Spatially Resolved Measurements of Laser Filamentation in Long Scale Length Underdense Plasmas with and without Beam Smoothing

The onset of filamentation, following the interaction of a relatively long (tau(L) similar or equal to 1 ns) and intense (I-L similar or equal to 5 x 10(14) W/cm(2)) laser pulse with a neopentane filled gas bag target, has been experimentally studied via the proton radiography technique, in conditions of direct relevance to the indirect drive inertial confinement fusion scheme. The density gradients associated with filamentation onset have been spatially resolved yielding direct and unambiguous evidence of filament formation and quantitative information about the filamentation mechanism in agreement with previous theoretical modelings. Experimental data confirm that, once spatially smoothed laser beams are used, filamentation is not a relevant phenomenon during the heating laser beams propagation through typical hohlraum gas fills.

Nuclear activation as a high dynamic range diagnostic of laser-plasma interactions

Proton imaging has become a common diagnostic technique for use in laser-plasma research experiments due to their ability to diagnose electric field effects and to resolve small density differences caused through shock effects. These interactions are highly dependent on the use of radiochromic film (RCF) as a detection system for the particle probe, and produces very high-resolution images. However, saturation effects, and in many cases, damage to the film limits the usefulness of this technique for high-flux particle probing. This paper outlines the use of a new technique using contact radiography of (p,n)-generated isotopes in activation samples to produce high dynamic range 2D images with high spatial resolution and extremely high dynamic range, whilst maintaining both energy resolution and absolute flux measurements. (C)007 Elsevier B.V. All rights reserved.

Employing Laser-Accelerated Proton Beams to Diagnose High Intensity Laser-Plasma Interactions

A review of the proton radiography technique will be presented. This technique employs laser-accelerated laminar bunches of protons to diagnose the temporal and spatial characteristic of the electric and magnetic fields generated during high-intensity laser-plasma interactions. The remarkable temporal and spatial resolution that this technique can achieve (of the order of a picosecond and a few microns respectively) candidates this technique as the preferrable one, if compared to other techniques, to probe high intensity laser-matterinteractions.

Electron microscopic features of experimental choroidal neovascularization

We produced choroidal neovascularization in the rhesus monkey by diminishing the blood supply to the inner retina and producing defects in Bruch's membrane by photocoagulation. The neovascular fronds which developed either infiltrated the subretinal space or proliferated through necrotic and gliotic retina into the vitreous cavity. Sequential electron microscopic sections of neovascular fronds in the subretinal space demonstrated that the advancing capillary sprouts were composed of primitive endothelial tubes surrounded by pericytes and enmeshed in a loose basement-membrane-like substance. More mature capillaris and displayed endothelial fenestrations and endothelial-pericyte membranous contacts. Large neovascular fronds developed major feeding vessels that closely resembled normal small choroidal arteries and veins. Retinal pigment epithelial cells in various guises were in constant association with proliferating neovascular networks.

Search protocols for hidden forensic objects beneath floors and within walls

The burial of objects (human remains, explosives, weapons) below or behind concrete, brick, plaster or tiling may be associated with serious crime and are difficult locations to search. These are quite common forensic search scenarios but little has been published on them to-date. Most documented discoveries are accidental or from suspect/witness testimony. The problem in locating such hidden objects means a random or chance-based approach is not advisable. A preliminary strategy is presented here, based on previous studies, augmented by primary research where new technology or applications are required. This blend allows a rudimentary search workflow, from remote desktop study, to non-destructive investigation through to recommendations as to how the above may inform excavation, demonstrated here with a case study from a homicide investigation. Published case studies on the search for human remains demonstrate the problems encountered when trying to find and recover sealed-in and sealed over locations. Established methods include desktop study, photography, geophysics and search dogs:these are integrated with new technology (LiDAR and laser scanning; photographic rectification; close quarter aerial imagery; ground-penetrating radar on walls and gamma-ray/neutron activation radiography) to propose this possible search strategy.

