Academic literature on the topic 'Tomographic reconstruction algorithms'

Non-intrusive acoustic thermometry using an acoustic impulse generator and two microphones is developed and integrated with tomographic techniques to reconstruct temperature contours. A low velocity plume at around 450 °F exiting through a rectangular duct (3.25 by 10 inches) was used for validation and reconstruction. 0.3 % static temperature relative error compared with thermocouple-measured data was achieved using a cross-correlation algorithm to calculate speed of sound. Tomographic reconstruction algorithms, the simplified multiplicative algebraic reconstruction technique (SMART) and least squares method (LSQR), are investigated for visualizing temperature contours of the heated plume. A rectangular arrangement of transmitter and microphones with a traversing mechanism collected two orthogonal sets of acoustic projection data. Both reconstruction techniques have successfully recreated the overall characteristic of the contour; however, for the future work, the integration of the refraction effect and implementation of additional angled projections are required to improve local temperature estimation accuracy. The root-mean-square percentage errors of reconstructing non-uniform, asymmetric temperature contours using the SMART and LSQR method are calculated as 20% and 19%, respectively.<br>Master of Science

Nephrolithiasis can be a painful problem due to presence of kidney stones. Kidney stone is among the common painful disorders of the urinary system. Various imaging modalities are used to diagnose patients with symptoms of renal or urinary tract disease such as plain kidney, ureter, bladder x-ray (KUB), intravenous pyelography (IVP), and computed tomography (CT). As a traditional three-dimensional (3D) nephrolithiasis and kidney stones detection technique, computed tomography (CT) provides detailed cross-sectional images as well as 3D structure of kidney from moving the x-ray beam in a circle around the body. However, the risk of CT scans of the kidney is relatively higher exposure to radiation which is more than regular x-rays. C-arm technique is a new x-ray imaging modality that uses 2D array detector and cone shaped x-ray beam to create 3D information about the scanned object. Both x-ray source and 2D array detector cells mounted on C-shaped wheeled structure (C-arm). A series of projection images are acquired by rotating the C-arm around the patient in along circular path with a single rotation. The characteristic structure of C-arm allows to provide wide variety of movements around the patient that helps to remain the patient stationary during scanning time. In this work, we investigated a C-arm technique to generate a series of tomographic images for nephrolithiasis and detection of kidney stones. C-arm tomographic technique (C-arm tomosynthesis) as a new three dimensional (3D) kidney imaging method that provides a series of two dimensional (2D) images along partial circular orbit over limited view angle. Our experiments were done with kidney phantom which formed from a pig kidney with two embedded kidney stones inside it and low radiation dosage. Radiation dose and scanning time needed for kidney imaging are all dramatically reduced due to the cone beam geometry and also to limitation of angular rotation. To demonstrate the capability of our C-arm tomosynthesis to generate 3D kidney information for kidney stone detection, two groups of tomographic image reconstruction algorithms were developed for C-arm tomosynthesis: direct algorithms such as filtered back projection (FBP) and iterative algorithms such as simultaneous algebraic reconstruction technique (SART), maximum likelihood expectation maximization (MLEM), ordered- subset maximum likelihood expectation maximization (OS-MLEM) and Pre-computed penalized likelihood reconstruction (PPL). Three reconstruction methods were investigated including: pixel-driven method (PDM), ray-driven method (RDM) and distance driven method (DDM). Each method differs in their efficiency of calculation accuracy per computing time. Preliminary results demonstrated the capability of proposed technique to generate volumetric data about the kidney for nephrolithiasis and kidney stone detection by using all investigated reconstruction algorithms. In spite of each algorithms differs in their strategies, embedded kidney stone can be clearly visualized in all reconstruction results. Computer simulation studies were also done on simulated phantom to evaluate the results for each reconstruction algorithm. To mimic kidney phantom, simulated phantom was simulated with two different size kidney stones. Dataset of projection images was collated by using a virtual C-arm tomosynthesis with geometric configuration similar to real technique. All investigated algorithms were used to reconstruct 3D information. Different of image quality functions were applied to evaluate the imaging system and the reconstruction algorithms. The results show the capability of C-arm tomosynthesis to generate 3D information of kidney structures and to identify the size and location of kidney stones with limited amount of radiation dose.

