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Miles, Brian Herndon. "Computed-tomography imaging spectropolarimeter (CTISP)." Diss., The University of Arizona, 1999. http://hdl.handle.net/10150/288965.
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A complete Stokes imaging spectropolarimeter has been developed based on the principles of computed-tomography, spectrometry and polarimetry. The Computed-Tomography Imaging SpectroPolarimeter (CTISP) is a polarization extension to the Computed Tomography Imaging Spectrometer (CTIS)¹. Imaging spectrometers estimate the object cube (x,y, λ), whose smallest subdivision is a voxel, while Stokes imaging spectrometers estimate four Stokes object cubes (x,y, Sp(λ); p = 0,1,2,3), one for each Stokes parameter. CTISP uses a two-dimensional disperser to diffract the image in the field stop into a 5-by-5 array of diffraction orders. As in computed tomography, each focal plane array (FPA) pixel effectively integrates a different path through the object cube, and when all pixels are recorded, a significant portion of the object cube's information is obtained. The frequency space representation of the object cube, however, indicates that two conical regions of information are not recorded, thereby limiting the reconstruction accuracy. CTISP scans only in the polarization domain (not spectral or spatial domains), acquiring four FPA frames, one behind each of the four polarization analyzers. Currently, CTISP's resolution is 33 by 33 spatially over a 3.5 degrees full angle field of view with 16 spectral bands of 20nm width covering 440nm-740nm. CTISP acquisition is modeled using the linear imaging equation gₐ=Hₐfₐ+ξₐ, which is inverted using the iterative expectation-maximization algorithm to solve for fₐ, the object cube as seen through analyzer a. The recorded diffraction images gₐ and the empirically determined calibration matrices Hₐ, are each acquired using analyzer a. The nth voxel reconstruction result is extracted from each of the four fₐ vectors to form a four element vector f(n) which is then multiplied by the inverse of the voxel characteristic matrix W(n) to obtain the estimate of the Stokes vector S(n). W(n) is derived from the four Hₐ matrices. A fully computer-controlled calibration facility and a suite of programs are used to calibrate CTISP. CTISP was validated using synthetically generated and real objects. Spectral agreement is consistent with CTIS, while Stokes parameter polarization errors were typically 0.04-0.07 for this instrument. Errors are most significant at the spectral limits of CTISP. An object dependent correction reduces these errors to below one percent.
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Williams, Michelle Claire. "Computed tomography imaging of the heart." Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/25852.
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Computed tomography imaging has revolutionised modern medicine and we can now study the body in greater detail than ever before. Cardiac computed tomography has the potential to provide information not just on coronary anatomy, but also on myocardial function, perfusion and viability. This thesis addresses the optimisation and validation of computed tomography imaging of the heart using a wide volume 320-multidetector scanner. Computed tomography coronary angiography now has diagnostic accuracy comparable to invasive coronary angiography. However, radiation dose remains an important concern. It is therefore important to minimise computed tomography radiation dose while maintaining image quality. I was able to demonstrate that iterative reconstruction and patient tailored imaging techniques led to a 39% reduction in radiation dose in computed tomography coronary angiography, while maintaining subjective and objective assessments of image quality. In addition, I demonstrated that diagnostic images can be obtained in 99% of unselected patients presenting with suspected coronary artery disease when using single heart-beat 320- multidetector computed tomography coronary angiography. Computed tomography myocardial perfusion imaging can provide additional and complementary information as compared to computed tomography coronary angiography that can aid diagnosis and management. I established both quantitative and qualitative assessment of computed tomography myocardial perfusion imaging and validated it against both a clinical “gold-standard”, fractional flow reserve during invasive coronary angiography, and a physiological “gold-standard”, positron emission tomography with oxygen-15 labelled water. Finally, I was able to show that techniques to reduce radiation dose can also be applied to computed tomography myocardial perfusion imaging, leading to a 60% reduction in radiation dose, while maintaining image quality. In my thesis, I have established that comprehensive cardiac angiographic and perfusion imaging can be performed with wide volume computed tomography in a broad generalizable population of patients with relatively low radiation exposure. These techniques provide both structural and functional assessments from a single imaging modality that are valid and readily applicable to the clinic in the assessment and management of patients with suspected coronary artery disease.
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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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Wang, Silun, and 王思倫. "Clinical applications of cardiac multi-detector computed tomography." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B36944087.
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Webb, John Alan Christopher. "Dynamic stereo-pair imaging of computed tomography data." Thesis, Queen's University Belfast, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235826.
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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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Balasundaram, Ashok Mol André. "Cone beam computed tomography imaging of periodontal bone." Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2008. http://dc.lib.unc.edu/u?/etd,2063.
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Thesis (M.S.)--University of North Carolina at Chapel Hill, 2008.<br>Title from electronic title page (viewed Feb. 17, 2009). "... in partial fulfillment of the requirements for the degree of Master of Science in the Department of Diagnostic Sciences and General Dentistry, School of Dentistry." Discipline: Diagnostic Sciences and General Dentistry; Department/School: Dentistry.
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Ford, Bridget K. "Computed tomography based spectral imaging for fluorescence microscopy." Diss., The University of Arizona, 2002. http://hdl.handle.net/10150/280122.
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Multispectral imaging has been used for decades in remote sensing to enhance the classification, discrimination and characterization of materials. Only recently has this same technology been similarly applied to fixed biological samples in cytogenetics, pathology and medicine. A further extension to in vivo studies is often limited by the low levels of associated fluorescence as well as the increased temporal resolution required to analyze physiological changes. In addition, the cellular response to a specific agonist is often heterogeneous across the cellular field requiring a combination of sufficient spatial and temporal resolutions. A computed tomography imaging spectrometer (CTIS) has been developed which overcomes these limitations by simultaneously collecting extended range spectral information (470-740 nm, 5 nm sampling) across a 2-D field of view (200 μm x 200 μm, 0.96 μm sampling). The CTIS uses a computer generated hologram to produce a 5 x 5 array of images with differing amounts and directions of dispersion. This set of images allows the 3-D signal (x, y, λ) from a fluorescent sample to be mapped onto a 2-D detector array. In this way, the full spectral and spatial information is acquired for a 2-D cellular field during a single integration time (presently 2 sec for biological specimens). The CTIS's design, calibration, and underlying theory are described in detail. In addition, the capability of the CTIS to simultaneously collect the fluorescence emission of multiple fluorophores across a 2-D cellular field is demonstrated. Specifically, the combined spectral variations of seminapthorhodafluor-I and enhanced green fluorescent protein were followed in rat insulinoma cells in order to extend the linear range of intracellular pH detection.
