for any relation with the phosphor. If there is no reaction, the protective clothing will be placed into an infectious control container. The technicians are then clear to leave the work place. The traditional X-Ray technique currently used in the hospital does not allow for early diagnosis of pulmonary consolidation. There is a new X-Ray technique that allows for early diagnosis and containment of the disease. Breaking out of the traditional routine imaging technique gives us a golden opportunity for early treatment. When a patient has cough and fever, he may be suspeeted of having respiratory infection. X- rays are usually used to diagnose the infection. However, early pulmonary consolidation has a relatively low absorption coefficient in the early stage alveolar infiltration. There is an x-ray imaging technique that can be used to contrast images to find pulmonary consolidation in the early stages. Computer Radiography uses a Dual-Energy Radiography to produce two different energy images: low-energy images and high-energy images. The images are then stored in the Picture Archiving Communication stem (PACS). After transmission and storage, it is possible to use subtraction technology so that pulmonary consolidation can be seen more clearly in the early stages of infection. The low energy image is organized by the computer in many windows on the screen in different widths and values. The high-energy image is organized together with the low energy image and can cover (mask) some parts of the low-energy image. The high-energy images can be subtracted (eliminated) one by one from the low energy images. After the high-energy images are subtracted (eliminated), the contrast image of tissues will appear more clearly on the screen. Patients with early stage pulmonary consolidation have relatively low absorption coefficient of the X-rays. The use of the subtraction method allows the pulmonary consolidation to be seen more easily. Early identification of pulmonary consolidation seen in the contrast image allows for early treatment of the patient. The staff working in the radiology department must not only use safety practices to protect themselves from infection. but also transmit information about any infections quickly and effectively to the hospital staff in order to avoid further spread of the infection. We should be rigorous in developing procedures and taking precautions to fight against the threat of Avian Flu. We can break out of using the traditional X-Ray techniques and experiment with new methods that are more effective and sensitive for diagnosing infections early. The main focus of this abstract is to introduce a dual-energy X-ray technique that will help us obtain the correct diagnosis and help the patients with acute infections to get early and effective treatment.
Molloi, Sabee Y. "Dynamic dual-energy X-ray techniques for cardiac imaging." 1987. http://catalog.hathitrust.org/api/volumes/oclc/44856483.html.
Full textTypescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 153-168).
Allec, Nicholas. "Multilayer Energy Discriminating Detector for Medical X-ray Imaging Applications." Thesis, 2012. http://hdl.handle.net/10012/7137.
Full text(8102429), Xuedong Zhai. "MECHANICAL BEHAVIORS OF BIOMATERIALS OVER A WIDE RANGE OF LOADING RATES." Thesis, 2019.
Find full textSolomon, Justin Bennion. "Advanced Techniques for Image Quality Assessment of Modern X-ray Computed Tomography Systems." Diss., 2016. http://hdl.handle.net/10161/12174.
Full textX-ray computed tomography (CT) imaging constitutes one of the most widely used diagnostic tools in radiology today with nearly 85 million CT examinations performed in the U.S in 2011. CT imparts a relatively high amount of radiation dose to the patient compared to other x-ray imaging modalities and as a result of this fact, coupled with its popularity, CT is currently the single largest source of medical radiation exposure to the U.S. population. For this reason, there is a critical need to optimize CT examinations such that the dose is minimized while the quality of the CT images is not degraded. This optimization can be difficult to achieve due to the relationship between dose and image quality. All things being held equal, reducing the dose degrades image quality and can impact the diagnostic value of the CT examination.
A recent push from the medical and scientific community towards using lower doses has spawned new dose reduction technologies such as automatic exposure control (i.e., tube current modulation) and iterative reconstruction algorithms. In theory, these technologies could allow for scanning at reduced doses while maintaining the image quality of the exam at an acceptable level. Therefore, there is a scientific need to establish the dose reduction potential of these new technologies in an objective and rigorous manner. Establishing these dose reduction potentials requires precise and clinically relevant metrics of CT image quality, as well as practical and efficient methodologies to measure such metrics on real CT systems. The currently established methodologies for assessing CT image quality are not appropriate to assess modern CT scanners that have implemented those aforementioned dose reduction technologies.
Thus the purpose of this doctoral project was to develop, assess, and implement new phantoms, image quality metrics, analysis techniques, and modeling tools that are appropriate for image quality assessment of modern clinical CT systems. The project developed image quality assessment methods in the context of three distinct paradigms, (a) uniform phantoms, (b) textured phantoms, and (c) clinical images.
