The effect of gamma on subjective quality and contrast of X-ray images

We have studied the influence of the parameter gamma on the perception of digital X-ray images. Gamma is the exponent of the function describing how grey values are transformed into luminance. We have applied several values of gamma to angiographic images, and we have presented these images on a monitor (soft copy) and also as films on a light box (hard copy). The perceived contrast and quality have been assessed with the aid of category scaling techniques. Radiologists, technical experts (people involved in the development of X-ray systems) and nonexperts participated in the experiments. We found that perceived contrast increases with gamma. Gamma also affects the perceived quality, but the effect depends on the image contents. Furthermore, we found slightly different judgments for different groups of subjects. Technical experts appreciated higher gamma values than nonexperts did. In the case of radiologists, the perceived quality depended on the image (and on its diagnostic purpose) to a much greater extent than in the case of nonexperts. No differences were found between the results for hard and soft copies

Multidimensional perceptual quality of noise-reduced Computed Tomography images

Judging the perceptual quality of processed images is a cognitive process in which the perceived impressions of basic image attributes, such as sharpness and presence of noise, play an important role. In this paper, we show how multidimensional scaling can be used to study the perceptual factors that influence the quality impression of computed tomography images processed by a noise reduction technique. We also show how intersubject differences in the assessment of image attributes can be characterized

Effects of the food contaminant semicarbazide on testicular morphology of juvenile Wistar rats

O objectivo do presente trabalho foi avaliar os efeitos da semicarbazida na morfologia testicular de ratos Wistar jovens. Os animais foram tratados durante 30 dias com hidrocloreto de semicarbazida incorporado na dieta, nas concentrações de 0, 3 e 6g/kg. Os resultados obtidos revelaram uma diminuição estatisticamente significativa no diâmetro dos túbulos seminíferos, no diâmetro do lúmen dos túbulos seminíferos e na área ocupada pelo epitélio seminífero nos animais dos grupos experimentais em comparação com os animais do grupo controlo. Estes resultados evidenciam que a semicarbazida induz alterações importantes no desenvolvimento testicular e sugerem um estudo mais aprofundado sobre os mecanismos de acção, dos efeitos a longo prazo, da reversibilidade das lesões e nas capacidades reprodutivas. Estes aspectos são relevantes numa perspectiva de segurança alimentar, em particular para as crianças, as quais representam um grupo de maior exposição e susceptibilidade à semicarbazida