Dissertations / Theses: 'X-Ray Computed'

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Moore, Jared William. "Adaptive X-ray Computed Tomography." Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/145396.

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An adaptive pre-clinical x-ray computed tomography system, named "FaCT" was designed, built, and tested at the University of Arizona's Center for Gamma-Ray Imaging (CGRI). The FaCT system possesses the unique ability to change its magnification and dynamically mask the x-ray beam profile. Using these two abilities, the FaCT system can adapt its configuration to the object being imaged, and the task being performed, while achieving a reduction in the radiation dose applied for imaging.Development of the system included the design of all mechanical components, motion systems, and safety systems. It also included system integration of all electronics, motors, and communication channels. Control software was developed for the system and several high-performance reconstruction algorithms were implemented on graphics processing units for reconstructing tomographic data sets acquired by the system. A new geometrical calibration method was developed for calibrating the system that makes use of the full image data gathered by the system and does not rely on markers.An adaptive imaging procedure consisting of a preliminary scout scan, human guidance, and a diagnostic quality scan was developed for imaging small volumes of interest in the interior of an object at substantially reduced dose. The adaptive imaging procedure makes use of FaCT's adjustable magnification, beam-masking capability, and high-performance reconstruction software to achieve high-quality reconstruction of a volume of interest with less dose than would be required by a traditional x-ray computed tomography system without adaptive capabilities.To address ongoing research into mathematical rules for adapting an imaging system, such as FaCT, to better perform a given estimation task, a method of quantifying a system's ability to estimate a parameter of interest in the presence of nuisance parameters based on the Fisher Information was proposed. The method requires a statistical model of object variability. Possible strategies for increasing the performance of an estimation task, given an adaptive system, were suggested.

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Halverson, Clinton. "Characterization of geomaterials with X-ray computed tomography (X-ray CT)." [Ames, Iowa : Iowa State University], 2008.

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Qiu, Wei. "Iterative algorithms for volumetric X-ray computed tomography." Thesis, University of Bath, 2012. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.571870.

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Cone beam computed tomography (CBCT) enables a volumetric image reconstruction from a set of 2D projection data. This thesis studies the performance of a wide range iterative algorithms in various aspects, aiming to generate a better CBCT image reconstruction, especially when projection data is limited. We have implemented a wide range of algebraic iterative algorithms. Hence, the performance of ART, SART and OS-SART is studied based on a range of image quality measures. The major limitations of traditional iterative methods are their computational time. The conjugate gradients (CG) algorithm and its variants can be used to solve linear systems of equations arising from CBCT. Their applications can be found in a general linear algebra context, but in tomography problems (e.g. CBCT reconstruction) they have not widely been used. Hence, CBCT reconstruction using the CG-type algorithm LSQR was implemented and studied. In CBCT reconstruction, the main computational challenge is that the matrix A usually is very large, and storing it in full requires an amount of memory well beyond the reach of commodity computers. Because of these memory capacity constraints, only a small fraction of the weighting matrix A is typically used, leading to a poor reconstruction. In this final part of the thesis, to overcome this diculty, the matrix A is partitioned and stored blockwise, and blockwise matrix-vector multiplications are implemented within LSQR. This implementation allows us to use the full weighting matrix A for CBCT reconstruction without further enhancing computer standards. Tikhonov regularization has been developed in this framework, and can produce significant improvement in the reconstructed images for limited data case.

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Eck, Brendan Lee. "Myocardial Perfusion Imaging with X-Ray Computed Tomography." Case Western Reserve University School of Graduate Studies / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case1525187076597075.

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Stirrup, James Elliott. "Mycardial applications of cardiovascular X-ray computed tomography." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/18969.

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This thesis evaluated the role of cardiovascular computed tomography (CCT) in assessing the left ventricular (LV) myocardium. The technical and clinical performance of single-slice CT for attenuation correction (CTAC) of SPECT myocardial perfusion scintigraphy (MPS) was evaluated. Early and delayed multi-slice CT (eCCT and dCCT respectively) myocardial enhancement patterns were validated against SPECT MPS (single-source CCT) and cardiovascular magnetic resonance imaging (CMR, dual-source CCT) for detection of chronic myocardial infarction (MI), as were CCT measures of segmental LV wall thickness and global and regional LV function. Impact of cardiac phase and reconstruction kernel on agreement with SPECT MPS was also measured. The following results were shown: CTAC showed no benefits on MPS report or reporter confidence when studied in a way that reflects clinical practice; dCCT best identifies segmental MI, showing good agreement and high specificity, negative predictive value and accuracy compared with SPECT MPS and CMR; choice of smooth or medium-smooth reconstruction kernel appears relatively unimportant; dual-energy dCCT may be more sensitive for segmental MI on CMR; CCT end-systolic wall thickness is a better predictor of myocardial scarring on MPS and CMR than end-diastolic wall thickness; CCT overestimates end-systolic and end-diastolic volumes on MPS but LV ejection fraction is equivalent; CCT shows no systematic differences in measures of global LV function when compared to CMR; measures of regional ventricular function on CCT show excellent and good agreement with MPS and CMR respectively; inter- and intraobserver agreement for dCCT myocardial enhancement patterns and regional LV function is excellent.

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Ghous, Abid Petroleum Engineering Faculty of Engineering UNSW. "Digital formation evaluation via x-ray micro-computed tomography." Awarded by:University of New South Wales. School of Petroleum Engineering, 2005. http://handle.unsw.edu.au/1959.4/20581.

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Machined fragments of 10 core plugs from oshore reservoirs have been analysed using a high resolution X-ray micro-computed tomography (micro-CT) facility. The facility includes a system capable of acquiring 3D images made up of 20003 voxels on core plugs up to 6 cm diameter with resolutions down to 2 um. The cores analysed include six cores from a gas reservoir and four cores from an oil reservoir. The cores exhibit a very broad range of pore and grain sizes, porosity, permeability and mineralogy. The petrological data, available only for gas reservoir cores, is compared with the data obtained from the tomographic images. Computational results made directly on the digitized tomographic images are presented for the permeability, formation factor, resistivity index and drainage capillary pressure across a range of . We show that data over a range of porosity can be computed from a single fragment. We compare the computations of petrophysical data on fragments to conventional laboratory measurements on the full plug. Permeability predictions from digital and conventional core analysis are consistent. It is shown that a characteristic length scale can be dened as a quality control parameter for the estimation of permeability. Results for formation factor, drainage capillary pressure and resistivity index are encouraging. The results demonstrate the potential to predict petrophysical properties from core material not suited for laboratory testing (e.g., sidewall or damaged core and drill cuttings) and the feasibility of combining digitized images with numerical calculations to predict properties and derive correlations for specic rock lithologies. The small sample size required for analysis makes it possible to produce multiple measurements on a single plug. This represents a potential multiplier on the quantity of core data allowing meaningful distributions or spreads in petrophysical properties to be estimated. We discuss the current limitations of the methodology and suggest improvements; in particular the need to calibrate the simulated data to parallel laboratory core measurements. We also describe the potential to extend the methodology to a wider range of petrophysical properties. This development could lead to a more systematic study of the assumptions, interpretations and analysis methods commonly applied within industry and lead to better correlations between petrophysical properties and log measurements.

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Nielsen, Brent Daniel. "Non-Destructive Soil Testing Using X-Ray Computed Tomography." Thesis, Montana State University, 2004. http://etd.lib.montana.edu/etd/2004/nielsen/NielsenB1204.pdf.

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The mechanical behavior of soils is highly dependent on the particle microstructure. Traditional geotechnical engineering soil tests generally do not measure soil properties on a micro-scale; instead, macro scale properties are commonly used as estimates of microstructure properties in determining soil engineering behavior. Additionally, traditional geotechnical engineering soil tests are destructive in nature, and many test methods destroy the same soil properties they intend to measure. The goal of this research was to develop non-destructive soil test methods using x-ray computer-aided tomography (CT) scanning techniques to determine soil index properties. The CT scanning process provides a promising method for examining soil microstructure in a non-destructive manner. This research had two main objectives. The first was to configure the Montana State University Civil Engineering Department\'s computer-aided tomography scanner to perform CT scans on soil samples. The second objective was to use the CT scanner to develop nondestructive test procedures to determine geotechnical index properties of soils. Test methods were developed in this study to determine porosity, grain size distribution, and pore size distribution. The results from the first objective showed that the MSU CT scanning equipment is capable of producing high quality CT scans of soil materials. Resolution limitations of the scanner define the smallest soil grain size that is detectable in a CT scan, but the scan resolution may be improved by using smaller sample sizes for small particle soils. The results of the second portion of the study show that the non-destructive CT scanning test methods compare favorably with traditional geotechnical laboratory mechanical test methods. CT-measured porosity values and grain size distributions compared well with mechanical testing results, which were used to validate the new test methods. In addition, the CT-measured pore size distributions were in good agreement with an accepted pore size mathematical model. Since traditional pore size distribution tests are time-consuming, labor intensive, and destructive in nature, the non-destructive x-ray CT scanning test methods developed in this study show strong promise as a means for measuring an elusive soil property that cannot be accurately measured using traditional geotechnical testing procedures.

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Lotz, Jeffrey Charles. "Hip fracture risk predictions by x-ray computed tomography." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/14410.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Harvard-MIT Division of Health Sciences and Technology Program in Medical Engineering and Medical Physics, 1988.
Includes bibliographical references.
by Jeffrey Charles Lotz.
Ph.D.

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Mishra, Sourav. "Collimator width Optimization in X-ray Luminescent Computed Tomography." Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/51118.

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X-ray Luminescent Computed Tomography (XLCT) is a new imaging modality which is under extensive trials at present. The modality works by selective excitation of X-ray sensitive nanophosphors and detecting the optical signal thus generated. This system can be used towards recreating high quality tomographic slices even with low X-ray dose. There have been many studies which have reported successful validation of the underlying philosophy. However, there is still lack of information about optimal settings or combination of imaging parameters, which could yield best outputs. Research groups participating in this area have reported results on basis of dose, signal to noise ratio or resolution only.
In this thesis, the candidate has evaluated XLCT taking into consideration noise and resolution in terms of composite indices. Simulations have been performed for various beam widths and noise & resolution metrics deduced. This information has been used in evaluating quality of images on basis of CT Figure of Merit & a modified Wang-Bovik Image Quality index. Simulations indicate the presence of an optimal setting which can be set prior to extensive scans. The conducted study, although focusing on a particular implementation, hopes to establish a paradigm in finding best settings for any XLCT system. Scanning with an optimal setting preconfigured can help in vastly reducing the cost and risks involved with this imaging modality.

Master of Science

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Ebert, Matthias. "Non-ideal projection data in X-ray computed tomography." [S.l. : s.n.], 2002. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB10605022.

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Murer, Fredrik Kristoffer. "X-ray Diffraction Computed Tomography of a Fossil Bone Sample." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-23618.

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A fossil bone sample, a humerus (”upper arm”) of a prehistoric fish, Eusthenopteron Foordi, has been studied using a combination of X-ray diffraction, computed tomography and synchrotron radiation. The technique has in this thesis been called X-ray diffraction computed tomography. It has been attempted to obtain three-dimensional tomographic images of sample regions containing different minerals, as well as to determine crystallite orientation properties of the different minerals.The sample has been found to consist of hydroxylapatite, barite, calcite, quartz and pyrite. Three-dimensional tomographic images of the four first minerals have been made using the filtered backprojection algorithm. Image artifacts were reduced by combining recorded intensity from several Bragg peaks and by combining data from two separate tomographic measurements of the sample.A fraction of the hydroxylapatite crystallites appear to have a preferredorientation. The direction of this preferred orientation has been deter-mined for some regions close to the sample edge.