The work in this dissertation used the “task-based” definition of image quality. That is, image quality was broadly defined as the effectiveness by which an image can be used for its intended task. Under this definition, any assessment of image quality requires three components: (1) A well defined imaging task (e.g., detection of subtle lesions), (2) an “observer” to perform the task (e.g., a radiologists or a detection algorithm), and (3) a way to measure the observer’s performance in completing the task at hand (e.g., detection sensitivity/specificity).
First, this task-based image quality paradigm was implemented using a novel multi-sized phantom platform (with uniform background) developed specifically to assess modern CT systems (Mercury Phantom, v3.0, Duke University). A comprehensive evaluation was performed on a state-of-the-art CT system (SOMATOM Definition Force, Siemens Healthcare) in terms of noise, resolution, and detectability as a function of patient size, dose, tube energy (i.e., kVp), automatic exposure control, and reconstruction algorithm (i.e., Filtered Back-Projection– FPB vs Advanced Modeled Iterative Reconstruction– ADMIRE). A mathematical observer model (i.e., computer detection algorithm) was implemented and used as the basis of image quality comparisons. It was found that image quality increased with increasing dose and decreasing phantom size. The CT system exhibited nonlinear noise and resolution properties, especially at very low-doses, large phantom sizes, and for low-contrast objects. Objective image quality metrics generally increased with increasing dose and ADMIRE strength, and with decreasing phantom size. The ADMIRE algorithm could offer comparable image quality at reduced doses or improved image quality at the same dose (increase in detectability index by up to 163% depending on iterative strength). The use of automatic exposure control resulted in more consistent image quality with changing phantom size.
Based on those results, the dose reduction potential of ADMIRE was further assessed specifically for the task of detecting small (<=6 mm) low-contrast (<=20 HU) lesions. A new low-contrast detectability phantom (with uniform background) was designed and fabricated using a multi-material 3D printer. The phantom was imaged at multiple dose levels and images were reconstructed with FBP and ADMIRE. Human perception experiments were performed to measure the detection accuracy from FBP and ADMIRE images. It was found that ADMIRE had equivalent performance to FBP at 56% less dose.
Using the same image data as the previous study, a number of different mathematical observer models were implemented to assess which models would result in image quality metrics that best correlated with human detection performance. The models included naïve simple metrics of image quality such as contrast-to-noise ratio (CNR) and more sophisticated observer models such as the non-prewhitening matched filter observer model family and the channelized Hotelling observer model family. It was found that non-prewhitening matched filter observers and the channelized Hotelling observers both correlated strongly with human performance. Conversely, CNR was found to not correlate strongly with human performance, especially when comparing different reconstruction algorithms.
The uniform background phantoms used in the previous studies provided a good first-order approximation of image quality. However, due to their simplicity and due to the complexity of iterative reconstruction algorithms, it is possible that such phantoms are not fully adequate to assess the clinical impact of iterative algorithms because patient images obviously do not have smooth uniform backgrounds. To test this hypothesis, two textured phantoms (classified as gross texture and fine texture) and a uniform phantom of similar size were built and imaged on a SOMATOM Flash scanner (Siemens Healthcare). Images were reconstructed using FBP and a Sinogram Affirmed Iterative Reconstruction (SAFIRE). Using an image subtraction technique, quantum noise was measured in all images of each phantom. It was found that in FBP, the noise was independent of the background (textured vs uniform). However, for SAFIRE, noise increased by up to 44% in the textured phantoms compared to the uniform phantom. As a result, the noise reduction from SAFIRE was found to be up to 66% in the uniform phantom but as low as 29% in the textured phantoms. Based on this result, it clear that further investigation was needed into to understand the impact that background texture has on image quality when iterative reconstruction algorithms are used.
To further investigate this phenomenon with more realistic textures, two anthropomorphic textured phantoms were designed to mimic lung vasculature and fatty soft tissue texture. The phantoms (along with a corresponding uniform phantom) were fabricated with a multi-material 3D printer and imaged on the SOMATOM Flash scanner. Scans were repeated a total of 50 times in order to get ensemble statistics of the noise. A novel method of estimating the noise power spectrum (NPS) from irregularly shaped ROIs was developed. It was found that SAFIRE images had highly locally non-stationary noise patterns with pixels near edges having higher noise than pixels in more uniform regions. Compared to FBP, SAFIRE images had 60% less noise on average in uniform regions for edge pixels, noise was between 20% higher and 40% lower. The noise texture (i.e., NPS) was also highly dependent on the background texture for SAFIRE. Therefore, it was concluded that quantum noise properties in the uniform phantoms are not representative of those in patients for iterative reconstruction algorithms and texture should be considered when assessing image quality of iterative algorithms.
