The impact of Sinogram-Affirmed Iterative Reconstruction on patient dose and image quality compared to filtered back projection: a narrative review

Objective: Summarize all relevant findings in published literature regarding the potential dose reduction related to image quality using Sinogram-Affirmed Iterative Reconstruction (SAFIRE) compared to Filtered Back Projection (FBP). Background: Computed Tomography (CT) is one of the most used radiographic modalities in clinical practice providing high spatial and contrast resolution. However it also delivers a relatively high radiation dose to the patient. Reconstructing raw-data using Iterative Reconstruction (IR) algorithms has the potential to iteratively reduce image noise while maintaining or improving image quality of low dose standard FBP reconstructions. Nevertheless, long reconstruction times made IR unpractical for clinical use until recently. Siemens Medical developed a new IR algorithm called SAFIRE, which uses up to 5 different strength levels, and poses an alternative to the conventional IR with a significant reconstruction time reduction. Methods: MEDLINE, ScienceDirect and CINAHL databases were used for gathering literature. Eleven articles were included in this review (from 2012 to July 2014). Discussion: This narrative review summarizes the results of eleven articles (using studies on both patients and phantoms) and describes SAFIRE strengths for noise reduction in low dose acquisitions while providing acceptable image quality. Conclusion: Even though the results differ slightly, the literature gathered for this review suggests that the dose in current CT protocols can be reduced at least 50% while maintaining or improving image quality. There is however a lack of literature concerning paediatric population (with increased radiation sensitivity). Further studies should also assess the impact of SAFIRE on diagnostic accuracy.

A comparison of Sinogram Affirmed Iterative Reconstruction and filtered back projection on image quality and dose reduction in paediatric head CT: a phantom study

Background: Computed tomography (CT) is one of the most used modalities for diagnostics in paediatric populations, which is a concern as it also delivers a high patient dose. Research has focused on developing computer algorithms that provide better image quality at lower dose. The iterative reconstruction algorithm Sinogram-Affirmed Iterative Reconstruction (SAFIRE) was introduced as a new technique that reduces noise to increase image quality. Purpose: The aim of this study is to compare SAFIRE with the current gold standard, Filtered Back Projection (FBP), and assess whether SAFIRE alone permits a reduction in dose while maintaining image quality in paediatric head CT. Methods: Images were collected using a paediatric head phantom using a SIEMENS SOMATOM PERSPECTIVE 128 modulated acquisition. 54 images were reconstructed using FBP and 5 different strengths of SAFIRE. Objective measures of image quality were determined by measuring SNR and CNR. Visual measures of image quality were determined by 17 observers with different radiographic experiences. Images were randomized and displayed using 2AFC; observers scored the images answering 5 questions using a Likert scale. Results: At different dose levels, SAFIRE significantly increased SNR (up to 54%) in the acquired images compared to FBP at 80kVp (5.2-8.4), 110kVp (8.2-12.3), 130kVp (8.8-13.1). Visual image quality was higher with increasing SAFIRE strength. The highest image quality was scored with SAFIRE level 3 and higher. Conclusion: The SAFIRE algorithm is suitable for image noise reduction in paediatric head CT. Our data demonstrates that SAFIRE enhances SNR while reducing noise with a possible reduction of dose of 68%.

Digital radiography detectors - A technical overview: Part 1

During the last two decades screen-film (SF) systems have been replaced by digital X-ray systems. The advent of digital technologies brought a number of digital solutions based on different detector and readout technologies. Improvements in technology allowed the development of new digital technologies for projection radiography such as computed radiography (CR) and digital radiography (DR). The large number of scientific papers concerning digital X-ray systems that have been published over the last 25 years indicates the relevance of these technologies in healthcare. There are important differences among different detector technologies that may affect system performance and image quality for diagnostic purposes. Radiographers are expected to have an effective understanding of digital X-ray technologies and a high level of knowledge and awareness concerning the capabilities of these systems. Patient safety and reliable diagnostic information are intrinsically linked to these factors. In this review article - which is the first of two parts - a global overview of the digital radiography systems (both CR and DR) currently available for clinical practice is provided.