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Lunel, Marie Monique France. "Structure characterisation of catalysts using X-ray micro-computed tomography." Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/5710/.

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Knowledge of internal porous structure is essential in improving the development of a catalytic system and consequently leading to an optimized performance. XRCT has been used to show differences in density and pore distribution and that differences can be related to the process route by which the specimen was prepared. Alumina samples with defects prepared using different conditions have been investigated in order to acquire information on the introduction and development of cracks. Results indicated that cracks became larger when the water content, the ram speed of the extruder and the drying temperature were higher. The calcination process increased the number and the 3-D size of the cracks. Both concentration of the bulk solution and impregnation time appeared to have a significant impact on the metal distribution profile during the impregnation process. Drying had a strong impact on the metal profile, as a redistribution of copper was noticed. The redistribution was observed exclusively in the case of weak adsorption of copper with alumina support. Experiments on the newly established I13 beamline synchrotron in Diamond was carried out in order to gain an understanding of the cracks induction/propagation and of the diffusion of metallic solution inside the catalyst support.

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Tseng, Hsin-Wu. "Task-Based Image Quality Assessment in X-Ray Computed Tomography." Diss., The University of Arizona, 2015. http://hdl.handle.net/10150/593630.

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In X-Ray CT, there is always a desire to maintain the image quality while reducing the radiation dose. Recently several dose reduction approaches in both software and hardware have been developed to achieve the goal of making radiation as low as possible. Thus, the assessment of image quality becomes an important factor for routine quality control of medical X-Ray devices. In this work, task-based image quality measurements using model observers were used to evaluate the performance of X-Ray CT systems. To evaluate the dose reduction ability, detection tasks as well as combined detection and estimation tasks were considered. In detection tasks and combined detection and estimation tasks, the channelized Hotelling observer (CHO) and channelized scanning linear observer (CSLO) (with Dense Difference of Gauss channels) were employed respectively. They were used to evaluate the dose reduction capability of the iterative reconstruction algorithm developed by GE compared to the traditional reconstruction algorithm, filtered backprojection (FBP). Additionally, CHO and CSLO were also used for optimization of CT protocols. Our methods were also applied to Cardiac CT systems for temporal resolution evaluations. Two reconstruction algorithms, FBP and the motion correction algorithm, Snapshot Freeze (SSF), operated at two heart-beating rates with two reconstruction windows were quantitatively evaluated using task-based measurements. Finally, due to the huge demand of data acquisitions in the conventional channelized model observers, a proposed High-Dose-Signal-LOOL CHO/CSLO (HL-CHO/CSLO) that could efficiently reduce the data requirement has also been investigated in the pure detection, and combined detection and estimation task. In all studies, the practicality and the use of real data is emphasized. The results of all these studies demonstrate the usefulness of the task-based measurements of image quality in X-Ray CT imaging.

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Smith, Jonathan Chase. "Examining soil based construction materials through X-ray computed tomography." Thesis, Durham University, 2015. http://etheses.dur.ac.uk/11113/.

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X-ray computed tomography (XRCT) enables the non-destructive analysis of samples internal structures down to a sub-micron resolution and has been used to examine the macrostructure of unstabilized soil based construction materials (SBCMs) alongside experiments on the materials unconfined compressive strength. SBCMs are manufactured mixtures of clay, sand and gravel which should be considered as highly unsaturated compacted soil where suction is the key source of strength. The use of XRCT in geotechnical literature is comprehensively reviewed before three laboratory investigations are described. Firstly crack propagation in SBCMs following unconfined compression is investigated and key lessons about XRCT scanning highlighted. Secondly the impact of altering sample size to match optimum XRCT scanning conditions is explored through experiments on void size distribution and unconfined compressive strength. Finally the effects of adding expansive clay to SBCM mixes on macrostructure are investigated and insights on how the unconfined compressive strength develops as SBCM dries are given. Conclusions from this thesis have applicability to both the SBCM industry, as the insights into the fundamental behaviour of SBCM can be used to inform building practice, and geotechnical researchers where the extensive use and development of XRCT can be applied to investigate the internal structure of a wide range of geotechnical materials.

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Christiansen, Edwin L. "Temporomandibular joint X-ray computed tomography methodology and clinical applications /." Stockholm : Kongl. Carolinska Medico Chirurgiska Institutet, 1988. http://catalog.hathitrust.org/api/volumes/oclc/18171171.html.

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Chapdelaine, Camille. "Bayesian iterative reconstruction methods for 3D X-ray Computed Tomography." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS092/document.

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Dans un contexte industriel, la tomographie 3D par rayons X vise à imager virtuellement une pièce afin d'en contrôler l'intérieur. Le volume virtuel de la pièce est obtenu par un algorithme de reconstruction, prenant en entrées les projections de rayons X qui ont été envoyés à travers la pièce. Beaucoup d'incertitudes résident dans ces projections à cause de phénomènes non contrôlés tels que la diffusion et le durcissement de faisceau, causes d'artefacts dans les reconstructions conventionnelles par rétroprojection filtrée. Afin de compenser ces incertitudes, les méthodes de reconstruction dites itératives tentent de faire correspondre la reconstruction à un modèle a priori, ce qui, combiné à l'information apportée par les projections, permet d'améliorer la qualité de reconstruction. Dans ce contexte, cette thèse propose de nouvelles méthodes de reconstruction itératives pour le contrôle de pièces produites par le groupe SAFRAN. Compte tenu de nombreuses opérations de projection et de rétroprojection modélisant le processus d'acquisition, les méthodes de reconstruction itératives peuvent être accélérées grâce au calcul parallèle haute performance sur processeur graphique (GPU). Dans cette thèse, les implémentations sur GPU de plusieurs paires de projecteur-rétroprojecteur sont décrites. En particulier, une nouvelle implémentation pour la paire duale dite à empreinte séparable est proposée. Beaucoup de pièces produites par SAFRAN pouvant être vues comme des volumes constants par morceaux, un modèle a priori de Gauss-Markov-Potts est introduit, à partir duquel est déduit un algorithme de reconstruction et de segmentation conjointes. Cet algorithme repose sur une approche bayésienne permettant d'expliquer le rôle de chacun des paramètres. Le caractère polychromatique des rayons X par lequel s'expliquent la diffusion et le durcissement de faisceau est pris en compte par l'introduction d'un modèle direct séparant les incertitudes sur les projections. Allié à un modèle de Gauss-Markov-Potts sur le volume, il est montré expérimentalement que ce nouveau modèle direct apporte un gain en précision et en robustesse. Enfin, l'estimation des incertitudes sur la reconstruction est traitée via l'approche bayésienne variationnelle. Pour obtenir cette estimation en un temps de calcul raisonnable, il est montré qu'il est nécessaire d'utiliser une paire duale de projecteur-rétroprojecteur
In industry, 3D X-ray Computed Tomography aims at virtually imaging a volume in order to inspect its interior. The virtual volume is obtained thanks to a reconstruction algorithm based on projections of X-rays sent through the industrial part to inspect. In order to compensate uncertainties in the projections such as scattering or beam-hardening, which are cause of many artifacts in conventional filtered backprojection methods, iterative reconstruction methods bring further information by enforcing a prior model on the volume to reconstruct, and actually enhance the reconstruction quality. In this context, this thesis proposes new iterative reconstruction methods for the inspection of aeronautical parts made by SAFRAN group. In order to alleviate the computational cost due to repeated projection and backprojection operations which model the acquisition process, iterative reconstruction methods can take benefit from the use of high-parallel computing on Graphical Processor Unit (GPU). In this thesis, the implementation on GPU of several pairs of projector and backprojector is detailed. In particular, a new GPU implementation of the matched Separable Footprint pair is proposed. Since many of SAFRAN's industrial parts are piecewise-constant volumes, a Gauss-Markov-Potts prior model is introduced, from which a joint reconstruction and segmentation algorithm is derived. This algorithm is based on a Bayesian approach which enables to explain the role of each parameter. The actual polychromacy of X-rays, which is responsible for scattering and beam-hardening, is taken into account by proposing an error-splitting forward model. Combined with Gauss-Markov-Potts prior on the volume, this new forward model is experimentally shown to bring more accuracy and robustness. At last, the estimation of the uncertainties on the reconstruction is investigated by variational Bayesian approach. In order to have a reasonable computation time, it is highlighted that the use of a matched pair of projector and backprojector is necessary

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Paziresh, 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.

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X-ray micro computed tomography (Micro-CT) has emerged as a powerful tool in petroleum industry for non-destructive 3D imaging of rock samples, that offers micron-scale spatial resolution images of the distribution of porosity, permeability, and fluid phases of the specimens. Micro-CT obtain the radiographic projections of a sample at different angles and use a mathematical procedure to reconstruct a 3D tomogram of the sample's X-ray attenuation coefficients. Through my thesis, the aim was to investigate and improve two main issue which micro-CT suffers from: 1) beam hardening (BH) artefacts and, 2) the requirement of material characterisation. This thesis contributes in addressing these fundamental issues by providing the "energy selective techniques" as follows. Chapter 1 provides an overview of the basics of tomography including physics of X-rays and energy dependent form of attenuation coefficient. Chapter 2 reviews the BH effects and the existing correction methods, followed by a brief review of the material characterisation methods. Chapter 3 assess the accuracy of five different linearisation BH correction models including polynomial, bimodal, power law, cubic spline and zero-order using the sample that have been imaged at ANU CT facility by measuring the BH curves directly and remapping the inverse of the models to data. Chapter 4 is based on a published conference proceeding paper [1] that applies the power law BH correction method of chapter 3 to correct the artefacts of specimens composed of concentric cylinders, e.g., a rock core within a container. Chapter 5 is based on a published paper in the Journal of Applied Physics [2] that uses dual-energy CT and the Alvarez and Macovski [3] transmitted intensity (AMTI) model to estimate the maps of density (rho) and atomic number (Z) of mineralogical samples. In this method, the attenuation coefficients are represented in the form of the two most important interactions of X-rays with atoms that is, PE and CS. This enables material discrimination as PE and CS are respectively dependent on Z and rho of materials [3]. Chapter 6 implements two simplified form of the full model of chapter 5: 1) Alvarez and Macovski polynomial (AMP) model [3], Alvarez and Macovski presented the full model but used a polynomial simplified form of it to estimate rho and Z of materials, 2) Siddiqui and Khamees (SK) model [4] that simplified the attenuation model, by assuming two monochromatic radiations. Chapter 7 presents a method to estimate the properties of sample materials from measurements of transmitted intensity and its statistical variance (TIV model). The method only requires single energy imaging, i.e., eliminates the need for requirements of dual-energy imaging for AMTI method and its simplified forms. The registered intensity on the detector is proportional to a form of "average" energy of detected quanta of X-ray spectra. The variance images can serve the same purpose as the higher energy information required in dual-energy imaging. Chapter 8 modified the TIV model of chapter 7 to apply it directly for BH correction without necessarily estimation of the properties of sample materials. The chapter also presents a simplified form of TIV model (STIV) that normalises the average intensity image.

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Zanini, Filippo. "X-ray computed tomography for coordinate metrology and industrial applications." Doctoral thesis, Università degli studi di Padova, 2017. http://hdl.handle.net/11577/3425370.

