Thesis (Ph. D.)--Duke University, 2008. / Includes bibliographical references.

Thesis (M.S.)--University of Alabama at Birmingham, 2010. / Title from PDF title page (viewed on June 25, 2010). Includes bibliographical references (p. 29-31).

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xxii, 212 p.; also includes graphics. Includes bibliographical references (p. 203-212). Available online via OhioLINK's ETD Center

Thesis (Ph.D.)--Ohio University, November, 2004. / Title from PDF t.p. Includes bibliographical references (p. 180-191)

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 178-188).

Είναι κοινά αποδεκτή η γνώμη ότι στις μέρες μας η υπολογιστική τομογραφία αποτελεί αναπόσπαστο μέσο διάγνωσης στην κλινική πράξη. Προκαταρκτικές όμως εξετάσεις ρουτίνας σε μικρά ζώα είναι επίσης ωφέλιμες με απώτερο στόχο την εφαρμογή νέων τεχνικών διάγνωσης και τη βελτίωση παλαιοτέρων, στον άνθρωπο. Αυτό τον ρόλο καλείται να παίξει η μικροτομογραφία, που ουσιαστικά αποτελεί μια παραλλαγή της κλασσικής Υπολογιστικής Τομογραφίας Κωνικής Δέσμης (CBCT). Στόχος της παρούσας διατριβής είναι η μελέτη, η ανάπτυξη, η εφαρμογή και η αξιολόγηση αλγορίθμων ανακατασκευής εικόνας μικρών ζώων και αντικειμένων, απο τις προβολικές εικόνες τους. Συνδυάζοντας προβολικά δεδομένα λήψης από διάφορες γεωμετρίες, όπως της επίπεδης ισοκεντρικής τροχιάς αλλά και της τρισορθογώνιας, της ελικοειδούς καθώς και αυτής του περιορισμένου γωνιακού κυκλικού τόξου, ανακατασκευάστηκαν λογισμικά κυρίως μοντέλα των υπό εξέταση δειγμάτων. Με απώτερο στόχο την εφαρμογή αλλά και τη βελτίωση γνωστών αλγορίθμων ανακατασκευής αλλά και τον πειραματισμό και την ανάπτυξη καινούργιων μεθόδων αναδημιουργίας στο χώρο της τομογραφίας, ένα νέο λογισμικό εργαλείο δημιουργήθηκε στα πλαίσια της διατριβής αυτής. Πρόκειται για την Υπολογιστική Βιβλιοθήκη CLCT, μια ενοποιημένη πλατφόρμα προσομοίωσης που έχει αναπτυχθεί στην αντικειμενοστραφή γλώσσα προγραμματισμού C++. Χρησιμοποιώντας το εργαλείο αυτό, είναι δυνατή η σύνθεση ενός σεναρίου υπολογιστικής τομογραφίας με χρήση των επιμέρους στοιχείων της βιβλιοθήκης. Στο πλαίσιο της βιλιοθήκης, έχει αναπτυχθεί πληθώρα εργαλείων που αφορούν την ανακατασκευή αλλά και την επεξεργασία εικόνας. Παραδείγματα χρήσης της βιβλιοθήκης αναφέρονται τόσο για την περίπτωση της μικροτομογραφίας κωνικής δέσμης (στην ανακατασκευή μοντέλων μικρών ζώων και πειραματικών δεδομένων) όσο και για άλλες γενικές εφαρμογές της κλασσικής υπολογιστικής τομογραφίας στην ιατρική. / It is common belief that nowadays Computed Tomography is an integral part of medical diagnosis. Preliminary studies on small animals are also useful as they allow applying new diagnostic techniques and imaging modalities on humans, while improving at the same time the well established traditional methods. This is a role to be played by micro Computed Tomography (μCT), a technique similar to the conventional Cone Beam CT. The aim of the current thesis is to study, develop, apply and evaluate image reconstruction algorithms using projection images of small animals and objects. Using different acquisition geometries like circular or three-orthogonal trajectories as well as helical and limited arc trajectories, reconstructions were performed using software phantoms. A new software tool, CLCT library, was created during this thesis aiming to contribute to the implementation and improvement of well-known image reconstruction algorithms but also to the experimental testing and evaluation of new image reconstruction techniques. CLCT is an object-oriented class library, implemented in C++. In the core of the library, fundamental elements are classes, tightened together in a logical hierarchy. Real world objects, like an X-Ray Source or a Flat- Detector, can be defined as instances of corresponding classes. Various utilities (like 3D transformations, loading, saving, filtering of images, creation of planar or curved objects of various dimensions) have been incorporated in the software tool as class methods. They allow the user to easily set up any arrangement of these objects in 3D space and to experiment with many different trajectories and configurations. The application of CLCT library confirms the flexibility of the approach which is presented in this thesis through simulations on software phantoms as well as on real projection data for both cases of μCT and conventional Cone Beam CT.

