Fluorescent x-ray screens are used in medical x-ray diagnostics to absorb x-ray photons and convert these x-ray photons to visible light. The light distribution from these screens are then registered on photographic film to give an x-ray image. Both the sensitivity and the resolution characteristics of these systems are dependent on the x-ray photon energy. To enable a study of these and some other energy dependent characteristics of x-ray screens a number of almost monoener-getic radiation sources were constructed, tested with regard to their purity and calibrated. Both film and a photo-multiplier tube were used as light detectors.The sensitivity of screens with three different screen phosphors were studied as a function of the photon energy and large variations in sensitivity was found for different photon energies and screen phosphors. The light from the screens has been compared to the absorbed energy in the screens and this comparison shows that the energy dependence of the screens can approximately be predicted by calculations of the absorbed energy, except at low photon energies where other effects like increased light absorption in the screens is present.The modulation transfer factor (MTF) was studied both experimentally and theoretically as a function of photon energy. Two effects were shown to influence the energy dependence of the MTF. At low energies an increased light diffusion will destroy the MTF and at energies above the K-edge of the high-Z elements in the screens the production and re-absorption of K-radiation will deteriorate the MTF.Both the energy dependence of the screen-film sensitivity and the MTF have been calculated for some normally used spectral distributions from x-ray tubes and significant changes due to choice of kV and filtration of the beam were found. Other effects such as the number of interacting photons in the screens per unit area, contribution of K-radiation from one screen to the other, and light contribution to the front emulsion of the film compared to the back emulsion have also been investigated as a function of photon energy.Optimization of x-ray systems and clinical routines to give the lowest possible radiation dose to the patient with an acceptable image quality is an important task to carry out. The energy dependent characteristi es of x-ray screens studied in this work is a lead in the optimizing of the system with regard to choice of x-ray screens, film and radiation quality. / digitalisering@umu

O presente trabalho de pesquisa trata da investigação de parâmetros de qualidade aplicados a sistemas de imagem em radiologia odontológica. Para isso, foram levantados parâmetros propostos pela Portaria nº 453 de 1998 da Secretaria de Vigilância Sanitária do Ministério da Saúde em aparelhos de raios X odontológicos e determinadas funções de transferência de modulação (FTM), como método para a avaliação da resolução espacial de sistemas de radiologia odontológica digital. Com base nesses dados, comparou-se três sistemas digitais diretos (DIGORA, DENOPTIX e CygnusRay) e um sistema digital indireto, baseado no scanner Umax PowerLook 1120. Essa comparação evidenciou, para esse caso, a melhor qualidade, em termos de resolução espacial, do sistema indireto estudado e a relativa equivalência dos sistemas digitais entre si, quando comparados em suas resoluções máximas (em número de pontos por polegada). Também foi possível validar o uso do método de simulação computacional para a obtenção da FTM de sistemas radiográficos odontológicos / This work has investigated quality parameters applied to odontologic radiographic image systems. In order to achieve this purpose, parameters related to the Portaria nº 453 of 1998 of Secretaria de Vigilância Sanitária do Ministério da Saúde have been checked and modulation transfer functions (MTF) have been determined. These information has been used to compare three differents direct radiographic images systems (DIGORA, DENOPTIX e CygnusRay) and one indirect, based on scanner Umax PowerLook 1120. The obtained data has showed, in this case, the better performance, in terms of spatial resolution, of the indirect system and the relative equivalency of the direct systems, when configured with the maximum resolution (in term of dpi). The work has validated the computer simulation process in order to generate the MTF of odontologic radiographic image systems