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X-ray computed tomography (CT) has emerged as innovative measuring technique for dimensional metrology in industry over the last years. Thanks to unique capabilities, CT provides several advantages in comparison with other well-established coordinate measuring systems (CMSs). In particular, CT allows obtaining a holistic three-dimensional model of the scanned workpiece and performing non-destructive and non-contact measurements of outer as well as inner features and geometries difficult to access. However, important drawbacks limit a wider acceptance of this technology in industry. One of the most critical problems is the complexity of metrological traceability establishment due to difficulties in evaluating the task-specific uncertainty, as well as specification and determination of metrological performances of CT systems. In fact, a dedicated international standard for CT acceptance test and performance verification is still under development. In this thesis, experimental activities were mainly oriented at evaluating and improving CT metrological performances. The material influence on length measurement errors was studied by investigations based on two reference objects: aluminium hole plate, with significant material effect and ruby ball plate, with negligible material influence. The obtained results contributed to the test survey organized on this topic by the ISO working group that is developing the future ISO standard for CT. The image quality of the 2D projections acquired by CT is fundamental for achieving a good reconstruction quality. It is directly connected to the image blurring content and, consequently, to the focal spot quality. In this thesis, new methods developed to assess the focal spot drift and size are presented. Considering the entire CT measurement procedure, an important metrological characteristic to be evaluated is the metrological structural resolution (MSR). Despite several methods for MSR evaluation have been proposed, a standard test to be included in the ISO standard for CT has still to be defined. In this thesis, the ‘Hourglass’ method –developed by the University of Padova– was selected to evaluate the MSR. The method was improved by measuring a high number of distances and by applying a definition of MSR similar to the one proposed by the guideline VDI/VDE 2617-13. Moreover, the method concept was compared with concepts of other proposed methods. Finally, the main influence quantities affecting the method were identified and evaluated. Since CT is a multi-purpose measuring technique, it has become attractive for many industrial applications. However, the accuracy of CT measurement results is often unknown. For this reason, the evaluation of CT accuracy for specific measurement tasks as well as the comparison with other well-established evaluation methods is crucial for the acceptance of CT in industry. In this thesis, two industrial case studies were addressed: (i) porosity analysis for metal additive manufactured parts and (ii) wear evaluation of polymeric prosthetic components. In the first study, CT was compared with other inspection techniques such as Archimedes method, gas pycnometry and microscopic analysis of cross-sections. A multisensory CMM was used as well in order to get reliable reference area values for pores lying on selected cut sections. In the second study, the proposed CT-based method was validated through comparison with the gravimetric method, which is the current reference method used for wear assessment.
La tomografia computerizzata a raggi-X (CT) si è affermata negli ultimi anni come tecnologia di misura innovativa per la metrologia dimensionale nel settore industriale. L’utilizzo di un sistema CT industriale comporta una serie di importanti vantaggi nei confronti di altri sistemi di misura a coordinate (CMSs). In particolare, il CT consente di ottenere un modello tridimensionale completo dell’oggetto scansionato e di condurre misure non distruttive e non a contatto di geometrie e caratteristiche sia esterne sia interne e di difficile accesso. Tuttavia, alcuni svantaggi rilevanti limitano una più estesa diffusione di questa tecnologia nel settore industriale. Uno dei problemi più critici risiede nella riferibilità metrologica delle misure CT, complicata dalla difficoltà nel determinare l’incertezza di misura e nel valutare le prestazioni metrologiche dei sistemi CT. Inoltre, uno standard internazionale dedicato ai test per l’accettazione e per la verifica delle prestazioni dei sistemi CT è tuttora in via di sviluppo. Le attività sperimentali presentate in questo lavoro di tesi sono state focalizzate principalmente sulla valutazione e sul miglioramento delle prestazioni metrologiche del CT. L’influenza del materiale sugli errori di misura di lunghezza è stata studiata mediante indagini basate su due campioni di riferimento: una hole plate di alluminio, caratterizzata da un’influenza significativa del materiale e una ball plate di rubino, caratterizzata da un’influenza del materiale trascurabile. I risultati ottenuti hanno contribuito alla campagna sperimentale incentrata su questo argomento organizzata dal working group dedicato allo sviluppo del futuro standard ISO per il CT. La qualità d’immagine delle proiezioni radiografiche bidimensionali acquisite mediante CT è fondamentale per ottenere una buona qualità nella ricostruzione del modello tridimensionale dell’oggetto scansionato. Essa è connessa al concetto di blurring o sfocatura dell’immagine e, di conseguenza, alla qualità della macchia focale da cui viene emesso il fascio di raggi X. All’interno di questa tesi vengono descritti nuovi metodi sviluppati per valutare l’effettiva dimensione della macchia focale e l’eventuale drift che essa può subire durante una scansione tomografica. Considerando l’intera procedura di misura CT, una caratteristica metrologica molto importante da considerare è la risoluzione strutturale metrologica (MSR). Nonostante siano stati proposti diversi metodi per la valutazione della MSR, un test univoco da includere nel futuro standard ISO dedicato al CT deve ancora essere definito. In questa tesi, il metodo ‘Hourglass’ – sviluppato dall’Università di Padova - è stato selezionato per valutare la MSR. Questo metodo è stato migliorato mediante la misura di un elevato numero di distanze e applicando una definizione di MSR simile a quella proposta dalla linea guida tedesca VDI/VDE 2617-13. Inoltre, il concetto alla base di tale metodo è stato confrontato con quello di altri metodi e i principali fattori che possono influenzarne i risultati sono stati identificati e valutati. Essendo la tomografia computerizzata a raggi-X una tecnica di misura molto versatile, il suo potenziale può essere sfruttato da un gran numero di applicazioni industriali. Tuttavia, l’accuratezza dei risultati di misura CT è spesso ignota. Per questa ragione, la determinazione dell’accuratezza di misura e il confronto con altri metodi di misura consolidati sono cruciali per una piena accettazione del CT in ambito industriale. In questa tesi sono stati affrontati due casi di rilevanza industriale: (i) analisi di porosità su componenti metallici realizzati mediante produzione additiva e (ii) determinazione dell’usura di componenti protesiche in polietilene. Per quanto riguarda il primo studio, il CT è stato confrontato con altre tecniche d’indagine: metodo di Archimede, picnometro a gas e analisi microscopica di sezioni di taglio. In aggiunta, una macchina di misura a coordinate (CMM) multi-sensore è stata utilizzata per ottenere valori di riferimento per l’area di un certo numero di pori distribuiti su alcune sezioni di taglio selezionate. Nel secondo studio, il metodo CT proposto è stato validato mediante confronto con il metodo gravimetrico, che è l’attuale metodo di riferimento utilizzato per la determinazione del grado di usura.

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Acito, Vito. "In situ X-ray computed tomography for soft contact mechanics." Electronic Thesis or Diss., Ecully, Ecole centrale de Lyon, 2023. http://www.theses.fr/2023ECDL0054.

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L'aire de contact réelle AR entre deux solides en contact est une quantité fondamentale qui contrôle le comportement de frottement d'une interface de contact. Bien que la plupart des techniques expérimentales visant à mesurer cette quantité soient basées sur le contraste optique entre les régions en contact et hors contact, ces méthodes sont limitées par la transparence optique requise par au moins l'un des deux corps en contact. En outre, ces techniques ne permettent d'accéder qu'à l'interface de contact sans fournir d'informations sur d'autres quantités physiques importantes telles que la déformation globale ou les phénomènes hors contact à la surface. À partir de quelques travaux pionniers, nous proposons la tomographie à rayons X (XRCT) in-situ comme méthode alternative pour surmonter ces limites et accéder à la morphologie complète du contact en 3D avec des paires de contacts potentiellement non transparentes. Dans toutes les études précédentes, les analyses ont été effectuées sur des surfaces complexes sans se concentrer sur des examens préliminaires des limites de la XRCT (comme l'estimation des erreurs dans la mesure de AR). Dans ce cadre, nous avons proposé l'utilisation d'un système modèle composé d'une sphère lisse en élastomère (PDMS) et d'une plaque rigide lisse (en PMMA) pour simplifier le problème et souligner les avantages et les inconvénients de cette méthode expérimentale. Nous nous sommes d'abord concentré sur la mesure in-situ de l'évolution de AR au cours d'un essai de compression et de cisaillement réalisé sur notre système modèle. Les résultats ont été comparés à ceux d'un dispositif opto-mécanique 2D déjà maîtrisé. Enfin, à partir de la reconstruction en 3D in-operando du contact modéle indenté cisaillé, nous avons pu extraire les champ de déplacement, déformation et contraintes dans le contact par corrélation numérique des volumes (DVC) en utilisant comme marqueurs des particules préalablement dispersés dans le PDMS. Tous ces résultats ont été mis en regard des prédictions théoriques de modèles de la littérature
The real contact area AR between two solids in contact is a fundamental quantity that controls the frictional behavior of a contact interface. Although most experimental techniques aimed at measuring this quantity are based on the optical contrast between in-contact and out-of-contact regions, these methods are limited by the optical transparency required for least one of the two contacting bodies. Furthermore, these techniques only provide access to the contact interface without providing information on other important physical quantities such as the global deformation or the out-of-contact phenomena at the surface. Building on some pioneering work, we propose in-situ X-ray tomography (XRCT) as an alternative method to overcome these limitations and access the full 3D contact morphology with potentially non-transparent contact pairs. In all previous studies, analyzes were performed on complex surfaces without focusing on preliminary examinations of the limitations of XRCT (such as estimating errors in measuring AR). In this context, we proposed the use of a model system composed of a smooth elastomer sphere (PDMS) and a smooth rigid plate (PMMA) to simplify the problem and highlight the advantages and disadvantages of this experimental method. We first focused on measuring in-situ the evolution of AR during a compression and shear test carried out on our model system. The results were compared to those of a 2D opto-mechanical device already mastered. Finally, from the in-operando 3D reconstruction of the indented and sheared contact , we were able to extract the displacement, deformation and stress fields in the contact by digital correlation of volumes (DVC) using as markers particles previously dispersed in PDMS. All these results were compared to theoretical predictions from models in the literature

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20

Onifade, Ibrahim. "Internal structure characterization of asphalt concrete using x-ray computed tomography." Thesis, KTH, Väg- och banteknik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-127689.

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This study is carried out to develop the workflow from image acquisition to numerical simulation for asphalt concrete (AC) microstructure. High resolution computed tomography (CT) images are acquired and the image quality is improved using digital image processing (DIP). Non-uniform illumination which results in inaccurate phase segmentation is corrected by applying an illumination profile to correct the background and flat-fields in the image. Distance map based watershed segmentation is used to accurately segment the phases and separate the aggregates. Quantitative analysis of the microstructure is used to determine the phase volumetric relationship and aggregates characteristics. The results of the phase reconstruction and internal structure quantification using this procedure shows a very high level of reliability. Numerical simulations are carried out in Two dimensions (2D) and Three dimensions (3D) on the processed AC microstructure. Finite element analysis (FEM) is used to capture the strength and deformation mechanisms of the AC microstructure. The micromechanical behaviour of the AC is investigated when it is considered as a continuum and when considered as a multi-phase model. The results show that the size and arrangement of aggregates determines the stress distribution pattern in the mix.

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21

Lorenzi, Massimo. "X-ray computed microtomography applications for complex geometries and multiphase flow." Thesis, City, University of London, 2017. http://openaccess.city.ac.uk/19794/.

