Showing papers on "Digital mammography published in 1998"

Computer-aided diagnosis: Automatic detection of malignant masses in digitized mammograms

Abstract: A computerized method to automatically detect malignant masses on digital mammograms based on bilateral subtraction to identify asymmetries between left and right breast images was developed. After the digitization, in order to align left and right mammograms the breast border and nipple were automatically detected. Images were corrected to avoid differences in brightness due to the recording procedure. Left and right mammograms were subtracted and a threshold was applied to obtain a binary image with the information of suspicious areas. The suspicious regions or asymmetries were delimited by a region growing algorithm. Size and eccentricity tests were used to eliminate false-positive responses and texture features were extracted from suspicious regions to reject normal tissue regions. The scheme, tested in 70 pairs of digital mammograms, achieved a true-positive rate of 71% with an average number of 0.67 false positives per image. Computerized detection was evaluated by using free-response operating characteristic analysis (FROC). An area under the AFROC (A1) of 0.667 was obtained. Our results show that the scheme may be helpful to the radiologists by serving as a second reader in mammographic screening. The low number of false positives indicates that our scheme would not confuse the radiologist by suggesting normal regions as suspicious.

Phase mammography - a new technique for breast investigation

Abstract: A new phase radiography technique for investigation and diagnosis of neoplasms in breast tissue is proposed. Forty-four mammography samples with adenocarcinoma that had been prepared after mastectomy were tested in a new phase radiography device. It was shown that the phase images manifest the changes in parenchyma structure due to malignancy and microcalcifications up to in size. Results obtained were verified by histological examination. A contrast of the phase images of small microcalcifications and distortions of the stroma architecture ranges up to 40-60%; spatial resolution is about . The proposed technique offers outstanding possibilities for digital mammography. The small and large details of structure manifest themselves with practically the same contrast. Phase images differ from those obtained in mammography and many details still require further decoding.

Computer-assisted method and apparatus for displaying x-ray images

Abstract: A computer-assisted diagnostic (CAD) method and apparatus are described for the enhancement and detection of suspicious regions in digital X-ray images, with particular emphasis on early cancer detection using digital mammography. An objective is to improve the sensitivity of detection of suspicious areas such as masses, while maintaining a low false positive detection rate, and to classify masses as benign or malignant. A modular CAD technique has been developed as a potentially automatic and/or second-opinion method for mass detection and classification in digital mammography that may in turn be readily modified for application with different digital X-ray detectors with varying gray-scale and resolution characteristics. The method consists of using a plurality of CAD modules to preprocess and enhance image features in the gray-level, the directional texture, and the morphological domains.

Mixture Modeling for Digital Mammogram Display and Analysis

Abstract: We have devised a mammogram modeling system which greatly simplifies the development of, and can improve the accuracy and consistency of, computer-aided display and analysis algorithms for digital mammography. Our system segments the five major components of a mammogram: background, uncompressed-fat, fat, dense, and muscle. Differences in the amount and distribution of these components account for much of the variation between mammograms. Via segmentation, the corresponding variations are isolated; automated algorithms can consider the components independently or adapt their parameters based on component-specific statistics.

A breast density index for digital mammograms based on radiologists’ randing

Abstract: The purpose of this study was to develop and evaluate a computerized method of calculating a breast density index (BDI) from digitized mammograms that was designed specifically to model radiologists’ perception of breast density. A set of 153 pairs of digitized mammograms (cranio-caudal, CC, and mediolateral oblique, MLO, views) were acquired and preprocessed to reduce detector biases. The sets of mammograms were ordered on an ordinal scale (a scale based only on relative rank-ordering) by two radiologists, and a cardinal (an absolute numerical score) BDI value was calculated from the oridinal ranks. The images were also assigned cardinal BDI values by the radiologists in a subsequent session. Six. mathematical features (including fractal dimension and others) were calculated from the digital mammograms, and were used in conjunction with single value decomposition and multiple linear regression to calculate a computerized BDI. The linear correlation coefficient between different ordinal ranking sessions were as follows: intraradiologist intraprojection (CC/CC):r=0.978; intraradiologist interprojection (CC/MLO):r=0.960; and interradiologist intraprojection (CC/CC):r=0.968. A separate breast density index was derived from three separate ordinal rankings by one radiologist (two with CC views, one with the MLO view). The computer derivedBDI had a correlation coefficient (r) of 0.907 with the radiologists’ ordinalBDI. A comparison between radiologists using a cardinal scoring system (which is closest to how radiologists actually evaluate breast density) showedr=0.914. A breast density index calculated by a computer but modeled after radiologist perception of breast density may be valuable in objectively measuring breast density. Such a metric may prove valuable in numerous areas, including breast cancer risk assessment and in evaluating screening techniques specifically designed to improve imaging of the dense breast.