The stability of the photon beam position on synchrotron beamlines is critical for most if not all synchrotron radiation experiments. On wiggler and bend magnet beamlines, the vertical position is most critical due to the large horizontal width of the beam. The position of the beam at the experiment or optical element location is set by the position and trajectory of the electron beam source as it traverses the magnetic field of the bend magnet or the insertion device. Thus an ideal photon beam monitor would be able to simultaneously measure the photon beam’s vertical position and angle, or its position in phase space. X-ray diffraction is commonly used to prepare a monochromatic beam on x-ray beamlines usually in the form of a double crystal monochromator using perfect crystals. Diffraction from crystals couples the photon wavelength or energy to the incident angle on the crystal or lattice planes within the crystal. A monochromatic beam from such a monochromator will contain a spread of energies due to the vertical divergence of the photon beam from the source. This range of energies can easily cover the absorption edge of an element such as iodine at 33.17keV. It has been found that a system composed of a double crystal monochromator and an iodine filter that horizontally covers part of the monochromatic beam and an imaging detector can be used to independently and simultaneously measure the position and angle of the photon beam. This information can then be translated back to determine the vertical position and angle, or vertical phase space, of the electron beam source. This approach to measurement of the phase space of the source has not been done before and thus this study is the first of its kind. The goal of this thesis is to investigate the use of this combined monochromator, filter and detector as a phase space beam position monitor. The system was tested for sensitivity to position and angle under a number of synchrotron operating conditions (normal operations and special operating modes where the beam is intentionally altered in position and angle). These results were compared to other methods of beam position measurement from the literature to assess the utility of such a system as a beam diagnostic, a feedback element for electron beam control and a source of information that could be used to correct the experimental data to account for beam position and angle motion.

