Analysis of the scale effect in different computed tomography systems on the evaluation of bone tissue parameters

Tra le patologie ossee attualmente riconosciute, l’osteoporosi ricopre il ruolo di protagonista data le sua diffusione globale e la multifattorialità delle cause che ne provocano la comparsa. Essa è caratterizzata da una diminuzione quantitativa della massa ossea e da alterazioni qualitative della micro-architettura del tessuto osseo con conseguente aumento della fragilità di quest’ultimo e relativo rischio di frattura. In campo medico-scientifico l’imaging con raggi X, in particolare quello tomografico, da decenni offre un ottimo supporto per la caratterizzazione ossea; nello specifico la microtomografia, definita attualmente come “gold-standard” data la sua elevata risoluzione spaziale, fornisce preziose indicazioni sulla struttura trabecolare e corticale del tessuto. Tuttavia la micro-CT è applicabile solo in-vitro, per cui l’obiettivo di questo lavoro di tesi è quello di verificare se e in che modo una diversa metodica di imaging, quale la cone-beam CT (applicabile invece in-vivo), possa fornire analoghi risultati, pur essendo caratterizzata da risoluzioni spaziali più basse. L’elaborazione delle immagini tomografiche, finalizzata all’analisi dei più importanti parametri morfostrutturali del tessuto osseo, prevede la segmentazione delle stesse con la definizione di una soglia ad hoc. I risultati ottenuti nel corso della tesi, svolta presso il Laboratorio di Tecnologia Medica dell’Istituto Ortopedico Rizzoli di Bologna, mostrano una buona correlazione tra le due metodiche quando si analizzano campioni definiti “ideali”, poiché caratterizzati da piccole porzioni di tessuto osseo di un solo tipo (trabecolare o corticale), incluso in PMMA, e si utilizza una soglia fissa per la segmentazione delle immagini. Diversamente, in casi “reali” (vertebre umane scansionate in aria) la stessa correlazione non è definita e in particolare è da escludere l’utilizzo di una soglia fissa per la segmentazione delle immagini.

Can aberrometry provide rapid and reliable measures of subjective depth of focus following multifocal intraocular lens implantation?

Purpose: To determine whether the ‘through-focus’ aberrations of a multifocal and accommodative intraocular lens (IOL) implanted patient can be used to provide rapid and reliable measures of their subjective range of clear vision. Methods: Eyes that had been implanted with a concentric (n = 8), segmented (n = 10) or accommodating (n = 6) intraocular lenses (mean age 62.9 ± 8.9 years; range 46-79 years) for over a year underwent simultaneous monocular subjective (electronic logMAR test chart at 4m with letters randomised between presentations) and objective (Aston open-field aberrometer) defocus curve testing for levels of defocus between +1.50 to -5.00DS in -0.50DS steps, in a randomised order. Pupil size and ocular aberration (a combination of the patient’s and the defocus inducing lens aberrations) at each level of blur was measured by the aberrometer. Visual acuity was measured subjectively at each level of defocus to determine the traditional defocus curve. Objective acuity was predicted using image quality metrics. Results: The range of clear focus differed between the three IOL types (F=15.506, P=0.001) as well as between subjective and objective defocus curves (F=6.685, p=0.049). There was no statistically significant difference between subjective and objective defocus curves in the segmented or concentric ring MIOL group (P>0.05). However a difference was found between the two measures and the accommodating IOL group (P<0.001). Mean Delta logMAR (predicted minus measured logMAR) across all target vergences was -0.06 ± 0.19 logMAR. Predicted logMAR defocus curves for the multifocal IOLs did not show a near vision addition peak, unlike the subjective measurement of visual acuity. However, there was a strong positive correlation between measured and predicted logMAR for all three IOLs (Pearson’s correlation: P<0.001). Conclusions: Current subjective procedures are lengthy and do not enable important additional measures such as defocus curves under differently luminance or contrast levels to be assessed, which may limit our understanding of MIOL performance in real-world conditions. In general objective aberrometry measures correlated well with the subjective assessment indicating the relative robustness of this technique in evaluating post-operative success with segmented and concentric ring MIOL.