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Ireland, Robert Henry. "Anatomically constrained image reconstruction applied to emission computed tomography & magnetic impedance tomography." Thesis, University of Sheffield, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269337.
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Rollano, Hijarrubia Maria Empar. "Imaging of small high-density structures in computed tomography." [S.l.] : Rotterdam : [The Author] ; Erasmus University [Host], 2007. http://hdl.handle.net/1765/10601.
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De, Geer Jakob. "On the use of computed tomography in cardiac imaging." Doctoral thesis, Linköpings universitet, Avdelningen för radiologiska vetenskaper, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-128276.
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Background Cardiac Computed Tomography Angiography (CCTA) is becoming increasingly useful in the work‐up of coronary artery disease (CAD). Several potential methods for increasing the diagnostic yield of cardiac CT are available. Purpose Study I: To investigate whether the use of a 2‐D, non‐linear adaptive noise reduction filter can improve CCTA image quality. Study II: To evaluate the variation in adenosine stress dynamic CT perfusion (CTP) blood flow as compared to stress 99mTc SPECT. Secondly, to compare the perfusion results from manual and automatic myocardial CTP segmentation. Study III: To evaluate the accuracy of non‐invasive, CCTA‐derived Fractional Flow Reserve (cFFR). Study IV: To evaluate the prognostic value of CCTA in terms of major adverse cardiac events (MACE). Materials and methods Study I: Single images from 36 consecutive CCTA exams performed with two different dose levels were used. Image quality in full dose, low‐dose and noise‐reduced low‐dose images was graded using visual grading analysis. Image noise was measured. Study II: CTP and SPECT were performed in 17 patients, and the variation in per AHA‐segment blood flow was evaluated and compared. CTP results from manual and automated image segmentation were compared. Study III: CCTA datasets from 21 patients were processed using cFFR software and the results compared to the corresponding invasively measured FFR (invFFR). Study IV: 1205 consecutive patients with chest pain of unknown origin underwent CCTA. Baseline data and data on subsequent MACE were retrieved from relevant registries. Survival, hazard ratios and the three‐year incidence of cardiac events and readmissions were calculated. Results Study I: There was significant improvement in perceived image quality for all criteria when the filter was applied, and a significant decrease in image noise. Study II: The correlation coefficients for CTP vs. SPECT were 0.38 and 0.41 (p<0.001, for manual and automated segmentation respectively. Mean per patient CTP blood flow in normal segments varied between 94‐183 ml/100 ml tissue/min for manual segmentation, and 104‐196 ml/100 ml tissue/min for automated segmentation. The Spearman rank correlation coefficient for manual vs. automated segmentation CTP was ρ = 0.88 (p<0.001) and the Intraclass Correlation Coefficient (ICC) was 0.93 (p<0.001). Study III: The Spearman rank correlation coefficient for cFFR vs. invFFR was ρ = 0.77 (p<0.001) and the ICC was 0.73 (p<0.001). Sensitivity, specificity, positive predictive value and negative predictive value for significant stenosis (FFR<0.80, per vessel) were 0.83, 0.76, 0.56 and 0.93 respectively. Study IV: The hazard ratio for non‐obstructive CAD vs. normal coronary arteries was 5.13 (95% C.I 1.03‐25.43, p<0.05), and 151.40 (95% C.I 37.03‐619.08, p<0.001) for obstructive CAD vs. normal coronary arteries. The three‐year incidence of MACE was 1.1% for patients with normal vessels on CCTA, 2.5% for patients with non‐obstructive CAD and 42.7% for patients with obstructive CAD (p<0.001). Conclusions: Study I: Image quality and noise levels of low dose images were significantly improved with the filter, even though the improvement was small compared to the image quality of the corresponding diastolic full‐dose images. Study II: Correlation between dynamic CTP and SPECT was positive but weak. There were large variations in CTP blood flow in normal segments on SPECT, rendering the definition of an absolute cut‐off value for normal vs. ischemic myocardium difficult. Manual and automatic segmentation were equally useful. Study III: The correlation between cFFR and invFFR was good, indicating that noninvasively estimated cFFR performs on a similar level as invasively measure FFR. Study IV: The long‐term risk for MACE was very low in patients without obstructive CAD on CCTA, though there seemed to be a substantial increase in the risk for MACE even in patients with non‐obstructive CAD as compared to normal coronary arteries. In addition, even patients with normal coronary arteries or non‐obstructive CAD continued to have a substantial number of readmissions for chest pain or angina pectoris.
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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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Alarady, Mamdooh R. "Characterization of Image Quality between Multi-Slice Computed Tomography and Cone Beam Computed Tomography for Clinical Used Protocols in Radiation Therapy Treatment Planning." University of Toledo Health Science Campus / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=mco151080400269082.
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Amurao, Maxwell Leland Ramirez. "Investigating collagen hydration with micro computed tomography a dissertation /." San Antonio : UTHSC, 2008. http://proquest.umi.com.libproxy.uthscsa.edu/pqdweb?did=1625775011&sid=1&Fmt=2&clientId=70986&RQT=309&VName=PQD.
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Weir, Iain Stewart. "Statistical modelling and reconstructions in single photon emission computed tomography." Thesis, University of Bristol, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335395.
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Xu, Minghua. "Photoacoustic computed tomography in biological tissues: algorithms and breast imaging." Texas A&M University, 2004. http://hdl.handle.net/1969.1/1275.
