Sistemas digitais directos vs indirectos : níveis de referência de diagnóstico locais na radiografia de tórax em projeção postero-anterior em dois hospitais portugueses

Este estudo teve como objetivo avaliar e comparar as doses de radiação recolhidas numa amostra de 69 pacientes, em dois hospitais, com diferentes métodos de aquisição de imagem digital, direta e indireta, que realizaram radiografia de tórax, em projeção postero-anterior (PA). Para os dois hospitais, a dose à entrada da pele (DEP) e efectiva (E), foram medidas usando o software PCXMC para comparação entre si e com referências internacionais. No Hospital A, com aquisição digital direta, a média de DEP foi de 0,089 mGy e a média de E foi 0,013 mSv. No Hospital B, com aquisição digital de indireta, a média de DEP foi de 0.151 mGy e a média de E foi 0.030mSv. Em ambos os hospitais, as doses médias não ultrapassaram os limites recomendados por lei (0,3 mGy). Para a radiografia de tórax PA, o nível de referência diagnostico (NRD) local calculado foi 0.107 mGy, para o Hospital A e 0.164 mGy, para o Hospital B. Na radiografia de tórax PA, a utilização de um sistema de aquisição direta implicou uma redução de dose de 41 %, concordante com as referências disponíveis que apontam para a redução da dose de cerca de 50 % entre os dois sistemas.

Systems thinking: learning or driving?

The ability to foresee how behaviour of a system arises from the interaction of its components over time - i.e. its dynamic complexity – is seen an important ability to take effective decisions in our turbulent world. Dynamic complexity emerges frequently from interrelated simple structures, such as stocks and flows, feedbacks and delays (Forrester, 1961). Common sense assumes an intuitive understanding of their dynamic behaviour. However, recent researches have pointed to a persistent and systematic error in people understanding of those building blocks of complex systems. This paper describes an empirical study concerning the native ability to understand systems thinking concepts. Two different groups - one, academic, the other, professional – submitted to four tasks, proposed by Sweeney and Sterman (2000) and Sterman (2002). The results confirm a poor intuitive understanding of the basic systems concepts, even when subjects have background in mathematics and sciences.

Systems thinking: learning or driving?

The ability to foresee how behaviour of a system arises from the interaction of its components over time - i.e. its dynamic complexity – is seen an important ability to take effective decisions in our turbulent world. Dynamic complexity emerges frequently from interrelated simple structures, such as stocks and flows, feedbacks and delays (Forrester, 1961). Common sense assumes an intuitive understanding of their dynamic behaviour. However, recent researches have pointed to a persistent and systematic error in people understanding of those building blocks of complex systems. This paper describes an empirical study concerning the native ability to understand systems thinking concepts. Two different groups - one, academic, the other, professional – submitted to four tasks, proposed by Sweeney and Sterman (2000) and Sterman (2002). The results confirm a poor intuitive understanding of the basic systems concepts, even when subjects have background in mathematics and sciences.