La popularité de l'imagerie TEP à l'yttrium 90 va grandissante. Cependant, la probabilité qu'une désintégration d'un noyau d'yttrium 90 mène à l'émission d'un positon n'est que de 3,2 × 10-5, et les images reconstruites sont par conséquent caractérisées par un niveau de bruit élevé, ainsi que par un biais positif dans les régions de faible activité. Pour corriger ces problèmes, les méthodes classiques consistent à utiliser des algorithmes pénalisés, ou autorisant des valeurs négatives dans l'image. Cependant, une étude comparant et combinant ces différentes méthodes dans le contexte spécifique de l'yttrium 90 manquait encore à l'appel au début de cette thèse. Cette dernière vise donc à combler ce manque. Malheureusement, les méthodes autorisant les valeurs négatives ne peuvent pas être utilisées directement dans le cadre d'une étude dosimétrique, et cette thèse commence donc par proposer une nouvelle méthode de posttraitement des images, visant à en supprimer les valeurs négatives en en conservant les valeurs moyennes le plus localement possible. Une analyse complète multi-objectifs de ces différentes méthodes est ensuite proposée. Cette thèse se termine en posant les prémices de ce qui pourra devenir un algorithme permettant de proposer un jeu d'hyperparamètres de reconstruction adéquats, à partir des seuls sinogrammes<br>Yttrium-90 PET imaging is becoming increasingly popular. However, the probability that decay of a yttrium-90 nucleus will lead to the emission of a positron is only 3.2 × 10-5, and the reconstructed images are therefore characterised by a high level of noise, as well as a positive bias in low activity regions. To correct these problems, classical methods use penalised algorithms or allow negative values in the image. However, a study comparing and combining these different methods in the specific context of yttrium-90 was still missing at the beginning of this thesis. This thesis, therefore, aims to fill this gap. Unfortunately, the methods allowing negative values cannot be used directly in a dosimetric study. Therefore, this thesis starts by proposing a new method of post-processing the images, aiming to remove the negative values while keeping the average values as locally as possible. A complete multi-objective analysis of these different methods is then proposed. This thesis ends by laying the foundations of what could become an algorithm providing a set of adequate reconstruction hyper parameters from sinograms alone

Les techniques de reconstruction tomographique sont toujours un sujet de recherche d'actualité. Des algorithmes de plus en plus sophistiqués s'adaptent de mieux en mieux aux techniques d'acquisition associées. Ces méthodes de reconstruction, malgré les énormes progrès de l'informatique, sont encore dépendantes du temps de calcul des machines, de leur encombrement et de leur coût élevé. Nous présentons un système de reconstruction optique, basé sur l'algorithme de rétroprojection en faisceaux droits parallèles. Les informations des projections sont codées optiquement, grâce à un ensemble modulateur et déflecteur acousto-optiques. Elles forment instantanément les images de rétroprojection optiques. Une caméra CCD placée au foyer image en fin de chaîne optique, assure l'intégration. La même séquence est mise en œuvre pour toutes les projections, et après une révolution complète de la caméra, restée en pause, on obtient sur la cellule l'image reconstruite de la coupe. Le seul facteur limitatif dans le temps concerne le temps d'acquisition des projections, qui est environ d'une seconde dans notre cas. Après avoir validé cette méthode à l'aide de projections simulées, nous avons entrepris de l'associer à un système d'acquisition ultrasonore. L'algorithme mis en œuvre sur la chaîne optique ne correspond pas à une méthode de reconstruction exacte. Cependant les images obtenues restituent correctement les structures explorées. Par ailleurs, dans le but de conduire à une reconstruction exacte, une dernière partie est consacrée aux améliorations envisagées concernant la chaîne optique.

