Comparaison objective de systèmes d'imagerie conventionnelle et numérique en mammographie

L'objectif de ce travail est le développement d'une méthode de caractérisation objective de la qualité d'image s'appliquant à des systèmes de mammographie analogique, utilisant un couple écran-film comme détecteur, et numérique, basé sur une technologie semi-conductrice, ceci en vue de la comparaison de leurs performances. La méthode développée tient compte de la gamme dynamique du détecteur, de la détectabilité de structures de haut contraste, simulant des microcalcifications, et de structures de bas contraste, simulant des opacités (nodules tumoraux). La méthode prend également en considération le processus de visualisation de l'image, ainsi que la réponse de l'observateur. Pour réaliser ceci, un objet-test ayant des propriétés proches de celles d'un sein comprimé, composé de différents matériaux équivalents aux tissus, allant du glandulaire à l'adipeux, et comprenant des zones permettant la simulation de structures de haut et bas contraste, ainsi que la mesure de la résolution et celle du bruit, a été développé et testé. L'intégration du processus de visualisation a été réalisée en utilisant une caméra CCD mesurant directement les paramètres de qualité d'image, à partir de l'image de l'objet-test, dans une grandeur physique commune au système numérique et analogique, à savoir la luminance arrivant sur l'oeil de l'observateur. L'utilisation d'une grandeur synthétique intégrant dans un même temps, le contraste, le bruit et la résolution rend possible une comparaison objective entre les deux systèmes de mammographie. Un modèle mathématique, simulant la réponse d'un observateur et intégrant les paramètres de base de qualité d'image, a été utilisé pour calculer la détectabilité de structures de haut et bas contraste en fonction du type de tissu sur lequel celles-ci se trouvent. Les résultats obtenus montrent qu'à dose égale la détectabilité des structures est significativement plus élevée avec le système de mammographie numérique qu'avec le système analogique. Ceci est principalement lié au fait que le bruit du système numérique est plus faible que celui du système analogique. Les résultats montrent également que la méthodologie, visant à comparer des systèmes d'imagerie numérique et analogique en utilisant un objet-test à large gamme dynamique ainsi qu'une caméra, peut être appliquée à d'autres modalités radiologiques, ainsi qu'à une démarche d'optimisation des conditions de lecture des images.<br/><br/>The goal of this work was to develop a method to objectively compare the performance of a digital and a screen-film mammography system in terms of image quality and patient dose. We propose a method that takes into account the dynamic range of the image detector and the detection of high contrast (for microcalcifications) and low contrast (for masses or tumoral nodules) structures. The method also addresses the problems of image visualization and the observer response. A test object, designed to represent a compressed breast, was constructed from various tissue equivalent materials ranging from purely adipose to purely glandular composition. Different areas within the test object permitted the evaluation of low and high contrast detection, spatial resolution, and image noise. All the images (digital and conventional) were captured using a CCD camera to include the visualization process in the image quality assessment. In this way the luminance reaching the viewer?s eyes can be controlled for both kinds of images. A global quantity describing image contrast, spatial resolution and noise, and expressed in terms of luminance at the camera, can then be used to compare the two technologies objectively. The quantity used was a mathematical model observer that calculates the detectability of high and low contrast structures as a function of the background tissue. Our results show that for a given patient dose, the detection of high and low contrast structures is significantly better for the digital system than for the conventional screen-film system studied. This is mainly because the image noise is lower for the digital system than for the screen-film detector. The method of using a test object with a large dynamic range combined with a camera to compare conventional and digital imaging modalities can be applied to other radiological imaging techniques. In particular it could be used to optimize the process of radiographic film reading.

Cationic and charge segregation in La2/3Ca1/3MnO3 thin films grown on (001) and (110) SrTiO3.

Electron energy-loss spectroscopy is used to map composition and electronic states in epitaxial La2/3Ca1/3MnO3 films grown on SrTiO3 001 and 110 substrates. It is found that in partially relaxed 110 films cationic composition and valence state of Mn3+/4+ ions are preserved across the film thickness. In contrast, in fully strained 001 films, the Ca/La ratio gradually changes across the film, being La rich at film/substrate interface and La depleted at free surface; Mn valence state changes accordingly. These observations suggest that a strongly orientation-dependent adaptative composition mechanism dominates stress accommodation in manganite films and provides microscopic understanding of their dissimilar magnetic properties.

