Film-screen magnification versus electronic magnification and enhancement of digitized contact mammograms in the assessment of subtle microcalcifications.

RATIONALE AND OBJECTIVES: To compare information drawn from magnification mammography with that extracted from electronic magnification, processing, and display of the digitized contact images. METHODS: Contact and magnification images of a mammographic statistical phantom were obtained. The magnification films versus the computer-enhanced, digitized images of the corresponding contact mammograms were separately presented to three observers. Receiver operating characteristic analysis was used to compare lesion detectability. The contact and magnification mammograms of 86 patients with subtle microcalcifications were also studied. The breast imaging reporting and data system (BI-RADS) scheme was used to compare the magnification patient films versus the corresponding digitized contact images. Differences in mammographic assessment were evaluated by using the kappa statistic. The dose to breast tissue from contact and magnification mammography was measured to evaluate dose reduction in instances where magnification mammography was to be avoided. RESULTS: Lesion detectability was found to be similar when either the digitized film image or the magnification hard-copy film was inspected. Interpretation of patient images by inspection of the contact and magnification screen-film mammograms on a view-box was in excellent agreement with that yielded by inspection of the contact image on a view-box and the computer-enhanced, digitized contact image on a display monitor. CONCLUSIONS: Electronic magnification and processing of the digitized contact image may provide valuable information concerning subtle microcalcifications, rendering magnification mammography unnecessary for many patients with such lesions.     

Digital mammography. ROC studies of the effects of pixel size and unsharp-mask filtering on the detection of subtle microcalcifications

We investigated the spatial resolution requirement and the effect of unsharp-mask filtering on the detectability of subtle microcalcifications in digital mammography. Digital images were obtained by digitizing conventional screen-film mammograms with a 0.1 X 0.1 mm2 pixel size, processed with unsharp masking, and then reconstituted on film with a Fuji image processing/simulation system (Fuji Photo Film Co., Tokyo, Japan). Twenty normal cases and 12 cases with subtle microcalcifications were included. Observer performance experiments were conducted to assess the detectability of subtle microcalcifications in the conventional, the unprocessed digital, and the unsharp-masked mammograms. The observer response data were evaluated using receiver operating characteristic (ROC) and LROC (ROC with localization) analyses. Our results indicate that digital mammograms obtained with 0.1 X 0.1 mm2 pixels provide lower detectability than the conventional screen-film mammograms. The detectability of microcalcifications in the digital mammograms is improved by unsharp-mask filtering; the processed mammograms still provide lower accuracy than the conventional mammograms, however, chiefly because of increased false-positive detection rates for the processed images at each subjective confidence level. Viewing unprocessed digital and unsharp-masked images in pairs resulted in approximately the same detectability as that obtained with the unsharp-masked images alone. However, this result may be influenced by the fact that the same limited viewing time was necessarily divided between the two images.     

Screen film vs full-field digital mammography: image quality,detectability and characterization of lesions

The objective of this study was to compare screen-film mammography (SFM) to full-field digital mammography (FFDM) regarding image quality as well as detectability and characterization of lesions using equivalent images of the same patient acquired with both systems. Two mammography units were used, one with a screen-film system (Senographe DMR) and the other with a digital detector (Senographe 2000D, both GEMS). Screen-film and digital mammograms were performed on 55 patients with cytologically or histologically proven tumors on the same day. Together with these, 75 digital mammograms of patients without tumor and the corresponding previous screen-film mammograms not older than 1.5 years were reviewed by three observers in a random order. Contrast, exposure, and the presence of artifacts were evaluated. Different details, such as the skin, the retromamillary region, and the parenchymal structures, were judged according to a three-point ranking scale. Finally, the detectability of microcalcifications and lesions were compared and correlated to histology. Image contrast was judged to be good in 76%, satisfactory in 20%, and unsatisfactory in 4% of screen-film mammograms. Digital mammograms were judged to be good in 99% and unsatisfactory in 1% of cases. Improper exposure of screen-film system occurred in 18% (10% overexposed and 8% underexposed). Digital mammograms were improperly exposed in 4% of all cases but were of acceptable quality after post-processing. Artifacts, most of them of no significance, were found in 78% of screen-film and in none of the digital mammograms. Different anatomical regions, such as the skin, the retromamillary region, and dense parenchymal areas, were better visualized in digital than in screen-film mammography. All malignant tumors were seen by the three radiologists; however, digital mammograms allowed a better characterization of these lesions to the Breast Imaging Reporting and Data System (BI-RADS;) [corrected] categories (FFDM better than SFM in 23 of 165 vs 9 of 165 judged cases in SFM). In conclusion, digital mammography offers a consistent, high image quality in combination with a better contrast and without artifacts. Lesion detection in digital images was equal to that in screen-film images; however, categorization of the lesions to the BI-RADS classification was slightly better.     