L'étude a été initiée à l'occasion de la disponibilité d'un algorithme itératif de reconstruction en tomographie par émission de positons, qui présente l'avantage d'atteindre la convergence grâce à une méthode de régularisation. Il a donc fallu évaluer ses performances et son éventuel apport en comparaison aux algorithmes de référence, puis étudier l'influence du seul paramètre accessible aux utilisateurs pour une optimisation en clinique. Pour cela, plusieurs tests ont été réalisés, sur fantômes d'abord, puis sur patients car les résultats obtenus n'étaient pas directement transposables en clinique. Cet algorithme a de nombreux avantages par rapport au standard actuel OSEM-MLEM (moins de bruit, meilleur contraste, meilleure détectabilité des lésions) mais pourrait encore être amélioré pour diminuer les artéfacts et la surestimation de certaines métriques, grâce à l'utilisation de fantômes plus anthropomorphiques et l'accès à plus de paramètres de reconstruction. Des travaux sont encore en cours avec l'éditeur<br>This study was initiated to evaluate an iterative reconstruction algorithm in positron emission tomography based on a regularization method to obtain convergence. Our aim was to assess its performance, in comparison with other currently available algorithms and to study the impact of the only parameter available to users for eventual optimization, both using anthropomorphic phantoms and clinical data. We confirm that this algorithm shows several advantages compared to the traditional OSEM-MLEM concerning noise, contrast and detectability. By using anthropomorphic phantoms and with access to more reconstruction parameters, the performance could be further improved to decrease the artefacts and the overestimation of certain metrics. Work in progress

Existe na indústria o interesse em utilizar as informações da tomografia computadorizada a fim de conhecer o interior (i) dos objetos industriais fabricados ou (ii) das máquinas e seus meios de produção. Nestes casos, a tomografia tem como finalidade (a) controlar a qualidade do produto final e (b) otimizar a produção, contribuindo na fase piloto dos projetos e na análise da qualidade dos meios sem interromper a produção. O contínuo controle de qualidade dos meios de produção é a chave mestra para garantir a qualidade e a competitividade dos produtos. O Centro de Tecnologia das Radiações (CTR), do Instituto de Pesquisas Energéticas e Nucleares (IPEN/CNEN-SP) vem desenvolvendo esta tecnologia para fins de análises de processos industriais há algum tempo. Atualmente, o laboratório tem desenvolvido três gerações de tomógrafos: (i) primeira geração; (ii) terceira geração; e (iii) tomógrafo Instant Non-Scanning. Os algoritmos de reconstrução de imagens tomográficas tem uma importância relevante para o funcionamento ideal desta tecnologia. Nesta tese, foram desenvolvidos e analisados os algoritmos de reconstrução de imagens tomográficas para serem implementados aos protocolos experimentais dos tomógrafos. Os métodos de reconstrução de imagem analítico e iterativo foram desenvolvidos utilizando o software Matlab&reg; r2013b. Os algoritmos iterativos apresentaram imagens com melhor resolução espacial comparado com as obtidas pelo método analítico. Entretanto as imagens por método analítico apresentaram menos ruídos. O tempo para obtenção de imagem pelo método iterativo é relativamente elevado, e aumenta conforme aumenta a matriz de pixels da imagem. Já o método analítico fornece imagens instantâneas. Para as reconstruções de imagens utilizando o tomógrafo Instant Non-Scanning, as imagens pelo método analítico não apresentaram qualidade de imagem satisfatória comparada aos métodos iterativos.<br>There is an interest in the industry to use the CT information in order to know the interior (i) of the manufactured industrial objects or (ii) the machines and their means of production. In these cases, the purpose of the tomography systems is to (a) control the quality of the final product and (b) to optimize production, contributing to the pilot phase of the projects and to analyze the quality of the means without interrupting he line production. Continuous quality assurance of the means of production is the key to ensuring product quality and competitiveness. The Radiation Technology Center of the Nuclear and Energy Research Institute (IPEN/CNEN-SP) has been developing this technology for the purpose of industrial analysis. Currently the laboratory has developed three generations of tomography systems: (i) first generation; (ii) third generation; and (iii) Instant Non-Scanning tomography. The algorithms for the reconstruction of tomographic images are of relevant importance for the optimal functioning of this technology. In this PhD thesis, the reconstruction algorithms of tomographic images were developed and analyzed to be implemented to the tomography systems developed. The analytical and iterative image reconstruction methods were developed using the software Matlab&reg; r2013b. The iterative algorithms presented images with better spatial resolution compared to those obtained by the analytical method; however the images of the analytical method presented be less image noisy. The time to obtain the image by the iterative method is high, and increases as the image matrix increases, while the analytical method provides fast images. For images reconstructions using the Instant Non-Scanning tomography system, the images by the analytical method did not present satisfactory image quality compared to the iterative methods.