Este trabalho tem por objetivo o desenvolvimento de uma nova técnica de pré-processamento de imagens mamográficas digitais para melhorar o desempenho dos esquemas computacionais de auxílio ao diagnóstico (CAD) e para auxiliar na detecção precoce do câncer de mama. O método proposto efetua uma restauração nas imagens mamográficas utilizando, em uma primeira etapa, a transformada de Anscombe e o filtro de Wiener para redução do ruído quântico. Posteriormente, é utilizado o filtro inverso da função de transferência de modulação (MTF) do sistema de imagem para realce das estruturas de interesse na mamografia, como as microcalcificações, que podem ser um indicativo de câncer de mama em seu estágio inicial. Imagens mamográficas restauradas pelo método proposto foram utilizadas na avaliação de um esquema CAD para detecção automática de microcalcificações. Os resultados mostraram que o desempenho do esquema CAD apresentou uma melhora significativa quando imagens restauradas foram utilizadas, mesmo para imagens de mamas densas, que resultam normalmente em baixa taxa de detecção devido ao baixo contraste. / This work aims to developing a new technique for pre-processing digital mammographic images in order to improve the performance of computer aided-diagnosis schemes (CAD) and to assist in early detection of breast cancer. The proposed method performs a restoration in mammographic images using in a first step, the Anscombe transform and Wiener filtering to reduce image quantum noise. Subsequently, it was used the inverse modulation transfer function filtering (MTF) considering the imaging system to enhance structures of interest in mammography, such as microcalcifications, which may be an indicative of breast cancer in its early stage. Mammographic images restored by the proposed method were used in the evaluation of a CAD scheme for automatic detection of microcalcifications. The results showed that the performance of the CAD scheme had a significant improvement when restored images were used, even for images of dense breasts, which often results in low detection rate due to low contrast.

Ces travaux sur la stabilisation de la Ligne de Visée d’un dispositif optronique s’inscrivent dans le contexte actuel de durcissement des exigences de stabilisation et de réduction du temps accordé à la synthèse des lois de commande.Ils incluent dans un premier temps l’amélioration de la performance intrinsèque de stabilisation du système. La solution proposée ici est l’ajout d’un étage de stabilisation supplémentaire à une structure de stabilisation existante. L’architecture de ce nouvel étage est définie. Les composants sont choisis parmi les technologies existantes puis caractérisés expérimentalement. Un modèle complet du système à deux étages de stabilisation est ensuite proposé.L’objectif de ces travaux comprend également la simplification des procédures d’élaboration des lois de commande par l’utilisation d’une fonction de coût F incluant notamment la Fonction de Transfert de Modulation (qui quantifie le flou introduit par l’erreur de stabilisation dans l’image) en lieu et place ducritère dérivé usuel qui nécessite des vérifications supplémentaires et qui peut s’avérer conservatif.L’évaluation de F étant coûteuse en temps de calcul, un algorithme d’optimisation bayésienne, adapté à l’optimisation des fonctions coûteuses, permet la synthèse des lois de commande du système dans un temps compatible avec les contraintes industrielles, à partir de la modélisation du système précédemment proposée. / The presented work on the Line of Sight stabilization of an optronic device meets the heightened demands regarding stabilization performances that come with the reduction of the time allowed to controller tuning.It includes the intrinsinc improvement of the system stabilization. The proposed solution features a double stabilization stage built from a single stabilization stage existing system. The new architecture is specified and the new components are chosen among the existing technology and experimentally characterized. A complete double stabilization stage model is then proposed.The simplification of the controller tuning process is another goal. The designed cost function F includes a high-level optronic criterion, the Modulation Transfer Function (that quantifies the level of blur broughtinto the image by the residual motion of the platform) instead of the usual low-level and potentially conservative criterion.The function F is costly to evaluate. In order to tune the controller parameters within industrial time constraints, a Bayesian algorithm, adapted to optimization with a reduced budget of evaluations, is implemented.Controllers of both stabilization stages are simultaneously tuned thanks to the previously developped system model.