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Photoacoustic computed tomography (PAT) has great potential for application in the biomedical field. It best combines the high contrast of electromagnetic absorption and the high resolution of ultrasonic waves in biological tissues.
In Chapter II, we present time-domain reconstruction algorithms for PAT. First, a formal reconstruction formula for arbitrary measurement geometry is presented. Then, we derive a universal and exact back-projection formula for three commonly used measurement geometries, including spherical, planar and cylindrical surfaces. We also find this back-projection formula can be extended to arbitrary measurement surfaces under certain conditions. A method to implement the back-projection algorithm is also given. Finally, numerical simulations are performed to demonstrate the performance of the back-projection formula.
In Chapter III, we present a theoretical analysis of the spatial resolution of PAT for the first time. The three common geometries as well as other general cases are investigated. The point-spread functions (PSF's) related to the bandwidth and the sensing aperture of the detector are derived. Both the full-width-at-half-maximum of the PSF and the Rayleigh criterion are used to define the spatial resolution.
In Chapter IV, we first present a theoretical analysis of spatial sampling in the PA measurement for three common geometries. Then, based on the sampling theorem, we propose an optimal sampling strategy for the PA measurement. Optimal spatial sampling periods for different geometries are derived. The aliasing effects on the PAT images are also discussed. Finally, we conduct numerical simulations to test the proposed optimal sampling strategy and also to demonstrate how the aliasing related to spatially discrete sampling affects the PAT image.
In Chapter V, we first describe a prototype of the RF-induced PAT imaging system that we have built. Then, we present experiments of phantom samples as well as a preliminary study of breast imaging for cancer detection.
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Joita, Pacureanu Alexandra. "Imaging the bone cell network with nanoscale synchrotron computed tomography." Phd thesis, INSA de Lyon, 2012. http://tel.archives-ouvertes.fr/tel-00778408.
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The osteocytes are the most abundant and longest living bone cells, embedded in the bone matrix. They are interconnected with each other through dendrites, located in slender canals called canaliculi. The osteocyte lacunae, cavities in which the cells are located, together with the canaliculi form a communication network throughout the bone matrix, permitting transport of nutrients, waste and signals. These cells were firstly considered passive, but lately it has become increasingly clear their role as mechanosensory cells and orchestrators of bone remodeling. Despite recent advances in imaging techniques, none of the available methods can provide an adequate 3D assessment of the lacuno-canalicular network (LCN). The aims of this thesis were to achieve 3D imaging of the LCN with synchrotron radiation X-ray computed tomography (SR-CT) and to develop tools for 3D detection and segmentation of this cell network, leading towards automatic quantification of this structure. We demonstrate the feasibility of parallel beam SR-CT to image in 3D the LCN (voxel~300 nm). This technique can provide data on both the morphology of the cell network and the composition of the bone matrix. Compared to the other 3D imaging methods, this enables imaging of tissue covering a number of cell lacunae three orders of magnitude greater, in a simpler and faster way. This makes possible the study of sets of specimens in order to reach biomedical conclusions. Furthermore, we propose the use of divergent holotomography, to image the ultrastructure of bone tissue (voxel~60 nm). The image reconstruction provides phase maps, obtained after the application of a suitable phase retrieval algorithm. This technique permits assessment of the cell network with higher accuracy and it enables the 3D organization of collagen fibres organization in the bone matrix, to be visualized for the first time. In order to obtain quantitative parameters on the geometry of the cell network, this has to be segmented. Due to the limitations in spatial resolution, canaliculi appear as 3D tube-like structures measuring only 1-3 voxels in diameter. This, combined with the noise, the low contrast and the large size of each image (8 GB), makes the segmentation a difficult task. We propose an image enhancement method, based on a 3D line filter combined with bilateral filtering. This enables improvement in canaliculi detection, reduction of the background noise and cell lacunae preservation. For the image segmentation we developed a method based on variational region growing. We propose two expressions for energy functionals to minimize in order to detect the desired structure, based on the 3D line filter map and the original image. Preliminary quantitative results on human femoral samples are obtained based on connected components analysis and a few observations related to the bone cell network and its relation with the bone matrix are presented.
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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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Khoei, Shadi. "Quantitative ultrasound computed tomography imaging of PAGAT radiation dosimetry gel." Thesis, Queensland University of Technology, 2013. https://eprints.qut.edu.au/63958/1/Shadi_Khoei_Thesis.pdf.
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This research developed and scientifically validated a new ultrasound transmission computed tomography system with the aim of quantitative assessment of a polymer gel dosimeter including dose response verification of ultrasonic parameters of attenuation, velocity and broadband ultrasound attenuation (BUA). This work was the first to investigate and report ultrasound frequency dependent attenuation in a gel dosimeter, demonstrating a dose dependence.
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Fentner, David A. "A Comparative Image Quality Analysis between Multi-Slice Computed Tomography and Cone Beam Computed Tomography for Radiation Treatment Planning Purposes." University of Toledo Health Science Campus / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=mco1372413982.
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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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Wajngot, David. "Improving Image Quality in Cardiac Computed Tomography using Deep Learning." Thesis, Linköpings universitet, Avdelningen för kardiovaskulär medicin, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-154506.
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Cardiovascular diseases are the largest mortality factor globally, and early diagnosis is essential for a proper medical response. Cardiac computed tomography can be used to acquire images for their diagnosis, but without radiation dose reduction the radiation emitted to the patient becomes a significant risk factor. By reducing the dose, the image quality is often compromised, and determining a diagnosis becomes difficult. This project proposes image quality enhancement with deep learning. A cycle-consistent generative adversarial neural network was fed low- and high-quality images with the purpose to learn to translate between them. By using a cycle-consistency cost it was possible to train the network without paired data. With this method, a low-quality image acquired from a computed tomography scan with dose reduction could be enhanced in post processing. The results were mixed but showed an increase of ventricular contrast and artifact mitigation. The technique comes with several problems that are yet to be solved, such as structure alterations, but it shows promise for continued development.
