Showing papers on "Digital mammography published in 1995"

Markov random field for tumor detection in digital mammography

Abstract: A technique is proposed for the detection of tumors in digital mammography. Detection is performed in two steps: segmentation and classification. In segmentation, regions of interest are first extracted from the images by adaptive thresholding. A further reliable segmentation is achieved by a modified Markov random field (MRF) model-based method. In classification, the MRF segmented regions are classified into suspicious and normal by a fuzzy binary decision tree based on a series of radiographic, density-related features. A set of normal (50) and abnormal (45) screen/film mammograms were tested. The latter contained 48 biopsy proven, malignant masses of various types and subtlety. The detection accuracy of the algorithm was evaluated by means of a free response receiver operating characteristic curve which shows the relationship between the detection of true positive masses and the number of false positive alarms per image. The results indicated that a 90% sensitivity can be achieved in the detection of different types of masses at the expense of two falsely detected signals per image. The algorithm was notably successful in the detection of minimal cancers manifested by masses /spl les/10 mm in size. For the 16 such cases in the authors' dataset, a 94% sensitivity was observed with 1.5 false alarms per image. An extensive study of the effects of the algorithm's parameters on its sensitivity and specificity was also performed in order to optimize the method for a clinical, observer performance study. >

Wavelets for contrast enhancement of digital mammography

Abstract: Multiresolution representations provided an adaptive mechanism for the local emphasis of features of importance to mammography In general, improvements in image contrast for multiscale image processing algorithms were superior to those obtained using existing competitive algorithms These initial results are encouraging and suggest that wavelet based image processing algorithms could play an important role in improving the imaging performance of digital mammography In part 2, features blended into the mammograms were "idealized" representations of the types of objects that are of primary interest to mammographers The resultant mammographic images were appropriate for the purpose of demonstrating improved image contrast made possible by wavelet based image processing algorithms These images were also useful for comparing multiscale wavelet based algorithms with existing image processing algorithms The test results obtained in this study, however, cannot be directly extrapolated to clinical mammography In addition, it is also important to study possible image artifacts introduced by new wavelet filters, which may increase the false positive rate >

New methods for imaging the breast: techniques, findings, and potential.

Abstract: Mammography is currently the best imaging technique for the early detection and diagnosis of breast cancer. Although numerous advances and improvements in mammography in the past decades have greatly improved image quality, the technique is not without shortcomings that limit its sensitivity and specificity. Multiple areas of research have therefore been sought not only to improve film/screen mammography, but also to consider entirely new techniques in the study of breast cancer. Although this review is not intended to include all methods currently under investigation, those chosen for discussion represent areas where major efforts have provided data that suggest exciting future applications. These include MR imaging, digital mammography, computer-aided diagnosis (CAD), positron-emission tomography (PET), and single-photon emission planar CT imaging (SPECT).

Computer assisted diagnosis for digital mammography

Abstract: This article describes the application of wavelet transform for image enhancement in medical imaging. The initial clinical application is the enhancement of microcalcification clusters (MCCs) in digitized mammograms to improve both their visualization and their detection using computer assisted diagnostic (CAD) methods. The potential universal application for improved visual interpretation of medical images using a computer monitor is also demonstrated. The early detection of MCCs is important in screening programs since their presence is often associated with a high incidence of breast cancer. The enhancement of MCCs is an excellent model for real world evaluation of the wavelet transform. The detection of MCCs presents a significant challenge to the performance characteristics of X-ray imaging sensors and image display monitors since microcalcifications vary in size, shape, signal intensity, and contrast and may be located in areas of very dense parenchymal tissue, making their detection difficult. The classification of MCCs, in turn, as benign or malignant, requires their morphology and detail to be preserved. >

Tree structured wavelet transform segmentation of microcalcifications in digital mammography

