Low-resource synchronous coincidence processor for positron emission tomography

We developed a new FPGA-based method for coincidence detection in positronemissiontomography. The method requires low device resources and no specific peripherals in order to resolve coincident digital pulses within a time window of a few nanoseconds. This method has been validated with a low-end Xilinx Spartan-3E and provided coincidence resolutions lower than 6 ns. This resolution depends directly on the signal propagation properties of the target device and the maximum available clock frequency, therefore it is expected to improve considerably on higher-end FPGAs.

Technical developments for computed tomography on the CENBG nanobeam line

The use of ion microbeams as probes for computedtomography has proven to be a powerful tool for the three-dimensional characterization of specimens a few tens of micrometers in size. Compared to other types of probes, the main advantage is that quantitative information about mass density and composition can be obtained directly, using specific reconstruction codes. At the Centre d’Etudes Nucléaires de Bordeaux Gradignan (CENBG), this technique was initially developed for applications in cellular biology. However, the observation of the cell ultrastructure requires a sub-micron resolution. The construction of the nanobeamline at the Applications Interdisciplinaires des Faisceaux d’Ions en Region Aquitaine (AIFIRA) irradiation facility has opened new perspectives for such applications. The implementation of computedtomography on the nanobeamline of CENBG has required a careful design of the analysis chamber, especially microscopes for precise sample visualization, and detectors for scanning transmission ion microscopy (STIM) and for particle induced X-ray emission (PIXE). The sample can be precisely positioned in the three directions X, Y, Z and a stepper motor coupled to a goniometer ensures the rotational motion. First images of 3D tomography were obtained on a reference sample containing microspheres of certified diameter, showing the good stability of the beam and the sample stage, and the precision of the motion.

Optimización de los procesos de medida e interpretación de la tomografía geoeléctrica en la prospección superficial

Debido al carácter innovador de los objetivos científico-tecnológicos planteados al inicio de la presente Tesis doctoral, además de la primera recopilación bibliográfica, a lo largo del desarrollo de la misma se ha realizado una actualización bibliográfica continua centrada en los desarrollos relativos a la instrumentación, las aplicaciones y los procesos de interpretación de las técnicas de tomografía eléctrica. Durante el desarrollo del presente trabajo, se han realizado una serie de campañas diferenciadas, tanto por los ambientes geológicos y las condiciones antrópicas en los que se han efectuado los perfiles geoeléctricos, como por la profundidad y los objetivos de la prospección. En esas campañas se han obtenido, mediante el programa Res2DInv, las secciones tomográficas con la configuración de variables por defecto y se ha realizado una interpretación estructural de las mismas. Como parte central del desarrollo de esta investigación se han efectuado varios procesos de optimización: Comparación y optimización de los dispositivos empleados para la medición de perfiles de resistividad de cara a la obtención de secciones tomográficas que presenten la mayor resolución en distintos ambientes geológicos. Selección de los rangos de representación (lineales y logarítmicos) y de la gradación cromática que, pudiendo adoptarse de forma generalizada, permita la mejor interpretación gráfica para usuarios no avanzados. Diseño de criterios para la selección del factor de amortiguamiento, como parámetro crítico en los procesos de inversión tomográfica de perfiles geoeléctricos de superficie, de forma que los modelos resultantes alcancen la mejor relación entre fiabilidad y error respecto a los valores medidos. Paralelamente a los procesos anteriores se ha definido un índice de calidad de la inversión, que es directamente normalizado y que permite evaluar el grado en el que pueden considerarse fiables tanto los valores de resistividad obtenidos como su distribución espacial. El índice desarrollado (IRI) está basado en la influencia que tiene la resistividad inicial del modelo de inversión en los valores de cada una de las celdas de la malla de inversión. Tras un exhaustivo análisis estadístico se ha verificado que, a diferencia de otros índices utilizados hasta la fecha, dicho índice no está afectado ni por la profundidad de investigación y la resolución de los dispositivos, ni por la distribución de resistividades que presente el subsuelo. ABSTRACT Due to the innovative character of the scientific and technological objectives proposed at the beginning of this thesis, in addition to preparatory bibliographic reference, a constant bibliographic update on developments related to instrumentation, applications and interpretation processes for electric tomography has been performed all through the development of the work. Several measuring campaigns were performed during the development of the thesis. These campaigns, in which the geoelectric profiles were measured, varied in several aspects, both in the geological and anthropic conditions, and also in the depth and objectives of the prospection. Tomographic sections were obtained and interpretated by making use of the Res2DInv software configured with the default variables. As part of the core development in this research, several optimization processes have been done: Comparison and optimization of the devices used in the measurement of resistivity profiles. This optimization allows increasing the resolution of tomographic sections in different geological conditions. Selection of the best visual representation for the tomographic sections. This involves the selection of the range of values and type of scale (linear vs. logarithmic) as well as the chromatic graduation. This selection allows improving the interpretation of tomographic sections for the non-expert eye. Devising of criteria for the selection of the damping factor, as the critical parameter in processes of tomographic inversion of superficial geoelectrical profiles. The use of these criteria allows selecting the best factors to obtain the best ratio between reliability and error (in relation to the mean values) for the resulting model. In addition to the aforementioned processes, and as part of the work within this thesis, it has been defined a normalized quality index for inversion. This index allows evaluating the degree of reliability of the obtained resistivity values and spatial distribution. The developed index, termed IRI in the thesis, is based on the influence shown by the initial resistivity of the inversion model on the values of each of the cells of the inversion mesh. After an exhaustive statistical analysis it was verified that the IRI index is neither affected by the investigation depth, nor the resolution of the devices, nor the resistivity’s distribution of the sub soil. This independency is a unique characteristic of the IRI index, not present in other indexes developed and used till date.

