Browsing by Author "Machado, Nuno"
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- Contributo para o estabelecimento de níveis de referência de diagnóstico em equipamentos de TC multidetectoresPublication . Borlinhas, Filipa; Moura, Marta; Machado, Nuno; Lança, Luís; Madeira, Paula; Costa, João PauloActualmente a Tomografia Computorizada (TC) é um dos métodos de diagnóstico por imagem que tem uma maior contribuição para a dose de radiação X recebida pelos pacientes. Pretende-se com este estudo avaliar as doses praticadas em TC e contribuir para o estabelecimento de Níveis de Referência de Diagnóstico (NRD) na região da Grande Lisboa, Portugal. Foram efectuadas medições de dose em 5 equipamentos de TC multidetectores, considerando o abdómen como área anatómica de interesse. Recorreu-se a uma câmara de ionização e a um fantoma para obter o índice de dose de TC (CTDI) e o produto dose-comprimento (DLP), que permitem determinar os NRD. Estes valores foram comparados com os NRD propostos pela Guideline Europeia e com os estudos desenvolvidos em outros países, como o Reino Unido, Grécia e Taiwan. Os resultados revelaram que os valores de NRD obtidos neste estudo (16,7 mGy para o CTDIvol e 436,5 mGy·cm para o DLP) são discrepantes relativamente à Guideline Europeia (±50%), mas muito próximos relativamente aos NRD estabelecidos nos países considerados. Estes valores podem ser eventualmente explicados pelos equipamentos em análise e pela utilização de protocolos de exame adoptados pelos profissionais de Radiologia nas instituições analisadas. ABSTRACT - Nowadays Computed Tomography (CT) is one of the imaging techniques which have a large contribution to radiation dose received by patients. The purpose of this study is to evaluate CT doses and contribute to the establishment of Diagnostic Reference Levels (DRL) in Lisbon, Portugal. Dose measurements on 5 multidetector CT scanners have been performed, considering the abdomen as the anatomic region of interest. All measurements were performed using an ionization chamber and a phantom to obtain the index CT dose (CTDI) and the dose-length product (DLP), which are used to determine DRL. These values were compared not only with European reference dose values but also with DRL studies developed in other countries like United Kingdom, Greece and Taiwan. The results revealed that DRL values obtained in this study (CTDIvol is 16,7 mGy and DLP is 436,5 mGy·cm) have a higher discrepancy to European Guideline (±50%), while the DRL´s of other countries are nearest to values obtained in this study. Those differences may be eventually explained by the type of the evaluated equipments but also by the exam protocols used by the Radiology professionals on the analyzed institutions.
- Contributo para o estabelecimento de níveis de referência de diagnóstico locais em tomografia computorizada nos exames de crânio e tórax em adultosPublication . Torres, Ana; Rodrigues, Dulce; Lança, Luís; Machado, Nuno; Martins, NunoAtualmente a Tomografia Computorizada (TC) é o método de imagem que mais contribui para a dose coletiva resultante de exposições médicas. Este estudo pretende determinar os valores de Índice de Dose de TC (CTDI) e produto dose-comprimento (DLP) para os exames de crânio e tórax em adultos num equipamento de TC multidetetores; e efetuar uma análise objetiva e subjetiva da qualidade da imagem. Determinaram-se os valores de CTDI e DLP utilizando uma câmara de ionização e fantomas de crânio e tórax. Efetuou-se ainda uma análise objetiva e subjetiva da qualidade da imagem com o fantoma Catphan® 500 e observadores, respetivamente. Os resultados obtidos foram superiores relativamente às Guidelines europeias no protocolo de crânio (CTDIvol = 80,13 mGy e DLP = 1209,22 mGy.cm) e inferiores no protocolo de tórax (CTDIvol = 8,37 mGy e DLP = 274,71 mGy.cm). Na análise objetiva da qualidade da imagem, à exceção da resolução de baixo contraste no protocolo de crânio, todos os outros critérios analisados estavam em conformidade com a legislação. Na análise subjetiva da qualidade da imagem existiu uma diferença estatisticamente significativa entre as classificações atribuídas pelos observadores às imagens nos parâmetros avaliados (p = 0,000-0,005).
- Effect of technical parameters on dose and image quality in a computed radiography systemPublication . Tavares, A.; Lança, Luís; Machado, NunoThe 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.