Abstract: A novel multistage algorithm is proposed for the automatic segmentation of microcalcification clusters (MCCs) in digital mammography. First, a previously reported tree structured nonlinear filter is proposed for suppressing image noise, while preserving image details, to potentially reduce the false positive (FP) detection rate for MCCs. Second, a tree structured wavelet transform (TSWT) is applied to the images for microcalcification segmentation. The TSWT employs quadrature mirror filters as basic subunits for both multiresolution decomposition and reconstruction processes, where selective reconstruction of subimages is used to segment MCCs. Third, automatic linear scaling is then used to display the image of the segmented MCCs on a computer monitor for interpretation. The proposed algorithms were applied to an image database of 100 single view mammograms at a resolution of 105 microns and 12 bits deep (4096 gray levels). The database contained 50 cases of biopsy proven malignant MCCs, 8 benign cases, and 42 normal cases. The measured sensitivity (true positive detection rate) was 94% with a low FP detection rate of 1.6 MCCs/image. The image details of the segmented MCCs were reasonably well preserved, for microcalcification of less than 500 microns, with good delineation of the extent of the microcalcification clusters for each case based on visual criteria.

Large area array, single exposure digital mammography

Abstract: A unique digital imaging device includes the digital imager, a mammography machine including the digital imager, a method for processing the digital image obtained by the digital imager, a local area network (LAN) comprising a number of mammography machines and one or more work stations, and a wide area network (WAN) for transmitting digital images to remote locations. The digital imager according to the present invention comprises a large area, single exposure digital imaging device is provided that allows a number of electronic imagers to be butted together to form an array of electronic imagers large enough to image an entire breast in a single exposure. A preferred embodiment of the digital imager comprises an optical system, such as fiber optic bundles, optically coupled with the surface of the electronic imager. The optical systems may have a surface larger than the electronic sensors, and may be butted together to provide a gap-free imaging surface.

Digital mammography with synchrotron radiation

Abstract: The SYRMEP (synchrotron radiation in medical physics) Collaboration is planning to use a beam of monochromatic x‐rays provided by Elettra, the synchrotron radiation facility in operation at Trieste (Italy), in conjunction with a novel silicon pixel detector to conduct research in digital mammography. A beamline dedicated to mammography is presently under construction in Trieste; it will provide, at a distance of about 20 m from an Elettra bending magnet, a monochromatic laminar‐section (150×4 mm2) x‐ray beam. This beam will illuminate in vitro samples and will be detected by a fixed silicon microstrip device forming a matrix of pixels. Digital images of phantoms having a size common in the diagnostic practice (150×150 mm2), can then be produced by scanning the sample itself in front of the detector. A prototype detector with a sensitive area of 24×1 mm2 and pixels of 0.5×0.5 mm2 has been built and tested. We present the current status of the SYRMEP beamline and a digital image of a mammographic phantom exposed to a radioactive x‐ray source.

Digital radiology using self-scanned readout of amorphous selenium: design considerations for mammography

Abstract: We are developing a large area, flat panel solid-state detector for general application to digital radiology. The proposed detector employs a continuous photoconductive layer of amorphous selenium ((alpha) -Se) to convert incident x rays to electron-hole pairs, which are then separated and drawn to the surface of the (alpha) -Se by an applied electric field. The resulting charge image is digitally read out in situ using a large area active matrix array made with cadmium selenide (CdSe) thin film transistors (TFTs). The relationship between the potential imaging properties and the design parameters of this detector concept for digital mammography were analyzed theoretically using measured characteristics of (alpha) -Se layers and CdSe active matrices.

Applying wavelets to mammograms

Abstract: This article briefly reviews the challenges faced as technology moves toward digital mammography, presents a necessarily brief overview of multiresolution analysis, and finally, gives current and future applications of wavelets to several areas of mammography. Topics covered include data compression and teleradiology, feature enhancement and classification, wavelets, fractals and texture, and de-noising. >

Solid state x-ray detectors for digital mammography

Abstract: In conventional mammography, x rays transmitted through the breast are converted to light in a phosphor screen, and the light exposes a film emulsion. The information in the image is degraded in this detector due to limitations in the screen and film. Photodiode arrays can convert the x rays directly into charge and overcome these problems. A preliminary investigation of a thick crystalline silicon photodiode array as a solid state digital detector was performed. The prototype device consists of a 300 micrometers thick, 256 X 256 photodiode array of 30 X 30 micrometers 2 pixels. The array was hybridized to two different readout structures for evaluation purposes, one structure being used for imaging and the other for single pixel experiments. Imaging performance, such as linearity, resolution, and noise were measured and used to predict the performance of a proposed clinical version of the prototype. Results show the detector response to be linear over the range of exposures required for mammography, the modulation transfer function (MTF) to be superior to that of screen-film detectors, and the noise to be dominated by x-ray quantum fluctuation. Based on results from the prototype devices, we predict that the detective quantum efficiency (DQE) of the clinical design will be significantly higher than that of a screen-film detector for all spatial frequencies of interest.