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Oh, Eun-Hwan. "Determinants of the diffusion of computed tomography and magnetic resonance imaging." 京都大学 (Kyoto University), 2007. http://hdl.handle.net/2433/137049.
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Levi, Jacob. "Automated Beam Hardening Correction for Myocardial Perfusion Imaging using Computed Tomography." Case Western Reserve University School of Graduate Studies / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=case1553868329519413.
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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.<br>Doctor of Philosophy<br>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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Secchi, F. "CARDIOVASCULAR COMPUTED TOMOGRAPHY AND MAGNETIC RESONANCE IMAGING IN CONGENITAL HEART DISEASE." Doctoral thesis, Università degli Studi di Milano, 2017. http://hdl.handle.net/2434/470146.
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Cardiac magnetic resonance (CMR) is a non-invasive imaging modality highly reliable for studying cardiovascular morphology and function. Cardiac computed tomography (CCT) can give valuable anatomic information on CHD in children but implies radiation exposure, a relevant issue in children and newborns who are more radiosensitive than adult patients and have a longer lifetime to develop stochastic effects from radiation. We contributed to show the possibility to obtain an impressively low ionizing dose reduction in CHD patients also using standard 64-slice CT scanners. Conversely, CMR holds a pivotal role when functional and flow imaging is required. We showed the role of CMR in evaluating of patients percutaneously implanted with a pulmonary valve. Moreover, we proposed two new approaches for post-processing CMR images, regarding volume estimation of patients with a single ventricle, a rare CHD and a method for quantifying the paradoxical septal motion. CMR and CCT are two fundamental imaging techniques to evaluate patients with complex CHD. Both imaging modalities have limitations and advantages. CMR can evaluate heart function vessel flow but require a long acquisition time and in same patients a long sedation time. CCT has a very high spatial resolution and short acquisition time but implies ionizing radiation exposure. On the one side, we confirming the crucial role of CMR when function analysis is required but also showed the relevant possibilities of x-ray dose reduction in CCT, also using standard 64-slice scanners in the study of CHD patients.
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Forsythe, Rachael Olivia. "Assessment of abdominal aortic aneurysm biology using magnetic resonance imaging and positron emission tomography-computed tomography." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/29619.
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Background Although abdominal aortic aneurysm (AAA) growth is non-linear, serial measurements of aneurysm diameter are the mainstay of aneurysm surveillance and contribute to decisions on timing of intervention. Aneurysm biology plays a key part in disease evolution but is not currently routinely assessed in clinical practice. Magnetic Resonance Imaging (MRI) and Positron Emission Tomography-Computed Tomography (PET-CT) provide insight into disease processes on a cellular or molecular level, and represent exciting new imaging biomarkers of disease activity. Macrophage-mediated inflammation may be assessed using ultrasmall superparamagnetic particles of iron oxide (USPIO) MRI and the PET radiotracer 18FSodium Fluoride (18F-NaF) identifies microcalcification which is a response to underlying necrotic inflammation. The central aim of this thesis was to investigate these imaging modalities in patients with AAA. Methods and Results USPIO MRI: MULTI-CENTRE STUDY In a prospective multi-centre observational cohort study, 342 patients (85.4% male, mean age 73.1±7.2 years, mean AAA diameter 49.6±7.7mm) with asymptomatic AAA ≥4 cm anteroposterior diameter underwent MRI before and 24-36 hours after intravenous administration of USPIO. Colour maps (depicting the change in T2* caused by USPIO) were used to classify aneurysms on the basis of the presence of USPIO uptake in the aneurysm wall, representing mural inflammation. Intra- and inter-observer agreement were found to be very good, with proportional agreement of 0.91 (kappa 0.82) and 0.83 (kappa 0.66), respectively. At 1 year, there was 29.3% discordant classification of aneurysms on repeated USPIO MRI and at 2 years, discordance was 65%, suggesting that inflammation evolves over time. In the observational study, after a mean of 1005±280 days of follow up, there were 126 (36.8%) aneurysm repairs and 17 (5.0%) ruptures. Participants with USPIO enhancement (42.7%) had increased aneurysm expansion rates (3·1±2·5 versus 2·5±2·4 mm/year; difference 0·6 [95% confidence intervals (CI), 0·02 to 1·2] mm/year, p=0·0424) and had higher rates of aneurysm rupture or repair (69/146=47·3% versus 68/191=35·6%; difference 11·7%, 95% CI 1·1 to 22·2%, p=0·0308). USPIO MRI was therefore shown to predict AAA expansion and the composite of rupture or repair, however this was not independent of aneurysm diameter (c-statistic, 0·7924 to 0·7926; unconditional net reclassification -13·5%, 95% confidence intervals -36·4% to 9·3%). 18F-NaF PET-CT: SINGLE-CENTRE STUDY A sub-group of 76 patients also underwent 18F-NaF PET-CT, which was evaluated using the maximum tissue-to-background ratio (TBRmax) in the most diseased segment (MDS), a technique that showed very good intra- (ICC 0.70-0.89) and inter-observer (ICC 0.637-0.856) agreement. Aneurysm tracer uptake was compared firstly in a case-control study, with 20 patients matched to 20 control patients for age, sex and smoking status. 18F-NaF uptake was higher in aneurysm when compared to control aorta (log2TBRmax 1.712±0.560 vs. 1.314±0.489; difference 0.398 (95% CI 0.057, 0.739), p=0.023), or to non-aneurysmal aorta in patients with AAA (log2TBRmax 1.647±0.537 vs. 1.332±0.497; difference 0.314 (95% CI 0.0685, 0.560), p=0.004). An ex vivo study was performed on aneurysm and control tissue, which demonstrated that 18F-NaF uptake on microPET-CT was higher in the aneurysm hotspots and higher in aneurysm tissue compared to control tissue. Histological analysis suggested that 18F-NaF was highest in areas of focal calcification and necrosis. In an observational cohort study, aneurysms were stratified by tertiles of TBRmax in the MDS and followed up for 510±196 days, with 6 monthly serial ultrasound measurements of diameter. Those in the highest tertile of tracer uptake expanded more than 2.5 times more rapidly than those in the lowest tertile (3.10 [3.58] mm/year vs. 1.24 [2.41] mm/year, p=0.008) and were also more likely to experience repair or rupture (15.3% vs. 5.6%, log-rank p=0.043). In multivariable analyses, 18F-NaF uptake on PET-CT emerged as an independent predictor of AAA expansion (p=0.042) and rupture or repair (HR 2.49, 95% CI1.07, 5.78; p=0.034), even when adjusted for age, sex, body mass index, systolic blood pressure, current smoking and, crucially, aneurysm diameter. Conclusion These are the largest USPIO MRI and PET-CT studies in AAA disease to date and the first to investigate 18F-NaF. Both USPIO MRI and 18F-NaF PET-CT are able to predict AAA expansion and the composite of rupture and repair, with 18F-NaF PETCT emerging as the first imaging biomarker that independently predicts expansion and AAA events, even after adjustment for aneurysm diameter. This represents an exciting new predictor of disease progression that adds incremental value to standard clinical assessments. Feasibility and randomised clinical trials are now required to assess the potential of this technique to change the management and outcome of patients with AAA.
