Digital Mammography Equipment Research Articles

MO‐SAMS‐L100J‐01: Digital Mammography Update: Design and Characteristics of Current Systems

Mammography still remains the best screening tool for early detection of breast cancer, and the recent ACRIN DMIST results draw attention to the fact that digital mammography is better at detecting cancers in dense breasts. Digital mammography equipment has continued to develop and improve and more vendors and models have entered the marketplace with FDA approval. The technology used in these systems generally falls into four main categories: direct capture detectors, indirect capture detectors, slot scanning, and cassette‐based storage phosphors (computed radiography). Additionally, a photon counting system is being developed. Each of these technologies has its advantages and disadvantages. A review of the systems currently available is presented, including the detector technology utilized. Features of these systems are also presented. This is a Self Assessment Module (SAM) to help fulfill the requirements of the Maintenance of Certification (MOC) process as defined by the American Board of Radiology (ABR). As such, audience participation through interactive questions will be provided during the course of the lecture.Educational Objectives:1. Become familiar with the detector technologies currently used in digital mammography systems.2. Become familiar with the digital mammography systems available from each manufacturer.3. Become familiar with the unique elements of each system.

How to Transition to Digital Mammography

To date, the transition to digital mammography has been cumbersome and difficult. In part, this is because digital mammography equipment could not be easily integrated into preexisting picture archiving and communication systems (PACS). Until the results of the ACR Imaging Network Digital Mammographic Imaging Screening Trial showed that digital mammography is more accurate than screen-film mammography for some patients, users have been reticent to switch. To make the transition as seamless as possible, several considerations should be made. First, an evaluation of a facility's current screen-film situation, including the condition of the analog units, work flow, patient capacity, staffing, and existing PACS components helps in understanding current status more clearly. After that, the facility's goals for a digital department should be determined. Next, the components of the digital imaging chain, the network infrastructure, and the PACS, as well as what clinical aspects each part of the chain affects, must be understood to avoid unexpected frustrations after the conversion is made. Then, education is required on the different acquisition options, display options, printing options, and archival options to facilitate the choice of equipment that will meet the digital goals set forth previously. Finally, a pace of conversion that is best suited to the facility should be determined.

Comparison of different commercial FFDM units by means of physical characterization and contrast‐detail analysis

The purpose of this study was to perform a complete evaluation of three pieces of clinical digital mammography equipment. Image quality was assessed by performing physical characterization and contrast-detail (CD) analysis. We considered three different FFDM systems: a computed radiography unit (Fuji "FCR 5000 MA") and two flat-panel units, the indirect conversion a-Si based GE "Senographe 2000D" and the direct conversion a-Si based IMS "Giotto Image MD." The physical characterization was estimated by measuring the MTF, NNPS, and DQE of the detectors with no antiscatter grid and over the clinical range of exposures. The CD analysis was performed using a CDMAM 3.4 phantom and custom software designed for automatic computation of the contrast-detail curves. The physical characterization of the three digital systems confirms the excellent MTF properties of the direct conversion flat-panel detector (FPD). We performed a relative standard deviation (RSD) analysis, for investigating the different components of the noise presented by the three systems. It turned out that the two FPDs show a significant additive component, whereas for the CR system the statistical noise is dominant. The multiplicative factor is a minor constituent for all the systems. The two FPDs demonstrate better DQE, with respect to the CR system, for exposures higher than 70 microGy. The CD analysis indicated that the three systems are not statistically different for detail objects with a diameter greater than 0.3 mm. However, the IMS system showed a statistically significant different response for details smaller than 0.3 mm. In this case, the poor response of the a-Se detector could be attributed to its high-frequency noise characteristics, since its MTF, NEQ, and DQE are not inferior to those of the other systems. The CD results were independent of exposure level, within the investigated clinical range. We observed slight variations in the CD results, due to the changes in the visualization parameters (window/level and magnification factor). This suggests that radiologists would benefit from viewing images using varied window/level and magnification.

