4-D Tomographic Inference: Application to SPECT and MR-driven PET

Emission tomographic imaging is framed in the Bayesian and information theoretic framework. The first part of the thesis is inspired by the new possibilities offered by PET-MR systems, formulating models and algorithms for 4-D tomography and for the integration of information from multiple imaging modalities. The second part of the thesis extends the models described in the first part, focusing on the imaging hardware. Three key aspects for the design of new imaging systems are investigated: criteria and efficient algorithms for the optimisation and real-time adaptation of the parameters of the imaging hardware; learning the characteristics of the imaging hardware; exploiting the rich information provided by depthof- interaction (DOI) and energy resolving devices. The document concludes with the description of the NiftyRec software toolkit, developed to enable 4-D multi-modal tomographic inference

Structural characterization of solid cellular polymers by X-ray tomography and light scattering

Estudio de los materiales celulares desde un punto de vista de la interacción radiación-materia. Los materiales estudiados corresponden al grupo de espumas micro y submicrocelulares, además de también espumas nanocelulares, que comprenden los materiales más prometedores dentro de este campo de investigación por sus grandes aplicaciones. Las peculiares características de estos nuevos materiales (en particular los muy reducidos tamaños de celda, por debajo de la micra y los extremadamente pequeños espesores de pared celular, del orden de las decenas de los nanómetros) hace que sea necesario desarrollar nuevos métodos de caracterización y/o adaptar los actuales para poder obtener información precisa acerca de los mecanismos que tienen lugar durante el proceso de fabricación y de la estructura celular de los mismos. En esta investigación centraremos nuestra atención en el desarrollo de técnicas basadas en la interacción radiación-materia para analizar estos sistemas. Es importante citar aquí que estás técnicas se han usado muy poco en este tipo de materiales, lo que hará que la investigación a realizar sea novedosa y de gran interés para la comunidad científica que trabaja en el campo de los materiales celulares. En particular, dos grandes técnicas han sido consideradas, la tomografía de rayos-X y el denominado "LIght Scattering". La tomografía de rayos-X permite obtener reconstrucciones 3D de la estructura interna de los materiales con resolución espacial de micras e incluso de nanómetros, lo que ha permitido estudiar por primera vez parámetros estructurales de las espumas consideradas y su influencia en las propiedades físicas. Por otro lado, el Light Scattering, ampliamente utilizado en el caso de materiales celulares en base acuosa, permite de una manera muy sencilla determinar dos parémetros cruciales de la estructura de los materiales celulares, el tamaño de celda y la anisotropía celular. Esta investigación ha conseguido adaptar los resultados existentes en las espumas acuosas para poder aplicar de manera efectiva el Light Scattering para el caso de las espumas poliméricas sólidas. Por último, una vez que ambas técnicas han sido exitosamente aplicadas al estudio de materiales celulares convencionales, han sido aplicadas en materiales celulares no convencionales, lo que ha permitido visualizar por primera vez su estructura en 3D y obtener las primeras evidencias sobre la posibilidad de fabricar materiales celulares poliméricos transparentes, siempre y cuando el tamaño de celdilla sea lo suficientemente pequeño.Departamento de Física de la Materia Condensada, Cristalografía y MineralogíaDoctorado en Físic

Nondestructive Testing Methods and New Applications

Nondestructive testing enables scientists and engineers to evaluate the integrity of their structures and the properties of their materials or components non-intrusively, and in some instances in real-time fashion. Applying the Nondestructive techniques and modalities offers valuable savings and guarantees the quality of engineered systems and products. This technology can be employed through different modalities that include contact methods such as ultrasonic, eddy current, magnetic particles, and liquid penetrant, in addition to contact-less methods such as in thermography, radiography, and shearography. This book seeks to introduce some of the Nondestructive testing methods from its theoretical fundamentals to its specific applications. Additionally, the text contains several novel implementations of such techniques in different fields, including the assessment of civil structures (concrete) to its application in medicine

On-belt Tomosynthesis: 3D Imaging of Baggage for Security Inspection

This thesis describes the design, testing and evaluation of `On-belt Tomosynthesis' (ObT): a cost-e ective baggage screening system based on limited angle digital x-ray tomosynthesis and close-range photogrammetry. It is designed to be retro tted to existing airport conveyor-belt systems and to overcome the limitations of current systems creating a pseudo-3D imaging system by combining x-ray and optical imaging to form digital tomograms. The ObT design and set-up consists of a con guration of two x-ray sources illuminating 12 strip detectors around a conveyor belt curve forming an 180 arc. Investigating the acquired ObT x-ray images' noise sources and distortions, improvements were demonstrated using developed image correction methods. An increase of 45% in image uniformity was shown as a result, in the postcorrection images. Simulation image reconstruction of objects with lower attenuation coe cients showed the potential of ObT to clearly distinguish between them. Reconstruction of real data showed that objects of bigger attenuation di erences (copper versus perspex, rather than air versus perspex) could be observed better. The main conclusion from the reconstruction results was that the current imaging method needed further re nements, regarding the geometry registration and the image reconstruction. The simulation results con rmed that advancing the experimental method could produce better results than the ones which can currently be achieved. For the current state of ObT, a standard deviation of 2 mm in (a) the source coordinates, and 2 in (b) the detector angles does not a ect the image reconstruction results. Therefore, a low-cost single camera coordination and tracking solution was developed to replace the previously used manual measurements. Results obtained by the developed solution showed that the necessary prerequisites for the ObT image reconstruction could be addressed. The resulting standard deviation was of an average of 0.4 mm and 1 degree for (a) and (b) respectively

Space-Varying Iterative Restoration of Diffuse Optical Tomograms Reconstructed by the Photon Average Trajectories Method

The possibility of improving the spatial resolution of diffuse optical tomograms reconstructed by the photon average trajectories (PAT) method is substantiated. The PAT method recently presented by us is based on a concept of an average statistical trajectory for transfer of light energy, the photon average trajectory (PAT). The inverse problem of diffuse optical tomography is reduced to a solution of an integral equation with integration along a conditional PAT. As a result, the conventional algorithms of projection computed tomography can be used for fast reconstruction of diffuse optical images. The shortcoming of the PAT method is that it reconstructs the images blurred due to averaging over spatial distributions of photons which form the signal measured by the receiver. To improve the resolution, we apply a spatially variant blur model based on an interpolation of the spatially invariant point spread functions simulated for the different small subregions of the image domain. Two iterative algorithms for solving a system of linear algebraic equations, the conjugate gradient algorithm for least squares problem and the modified residual norm steepest descent algorithm, are used for deblurring. It is shown that a 27% gain in spatial resolution can be obtained