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Olivecrona, Henrik. "Assessment of acetabular cup position with computed tomography /." Stockholm, 2004. http://diss.kib.ki.se/2004/91-7349-816-5/.
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Winkelmann, Christopher Todd. "Micro-imaging characterization of mouse models of metastasis." Diss., Columbia, Mo. : University of Missouri-Columbia, 2005. http://hdl.handle.net/10355/5820.
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Thesis (Ph. D.)--University of Missouri-Columbia, 2005.<br>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. Vita. "December 2005" Includes bibliographical references.
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Thomas, Howard David. "Non-destructive evaluation of wood utility poles using computed axial tomography imaging." Diss., Columbia, Mo. : University of Missouri-Columbia, 2006. http://hdl.handle.net/10355/4523.
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Thesis (M.S.) University of Missouri-Columbia, 2006.<br>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 28, 2007) Vita. Includes bibliographical references.
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Mills, J. A. "Theory of longitudinal emission computed tomography and the practical application to cardiac imaging." Thesis, University of Warwick, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383293.
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Villafuerte, Mercedes Rodriguez. "The use of emission-transmission computed tomography for improved quantification in SPECT." Thesis, University College London (University of London), 1994. http://discovery.ucl.ac.uk/1317737/.
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The attenuation of photons within the body has been recognised as the major limiting factor hindering the ability of single photon emission computed tomography (SPECT) as a quantitative technique. This thesis investigates several aspects of an emission-transmission SPECT system using the Monte Carlo method and experimental techniques. The system was based on a rotating gamma camera fitted with a parallel hole collimator. The simulation of a transmission study was performed using a simple non-uniform mathematical phantom with two different external sources, a collimated line source and a flood source. The results showed that the attenuation maps were highly dependent on the geometry and photon energy of the source. The collimated line source produced improved image quality with lower statistical noise than the flood source. The results showed that, when high atomic number elements are present in the tissue composition, the attenuation coefficients at different energies are related through a second order polynomial transformation. If the object under study is formed of soft tissue equivalent materials, a linear transformation holds. The attenuation maps generated in the transmission study were used to correct for non-uniform attenuation compensation of an emission phantom. The results showed that non-uniform attenuation compensation improved image quality and reduced noise when compared to data without attenuation compensation. The presence of scattered photons in the emission data reduced the quality of the images and precluded accurate quantification. Absolute quantification was performed using the percent air sensitivity criterion. The largest difference between the theoretical and the Monte Carlo simulated images was approximately 8%. An emission-transmission myocardial perfusion study was simulated using an anthropomorphic phantom. Two photon energies of clinical interest were used, 75 keV and 140 keV, corresponding to the main photon emission energies of 201Tl and 99mTC. The results showed that 99mTc provided better image quality than 201Tl. Non-uniform attenuation compensation produced a very good agreement between the theoretical prediction and the simulation when scatter-free data were considered. The results presented in this thesis indicate that it is not possible to accomplish accurate attenuation compensation in general situations if scatter correction is not applied.
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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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Clayton, Benjamin James. "Advanced applications of cardiac computed tomography for the difficult-to-image patient." Thesis, University of Plymouth, 2015. http://hdl.handle.net/10026.1/4188.
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Throughout the development of computed tomographic (CT) imaging the challenges of capturing the heart, with its perpetual, vigorous motion, and in particular the tiny detail within the coronary arteries, has driven technological progress. Today, CT is a widely used and rapidly growing modality for the investigation of coronary artery disease, as well as other cardiac pathology. However, limitations remain and particular patient groups present a significant challenge to the CT operator. This thesis adds new knowledge to the assessment of these difficult-to-image patients. It considers patients with artefact from coronary artery calcification or stents, examining the remarkable diagnostic performance of high definition scanning, as well as material subtraction techniques using dual energy CT, alongside ways in which current technology might be revisited and refined with the use of alternative image reconstruction methods. Patients with challenging heart rate or rhythm abnormalities are considered in three studies; how to achieve diagnostic image quality in atrial fibrillation, the safety of an aggressive approach to intravenous beta-blocker use prior to coronary imaging, and the development of patient information to address anxiety as a source of tachycardia and motion artefact. Finally, the novel application of a single source, dual energy CT scanner to additional cardiac information is considered, with studies of myocardial perfusion CT and delayed iodine enhancement imaging, to identify ways in which non-coronary imaging might be exploited to more thoroughly evaluate a patient’s coronary artery status. These findings are presented in the context of developing technology and together offer a range of potential options for operators of cardiac CT when faced with a difficult-to-image patient.
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Dowdy, Regina Alma Evelyn. "Using Computed Tomography to Predict Difficult Tracheal Intubation." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1586195479987532.
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Markwell, Timothy S. "MegaVoltage Cone Beam Computed Tomography with a standard medical linear accelerator." Thesis, Queensland University of Technology, 2015. https://eprints.qut.edu.au/87438/1/Timothy_Markwell_Thesis.pdf.