The Dutch experience of digital mammography in screening

In The Netherlands a number of (screening) trials with digital mammography have started. The first trial began in 1999, in which the applicability of digital mammography was tested in a clinical environment. For this purpose a GE Senographe 2000D was installed in the Radboud University Nijmegen Medical Centre. The outcome of this trial was positive. Therefore in 2002 a second trial started at a static screening site in Utrecht with a Lorad Selenia system. In this trial, digital mammography was evaluated in a screening environment with its specific demands regarding workflow. In 2004 two more trials were started with mobile digital screening units. In these trials, a Fuji FCR Profect and an Agfa DM 1000 system were installed in the screening units. This summer a new trial will start at a static screening unit in Nijmegen in which digital mammography equipment from different vendors (General Electric, IMS, Sectra, Planmed) will be installed to test connectivity. Results of all trials will be presented with emphasis on physical and technical aspects and workflow issues. Problems with the mammography systems in the trials will be discussed. Besides this, some experiences with digital mammography equipment in Dutch hospitals will be discussed with emphasis on possible pitfalls.

Status of Mammography after the Digital Mammography Imaging Screening Trial: Digital versus Film

Well-publicized results of the recent Digital Mammography Imaging Screening Trial (DMIST) have again shown that there is no clear advantage in mammographic screening of the general population with digital versus film mammography. However, several subgroups--women less than 50 years old, pre- or perimenopausal, and denser breasts--did better with digital mammography than with film. Data also suggest that women with the opposite characteristics might do better with film mammography. This article reviews the data of the four studies comparing digital and film mammographic screening. In addition, it describes the technology involved in the two types of mammographic image capture, the advantages and disadvantages of each type of imaging, and the future possibilities opened by digital technique. Because less than one-tenth of mammography units in use in the United States are digital, the availability of this technology to women undergoing screening and to physicians referring patients to screening sites is very limited. The author suggests that the quality of mammography, rather than the technique used to capture the image, is more important in selecting a mammography facility. For those who have a facility that offers both digital and film mammography, consultation on which type of imaging might be better for an individual woman would be appropriate. Because digital mammography from different manufacturers is based on differing technologies and because data comparing the advantages or disadvantages of these differing types of equipment are not available, it is impossible to recommend which type of digital mammography equipment is best for those undergoing mammography with these types of units.

American College of Radiology Imaging Network Digital Mammographic Imaging Screening Trial: Objectives and Methodology

This study was approved by the Institutional Review Board (IRB) of the American College of Radiology Imaging Network (ACRIN) and each participating site and by the IRB and the Cancer Therapy Evaluation Program at the National Cancer Institute. The study was monitored by an independent Data Safety and Monitoring Board, which received interim analyses of data to ensure that the study would be terminated early if indicated by trends in the outcomes. The ACRIN, which is funded by the National Cancer Institute, conducted the Digital Mammographic Imaging Screening Trial (DMIST) primarily to compare the diagnostic accuracy of digital and screen-film mammography in asymptomatic women presenting for screening for breast cancer. Over the 25.5 months of enrollment, a total of 49 528 women were included at the 33 participating sites, which used five different types of digital mammography equipment. All participants underwent both screen-film and digital mammography. The digital and screen-film mammograms of each subject were independently interpreted by two radiologists. If findings of either examination were interpreted as abnormal, subsequent work-up occurred according to the recommendations of the interpreting radiologist. Breast cancer status was determined at biopsy or follow-up mammography 11-15 months after study entry. In addition to the measurement of diagnostic accuracy by using the interpretations of mammograms at the study sites, DMIST included evaluations of the relative cost-effectiveness and quality-of-life effects of digital versus screen-film mammography. Six separate reader studies using the de-identified archived DMIST mammograms will also assess the diagnostic accuracy of each of the individual digital mammography machines versus screen-film mammography machines, the effect of breast density on diagnostic accuracy of digital and screen-film mammography, and the effect of different rates of breast cancer on the diagnostic accuracy in a reader study.