At the frontiers of digital mammography: SYRMEP

Abstract: The SYRMEP (SYnchrotron Radiation for MEdical Physics) collaboration is presently taking data at a beamline at the synchrotron ELETTRA in Trieste to study the performances of a digital silicon pixel imaging system for mammography. Images are obtained with a scanning technique in the energy range 15–30 keV. The readout electronics operates in a single photon counting mode with a photon rate of about 10 6 /( mm 2 s ) , which is still 4 times lower than the maximum rate reachable with the present beamline configuration. Two different detector layouts have been designed, the first one consisting of a single-layer silicon microstrip detector positioned edge-on with respect to the beam, and the second innovative one represented by a matrix of these detectors stacked to cover the full beam dimension (100×4 mm 2 ) . We present here the results obtained with a single-layer detector and a double-layer detector (both 5 cm wide) with mammographic phantoms and human breast tissue.

Establishing minimum performance standards, calibration intervals, and optimal exposure values for a whole breast digital mammography unit

Abstract: Methods are developed to establish minimum performance standards, calibration intervals, and criteria for exposure control for a whole breast digital mammography system. A prototype phantom was designed, and an automatic method programmed, to analyze CNR, resolution, and dynamic range between CCD components in the image receptor and over time. The phantom was imaged over a 5 month period and the results are analyzed to predict future performance. White field recalibration was analyzed by subtracting white fields obtained at different intervals. Exposure effects were compared by imaging the prototype phantom at different kVp, filtration (Mo vs Rh) and mAs. Calcification detection tests showed that phantom images, obtained at 28 kVp with a Mo/Mo anode/filter and low mAs technique, often could not depict Al 2 O 3 specks 0.24 mm in diameter, while a 28 kVp Mo/Rh, higher mAs technique usually could. Stability of the system tested suggests that monthly phantom imaging may suffice. Differences in CCD performance are greater (12%) than differences in a single CCD over time (6%). White field recalibration is needed weekly because of pixel variations in sensitivity which occur if longer intervals between recalibration occur. When mean glandular dose is matched, Rh filtration gives better phantom performance at 28 kVp than Mo filtration at 26 kVp and is recommended for clinical exposures. An aluminum step wedge shows markedly increased dynamic range when exit exposure is increased by using a higher energy spectrum beam. Phantoms for digital mammography units should cover the entire image receptor, should test intersections between components of the receptor, and should be automatically analyzed.

Multiresolution wavelet approach for separating the breast region from the background in high resolution digital mammography

Abstract: There are many computer aided diagnosis (CAD) techniques applied to the analysis of digitized mammograms. A general overview of these methods can be found in Refs. 1 and 2. Often the CAD methods are used to detect and highlight abnormalities for aiding in the diagnosis performed via computer reading. In some instances, overall image enhancement without specific abnormality detection may be the desired CAD goal. In any event, CAD methods as well as efficient image storage and transfer require an initial stage of processing that can locate and mark the breast region [3], remove the off-breast noise field, eliminate patient markings that are often of very high intensity, and remove other artifacts that may found off the breast region of the image.

Voice-activated retrieval of mammography reference images.