Clinical use of digital mammography: The present and the prospects

Abstract: Digital mammography is likely to replace the current routine breast imaging technology in the future because it offers advantages that should lead to both improved image quality and interpretation Hopefully, this will result in earlier detection in breast screening programs and decreased mortality from the most frequently diagnosed of all cancers after skin cancer, which is far less deadly At present, digital mammography has a limited clinical role; in the United States, it has been used for several years to localize lesions for tissue sampling using small field of view digital detectors Once whole breast digital detectors are available, it seems clear that applying computer techniques to enhance and analyze the collected digital data will become routine Results reported over the last decade indicate that computer-aided diagnosis can improve radiologists’ observational performance, and it is likely that computer techniques to routinely enhance the decision-making ability of the average to below-average radiologist to the level of an expert will be developed There are obstacles to these advances, but the combination of realizable technological solutions and the importance of the breast cancer problem clinically should provide sufficient wherewithal and impetus to make digital mammography a clinical reality

Evaluating quality and utility in digital mammography

Abstract: Image quality and utility become crucial issues for engineers, scientists, patients, regulators, administrators, insurance companies, and lawyers whenever there are changes in the technology by which medical images are produced. Examples of such changes include analog-to-digital conversion, lossy compression for efficient transmission and storage, image enhancement, and computer-aided methodology for diagnosis that affects the appearances of images. This paper is a summary of some principles for designing protocols for clinical experiments to quantify the relative qualities and utilities of different images, here analog, digital, and lossy compressed digital mammograms. A talk supplemented this paper with a status report on the specific experiment described which is scheduled to be conducted during summer 1995.

Image quality control for digital mammographic systems: initial experience and outlook.

Abstract: This report presents (1) a broad topical review and a tutorial of the possibilities for image quality control (IQC) with digital systems, and (2) results and initial experience for IQC with two commercial digital imaging systems, but with limited discussion on any particular method. Digital imaging systems used for mammographically guided digital stereotactic breast biopsy were evaluated extensively at the University of Arizona. Measurements were made of linearity, sensitivity, signal-to-noise ratio, and square-wave modulation. Images of phantoms such as the American College of Radiology Accreditation Phantom and the contrast detail mammography Phantom were evaluated as well as images of the x-ray source’s focal spot. The evaluation also included the cathode ray tubes for the imaging systems. The data collected show that digital imaging systems have an important advantage over film-screen systems because they provide a digital signal as output that can be used for quantitative analysis. As a result, IQC can become a much more quantitative discipline than presently practiced, providing more information on the imaging systems under evaluation, and providing better control over their properties during actual operation.

Telemammography: implementation issues.

Abstract: Telemammography has the potential to improve access to centralized expertise for the interpretation of breast imaging studies. Digital mammography has more demanding spatial resolution requirements than other forms of medical imaging because of the need to detect microcalcifications, the fine details of lesion margins, and subtle architectural distortion. The resolution requirements for mammography have important implications for image acquisition and display technologies. The large size of the resulting image data sets places significant demands on local and wide area networks as well as storage media. Image data compression will be particularly important for telemammography to help make systems practical and affordable. This article describes how existing technologies can be adapted to implement telemammography systems in the near future.