Digital radiography detectors - A technical overview: Part 2

Digital X-ray detector technologies provide several advantages when compared with screen-film (SF) systems: better diagnostic quality of the radiographic image, increased dose efficiency, better dynamic range and possible reduction of radiation exposure to the patient. The transition from traditional SF systems to digital technology-based systems highlights the importance of the discussion around technical factors such as image acquisition, themanagement of patient dose and diagnostic image quality. Radiographers should be aware of these aspects concerning their clinical practice regarding the advantages and limitations of digital detectors. Newdigital technologies require an up-to-date of scientific knowledge concerning their use in projection radiography. This is the second of a two-part review article focused on a technical overview of digital radiography detectors. This article provides a discussion about the issues related to the image acquisition requirements and advantages of digital technologies, the management of patient dose and the diagnostic image quality.

Avaliação da dose glandular média (MGD) em três sistemas mamográficos

Este estudo tem por objectivos determinar a Dose Glandular Média - Mean Glandular Dose (MGD) - em 3 sistemas de Mamografia e comparar os valores obtidos com os referenciais internacionais. O estudo foi realizado num sistema analógico de Écran-Película (EP) e em dois sistemas de imagem digital (CR e DR). Foi efectuado o cálculo da Entrance Surface Air Kerma (ESAK) e da MGD em três equipamentos a partir de uma amostra de dados referentes a 30 mulheres assintomáticas, com idades compreendidas entre os 40 e 64 anos. Em cada equipamento objecto de análise, foram recolhidos os dados referentes a 10 mulheres. Foram consideradas as projecções crânio-caudal (CC) e oblíqua médio-lateral (MLO). A análise de resultados revelou que o valor de MGD varia quando se compara os três sistemas. Nas incidências CC os valores de MGD obtidos foram de 1,54 mGy (EP), 1,78 mGy (CR) e 0,82 mGy (DR). Nas incidências MLO o valor de MGD foi de 1,53 mGy no sistema EP, de 1,78 mGy no CR e 0,87 mGy no sistema DR. Constata-se que o valor de MGD na incidência de CC é inferior ao valor de MGD na incidência MLO, excepto para o sistema EP. Verifica-se também que o sistema EP apresenta maior variabilidade nos dados de MGD comparativamente com os restantes sistemas. O sistema DR é o que apresenta a menor variabilidade de valores MGD e também valores de MGD mais baixos. Comparando os resultados deste estudo com as referências internacionais, verifica-se que a MGD se encontra abaixo do limite de 2 mGy recomendado. ABSTRACT - This study aims to estimate the Mean Glandular Dose (MGD) associated with three different mammographic systems and compare the results with recommended international reference values. The systems included in the study included a conventional Screen-Film (SF) system and two digital mammography systems (CR and DR). Entrance Surface Air Kerma (ESAK) and MGD associated with each equipment were calculated. A sample of 30 healthy women (age ranging from 40 to 64 years old) undertaking screening mammography was considered in this study. The mammographic exam includes two projections, cranio-caudal (CC) and medio-lateral oblique (MLO). The MGD results obtained for CC projection were 1,54 mGy (SF), 1,78 mGy (CR) and 0,82 mGy (DR). MGD values for the MLO projection were 1,53 mGy (SF), 1,78 mGy (CR) and 0,87 mGy (DR). Results show that MGD value is slightly lower in the CC projection than in MLO, except for the SF system (1,54 mGy; 1,53 mGy). In addition the MGD for the SF system varied more than that associated with the digital systems. The DR system allows a narrow variation of MGD values and also lower MGD values. Comparing this study results with the international references we concluded that MGD values are below the 2 mGy recommended value for the three systems evaluated.