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In all fields, fundamental and applied research seek to produce experimental measurements without causing interferences to the process being observed. This capability is of paramount importance, since small perturbations of the phenomenon can alter it to the point of producing biased or even incorrect results. Xray techniques, based on synchrotron or laboratory X-ray sources, have attracted the attention of the research and industrial R&D community thanks to their characteristic of having little to no detectable influence on the subject under study. Moreover, if declined as tomography, this technique can provide localized full volume information at the micrometre scale, from which arbitrary shaped geometries and material densities can be deduced. During this thesis an X-ray microtomography instrument, based on a laboratory X-ray source, has been exploited to gain three main objectives. The first one is the analysis of how a liquid drop, of water or glycol, adapts its shape to reach an equilibrium state when gently deposed on a flat or patterned surface. So far this has been done using 2D techniques but introducing the knowledge of the third dimension and being able to see the drop shape even in not optically accessible locations, opens new possibilities to better understand the physics that regulate it. The second one is the reconstruction of the internal geometries of automotive diesel injectors with high resolution to detect and highlight differences between nominal and real geometries, key information to produce more realistic CFD simulations of the flow inside production grade injectors geometries. A scaled -up model made of PEEK was also studied, producing successive tomographies, to detect small geometrical changes induced by part usage, giving an in-depth view of the locations more prone to be damaged by cavitation flow. The third one is the study of a multiphase flow inside the same scaled-up model injection channel with flowing conditions exhibiting cavitation. The geometry of the non-axisymmetric model mimics the flow pattern of a real diesel injection channel and automotive grade diesel was consequently selected as fluid. Understanding the dependence of cavitation development on flow characteristics in a three-dimensional way, through the determination of the localized void fraction of the multiphase flow, can lead to improvements in the knowledge of such a phenomenon that can guide the design of future fuel injection equipment.

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Sjölin, Martin. "Methods of image acquisition and calibration for x-ray computed tomography." Doctoral thesis, KTH, Medicinsk bildfysik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-195024.

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X-ray computed tomography (CT) is a common medical imaging device for acquiring high-resolution 3D images of the interior of the human body. The images are formed by mathematical reconstruction from hundreds of planar x-ray images that have been acquired during less then a second. Photon-counting spectral detectors are seen by many as the next big step in the development of medical CT. The potential benefits include: quantitative CT, ultra-low dose imaging and optimal contrast-to-noise performance. The current aim for the research pursued by the Physics of Medical Imaging Group at KTH is to develop, and commercialize, a photon-counting spectral detector using silicon wafers in edge-on geometry. With the introduction of a new detector comes many challenges, some of which this Thesis aims to address. Efficient calibration schemes will be an essential part of the realization of photon-counting spectral detectors in clinical CT. In the first part of the Thesis, three calibration methods are presented: two methods for calibration of the energy thresholds on multi-bin spectral detectors and one method for geometric calibration of edge-on detectors that are mounted in a CT gantry. The CT image acquisition produces large amounts of data that have to be transported out of the system, preferably in real-time. Already today, fewer samples are acquired when operating at very high rotation speeds due to bandwidth limitations. For photon-counting spectral detectors, the amount of data will be even larger due to the additional energy information and the generally smaller pixels, and it is therefore desirable to minimize the number of angular samples acquired per revolution. In the second part of the Thesis, two methods for relaxing the angular sampling requirement are presented. The first method uses the built-in redundancy of multi-layer detectors to increase the angular sampling rate via a temporal offset between the detector layers. The second method uses decimation in the view (angular) direction as a means for compression of CT sinogram data. The compression can be performed on the CT gantry and thus lower the required bandwidth of the data transfer. Although the overall aim of this work has been to develop methods that facilitate the introduction of photon-counting spectral detectors for medical CT, the presented methods are also applicable in the broader context of calibration of x-ray detectors and CT image acquisition.
Datortomografi (CT) är en vanligt förekommande medicinsk avbildningsteknik som används för att ta högupplösta 3D bilder av människans inre. Bilderna rekonstrueras matematiskt från hundratals 2D röntgenbilder som har tagits under mindre än en sekund. Introduktionen av spektrala fotonräknande röntgendetektorer anses vara nästa stora steg i utvecklingen av medicinsk CT. De potentiella fördelarna innefattar: kvantitativ CT, avbildning vid ultra-låg dos och optimalt kontrast-brus förhållande. Målet för det arbete som utförs av gruppen för Medicinsk Bildfysik på KTH är att utveckla och kommersialisera en spektral fotonräknande detektor baserad på kiselskivor som är monterade ”edge-on” (med kanten pekandes mot röntgenkällan). Den här avhandlingen adresserar några utav de utmaningar som följer införandet av denna nya typ av detektor. Tillgången till effektiva kalibreringstekniker kommer att vara nödvändig för realisationen av spektrala fotonräknande detektorer i medicinsk CT. I den första delen av avhandlingen presenteras tre kalibreringsmetoder, varav två relaterar till kalibrering av energitrösklarna på spektrala röntgendetektorer och en relaterar till geometrisk kalibrering av ”edge-on” detektorer monterade i en CT scanner. Bildtagningen i CT producerar stora mängder data som måste transporteras ut ur systemet, gärna i realtid. Redan idag tvingas man ofta ha färre mätpunkter när man använder höga rotationshastigheter på grund av begränsningar i utläsningens bandbredd eller mätelektronikens hastighet. För spektrala fotonräknande detektorer kommer mängden data att öka på grund av den extra energiinformationen och de generellt mindre pixlarna. Därför är det önskvärt att minimera antalet mätpunkter i vinkelled per varv. I den andra delen av avhandlingen presenteras två metoder som minskar kravet på antalet mätpunkter per varv. Den första metoden använder den inbyggda redundansen hos detektorer med flera lager för att ökan antalet mätpunkter i vinkelled genom att förskjuta mätpunkterna för dom olika lagerna i tiden. Den andra metoden använder decimering i vinkelled för att komprimera CT data. Kompressionen kan utföras på CT scannern och kan användas för att minska kravet på datautläsningens bandbredd. Det övergripande målet för arbetet som utgör avhandling har varit att utveckla metoder som möjliggör introduktionen av spektrala fotonräknande detektorer för medicinsk CT. De presenterade metoderna är emellertid även användbara i den mer generella kontexten av kalibrering av röntgendetektorer och bildtagning i CT.

QC 20161104

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23

Ortner, Margarete. "Morpho-functional markers in X-ray computed tomography for respiratory diseases." Paris 5, 2011. http://www.theses.fr/2011PA05S007.

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Ce travail vise à développer un système de diagnostic assisté par ordinateur ciblant les maladies pulmonaires responsables de changements biologiques et morphologiques dans les voies respiratoires. L'intérêt clinique est la compréhension des mécanismes et relations entre la physiologie et le phénotype / génotype du patient. Ce système DAO adopte le concept "image comme marqueur" et explore les données MDCT obtenues en routine clinique. Ainsi, des approches d’investigation basées sur l'image sont abordées pour identifier les marqueurs pathologiques en jeu. L’enjeu majeur est la segmentation volumétrique de la paroi bronchique. La méthode originale développée dans ce travail utilise un modèle de surface active spécifique au patient et évoluant selon une dynamique lagrangienne contrainte par un champ de diffusion. Les autres contributions concernent l’évaluation semi-quantitative de la variation de la forme des bronches et la détection automatique des anomalies. Pour cela, une notion de calibre local a été exploitée. L'épaisseur pariétale ainsi que les simulations d’écoulement quantifient l’effet du remodelage bronchique. Le système est complété par des outils de visualisation intuitive, navigation et interaction. Les solutions développées ont été validées aussi bien sur des données réelles provenant d’études cliniques qui incorporent 150 patients, que sur des données simulées. Ces dernières ont été obtenues en générant des fantômes numériques avec des géométries spécifiques au patient et en simulant l'acquisition TDM. Les résultats montrent une précision de l'ordre de la résolution axiale de l'image et une robustesse vis-à-vis de la variabilité inter-patient et inter-protocole
The motivation of this work is the development of a computer-aided diagnosis system targeting pulmonary diseases which induce biological and morphological changes to the airway system. The clinical interest lies in understanding the mechanisms and relationships between airway physiology and the clinical phenotype and genotype. Such a CAD system adopts the concept of “Image as Marker” and exploits routinely available MDCT image data. Thus image-based investigation approaches are tackled in order to identify relevant pathological markers. The key issue of our work is the volumetric segmentation of the airway wall. The developed original approach relies on a patient-specific, deformable mesh model evolving according to Lagrangian dynamics, under the constraints of an external diffusion vector field. Other contributions concern semi-quantitative assessment of the airway shape variation and the automatic detection of shape abnormalities exploiting the notion of local maximal airway lumen caliber. The local wall thickness information as well as computational fluid dynamics simulations capture the airway remodeling. Intuitive visualization, navigation and interaction capabilities associated with the extracted quantitative data complete the developed system. All the solutions were quantitatively and qualitatively validated, either on real MDCT images during clinical studies including 150 patients or on simulated data. Latter were achieved by computer phantoms involving patient-specific geometries and CT acquisition simulation. The results reported a precision in the range of the CT image resolution and the robustness towards acquisition and inter-patient variability

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Gulam, Misbah. "Phalangeal bone mineral density measurements using x-ray absorptiometry and computed tomography." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0017/MQ58041.pdf.

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Lee, Sang Soo. "Soil surface-seal measurement using high-resolution x-ray computed tomography (HRCT)." Diss., Columbia, Mo. : University of Missouri-Columbia, 2006. http://hdl.handle.net/10355/4507.

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Thesis (M.S.) University of Missouri-Columbia, 2006.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on August 24, 2007) Vita. Includes bibliographical references.

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Kourra, Nadia. "The application of X-ray computed tomography in aerospace industry : innovation report." Thesis, University of Warwick, 2016. http://wrap.warwick.ac.uk/93226/.

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In the 2015 report of ‘The aerospace industry: statistics and policy’, UK Government presents the aerospace industry as “phenomenal success story” with “tremendous opportunities for growth” (Rhodes, et al., 2015). The success of this sector depends on high efficiency and productivity levels while maintaining quality and satisfying market demands which request aircraft to stay safely in service for longer with reduced maintenance budgets. One of the strategic objectives of the aerospace companies is continuous improvement of the technologies and engineering capabilities. X-ray Computed Tomography (CT) is a growing Non-Destructive Evaluation (NDE) method with various applications in several sectors of industry. CT collects numerous radiographs that are then reconstructed to create a 3D model of the examined object. The results demonstrate the outer and inner structure of the part including any defects, altered densities and hidden constructions in the case of Additive Layer Manufacturing (ALM) parts. Product development in the aerospace industry is a challenging task with significant risks that are handled by complex processes for quality control. The product development steps in this industry follow the products from concept to manufacturing and from service to disposal. This project examines the capabilities and limitations of CT in order to identify potential applications in this sector by considering all of the stages of development. Several case studies demonstrate its application in the research and development phase of composite design and machining selection as well as in the production phase with metrological and non-destructive evaluation applications. Finally, the application of CT in failure investigations and forensic examinations, close to the end of the life and disposal of the product was also considered. The results of these investigations demonstrate the possibilities of this technology as well as its limitations and led the sponsoring company to purchase a digital radiography system with CT capabilities. The presented investigations answer the research question of ‘How can CT be applicable in aerospace industry?’ by identifying the product development phases where CT is applicable. The developed innovative methods provide CT inspections and measurements while reducing human error. They identify the capabilities and limitations of this technology and develop improved scanning methods and standard operating procedures. This report summarises the results of these investigations that clearly demonstrate the potential applications of this technology as well as their limitations while it also introduces and demonstrates innovative methods to overcome these limitations. The innovation of this project is in the novel methods that allow this technology to be used in this industrial sector and provide the required results that are unobtainable with other NDT methods.

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Banjak, Hussein. "X-ray computed tomography reconstruction on non-standard trajectories for robotized inspection." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI113/document.