Comparing the performance of mammographic enhancement algorithms: a preference study

OBJECTIVE: The objective of this study was to compare the performance of four image enhancement algorithms on secondarily digitized (i.e., digitized from film) mammograms containing masses and microcalcifications of known pathology in a clinical soft-copy display setting. MATERIALS AND METHODS: Four different image processing algorithms (adaptive unsharp masking, contrast-limited adaptive histogram equalization, adaptive neighborhood contrast enhancement, and wavelet-based enhancement) were applied to one image of secondarily digitized mammograms of forty cases (10 each of benign and malignant masses and 10 each of benign and malignant microcalcifications). The four enhanced images and the one unenhanced image were displayed randomly across three high-resolution monitors. Four expert mammographers ranked the unenhanced and the four enhanced images from 1 (best) to 5 (worst). RESULTS: For microcalcifications, the adaptive neighborhood contrast enhancement algorithm was the most preferred in 49% of the interpretations, the wavelet-based enhancement in 28%, and the unenhanced image in 13%. For masses, the unenhanced image was the most preferred in 58% of cases, followed by the unsharp masking algorithm (28%). CONCLUSION: Appropriate image enhancement improves the visibility of microcalcifications. Among the different algorithms, the adaptive neighborhood contrast enhancement algorithm was preferred most often. For masses, no significant improvement was observed with any of these image processing approaches compared with the unenhanced image. Different image processing approaches may need to be used, depending on the type of lesion. This study has implications for the practice of digital mammography.     

Radiologists' preferences for digital mammographic display. The International Digital Mammography Development Group

PURPOSE: To determine the preferences of radiologists among eight different image processing algorithms applied to digital mammograms obtained for screening and diagnostic imaging tasks. MATERIALS AND METHODS: Twenty-eight images representing histologically proved masses or calcifications were obtained by using three clinically available digital mammographic units. Images were processed and printed on film by using manual intensity windowing, histogram-based intensity windowing, mixture model intensity windowing, peripheral equalization, multiscale image contrast amplification (MUSICA), contrast-limited adaptive histogram equalization, Trex processing, and unsharp masking. Twelve radiologists compared the processed digital images with screen-film mammograms obtained in the same patient for breast cancer screening and breast lesion diagnosis. RESULTS: For the screening task, screen-film mammograms were preferred to all digital presentations, but the acceptability of images processed with Trex and MUSICA algorithms were not significantly different. All printed digital images were preferred to screen-film radiographs in the diagnosis of masses; mammograms processed with unsharp masking were significantly preferred. For the diagnosis of calcifications, no processed digital mammogram was preferred to screen-film mammograms. CONCLUSION: When digital mammograms were preferred to screen-film mammograms, radiologists selected different digital processing algorithms for each of three mammographic reading tasks and for different lesion types. Soft-copy display will eventually allow radiologists to select among these options more easily.     