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Accurate patient positioning is vital for improved clinical outcomes for cancer treatments using radiotherapy. This project has developed Mega Voltage Cone Beam CT using a standard medical linear accelerator to allow 3D imaging of the patient position at treatment time with no additional hardware required. Providing 3D imaging functionality at no further cost allows enhanced patient position verification on older linear accelerators and in developing countries where access to new technology is limited.
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Sanders, William F. IV. "Computed Tomography Reconstruction: Investigating the Effect of Varying Circle Diameter." Wright State University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=wright1308095868.
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Kock, Marcus Cornelius Johannes Maria. "Diagnostic imaging of peripheral arterial disease with multi-detector row computed tomography angiography." [S.l.] : Rotterdam : [The Author] ; Erasmus University [Host], 2007. http://hdl.handle.net/1765/10509.
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ALI', MARCO. "COMPUTED TOMOGRAPHY AND MAGNETIC RESONANCE IMAGING FOR THE STUDY OF CONGENITAL HEART DISEASES." Doctoral thesis, Università degli Studi di Milano, 2019. http://hdl.handle.net/2434/608210.
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Background:
Cardiovascular disease (CVD) is a leading cause of morbidity and mortality worldwide causing in only Europe 3.9 million deaths corresponding the 45% of total deaths. In particular, among CVD, the congenital heart disease (CHD) is one of the most serious heart defect with an incidence of 8 per 1,000 live births.
Purpose:
In recent years, the role of imaging techniques in the diagnosis and follow-up of these patients has become increasingly important due to their progressive technological advancement. This doctoral thesis shows the results that we achieved in the use of cardiac computed tomography (CCT) and cardiac magnetic resonance (CMR) examination in patients with CHD.
Section I – Cardiac computed tomography in CHD patients:
In this chapter, we propose a study showing the possibility to obtain an impressively low ionizing dose reduction in pediatric CHD patients. Indeed, because the CCT can give valuable anatomic information on CHD in children but implies radiation exposure in subjects who are more radiosensitive than adult patients and that have a longer lifetime to develop stochastic effects from radiation, is very important to perform high-quality but low-dose examinations in this kind of patients. Thus, we evaluated a total of 100 pediatric CCT performed using 80, 100, or 120 kVp, showing that a high-quality pediatric CT can be performed using a 64-slice scanner, with a radiation effective dose close to 2 mSv in about 50% of the cases.
Section II – Heart and great vessels CMR evaluation:
In this section, are shown four studies focused on the use of CMR as a non-invasive imaging tool for the morpho-functional evaluation of heart and great vessels in patients with CHD. Concerning the study of heart dysfunction we published one paper on patients with non-obstructive hypertrophic cardiomyopathy (HCM) and another one on patients with functional univentricular heart (FUH); while regarding the study of great vessels we focused on the evaluation of the aortic strain and flow measurement in patients with different CVD, including CHD.
The 2% HCM patients have a left ventricle wall thickness that reaches 13-15 mm, overlapped with those measured in mild forms of HCM. This overlap makes clinically relevant to differentiate athlete’s heart from mild forms of non-obstructive HCM. Thus, we decide to assess the left ventricle wall thickness and the myocardial metabolism of HCM patients compared to competitive athletes (CAs) using the magnetic resonance spectroscopy (MRS). We demonstrated that at the 1H-MRS there is a significant increase in myocardial lipids in HCM patients compared to competitive athletes, leading to the fact that it may be used as an additional final phase of a CMR protocol including standard morphologic and functional imaging in the differential diagnosis between HCM and athlete’s heart.
Starting from the results of an our previous study showing that the inclusion of the hypoplastic chamber during the segmentation of cine images of FC patients may result in a less accurate measurement of the ejection fraction, we decided to validated a blood-threshold (BT) segmentation method for CMR cine images in FUH patients. Thus, we successfully validated in a pool of 44 FUH patients the use of a BT technique for the segmentation of cine images observing that a high intra- and inter-reader reproducibility for the assessment of ventricular stroke volume (SV) and an excellent agreement with aortic flow values used as a benchmark.
Arterial stiffness is one of the earliest manifestations of adverse structural and functional changes within the vessel wall. When the aorta is considered, stiffness is a main determinant of age-related systolic and pulse pressure increase, a major predictor of stroke and myocardial infarction, and has been associated with heart failure. Previous authors showed that ascending aortic strain (AAS) measured at CMR is markedly decreased before the fifth decade of life and that can be considered as an early manifestation of vascular aging. Our aim was to evaluate the AAS in 1,027 consecutive patients with different types of CVD who underwent CMR , showing that differences in age, gender, and cardiovascular disease independently affect ascending aorta strain; in particular the lower ascending aorta strain observed in tetralogy of Fallot (ToF) fosters its assessment during follow-up in adulthood.
Blood flow measurements are based on the segmentation of a vessel contour that may be performed manually or, more typically, semi-automatically, with the use of computer software likely impacting on measurement reproducibility. Reader experience may play a role as well. Thus, we aimed to estimate the intra- and inter-reader reproducibility of blood flow CMR measurements through the ascending aorta and main pulmonary artery in 50 patients affected with CHD or with aortic and/or pulmonary valve disease; also investigating the impact on reproducibility of the reader’s experience with CMR. Our results showed a good-to-excellent reproducibility for all variables except the backward flow of the ascending aorta, with a limited impact of operator’s training.
Section III – To share or not to share our trial data?:
In clinical research, spontaneous data sharing is not yet as common as it is in other fields such as genetics, astronomy or physics. However, the concept of data sharing has been suggested for many reasons, including the patient-centred nature of medical research and healthcare and the expectation that knowledge from existing data should be maximized to benefit all stakeholders. Although a transition to data sharing is a process that will take time and planning, those who adopt the principles and practices of open science will likely benefit from it. In addition, the emergence of data sharing as a potential requirement by some agencies and journals warrants attention by the imaging community. Indeed, from July 1st, 2018 the International Committee of Medical Journal Editors (ICMJE) will require a data sharing statement as a condition of consideration for publication of clinical trials.