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La tomographie par rayons X ou CT pour "Computed Tomography" est un outil puissant pour caractériser et localiser les défauts internes et pour vérifier la conformité géométrique d’un objet. Contrairement au cas des applications médicales, l’objet inspecté en Contrôle Non Destructif (CND) peut être très grand et composé de matériaux de haute atténuation, auquel cas l’utilisation d’une trajectoire circulaire pour l’inspection est impossible à cause de contraintes dans l’espace. Pour cette raison, l’utilisation de bras robotisés est l’une des nouvelles tendances reconnues dans la CT, car elle autorise plus de flexibilité dans la trajectoire d’acquisition et permet donc la reconstruction 3D de régions difficilement accessibles dont la reconstruction ne pourrait pas être assurée par des systèmes de tomographie industriels classiques. Une cellule de tomographie X robotisée a été installée au CEA. La plateforme se compose de deux bras robotiques pour positionner et déplacer la source et le détecteur en vis-à-vis. Parmi les nouveaux défis posés par la tomographie robotisée, nous nous concentrons ici plus particulièrement sur la limitation de l’ouverture angulaire imposée par la configuration en raison des contraintes importantes sur le mouvement mécanique de la plateforme. Le deuxième défi majeur est la troncation des projections qui se produit lorsque l’objet est trop grand par rapport au détecteur. L’objectif principal de ce travail consiste à adapter et à optimiser des méthodes de reconstruction CT pour des trajectoires non standard. Nous étudions à la fois des algorithmes de reconstruction analytiques et itératifs. Avant d’effectuer des inspections robotiques réelles, nous comptons sur des simulations numériques pour évaluer les performances des algorithmes de reconstruction sur des configurations d’acquisition de données. Pour ce faire, nous utilisons CIVA, qui est un outil de simulation pour le CND développé au CEA et qui est capable de simuler des données de projections réalistes correspondant à des configurations d’acquisition définies par l’utilisateur
X-ray computed tomography (CT) is a powerful tool to characterize or localize inner flaws and to verify the geometric conformity of an object. In contrast to medical applications, the scanned object in non-destructive testing (NDT) might be very large and composed of high-attenuation materials and consequently the use of a standard circular trajectory for data acquisition would be impossible due to constraints in space. For this reason, the use of robotic arms is one of the acknowledged new trends in NDT since it allows more flexibility in acquisition trajectories and therefore could be used for 3D reconstruction of hardly accessible regions that might be a major limitation of classical CT systems. A robotic X-ray inspection platform has been installed at CEA LIST. The considered system integrates two robots that move the X-ray generator and detector. Among the new challenges brought by robotic CT, we focus in this thesis more particularly on the limited access viewpoint imposed by the setup where important constraints control the mechanical motion of the platform. The second major challenge is the truncation of projections that occur when only a field-of-view (FOV) of the object is viewed by the detector. Before performing real robotic inspections, we highly rely on CT simulations to evaluate the capability of the reconstruction algorithm corresponding to a defined scanning trajectory and data acquisition configuration. For this purpose, we use CIVA which is an advanced NDT simulation platform developed at CEA and that can provide a realistic model for radiographic acquisitions and is capable of simulating the projection data corresponding to a specific CT scene defined by the user. Thus, the main objective of this thesis is to develop analytical and iterative reconstruction algorithms adapted to nonstandard trajectories and to integrate these algorithms in CIVA software as plugins of reconstruction

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Favretto, Stefano. "Applications of x-ray computed microtomography to material science: devices and prespectives." Doctoral thesis, Università degli studi di Trieste, 2008. http://hdl.handle.net/10077/2756.

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2006/2007
The three-dimensional visualization of the inner microstructural features of objects and materials is an aspect of relevant interest for a wide range of scientific and industrial applications. X-ray computed microtomography (μ-CT) is a powerful non-destructive technique capable to satisfy these needs. Once the complete reconstruction of the sample is available, a quantitative characterisation of the microstructure is essential. Through digital image processing tools, image analysis software or custom developed algorithms, it is possible to obtain an exhaustive geometrical, morphological and topological description of the features inside the volume, or to extract other particular parameters of interest (e.g. porosity, voids distribution, cell size distribution, average struts length, connectivity between the cells, tortuosity). This thesis was carried out at the third-generation Elettra Synchrotron Radiation Facility (Trieste, Italy), where a hard X-ray imaging beamline is available. The experience developed at this beamline has leaded scientists to design a complementary state-of-the-art μ-CT facility based on a micro-focus X-ray source, working both in absorption and phase contrast mode. In this dissertation a detailed description of this facility is given together with a rigorous characterization of the imaging system capabilities, in terms of the actual achievable spatial resolution, in order to optimize the working parameters for the different experiments. The main artefacts that concur to the degradation of the quality of the reconstructed images have been considered (e.g. beam hardening effects, ring artefacts, uncertainness associated with the cone-beam geometry): procedures are presented in order to eliminate, or at least to reduce, the causes of these artefacts. The aspects related to the digital image processing of the reconstructed data are intensively developed in this study: appropriated methodologies have been elaborated capable to deal with the different three-dimensional data of complex porous media, providing a correlation between the microstructure and the macroscopic behaviour of the observed materials. Three representative examples obtained with the described methods are used to demonstrate the application of μ-CT, combined with the developed image processing tools, to material science: the geometrical and morphological characterisation of polyurethane foams employed in the automotive industry due their vibro-acoustic properties; a new approach to characterize the resonance spruce wood microstructure in order to study its acoustical behaviour; finally, the possibility of revealing defects in hybrid-friction stir welded aluminium joints, guiding the optimization of the process parameters.
La visualizzazione tridimensionale della struttura interna di oggetti e materiali costituisce un aspetto di notevole interesse per una ampia gamma di applicazioni scientifiche ed industriali. La microtomografia computerizzata a raggi X (μ-CT) rappresenta una potente tecnica di indagine adeguata a soddisfare tali richieste. Una volta completata la ricostruzione del campione in esame, è essenziale poter fornire una caratterizzazione quantitativa della microstruttura evidenziata. Attraverso gli strumenti messi a disposizione dalle moderne tecniche di analisi di immagine, per mezzo di software dedicati o algoritmi personalizzati, è possibile ottenere una descrizione esaustiva della geometria, morfologia e topologia degli elementi microstrutturali presenti, che consenta l’estrazione dei parametri di interesse per la particolare applicazione (porosità, distribuzione dei vuoti, dimensione degli elementi, lunghezze caratteristiche, grado di interconnessione, tortuosità etc.). Il presente lavoro di tesi è stato svolto presso il laboratorio di luce sincrotrone di terza generazione Elettra (Trieste, Italia), dove è disponibile una linea sperimentale dedicata all’imaging con raggi X duri. L’esperienza acquisita da parte dei ricercatori di questa linea ha consentito poi la progettazione di una stazione per μ-CT complementare, allo stato dell’arte e basata su una sorgente di radiazione a microfuoco, capace di operare con modalità di raccolta delle immagini sia in assorbimento sia in contrasto di fase. In questa tesi viene fornita una dettagliata descrizione della stazione, accompagnata da una rigorosa caratterizzazione del sistema impiegato per l’acquisizione e la ricostruzione delle immagini, in termini di risoluzione spaziale raggiungibile, così da consentire l’ottimizzazione dei parametri critici di lavoro nelle differenti condizioni sperimentali. Vengono poi presi in considerazione i principali artefatti che contribuiscono al deterioramento della qualità delle immagini ottenute (come il beam hardening, gli artefatti ad anello, gli artefatti legati all’incertezza geometrica associata al fascio conico etc.): vengono quindi proposti dei metodi per l’eliminazione, o almeno la riduzione, delle cause che li determinano. Nella tesi inoltre sono sviluppati in maniera approfondita gli aspetti connessi al trattamento dei dati digitali raccolti: sono state infatti elaborate delle metodologie appropriate, capaci di trattare i diversi tipi di dato provenienti dall’analisi di mezzi porosi, determinanti per la comprensione della correlazione tra la microstruttura del materiale ed il suo comportamento macroscopico. Infine, vengono proposti tre esempi rappresentativi per dimostrare l’efficacia dell’applicazione della μ-CT, in combinazione con gli strumenti di analisi di immagine messi a punto, alla scienza dei materiali: la caratterizzazione geometrica e morfologica di schiume di poliuretano impiegate nell’industria automobilistica come isolante vibro-acustico; un nuovo approccio rivolto alla caratterizzazione della struttura del legno di risonanza al fine di studiarne il comportamento acustico; la possibilità di mettere in luce i difetti in giunti di saldatura di leghe d’alluminio realizzati con la tecnica ibrida friction stir welding/TIG in maniera da ottimizzare i parametri di processo.
XX Ciclo
1978

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29

Hermanek, Petr. "Reference standards and methods for traceable X-ray computed tomography dimensional metrology." Doctoral thesis, Università degli studi di Padova, 2017. http://hdl.handle.net/11577/3426671.