Recent advances in screen-film mammography

Today there are many dedicated mammographic x-ray units available that are capable of providing high-quality screen-film mammograms. Likewise, screen-film combinations designed for mammography are capable of providing images with appropriate contrast, resolution, and noise levels. Proper film processing is most important in order to obtain the appropriate film speed and contrast. A higher-speed screen-film combination designed for mammography can provide mammograms with significantly lower radiation dose, especially for grid and magnification techniques. Designing x-ray units and techniques as well as screen-film combinations with the singular goal of reducing radiation dose will always involve compromises and trade-offs. The key is to always consider optimizing all of the factors that affect image quality: (1) appropriate beam quality, (2) breast compression, (3) consideration of the use of grids, (4) good geometry, (5) selection of an appropriate screen-film combination, and (6) proper film processing. Optimization of all appropriate imaging factors will produce high-quality mammograms at the lowest radiation dose to the patient.     

Evaluation of CRT images of digitized film angiographs

X-ray sheet film images of the test chart, the vascular phantom and angiography were digitized at sampling pitch of 0.2 mm and 0.15 mm using film digitizer TFR-01 (Toshiba) and transferred to a device for image storage and display system with 1635-line display monitor (TDF-500AS, Toshiba). Comparison of image qualities between film- and CRT-images was performed in fundamental and clinical studies. Resolution of the test chart image of conventional radiography was worse on CRT than on the original film, although it was improved when film image was digitized at resolution of 0.15 mm/pixel in comparison with that at resolution of 0.2 mm/pixel. Moiré stripes which occurred due to interference were found on CRT images taken using a grid technique. On CRT images of X-ray sheet film using direct magnification technique moiré stripes were not produced because of non grid technique, and the resolution approached that of the original film. In the study using vascular phantom, the optimal image on CRT could be obtained by various image processing procedures, and image quality on CRT with resolution of 0.15 mm approached that of original film. In case of direct magnification CRT images were superior to film images. Subtraction image of the vascular phantom at resolution of 0.2 mm/pixel was obtained on CRT and compared with film subtraction image. On conventional subtraction CRT image moiré stripes impaired the image quality in comparison with the film subtraction. However, magnification subtraction image of the vascular phantom on CRT was superior to the film subtraction. The results obtained in the test chart studies and phantom studies were also confirmed in clinical studies using various kind of angiograms. In addition, ROC study using clinical angiograms showed no significant statistical differences between the original film and CRT image even with 0.2 mm matrix size. Angiographic image on CRT at resolution of 0.15 mm/pixel or less is available for clinical use in place of conventional film image.     

Magnification mammography: a comparison of full-field digital mammography and screen-film mammography for the detection of simulated small masses and microcalcifications

The objective of this study was a comparison of a full-field digital mammography (FFDM) system and a conventional screen-film mammography (SFM) system with respect to the detectability of simulated small masses and microcalcifications in the magnification mode. All images were obtained using 1.8 times magnification. The FFDM images were obtained at radiation dose levels of 1.39, 1.0, 0.7, 0.49 and 0.24 times that of the SFM images. A contrast-detail phantom was used to compare the detection of simulated lesions using a four alternative forced-choice reader study with three readers. The correct observation ratio (COR) was calculated as the fraction of correctly identified lesions to the total number of simulated lesions. Soft-copy reading was performed for all digital images. Direct magnification images acquired with the digital system showed a lower object contrast threshold than those acquired with the conventional system. For equal radiation dose, the digital system provided a significantly increased COR (0.95) compared with the screen-film system (0.82). For simulated microcalcifications, the corresponding difference was 0.90 to 0.72. The digital system allowed equal detection to screen-film at 40% of the radiation dose used for screen film. Digital magnification images are superior to screen-film magnification images for the detection of simulated small masses and microcalcifications even at a lower radiation dose.     

Microfocal spot magnification mammography using xeroradiographic and screen-film recording systems.