Dose to population as a metric in the design of optimised exposure control in digital mammography

This paper describes a method for automatic optimisation of parameters (AOP) in digital mammography systems. Using a model of the image chain, contrast to noise ratio (CNR) and average glandular dose (AGD) are computed for possible X-ray parameters and breast types. The optimisation process consists of the determination of the operating points providing the lowest possible AGD for each CNR level and breast type. The proposed metric for the dose used in the design of an AOP mode is the resulting dose to the population, computed by averaging the AGD values over the distribution of breast types in the population. This method has been applied to the automatic exposure control of new digital mammography equipment. Breast thickness and composition are estimated from a low dose pre-exposure and used to index tables containing sets of optimised operating points. The resulting average dose to the population ranges from a level comparable to state-of-the-art screen/film mammography to a reduction by a factor of two. Using this method, both CNR and dose are kept under control for all breast types, taking into consideration both individual and collective risk.

Implementing digital quality control in a breast center

Breast imaging centers in the United States are currently transitioning from traditional screen-film mammography to full-field digital mammography. Quality control for full-field digital mammography is more difficult, time consuming, and expensive than for traditional screen-film mammography. Full-field digital mammography quality control is more precise than screen-film mammography quality control at identifying noncompliant components. As per U.S. Food and Drug Administration requirements, each manufacturer of full-field digital mammography equipment designs and establishes its own quality control process.

Digital and Computer-Aided Mammography.

Digital mammography uses an electronic system to record an image of the breast that can be stored on a computer instead of on hardcopy films. There are a number of digital mammography technologies under evaluation. The potential advantages of digital mammography include improvements in image contrast, manipulation of the image after it is performed (avoiding repeats for technical problems), elimination of lost films, reduction in film library maintenance costs, and the ability to transmit the images over long distances (telemammography). Challenges and potential problems for digital mammography include a need to prove equivalence in detection and diagnosis with conventional mammography, the high cost of digital mammography equipment, and lagging workstation technology. Computer-aided detection and diagnosis (CAD) uses analysis by a computer program to assist the interpreting physician in identifying abnormal findings on mammograms and in making a benign versus malignant diagnosis of calcifications and masses. Several studies suggest that this technology can reduce the incidence of missed cancers and improve the positive predictive value for biopsies. CAD can be performed after digitization of hardcopy films but is best suited to digitally acquired soft copy images.

Use of digital mammography in needle localization procedures.

With digital technology, images can be displayed rapidly and manipulated. This study was undertaken to assess the duration and accuracy of needle localizations performed with digital vs film-screen technology. These two technologies also were compared with respect to radiation doses and ability to image a standard phantom. A prototype digital mammographic system with both a 512 x 512 matrix and a 1024 x 1024 matrix was evaluated by using the American College of Radiology mammography accreditation phantom, and these results were compared with testing done on commercially available, dedicated, analog mammography equipment. Duration, accuracy of needle placement, and number of exposures needed to perform localization were recorded for 157 consecutive needle localizations done with digital technology, and these results were compared with data collected from 103 needle localizations done with film-screen technology. Another 33 localizations attempted with digital imaging were aborted because of technical factors. Average glandular doses were calculated for those women who had a compressed breast thickness of 4-5 cm. The time to complete needle localization was reduced by almost 50%, from 20 to 11 min, when digital technology was used. Because of the small (5 x 5 cm) field of view of the digital system, an additional mammogram obtained at the onset of the procedure was found to be helpful in localization, but otherwise the number of images was the same regardless of imaging receptor. Mean glandular dose was reduced by about 50% with digital imaging from 0.219 to 0.120 cGy. In those 17% (33/190) of needle localizations that could not be completed with digital imaging, failure was due to a variety of factors. Despite improved detectability of fibrils, specks, and masses on digital images, digital systems did not show some fine calcifications or soft-tissue masses during needle localizations. Difficulty in imaging lesions near the chest wall or in the axilla and the small field of view also caused procedures attempted with digital imaging to be aborted and completed with film-screen systems. The time to complete needle localization was reduced by 50%, with a similar reduction in patients' radiation dose, when digital mammography was used. These findings should be applicable to stereotaxic procedures done with digital mammography. Factors limiting the use of digital mammography equipment included inability to image some fine calcifications and some masses, difficulty in imaging near the chest wall and in the axilla, and a small field of view.