Thus, considering the amount of results that we collected in these three years of my PhD program, we asked ourselves about the potential advantages and disadvantages in sharing our source data with the scientific world. Our conclusions, enclosed in a paper published this year on European Radiology, have been discussed in this section.
Conclusions:
Both imaging modalities have limitations and advantages. CMR can evaluate heart function and vessel flow but require a long acquisition time and in same patients a long sedation time. CCT has a very high spatial resolution and short acquisition time but implies ionizing radiation exposure.
This PhD thesis confirms the crucial role of CMR in functional analysis and the relevant possibilities of x-ray dose reduction in CCT, leading the foundations for future studies on the application of imaging techniques in the diagnosis and prognosis of CVD.
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Barreto, Mitya M. "Application of Dual-Energy Computed Tomography to the Evaluation of Coronary Atherosclerotic Plaque." Cleveland State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=csu1266528762.
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Dube, Jonathan. "Follow-up computed tomography imaging in patients who have suffered traumatic brain injury in Zimbabwe." Thesis, Cape Peninsula University of Technology, 2019. http://hdl.handle.net/20.500.11838/2971.
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Thesis (MSc (Radiography))--Cape Peninsula University of Technology, 2019<br>Introduction: Traumatic brain injury (TBI) is frequently associated with mortality and morbidity in low-income countries. Computed Tomography Brain (CTB) imaging aid in the management of patients by accurately exploring primary and secondary brain injuries following trauma. However, there is controversy among researchers on the benefits of follow-up CTB imaging (FCTBI) amongst patients presenting with TBI showing a normal baseline scan. As such, in an attempt to address the contention, the primary focus of this research study was to explore the role of FCTBI with regards to the clinical status of such patients. The secondary focus was to determine the timing of performing FCTBI post TBI. Method: A retrospective cross sectional quantitative design was conducted for this research study. A total sampling strategy was employed on medical records of 85 patients treated at the research site in Zimbabwe. Data were collected over a two year period. Adult patients between the ages of 18 and 75, with TBI and who had a normal first CTBI1 (primary scan done upon hospital admission) were included in this research study. The evolution of different types of brain pathology diagnosed on FCTBI in affected patients were recorded on data collection sheets. An analysis then followed to establish whether the sample patients had developed any neurological complications. Results: The study showed that in 85 patients with TBI, 36% recorded abnormal radiological findings on FCTBI with subdural haematoma (19%) being the most common intracranial lesion followed by intracerebral haemorrhage (8%), subarachnoid haemorrhage (6%) and lastly, pneumocephalus and epidural haematoma (1% respectively). The most frequent causal mechanism of trauma was road traffic accidents (RTAs) at 58%. Males with TBI comprised a higher proportion (53%) than did females (47%). The performance of CTBI1 at 8 hours post trauma occurrence, within a recommended hospital observation period of 20 hours post trauma occurrence, may provide sufficient time for lesions to evolve and thus determine the appropriate patient management. The young adult age group of 26-35 years was found to be more susceptible to TBI. Conclusion: FCTBI was found to be of value in timely detection of evolving intracranial lesions which enabled appropriate management of patients. The current study recommends that patients who exhibit a declining Glasgow Coma Scale (GCS) score and deteriorating neurological status undergo a FCTBI.
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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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Townsend, Katy Louise. "The Use of Radiographs, Dual-energy X-ray Absorptiometry, Quantitative Computed Tomography and Micro-computed Tomography to Determine Local Cancellous Bone Quality in the Canine Proximal Femur." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1336769521.
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Salhani, Maat Bilhal. "Backprojection-then-filtering reconstruction along the most likely path in proton computed tomography." Thesis, KTH, Skolan för teknik och hälsa (STH), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-189495.
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The backprojection-then-filtering algorithm was applied to proton CT data to reconstruct a map of proton stopping power relative to water (RSP) in air, water and bone. Backprojections were performed along three commonly used path estimates for the proton: straight line path, cubic spline path, and most likely path. The proton CT data was obtained through simulations using the GEANT4 simulation toolkit. Two elliptical phantoms were inspected, and an accuracy of 0.2% and 0.8% was obtained for the RSP in water and bone respectively in the region of interest, while the RSP of air was significantly underestimated.
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Moore, Craig Steven. "Optimisation of computed radiography chest imaging utilising a novel simulation technique derived from real patient computed tomography data sets." Thesis, University of Hull, 2011. http://hydra.hull.ac.uk/resources/hull:5762.
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To optimise any medical digital imaging system for chest radiography, it is vital that the images used for optimisation contain projected anatomy, or in other words, anatomical noise. In this thesis, a method to produce and validate a digitally reconstructed radiograph (DRR) computer algorithm that utilises real patient computed tomography (CT) data sets is presented. The algorithm uses a ray casting DRR calculation method to project X-ray pencil beams through CT data and derive the photon energy absorbed in a virtual computed radiography (CR) phosphor. Radiation scatter and CR system noise are added post DRR calculation. Quantitative and qualitative validation has shown the algorithm simulates chest CR images of average and obese patients with realistic anatomical and system noise. This has allowed images to be generated using various X-ray exposure parameters, i.e. tube potential, scatter rejection and receptor dose, which can then be used in the optimisation exercise. However, the algorithm is not without limitations; the impact of these on the resulting images is discussed. Simulated images reconstructed at the various X-ray exposure parameters and techniques were scored by experienced image evaluators; optimum tube potential, scatter rejection technique and receptor doses for clinical CR chest radiography have been derived. At the outset of this work, CR chest exposure factors across the Hull & East Yorkshire Hospitals NHS Trust (HEY) were not standardised, and therefore not optimised; this thesis concludes with recommendations to the HEY Radiology Department for optimum exposure factors and technique for chest radiography. These were implemented across the Trust as a result of this work. In summary, a DRR computer algorithm has been produced (and validated) that adequately simulates anatomical and system noise; image evaluators are able to grade simulated chest images presented at different X-ray exposure parameters in order to optimise radiographic technique for clinical CR chest radiography, without the need for repeat patient exposures.