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X-ray computed tomography (CT) is an imaging technique, which originally found its application in the medical field and over years of research extended its use to industry, mainly to nondestructive testing. In the last years, CT has been also used as a tool for dimensional metrology, and is considered the third generation of measuring techniques in coordinate metrology, after tactile and optical coordinate measuring systems. The main advantage of CT over other measuring instruments is the fact that both internal and external geometries of the measured workpiece can be visualized as a 3D model, and analyzed without destruction. CT measurement chain is affected by numerous and often complex influence factors. Furthermore, due to the fact that it is still relatively new technique for coordinate metrology, and because of the lack of research and standardized procedures, CT has not yet reached maturity as a dimensional measurement technology. Sources of CT measurement uncertainty are still not completely understood in some cases and, as a result, achieving CT measurement traceability is difficult. Traceability of measurements is an important property ensuring that the measurement results are traceable to the SI unit through unbroken chains of calibrations. Reference standards are a typical means to test metrological systems and investigate various factors that influence the measurement results. In this thesis, several standards dedicated to different mainstays towards the establishment of measurement traceability – namely metrological performance verification according to international standards, metrological performance verification of CT specific applications, calibration, and evaluation of measurement uncertainty – were developed. Furthermore, as an output of experience and findings gained during the project, a good practice guide for developing reference standards for CT dimensional metrology was compiled. The first standard proposed in this Ph.D. work was developed for the evaluation of accuracy of CT porosity measurements and for establishing their metrological traceability. The design of the standard contains hemispherical features resembling artificial internal porosity and its dismountable configuration ensures calibration by different measuring instruments. It was proved that not only the accuracy of CT porosity measurements can be evaluated using this standard, but the accuracy can also be improved by using the artifact. Moreover, a procedure for establishing the traceability of CT porosity measurements obtained from industrial parts was proposed. Calibration of CT instrument geometry was achieved by using a standard developed during this project, namely the CT calibration tube (CT2), in combination with the so-called “minimization procedure” used for estimating CT geometrical parameters, and a Monte Carlo method for evaluating the measurement uncertainty. Furthermore, based on results from experimental implementations of the developed standard and method, it was proven that it is possible to align the CT system to its nearly ideal geometry. Moreover, a comprehensive CT instrument geometry alignment method was proposed, which is based on the use of the CT2 standard, the minimization procedure, and a novel advanced reconstruction algorithm (the so called FlexCT, developed by KU Leuven). Multi-material aspects of CT dimensional measurements were also addressed in this Ph.D. thesis. A series of reference standards were developed for evaluating the multi-material effects on gap measurements. Different behavior between results obtained on mono- and multi-material samples confirmed the existence of the multi-material influence. Furthermore, an alternative dual-energy CT scanning approach was applied to enhance the measurement results.
La tomografia computerizzata a raggi X (computed tomography, CT) è una tecnica diagnostica per immagini, che originalmente trovava la sua applicazione in campo medico e con anni di ricerca ha ampliato il suo uso per l’industria, principalmente per controlli non distruttivi. Negli ultimi anni, la CT è stata utilizzata anche come uno strumento per metrologia dimensionale, ed può essere considerata la terza generazione delle tecniche di misura a coordinate, dopo i sistemi di misura a contatto e quelli ottici. Il vantaggio principale della CT rispetto ad altre tecnologie di misura è che sia le geometrie interne sia quelle esterne del pezzo misurato possono essere visualizzate in un modello tridimensionale e analizzate in modo non distruttivo. La catena di misura della CT è influenzata da numerosi e spesso complessi fattori. Inoltre, poiché la CT è ancora una tecnica relativamente nuova per la metrologia a coordinate che necessita di ulteriori investimenti in attività di ricerca e nello sviluppo di procedure standardizzate, non ha ancora raggiunto la piena maturità richiesta per gli strumenti di misura dimensionali. Le fonti di incertezza di misura non sono ancora completamente analizzate in alcuni casi e, di conseguenza, è difficile ottenere la riferibilità delle misure CT. La riferibilità delle misure è una proprietà importante che garantisce che i risultati delle misure siano riferibili alle unità SI attraverso catene ininterrotte di tarature. I campioni di riferimento sono mezzi tipici per testare i sistemi metrologici ed investigare i vari fattori che influenzano i risultati delle misure. In questa tesi, sono stati sviluppati diversi campioni, dedicati ai diversi requisiti della riferibilità delle misure, e in particolare: la verifica delle prestazioni metrologiche secondo la normativa internazionale, la verifica delle prestazioni metrologiche in specifiche applicazioni CT, la taratura e la valutazione dell’incertezza delle misure. Inoltre, come risultato finale delle esperienze e delle conoscenze ottenute durante il progetto, è stata compilata una guida di buone pratiche per lo sviluppo dei campioni di riferimento per la metrologia dimensionale con CT. Il primo campione proposto in questa tesi di dottorato è stato sviluppato per valutare l’accuratezza della CT utilizzata per misure di porosità e per stabilirne la riferibilità metrologica. La progettazione del campione è basata su geometrie emisferiche che riproducono una porosità interna artificiale. La configurazione disassemblabile del campione garantisce la possibilità di taratura mediante diversi strumenti di misura. É stato provato che, usando questo campione, l’accuratezza delle misure CT della porosità non solo può essere valutata, ma può anche essere migliorata. Inoltre, è stata proposta una procedura per stabilire la riferibilità delle misure CT di porosità ottenute da parti industriali. La taratura della geometria dello strumento CT e stata studiata sviluppando un campione – denominato CT calibration tube (CT2) – utilizzato assieme alla cosiddetta “minimization procedure”, utile per stimare i parametri geometrici dello strumento CT, e ad un metodo Monte Carlo per valutare l’incertezza di misura. Inoltre, sulla base dei risultati sperimentali ottenuti usando il metodo e il campione sviluppato, è stato dimostrato come sia possibile l’allineamento del sistema CT alla sua geometria quasi ideale. In aggiunta, è stato proposto un metodo completo per l’allineamento del sistema CT. Tale metodo è basato sull’uso dello standard CT2, della minimization procedure e di un nuovo algoritmo avanzato di ricostruzione (denominato FlexCT e sviluppato da KU Leuven). Una parte ulteriore di questo lavoro è stata dedicata allo studio degli aspetti multi-materiale delle misure dimensionali CT. Una serie di campioni di riferimento è stata sviluppata per valutare gli effetti della presenza di materiali multipli sulle misure di “gap”. Il comportamento diverso tra i risultati ottenuti su campioni mono- e multi-materiale ha confermato l’esistenza dell’influenza multi-materiale. Inoltre, un approccio alternativo delle scansioni CT basato sull’uso di diversi livelli di energia dei raggi X, il cosiddetto “dual-energy CT”, è estato applicato per migliorare i risultati delle misure.

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Dawson, Sarah P. "Digital X-ray analysis for monitoring fracture healing." Thesis, University of Edinburgh, 2009. http://hdl.handle.net/1842/4285.

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X-ray based evaluation of different stages of fracture healing is a well established clinical standard. However, several studies have shown plain radiography alone to be an unreliable method to assess healing. The advent of digital X-ray systems provides the potential to perform quantitative analysis on X-ray images without disrupting normal clinical practice. Two aspects were explored in this study. The first was the measurement of mechanical fracture stiffness under four point bending and axial loading. The second was the inclusion of an Aluminium step wedge to provide Aluminium-equivalent thickness calibration information. Mechanical sti ness studies involved the development of equipment to perform four point bending on intra-medullary (IM) nailed tibial fractures, equipment to perform axial loading on conservatively treated humeral fractures, and fracture models to ex- amine the developed systems. Computational procedures to automatically measure the angle and offset occurring at the fracture site by comparing loaded and unloaded X-ray images were developed utilising cross-correlation. The apparatus and procedures were tested using the fracture models both in X-ray and using the Zwick materials testing machine. The four point bending system was applied clinically to a series of IM nailed tibial fracture patients and the axial loading system to two conservatively treated humeral fracture patients. Mechanical stiffness results showed that the apparatus worked well in the clinical radiography environment and was unobtrusive to normal practice. The developed X-ray analysis procedure provided reliable measurements. However, in the case of IM nailed tibial fractures, both angular and displacement movements were too small to be accurately assessed or to provide reliable stiffness measurements. This indicated that this patient group was possibly unsuitable for mechanical stiffness measurements or that higher loads needed to be applied to the fracture site. The case studies of conservatively treated humeral fractures showed potential in detecting movement between loaded and unloaded X-rays and using this to provide sti ness information. Further investigation is required to show that this technique has the potential to aid fracture healing monitoring. Investigation into Aluminium step wedge calibration began with the design of different step wedges and X-ray phantoms. Initial image analysis involved studying the automatic processing applied by a digital Computed Radiography (CR) Fuji sys- tem and modelling of the inhomogeneities in X-ray images as well as investigation into the effect of and correction for scatter, overlying soft tissue and bone thickness. Computational procedures were developed to semi-automatically detect the steps of the step wedge, form an exponential Aluminium step thickness to grey level calibration graph, measure soft tissue and bone thickness, and correct for the heel effect and scatter contributions. Tests were carried out on pre-clinical models and results compared to ash weight and peripheral quantitative computed tomography (pQCT). A clinical study of radial fractures was used to investigate the effectiveness of the step wedge calibration system in monitoring fracture healing changes. Results using the step wedge indicated that the calibration technique was e ective in detecting and correcting for aspects in uencing Aluminium-equivalent thickness measures. With careful processing, useful information was obtained from digital X- rays that included the Aluminium step wedge and these correlated well with existing density measures. The use of the wedge in patient images showed that small increases in Aluminium-equivalent thickness of the fracture site could be detected. This was most useful for intra-patient comparisons throughout the course of healing rather than providing quantitative measurements which were comparable to other density measures. In conclusion, this thesis shows the potential for accurate analysis of digital X- rays to aid the monitoring of healing changes in fracture patients, particularly with application of axial loading and the use of step wedge calibration.

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Masoudi, Ahmad, Ratchaneekorn Thamvichai, and Mark A. Neifeld. "Computed tomography imaging system design for shape threat detection." SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2016. http://hdl.handle.net/10150/624371.

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In the first part of this work, we present two methods for improving the shape-threat detection performance of x-ray computed tomography. Our work uses a fixed-gantry system employing 25 x-ray sources. We first utilize Kullback-Leibler divergence and Mahalanobis distance to determine the optimal single-source single-exposure measurement. The second method employs gradient search on Bhattacharyya bound on error rate (P-e) to determine an optimal multiplexed measurement that simultaneously utilizes all available sources in a single exposure. With limited total resources of 10(6) photons, the multiplexed measurement provides a 41.8x reduction in P-e relative to the single-source measurement. In the second part, we consider multiple exposures and develop an adaptive measurement strategy for x-ray threat detection. Using the adaptive strategy, we design the next measurement based on information retrieved from previous measurements. We determine both optimal "next measurement" and stopping criterion to insure a target P-e using sequential hypothesis testing framework. With adaptive single-source measurements, we can reduce P-e by a factor of 40x relative to the measurements employing all sources in sequence. We also observe that there is a trade-off between measurement SNR and number of detectors when we study the performance of systems with reduced detector numbers. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)

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32

Pei, Ruizhi. "Self-healing behaviour of MAX phase ceramics studied by computed X-ray tomography." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/selfhealing-behaviour-of-max-phase-ceramics-studied-by-computed-xray-tomography(6950ce07-616b-4c0a-8ded-77d811735791).html.

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MAX phase ceramics are promising candidates as high temperature materials. The self-healing capabilities of these materials may further improve their reliability and reduce maintenance costs during service. However, previous two dimensional research on their healing behaviour is either inadequate or sometimes even biased, because crack healing is essentially a three dimensional process. In this study, the self-healing behaviour of two MAX phase ceramics: Ti2AlC and Cr2AlC were investigated in three dimensions using high resolution synchrotron and laboratory X-ray tomography. The Ti2AlC showed remarkable healing ability of repeatedly repairing cracks at 1150 °C for three healing cycles with each healing cycle lasting less than 66 minutes. The healing kinetics of Ti2AlC was revealed to have a strong dependence on crack location, which deviates from a previously proposed uniform healing model. The Ti2AlC maintains its healing kinetics when the post-healing crack propagation follows a different growth path to the original crack. While a decreased healing kinetics was observed if the crack grows through a previous healed zone. The strength recovery is closely related to the healing percentage, where a full strength recovery was achieved with a healing percentage of over 90 %. In comparison, the Cr2AlC showed a much slower healing kinetics, with a parabolic constant of 4.3×10-3 µm2•s-1. The healing process of Cr2AlC was revealed to be more or less independent of crack location, where crack tip is always healed first. The crack gap is filled by purely Al2O3 after healing without the formation of Cr2O3. The composition of the healed area varies along the crack. A Cr7C3 sublayer beneath the Al2O3 layer was found at the healed zone of crack root, while missing in the healed zone at crack tip. The influence of impurity Cr particles on healing kinetics was investigated through a correlative microscopy study, combining X-ray tomographic slices with SEM images. The existence of Cr particles was found to accelerate the healing rate. However, this was always accompanied by the formation of large pores, which may be detrimental to the strength recovery after healing.

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Lebedev, Sergej [Verfasser], and Peter [Akademischer Betreuer] Bachert. "Motion Compensation in Cardiac X-Ray Computed Tomography / Sergej Lebedev ; Betreuer: Peter Bachert." Heidelberg : Universitätsbibliothek Heidelberg, 2021. http://d-nb.info/1237499526/34.

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Amos, Mathew. "Advanced industrial X-ray computed tomography for defect detection and characterisation of composite structures." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/advanced-industrial-xray-computed-tomography-for-defect-detection-and-characterisation-of-composite-structures(7da52044-004e-4253-b1d2-0cb1e85ce28d).html.