Digital mammography at the Trieste synchrotron light source

Abstract: The SYRMEP collaboration is developing a digital mammography project using a synchrotron radiation monochromatic X-ray beam and a silicon pixel detector. The combination of a monochromatic laminar beam with a high efficiency laminar detector, capable of single-photon counting, allows one to minimize the radiation dose delivered to the sample, while maximizing contrast resolution and dynamic range. The SYRMEP detector is a silicon microstrip device used in an innovative configuration in which radiation impinges on the side rather than on the surface of the chip and is therefore totally absorbed within the detector active volume. The high contrast resolution and spatial resolution (<100 microns) of the system have been demonstrated by producing images of details from an Ackermann Mammographic Phantom RMI 160 illuminated by a conventional X-ray tube.

Digital mammography: tradeoffs between 50- and 100-micron pixel size

Abstract: Improvements in mammography equipment related to a decrease in pixel size of digital mammography detectors raise questions of the possible effects of these new detectors. Mathematical modeling suggested that the benefits of moving from 100 to 50 micron detectors were slight and might not justify the cost of these new units. Experiments comparing screen film mammography, a storage phosphor 100 micron digital detector, a 50 micron digital breast spot device, 100 micron film digitization and 50 micron film digitization suggests that object conspicuity should be better for digital compared to conventional systems, but that there seemed to be minimal advantage to going from 100 to 50 microns. The 50 micron pixel system appears to provide a slight advantage in object contrast and perhaps in shape definition, but did not allow smaller objects to be detected.

Evaluation of digital mammography in diagnosis of breast cancer.

Abstract: Mammography has been digitized in all cases at our hospital. Digital mammography (MMG) of our hospital and its diagnostic accuracy were described in this report. Fuji Computed Radiography (FCR; Fuji Medical Systems, Tokyo, Japan) imaging plate was used and imaging data were processed with FCR 7000 or FCR 9000. Each image was output to a single hard copy. Sampling pitches for reading and output were 0.1 mm. The rate of breast cancer diagnosis by digital MMG was 67%, 95%, 94%, and 100% for unpalpable tumor, tumor less than ϕ 2 cm, tumor of ϕ 2 to 5 cm, and tumor greater than ϕ 5 cm, respectively, being 94% overall. Digital MMG enables us to establish goal-oriented image-processing conditions. The use of digital MMG, which provides an excellent diagnostic rate similar to that of screen-film MMG, is expected to became wide-spread in the near future.

Large-field high spatial resolution digital x-ray mammography

Abstract: This paper reports the results of our preliminary investigation into developing imaging techniques for full-size digital x-ray mammography. We have explored a novel `radiation shielding, CCD scanning' concept. Two system configurations were studied: one uses a lens coupled CCD module with a mirror scanning mechanism; the other uses a lens coupled CCD which is mounted on a scanning carrier platform. Using this technique, small CCD imagers can be used effectively to cover a large field without losing spatial resolution.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Silicon detectors for synchrotron radiation digital mammography

Abstract: The knowledge of the dose and of the energy spectrum of the X-rays delivered to the patient during a radiological examination allows in principle the computation of the number of photons per unit surface useful for a good mammography. The film-screen assembly detectors used in the present standard practice require a number of photons per unit surface which, from a statistical point of view, would be unnecessarily high if single photon counting detectors with efficiency near to one were available. We discuss a possible solid state detector with these characteristics. Moreover, we propose the use of an X-ray monochromatic beam from a synchrotron radiation source in order to perform the examination at the energy where the signal to noise ratio has a maximum. Using the proposed detector in such a beam a substantial dose reduction can be foreseen.

A multiparameter optimization of digital mammography

Abstract: Multiparameter optimizations have been carried out for a wide range of digital mammography system configurations and requirements, with the aim of optimizing the image quality for a given patient dose These conditions include a range of slot widths for scanning mammography systems, exposure times from 1 to 10 s, focal spot sizes from 80 to 800 mu m, a range of detector resolutions and noise levels, dose restrictions, patient thicknesses and targets, and X-ray tube targets The influences of these on the optimum system configuration in terms of tube potential, filtration, source to patient distance and target magnification are discussed It is demonstrated that X-ray tube power constraints can significantly restrict the optimum magnification for slot scanning systems, with the result that poor-resolution detectors are not suited for use in a scanning configuration, and that large-focal-spot-good-detector resolution combinations are more suitable The use of a detector with increased width, raised tube potential and reduced amount of added filtration is shown to be helpful in reducing X-ray tube power limitations It is shown that, in many cases, correct optimization can bring the detail SNR for an examination using a given detector-X-ray tube configuration to within 10-15% of the SNR achieved with the optimum combination This gives the designer some scope to consider other factors such as cost and the implications of image size on storage space

