Continuous improvement of image quality is one of the priorities in medical imaging. Therefore, development of a simulation tool allowing to generate realistic images would be of great value to understand better the impact of the components on the image quality metrics and to choose imaging set-ups or new design features to optimize output of existing systems and to prototype new ones and to formalize the link between objective and subjective image quality metrics. Therefore, the purpose of this project, was to contribute to adaptation and validation of an existing simulator for simulation of C-arm X-ray imaging. Firstly, the study of the existing simulation tool was performed to choose further development axes. Afterwards, preliminary estimations of simulation complexity by evaluating the number of photons for a given imaging examination were performed. Previous studies[1] showed the determining impact of focal spot on imaging performance (reducing the limiting spatial frequency in common examination conditions) of X-ray interventional imaging systems.  Therefore, the work focused on the improvements of source model, in particular realistic focal spot was defined and simulations of images with close-to-real sharpness were performed and compared to experimentally acquired images. Finally, a part of this project was dedicated to scatter study. An experimental set-up and "scatter map" analysis were designed to determine the scatter evolution as function of imaging field-of-view.  First simulations were also performed. [1] Samei, E., Ranger, N., MacKenzie, A., Honey, I., Dobbins, J. and Ravin, C. (2008). Detector or System? Extending the Concept of Detective Quantum Efficiency to Characterize the Performance of Digital Radiographic Imaging Systems 1. Radiology, 249(3), pp.926-937.

Experimental work evaluated the dependence of the thickness of the cutting edge, its roughness and assessment of appearance with regard to the defects resulting from the diameter of the focal spot during oxidative cutting Yb:YAG laser. Other variables include the experiment: process parameters such as laser power, cutting speed, oxygen pressure and focus position. Experiment is based on the Taguchi tables. Test samples were cut off from sheet thickness 10, 15 and 20 mm. Representatives of conventional steel were S235JRC+N, S235JR, S235JR+N and steel type RAEX developed for laser and plasma cutting. Samples were evaluated according to the ČSN EN ISO 9013. The evaluation of samples was into classes according to standards of quality. Hardness measurements were performed on the samples thickness 20 mm of convectional steel and steel type RAEX.

A presente tese demonstra, a partir da avaliação convencional pelo método das Funções de Transferência de sistemas de imagem radiológica, que é necessário obter imagens de fenda em diversas orientações no campo para que essa análise tenha um significado mais real no caso de sistemas não isotrópicos. Isso provém da não linearidade na variação entre as FTMs obtidas para diversas direções 0 e 90&#176C relativas ao eixo do tubo de raios-X. Essa verificação, entretanto, representa um sério problema prático, pois indica um aumento no grau de complexidade de um método que, embora considerado o mais preciso pela maioria dos pesquisadores, tem sido utilizado apenas por laboratórios muito bem equipados. Assim, visando solucionar esse problema, esta tese propõe um novo método de simulação por computador que calcula a FEL e a FTM devidas ao ponto focal, dispensando, portanto, todo o complexo aparato experimental convencionalmente utilizado, o que contribui para tornar acessível à avaliação pelas funções de transferência a qualquer unidade radiológica. Por fim, faz parte desse trabalho também uma investigação do significado físico das variações registradas entre as FTMs e um estudo formal desenvolvido acerca dos conceitos da característica de campo e da magnificação lateral. / From the conventional evaluation by the radiological systems Transfer Functions, this work shows that it is necessary to obtain slit images at several field orientations so that this annalysis has a more real significance for non-isotropic systems. This is achieved from the non-linearity on the variations among the MTFs obtained in several directions between 0 and 90&#176C relative to the X-ray tube axis. This notification, however, represents a serious practical matter, because it shows an increase on the complexity of a method which has been used just by well structured laboratories, although many researchers have considered it the most accurate. Hence, in order to solve this problem, we present a new computer simulation method which calculates the LSF and the MTF due to the focal spot, without all the conventional complex experimental apparatus. This makes the evaluation by the transfer functions suitable to any radiological unit. Finally, it is also part of this work an investigation of the physical meaning of the variations among the MTFs and a formal study about the field characteristics and the lateral magnification concepts.

A presente tese demonstra, a partir da avaliação convencional pelo método das Funções de Transferência de sistemas de imagem radiológica, que é necessário obter imagens de fenda em diversas orientações no campo para que essa análise tenha um significado mais real no caso de sistemas não isotrópicos. Isso provém da não linearidade na variação entre as FTMs obtidas para diversas direções 0 e 90&#176C relativas ao eixo do tubo de raios-X. Essa verificação, entretanto, representa um sério problema prático, pois indica um aumento no grau de complexidade de um método que, embora considerado o mais preciso pela maioria dos pesquisadores, tem sido utilizado apenas por laboratórios muito bem equipados. Assim, visando solucionar esse problema, esta tese propõe um novo método de simulação por computador que calcula a FEL e a FTM devidas ao ponto focal, dispensando, portanto, todo o complexo aparato experimental convencionalmente utilizado, o que contribui para tornar acessível à avaliação pelas funções de transferência a qualquer unidade radiológica. Por fim, faz parte desse trabalho também uma investigação do significado físico das variações registradas entre as FTMs e um estudo formal desenvolvido acerca dos conceitos da característica de campo e da magnificação lateral. / From the conventional evaluation by the radiological systems Transfer Functions, this work shows that it is necessary to obtain slit images at several field orientations so that this annalysis has a more real significance for non-isotropic systems. This is achieved from the non-linearity on the variations among the MTFs obtained in several directions between 0 and 90&#176C relative to the X-ray tube axis. This notification, however, represents a serious practical matter, because it shows an increase on the complexity of a method which has been used just by well structured laboratories, although many researchers have considered it the most accurate. Hence, in order to solve this problem, we present a new computer simulation method which calculates the LSF and the MTF due to the focal spot, without all the conventional complex experimental apparatus. This makes the evaluation by the transfer functions suitable to any radiological unit. Finally, it is also part of this work an investigation of the physical meaning of the variations among the MTFs and a formal study about the field characteristics and the lateral magnification concepts.