Temporal Coding of Volumetric Imagery

'Image volumes' refer to realizations of images in other dimensions such as time, spectrum, and focus. Recent advances in scientific, medical, and consumer applications demand improvements in image volume capture. Though image volume acquisition continues to advance, it maintains the same sampling mechanisms that have been used for decades; every voxel must be scanned and is presumed independent of its neighbors. Under these conditions, improving performance comes at the cost of increased system complexity, data rates, and power consumption.

This dissertation explores systems and methods capable of efficiently improving sensitivity and performance for image volume cameras, and specifically proposes several sampling strategies that utilize temporal coding to improve imaging system performance and enhance our awareness for a variety of dynamic applications.

Video cameras and camcorders sample the video volume (x,y,t) at fixed intervals to gain understanding of the volume's temporal evolution. Conventionally, one must reduce the spatial resolution to increase the framerate of such cameras. Using temporal coding via physical translation of an optical element known as a coded aperture, the compressive temporal imaging (CACTI) camera emonstrates a method which which to embed the temporal dimension of the video volume into spatial (x,y) measurements, thereby greatly improving temporal resolution with minimal loss of spatial resolution. This technique, which is among a family of compressive sampling strategies developed at Duke University, temporally codes the exposure readout functions at the pixel level.

Since video cameras nominally integrate the remaining image volume dimensions (e.g. spectrum and focus) at capture time, spectral (x,y,t,\lambda) and focal (x,y,t,z) image volumes are traditionally captured via sequential changes to the spectral and focal state of the system, respectively. The CACTI camera's ability to embed video volumes into images leads to exploration of other information within that video; namely, focal and spectral information. The next part of the thesis demonstrates derivative works of CACTI: compressive extended depth of field and compressive spectral-temporal imaging. These works successfully show the technique's extension of temporal coding to improve sensing performance in these other dimensions.

Geometrical optics-related tradeoffs, such as the classic challenges of wide-field-of-view and high resolution photography, have motivated the development of mulitscale camera arrays. The advent of such designs less than a decade ago heralds a new era of research- and engineering-related challenges. One significant challenge is that of managing the focal volume (x,y,z) over wide fields of view and resolutions. The fourth chapter shows advances on focus and image quality assessment for a class of multiscale gigapixel cameras developed at Duke.

Along the same line of work, we have explored methods for dynamic and adaptive addressing of focus via point spread function engineering. We demonstrate another form of temporal coding in the form of physical translation of the image plane from its nominal focal position. We demonstrate this technique's capability to generate arbitrary point spread functions.

Evaluation of a ToF Camera for Remote Surveying of Underground Cavities Excavated by Jet Boring

Cigar Lake is a high-grade uranium deposit, located in northern Saskatchewan, Canada. In order to extract the uranium ore remotely, thus ensuring minimal radiation dose to workers and also to access the ore from stable ground, the Jet Boring System (JBS) was developed by Cameco Corporation. This system uses a high-powered water jet to remotely excavate cavities. Survey data is required to determine the final shape, volume, and location of the cavity for mine planning purposes and construction. This paper provides an overview of the challenges involved in remotely surveying a JBS-mined cavity and studies the potential use of a time-of-flight (ToF) camera for remote cavity surveying. It reports on data collected and analyzed from inside an experimental environment as well as on real data acquired on site from the Cigar Lake and Rabbit Lake mines.

Usability of clay mixed red mud in Hungarian building material production industry

The naturally occurring radionuclide (²²⁶Ra,²³²Th and⁴⁰K) content of building Materials (NORM) contributes to the total radiation dose experienced by humans. In this survey 27 clay and 68 red mud samples were surveyed with gamma spectrometry and screened according to European Basic Safety Standards (BSS) I-index. It was found that average I-index of clays was 0.6 (0.4–0.8) less than the I-index of 1, which makes them suitable for building material production. The average I-index of red mud 2.3 (1.3–3.0). The maximal mixing ratio of red mud was calculated, varied between 12 and 39 %, with 23 % average.