Approved for public release, distribution is unlimited / In this study, the use of multi narrow-band filters was explored to correlate or fuse information to improve detection and recognition for specific targets of interest. To fully understand the viability and limitations of narrow band filters in thermal imaging, laboratory test procedures were first designed to characterize thermal images using common performance parameters, particularly the Noise Equivalent Temperature Difference (NETD), the Modulation Transfer Function (MTF) and the Minimum Resolvable Temperature (MRT). An available thermal imager, the Cincinnati Electronics IRRIS-256LN, and a newly purchased thermal imager, the Indigo Systems Merlin InSb Laboratory Camera, were investigated and compared. The MRT measurement showed a superior cut-off spatial frequency of 1.33 cycle/mrad for the Merlin camera, compared with 1.18 cycle/mrad for the Cincinnati, with similar sensitivity of about 0.1 ʻC for both cameras. Below cut-off the Modulation Transfer for the Merlin was approximately twice that of the Cincinnati. NETD measurements for both systems were inhibited by excess noise in the measurement system. The Merlin camera was consequently employed for further research on narrow band images. Three commercially available narrow band filters, 4110/4720 nm, 4540/4720 nm and 3750/4020 nm, were selected to isolate the "red" and "blue" spike signatures of plume emission and aerodynamic heating found in the signature of fast moving air targets. Similar sensor characterization was carried out with these filters, however, quantitative performance parameter measurements were hindered by excessive measurement system noise. As a preliminary study in multi-spectral image analysis, spectral features of hydrocarbon combustion were extracted from correlated narrow-band images of a laboratory propane flame. Digital analysis using software statistical tools showed potential for discrimination of hydrocarbon emission from other thermal sources by correlating pixel number and pixel radiant intensity. / Captain, Singapore Armed Forces

Approved for public release; distribution in unlimited. / Night Vision Devices (NVD) using Image Intensification (II) technology are among the most important sensors used by ground troops and aviators in night operations for modern combat. With the intensified images from these devices, soldiers can see an enemy's movement better and further in darkness. This thesis explores different test methods in evaluating the performances and sensitivities of several NVDs for future image fusion studies. Specification data such as sensitivity, resolution (Modulation Transfer Function) and pixel size are obtained. Comparative analyses of the collected results are made to characterize the performances of the different NVDs. A new method using MATLAB programming to objectively analyze digitized images for characterization of II based NVDs is proposed. This test method can also be extended to the evaluation of Thermal Imaging (TI) systems for comparative analysis with II NVDs. In addition, the feasibility of testing NVDs using both II and TI technologies, with common operating conditions and target boards is discussed. Finally, the potential of using these digitized images for image fusion studies is verified with the test and evaluation results. / Republic of Singapore

