Monte Carlo derivation of filtered tungsten anode X-ray spectra for dose computation in digital mammography.

OBJECTIVE: Derive filtered tungsten X-ray spectra used in digital mammography systems by means of Monte Carlo simulations. MATERIALS AND METHODS: Filtered spectra for rhodium filter were obtained for tube potentials between 26 and 32 kV. The half-value layer (HVL) of simulated filtered spectra were compared with those obtained experimentally with a solid state detector Unfors model 8202031-H Xi R/F & MAM Detector Platinum and 8201023-C Xi Base unit Platinum Plus w mAs in a Hologic Selenia Dimensions system using a direct radiography mode. RESULTS: Calculated HVL values showed good agreement as compared with those obtained experimentally. The greatest relative difference between the Monte Carlo calculated HVL values and experimental HVL values was 4%. CONCLUSION: The results show that the filtered tungsten anode X-ray spectra and the EGSnrc Monte Carlo code can be used for mean glandular dose determination in mammography.

OBJETIVO: Derivar espectros filtrados de raios X de tungstênio utilizados em sistemas de mamografia digital por meio de simulações Monte Carlo. MATERIAIS E MÉTODOS: Espectros filtrados por filtro de ródio foram obtidos para potenciais do tubo entre 26 e 32 kV. Os valores de camada semirredutora (CSR) dos espectros filtrados simulados foram comparados aos valores obtidos experimentalmente com um detector de estado sólido Unfors modelo 8202031-H Xi R/F & MAM Detector Platinum e unidade base 8201023-C Xi Platinum Plus w mAs em um sistema Hologic Selenia Dimensions utilizado no modo radiografia direta. RESULTADOS: Os valores de CSR calculados mostraram boa concordância quando comparados com os valores obtidos experimentalmente. A maior diferença relativa entre os valores de CSR calculados com Monte Carlo e os valores de CSR experimentais foi 4%. CONCLUSÃO: Os resultados demonstram que os espectros filtrados de raios X de ânodo de tungstênio e o código de Monte Carlo EGSnrc podem ser utilizados para determinar a dose glandular média em mamografia.

Dosimetry and image quality assessment in a direct radiography system.

OBJECTIVE: To evaluate the mean glandular dose with a solid state detector and the image quality in a direct radiography system, utilizing phantoms. MATERIALS AND METHODS: Irradiations were performed with automatic exposure control and polymethyl methacrylate slabs with different thicknesses to calculate glandular dose values. The image quality was evaluated by means of the structures visualized on the images of the phantoms. RESULTS: Considering the uncertainty of the measurements, the mean glandular dose results are in agreement with the values provided by the equipment and with internationally adopted reference levels. Results obtained from images of the phantoms were in agreement with the reference values. CONCLUSION: The present study contributes to verify the equipment conformity as regards dose values and image quality.

OBJETIVO: Avaliar a dose glandular média utilizando um detector de estado sólido e a qualidade da imagem de um sistema de radiografia direta a partir de objetos simuladores. MATERIAIS E MÉTODOS: Irradiações foram realizadas utilizando o controle automático de exposição e placas de polimetilmetacrilato com diferentes espessuras para o cálculo da dose glandular média. A qualidade da imagem foi avaliada por meio das estruturas visualizadas nas imagens dos objetos simuladores. RESULTADOS: Considerando a incerteza das medições, os resultados de dose glandular média estão de acordo com os valores fornecidos pelo equipamento e com os níveis de referência adotados internacionalmente. Os resultados obtidos a partir das imagens dos objetos simuladores estavam em conformidade com os valores de referência. CONCLUSÃO: Este trabalho contribui para verificar a conformidade do equipamento em relação a dose e qualidade da imagem.

Hand digit control in children: motor overflow in multi-finger pressing force vector space during maximum voluntary force production.

The aim of this study was to investigate the contralateral motor overflow in children during single-finger and multi-finger maximum force production tasks. Forty-five right handed children, 5-11 years of age produced maximum isometric pressing force in flexion or extension with single fingers or all four fingers of their right hand. The forces produced by individual fingers of the right and left hands were recorded and analyzed in four-dimensional finger force vector space. The results showed that increases in task (right) hand finger forces were linearly associated with non-task (left) hand finger forces. The ratio of the non-task hand finger force magnitude to the corresponding task hand finger force magnitude, termed motor overflow magnitude (MOM), was greater in extension than flexion. The index finger flexion task showed the smallest MOM values. The similarity between the directions of task hand and non-task hand finger force vectors in four-dimensional finger force vector space, termed motor overflow direction (MOD), was the greatest for index and smallest for little finger tasks. MOM of a four-finger task was greater than the sum of MOMs of single-finger tasks, and this phenomenon was termed motor overflow surplus. Contrary to previous studies, no single-finger or four-finger tasks showed significant changes of MOM or MOD with the age of children. We conclude that the contralateral motor overflow in children during finger maximum force production tasks is dependent upon the task fingers and the magnitude and direction of task finger forces.

Strength and isometric torque control in individuals with Parkinson's disease.

It has been previously reported that patients with Parkinson's disease (PD) struggle with fine adjustments of finger forces while manipulating an object. However, impairments in everyday activities can not only be attributed to difficulties with the linear forces applied on an object, but also to the application of rotational forces (torque). This study examined finger strength and isometric torque control in elderly persons with PD. Six individuals with PD (66.1 +/- 0.7 years), six elderly healthy controls (65.3 +/- 0.2 years) matched by age, gender and handedness, and six young adults (22.3 +/- 0.2 years) participated in this study. The subjects were asked to perform two tasks: maximum voluntary thumb-index pinching torque production (MVT) and constant isometric thumb-index torque control at 40% of their MVT for 20 s. The results showed decreased strength and increased difficulty in isometric torque control in individuals with PD as compared to their healthy peers. This study demonstrates that PD affects isometric finger torque production and control.