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X-ray Computer Tomography (CT) is well suited to the inspection of Fibre-Reinforced-Plastic (FRP) composite materials. However, a range of limitations currently restrict its uptake. The aim of the present research was to develop advanced inspection procedures that overcome these limitations and increase the scope of composite structures that can be inspected by industrial cone beam CT. Region of Interest (ROI) CT inspection of FRP laminated panels was investigated and two data completion methods developed to overcome reconstruction errors caused by truncated projection data. These allow accurate, highly magnified regions to be reconstructed on objects that extend beyond the Field-of-View (FOV) of the detector. The first method extended the truncated projection data using a cosine signal tailing off to zero attenuation. This method removed the strong 'glowing' artefacts but an inherent error existed across the reconstructed ROI. This did not affect the defect detectability of the inspection but was viewed as problematic for applications requiring accurate density measurements. The second method used prior knowledge of the test object so that a model could be created to estimate the missing data. This technique removed errors associated with ROI reconstruction thus significantly improving the accuracy. Techniques for extending the FOV were developed and applied to the inspection of FRP wind turbine blades; over 1.5X larger than the conventional scanning FOV. Two data completion methods were developed requiring an asymmetrically positioned detector. The first was based on the cosine tailing technique and the second used fan beam ray redundancy properties to estimate the missing data. Both produced accurate reconstructions for the 'offset' projection data, demonstrating that it was possible to approximately double the FOV. The cosine tailing method was found to be the more reliable. A dual energy image CT technique was developed to extend the optimum dynamic range and improve defect detectability for multi-density objects. This was applied to FRP composite/Titanium lap joints showing improved detectability of both volumetric and planar defects within the low density FRP. The dual energy procedure was validated using statistical performance measures on a specially fabricated multi-density phantom. The results showed a significant improvement in the detail SNR when compared to conventional CT scans.

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Stenström, Mats. "Computerised microtomography : non-invasive imaging and analysis of biological samples, with special reference to monitoring development of osteoporosis in small animals /." Linköping : Univ, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-5030.

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Butzer, Jochen Sieghard. "MARS-CT: Biomedical Spectral X-ray Imaging with Medipix." Thesis, University of Canterbury. Physics and Astronomy, 2009. http://hdl.handle.net/10092/3863.

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Computed Tomography is one of the most important image modalities in medical imaging nowadays. Recent developments have led to a new acquisition technique called 'dual-energy', where images are taken with different x-ray spectra. This enables for the first time spectral information in the CT dataset. Our approach was to use an energy resolving detector (Medipix) and investigate its potential in the medical imaging domain. Images are taken in different energy bins. For acquisition of the data, a CT scanner called 'Medipix All Resolution System' (MARS) scanner was constructed. It was upgraded to achieve better image quality as well as faster scan time and a stable operation. In medical imaging, it is important to achieve a high contrast and a good detail recognition at a low dose. Therefore, it is common practice to use contrast agents to highlight certain regions of the body like e.g. the vascular system. But with a broad spectrum acquisition, it is often impossible to distinguish highly absorbing body elements like bones from the contrast agent. We target this problem by a contrast agent study using different energy bins. This so called spectral contrast agent study has been conducted with small animals using the MARS scanner. The data has been processed to create an optimal CT reconstruction. The image enhancement techniques consist of corrections for noisy pixels, intensity fluctuations and eliminating streaks in the sinograms to reduce ring artifacts. In order to evaluate the data, we used two methods of material identification. The material reconstruction method works on projection data and uses a maximum-likelihood estimation to reconstruct images of base materials. The second method, the principal component analysis (PCA), identifies the relevant information from the spectral dataset in a few derived variables that account for most of the variance in the dataset. This resulted in images with enhanced contrast and removed redundancies. It is possible to combine these images in one colour image where anatomical structures are shown in good detail and certain materials show up in different colors. Based on this new information from spectral data, we could show that it is possible to distinguish the spinal bone from contrast agent.

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Nik, Syen Jien. "Optimising the benefits of spectral x-ray imaging in material decomposition." Thesis, University of Canterbury. Physics and Astronomy, 2013. http://hdl.handle.net/10092/8398.

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The extra energy information provided by spectral x-ray imaging using novel photon counting x-ray detectors may allow for improved decomposition of materials compared to conventional and dual-energy imaging. The information content of spectral x-ray images, however, depends on how the photons are grouped together. This thesis deals with the theoretical aspect of optimising material discrimination in spectral x-ray imaging. A novel theoretical model was developed to map the confidence region of material thicknesses to determine the uncertainties in thickness quantification. Given the thickness uncertainties, photon counts per pixel can be optimised for material quantification in the most dose efficient manner. Minimisation of the uncertainties enables the optimisation of energy bins for material discrimination. Using Monte Carlo simulations based on the BEAMnrc package, material decomposition of up to 3 materials was performed on projection images, which led to the validation of the theoretical model. With the inclusion of scattered radiation, the theoretical optima of bin border energies were accurate to within 2 keV. For the simulated photon counts, excellent agreement was achieved between the theoretical and the BEAMnrc models regarding the signal-to-noise ratio in a decomposed image, particularly for the decomposition of two materials. Finally, this thesis examined the implementation of the Medipix detector. The equalisation of pixel sensitivity variations and the processing of photon counting projection images were studied. Measurements using the Medipix detector demonstrated promising results in the charge summing and the spectroscopic modes of acquisition, even though the spectroscopic performance of the detector was relatively limited due to electronic issues known to degrade the equalisation process. To conclude, the theoretical model is sufficient in providing guidelines for scanning parameters in spectral x-ray imaging and may be applied on spectral projection measurements using e.g. the redesigned MedipixRX detector with improved spectroscopic performance, when it becomes available.

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Han, Dong. "Advances in dual-energy computed tomography imaging of radiological properties." VCU Scholars Compass, 2018. https://scholarscompass.vcu.edu/etd/5447.

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Dual-energy computed tomography (DECT) has shown great potential in the reduction of uncertainties of proton ranges and low energy photon cross section estimation used in radiation therapy planning. The work presented herein investigated three contributions for advancing DECT applications. 1) A linear and separable two-parameter DECT, the basis vector model (BVM) was used to estimate proton stopping power. Compared to other nonlinear two-parameter models in the literature, the BVM model shows a comparable accuracy achieved for typical human tissues. This model outperforms other nonlinear models in estimations of linear attenuation coefficients. This is the first study to clearly illustrate the advantages of linear model not only in accurately mapping radiological quantities for radiation therapy, but also in providing a unique model for accurate linear forward projection modelling, which is needed by the statistical iterative reconstruction (SIR) and other advanced DECT reconstruction algorithms. 2) Accurate DECT requires knowledge of x-ray beam properties. Using the Birch-Marshall1 model and beam hardening correction coefficients encoded in a CT scanner’s sinogram header files, an efficient and accurate way to estimate the x-ray spectrum is proposed. The merits of the proposed technique lie in requiring no physical transmission measurement after a one-time calibration against an independently measured spectrum. This technique can also be used in monitoring the aging of x-ray CT tubes. 3) An iterative filtered back projection with anatomical constraint (iFBP-AC) algorithm was also implemented on a digital phantom to evaluate its ability in mitigating beam hardening effects and supporting accurate material decomposition for in vivo imaging of photon cross section and proton stopping power. Compared to iFBP without constraints, both algorithms demonstrate high efficiency of convergence. For an idealized digital phantom, similar accuracy was observed under a noiseless situation. With clinically achievable noise level added to the sinograms, iFBP-AC greatly outperforms iFBP in prediction of photon linear attenuation at low energy, i.e., 28 keV. The estimated mean errors of iFBP and iFBP-AC for cortical bone are 1% and 0.7%, respectively; the standard deviations are 0.6% and 5%, respectively. The achieved accuracy of iFBP-AC shows robustness versus contrast level. Similar mean errors are maintained for muscle tissue. The standard deviation achieved by iFBP-AC is 1.2%. In contrast, the standard deviation yielded by iFBP is about 20.2%. The algorithm of iFBP-AC shows potential application of quantitative measurement of DECT. The contributions in this thesis aim to improve the clinical performance of DECT.

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Li, Zhu. "Investigation of granular materials deformations under an unconfined compaction with x-ray computed tomography." Thesis, KTH, Väg- och banteknik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-127690.

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The behavior of the asphalt mixtures under large deformations, for example an unconfined compaction is of high practical importance. Quantitative measurement of the spatial distribution of internal structure of asphalt mixtures is crucial to study deformation behavior of asphalt mixtures. Deformation of granular material under an unconfined compaction is investigated in this study, as a groundwork for further research on deformation behavior of asphalt mixtures. Two sets of 3D images of specimens are obtained using X-Ray computed tomography (CT) under an unconfined compaction. Digital image analysis procedure is developed to segment different phases for characterizing spatial distribution of internal structure. Comparative volumetric relationship before and after compaction showed that air void distribution is not changed heavily due to absence of interlocking. Initial and final spatial positions of individual granules are investigated to trace their movement under compaction. It is shown that X-Ray CT could be a useful tool to characterize internal structure of asphalt mixtures and its evolution during deformation.

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Razavi, Mohammad Reza. "Characterization of microstructure and internal displacement field of sand using X-ray computed tomography." Online access for everyone, 2006. http://www.dissertations.wsu.edu/Dissertations/Fall2006/M_Razavi_121206.pdf.

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Farcas, Florentina Angela. "Evaluation of Asphalt Field Cores with Simple Performance Tester and X-ray Computed Tomography." Licentiate thesis, KTH, Väg- och banteknik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-91803.

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The importance of aggregate structure and air voids distribution for asphalt mixture rutting and cracking performance has been well established on the basis of experience and is well documented in the literature. Past and current investigations are limited to assessment of performance based on macroscopic behavior due to the difficulty associated with the quantitative measurement and analysis of the internal structure of asphalt mixtures. Lately, technical advances in X-ray Computed Tomography (CT) and image processing and analysis has made possible to bring the attention also to the internal structure of asphalt mixtures. SPT results from asphalt field cores, including dynamic modulus (before and after loading) and microstrain accumulation (flow number), exhibited significant variability; most likely, induced by irregularities in the core shape. The analysis of aggregate structure and air voids distribution performed trough X-ray CT, clearly identified segregation in the asphalt mixture as a key factor that induced variability in SPT results.
QC 20120320

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Hunter, Opio K. "Characterization of pore structure and crack propagation in concrete using X-ray computed tomography." College Park, Md. : University of Maryland, 2004. http://hdl.handle.net/1903/2153.

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Thesis (M.S.) -- University of Maryland, College Park, 2004.
Thesis research directed by: Dept. of Civil and Environmental Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

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McKenna, Gregory Patrick. "Visualization of bacterial density distributions in saturated sand columns using X-ray computed tomography." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=19266.

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The transport of bacteria in granular porous media is important to many environmental applications. Traditionally, the fate of bacteria in porous media has been studied using bench-scale column experiments while monitoring the suspended effluent concentration. Determining the spatial distribution of deposited bacteria in the column using a non-invasive and non-destructive technique has the potential to improve the understanding of some bacteria transport processes. In this study, a preliminary X-ray computed tomography (X-ray CT) technique is developed to analyze the density distribution of bacteria within a saturated column. Bacteria cells are generally not detectable in water saturated columns because their X-ray attenuation properties are similar to water. Nanosized gold particles were synthesized in the presence of cetyltrimethylammonium bromide and were attached to the bacteria forming a monolayer of gold coverage at the bacteria surface. These gold-labelled cells were detectable during CT scanning at concentrations of 3 x 107 cells/mL when injected into water saturated sand columns and thus allowed for the determination of areas of high deposition in packed sand columns.
Le transport des microbes est important pour une variété d'applications environmentales. Traditionellement, le destin des microbes en média poreux est examiné utilisant des expériences en colonne en observant la concentration de l'effluent. La détermination de la distribution spatiale des microbes déposés dans la colonne en relation à la structure des pores en utilisant une méthode non-déstructive pourrait améliorer nos connaissances des mécanismes pour le transport des microbes. Dans cette étude, une technique préliminaire est dévelopée afin d'étudier la distribution des microbes dans des colonnes saturées en utilisant la tomographie calculée aux rayons X. Des nanoparticules en or sont synthétisées dans la présence de la bromure de cyltriméthylammonium et sont attachées aux microbes afin de couvrir la surface des bactéries. Ces bactéries recouvertes en or peuvent être détectés avec la tomographie calculée aux rayons X à partir d'une concentration de 3 x 107 microbes/mL lors de l'injection dans des colonnes saturées nous permettes de déterminer les régions de déposition élèvées dans des colonnes de sable saturées.

