Comparisons of different contrast resolution effects on a computer-aided detection system intended to cluster microcalcifications detected in dense breast images.

Clustered microcalcifications, which are frequently an important signal of possible cancer, are usually hidden in dense breast images, adding more difficulty in mammogram medical analysis. In this work we evaluate the performance of a previously developed computer-aided detection scheme, modified for application to dense breast images. The main focus of this investigation was on the effect of different contrast resolutions on the processing performance. We have processed dense breast images digitized with 8 and 12 bits to evaluate the performance of this computer-aided detection scheme with different contrast resolutions. As expected, for most of the 12-bit images, the number of detected signals was greater or at least equal to that of the 8-bit images.

Investigations on the effect of different characteristics of images sets on the performance of a processing scheme for microcalcifications detection in digital mammograms.

The performance of a computer-aided diagnosis (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 microcalcifications 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.

Subtraçäo de imagens digitais: vantagens e inconvenientes dos métodos de comparaçäo e de complemento / Digital images subtration: advantages and disadvantages of comparison and complement methods

Este trabalho apresenta um estudo comparativo de dois métodos de substração de angiografias determinando as vantagens e desvantagens de cada um em relação ao ruido das imagens.

A formal study of lateral magnification and its influence on mammographic imaging sharpness.

Radiographic magnification is often employed in mammography to improve detection of small anatomical details of clinical interest, such as microcalcifications. The image size depends on the conventional magnification factor, on the focal spot size, and on the x-ray angulation. In this paper magnification effects are investigated for an object which lays off the radiation field center, for which there is a "lateral magnification" that makes it possible to obtain a sharper image of the object. This occurs because the true image size (i.e., the shadow) becomes larger as the distance from the beam center to the object increases, while the total blurring (penumbra) which is responsible for the unsharpness remains constant. The statement is valid only in the boundary of the perpendicular axis, which for most mammographic units corresponds to the position where the thickest portion of the breast is placed. Calculations are presented which show that the lateral magnification can be useful for enhancing breast microcalcifications using radiographic magnification.

The need for investigating the optical transfer functions in several field orientations for nonisotropic radiographic systems.

In this paper, it is demonstrated that obtaining OTF's for only two directions, parallel and perpendicular to the x-ray tube axis, is insufficient to completely describe the performance of nonisotropic radiographic systems. By performing experiments with three radiological systems in which slit images were obtained for ten different directions, we confirmed that OTF's vary in a nonlinear fashion for directions that are intermediate to the parallel and perpendicular ones. Moreover, we have also identified for each system a range of field orientations--referred to as "Optimum Region"--where sharper images can be obtained. These experimental results can be accounted for by the transfer functions theory.