The move beyond just assessing noise properties in textured phantoms towards assessing detectability, a series of new phantoms were designed specifically to measure low-contrast detectability in the presence of background texture. The textures used were optimized to match the texture in the liver regions actual patient CT images using a genetic algorithm. The so called “Clustured Lumpy Background” texture synthesis framework was used to generate the modeled texture. Three textured phantoms and a corresponding uniform phantom were fabricated with a multi-material 3D printer and imaged on the SOMATOM Flash scanner. Images were reconstructed with FBP and SAFIRE and analyzed using a multi-slice channelized Hotelling observer to measure detectability and the dose reduction potential of SAFIRE based on the uniform and textured phantoms. It was found that at the same dose, the improvement in detectability from SAFIRE (compared to FBP) was higher when measured in a uniform phantom compared to textured phantoms.
The final trajectory of this project aimed at developing methods to mathematically model lesions, as a means to help assess image quality directly from patient images. The mathematical modeling framework is first presented. The models describe a lesion’s morphology in terms of size, shape, contrast, and edge profile as an analytical equation. The models can be voxelized and inserted into patient images to create so-called “hybrid” images. These hybrid images can then be used to assess detectability or estimability with the advantage that the ground truth of the lesion morphology and location is known exactly. Based on this framework, a series of liver lesions, lung nodules, and kidney stones were modeled based on images of real lesions. The lesion models were virtually inserted into patient images to create a database of hybrid images to go along with the original database of real lesion images. ROI images from each database were assessed by radiologists in a blinded fashion to determine the realism of the hybrid images. It was found that the radiologists could not readily distinguish between real and virtual lesion images (area under the ROC curve was 0.55). This study provided evidence that the proposed mathematical lesion modeling framework could produce reasonably realistic lesion images.
Based on that result, two studies were conducted which demonstrated the utility of the lesion models. The first study used the modeling framework as a measurement tool to determine how dose and reconstruction algorithm affected the quantitative analysis of liver lesions, lung nodules, and renal stones in terms of their size, shape, attenuation, edge profile, and texture features. The same database of real lesion images used in the previous study was used for this study. That database contained images of the same patient at 2 dose levels (50% and 100%) along with 3 reconstruction algorithms from a GE 750HD CT system (GE Healthcare). The algorithms in question were FBP, Adaptive Statistical Iterative Reconstruction (ASiR), and Model-Based Iterative Reconstruction (MBIR). A total of 23 quantitative features were extracted from the lesions under each condition. It was found that both dose and reconstruction algorithm had a statistically significant effect on the feature measurements. In particular, radiation dose affected five, three, and four of the 23 features (related to lesion size, conspicuity, and pixel-value distribution) for liver lesions, lung nodules, and renal stones, respectively. MBIR significantly affected 9, 11, and 15 of the 23 features (including size, attenuation, and texture features) for liver lesions, lung nodules, and renal stones, respectively. Lesion texture was not significantly affected by radiation dose.
The second study demonstrating the utility of the lesion modeling framework focused on assessing detectability of very low-contrast liver lesions in abdominal imaging. Specifically, detectability was assessed as a function of dose and reconstruction algorithm. As part of a parallel clinical trial, images from 21 patients were collected at 6 dose levels per patient on a SOMATOM Flash scanner. Subtle liver lesion models (contrast = -15 HU) were inserted into the raw projection data from the patient scans. The projections were then reconstructed with FBP and SAFIRE (strength 5). Also, lesion-less images were reconstructed. Noise, contrast, CNR, and detectability index of an observer model (non-prewhitening matched filter) were assessed. It was found that SAFIRE reduced noise by 52%, reduced contrast by 12%, increased CNR by 87%. and increased detectability index by 65% compared to FBP. Further, a 2AFC human perception experiment was performed to assess the dose reduction potential of SAFIRE, which was found to be 22% compared to the standard of care dose.
In conclusion, this dissertation provides to the scientific community a series of new methodologies, phantoms, analysis techniques, and modeling tools that can be used to rigorously assess image quality from modern CT systems. Specifically, methods to properly evaluate iterative reconstruction have been developed and are expected to aid in the safe clinical implementation of dose reduction technologies.
Dissertation
"Effects of inorganic mercury on developing zebrafish (Danio rerio) larvae." Thesis, 2015. http://hdl.handle.net/10388/ETD-2015-10-2243.
Full text"DEVELOPMENT OF HYBRID-CONSTRUCT BIOPRINTING AND SYNCHROTRON-BASED NON-INVASIVE ASSESSMENT TECHNIQUES FOR CARTILAGE TISSUE ENGINEERING." Thesis, 2015. http://hdl.handle.net/10388/ETD-2015-12-2355.
Full text