Obtenção de filmes espessos de seleneto de cobre sobre carbono vítreo, ouro, titânio e cobre

Copper selenide (berzelianite) films were prepared on the title substrates using the chemical bath deposition technique (CBD). Film composition was determined by energy dispersion of x-rays. The kinetics of film growth is parabolic and film adherence limits the film thickness. On titanium, copper selenide forms islands that do not completely cover the surface, unless the substrate is prepared with a tin oxide layer; film composition also depends on the titanium oxide layer. On vitreous carbon, CBD and mechanical immobilization techniques lead to films with similar resistances for the electron transfer across the film/substrate interface. On gold, composition studies revealed that film composition is always the same if the pH is in the range from 8 to 12, in contrast to films prepared by an ion-ion combination route. On copper, a new procedure for obtaining copper selenide films as thick as 5 µm has been developed.

Modelling the uptake and growth kinetics of Penicillium glabrum in a tannic acid-containing solid-state fermentation for tannase production

A mathematical growth model for the batch solid-state fermentation process for fungal tannase production was developed and tested experimentally. The unstructured model describes the uptake and growth kinetics of Penicillium glabrum in an impregnated polyurethane foam substrate system. In general, good agreement between the experimental data and model simulations was obtained. Biomass, tannase and spore production are described by logistic kinetics with a time delay between biomass production and tannase and spore formation. Possible induction mechanisms for the latter are proposed. Hydrolysis of tannic acid, the main carbon source in the substrate system, is reasonably well described with Michaelis-Menten kinetics with time-varying enzyme concentration but a more complex reaction mechanism is suspected. The metabolism of gallic acid, a tannase-hydrolysis product of tannic acid, was shown to be growth limiting during the main growth phase. (c) 2004 Elsevier Ltd. All rights reserved.

Structure variation and evolution in microphase-separated grafted diblock copolymer films

The phase behavior of grafted d-polystyrene-block-poly(methyl methacrylate) diblock copolymer films is examined, with particular focus on the effect of solvent and annealing time. It was observed that the films undergo a two-step transformation from an initially disordered state, through an ordered metastable state, to the final equilibrium configuration. It was also found that altering the solvent used to wash the films, or complete removal of the solvent prior to thermal annealing using supercritical CO2, could influence the structure of the films in the metastable state, though the final equilibrium state was unaffected. To aid in the understanding to these experimental results, a series of self-consistent field theory calculations were done on a model diblock copolymer brush containing solvent. Of the different models examined, those which contained a solvent selective for the grafted polymer block most accurately matched the observed experimental behavior. We hypothesize that the structure of the films in the metastable state results from solvent enrichment of the film near the film/substrate interface in the case of films washed with solvent or faster relaxation of the nongrafted block for supercritical CO2 treated (solvent free) films. The persistence of the metastable structures was attributed to the slow reorganization of the polymer chains in the absence of solvent.

Amorphous carbon nitrogenated films prepared by plasma immersion ion implantation and deposition

In this work, an investigation was conducted on amorphous hydrogenated-nitrogenated carbon films prepared by plasma immersion ion implantation and deposition. Glow discharge was excited by radiofrequency power (13.56 MHz, 40 W) whereas the substrate-holder was biased with 25 kV negative pulses. The films were deposited from benzene, nitrogen and argon mixtures. The proportion of nitrogen in the chamber feed (R-N) was varied against that of argon, while keeping the total pressure constant (1.3 Pa). From infrared reflectance-absorbance spectroscopy it was observed that the molecular structure of the benzene is not preserved in the film. Nitrogen was incorporated from the plasma while oxygen arose as a contaminant. X-ray photoelectron spectroscopy revealed that N/C and O/C atomic ratios change slightly with R-N. Water wettability decreased as the proportion of N in the gas phase increased while surface toughness underwent just small changes. Nanoindentation measurements showed that film deposition by means of ion bombardment was beneficial to the mechanical properties of the film-substrate interface. The intensity of the modifications correlates well with the degree of ion bombardment. (c) 2006 Elsevier B.V. All rights reserved.