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ISHIGAKI, TAKEO, MITSUHIKO HIROSE, KIYOKO NAKAMURA, MITSURU IKEDA, KENGO ITO, and NICOLAS MILLA. "FUNDAMENTAL AND CLINICAL EVALUATION OF CHEST COMPUTED TOMOGRAPHY IMAGING IN DETECTABILITY OF PULMONARY NODULE." Nagoya University School of Medicine, 1994. http://hdl.handle.net/2237/16074.
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Houslay, Emma S. "The role of computed tomography and magnetic resonance imaging in patients with cardiovascular disease." Thesis, University of Edinburgh, 2008. http://hdl.handle.net/1842/24716.
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Methods: In 16 patients, coronary artery calcification was assessed twice within 4 weeks by helical computed tomography. As part of a randomised controlled trial, patients received atorvastatin 80 mg daily or matching placebo, and had coronary calcification assessed annually. Fifty patients with previous coronary artery bypass surgery who were listed for diagnostic coronary angiography underwent contrast enhanced computed tomography angiography using a 16-slice computed tomography scanner. Finally, 15 patients with recent symptoms and signs of an acute transient ischaemic attack, amaurosis fugax or stroke underwent magnetic resonance angiography of the carotid arteries using dedicated surface coils. Results: Quantification of coronary artery calcification demonstrated good reproducibility in patients with scores >100 AU. Despite reducing systemic inflammation and halving serum low-density lipoprotein cholesterol concentrations, atorvastatin therapy did not affect the rate of progression of coronary artery calcification. Computed tomography angiography was found to be highly specific for the detection of graft patency. Assessment of plaque characteristics by magnetic resonance scanning in patients with recent acute carotid plaque was feasible and reproducible. Conclusions: Coronary artery calcium scores can be determined in a reproducible manner. Although they correlate well with the presence of atherosclerosis and predict future coronary risk, there is little role for monitoring progression of coronary artery calcification in order to assess the response to lipid lowering therapy. Computed tomography can be used reliably to predict graft patency in patients who have undergone coronary artery bypass grafting, and is an acceptable non-invasive alternative to invasive coronary angiography. Magnetic resonance imaging techniques can be employed in a feasible, timely and reproducible manner to detect plaque characteristics associated with acute atherothrombotic disease.
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Xia, Yan [Verfasser], and Andreas [Akademischer Betreuer] Maier. "Region-of-Interest Imaging with C-arm Computed Tomography / Yan Xia. Gutachter: Andreas Maier." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2016. http://d-nb.info/1095885588/34.
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Fieselmann, Andreas [Verfasser]. "Interventional Perfusion Imaging Using C-arm Computed Tomography: Algorithms and Clinical Evaluation / Andreas Fieselmann." Aachen : Shaker, 2012. http://d-nb.info/106773645X/34.
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Willows, Brooke. "Computed Tomography Perfusion Imaging In Acute Ischemic Stroke: Do The Benefits Outweigh The Costs?" Thesis, The University of Arizona, 2017. http://hdl.handle.net/10150/623622.
Full textAbstract:
A Thesis submitted to The University of Arizona College of Medicine - Phoenix in partial fulfillment of the requirements for the Degree of Doctor of Medicine.<br>Current stroke imaging protocol at Barrow Neurological Institute calls for a noncontrast computed tomography (NCCT), a computed tomography angiography (CTA), and a computed tomography perfusion (CTP) at the time of presentation to the emergency department (ED), and follow up imaging includes magnetic resonance diffusion weighted imaging (MR‐DWI). This information is used to determine the appropriateness and safety of tissue plasminogen activator (tPA) administration. Previous studies have shown the risk for post‐tPA hemorrhagic conversion rises significantly as the size of the infarct core increases. Thus, it is of great importance to have an accurate method of measuring core infarct size in patients presenting with acute ischemic stroke. The purpose of our study is to determine if CTP correctly identifies the infarct core and if post‐tPA hemorrhagic conversion is related to the size of the infarct core and/or the accuracy of CTP in identifying the infarct core. The ultimate goal is to improve patient outcomes by decreasing the morbidity and mortality associated with tPA administration. This study is a retrospective chart review of all patients who presented to the ED during a one year period with signs and symptoms of acute ischemic stroke who then subsequently received tPA. Imaging was also reviewed, including the NCCT, CTA, CTP, and MRDWI for each patient. In this study, MR‐DWI is used as the gold standard for determining the presence or absence of an infarct core. CTP and MR‐DWI are in agreement of the presence of an infarct core in 7 patients, or 10 percent of the time. Similarly, CTP and MR‐DWI are in agreement of the absence of an infarct core in 31 patients, or 44 percent of the time. In the other 32 patients, CTP and MR‐DWI are in disagreement. The percent correlation between CTP and MR‐DWI was found to be 24 percent with a p‐value < 0.05. As for post‐tPA hemorrhagic conversion, 12 percent of patients had hemorrhagic conversion, and when the hemorrhage rate was compared to the size of the infarct core, the odds of post‐tPA hemorrhagic conversion were 56 times higher in the group of patients with infarct cores larger than one‐third of a vascular territory than in patients with smaller infarct cores with a p‐value < 0.001. Although no significant correlation was found between the accuracy of CTP data and the rate of post‐tPA hemorrhagic conversion, patients with concordant CTP and MR data had a 46% lower likelihood of post‐tPA hemorrhagic conversion than did patients with contradictory CTP and MR‐DWI data. Conclusion: Because patients with infarct cores larger than one‐third of a vascular territory are 56 times more likely to hemorrhage than patients with smaller infarct cores and CTP is less accurate than MR‐DWI in identifying the infarct core in patients presenting with acute ischemic stroke, CTP studies should not be part of the acute stroke imaging protocol. Another imaging modality, such as MR‐DWI, may be preferential in the setting of acute ischemic stroke to identify the infarct core.