Um grande número de equipamentos utilizam sistemas ópticos ou eletro-ópticos em suas estruturas, dentre esses equipamentos tem-se os microscópios, telescópios, equipamentos médicos, câmeras de satélites, entre outros. Com isso a necessidade de métodos e ferramentas que auxiliem na determinação do desempenho e da qualidade dos sistemas ópticos é crescente. Um dos métodos mais utilizados para realizar a análise de sistemas ópticos é a determinação da Função de Transferência de Modulação (Modulation Transfer Function - MTF). A MTF representa uma verificação quantitativa e direta da qualidade da imagem, e, além disso, é um teste objetivo que pode ser utilizado em sistemas ópticos concatenados. Esse trabalho apresenta a implementação de um software, denominado de SMTF (Software Modulation Transfer Function), para cálculo da MTF de equipamentos eletro-ópticos. O software foi utilizado para realizar o cálculo da MTF do Retinógrafo Digital, Imageador Termal e Microscópio Cirúrgico Oftalmológico. A informação da MTF auxilia na análise do alinhamento e medição da qualidade óptica, e também define o limite de resolução dos sistemas ópticos, por meio do gráfico da MTF. Os resultados obtidos, com o Retinógrafo e o Imageador Termal, foram comparados com os valores teóricos adquiridos pelo Zemax, que é um software utilizado para desenvolvimento e análise de lentes ou conjuntos ópticos. Já para o Microscópio os resultados obtidos da MTF foram comparados com os resultados obtidos pela MTF medida do Microscópio marca Zeiss, considerado como padrão de qualidade de Microscópios Oftalmológicos. Os resultados obtidos demonstram que o software apresentou ótimo desempenho permitindo uma análise direta e objetiva do comportamento de sistemas ópticos. Com auxílio do software foi feito o alinhamento do Retinógrafo Digital e do Imageador Termal e foi verificada a qualidade da imagem do Microscópio Cirúrgico Oftalmológico. / A number of devices use optics or electro-optics in their structures, such as microscopes, telescopes, medical equipments, satellites cameras, among others. The need for methods and tools that assist in determining the performance and quality of optical systems is increasing. One of the methods most used to perform analysis of optical systems is to measure the Modulation Transfer Function (MTF). The MTF represents a direct and quantitative verification of the image quality, and moreover, it is an objective test that can be used in concatenated optical systems. This paper presents the implementation of software, called SMTF (Software Modulation Transfer Function), in order to calculate the MTF of electro-optical systems. The software was used for calculating the MTF of Digital Fundus Camera, Thermal Imager and Ophthalmologic Surgery Microscope. The information MTF aids the analysis of alignment and measurement of optical quality, and also defines the limit resolution of optical systems, from the graph of MTF. The results obtained with the Fundus Camera and de Thermal Imager were compared with the theorical values acquired by the Zemax, wich is a software used for analysis and development of optical assemblies or lenses. For the Microscope, the results were compared with MTF measured of Microscope Zeiss model, which is the quality standard of ophthalmological microscope. The results show that the software has a good performance by allowing a straightforward analysis of the behavior of optical systems. With the aid of the software was made to align the Fundus Camera and the Thermal Imager and the image quality of Surgical Microscope Ophthalmology was verified.

Esta tese propõe um método de avaliação de sistemas de obtenção de imagem radiológica através das Funções de Transferência simuladas para qualquer região do campo de radiação. Esse processo de simulação reflete as mudanças sofridas pelo ponto focal e, portanto, pela Função de Espalhamento de Ponto (FEP) ao longo do campo. A avaliação utiliza informações obtidas de Funções de Transferência ótica bi-dimensionais calculadas através da aplicação de Transformadas de Fourier sobre as Funções de Espalhamento de Ponto simuladas. O método permite realizar um mapeamento da resposta em freqüências espaciais dos sistemas radio1ógicos para todo o campo de radiação, comparar a nitidez da imagem de sistemas distintos com relação a regiões equivalentes e estudar uma região especifica para prever as distorções que serão inseridas na imagem. / In this work a method of evaluation for the radiological imaging systems performance by simulated transfer functions for any X-ray field region is proposed. The simulation procedures provide information of the changes of the focal spot sizes and, therefore, of the Point Spread Function (PSF) along the field. The evaluation yields the bi-dimensional optical Transfer Functions calculated from Fourier Transformation of the simulated PSFs. This method provides: the spatial frequency response for the entire radiation field of the radiological systems; comparisons of the image sharpness relative to equivalent field regions for different systems; and the study of a singular region in order to predict image distortions.

Esta tese propõe um método de avaliação de sistemas de obtenção de imagem radiológica através das Funções de Transferência simuladas para qualquer região do campo de radiação. Esse processo de simulação reflete as mudanças sofridas pelo ponto focal e, portanto, pela Função de Espalhamento de Ponto (FEP) ao longo do campo. A avaliação utiliza informações obtidas de Funções de Transferência ótica bi-dimensionais calculadas através da aplicação de Transformadas de Fourier sobre as Funções de Espalhamento de Ponto simuladas. O método permite realizar um mapeamento da resposta em freqüências espaciais dos sistemas radio1ógicos para todo o campo de radiação, comparar a nitidez da imagem de sistemas distintos com relação a regiões equivalentes e estudar uma região especifica para prever as distorções que serão inseridas na imagem. / In this work a method of evaluation for the radiological imaging systems performance by simulated transfer functions for any X-ray field region is proposed. The simulation procedures provide information of the changes of the focal spot sizes and, therefore, of the Point Spread Function (PSF) along the field. The evaluation yields the bi-dimensional optical Transfer Functions calculated from Fourier Transformation of the simulated PSFs. This method provides: the spatial frequency response for the entire radiation field of the radiological systems; comparisons of the image sharpness relative to equivalent field regions for different systems; and the study of a singular region in order to predict image distortions.