Abstract: We undertook this project to integrate context sensitive computer-based educational and decision making aids into the film interpretation and reporting process, and to determine the clinical utility of this method as a guide for further system development. An image database of 347 digital mammography images was assembled and image features were coded. An interface was developed to a computerized speech recognition radiology reporting system which was modified to translate reported findings into database search terms. These observations were used to formulate database search strategies which not only retrieved similar cases from the image database, but also other cases that were related to the index case in different ways. The search results were organized into image sets intended to address common questions that arise during image interpretation. An evaluation of the clinical utility of this method was performed as a guide for further system development. We found that voice dictation of prototypical mammographic cases resulted in automatic retrieval of reference images. The retrieved images were organized into sets matching findings, diagnostic hypotheses, diagnosis, spectrum of findings or diagnoses, closest match to dictated case, or user specified parameters. Two mammographers graded the clinical utility of each form of system output. We concluded that case specific and problem specific image sets may be automatically generated from spoken case dictation. A potentially large number of retrieved images may be divided into subsets which anticipate common clinical problems. This automatic method of context sensitive image retrieval may provide a “continuous’; form of education integrated into routine case interpretation.

Enhancement and analysis of digital mammograms using fuzzy models

Abstract: This paper describes our work in enhancing and analyzing digital mammograms form the digital database for screening mammography (DDSM). The DDSM will ultimately contain 3000 cases and provides a unique opportunity for researchers form around the world to compare results on a large, diverse data set. However, the size of the database and images within it require careful consideration of memory limitation issues, display device constraints, etc. We address research problems connected with the modification and application of existing fuzzy modeling approaches to this digital mammography domain. Segmentation and edge detection are sued as benchmark applications for the comparisons we make.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Enhancement of mammographic images for detection of microcalcifications

Abstract: A novel approach to image enhancement of digital mammography images is introduced, for more accurate detection of microcalcification clusters. In original mammographic images obtained by X-ray radiography, most of the information is hidden to the human observer. The method is based on redundant discrete wavelet transform due to its good properties: shift invariance and numeric robustness. The procedure consists of three steps: low-frequency tissue density component removal, noise filtering, and microcalcification enhancement. The experimental results have shown good properties of the proposed method.

Digital mammography : Nijmegen, 1998

Abstract: Digital Breast Imaging Techniques. Detection of Masses. Detection of Microcalcifications. Classification of Breast Lesions. Quantitative Analysis and Segmentation. Image Processing and Display. Observer Performance and Prompting. Clinical Impact of Digital Mammography. Image Quality and Compression. Extended Abstracts. Author Index.

Adaptive CAD modules for mass detection in digital mammography

Abstract: The development and evaluation of a new class of algorithms for computer assisted diagnostic (CAD) methods for segmentation and detection of masses in digitized mammograms is reported. Both non-adaptive and adaptive CAD MODULES are reported that employ three key novel image processing CAD modules, specifically tailored for digital mammography, namely: (a) a tree-structured non-linear filter for noise suppression, (b) a multiorientation directional wavelet transform (DWT) for removal of directional features and for the direct detection of spiculations for spiculated lesions, and (c) a multiresolution wavelet transform for image enhancement to improve the segmentation of suspicious areas. The aim of the work is to provide a brief overview of both the non-adaptive and adaptive methods and comparison of their performance using computer ROC curves. The results confirmed the importance of using adaptive CAD methods, where progressive improvement in Az values was observed for each adaptive CAD module. The methods proposed here are useful for other CAD applications such as the detection of microcalcifications and lung nodules.

Routine receiver operating characteristic analysis in mammography as a measure of radiologists' performance.