Hybrid topological derivative and gradient-based methods for electrical impedance tomography

We present a technique to reconstruct the electromagnetic properties of a medium or a set of objects buried inside it from boundary measurements when applying electric currents through a set of electrodes. The electromagnetic parameters may be recovered by means of a gradient method without a priori information on the background. The shape, location and size of objects, when present, are determined by a topological derivative-based iterative procedure. The combination of both strategies allows improved reconstructions of the objects and their properties, assuming a known background.

Super-Resolution in Respiratory Synchronized Positron Emission Tomography

Respiratory motion is a major source of reduced quality in positron emission tomography (PET). In order to minimize its effects, the use of respiratory synchronized acquisitions, leading to gated frames, has been suggested. Such frames, however, are of low signal-to-noise ratio (SNR) as they contain reduced statistics. Super-resolution (SR) techniques make use of the motion in a sequence of images in order to improve their quality. They aim at enhancing a low-resolution image belonging to a sequence of images representing different views of the same scene. In this work, a maximum a posteriori (MAP) super-resolution algorithm has been implemented and applied to respiratory gated PET images for motion compensation. An edge preserving Huber regularization term was used to ensure convergence. Motion fields were recovered using a B-spline based elastic registration algorithm. The performance of the SR algorithm was evaluated through the use of both simulated and clinical datasets by assessing image SNR, as well as the contrast, position and extent of the different lesions. Results were compared to summing the registered synchronized frames on both simulated and clinical datasets. The super-resolution image had higher SNR (by a factor of over 4 on average) and lesion contrast (by a factor of 2) than the single respiratory synchronized frame using the same reconstruction matrix size. In comparison to the motion corrected or the motion free images a similar SNR was obtained, while improvements of up to 20% in the recovered lesion size and contrast were measured. Finally, the recovered lesion locations on the SR images were systematically closer to the true simulated lesion positions. These observations concerning the SNR, lesion contrast and size were confirmed on two clinical datasets included in the study. In conclusion, the use of SR techniques applied to respiratory motion synchronized images lead to motion compensation combined with improved image SNR and contrast, without any increase in the overall acquisition times.

Detailed damage mechanisms assessment in composite materials by means of X-ray tomography

This research focused on the evaluation of damage formation on ±45º carbon fiber laminates subjected to tensile tests. The damage was evaluated by means of X-ray tomography. A high density of cracks developed during the plateau of the stress-strain curve and were qualitatively analyzed, showing that the inner plies eventually developed a higher crack concentration than the outer plies. Delamination started to occur in the outermost ply interface when the slope after the plateau of the stress-strain curve began to increase.

Estudio de estabilidad de barreras de contención hidráulicas mediante tomografia eléctrica y placa de carga en Zaragoza

El objetivo del presente proyecto es definir las actuaciones encaminadas a restaurar el sistema actual de defensa del río Ebro en el tramo Pradilla de Ebro- Boquiñeni (Zaragoza), con el propósito de reducir el riesgo por inundaciones en los núcleos de población del mismo nombre, para lo que se ha realizado una campaña de reconocimiento del Terreno mediante técnicas geofísicas. La campaña de prospección ha consistido en la realización de perfiles de tomografía eléctrica para determinar la distribución de los niveles geoeléctricos en la zona obteniéndose la profundidad y variabilidad del nivel freático y la distribución aparente de los niveles biológicos. En base a las anomalías detectadas en las secciones de resistividad se han llevado a cabo ensayos in situ con placa de carga dinámica con el fin de determinar las características portantes de las barreras. La correlación de ambos estudios permite localizar las zonas de debilidad estructural para así poder establecer las recomendaciones oportunas de cara a restaurar los diques de protección, de forma que puedan cumplir con su función de contención frente a los caudales de crecida. ABSTRACT The aim of this project is so define the interventions required to restore the current defense system of Ebro River in the stretch between Pradilla de Ebro and Boquiñeni (Zaragoza), in order to reduce flood risk in the population centers of the same name, for what a soil survey has been done using geophysical techniques. The geophysical prospecting campaign has consisted on the realization of electrical tomography profiles to determine the distribution of due geoelectric levels in the area, the depth and variability of the water table and the distribution of apparent lithology level. Based on anomalies detected in resistivity sections, dynamic loading plate test were carried out in situ in order to determine the load bearing characteristics of the safety barriers. The correlation o f both studies makes possible to locate die areas o f structural weakness, with the objective of establishing appropriate recommendations to restore the embankments so that they can meet their retaining functions against flood flows.