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Mairhofer, Stefan. "Extracting root system architecture from X-ray micro computed tomography images using visual tracking." Thesis, University of Nottingham, 2014. http://eprints.nottingham.ac.uk/27739/.

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X-ray micro computed tomography (µCT) is increasingly applied in plant biology as an imaging system that is valuable for the study of root development in soil, since it allows the three-dimensional and non-destructive visualisation of plant root systems. Variations in the X-ray attenuation values of root material and the overlap in measured intensity values between roots and soil caused by water and organic matter represent major challenges to the extraction of root system architecture. We propose a novel technique to recover root system information from X-ray CT data, using a strategy based on a visual tracking framework embedding a modiffed level set method that is evolved using the Jensen-Shannon divergence. The model-guided search arising from the visual tracking approach makes the method less sensitive to the natural ambiguity of X-ray attenuation values in the image data and thus allows a better extraction of the root system. The method is extended by mechanisms that account for plagiatropic response in roots as well as collision between root objects originating from different plants that are grown and interact within the same soil environment. Experimental results on monocot and dicot plants, grown in different soil textural types, show the ability of successfully extracting root system information. Various global root system traits are measured from the extracted data and compared to results obtained with alternative methods.

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Thompson, Mark. "The application of X-ray computed tomography for studying root behaviour in compacted soil." Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/51680/.

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Tomography (CT) offered a distinctive method for visualising undisturbed RSA which was used to develop an understanding of the response of wheat (Triticum aestivum L.) to compaction. The first aim was to assess the impact of soil properties and X-ray scanning parameters have on image quality, and identify which settings are optimum for balancing against acquisition time. The second aim was to investigate how soil compaction affects the growth and RSA of wheat, while also considering the impact of soil texture. The third aim was to test if and how soil compaction alters a roots mechanical properties, and what anatomical changes are responsible for these changes. Using complementary techniques including root tensile strength testing and root sectioning, insights have been gained on the anatomical adaptions of roots and how these changes affect their material properties and behaviour in compacted soil. This will allow more efficient phenotyping of wheat varieties for soil exploration and resource uptake.

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Hand, Davis Kyle. "A Manufacturing Process for Single Micron Resolution Optical Gratings Used in X-ray Computed Tomography." Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/33804.

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X-ray Computed Tomography (CT) is a process that produces three-dimensional x-ray images, allowing for better diagnosis and analysis of complex internal medical conditions. New advances in the optical techniques used in this process promise to produce better results while reducing patient risk. One of these developments calls for precise optical gratings that can be expensive and difficult to manufacture. This paper presents a simple process developed specifically for the production of these gratings using cost effective techniques. The process uses well understood semiconductor fabrication steps including oxidation, deep reactive ion etching and electroplating. While not entirely successful, the process presented within provides a proof of concept for development of the gratings and discusses improvements that could be made to allow for success.
Master of Science

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Dong, Xu. "Material-Specific Computed Tomography for Molecular X-Imaging in Biomedical Research." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/88869.

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X-ray Computed Tomography (CT) imaging has been playing a central role in clinical practice since it was invented in 1972. However, the traditional x-ray CT technique fails to distinguish different materials with similar density, especially for biological tissues. The lack of a quantitative imaging representation has constrained the application of CT technique from a broadening application such as personal or precision medicine. Therefore, my major thesis statement is to develop novel material-specific CT imaging techniques for molecular imaging in biological bodies. To achieve the goal, comprehensive studies were conducted to investigate three different techniques: x-ray fluorescence molecular imaging, material identification (specification) from photon counting CT, and photon counting CT data distortion correction approach based on deep learning. X-ray fluorescence molecular imaging (XFMI) has shown great promise as a low-cost molecular imaging modality for clinical and pre-clinical applications with high sensitivity. In this study, the effects of excitation beam spectrum on the molecular sensitivity of XFMI were experimentally investigated, by quantitatively deriving minimum detectable concentration (MDC) under a fixed surface entrance dose of 200 mR at three different excitation beam spectra. The result shows that the MDC can be readily increased by a factor of 5.26 via excitation spectrum optimization. Furthermore, a numerical model was developed and validated by the experimental data (≥0.976). The numerical model can be used to optimize XFMI system configurations to further improve the molecular sensitivity. Findings from this investigation could find applications for in vivo pre-clinical small-animal XFMI in the future. PCCT is an emerging technique that has the ability to distinguish photon energy and generate much richer image data that contains x-ray spectral information compared to conventional CT. In this study, a physics model was developed based on x-ray matter interaction physics to calculate the effective atomic number () and effective electron density () from PCCT image data for material identification. As the validation of the physics model, the and were calculated under various energy conditions for many materials. The relative standard deviations are mostly less than 1% (161 out of 168) shows that the developed model obtains good accuracy and robustness to energy conditions. To study the feasibility of applying the model with PCCT image data for material identification, both PCCT system numerical simulation and physical experiment were conducted. The result shows different materials can be clearly identified in the − map (with relative error ≤8.8%). The model has the value to serve as a material identification scheme for PCCT system for practical use in the future. As PCCT appears to be a significant breakthrough in CT imaging field, there exists severe data distortion problem in PCCT, which greatly limits the application of PCCT in practice. Lately, deep learning (DL) neural network has demonstrated tremendous success in medical imaging field. In this study, a deep learning neural network based PCCT data distortion correction method was proposed. When applying the algorithm to process the test dataset data, the accuracy of the PCCT data can be greatly improved (RMSE improved 73.7%). Compared with traditional data correction approaches such as maximum likelihood, the deep learning approach demonstrate superiority in terms of RMSE, SSIM, PSNR, and most importantly, runtime (4053.21 sec vs. 1.98 sec). The proposed method has the potential to facilitate the PCCT studies and applications in practice.
Doctor of Philosophy
X-ray Computed Tomography (CT) has played a central role in clinical imaging since it was invented in 1972. It has distinguishing characteristics of being able to generate three dimensional images with comprehensive inner structural information in fast speed (less than one second). However, traditional CT imaging lacks of material-specific capability due to the mechanism of image formation, which makes it cannot be used for molecular imaging. Molecular imaging plays a central role in present and future biomedical research and clinical diagnosis and treatment. For example, imaging of biological processes and molecular markers can provide unprecedented rich information, which has huge potentials for individualized therapies, novel drug design, earlier diagnosis, and personalized medicine. Therefore there exists a pressing need to enable the traditional CT imaging technique with material-specific capability for molecular imaging purpose. This dissertation conducted comprehensive study to separately investigate three different techniques: x-ray fluorescence molecular imaging, material identification (specification) from photon counting CT, and photon counting CT data distortion correction approach based on deep learning. X-ray fluorescence molecular imaging utilizes fluorescence signal to achieve molecular imaging in CT; Material identification can be achieved based on the rich image data from PCCT; The deep learning based correction method is an efficient approach for PCCT data distortion correction, and furthermore can boost its performance on material identification. With those techniques, the material-specific capability of CT can be greatly enhanced and the molecular imaging can be approached in biological bodies.

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Ford, Jason J. "Using X-ray computed tomography to measure local gas holdup in a stirred tank reactor." [Ames, Iowa : Iowa State University], 2006.

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Johansson, Adam. "Magnetic resonance imaging with ultrashort echo time as a substitute for X-ray computed tomography." Doctoral thesis, Umeå universitet, Radiofysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-93053.

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Radiotherapy dose calculations have evolved from simple factor based methods performed with pen and paper, into computationally intensive simulations based on Monte Carlo theory and energy deposition kernel convolution. Similarly, in the field of positron emission tomography (PET), attenuation correction, which was originally omitted entirely, is now a crucial component of any PET reconstruction algorithm. Today, both of these applications – radiotherapy and PET – derive their needed in-tissue radiation attenuation coefficients from images acquired with X-ray computed tomography (CT). Since X-ray images are themselves acquired using ionizing radiation, the intensity at a point in an image will reflect the radiation interaction properties of the tissue located at that point. Magnetic resonance imaging (MRI), on the other hand, does not use ionizing radiation. Instead MRI make use of the net transverse magnetization resulting from the spin polarization of hydrogen nuclei. MR image contrast can be varied to a greater extent than CT and the soft tissue contrast is, for most MR sequences, superior to that of CT. Therefore, for many cases, MR images provide a considerable advantage over CT when identifying or delineating tumors or other diseased tissues. For this reason, there is an interest to replace CT with MRI for a great number of diagnostic and therapeutic workflows. Also, replacing CT with MRI would reduce the exposure to ionizing radiation experienced by patients and, by extension, reduce the associated risk to induce cancer. In part MRI has already replaced CT, but for radiotherapy dose calculations and PET attenuation correction, CT examinations are still necessary in clinical practice. One of the reasons is that the net transverse magnetization imaged in MRI cannot be converted into attenuation coefficients for ionizing radiation in a straightforward way. More specifically, regions with similar appearance in magnetic resonance (MR) images, such as bone and air pockets, are found at different ends of the spectrum of attenuation coefficients present in the human body. In a CT image, bone will appear bright white and air as black corresponding to high and no attenuation, respectively. In an MR image, bone and air both appear dark due to the lack of net transverse magnetization. The weak net transverse magnetization of bone is a result of low hydrogen density and rapid transverse relaxation. A particular category of MRI sequences with so-called ultrashort echo time (UTE) can sample the MRI signal from bone before it is lost due to transverse relaxation. Thus, UTE sequences permit bone to be imaged with MRI albeit with weak intensity and poor resolution. Imaging with UTE in combination with careful image analysis can permit ionizing-radiation attenuation-maps to be derived from MR images. This dissertation and appended articles present a procedure for this very purpose. However, as attenuation coefficients are radiation-quality dependent the output of the method is a Hounsfield unit map, i.e. a substitute for a CT image. It can be converted into an attenuation map using conventional clinical procedure. Obviating the use of CT would reduce the number of examinations that patients have to endure during preparation for radiotherapy. It would also permit PET attenuation correction to be performed on images from the new imaging modality that combines PET and MRI in one scanner – PET/MR.

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Melean, Y., Kathryn E. Washburn, P. T. Callaghan, and Christoph H. Arns. "A numerical analysis of NMR pore-pore exchange measurements using micro X-ray computed tomography." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-192412.

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Pore-pore relaxation exchange experiments are a recent development and hold great promise to spectrally derive length scales and connectivity information relevant for transport in porous media. However, for large pores, NMR diffusion-relaxation techniques reach a limit because bulk relaxation becomes dominant. A combination of NMR and Xray-CT techniques could be beneficial and lead to better models for regions of unresolved porosity in CT images, increasing the accuracy of image based calculations of transport properties. In this study we carry out numerical NMR pore-pore exchange experiments on selected Xray-CT images of sandstones and carbonate rock, while at the same time tracking information about the geometry and topology of the pore space. We use pore partitioning techniques and geometric distance fields to relate T2-T2 relaxation exchange spectra to underlying structural quantities. It is shown that T2-T2 pore-pore exchange measurements at room temperatures for the samples considered likely reflect exchange between pores and throats or pores and roughness.

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Dissertations / Theses on the topic 'X-Ray Computed'

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