Abstract: A system for calculating receiver operating characteristic (ROC) curves from routine audit data is described. Both diagnostic opinion and pathology outcome data from the symptomatic mammography department were recorded in an audit database, from which ROC curves were calculated. A comparison of overall radiologists' performance was made and the appropriate performance indices discussed. Similar data were collected from the breast screening centre where the same radiologists read mammograms. The radiologists' performance in the symptomatic department was compared with that in the breast screening centre and was found to be better in the screening centre. The diVerence could not be wholly attributed to the diVerent age distribution of women and highlighted the diVerent nature of the diagnostic task and the diVering sampled populations. ROC curves were drawn for diVerent clinical signs to determine any particular area of diYculty the radiologist may experience. ROC analysis as part of routine audit can be used for maintaining and improving the quality of an individual's performance, and targeting learning on areas of particular weakness. The quality of medical care is paramount for of the individual radiologist. The use of receiver both patient and management. Suitable determi- operating characteristic (ROC) analysis allows for nants are required to assess the level of quality in this spectrum of thresholds. Sensitivity and speci- the health service. Quality assurance of a radiologi- ficity values are determined at diVering threshold cal procedure should consider not only the assess- levels, so that inaccuracies which arise from ment of equipment and image processing, but also assuming that imaging findings are absolutely of interpretation (1). The former is now assessed normal or abnormal are avoided (2, 3). by quality control programmes run by medical ROC analysis is now extensively used in radi- physics departments. The latter, medical audit, is ology to investigate the eVect of one parameter on often instigated by clinicians themselves to deter- an imaging system or to compare the performance mine how best they may improve their performance of one system with another. Many of the stages in and the performance of the service. the radiological process have been studied with To this end, a system of audit was developed ROC analysis: the film-screen combination (4, 5), within the symptomatic mammography depart- the quality of viewing conditions (6), the eVects ment at Aberdeen Royal Infirmary. Data on clini- of digitization (7, 8) and the pixel size (9, 10). It cal referral (source, reason for referral for imaging), is only recently that ROC analysis has been used radiologist report and pathological outcome where to study individual performance (11-13) and available were collected in a computer database. within the context of a medical audit (14). Medical From this, sensitivity and specificity of the report audit is an expensive process and the benefits must as a test could be calculated. It is, however, mislead- outweigh the costs involved. Thus, in the present ing to quote single sensitivity and specificity values study, it was considered necessary to assess and for an imaging test, as this fails to take account of audit radiologists' performance under normal the threshold used by radiologists to define a working conditions and to identify patterns of positive result. Radiologists report radiographs mammographic abnormality where there are with a continuum of responses ranging from defi- established diagnostic diYculties, albeit perceptual nitely normal through equivocal to definitely or interpretational. A system was therefore devel- abnormal, depending on the subjectivity and bias oped for the routine calculation of ROC curves

Mammographic Screening: Sensitivity of General Radiologists

Abstract: High quality mammography can detect early, curable breast cancer and decrease mortality. Much research effort is being expended to improve mammography (digital mammography, computer-aided diagnosis [CAD]), and develop alternative modalities (ultrasound, MRI, radionuclide imaging). However, the human observer is at this point potentially the weakest link in the diagnostic imaging chain, and the range of performance in routine practice is unknown. We have conducted a large observer study using a standardized test base to further investigate this issue.

Tumor Detection System for Full-Digital Mammography

Abstract: Mammogram is considered to be the most reliable modality for the screening of breast cancer, and screening programs using mammography has become popular for the detection of early breast cancer. Computer aided diagnosis (CAD) system for mammography has the possibility to be used as a second reader to increase the reliability of the mass screening.

X-ray exposure apparatus for digital mammography

Abstract: An X-Ray exposure apparatus for digital mammography allows an exposure of the entire breast to be obtained with a single solid state detector. To this end, an apparatus housing is provided has an acute angle at the patient side, with a device for the deflection of the image from a luminescent screen and optics for imaging this image on the solid state detector are arranged at this side. The solid state detector is arranged at the patient-remote side of the X-ray exposure apparatus.

Development of Full Field Digital Mammography

Abstract: Screen-film mammography is well-established as a tool for screening and for diagnostic workup of suspicious lesions prior to biopsy. While mammography can be very accurate, its effectiveness can be limited because of several technical limitations in image formation and display, particularly when the breast contains a large proportion of fibroglandular tissue. The most significant limitation arises due to the use of photographic film as a means for image acquisition and display. The response of film is highly nonlinear, both for low and high exposures causing radiological contrast to be greatly reduced in regions of the image corresponding to both the most radio-lucent and the most radio-opaque parts of the breast. Bunch et al. [1] have shown that the signal to noise ratio (SNR) of information recorded by a mammographic screen-film system is low at both low and high exposure levels, and achieves its maximum at an intermediate exposure level, even though the inherent SNR of the image due to quantum statistics increases monotonically with exposure.