Dental Implants Success Prediction: Tomography Based and Data Mining Based Approach.

There are a number of factors that contribute to the success of dental implant operations. Among others, is the choice of location in which the prosthetic tooth is to be implanted. This project offers a new approach to analyse jaw tissue for the purpose of selecting suitable locations for teeth implant operations. The application developed takes as input jaw computed tomography stack of slices and trims data outside the jaw area, which is the point of interest. It then reconstructs a three dimensional model of the jaw highlighting points of interest on the reconstructed model. On another hand, data mining techniques have been utilised in order to construct a prediction model based on an information dataset of previous dental implant operations with observed stability values. The goal is to find patterns within the dataset that would help predicting the success likelihood of an implant.

Automatic quantification of matrix cracking and fiber rotation by X-ray computed tomography in shear-deformed carbon fiber-reinforced laminates

The deformation and damage mechanisms of carbon fiber-reinforced epoxy laminates deformed in shear were studied by means of X-ray computed tomography. In particular, the evolution of matrix cracking, interply delamination and fiber rotation was ascertained as a function of the applied strain. In order to provide quantitative information, an algorithm was developed to automatically determine the crack density and the fiber orientation from the tomograms. The investigation provided new insights about the complex interaction between the different damage mechanisms (i.e. matrix cracking and interply delamination) as a function of the applied strain, ply thickness and ply location within the laminate as well as quantitative data about the evolution of matrix cracking and fiber rotation during deformation

Geometrical characterization of undisturbed soil samples using X-ray computed tomography image analysis. Effect of soil management on soil structure

El estudio de la estructura del suelo es de vital importancia en diferentes campos de la ciencia y la tecnología. La estructura del suelo controla procesos físicos y biológicos importantes en los sistemas suelo-planta-microorganismos. Estos procesos están dominados por la geometría de la estructura del suelo, y una caracterización cuantitativa de la heterogeneidad de la geometría del espacio poroso es beneficiosa para la predicción de propiedades físicas del suelo. La tecnología de la tomografía computerizada de rayos-X (CT) nos permite obtener imágenes digitales tridimensionales del interior de una muestra de suelo, proporcionando información de la geometría de los poros del suelo y permitiendo el estudio de los poros sin destruir las muestras. Las técnicas de la geometría fractal y de la morfología matemática se han propuesto como una poderosa herramienta para analizar y cuantificar características geométricas. Las dimensiones fractales del espacio poroso, de la interfaz poro-sólido y de la distribución de tamaños de poros son indicadores de la complejidad de la estructura del suelo. Los funcionales de Minkowski y las funciones morfológicas proporcionan medios para medir características geométricas fundamentales de los objetos geométricos tridimensionales. Esto es, volumen, superficie, curvatura media de la superficie y conectividad. Las características del suelo como la distribución de tamaños de poros, el volumen del espacio poroso o la superficie poro-solido pueden ser alteradas por diferentes practicas de manejo de suelo. En este trabajo analizamos imágenes tomográficas de muestras de suelo de dos zonas cercanas con practicas de manejo diferentes. Obtenemos un conjunto de medidas geométricas, para evaluar y cuantificar posibles diferencias que el laboreo pueda haber causado en el suelo. ABSTRACT The study of soil structure is of vital importance in different fields of science and technology. Soil structure controls important physical and biological processes in soil-plant-microbial systems. Those processes are dominated by the geometry of soil pore structure, and a quantitative characterization of the spatial heterogeneity of the pore space geometry is beneficial for prediction of soil physical properties. The technology of X-ray computed tomography (CT) allows us to obtain three-dimensional digital images of the inside of a soil sample providing information on soil pore geometry and enabling the study of the pores without disturbing the samples. Fractal geometry and mathematical morphological techniques have been proposed as powerful tools to analyze and quantify geometrical features. Fractal dimensions of pore space, pore-solid interface and pore size distribution are indicators of soil structure complexity. Minkowski functionals and morphological functions provide means to measure fundamental geometrical features of three-dimensional geometrical objects, that is, volume, boundary surface, mean boundary surface curvature, and connectivity. Soil features such as pore-size distribution, pore space volume or pore-solid surface can be altered by different soil management practices. In this work we analyze CT images of soil samples from two nearby areas with contrasting management practices. We performed a set of geometrical measures, some of them from mathematical morphology, to assess and quantify any possible difference that tillage may have caused on the soil.