Topology of megagauss magnetic fields and of heat-carrying electrons produced in a high-power laser-solid interaction

The intricate spatial and energy distribution of magnetic fields, self-generated during high power laser irradiation (at Iλ2∼1013-1014W.cm-2.μm2) of a solid target, and of the heat-carrying electron currents, is studied in inertial confinement fusion (ICF) relevant conditions. This is done by comparing proton radiography measurements of the fields to an improved magnetohydrodynamic description that fully takes into account the nonlocality of the heat transport. We show that, in these conditions, magnetic fields are rapidly advected radially along the target surface and compressed over long time scales into the dense parts of the target. As a consequence, the electrons are weakly magnetized in most parts of the plasma flow, and we observe a reemergence of nonlocality which is a crucial effect for a correct description of the energetics of ICF experiments.

Limitations of Dental Panoramic Tomography in the anterior mandible

Dental Panoramic Tomography (DPT) is a widely used and valuable examination in dentistry. One area prone to artefacts and therefore misinterpretation is the anterior region of the mandible. This case study discusses a periapical radiolucency related to lower anterior teeth that is discovered to be a radiographic artefact. Possible causes of the artefact include a pronounced depression in the mental region of the mandible or superimposition of intervertebral spaces. Additional limitations of the DPT image include superimposition of radio-opaque structures, reduced image detail compared to intra-oral views and uneven magnification. These problems often make the DPT inappropriate for imaging the anterior mandible.

CLINICAL RELEVANCE: Panoramic radiography is often unsuitable for radiographic examination of the anterior mandible.

Laser-driven x-ray and neutron source development for industrial applications of plasma accelerators

Pulsed beams of energetic x-rays and neutrons from intense laser interactions with solid foils are promising for applications where bright, small emission area sources, capable of multi-modal delivery are ideal. Possible end users of laser-driven multi-modal sources are those requiring advanced non-destructive inspection techniques in industry sectors of high value commerce such as aerospace, nuclear and advanced manufacturing. We report on experimental work that demonstrates multi-modal operation of high power laser-solid interactions for neutron and x-ray beam generation. Measurements and Monte Carlo radiation transport simulations show that neutron yield is increased by a factor ∼2 when a 1 mm copper foil is placed behind a 2 mm lithium foil, compared to using a 2 cm block of lithium only. We explore x-ray generation with a 10 picosecond drive pulse in order to tailor the spectral content for radiography with medium density alloy metals. The impact of using >1 ps pulse duration on laser-accelerated electron beam generation and transport is discussed alongside the optimisation of subsequent bremsstrahlung emission in thin, high atomic number target foils. X-ray spectra are deconvolved from spectrometer measurements and simulation data generated using the GEANT4 Monte Carlo code. We also demonstrate the unique capability of laser-driven x-rays in being able to deliver single pulse high spatial resolution projection imaging of thick metallic objects. Active detector radiographic imaging of industrially relevant sample objects with a 10 ps drive pulse is presented for the first time, demonstrating that features of 200 μm size are resolved when projected at high magnification.

Laser Driven Neutron Sources: Characteristics, Applications and Prospects

The basics of laser driven neutron sources, properties and possible applications are discussed. We describe the laser driven nuclear processes which trigger neutron generation, namely, nuclear reactions induced by laser driven ion beam (ion n), thermonuclear fusion by implosion and photo-induced nuclear (gamma n) reactions. Based on their main properties, i.e. point source (< 100 μm) and short durations (< ns), different applications are described, such as radiography, time-resolved spectroscopy and pump-probe experiments. Prospects on the development of laser technology suggest that, as higher intensities and higher repetition rate lasers become available (for example, using DPSSL technology), laser driven methodologies may provide neutron fluxes comparable to that achieved by accelerator driven neutron sources in the near future.