- Learning biophysics by building models: is it possible?Publication . Machado, Nuno; Baptista, MónicaThe curricula of higher education courses in the area of Health usually place the curricular units of Basic Sciences in the first years of the course. This knowledge, supposedly, is ‘stored’ by the students in order to be applied in later curricular units. One of the major disadvantages of this structure is that knowledge and skills will have to be acquired in the long term. In this way, it is necessary to use teaching methodologies that guarantee retention of the acquired knowledge in the long term, so that students take the knowledge as if it were their own so that it can be correlated with the new knowledge. But on the other side, this kind of structure is not very well accepted by the students because the importance of the learning the fundamentals sciences is not immediately understood by them. This implies that the motivation for this kind of basic science disciplines is very low. The building of numerical models of biophysical phenomena, such as the mechanics of breathing, or blood circulation, has the potential for student motivation as well as long-term learning. Our theory is that by building well known numerical models of physiological phenomena in a spreadsheet, students have the opportunity to change their perceptions about the relevance of the contents addressed, simultaneously improving their learning in the topics covered and increasing their motivation in the discipline. The option for the use of a spreadsheet is justified because it does not require prior knowledge of programming languages, or about complex mathematical software, which would an obstacle to the biophysics learning. There is also the side effect of learning how to use a spreadsheet that is a plus in itself. After the development time of the model, the students have an individual oral assessment, which includes a final assessment of the developed model. Following this, the student delivers a written report. It is in this report that the students show the tests they have done to the model, as well as a reflection on the model they used, its limitations, some possible applications, and some considerations about possible future developments. It is intended to recognize the challenges that students face when building the models, and also know the evolution of the learning and to know the students' perception about the importance of the construction of models in biophysics and in the learning of biophysics. At this moment we have done already two complete cycles. At the end of each cycle, there is an evaluation which is used to develop the next cycle, the third one at this moment. In the very near future, we will try to apply this learning methodology to other disciplines, using different models according to each discipline. In this way, we would be able to compare results of different implementations of this new learning methodology.
- Modelling based teaching with spreadsheet: a study in a health care coursePublication . Machado, Nuno; Baptista, MónicaComputer-based modeling tools allow students to express their theories in models that can be simulated. In this way, students can use their theories operationally, confronting themselves with the consequences of their ideas. The ability of students to form and express a mental model will be expanded if they are given an opportunity to become aware of their own mental model by expressing this same model and comparing it to other models, like a consensus model. The building of numerical models of biophysical phenomena, such as the mechanics of breathing, or blood circulation, has the potential for student motivation as well as long-term learning. Our theory is that by re-building well known numerical models of physiological phenomena students will have the opportunity to change their perceptions about the relevance of the contents addressed, simultaneously improving their learning in the topics covered and increasing their motivation in the basic science disciplines in their curricula. For the implementation of computer numerical models historically it was necessary to use some programming language, such as MATLAB, BASIC, C++, JAVA. With the development of computer science, it is now possible to these students ‘construc’ models of physical phenomena expressed through dedicated computer tools without necessarily having to do so in a programming language. As for example, we have STELLA, MODELLUS, or STARLOGO. There is also the possibility of using a spreadsheet such as Microsoft Excel, Open Office CALC, Google SHEETS, or others, as tools that allow students to express physical models. The current spreadsheets, even those available for free, are very powerful, having many integrated tools, in terms of calculation, and we can count on several other features, such as graphs of various types, buttons and other tools that allow interaction with the model, and databases that can be integrated into the spreadsheet. There are several advantages of using spreadsheets in science education due to its general access, through smartphones, tablet’s and computers, ease of implementation for the basic operations, and ease of the “debug” process, relative to other types of software. Also, it does not require prior knowledge of programming languages, or about complex mathematical software, which would an obstacle to the learning in itself. There is also the positive side effect of learning how to use a spreadsheet that is a plus in itself for the future professional’s. This paper will have a review of the state of the art of using spreadsheets in Modelling Based Learning. Also, it will be presented a study with first-year undergraduate students of a health care course, using Biophysical models historically very important in the physiology and medicine development.
- Níveis de referência de diagnóstico em mamografiaPublication . Martins, Bruno; Machado, Nuno; Parafita, Rui; Carvoeiras, Pedro; Azevedo, João; Trindade, Hugo; Pinto, Ildefonso; Teixeira, NunoNíveis de exposição em exames de mamografia: 1) os NRD permitem a orientação em relação às doses a utilizar num exame radiológico específico para um doente padrão; 2) não representam um limite de dose; 3) são normalmente definidos pelo valor que engloba 75% das doses mais baixas da população alvo, para um determinado exame; 4) permitem uma triagem dos resultados observados, com o fim de evitar exposições injustificadamente altas ou baixas; 5) promover a utilização de uma pequena gama de valores que representem uma boa prática para uma imagem médica específica.
- Results of radiation protection programmes on mammographyPublication . Machado, Nuno; Carvoeiras, Pedro; Teixeira, NunoIn this paper, we present the results of mammography quality control tests related to the work with Portuguese mammography equipment, either in conventional or in digital mammography computed radiography, showing the main differences in the tested equipments. Quality control in mammography is a very special area of quality control in radiology, which demands relatively high knowledge on physics. Digital imaging is changing the standards of the radiographic imaging. Regarding mammography, this is yet a controversial issue owing to some limitations of the digital detectors, like the resolution for instance. A complete set of results regarding radiation protection of the patients submitted to mammography diagnosis is presented. A discussion of the quality image parameters and its interpretation in conventional and digital mammography is presented. In conclusion, we present a sample of results that can be considered as characteristics of mammography equipment in Portugal.