Digitized mammogram standardization for display and CAD

Abstract: Softcopy reading and CAD in mammography are both dependent upon the characteristics of the source of the digital data, either direct digital mammography or digitized screen-film mammography. In this work, a standardization is proposed based on geometric and intensity transformation that are discovered using a set of calibration images. A genetic algorithm is used to search for the best transformations. Results indicate that standardization for display can be achieved, but that CAD performance varies even after standardization: both sensitivity and false-positive rates appear to be reduced.

Digital Mammography: From Theory to Practice.

Abstract: Mammography is the screening technique with the highest sensitivity for detecting early breast cancer, yielding a significant improvement in breast cancer survival. Since the first mammography units (xeromammography and screen-film mammography in the 1970s) became available, both the equipment and the examination procedure have changed and progressed. Technology advancements have affected almost all parts of the mammography units, with the highest impact on films and intensifying screens.2,3 Screen-film systems are currently dominating the market and offer excellent detection capabilities of early or occult breast tumors with minimum radiation exposure to the patient and at a relatively low cost compared with other diagnostic imaging modalities such as computed tomography (CT) or magnetic resonance imaging (MRI).

Impact of the diagnostic methods on the therapeutic strategies.

Abstract: Over the last 25 years the diagnostic approaches and therapeutic strategies of breast cancer have dramatically changed. The relationship between diagnosis and therapy has gradually become more complex due to the ever more sophisticated diagnostic tools (mammographic screening, digital mammography, magnetic resonance, SPECT scan and FDG-PET), which have improved resolution limits and accuracy, and also due to the different therapeutic planning applied to breast cancer in these years (conservative surgery, neo-adjuvant chemotherapy, axillary dissection or not). Thus, in this paper, we have briefly analyzed the many open questions in breast cancer management and the clinical challenges of present diagnostic tools in relation to pre-, peri- and postoperative phases, and to therapeutic strategies in general. The main goal of mammographic screening is to detect early invasive cancers and to treat them at the first useful moment. However, at which age should one begin screening, and what is the impact on overall survival, the cost-effectiveness, and, most of all, the best operative approach to suspect lesions? Can digital mammography give a better quality of imaging with respect to conventional mammography? Does unexpected multicentricity and/or multifocality, which is sometimes showed by magnetic resonance, have any clinical relevance? Is this technique really better than traditional methods for the identification of local recurrence? Is scintimammography able to improve the low diagnostic accuracy of mammography on non-palpable breast lesions? Moreover, at present, the need for axillary dissection and its therapeutic and staging value is deeply debated: however, clinical detection of axillary metastases is not a reliable diagnostic tool and there are no conventional radiologic techniques to be used: recently nuclear medicine imaging has provided various approaches, such as SPECT scan with different tracers, FDG-PET, or lymphoscintigraphy with gamma probe sentinel biopsy: there are not only methodologic but also phylosophic differences in using these techniques. Neo-adjuvant chemotherapy has allowed a dramatic reduction of primary breast cancer with a replanning of the surgical approach to large breast tumours but, at the same time, has posed new questions such as the adequacy of diagnostic pre- and perioperative revaluation. Finally, does postoperative follow-up take advantage of intensive diagnostic programs and are there therapeutic margins which would improve survival of patients with metastatic disease? This paper is an attempt to analyze the answers given in the literature. Nevertheless, at present, this matter is globally in progress and a scientific debate will provide, in the near future, a new promising scenario for breast cancer management.