Autenticação de vídeo H.264/AVC

Hoje em dia, há cada vez mais informação audiovisual e as transmissões ou ficheiros multimédia podem ser partilhadas com facilidade e eficiência. No entanto, a adulteração de conteúdos vídeo, como informação financeira, notícias ou sessões de videoconferência utilizadas num tribunal, pode ter graves consequências devido à importância desse tipo de informação. Surge então, a necessidade de assegurar a autenticidade e a integridade da informação audiovisual. Nesta dissertação é proposto um sistema de autenticação de vídeo H.264/Advanced Video Coding (AVC), denominado Autenticação de Fluxos utilizando Projecções Aleatórias (AFPA), cujos procedimentos de autenticação, são realizados ao nível de cada imagem do vídeo. Este esquema permite um tipo de autenticação mais flexível, pois permite definir um limite máximo de modificações entre duas imagens. Para efectuar autenticação é utilizada uma nova técnica de autenticação de imagens, que combina a utilização de projecções aleatórias com um mecanismo de correcção de erros nos dados. Assim é possível autenticar cada imagem do vídeo, com um conjunto reduzido de bits de paridade da respectiva projecção aleatória. Como a informação de vídeo é tipicamente, transportada por protocolos não fiáveis pode sofrer perdas de pacotes. De forma a reduzir o efeito das perdas de pacotes, na qualidade do vídeo e na taxa de autenticação, é utilizada Unequal Error Protection (UEP). Para validação e comparação dos resultados implementou-se um sistema clássico que autentica fluxos de vídeo de forma típica, ou seja, recorrendo a assinaturas digitais e códigos de hash. Ambos os esquemas foram avaliados, relativamente ao overhead introduzido e da taxa de autenticação. Os resultados mostram que o sistema AFPA, utilizando um vídeo com qualidade elevada, reduz o overhead de autenticação em quatro vezes relativamente ao esquema que utiliza assinaturas digitais e códigos de hash.

Digital imaging systems for plain radiography

Advances in digital technology led to the development of digital x-ray detectors that are currently in wide use for projection radiography, including Computed Radiography (CR) and Digital Radiography (DR). Digital Imaging Systems for Plain Radiography addresses the current technological methods available to medical imaging professionals to ensure the optimization of the radiological process concerning image quality and reduction of patient exposure. Based on extensive research by the authors and reference to the current literature, the book addresses how exposure parameters influence the diagnostic quality in digital systems, what the current acceptable radiation doses are for useful diagnostic images, and at what level the dose could be reduced to maintain an accurate diagnosis. The book is a valuable resource for both students learning the field and for imaging professionals to apply to their own practice while performing radiological examinations with digital systems.

Technical considerations concerning digital technologies

This chapter addresses technical issues concerning digital technologies. Radiological equipment and technique are briefly introduced together with a discussion about requirements and advantages of digital technologies. Digital technologies offer several advantages when compared to conventional analogical systems, or screen–film (SF) systems. While in clinical practice the practitioners should be aware of technical factors such as image acquisition, management of patient dose, and diagnostic image quality. Thus, digital technologies require an up-to-date scientific knowledge concerning their use in projection radiography. In this chapter, technical considerations concerning digital technologies are provided.

O impacto da entrada das agências de rating nos países emergentes: estudo comparativo Brasil/Angola

Mestrado em Contabilidade e Gestão das Instituições Financeiras

Study of the influence of count’s number in myocardium in the determination of reproducible functional parameters in Gated-SPECT studies simulated with GATE

Myocardial Perfusion Gated Single Photon Emission Tomography (Gated-SPET) imaging is used for the combined evaluation of myocardial perfusion and left ventricular (LV) function. But standard protocols of the Gated-SPECT studies require long acquisition times for each study. It is therefore important to reduce as much as possible the total duration of image acquisition. However, it is known that this reduction leads to decrease on counts statistics per projection and raises doubts about the validity of the functional parameters determined by Gated-SPECT. Considering that, it’s difficult to carry out this analysis in real patients. For ethical, logistical and economical matters, simulated studies could be required for this analysis. Objective: Evaluate the influence of the total number of counts acquired from myocardium, in the calculation of myocardial functional parameters (LVEF – left ventricular ejection fraction, EDV – end-diastolic volume, ESV – end-sistolic volume) using routine software procedures.

Dosimetria numa população de profissionais expostos a radiações ionizantes

Mestrado em Radiações Aplicadas às Tecnologias da Saúde - Área de especialização: Proteção Contra as Radiações.