Direct radiographic magnification (1.5X) of the breast, using a microfocal spot x-ray tube and either a xeroradiographic or screen-film recording system, produces images superior in quality (improved resolution, reduced noise) to conventional contact mammograms. Six hundred twenty-one patients had a single magnification mammogram in addition to conventional mammography; 216 subsequently underwent biopsy within one month of study. The additional magnification mammogram increased the diagnostic accuracy of the conventional examination in 40% of the pathologically proved cases, particularly among those for which conventional mammograms were interpreted as equivocal for malignancy. The superior image quality of magnification mammograms appears useful in distinguishing malignant from benign breast disease.     

A demonstration comparing film mammography with the new high sensitivity xeromammography

The author has performed a subjective comparison of breast images recorded with a new liquid-toner xerographic system and images of the same breasts recorded on Kodak OM-1 film exposed with a MinR screen and a 5 to 1 grid. The xeromammograms are judged to be superior to the mammograms recorded on film with respect to: (1) the demonstration of calcifications, circumscribed masses, and the back of the breast; (2) the "resolution" of dense connective tissue; and (3) the overall image quality. Radiation doses to the breast associated with the two types of study are said to be comparable. Thirteen pairs of excellent images comparing xeromammograms with conventional breast films are presented.     

Can electronic zoom replace magnification in mammography? A comparative Monte Carlo study

Magnification, which is considered to be a relatively high "dose cost" mammographic technique, is a complementary examination performed on women exhibiting breast complaints or abnormalities. Particular attention is given to the imaging procedure as the primary aim is to confirm the existence of suspected abnormalities, despite the additional dose. The introduction of post-processing capabilities and the widespread use of digital mammography promoted some controversy in the last decades on whether electronic zoom performed on the derived initial screening mammogram can effectively replace this technique. This study used Monte Carlo simulation methods to derive simulated screening mammograms produced under several exposure conditions, aiming to electronically magnify and compare them to the corresponding magnification mammograms. Comparison was based on quantitative measurements of image quality, namely contrast to noise ratio (CNR) and spatial resolution. Results demonstrated that CNR was higher for geometric magnification compared to the case of electronic zooming. The percentage difference was higher for lesions of smaller radius and achieved 29% for 0.10 mm details. Although spatial resolution is maintained high in the zoomed images, when investigating microcalcifications of 0.05 mm radius or less, only with geometric magnification can they be visualised.The carcinogenic risk associated with the delivery of high radiation doses such as those related to magnification views in mammography, in addition to the requirements for high image quality, have made it essential to optimise this technique. Although this radiation risk is considered to be relatively insignificant in the context of accurate diagnosis, work-up and treatment, an investigation has started for alternative techniques that could provide equivalent or improved characterisation of lesions and improved diagnostic information compared with that obtained from magnification views. The psychological “cost” of a woman being recalled for a second mammographic examination, the discomfort from the breast compression and the economic impact of an additional examination are also factors that have promoted research into alternative procedures that complement the information provided by standard mammography.For many decades, magnification mammographic images of selected breast regions have been considered the most effective diagnostic tool for enhancing the visibility of subtle suspicious breast lesions and microcalcifications, thus providing improved diagnostic sensitivity and specificity. To this end, screen-film radiography was the gold standard for many decades and has now been replaced with digital radiography, which can also be combined with digital post-processing methods. The enhancement of visibility in magnification views is attributed to the