Effect of the bath pH on the electrodeposition of nanocrystalline Pd-Co alloys and their magnetic properties

The effect of the bath pH on the electrodeposition of nanocrystalline Pd-Co alloys and on their magnetic properties was studied. The pH practically did not affect the alloy composition. Conversely, the pH showed a significant influence on the shape and size of crystallites. Two different crystallites morphology were observed depending on the bath pH. A crystallite size ranging from 18.2 to 30 nm was obtained from X-ray diffractometry (XRD) patterns using the Scherrer's method. Also from the XRD patterns the lattice strain percentage was calculated and correlated with the residual stress, which probably originated during the film electrodeposition on the substrate. Some alloy magnetic properties showed small variations. In contrast, high and unexpected coercivities were obtained reaching a maximum of 1.69 kOe at pH 5.5. The high coercivity values were attributed to the presence of residual stress at the film-substrate interface, which increased as the bath pH and crystallite size decrease, both of them contributing simultaneously to increase in coercivity. (C) 2006 Elsevier B.V. All rights reserved.

Thickness dependence of structure and piezoelectric properties at nanoscale of polycrystalline PZT thin films

Lead zirconate titanate Pb(Zr 0.50Ti 0.50)O 3 (PZT) thin films were deposited by a polymeric chemical method on Pt(111)/Ti/SiO2/Si substrates to understand the mechanisms of phase transformations and the effect of film thickness on the structure, dielectric and piezoelectric properties in these films. PZT films pyrolyzed at temperatures higher than 350 °C present a coexistence of pyrochlore and perovskite phases, while only perovskite phase grows in films pyrolyzed at temperatures lower than 300 °C. For pyrochlore-free PZT thin films, a small (100) orientation tendency near the film-substrate interface was observed. Finally, we demonstrate the existence of a self-polarization effect in the studied PZT thin films. Results suggest that Schottky barriers and/or mechanical coupling near the filmsubstrate interface are not primarily responsible for the observed self-polarization effect in our films. © 2012 IEEE.

Thickness dependence of structure and piezoelectric properties at nanoscale of polycrystalline lead zirconate titanate thin films

Lead zirconate titanate Pb(Zr0.50Ti0.50)O3 (PZT) thin films were deposited by a polymeric chemical method on Pt(111)/Ti/SiO2/Si substrates to understand the mechanisms of phase transformations and the effect of film thickness on the structure, dielectric, and piezoelectric properties in these films. PZT films pyrolyzed at temperatures higher than 350 °C present a coexistence of pyrochlore and perovskite phases, while only perovskite phase grows in films pyrolyzed at temperatures lower than 300 °C. For pyrochlore-free PZT thin films, a small (100)-orientation tendency near the film-substrate interface was observed. Finally, we demonstrate the existence of a self-polarization effect in the studied PZT thin films. The increase of self-polarization with the film thickness increasing from 200 nm to 710 nm suggests that Schottky barriers and/or mechanical coupling near the film-substrate interface are not primarily responsible for the observed self-polarization effect in our films. © 2013 AIP Publishing LLC.

Effect of Composition on the Physical Properties at Nanoscale of PZT Thin Films

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Corrosion resistance of 2024 aluminum alloy coated with plasma deposited a-C:H:Si:O films

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Metodologia númerico-experimental para avaliação da espessura de filmes de nitreto de titânio obtidos por processamento a plasma