A radiologia dentária na gravidez

Aborda-se a biossegurança aplicada a radiologia dentária relativa à radiação ionizante e a exposição aos agentes biológicos, a que pacientes, grávidas / feto e profissionais são submetidos durante os procedimentos radiológicos. As diferentes doses de radiação emitidas, pelos equipamentos utilizados em radiologia oral, quer nos sistemas analógicos, como digitais. As diversas formas de propagação de micro-organismos, durante a obtenção de imagens radiográficas. As medidas de biossegurança, para prevenção desses riscos em radiologia dentária, através da radioprotecção e do controlo da infeção. A radiação ionizante pela sua elevada energia, é capaz de penetrar na matéria, ionizar os átomos, romper ligações químicas e causar danos nos tecidos biológicos. A exposição a doses elevadas de radiação ionizante pode ainda resultar, na destruição de células ou na indução de cancro. Atualmente a biossegurança em radiologia dentária, tem como principais objetivos, a redução da dose de radiação e evitar a infeção cruzada entre os diferentes agentes envolvidos.

Avaliação da qualidade de vida e da autopercepção corporal em mulheres com câncer de mama submetidas à reconstrução mamária

O câncer de mama compõe-se de 22% dos casos novos verificados a cada ano, configurando o segundo tipo de doença mais frequente entre as mulheres. O tratamento para esse tipo de enfermidade, bem como os sintomas apresentados, provocam alterações psicológicas nas mulheres, afetando a dimensão da auto-imagem do dado existencial do ser. Logo, a escolha pela reconstrução mamária tem mostrado uma adaptação da imagem que cada mulher produz de si, e isso concorre para restabelecer o equilíbrio psicológico que é afetado, diante do diagnóstico e da perda da mama. A fisioterapia é essencial tanto na preparação, quanto após a intervenção cirúrgica das pacientes, tendo como premissa a recuperação das suas funções e também, no restabelecimento da sua autoimagem corporal, podendo minimizar os efeitos adversos da reconstrução mamária. Nesse ínterim, em uma forma transversal prospectiva, este estudo teve como objetivo, avaliar a qualidade de vida e da autopercepção corporal em pacientes com câncer de mama submetidas à reconstrução mamária, relacionando a qualidade de vida com a realização ou não da fisioterapia, após o processo da intervenção cirúrgica. Como resultados, observou-se a existência de correlações entre a IC - Imagem Corporal e os domínios da qualidade de vida, com uma correlação moderada significativa apenas no domínio psicológico e que correspondeu à melhor imagem corporal da paciente. Quanto à imagem corporal, todas as pacientes demonstraram um índice satisfatório na escala corporal. Quando comparado à execução ou não da fisioterapia apresentaram igual comportamento para quem fez e para aquelas que não realizaram fisioterapia. Na verificação de quem fez ou não fisioterapia, a satisfação foi superior no grupo que fez, e a insatisfação foi menor nesse grupo do que naquele que não realizou fisioterapia.

Electrical and dielectric properties of uncoated and coated wood-free paper for electrophotography

