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Ultrasonic phantoms are objects that mimic some features of biological tissues, allowing the study of their interactions with ultrasound (US). In the diagnostic-imaging field, breast phantoms are an important tool for testing performance and optimizing US systems, as well as for training medical professionals. This paper describes the design and manufacture of breast lesions by using polyvinyl chloride plastisol (PVCP) as the base material. Among the materials available for this study, PVCP was shown to be stable, durable, and easy to handle. Furthermore, it is a nontoxic, nonpolluting, and low-cost material. The breast's glandular tissue (image background) was simulated by adding graphite powder with a concentration of 1% to the base material. Mixing PVCP and graphite powder in differing concentrations allows one to simulate lesions with different echogenicity patterns (anechoic, hypoechoic, and hyperechoic). From this mixture, phantom materials were obtained with speed of sound varying from 1379.3 to 1397.9ms(-1) and an attenuation coefficient having values between 0.29 and 0.94dBcm(-1) for a frequency of 1MHz at 24°C. A single layer of carnauba wax was added to the lesion surface in order to evaluate its applicability for imaging. The images of the phantoms were acquired using commercial ultrasound equipment; a specialist rated the images, elaborating diagnoses representative of both benign and malignant lesions. The results indicated that it was possible to easily create a phantom by using low-cost materials, readily available in the market and stable at room temperature, as the basis of ultrasonic phantoms that reproduce the image characteristics of fatty breast tissue and typical lesions of the breast.

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CONTEXT AND OBJECTIVE: Impact factors are currently the bibliometric index most used for evaluating scientific journals. However, the way in which they are used, for instance concerning the study or journal types analyzed, can markedly interfere with estimate reliability. This study aimed to analyze the citation distribution pattern in three Brazilian journals of general medicine. DESIGN AND SETTING: This was a descriptive study based on numbers of citations of scientific studies published by three Brazilian journals of general medicine. METHODS: The journals analyzed were São Paulo Medical Journal, Clinics and Revista da Associação Médica Brasileira. This survey used data available from the Institute for Scientific Information (ISI) platform, from which the total number of papers published in each journal in 2007-2008 and the number of citations of these papers in 2009 were obtained. From these data, the citation distribution was derived and journal impact factors (average number of citations) were estimated. These factors were then compared with those directly available from the ISI Journal of Citation Reports (JCR). RESULTS: Respectively, 134, 203 and 192 papers were published by these journals during the period analyzed. The observed citation distributions were highly skewed, such that many papers had few citations and a small percentage had many citations. It was not possible to identify any specific pattern for the most cited papers or to exactly reproduce the JCR impact factors. CONCLUSION: Use of measures like "impact factors", which characterize citations through averages, does not adequately represent the citation distribution in the journals analyzed.

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CONTEXT AND OBJECTIVE: Impact factors are currently the bibliometric index most used for evaluating scientific journals. However, the way in which they are used, for instance concerning the study or journal types analyzed, can markedly interfere with estimate reliability. This study aimed to analyze the citation distribution pattern in three Brazilian journals of general medicine. DESIGN AND SETTING: This was a descriptive study based on numbers of citations of scientific studies published by three Brazilian journals of general medicine. METHODS: The journals analyzed were São Paulo Medical Journal, Clinics and Revista da Associação Médica Brasileira. This survey used data available from the Institute for Scientific Information (ISI) platform, from which the total number of papers published in each journal in 2007-2008 and the number of citations of these papers in 2009 were obtained. From these data, the citation distribution was derived and journal impact factors (average number of citations) were estimated. These factors were then compared with those directly available from the ISI Journal of Citation Reports (JCR). RESULTS: Respectively, 134, 203 and 192 papers were published by these journals during the period analyzed. The observed citation distributions were highly skewed, such that many papers had few citations and a small percentage had many citations. It was not possible to identify any specific pattern for the most cited papers or to exactly reproduce the JCR impact factors. CONCLUSION: Use of measures like "impact factors", which characterize citations through averages, does not adequately represent the citation distribution in the journals analyzed.

CONTEXTO E OBJETIVO: O fator de impacto é atualmente o índice bibliométrico mais utilizado para a avaliação de revistas científicas. No entanto, as condições de seu uso, por exemplo, em relação ao tipo de estudos ou revistas analisadas, podem interferir significativamente com a confiabilidade de suas estimativas. Este trabalho teve como objetivo estudar o padrão de distribuição de citações em três periódicos brasileiros de medicina geral. TIPO DE ESTUDO E LOCAL: Trata-se de um estudo descritivo, baseado nos números de citações de trabalhos científicos publicados por três revistas brasileiras de Medicina Geral. MÉTODOS: As revistas analisadas foram São Paulo Medical Journal, Clinics e Revista da Associação Médica Brasileira. A pesquisa utilizou-se de dados disponibilizados pela plataforma do Institute for Scientific Information (ISI), da qual foram obtidos o total de publicações de cada revista no período de 2007-2008 e o número de citações a esses trabalhos em 2009. A distribuição de citações e os fatores de impacto (média do número de citações) para cada revista foram estimados a partir desses dados, e os fatores de impacto assim obtidos foram comparados aos fornecidos diretamente pelo ISI Journal of Citation Reports (JCR). RESULTADOS: No período, foram publicados respectivamente 134, 203 e 192 artigos pelas revistas analisadas. Observou-se que a distribuição das citações a esses artigos é altamente enviesada, com um grande número de trabalhos pouco citados e um pequeno percentual com muitas citações. Não foi possível identificar um padrão específico para os trabalhos mais citados ou reproduzir exatamente os fatores de impacto JCR. CONCLUSÃO: O uso de medidas como "fatores de impacto" que caracterizam citações por meio de médias não representa adequadamente a distribuição de citações nas revistas analisadas.

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