The performance of a computer-aided dianosis (CAD) scheme is closely dependent on the database used for its development and tests. The scheme sensitivity can be reduced by 15% to 25%, with only 20% of changes in the database cases. Previously, we have developed a processing scheme in order to detect clustered mlcrocalcifications in digital mammograms, and we have tested such a procedure with two different databases. Further evaluations in developing a CAD scheme for mammography have indicated the need for more extensive investigation on the effects resulting from different characteristics of the images bank used for tests. Therefore, this work reports some results regarding such an investigation, with a further discussion over characteristics that can affect the performance of a CAD scheme. Copyright © 2001 by W.B. Saunders CompanyT HE PERFORMANCE of a computer-aided diagnosis (CAD) scheme is strongly dependent on the database used for testing the procedures. I In a previous work? we developed a computerized procedure as part of a mammography CAD scheme intended to detect clustered microcalcifications in digitized mammograms. The first tests with this scheme indicated an efficacy rate of 94% for a particular set of images. With the goal to study the effect of the characteristics of different sets of images on the performance of such a procedure, we have checked the results yielded from five different sets of mammograms. METHODSThe following sets of images were used for the investigation: (I) a set of actual mammograms, obtained from the archives of Hospital das Clfnicas . same set digitized by a LUl\lISCAN (Lumisys, Sunnyvale, CA) laser scanner, with 0.15 mm and 8 bits; (3) another set of mammograms obtained from that same hospital in 1995, and digitized in a UMAX UCI260-Pro, with the same resolutions as the first group; (4) a set of mammograms obtained from recent examinations performed at the Santa Casa hospital at S. Carlos (Brazil), only corresponding to dense breast cases and digitized by the LUl\lISCAN scanner, with the same resolutions as the second group above; and (5) a previously used set obtained off the internet from the National Expert and Training Center for Breast Cancer Screening (the University of Nijmegen, the Netherlands), also with the same resolutions as the second and fourth groups.The steps of the processing scheme for clusters detection were as follows: identification of regions of interest (ROIs); ROI segmentation; area-point transformation.' which converts each detected signal in a unique pixel; and microcalcification grouping, where clusters are identified and marked in the final image. Initially, the procedure was applied to all of the image sets with no changes in the processing parameters, in order to investigate the effect of the acquisition and digitization processes. Then, some parameters were changed according to the database characteristics under test in order to determine the best result possible for that set of images. Figure I illustrates the resultant images after some step...

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To evaluate the performance of three digital devices regarding the noise added to digital radiographic images containing different optical densities.Methods:A radiographic image was digitized repeatedly ten times using two scanners (HP 4c/T and HP 5370C) and a digital camera (Nikon 990). A histogram tool measured a mean pixel value and the standard deviation of the region of interest in each image. Both values were used to calculate the image noise at the different optical densities.Results:The noise values found were different for all devices and optical densities. There was a statistically significant difference (p<0.05) between the scanner HP 4c/T and the digital camera regarding the noise values. There was a significant correlation (p<0.05) between the noise values found for the HP 4c/T scanner and the digital camera and between both scanners (p<0.01).Conclusions:The noise added to the image was higher for scanner HP 4c/T and less for the digital camera. The noise was higher at the lower optical densities for the scanners. It seems that depending on the equipment and the optical density, a variable amount of noise can be incorporated to the images.

ABSTRACT:The objective of the present study was to determine the reproducibility of the pixel values obtained with the Digora system (Soredex, Finland). Exposures were standardized, with variation in exposure and scanning time of two photostimulable phosphor plates containing a stepwedge image. The smallest variation in pixel values ranged from 50 to 75%, with the widest variations being observed in less dense steps. A signifi cant difference in pixel values was observed in terms of X-ray exposure and scanning times and between the two plates themselves (ANOVA, p < 0.01). Using the present methodology, the reproducibility of pixel values was not satisfactory for the tested white photostimulable plates. This wide variation in digitalization might be infl uenced by the amount of X-rays that sensitized the plates. It may be important to establish the reproducibility of the pixel values in quantitative studies using digital image. DESCRIPTORS:Radiography, dental, digital; Reproducibility of results. RESUMO:O objetivo do presente trabalho foi determinar a reprodutibilidade dos valores de "pixels" obtidos com o sistema Digora (Soredex, Finlândia). As exposições foram padronizadas, com variação no tempo de exposição e leitura de duas placas de fósforo fotoestimuláveis contendo a imagem de um penetrômetro. A menor variação nos valores de "pixels" foi de 50 a 75%, sendo as maiores variações oriundas nas faixas mais claras. Uma diferença signifi cante nos valores de "pixels" foi observada em relação ao tempo de exposição e leitura das placas e entre as duas placas (ANOVA, p < 0,01). Utilizando a presente metodologia, a reprodutibilidade dos valores de "pixels" das placas testadas do sistema Digora não foi satisfatória. Essa grande variação na digitalização pode ter sido infl uenciada pela quantidade de Raios X que sensibilizou as placas. Isso pode ser importante para estabelecer a reprodutibilidade dos valores de "pixels" em estudos quantitativos usando imagem digital. DESCRITORES:Radiografi a dentária digital; Reprodutibilidade dos resultados.

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Escarpinati -FACOM/UFU (coorientador) e André Ricardo Backes -FACOM/UFU, orientador do candidato. Ressalta-se que o Prof. Dr. Maurício Marengoni participou da defesa por meio de videoconferência desde a cidade de São Paulo -SP. Os outros membros da banca e o aluno participaram in loco. Iniciando os trabalhos o presidente da mesa, Prof. Dr. André Ricardo Backes, apresentou a Comissão Examinadora e o candidato, agradeceu a presença do público, e concedeu ao Discente a palavra para a exposição do seu trabalho. A duração da apresentação do Discente e o tempo de arguição e resposta foram conforme as normas do Programa. A seguir o senhor presidente concedeu a palavra, pela ordem sucessivamente, aos examinadores, que passaram a arguir o candidato. Ultimada a arguição, que se desenvolveu dentro dos termos regimentais, a Banca, em sessão secreta, atribuiu o resultado final, considerando o candidato: Aprovado Esta defesa faz parte dos requisitos necessários à obtenção do título de Mestre.O competente diploma será expedido após cumprimento dos demais requisitos,

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