In recent decades, changes in the surface properties of materials have been used to improve their tribological characteristics. However, this improvement depends on the process, treatment time and, primarily, the thickness of this surface film layer. Physical vapor deposition (PVD) of titanium nitrate (TiN) has been used to increase the surface hardness of metallic materials. Thus, the aim of the present study was to propose a numerical-experimental method to assess the film thickness (l) of TiN deposited by PVD. To reach this objective, experimental results of hardness (H) assays were combined with a numerical simulation to study the behavior of this property as a function of maximum penetration depth of the indenter (hmax) into the film/substrate conjugate. Two methodologies were adopted to determine film thickness. The first consists of the numerical results of the H x hmax curve with the experimental curve obtained by the instrumental indentation test. This methodology was used successfully in a TiN-coated titanium (Ti) conjugate. A second strategy combined the numerical results of the Hv x hmax curve with Vickers experimental hardness data (Hv). This methodology was applied to a TiN-coated M2 tool steel conjugate. The mechanical properties of the materials studied were also determined in the present study. The thicknesses results obtained for the two conjugates were compatible with their experimental data.

Near-field coupling and resonant cavity modes in plasmonic nanorod metamaterials

Plasmonic resonant cavities are capable of confining light at the nanoscale, resulting in both enhanced local electromagnetic fields and lower mode volumes. However, conventional plasmonic resonant cavities possess large Ohmic losses at metal-dielectric interfaces. Plasmonic near-field coupling plays a key role in a design of photonic components based on the resonant cavities because of the possibility to reduce losses. Here, we study the plasmonic near-field coupling in the silver nanorod metamaterials treated as resonant nanostructured optical cavities. Reflectance measurements reveal the existence of multiple resonance modes of the nanorod metamaterials, which is consistent with our theoretical analysis. Furthermore, our numerical simulations show that the electric field at the longitudinal resonances forms standing waves in the nanocavities due to the near-field coupling between the adjacent nanorods, and a new hybrid mode emerges due to a coupling between nanorods and a gold-film substrate. We demonstrate that this coupling can be controlled by changing the gap between the silver nanorod array and gold substrate.

Seed layer technique for high quality epitaxial manganite films

We introduce an innovative approach to the simultaneous control of growth mode and magnetotransport properties of manganite thin films, based on an easy-to-implement film/substrate interface engineering. The deposition of a manganite seed layer and the optimization of the substrate temperature allows a persistent bi-dimensional epitaxy and robust ferromagnetic properties at the same time. Structural measurements confirm that in such interface-engineered films, the optimal properties are related to improved epitaxy. A new growth scenario is envisaged, compatible with a shift from heteroepitaxy towards pseudo-homoepitaxy. Relevant growth parameters such as formation energy, roughening temperature, strain profile and chemical states are derived.

Computational modeling of laser-induced delamination testing of thin films

Thin film adhesion often determines microelectronic device reliability and it is therefore essential to have experimental techniques that accurately and efficiently characterize it. Laser-induced delamination is a novel technique that uses laser-generated stress waves to load thin films at high strain rates and extract the fracture toughness of the film/substrate interface. The effectiveness of the technique in measuring the interface properties of metallic films has been documented in previous studies. The objective of the current effort is to model the effect of residual stresses on the dynamic delamination of thin films. Residual stresses can be high enough to affect the crack advance and the mode mixity of the delimitation event, and must therefore be adequately modeled to make accurate and repeatable predictions of fracture toughness. The equivalent axial force and bending moment generated by the residual stresses are included in a dynamic, nonlinear finite element model of the delaminating film, and the impact of residual stresses on the final extent of the interfacial crack, the relative contribution of shear failure, and the deformed shape of the delaminated film is studied in detail. Another objective of the study is to develop techniques to address issues related to the testing of polymeric films. These type of films adhere well to silicon and the resulting crack advance is often much smaller than for metallic films, making the extraction of the interface fracture toughness more difficult. The use of an inertial layer which enhances the amount of kinetic energy trapped in the film and thus the crack advance is examined. It is determined that the inertial layer does improve the crack advance, although in a relatively limited fashion. The high interface toughness of polymer films often causes the film to fail cohesively when the crack front leaves the weakly bonded region and enters the strong interface. The use of a tapered pre-crack region that provides a more gradual transition to the strong interface is examined. The tapered triangular pre-crack geometry is found to be effective in reducing the stresses induced thereby making it an attractive option. We conclude by studying the impact of modifying the pre-crack geometry to enable the testing of multiple polymer films.