Radiological imaging in digital systems: the effect of exposure parameters in diagnostic quality and patient dose

Esta tese pretende contribuir para o estudo e análise dos factores relacionados com as técnicas de aquisição de imagens radiológicas digitais, a qualidade diagnóstica e a gestão da dose de radiação em sistema de radiologia digital. A metodologia encontra-se organizada em duas componentes. A componente observacional, baseada num desenho do estudo de natureza retrospectiva e transversal. Os dados recolhidos a partir de sistemas CR e DR permitiram a avaliação dos parâmetros técnicos de exposição utilizados em radiologia digital, a avaliação da dose absorvida e o índice de exposição no detector. No contexto desta classificação metodológica (retrospectiva e transversal), também foi possível desenvolver estudos da qualidade diagnóstica em sistemas digitais: estudos de observadores a partir de imagens arquivadas no sistema PACS. A componente experimental da tese baseou-se na realização de experiências em fantomas para avaliar a relação entre dose e qualidade de imagem. As experiências efectuadas permitiram caracterizar as propriedades físicas dos sistemas de radiologia digital, através da manipulação das variáveis relacionadas com os parâmetros de exposição e a avaliação da influência destas na dose e na qualidade da imagem. Utilizando um fantoma contrastedetalhe, fantomas antropomórficos e um fantoma de osso animal, foi possível objectivar medidas de quantificação da qualidade diagnóstica e medidas de detectabilidade de objectos. Da investigação efectuada, foi possível salientar algumas conclusões. As medidas quantitativas referentes à performance dos detectores são a base do processo de optimização, permitindo a medição e a determinação dos parâmetros físicos dos sistemas de radiologia digital. Os parâmetros de exposição utilizados na prática clínica mostram que a prática não está em conformidade com o referencial Europeu. Verifica-se a necessidade de avaliar, melhorar e implementar um padrão de referência para o processo de optimização, através de novos referenciais de boa prática ajustados aos sistemas digitais. Os parâmetros de exposição influenciam a dose no paciente, mas a percepção da qualidade de imagem digital não parece afectada com a variação da exposição. Os estudos que se realizaram envolvendo tanto imagens de fantomas como imagens de pacientes mostram que a sobreexposição é um risco potencial em radiologia digital. A avaliação da qualidade diagnóstica das imagens mostrou que com a variação da exposição não se observou degradação substancial da qualidade das imagens quando a redução de dose é efectuada. Propõe-se o estudo e a implementação de novos níveis de referência de diagnóstico ajustados aos sistemas de radiologia digital. Como contributo da tese, é proposto um modelo (STDI) para a optimização de sistemas de radiologia digital.

virtX - Ein rechnergestütztes System zum Training des intraoperativen Einsatzes eines mobilen Bildverstärkers