High-resolution scanned-slit x-ray imaging using a refractive lens for x-ray focusing

Abstract: We are developing a slit-scanning digital mammography system with the goal of reducing radiation dose and improving dynamic range in comparison to conventional film-screen mammography. The system is based on a linear silicon detector connected to a fast parallel processing ASIC controlled from a PC. The detector system is configured from a silicon wafer such that the X-rays enter the wafer edge-on, resulting in a high efficiency over the entire range of diagnostic X-ray energies since the absorption length of the detector can be made large. An evaluation of the system gives an MTF close to that predicted theoretically for a 100-micrometer pitch pixel detector. We also propose to reduce tube-loading in the slit- scanning system with a refractive X-ray lens that can increase the incident photon flux by about 5-fold according to ray tracing simulations. Moreover the lens shapes the energy spectrum to obtain pseudo-monochromatic beam thus enhancing contrast sensitivity, for example in mammography. We estimate a scan time with the final system of the order of a few seconds for a full-field digital mammogram. Phantom images of microcalcifications and of tumor-like masses, and an initial evaluation of a scanned-slit photon-counting X-ray imaging system, are presented.

High Resolution Mammography Using a Scanned Slit Silicon Strip Detector

Abstract: It is generally believed that digital mammography is the most promising technique for early detection of breast-cancer[1]. However, there are many technological challenges associated with digital mammography. With the high resolution and low noise needed for detection of micro-calcifications and low contrast tumors, a tremendous amount of data has to be acquired and read out in a few seconds. This puts difficult constraints on electronics and the data-acquisiton system.

Computer-Aided Diagnosis of Digital Mammography and Ultrasound Images of Breast Mass Lesions

Abstract: Although general rules for the differentiation between benign and malignant mammographically-identified breast lesions exist, considerable misclassification of lesions occurs with current imaging and interpretation methods [1]–[6]. The purpose of our study is to develop computerized methods for the analysis of mass lesions on digitized mammograms and on ultrasound images for aiding in the task of distinguishing between malignant and benign lesions. This should lead to (1) an improvement in the classification sensitivity for malignant lesions and (2) an increase in the classification specificity and thus, a reduction in the number of unnecessary biopsies. Higher performance is expected when a combination of features from mammographie and ultrasound images is used as an aid to radiologists in the task of distinguishing between malignant and benign lesions.

Application of computer analysis of mammography phantom images (CAMPI) methodology to the comparison of two digital biopsy machines

Abstract: The objective of this research was to compare a Fischer MammoVision/MammoTest and a LoRad DSM digital biopsy machine using the Computer Analysis of Mammography Phantom Images (CAMPI) methodology. This study reports on analysis of the 4 largest microcalcification groups (M1, M2, M3 and M4) and the largest nodule (N1) in a mammography accreditation phantom on images acquired at 26 kVp and different mAs values on the two machines. Both machines were linear in response but the MammoTest was more sensitive (i.e., it yielded a larger gray- scale value for a given x-ray technique). However, even after correcting for this difference, the CAMPI noise measure was substantially smaller for the LoRad than the MammoTest over the range of mAS values studied. Similarly, the CAMPI signal- to-noise-ratio and correlation measures were higher for the LoRad than the MammoTest over the same range of mAs, especially for the larger objects (M1/M2 and N1). For the smaller specks in M3/M4 somewhat closer performance was observed. The overall differences are attributed to better contrast/noise performance of the LoRad which appear to outweigh its lesser resolution capability. Our results are in agreement with earlier physical and psychophysical measurements using different methodologies. This work also describes better predictive models (i.e., fits) to describe the variation of all CAMPI measures with mAs at constant kVp. For example, the noise measure was fitted to a function that included physically reasonable sources of noise e.g., dark noise and detector gain fluctuations, in addition to the usual quantum noise. These fits can be used to summarize machine performance and to predict dependencies on other variables (e.g., exposure or dose) that are related to the mAs.

Design Considerations for a CDZNTE Digital Mammography System

Abstract: In an effort to improve the performance of x-ray detectors for digital mammography, we are investigating the design of new direct conversion detectors for application in a slot-scanned system. The narrow slot geometry provides a dose-efficient means of scatter rejection and it allows the use of small detector modules to produce a full area image. The slot-scanned technique relies on CCD technology, using time-delay integration (TDI) for signal acquisition.