The High Radiation to Materials facility employs a high intensity pulsed beam imposing several challenges on the beam position monitors. Diamond has been shown to be a resilient material with its radiation hardness and mechanical strength, while it is also simple due to its wide bandgap removing the need for doping. A new type of diamond based beam position monitor has been constructed, which includes a hole in the center of the diamond where the majority of the beam is intended to pass through. This increases the longevity of the detectors as well as allowing them to be used for high intensity beams. The purpose of this thesis is to evaluate the performance of the detectors in the High Radiation to Materials facility for various beam parameters, involving differences in position, size, bunch intensity and bunch number. A prestudy consisting of calibration of the detectors using single incident particles is also presented. The detectors are shown to work as intended after a recalibration of the algorithm, albeit with a slightly lower precision than requested, giving a promising new beam position monitoring system. They work for the full intensity range and a single bunch resolution is achieved. Functionality is also shown with backscattering from dense targets.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: This project comprises the design, analysis, and construction of a Rotman lens with reduced conjugate-port coupling. The Rotman lens is a beam-forming network, used in wide-angle scanners to feed an antenna array. The scanning operation is based on optics and is therefore frequency invariant, a desirable feature of the Rotman lens compared to other beam-forming networks which employ phase shifters. The antenna array is connected to the lens's array ports via transmission lines. These array ports lie on the array contour which is designed so that a signal incident onto the antenna array will propagate into the lens and focus at a particular point. The position of this focal point depends on the signals direction of arrival at the array. Ports are placed on these focal points to feed and receive signals. Bootlace lenses allow up to four focal points for linear arrays whereas the Rotman lens is designed for three foci. Scanners usually require to scan many beam-widths, thus ports are employed along a focal arc which intersect these foci. Inter-focal ports do not focus perfectly and result in phase errors distributed across the array aperture. The derivation of three and four foci lenses is provided. There are several degrees of freedom at the designer's disposal, the e ect which these available parameters have on the lens geometry and phase errors is investigated. The waveguide implementa- tion of these lenses is examined, in which we use vertically polarised horns as feed ports and coaxial probes as array ports. Some designs of Rotman lenses published in literature show excess mutual cou- pling between symmetrically opposed feed ports. Using a model which approximates the array contour as a re ecting wall, we show that this is due to the re ected energy focusing on conjugate ports. It is identi ed that Rotman lenses designed for mini- mum phase errors will have near maximum conjugate-port coupling. Two Rotman lenses have been designed at 3; 5GHz for ve feed ports, eleven elements, and up to 30 scan angles. The rst is designed for minimum phase errors, and the second for the defocusing of the re ected energy from the focal arc. Simulations show up to a 10dB reduction in conjugate-port coupling for the second lens with a negligible degradation in performance from the phase errors. Measurements show that the re ected energy is spread between the feed ports as expected, compared to the focusing at a single port of the traditional Rotman lens. / AFRIKAANSE OPSOMMING: Hierdie projek behels die ontwerp, analise en konstruksie van 'n Rotmanlens met verminderde simmetries oorstaande poort koppeling. Die Rotmanlens is 'n patroon- vormingsnetwerk wat gebruik word as samestellingvoer in wye hoek skandeerders. 'n Gewensde eienskap van die Rotmanlens bo faseskuif voernetwerke is dat die skan- deerwerking gebasseer is op optika en dus frekwensie onafhanklik is. Die antennasamestelling word deur transmissielyne verbind aan die antennapoorte van die lens. Hierdie poorte l^e op die samestellingkontoer wat ontwerp is om te verseker dat seine wat inval op die antennasamestelling sal voortplant in die lens en fokus op 'n spesi eke punt. Die posisie van die fokuspunt hang af van die invalshoek van die sein op die samestelling. Poorte word op hierdie fokuspunte geplaas om te seine te ontvang en te lanseer. Hierdie tipe lense kan tot vier fokuspunte h^e , waar die Rotman lens spesi ek vir drie fokuspunte ontwerp word. Skandeerders moet normaalweg etlike bundelwydtes wyd kan skandeer, en daarom word poorte geplaas op 'n straal wat die fokuspunte onderskep. Poorte wat weg van die fokus geplaas word toon 'n e ens uit fokus gedrag, wat vertaal na fasefoute in die samestelling stralingsvlak. Die a eiding van drie en vier fokus lense word verskaf. Daar is verskeie grade van vryheid tot die beskikking van die ontwerper, en die e ek wat die beskikbare parameters op die geometrie van die lens en die fase foute het word ondersoek. Die gol eier implimetering van hierdie lense word beskryf, waar vertikaal gepolariseerde horings as voerpoorte, en ko-aksiale lyne as antennapoorte gebruik word. Sommige Rotman lens ontwerpe in die literatuur toon beduidende koppeling tussen die simmetries oorstaande voerpoorte. Deur van 'n model gebruik te maak wat die samestellingkontoer as 'n weerkaatsende muur benader toon ons aan dat die koppeling geskied as gevolg van die weerkaatsde energie wat fokus in die simme- tries oorstaande poorte. Dit word identi seer dat Rotman lense wat vir minimum fasefoute ontwerp word bykans maksimum koppeling tussen simmetries oorstaande poorte tot gevolg het. Twee Rotman lense is ontwerp by 3; 5GHz vir vyf voerpoorte, elf antenna ele- mente en skandeer hoeke van 30. Die eerste is ontwerp vir minimum fasefoute en die tweede vir uit fokus weerkaatsde energie vanuit die fokus straal. Simulasies toon tot 10 dB vermindering in koppeling tussen simmetries oorstaande poorte vir die tweede lens met weglaatbare werkverrigting verswakking as gevolg van fasefoute. Metings toon dat die weerkaatsde energie, soos verwag, versprei word tussen die voerpoorte vergeleke met energie gefokus in 'n enkele poort soos by die tradisionele Rotman lens.

Made available in DSpace on 2014-10-09T12:27:10Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:19Z (GMT). No. of bitstreams: 0 / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP