Full-field Digital Mammography System Research Articles

Visibility of simulated microcalcifications—A hardcopy‐based comparison of three mammographic systemsa)

Full-field digital mammography systems are currently available for clinical use. These digital systems offer improved image quality, flexible image processing, display, storage, retrieval, and transmission. These systems employ a variety of different x-ray detectors based on storage phosphors (in computed radiography), charge-coupled devices (CCDs), or amorphous silicon flat panels (FPs). The objective of this study is to compare three different types of mammographic detectors: screenfilm (SF) combination, a CsI-based FP detector, a CCD and x-ray phosphor-based detector for their performance in detection of simulated microcalcifications. Microcalcifications (MCs) were simulated with calcium carbonate grains of various sizes (90-355 microm). They were overlapped with a slab of simulated 50% adipose/50% glandular breast tissue for a uniform background or an anthropomorphic breast phantom for a tissue structure background. Images of the phantoms, acquired with and without magnification, were reviewed by mammographers, physicists, and students. A five-point confidence level rating was given for each MC reviewed. Average ratings from the mammographers were used to compare the performances of the three imaging systems, various MC size groups, and two magnification modes. The results indicate that with uniform background and no magnification, the FP system performed the best while the SF system did slightly better than the CCD system. With magnification added, all detection tasks were improved except for the smallest and largest one or two size groups. In particular, detection in the SF and CCD images was significantly improved over that in the FP images. With tissue structure background and no magnification, the FP system was outperformed by the SF and the CCD systems. With magnification added, the performance of the FP and the CCD systems was improved significantly. With this improvement, the SF and FP systems were outperformed by the CCD system.

The current status of full-field digital mammography quality control

U.S. Food and Drug Administration (FDA) regulations require that medical physicists and technologists adhere to the procedures, testing frequencies, and performance criteria outlined in the quality control (QC) manuals provided by the manufacturers of full-field digital mammography (FFDM) systems. As a result of this requirement, QC for digital equipment has become both complicated and inconsistent. The objective of this study was to compare the current QC protocols for the tests to be performed by medical physicists for three commercially available FFDM systems (the Senographe 2000D, the SenoScan, and the Selenia). Although not yet approved by the FDA, the 5000 MA was also included because of its unique design and extensive use in a major ongoing clinical research trial involving the other three FFDM systems. It was found that currently, a high degree of discord exists between the FFDM QC protocols of the early commercial systems, with wide variation in opinion with respect to the minimum performance criteria and testing intervals and with respect to which tests are necessary and what quantities should be measured. Additionally, very few digital detector-specific tests are currently in place. Although technological differences between the early FFDM systems prohibit a strictly uniform set of QC procedures and performance guidelines, a much greater degree of consensus among manufacturers is desirable as FFDM continues to gain clinical presence during the next few years.

Physical characteristics of a full-field digital mammography system

Physical characteristics of a full-field digital mammography system

AAPM/RSNA Physics Tutorial for Residents

Recent advances in digital detector technology have paved the way to full-field digital mammography (FFDM) systems. The performance of these systems has evolved to the point where replacement of screen-film mammography (SFM) systems is becoming realistic. Despite some commonality between the two techniques, there are fundamental differences in how images are recorded, displayed, and stored. These differences necessitate an understanding of the principles of detection and the characteristics of digital images. Several approaches have been taken in the development of FFDM systems: (a) slot scanning with a scintillator and a charge-coupled device (CCD) array, (b) a flat-panel scintillator and an amorphous silicon diode array, (c) a flat-panel amorphous selenium array, (d) a tiled scintillator with fiberoptic tapers and a CCD array, and (e) photostimulable phosphor plates (computed radiography). Although the initial cost of an FFDM system is high compared with that of an SFM system, digital mammography has inherent advantages, such as wide dynamic range, reduction in recall rates, potential for reduction in radiation dose, increased patient throughput, postprocessing capability, and digital acquisition. These advantages and the rapidly occurring technologic developments will help establish FFDM as a mainstay of breast evaluation.

Physical characteristics of a full-field digital mammography system

The physical performance characteristics of a flat-panel clinical full-field digital mammography (FFDM) system were investigated for a variety of mammographic X-ray spectral conditions. The system was investigated using 26kVp: Mo/Mo, 28kVp: Mo/Rh, and 30kVp: Rh/Rh, with polymethyl methacrylate (PMMA) “tissue equivalent material” of thickness 20, 45, and 60mm for each of three X-ray spectra, resulting in nine different spectral conditions. The experimental results were compared with a theoretical cascaded linear systems-based model that has been developed independently by other investigators. The FFDM imager (Senographe 2000D, GE Medical Systems, Milwaukee, WI) uses an amorphous silicon (aSi:H) photodiode (100μm pixel) array directly coupled to a cesium iodide (CsI) scintillator. The spatial resolution of the digital mammography system was determined by measuring the presampling modulation transfer function (MTF). The noise power spectra (NPS) of the system were measured under the different mammographic X-ray spectral conditions at an exposure of approximately 10mR to the detector from which corresponding detective quantum efficiencies (DQE) were determined. The experimental results provide additional information on the performance of the mammographic system for a broader range of experimental conditions than have been reported in the past. The flat-panel imager exhibits favorable physical quality characteristics under the conditions investigated. The experimental results were compared with theoretical estimates under various spectral conditions and demonstrated good agreement.

Breast imaging in the new era.

In the last decade, there have been huge advances in the field of breast imaging. Full field digital mammography systems optimise lesion to background contrast with resultant improvement in the sensitivity of the technique for cancer detection, facilitated by computer-aided detection. Though mammography remains the only established modality for population-based screening, preliminary results from several large studies indicate that magnetic resonance imaging (MRI) has a role in high-risk patients. On the other hand, advances in ultrasound, MRI and nuclear medicine have the potential to greatly improve the specificity of breast imaging with regard to cancer detection and lesion characterisation. A number of new and experimental techniques are being developed which may have great impact in this area and these will be discussed. Though MRI now has an established place in the diagnosis of breast cancer, it is becoming clear that it can directly affect surgical and medical management by enabling assessment of response to chemotherapy and endocrine therapy, and facilitating choice of the most appropriate surgery. Just as the role of MRI has evolved, so too the place of nuclear medicine, particularly positron emission tomography and radio-immunoscintigraphy should become clearer in the next few years.

Full-field digital mammography with amorphous silicon-based flat- panel detector: physical imaging characteristics and signal detection

The physical characteristics of a clinical amorphous silicon-based flat-panel imager for full-field digital mammography were investigated. Pre-sampled modulation transfer functions (MTF) were measured by using a slit method. Noise power spectra were determined for different input exposures by fast Fourier transform. The MTFs of full-field digital mammography systems showed significantly higher values than those of the computed radiography (CR) system. The full-field digital mammography system showed a lower noise level than that of the CR system under the same exposure conditions. Contrast detail analysis has been performed to compare the detectability of the full-field digital mammography system with that of the screen-film (Min-R 2000/Min-R 2000) system. The average contrast-detail curves of digital and film images were obtained from the results of observation. Image quality figures (IQF) were also calculated from the individual observer performance tests. The results indicated that the digital contrast-detail curves and IQF, on average, are superior to those of the screen-film system.

Effects of magnification and zooming on depth perception in digital stereomammography: an observer performance study

We are evaluating the application of stereoscopic imaging to digital mammography. In the current study, we investigated the effects of magnification and zooming on depth perception. A modular phantom was designed which contained six layers of 1-mm-thick Lexan plates, each spaced 1 mm apart. Eight to nine small, thin nylon fibrils were pasted on each plate in horizontal or vertical orientations such that they formed 25 crossing fibril pairs in a projected image. The depth separation between each fibril pair ranged from 2 to 10 mm. A change in the order of the Lexan plates changed the depth separation of the two fibrils in a pair. Stereoscopic image pairs of the phantom were acquired with a GE full-field digital mammography system. Three different phantom configurations were imaged. All images were obtained using a Rh target/Rh filter spectrum at 30 kVp tube potential and a ±3° stereo shift angle. Images were acquired in both contact and 1.8X magnification geometry and an exposure range of 4 to 63 mAs was employed. The images were displayed on a Barco monitor driven by a Metheus stereo graphics board and viewed with LCD stereo glasses. Five observers participated in the study. Each observer visually judged whether the vertical fibril was in front of or behind the horizontal fibril in each fibril pair. It was found that the accuracy of depth discrimination increased with increasing fibril depth separation and x-ray exposure. The accuracy was not improved by electronic display zooming of the contact stereo images by 2X. Under conditions of high noise (low mAs) and small depth separation between the fibrils, the observers' depth discrimination ability was significantly better in stereo images acquired with geometric magnification than in images acquired with a contact technique and displayed with or without zooming. Under our experimental conditions, a 2 mm depth discrimination was achieved with over 60% accuracy on contact images with and without zooming, and with over 90% accuracy on magnification images. This study indicates that stereoscopic imaging, especially with magnification, may be useful for visualizing the spatial distribution of microcalcifications in a cluster and for differentiating overlapping tissues from masses on mammograms.

Dual-energy imaging in full-field digital mammography: a phantom study

A dual-energy technique which employs the basis decomposition method is being investigated for application to digital mammography. A three-component phantom, made up of plexiglas, polyethylene and water, was doubly exposed with the full-field digital mammography system manufactured by General Electric. The ‘low’ and ‘high’ energy images were recorded with a Mo/Mo anode-filter combination and a Rh/Rh combination, respectively. The total dose was kept within the acceptable levels of conventional mammography. The first hybrid images obtained with the dual-energy algorithm are presented in comparison with a conventional radiograph of the phantom. Image-quality characteristics at contrast cancellation angles between plexiglas and water are discussed. Preliminary results show that a combination of a standard Mo-anode 28 kV radiograph with a Rh-anode 49 kV radiograph provides the best compromise between image-quality and dose in the hybrid image.

Average glandular dose with amorphous silicon full-field digital mammography - Clinical results.

Determination of average glandular dose with a full-field digital mammography system using a flat-panel X-ray detector based on amorphous silicon technology for a large group of patients. The patient group includes women who were examined in a 4-month period with the digital mammographic system Senographe 2000D. The number of women was 591 and the number of exposures was 1116; only cranio-caudal projections were considered. Various quantities, including entrance surface air kerma, tube loading, and compressed breast thickness, were determined during actual mammography. Average glandular dose was determined using conversion factors g for standard breast composition. The mean average glandular dose was 1.51 mGy (0.66 - 4.05 mGy) for a single view. The mean compressed breast thickness was 55.7 mm. The mean age of patients was 55 years (34 - 81 years). The results demonstrate that full-field digital mammography with a flat-panel detector based on amorphous silicon needs about 25 % less dose in comparison with conventional screen-film mammography.

Spectral analysis of full field digital mammography data.

The spectral content of mammograms acquired from using a full field digital mammography (FFDM) system are analyzed. Fourier methods are used to show that the FFDM image power spectra obey an inverse power law; in an average sense, the images may be considered as 1/f fields. Two data representations are analyzed and compared (1) the raw data, and (2) the logarithm of the raw data. Two methods are employed to analyze the power spectra (1) a technique based on integrating the Fourier plane with octave ring sectioning developed previously, and (2) an approach based on integrating the Fourier plane using rings of constant width developed for this work. Both methods allow theoretical modeling. Numerical analysis indicates that the effects due to the transformation influence the power spectra measurements in a statistically significant manner in the high frequency range. However, this effect has little influence on the inverse power law estimation for a given image regardless of the data representation or the theoretical analysis approach. The analysis is presented from two points of view (1) each image is treated independently with the results presented as distributions, and (2) for a given representation, the entire image collection is treated as an ensemble with the results presented as expected values. In general, the constant ring width analysis forms the foundation for a spectral comparison method for finding spectral differences, from an image distribution sense, after applying a nonlinear transformation to the data. The work also shows that power law estimation may be influenced due to the presence of noise in the higher frequency range, which is consistent with the known attributes of the detector efficiency. The spectral modeling and inverse power law determinations obtained here are in agreement with that obtained from the analysis of digitized film-screen images presented previously. The form of the power spectrum for a given image is approximately l/f2beta with beta approximately 1.4-1.5.

Mammographic Tissue, Breast Cancer Risk, Serial Image Analysis, and Digital Mammography: Part 1. Tissue and Related Risk Factors

This work is presented as a sequence of two parts. In this leading section, a review of the breast tissue–risk research is provided. Although controversy remains, there is substantial evidence indicating that dense mammographic tissue (a) is a breast cancer risk factor that is at least similar, if not greater, in magnitude with the other known breast cancer risk factors and (b) may be a partial biomarker for some of the other risk factors. Understanding these influences may provide a mechanism for measuring the dynamics of breast cancer risk. The totality of this work is to provide support for an automated serial mammography study under way at the authors' institution, where digital mammographic images are acquired with a full–field digital mammography system. This is a filmless imaging system, where the image is acquired in digital format. This electronic imaging acquisition system provides a prime opportunity to easily couple and manipulate the image data with patient information such as risk probability analysis or other pertinent personal history data for improved automated decision making. In this leading section, the main focus is on understanding elements that will assist in fusing risk probability analysis with automated computer–aided diagnosis. The evidence indicates that there are many factors that influence breast tissue at any given time and thus have the ability to alter the associated radiographic image appearance over time. At the initiation of the serial study it was clear that the authors did not fully understand the nature of the problem: automatically comparing similar mammographic scenes acquired at different times. In the second part of this sequence, the more time–related tissue influences are reviewed.

