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 contraste de detalhe, 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.

Assessment of patient dose in digital systems

The assessment of patient dose has gained increased attention, still being an issue of concern that arises from the use of digital systems. The development of digital technology offers the possibility for a reduction of radiation dose around 50% without loss in image quality when compared to a conventional screen–film system. Digital systems give an equivalent or superior diagnostic performance and also several other advantages, but the risk of overexposure with no adverse effect on image quality could be present. This chapter refers to the management of patient dose and provides an explanation of dose-related concepts. In this chapter, exposure influence in dose and image representation and the effects of radiation exposure are also discussed.

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.

Practical insights into digital radiology

Digital radiography detectors—based on different technological solutions—are currently available for clinical applications and widespread in clinical practice. Computed radiography (CR) and digital radiology systems have been available for clinical applications and the trend over the last few years has become digital. Radiology departments have been changing from traditional screen–film technology to digital technology. This chapter is intended to give the reader a practical understanding about the key aspects concerning digital systems, related to the performance of different technologies, image quality, and dose and patient safety/protection. The discussion around an optimization framework for digital systems is provided.

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.

Effect of technical parameters on dose and image quality in a computed radiography system

The discovery of X-rays was undoubtedly one of the greatest stimulus for improving the efficiency in the provision of healthcare services. The ability to view, non-invasively, inside the human body has greatly facilitated the work of professionals in diagnosis of diseases. The exclusive focus on image quality (IQ), without understanding how they are obtained, affect negatively the efficiency in diagnostic radiology. The equilibrium between the benefits and the risks are often forgotten. It is necessary to adopt optimization strategies to maximize the benefits (image quality) and minimize risk (dose to the patient) in radiological facilities. In radiology, the implementation of optimization strategies involves an understanding of images acquisition process. When a radiographer adopts a certain value of a parameter (tube potential [kVp], tube current-exposure time product [mAs] or additional filtration), it is essential to know its meaning and impact of their variation in dose and image quality. Without this, any optimization strategy will be a failure. Worldwide, data show that use of x-rays has been increasingly frequent. In Cabo Verde, we note an effort by healthcare institutions (e.g. Ministry of Health) in equipping radiological facilities and the recent installation of a telemedicine system requires purchase of new radiological equipment. In addition, the transition from screen-films to digital systems is characterized by a raise in patient exposure. Given that this transition is slower in less developed countries, as is the case of Cabo Verde, the need to adopt optimization strategies becomes increasingly necessary. This study was conducted as an attempt to answer that need. Although this work is about objective evaluation of image quality, and in medical practice the evaluation is usually subjective (visual evaluation of images by radiographer / radiologist), studies reported a correlation between these two types of evaluation (objective and subjective) [5-7] which accredits for conducting such studies. The purpose of this study is to evaluate the effect of exposure parameters (kVp and mAs) when using additional Cooper (Cu) filtration in dose and image quality in a Computed Radiography system.

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.

Caracterização tecnológica da mamografia digital em Portugal: progresso de um projeto em implementação

Introdução – A mamografia é o principal método de diagnóstico por imagem utilizado no rastreio e diagnóstico do cancro da mama, sendo a modalidade de imagem recomendada em vários países da Europa e Estados Unidos para utilização em programas de rastreio. A implementação da tecnologia digital causou alterações na prática da mamografia, nomeadamente a necessidade de adaptar os programas de controlo de qualidade. Objetivos – Caracterizar a tecnologia instalada para mamografia em Portugal e as práticas adotadas na sua utilização pelos profissionais de saúde envolvidos. Concluir sobre o nível de harmonização das práticas em mamografia em Portugal e a conformidade com as recomendações internacionais. Identificar oportunidades para otimização que permitam assegurar a utilização eficaz e segura da tecnologia. Metodologia – Pesquisa e recolha de dados sobre a tecnologia instalada, fornecidos por fontes governamentais, prestadores de serviços de mamografia e indústria. Construção de três questionários, orientados ao perfil do médico radiologista, técnico de radiologia com atividade em mamografia digital e técnico de radiologia coordenador. Os questionários foram aplicados em 65 prestadores de serviços de mamografia selecionados com base em critérios de localização geográfica, tipo de tecnologia instalada e perfil da instituição. Resultados – Foram identificados 441 sistemas para mamografia em Portugal. A tecnologia mais frequente (62%) e vulgarmente conhecida por radiografia computorizada (computed radiography) é constituída por um detector (image plate) de material fotoestimulável inserido numa cassete de suporte e por um sistema de processamento ótico. A maioria destes sistemas (78%) está instalada em prestadores privados. Aproximadamente 12% dos equipamentos instalados são sistemas para radiografia digital direta (Direct Digital Radiography – DDR). Os critérios para seleção dos parâmetros técnicos de exposição variam, observando-se que em 65% das instituições são adotadas as recomendações dos fabricantes do equipamento. As ferramentas de pós-processamento mais usadas pelos médicos radiologistas são o ajuste do contraste e brilho e magnificação total e/ou localizada da imagem. Quinze instituições (em 19) têm implementado um programa de controlo de qualidade. Conclusões – Portugal apresenta um parque de equipamentos heterogéneo que inclui tecnologia obsoleta e tecnologia “topo de gama”. As recomendações/guidelines (europeias ou americanas) não são adotadas formalmente na maioria das instituições como guia para fundamentação das práticas em mamografia, dominando as recomendações dos fabricantes do equipamento. Foram identificadas, pelos técnicos de radiologia e médicos radiologistas, carências de formação especializada, nomeadamente nas temáticas da intervenção mamária, otimização da dose e controlo da qualidade. A maioria dos inquiridos concorda com a necessidade de certificação da prática da mamografia em Portugal e participaria num programa voluntário. ABSTRACT - Introduction – Mammography is the gold standard for screening and imaging diagnosis of breast disease. It is the imaging modality recommended by screening programs in various countries in Europe and the United States. The implementation of the digital technology promoted changes in mammography practice and triggered the need to adjust quality control programs. Aims –Characterize the technology for mammography installed in Portugal. Assess practice in use in mammography and its harmonization and compliance to international guidelines. Identify optimization needs to promote an effective and efficient use of digital mammography to full potential. Methodology – Literature review was performed. Data was collected from official sources (governmental bodies, mammography healthcare providers and medical imaging industry) regarding the number and specifications of mammography equipment installed in Portugal. Three questionnaires targeted at radiologists, breast radiographers and the chief-radiographer were designed for data collection on the technical and clinical practices in mammography. The questionnaires were delivered in a sample of 65 mammography providers selected according to geographical criteria, type of technology and institution profile. Results – Results revealed 441 mammography systems installed in Portugal. The most frequent (62%) technology type are computerized systems (CR) mostly installed in the private sector (78%). 12% are direct radiography systems (DDR). The criteria for selection of the exposure parameters differ between the institutions with the majority (65%) following the recommendations from the manufacturers. The use of available tools for post-processing is limited being the most frequently reported tools used the contrast/ brightness and Zoom or Pan Magnification tools. Fifteen participant institutions (out of 19) have implemented a quality control programme. Conclusions – The technology for mammography in Portugal is heterogeneous and includes both obsolete and state of the art equipment. International guidelines (European or American) are not formally implemented and the manufacturer recommendations are the most frequently used guidance. Education and training needs were identified amongst the healthcare professionals (radiologists and radiographers) with focus in the areas of mammography intervention, patient dose optimization and quality control. The majority of the participants agree with the certification of mammography in Portugal.