The print substrate influences the print result in dry toner electrophotography, which is a widely used digital printing method. The influence of the substrate can be seen more easily in color printing, as that is a more complex process compared to monochrome printing. However, the print quality is also affected by the print substrate in grayscale printing. It is thus in the interests of both substrate producers and printing equipment manufacturers to understand the substrate properties that influence the quality of printed images in more detail. In dry toner electrophotography, the image is printed by transferring charged toner particles to the print substrate in the toner transfer nip, utilizing an electric field, in addition to the forces linked to the contact between toner particles and substrate in the nip. The toner transfer and the resulting image quality are thus influenced by the surface texture and the electrical and dielectric properties of the print substrate. In the investigation of the electrical and dielectric properties of the papers and the effects of substrate roughness, in addition to commercial papers, controlled sample sets were made on pilot paper machines and coating machines to exclude uncontrolled variables from the experiments. The electrical and dielectric properties of the papers investigated were electrical resistivity and conductivity, charge acceptance, charge decay, and the dielectric permittivity and losses at different frequencies, including the effect of temperature. The objective was to gain an understanding of how the electrical and dielectric properties are affected by normal variables in papermaking, including basis weight, material density, filler content, ion and moisture contents, and coating. In addition, the dependency of substrate resistivity on the electric field applied was investigated. Local discharging did not inhibit transfer with the paper roughness levels that are normal in electrophotographic color printing. The potential decay of paper revealed that the charge decay cannot be accurately described with a single exponential function, since in charge decay there are overlapping mechanisms of conduction and depolarization of paper. The resistivity of the paper depends on the NaCl content and exponentially on moisture content although it is also strongly dependent on the electric field applied. This dependency is influenced by the thickness, density, and filler contents of the paper. Furthermore, the Poole-Frenkel model can be applied to the resistivity of uncoated paper. The real part of the dielectric constant ε’ increases with NaCl content and relative humidity, but when these materials cannot polarize freely, the increase cannot be explained by summing the effects of their dielectric constants. Dependencies between the dielectric constant and dielectric loss factor and NaCl content, temperature, and frequency show that in the presence of a sufficient amount of moisture and NaCl, new structures with a relaxation time of the order of 10-3 s are formed in paper. The ε’ of coated papers is influenced by the addition of pigments and other coating additives with polarizable groups and due to the increase in density. The charging potential decreases and the electrical conductivity, potential decay rate, and dielectric constant of paper increase with increasing temperature. The dependencies are exponential and the temperature dependencies and their activation energies are altered by the ion content. The results have been utilized in manufacturing substrates for electrophotographic color printing.

Qualidade de imagem em mamografia: apresentação do músculo grande peitoral na incidência oblíqua médio-lateral

A mamografia é, atualmente, o principal método de diagnóstico imagiológico da patologia mamária, sendo, por isso, essencial a produção consistente de imagens mamográficas de elevada qualidade. Assim, e uma vez que a mamografia visa a maximização da visualização do tecido mamário, o principal objetivo deste estudo consiste em investigar a apresentação mamográfica do músculo grande peitoral na incidência oblíqua médio-lateral (OML) da mama. Pretendeu-se relacionar os padrões técnicos de aquisição de imagem à forma de apresentação do referido músculo, avaliando-os de acordo com os atuais critérios de qualidade de imagem. As imagens mamográficas foram recolhidas a partir de duas instituições hospitalares de referência do Porto, sendo posteriormente efetuada uma análise e tratamento estatístico dos indicadores qualitativos e quantitativos de qualidade das mesmas. Numa análise global por instituição, e tendo por base estes indicadores, a instituição que utiliza uma angulação fixa do potter-bucky, independentemente do biótipo corporal da paciente, apresentou resultados melhores, indicando assim que a existência de falhas devido a erros de posicionamento é menor por comparação aos critérios de qualidade padrão. Constatou-se, portanto, que a angulação do potter-bucky tem um impacto relevante e estatisticamente significativo na qualidade das imagens mamográficas.

Optical micro-tomography “OPenT” allows the study of large toadfish Halobatrachus didactylus embryos and larvae

Batrachoidids, which include midshipman and toadfish are less known among embryologists, but are common in other fields. They are characteristic for their acoustic communication, and develop hearing and sound production while young juveniles. They lay large benthic eggs (>5mm) with a thick chorion and adhesive disk and slow development, which are particularly challenging for studying embryology. Here we took advantage of a classical tissue clearing technique and the OPenT open-source platform for optical tomography imaging, to image a series of embryos and larvae from 3 to 30mm in length, which allowed detailed 3D anatomical reconstructions non-destructively. We documented some of the developmental stages (early and late in development) and the anatomy of the delicate stato-acoustic organs, swimming bladder and associated sonic muscles. Compared to other techniques accessible to developmental biology labs, OPenT provided advantages in terms of image quality, cost of operation and data throughput, allowing identification and quantitative morphometrics of organs in larvae, earlier and with higher accuracy than is possible with other imaging techniques.

Desenvolvimento de fontes radioativas seladas imobilizadas em resina epóxi para verificação de detectores utilizados em medicina nuclear

Dissertação (Mestrado em Tecnologia Nuclear)