increase in contrast to noise ratio (CNR) caused by the increased fluence per irradiated area. The CNR increases with the degree of magnification, particularly for low degrees (increase of 75% between degrees 1.0 and 1.4) [5]. By contrast, a major disadvantage of magnification is the additional and significantly high dose of radiation delivered to the breast compared with the contact case. Owing to the fact that the breast is placed closer to the X-ray focal spot, both the entrance dose at the skin surface and the mean glandular dose (MGD) to the irradiated part of the breast are considerably higher than for the corresponding contact view. Typically, MGD is doubled at 1.5× magnification compared with a standard mammogram. Thus, there is an increased radiation risk [6, 7]. Regarding spatial resolution, this is significantly degraded as magnification increases owing to the finite dimensions of the focal spot and the detrimental penumbra effects [8, 9]. At the same time, however, spatial resolution is improved due to the effective detector resolution, which depends on the irradiated object''s size on the detector plane [9]. For the low degrees of magnification usually applied in clinical practice, the overall system resolution is improved with magnification. However, for higher degrees it is degraded owing to the dominant effect of the focal spot dimensions [9, 10].Among the new techniques introduced in the effort to replace magnification views, image post-processing, often facilitated by digital mammography, has become very popular [11–13]. Electronic magnification (zoom) of digital (or digitised) screening mammograms has recently come to the foreground of this research area and many authors are addressing this alternative. A question that arises is whether the image quality provided by electronic zoom is comparable to that provided by the (original) geometric magnification views. If not, another question arises – whether the dose-saving provided by electronic zooming can compensate for a potential detriment in image quality.Several studies have been performed, most involving observers, to evaluate the image quality provided by the two techniques. Perisinakis et al [4] demonstrated that the enhancement of image features through post-processing (zooming) of both digitised contact images and geometric magnification mammograms equally improved the visualisation of subtle microcalcifications that are only rarely identified in standard full-field screen-film mammograms. Similar results have been reported by Vyborny et al [11], Smathers et al [14] and Powell et al [15]. These authors also showed that lesion visualisation achieved with geometric magnification mammograms (without the application of further post-processing) was similar to that achieved by electronic magnification and processing of the contact full-field image. Chan et al [16] showed that geometric magnification combined with stereotactic imaging in mammography provides better results than electronic display zooming of the contact stereotactic images.Smith et al [17] included the radiologist''s experience in their study; the authors demonstrated that, when evaluating microcalcifications, radiologists less experienced in mammography should not replace digitised and enhanced contact mammograms for microfocal-spot magnified mammograms. Other studies in this area have been reported in recent years [18–23] and, despite the fact that their conclusions vary, most exhibit a common characteristic: they are based on subjective human perception and decision criteria, known to vary significantly, rather than on objective metrics of image quality such as CNR and spatial resolution. Moreover, to our knowledge, to date no studies have been published comparing the primary image for both techniques without the application of additional post-processing methods (e.g. denoising or enhancement), based only on objective metrics of image quality.In this study, a validated Monte Carlo model developed for producing simulated mammographic images under exposure conditions representative of clinical mammography was used. Sets of standard contact and geometrically magnified mammograms were produced using the same output. The contact mammograms were then electronically magnified (zoomed) and compared with the corresponding images produced with the geometric magnification with no further post-processing undertaken. The comparison was based on CNR (derived from signal and noise measured in the images and their background) and spatial resolution.     