Hintergrund und Fragestellung: Die korrekte intraoperative Positionierung und Einstellung eines mobilen Bildverstärkers (auch C-Bogen) kann zurzeit theoretisch mit Hilfe von Lehrbüchern erlernt, am Gerät selbst aber nur ohne visuelle Rückmeldung, d.h. ohne ein zur Ausrichtung korrespondierendes Röntgenbild, trainiert werden. Hieraus ergibt sich die Fragestellung, inwiefern das Training der Handhabung und richtigen Einstellung des C-Bogens in verschiedenen Operationsszenarien durch ein C-Bogen Simulationssystem als Teil eines CBT-Systems (Computer Based Training) unterstützt werden kann. Methoden: In Kooperation mit Ärzten aus Unfallchirurgie und Radiologie wurde das computer-basierte Trainingssystem virtX entwickelt. virtX kann dem Nutzer verschiedene Aufgaben zur Einstellung eines C-Bogens stellen und die Ausführung und das Ergebnis bewerten. Die Aufgaben können mit Hilfe eines Autorensystems erstellt und vom Trainierenden in verschiedenen Modi erfüllt werden: im rein virtuellen Modus oder im kombinierten virtuell-realen Modus. Im rein virtuellen Modus steuert der Nutzer den virtuellen C-Bogen in einem virtuellen OP-Saal mittels einer grafisch-interaktiven Benutzungsoberfläche. Im virtuell-realen Modus hingegen wird die Ausrichtung eines realen C-Bogens erfasst und auf den virtuellen C-Bogen übertragen. Während der Aufgabenerfüllung kann der Benutzer zu jeder Zeit ein realitätsnahes, virtuelles Röntgenbild erzeugen und dabei alle Parameter wie Blendenstellung, Röntgenintensität, etc. wie bei einem realen C-Bogen steuern. virtX wurde auf einem dreitägigen Kurs für OP-Personal mit 120 Teilnehmern eingesetzt und auf der Basis von Fragebögen evaluiert. Ergebnisse: Von den Teilnehmern gaben 79 einen ausgefüllten Evaluations-Fragebogen ab. Das Durchschnittsalter der 62 weiblichen und 15 männlichen Teilnehmer (zwei o.A.) lag bei 34 ± 9 Jahren, die Berufserfahrung bei 8,3 ± 7,6 Jahren. 18 Personen (23%) gaben an, gelegentlich mit einem C-Bogen zu arbeiten, 61 (77%) arbeiteten regelmäßig damit. Über 83% der befragten Teilnehmer empfanden virtX als eine sinnvolle Ergänzung zur herkömmlichen Ausbildung am C-Bogen. Das virtuelle Röntgen wurde mit einer Zustimmung von 91% der befragten Teilnehmer als besonders wichtig für das Verständnis der Arbeitsweise eines C-Bogens beurteilt. Ebenso erhielt der kombinierte virtuell-reale Modus mit 84% Zustimmung einen vergleichsweise hohen Stellenwert. Schlussfolgerung: Die Befragung zeichnet ein positives Bild der Akzeptanz des virtX-System als substanzielle Ergänzung zur herkömmlichen Ausbildung am C-Bogen.

Una mamografía le podría salvar la vida

This Spanish language sheet tells about mammograms.

Prevalência, gravidade e fatores associados à cárie precoce da infância no distrito de Lisboa

Tese de doutoramento, Medicina Dentária (Medicina Dentária Preventiva e Comunitária), Universidade de Lisboa, Faculdade de Medicina Dentária, 2014

Finding ‘Good Friday’ An explorative study into the sedimentary structures left from the Good Friday tsunami

Senior thesis written for Oceanography 444

Estudo de caso de malformação congénita, com quantificação do êmbolo em 4 sistemas de suspensão para próteses endosqueléticas transtibiais com encaixe TSB

Introdução – O efeito de êmbolo é um dos principais problemas relacionados com a eficácia de uma prótese. Uma diminuição do mesmo pode levar a uma marcha mais natural através do aumento da propriocetividade. Objetivos – Verificar se existe diferença de valores do efeito de êmbolo entre vários sistemas de suspensão para próteses transtibiais com a utilização de Liners e testar a aplicação de testes de imagiologia na análise da melhor solução protésica para um determinado indivíduo. Metodologia – Foi obtida uma radiografia da prótese em carga na posição ortostática, mantendo o peso do indivíduo igualmente distribuído pelos dois pés. Seguidamente foi realizada outra radiografia no plano sagital com o joelho com 30° de flexão, com a prótese suspensa e um peso de 5kg aplicado na extremidade distal da mesma durante 30 seg. Através destes dois exames efetuaram-se as medições do êmbolo para cada tipo de sistema de suspensão. Resultados – Dos quatro sistemas estudados apenas três apresentam valores de êmbolo, visto que um dos sistemas não criou suspensão suficiente para suportar o peso colocado na extremidade distal da prótese. Através das medições realizadas nos exames imagiológicos dos três sistemas pudemos encontrar variações de efeito de êmbolo que vão dos 47,91mm aos 72,55mm. Conclusão – Através da realização do estudo imagiológico verificaram-se diferenças a nível do efeito de êmbolo nos vários sistemas de suspensão, provando que esta é uma ferramenta viável na avaliação do mesmo. Também através da análise dos resultados ficou notório que o sistema de suspensão Vacuum Assisted Suspention System (VASS) é o que apresenta menos êmbolo.