Steerable dyadic wavelet transform and interval wavelets for enhancement of digital mammography

Abstract: This paper describes two approaches for accomplishing interactive feature analysis by overcomplete multiresolution representations. We show quantitatively that transform coefficients, modified by an adaptive non-linear operator, can make more obvious unseen or barely seen features of mammography without requiring additional radiation. Our results are compared with traditional image enhancement techniques by measuring the local contrast of known mammographic features. We design a filter bank representing a steerable dyadic wavelet transform that can be used for multiresolution analysis along arbitrary orientations. Digital mammograms are enhanced by orientation analysis performed by a steerable dyadic wavelet transform. Arbitrary regions of interest (ROI) are enhanced by Deslauriers-Dubuc interpolation representations on an interval. We demonstrate that our methods can provide radiologists with an interactive capability to support localized processing of selected (suspicion) areas (lesions). Features extracted from multiscale representations can provide an adaptive mechanism for accomplishing local contrast enhancement. By improving the visualization of breast pathology can improve changes of early detection while requiring less time to evaluate mammograms for most patients.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Clinical aspects of Direct digital mammography

Abstract: Since 1990, computed radiography (CR) has been used routinely in our symptomatic mammography service, imaging approximately 2,000 patients per year. Careful selection of the appropriate image processing parameters results in high-quality images of diagnostic value equivalent to conventional film-screen mammograms. Problems encountered included dust artifacts, black films, and white films, but these constituted only a very small proportion of images obtained and the remedies are discussed. Hard-copy reporting is used and improved image presentation is considered. New processing algorithms and the development of soft-copy reporting at dedicated workstations are expected in the near future.

A hierarchical neural network architecture that learns target context: applications to digital mammography

Abstract: An important problem in image analysis is finding small objects in large images. The problem is challenging because: 1) searching a large image is computationally expensive; and 2) small targets (on the order of a few pixels in size) have relatively few distinctive features which enable them to be distinguished from non-targets. To overcome these challenges the authors have developed a hierarchical neural network architecture which combines multiresolution pyramid processing with neural networks. Here the authors discuss the application of their hierarchical neural network architecture to the problem of detecting microcalcifications in digital mammograms. Microcalcifications are cues for breast tumors. 30% to 50% of breast carcinomas have microcalcifications visible in mammograms while 60% to 80% of all breast tumors eventually show microcalcifications via histology. Similar to the building/ATR problem, microcalcifications are generally very small point-like objects (<10 pixels in mammograms) which are hard to detect. Radiologists must often exploit other information in the imagery (e.g. location of blood vessels, ducts, etc.) in order to detect these microcalcifications. Here the authors examine how well their hierarchical neural network architecture learns and exploits contextual information in mammograms.

New modalities in breast imaging: digital mammography and magnetic resonance imaging.

Abstract: Mammography is currently the only screening method available with proven capability to diagnose nonpalpable breast cancer. However, mammography does not detect all cancers. Cancers are more difficult to detect in radiographically dense breasts because lesions are obscured by breast tissue. Digital mammography and magnetic resonance imaging of the breast may minimize the problems associated with screening dense breasts. If these methods prove to be useful, more cancers could be detected at an earlier stage.

Application of hybrid detector technology for digital mammography

Abstract: A digital x-ray detector applying hybrid detector technology based on indium metal bump- bonding techniques was evaluated at x-ray energies of about 19.5 keV. Silicon of about 1 mm thickness forms the actual detector, converting x-rays directly into electrons (rather than generating light and converting light to photo-electrons). Time-delay-integration increases the sensitivity. Linearity, modulation transfer function, and noise power spectrum were evaluated. The results demonstrate that the system is useful as scanning x-ray detector for digital mammography and can meet and even exceed the performance of the conventional film/screen system.