3D-2D image registration by nonlinear regression

We propose a 3D-2D image registration method that relates image features of 2D projection images to the transformation parameters of the 3D image by nonlinear regression. The method is compared with a conventional registration method based on iterative optimization. For evaluation, simulated X-ray images (DRRs) were generated from coronary artery tree models derived from 3D CTA scans. Registration of nine vessel trees was performed, and the alignment quality was measured by the mean target registration error (mTRE). The regression approach was shown to be slightly less accurate, but much more robust than the method based on an iterative optimization approach.

Relações públicas e comunicação a internacionalização da banda Cambatango

O presente trabalho de projeto tem como tema Comunicação e Relações Públicas na internacionalização da banda Cambatango. Os Cambatango são uma orquestra típica de tango argentino que deseja consolidar a sua presença no mercado musical europeu. Assim, a pergunta de partida desta investigação é: como é que uma banda musical de origem argentina consegue promover o seu trabalho em território ibérico? O objetivo principal da investigação é associar as atividades de Relações Públicas à indústria da música. Para este fim, foi escolhido um objeto de estudo real, a orquestra Cambatango e proposto um Plano de Relações Públicas que ajude a: fortalecer a gestão e a imagem do grupo; fomentar a visibilidade da banda na indústria musical internacional; conquistar novos públicos e dinamizar a relação com os stakeholders de forma a impulsionar a presença do grupo em território ibérico. Esta investigação tem uma abordagem predominantemente qualitativa, nesse sentido, os métodos de pesquisa utilizados foram: análise SWOT; análise PEST; mapeamento de stakeholders; entrevistas (e respetiva análise categorial temática); pesquisa documental; auditoria em comunicação e pesquisa informal. As principais conclusões foram: existe uma vertente de Relações Públicas para a música, mas que ainda não é muito explorada pelos artistas independentes; um plano de Relações Públicas elaborado com base nas necessidades e objetivos dos artistas pode ajudar a projetar a sua carreira internacional; a indústria da música tem vindo a mudar face às novas tecnologias e os artistas precisam de acompanhar estas tendências; a comunicação é fundamental para estabelecer o diálogo com os diferentes públicos e ganhar maior projeção e visibilidade internacional.

As parcerias público-privadas e o seu impacto na sustentabilidade da dívida pública

Mestrado em Auditoria

The influence of the blood pressure on the venous cerebral flow measured by magnetic susceptibility (SWI) technique

Susceptibility Weighted Image (SWI) is a Magnetic Resonance Imaging (MRI) technique that combines high spatial resolution and sensitivity to provide magnetic susceptibility differences between tissues. It is extremely sensitive to venous blood due to its iron content of deoxyhemoglobin. The aim of this study was to evaluate, through the SWI technique, the differences in cerebral venous vasculature according to the variation of blood pressure values. 20 subjects divided in two groups (10 hypertensive and 10 normotensive patients) underwent a MRI system with a Siemens® scanner model Avanto of 1.5T using a synergy head coil (4 channels). The obtained sequences were T1w, T2w-FLAIR, T2* and SWI. The value of Contrast-to-Noise Ratio (CNR) was assessed in MinIP (Minimum Intensity Projection) and Magnitude images, through drawing free hand ROIs in venous structures: Superior Sagittal Sinus (SSS) Internal Cerebral Vein (ICV) and Sinus Confluence (SC). The obtained values were presented in descriptive statistics-quartiles and extremes diagrams. The results were compared between groups. CNR shown higher values for normotensive group in MinIP (108.89 ± 6.907) to ICV; (238.73 ± 18.556) to SC and (239.384 ± 52.303) to SSS. These values are bigger than images from Hypertensive group about 46 a.u. in average. Comparing the results of Magnitude and MinIP images, there were obtained lower CNR values for the hypertensive group. There were differences in the CNR values between both groups, being these values more expressive in the large vessels-SSS and SC. The SWI is a potential technique to evaluate and characterize the blood pressure variation in the studied vessels adding a physiological perspective to MRI and giving a new approach to the radiological vascular studies.