Um grande número de equipamentos utilizam sistemas ópticos ou eletro-ópticos em suas estruturas, dentre esses equipamentos tem-se os microscópios, telescópios, equipamentos médicos, câmeras de satélites, entre outros. Com isso a necessidade de métodos e ferramentas que auxiliem na determinação do desempenho e da qualidade dos sistemas ópticos é crescente. Um dos métodos mais utilizados para realizar a análise de sistemas ópticos é a determinação da Função de Transferência de Modulação (Modulation Transfer Function - MTF). A MTF representa uma verificação quantitativa e direta da qualidade da imagem, e, além disso, é um teste objetivo que pode ser utilizado em sistemas ópticos concatenados. Esse trabalho apresenta a implementação de um software, denominado de SMTF (Software Modulation Transfer Function), para cálculo da MTF de equipamentos eletro-ópticos. O software foi utilizado para realizar o cálculo da MTF do Retinógrafo Digital, Imageador Termal e Microscópio Cirúrgico Oftalmológico. A informação da MTF auxilia na análise do alinhamento e medição da qualidade óptica, e também define o limite de resolução dos sistemas ópticos, por meio do gráfico da MTF. Os resultados obtidos, com o Retinógrafo e o Imageador Termal, foram comparados com os valores teóricos adquiridos pelo Zemax, que é um software utilizado para desenvolvimento e análise de lentes ou conjuntos ópticos. Já para o Microscópio os resultados obtidos da MTF foram comparados com os resultados obtidos pela MTF medida do Microscópio marca Zeiss, considerado como padrão de qualidade de Microscópios Oftalmológicos. Os resultados obtidos demonstram que o software apresentou ótimo desempenho permitindo uma análise direta e objetiva do comportamento de sistemas ópticos. Com auxílio do software foi feito o alinhamento do Retinógrafo Digital e do Imageador Termal e foi verificada a qualidade da imagem do Microscópio Cirúrgico Oftalmológico. / A number of devices use optics or electro-optics in their structures, such as microscopes, telescopes, medical equipments, satellites cameras, among others. The need for methods and tools that assist in determining the performance and quality of optical systems is increasing. One of the methods most used to perform analysis of optical systems is to measure the Modulation Transfer Function (MTF). The MTF represents a direct and quantitative verification of the image quality, and moreover, it is an objective test that can be used in concatenated optical systems. This paper presents the implementation of software, called SMTF (Software Modulation Transfer Function), in order to calculate the MTF of electro-optical systems. The software was used for calculating the MTF of Digital Fundus Camera, Thermal Imager and Ophthalmologic Surgery Microscope. The information MTF aids the analysis of alignment and measurement of optical quality, and also defines the limit resolution of optical systems, from the graph of MTF. The results obtained with the Fundus Camera and de Thermal Imager were compared with the theorical values acquired by the Zemax, wich is a software used for analysis and development of optical assemblies or lenses. For the Microscope, the results were compared with MTF measured of Microscope Zeiss model, which is the quality standard of ophthalmological microscope. The results show that the software has a good performance by allowing a straightforward analysis of the behavior of optical systems. With the aid of the software was made to align the Fundus Camera and the Thermal Imager and the image quality of Surgical Microscope Ophthalmology was verified.