Full-field digital mammography: a phantom study for detection of microcalcification

The study compares direct full-field digital mammography (FFDM) to the state-of-the-art conventional screen-film mammography (SFM) concerning the detectability of simulated microcalcifications. The investigations were performed with a FFDM system (Senographe 2000D, GEMS) and a SFM system (Senographe DMR, GEMS, Fuji UM MA film with Fuji UM MAMMO FINE screen). An anthropomorphic breast phantom with superimposed microcalcifications (50-200 microns) was used to evaluate the detectability of microcalcifications with a confidence level ranging from 1 to 5. Contact mammograms and magnification spot views (m = 1.8) of the FFDM and SFM systems were compared. A receiver operating characteristic (ROC) analysis was performed by three well-experienced readers. The ROC analysis revealed a higher performance of the digital images compared to the conventional screen-film mammograms. The area under the ROC-curve (Az) in the digital contact mammograms was 0.68 versus 0.63 in the conventional technique. The results were not significantly different. In digital spot views, Az was 0.79 versus 0.70 in the conventional spot views. The results suggest that FFDM is at least equivalent or--as far as spot views are concerned--may be superior to conventional SFM in the detection of microcalcifications.

Contrast-detail evaluation of a full-field digital mammography system

We have been investigating the potential of large-area flat-panel a-Si:H imaging devices for full-field digital mammography. The performance of a clinical mammographic system specially developed to provide geometric direct magnification equipped with an a-Si:H digital detector in conjunction with a series of Gd/sub 2/O/sub 2/S:Tb phosphor screens was evaluated in terms of image quality and entrance surface dose by using the contrast-detail CDMAM phantom over a range of exposure levels. We also compared the contrast-detail detectability properties of the a-Si:H-based digital imaging system with those of a conventional screen-film combination. The results from this study reveal the superiority of this prototype a-Si:H-based digital imaging system both in terms of contrast-detail resolution and significant entrance surface dose reduction in comparison with the conventional screen-film combination. These advantages are of particular significance in the breast imaging. Therefore, the combination of a-Si:H digital array with the direct magnification mammography system has the potential to fulfil the image quality requirements for full-field digital mammogarphy and to offer significant improvements in the efficient early detection of breast cancer.

Full-field digital mammography designed as a complete system

Although mammography is currently considered by many to be the best tool for the early detection of breast cancer, conventional film-screen imaging is still far from perfect. A fundamental limitation of film-screen mammography is the fact that the detection, display and storage devices are one and the same, making it impossible to separately optimize each device. In addition to a potentially equivalent or better image quality compared to the film-screen technology, full-field digital mammography (FFDM) will provide the radiologist with numerous advantages: digital image management, digital data transfer and new medical applications. Nevertheless, to fulfil the potential of digital mammography, an FFDM unit must not only provide an outstanding technology for X-ray detection, but should be designed as a complete system. Each component of the FFDM system should be designed to provide or to increase the current image quality, the current ease of use and the current throughput: the X-ray tube, the gantry, the image receptor packaging, the detector, the acquisition electronics, the softcopy review workstation, the user interface, as well as the network capabilities.

Interpolation algorithms for digital mammography systems with multiple detectors

In some full-field digital mammography systems, multiple detectors are abutted together, and the physical gaps between adjacent detectors produce seams between the resultant subimages. In this study, a variety of interpolation algorithms for estimating the missing information in the seams were compared, and their effect on image quality was evaluated. Eight representative interpolation algorithms were selected, including nearest neighbor, one-dimensional and two-dimensional weighting, mean value, one-dimensional and two-dimensional polynomial, and one-dimensional and two-dimensional cubic spline interpolation methods. These methods were applied to digital mammograms and phantom images. The effectiveness of each algorithm was evaluated for accuracy and geometric distortion. These interpolation algorithms offered similar accuracy in estimating missing image information. The weighting, polynomial, and cubic spline interpolation algorithms introduced less geometric distortion than the nearest neighbor and mean value interpolation algorithms. All algorithms were more effective in estimating larger, lower-contrast features (such as breast masses) than in estimating smaller, higher-contrast features (such as breast microcalcifications). Small microcalcifications within the seams cannot be recovered with interpolation. The probability of a microcalcification in a seam is small, however, and the failure to image a few microcalcifications of a cluster generally does not substantially alter diagnostic performance. In the development of full-field digital breast imaging systems, appropriate interpolation algorithms can satisfactorily fill in narrow gaps between adjacent detectors. The one-dimensional weighting interpolation method seems an effective and efficient choice.

Adaptive image interpolation for full-field digital x-ray mammography

Some full-field digital x-ray mammography systems use multiple abutted two-dimensional detectors. Gaps between adjacent detectors produce seams in the composite image. We develop an adaptive linear interpolation method for estimation of missing data in the seams. In this method, the interpolation path is determined on the basis of the similarity between adjacent subimage boundary profiles. In experiments with phantom images and clinical mammograms, the adaptive method performed significantly better than the conventional linear interpolation.

Initial clinical experience with a high resolution full field digital mammography system

Initial clinical experience with a high resolution full field digital mammography system