Catálogo de publicaciones - libros

The purpose of this study was to review the dose and image characteristics of three different FFDM systems; Sectra MDM, GE SenoDS, Lorad Selenia. The dose and image quality characteristics were assessed in terms of both physics and clinical performance. A phantom study was carried out to look at the mean glandular dose delivered to breasts of varying thickness. The dose was also investigated by carrying out a clinical dose survey of a random sample of women on each of the three units. The CDMAM 3.4 was imaged on each unit with varying thicknesses of PMMA and the results correlated with the dose results at each equivalent thickness. The CNR of each unit at varying breast thicknesses was also calculated.

CDMAM phantom scoring is widely used to assess the detectability performance of mammography systems. We propose to study the impact of structured background on this performance assessment, using simulated CDMAM phantom images with flat and textured backgrounds. Three dose levels have been investigated, ranging from -50% to +50% around the reference dose computed by the acquisition system. For textured backgrounds, the simulated projected breast corresponds to a 50mm thick, 60% glandular breast, with a texture generated by a power-law filtered noise model. Images have been scored by four image quality experts. For the smaller insert sizes, Image Quality Factor (IQF) scores obtained in textured backgrounds are lower than and well correlated with those obtained in flat backgrounds. IQF values increased with dose. For the larger insert sizes, detectability performance in textured background is even more degraded and is not as dose dependent as it is in flat backgrounds.

A new breast imaging approach is proposed and implemented that combines Magnetic Resonance Mammography and Electrical Impedance Scanning. In this paper, we report the results of a pilot study that demonstrated the feasibility of this new breast imaging approach. We also discuss our initial experience with the MR imaging parameters and sequences that are critical in observing the desired signal.

The purpose of this work was to investigate whether extra flat field corrections should be applied prior to the calculations of quality control quantities and whether there are necessary precautions regarding flat fielding in digital mammography. Effects from using one standard flat field correction for all imaging situations or absence of correction procedures were examined using homogenous PMMA slabs. Differences in field profiles for various exposure geometries and breast thicknesses were quantified. For three systems the maximal deviation of averaged pixel values (along a profile of ROIs parallel to the chest wall) varied from 1.3 % to 6.8 % over the whole image and from 0.6 % to 2.6 % if the analysis is limited to the central part. Extra flat field corrections are not necessary for most applications. If required, the corrections should be performed from images acquired with the same manual exposure and not after a time gap.

Two observer experiments were performed to evaluate the performance of wavelet enhancement and compression methodologies for digitized mammography. One experiment was based on the localization response operating characteristic (LROC) model. The other estimated detection and localization accuracy rates. The results of both studies showed that the two algorithms consistently improved radiologists’ performance although not always in a statistically significant way. An important outcome of this work was that lossy wavelet compression was as successful in improving the quality of digitized mammograms as the wavelet enhancement technique. The compression algorithm not only did not degrade the readers’ performance but it improved it consistently while achieving compression rates in the range of 14 to 2051:1. The proposed wavelet algorithms yielded superior results for digitized mammography relative to conventional processing methodologies. Wavelets are valuable and diverse tools that could make digitized screen/film mammography equivalent to its direct digital counterpart leading to a filmless mammography clinic with full inter- and intra-system integration and real-time telemammography.

Breast tomosynthesis has the potential to improve lesion visibility and localization compared to conventional mammography. To be clinically useful, tomosynthesis must be able to achieve high image quality at acceptable radiation doses. Tomosynthesis data sets of simple low-contrast phantoms were acquired at varying dose levels. Image quality in the reconstructed volumes was analyzed by evaluating the voxel-to-voxel signal difference to noise ratio between a simulated lesion and the surrounding “tissue”. Preliminary results indicate that image quality of small lesions is limited by scatter and reconstruction artifacts. In uniform backgrounds image quality appears to be quantum-noise limited, while in more complex backgrounds the structural noise tends to dominate.

Digital breast tomosynthesis is becoming a clinically attractive modality based on its potential to combine the high resolution and high contrast images, and affordability of digital mammography, with the advantages of 3D image acquisition. In order to facilitate comparison of tomosynthesis images with previous mammographic exams of the same women, there is a need for a method of registering a mammogram with a tomosynthetic image of the same breast; this is the focus of this paper. We have chosen to approach this multimodality registration problem, starting from the simpler problem of registering a mammogram and the central tomosynthesis source image. Such a registration pair represents the most similar breast images obtained from different clinical modalities. In this study of 15 pairs of mammograms and central tomosynthesis projections of the same breast, on average we were able to compensate 94 percent of the per-pixel intensity differences that existed between the two images before the registration.

The experience of clinical use of breast CAD system at the hospital of Gifu University School of Medicine was reported. The CAD system was Image Checker M1000-DM available for Senographe 2000D.During February 4, 2005 to May 16, 125 cases was examined by this device and 22cases of breast cancers were found. A case was misdiagnosed by radiologist before CAD, and CAD detected the lesion. Another case was correctly detected by radiologist before CAD, but CAD could not point out the lesion. 20 remain cases were detected correctly by both radiologist and CAD. CAD was supposed to be useful for the mammographic diagnosis of breast cancer.

Most of the CAD Systems for Mammograms are composed of algorithms analysing the four X-ray images individually. It is a general experience, that algorithms in search of microcalcification clusters can obtain high sensitivity only if specificity is low. To overcome efficiency problem this paper proposes a simple algorithm to combine information of the two views (MLO/CC) of the breast. The procedure is based upon the experiences of radiologists: masses and calcifications should emerge on both views, so if no matching is found, the given object is a false positive hit. A positioning system is evolved to find corresponding regions on the two images. Calcification clusters obtained in individual images are matched in “2.5-D” provided by the positioning system. The credibility value of the hit is reassessed by the matching. The proposed approach can significantly reduce the number of false positive hits in calcification.

In general, the use of more projections results in fewer tomosynthesis reconstruction artifacts. However, under a fixed dose, an excess number of projections will make the detector noise more pronounced in each of the x-ray shots and thus degrade image quality. Even in the absence of detector noise the advantages of higher projection numbers eventually have diminishing returns, making more projections unnecessary. In this study, we explore the dependence of tomosynthesis imaging performance on the number of projections, while keeping other factors fixed. We take the contrast-to-noise ratio as the figure of merit to search for the range of optimal projection number. The study is carried out through both simulations and experiments, with phantoms consisting of micro-calcification and mass objects, and a cadaver breast. The goal of this paper is to describe our methodology in general, and use a prototype tomosynthesis system as an example. The knowledge learned will help the design of future generation clinical tomosynthesis systems.