Digital radiography detectors: a technical overview

Developments in digital detector technologies have been taking place and new digital technologies are available for clinical practice. This chapter is intended to give a technical state-of-the-art overview about computed radiography (CR) and digital radiography (DR) detectors. CR systems use storage-phosphor image plates with a separate image readout process and DR technology converts X-rays into electrical charges by means of a readout process using TFT arrays. Digital detectors offer several advantages when compared to analogue detectors. The knowledge about digital detector technology for use in plain radiograph examinations is thus a fundamental topic to be acquired by radiology professionals and students. In this chapter an overview of digital radiography systems (both CR and DR) currently available for clinical practice is provided.

Digital radiography detector performance

The characterization of physical properties of digital imaging systems requires the determination and measurement of detectors’ physical performance. Those measures such as modulation transfer function (MTF), noise power spectra (NPS), and detective quantum efficiency (DQE) provide objective evaluations of digital detectors’ performance. To provide an MTF, NPS, and DQE calculation from raw-data images it is necessary to implement a method that is undertaken by two major steps: (1) image acquisition and (2) quantitative measure determination method. In this chapter a comprehensive description about a method to provide the measure of performance of digital radiography detectors is provided.

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.

Image enhancement for digital radiography

Once in a digital form, a radiographic image may be processed in several ways in order to turn the visualization an act of improved diagnostic value. Practitioners should be aware that, depending on each clinical context, digital image processing techniques are available to help to unveil visual information that is, in fact, carried by the bare digital radiograph and may be otherwise neglected. The range of visual enhancement procedures includes simple techniques that deal with the usual brightness and contrast manipulation up to much more elaborate multi-scale processing that provides customized control over the emphasis given to the relevant finer anatomical details. This chapter is intended to give the reader a practical understanding of image enhancement techniques that might be helpful to improve the visual quality of the digital radiographs and thus to contribute to a more reliable and assertive reporting.

Digital radiology and Picture Archiving and Communication System (PACS)

Plain radiography still accounts for the vast majority of imaging studies that are performed at multiple clinical instances. Digital detectors are now prominent in many imaging facilities and they are the main driving force towards filmless environments. There has been a working paradigm shift due to the functional separation of acquisition, visualization, and storage with deep impact in the imaging workflows. Moreover with direct digital detectors images are made available almost immediately. Digital radiology is now completely integrated in Picture Archiving and Communication System (PACS) environments governed by the Digital Imaging and Communications in Medicine (DICOM) standard. In this chapter a brief overview of PACS architectures and components is presented together with a necessarily brief account of the DICOM standard. Special focus is given to the DICOM digital radiology objects and how specific attributes may now be used to improve and increase the metadata repository associated with image data. Regular scrutiny of the metadata repository may serve as a valuable tool for improved, cost-effective, and multidimensional quality control procedures.

Comparison of inverse planning systems based on biological or physical factors: Pinnacle®, Corvus® and Monaco®

Radiotherapy (RT) is one of the most important approaches in the treatment of cancer and its performance can be improved in three different ways: through the optimization of the dose distribution, by the use of different irradiation techniques or through the study of radiobiological initiatives. The first is purely physical because is related to the physical dose distributiuon. The others are purely radiobiological because they increase the differential effect between the tumour and the health tissues. The Treatment Planning Systems (TPS) are used in RT to create dose distributions with the purpose to maximize the tumoral control and minimize the complications in the healthy tissues. The inverse planning uses dose optimization techniques that satisfy the criteria specified by the user, regarding the target and the organs at risk (OAR’s). The dose optimization is possible through the analysis of dose-volume histograms (DVH) and with the use of computed tomography, magnetic resonance and other digital image techniques.