Digital processing of film radiographs

Initial clinical experience with a system for the digitization, processing, and display of film radiographs is described. Film is digitized using a high-intensity laser scanner; the recorded image data may then be subjected to a wide variety of processing options, with display of processed images on television monitors. The possibilities of clinical applications to processing and display of chest radiographs and film mammograms are described. A comparison of conventional analog subtraction and digitized film subtraction angiography indicated equivalent diagnostic capability, with the advantage of flexible, interactive image processing with the digital technique. A specially designed, energy-selective cassette permits dual-energy imaging from two films effectively exposed to different x-ray energy spectra. Dual-energy imaging may be capable of the characterization of body materials, including lung nodules, and useful for eliminating obscuring radiographic shadows overlying regions of interest.     

Visually detectable resolution of intraoral dental films

OBJECTIVES: The visually utilizable resolution of intraoral dental films was examined with the naked eye, with two-fold optical magnification and after digitization using a computer display. METHODS: Agfa Dentus M2, Kodak Ektaspeed Plus and Kodak InSight dental films were exposed with a line pair (lp) test pattern providing frequencies up to 16.6 lp mm(-1). Films were developed at 24 degrees C in a Dürr Periomat machine and at 28 degrees C in a Dürr AC245 machine. Forty dental students evaluated the maximum visually detectable resolution with their naked eye, with an X-ray viewer (providing two-fold magnifying lenses and eliminating disturbing light) and following digitization and monitor display examination. RESULTS: The best detectable resolution was achieved through digitization, reaching a mean of up to 16.5 lp mm(-1). With two-fold magnification, a mean of up to 13.3 lp mm(-1) could be resolved, while only 11.7 lp mm(-1)could be resolved with the naked eye. Unlike the other film types, the resolution of Ektaspeed depended on the processing type when viewing digitized images or when viewing with the naked eye. There was a trend for students above 29 years of age to detect a lower resolution with the naked eye, although they performed comparably with students below 29 years when using the X-ray viewer or viewing digitized images. CONCLUSIONS: Film resolution is utilized best through digitization and secondly using a magnifying lens. With the naked eye, a mean of 11 lp mm(-1) with a broad distribution can be resolved. A magnifying lens is recommended if resolution is important or if the viewer's eyesight is reduced. Compared with E-speed films, Kodak Insight was less dependent on processing conditions.     

Zooming method (× 2.0) of digital mammography vs digital magnification view (× 1.8) in full-field digital mammography for the diagnosis of microcalcifications

The purpose of this study was to determine whether the interpretation of microcalcifications assessed on images zoomed (× 2.0) from digital mammograms is at least equivalent to that from digital magnification mammography (× 1.8) with respect to diagnostic accuracy and image quality. Three radiologists with different levels of experience in mammography reviewed each full-field digital mammography reader set for 185 patients with pathologically proven microcalcification clusters, which consisted of digital magnification mammograms (MAGs) with a magnification factor of 1.8 and images zoomed from mammograms (ZOOM) with a zoom factor of 2.0. Each radiologist rated their suspicion of breast cancer in microcalcific lesions using a six-point scale and the image quality and their confidence in the decisions using a five-point scale. Results were analysed according to display methods using areas under the receiver operating characteristic curves (A_z value) for ZOOM and MAGs to interpret microcalcifications, and the Wilcoxon matched pairs signed rank test for image quality and confidence levels. There was no statistically significant difference in the level of suspicion of breast cancer between the ZOOM and MAG groups (A_z = 0.8680 for ZOOM; A_z = 0.8682 for MAG; p = 0.9897). However, MAG images were significantly better than ZOOM images in terms of visual imaging quality (p < 0.001), and the confidence level with MAG was better than with ZOOM (p < 0.001). In conclusion, the performance of radiologists in the diagnosis of microcalcifications using ZOOM was similar to that using MAGs, although image quality and confidence levels were better using MAGs.Magnification mammography produces better spatial resolution and signal-to-noise ratio than does contact mammography. It is well established as a valuable adjunct to contact mammography, especially for the diagnosis of microcalcifications, despite the additional radiation exposure and increased radiation dose because of the shorter distance between the breast and X-ray source during examination [1–4].However, with respect to full-field digital mammography (FFDM), a few studies using zoomed images from contact mammograms have recently been reported and, as a result, a debate has arisen over whether a digital zooming system of FFDM can replace the magnification view of digital mammography [5–7]. Whereas Fischer et al [5] reported that zoomed images of a digital contact mammogram were equivalent to direct magnification of FFDM for the interpretation of microcalcifications, our previous report suggested that magnification mammography yielded better sensitivity and receiver operating characteristic (ROC) analysis than did zoomed images [7]. However, that study compared images zoomed by a factor of 1.3 with images magnified by a factor of 1.8. Therefore, we wondered whether using a zooming factor comparable to a magnification factor of 1.8 would yield the same results.The purpose of this study was to determine whether the diagnostic accuracy and image quality of microcalcification assessments using images twice zoomed from contact mammograms were equivalent to those obtained using digital magnification mammography by a magnification factor of 1.8.     

Digitizing and consolidating mammograms and other images for teaching applications

RATIONALE AND OBJECTIVES: Most mammograms are obtained using screen-film technique and must be digitized for teaching purposes. Digitizing mammograms poses special problems because of high contrast and multiple views. We describe the equipment and process for digitizing and consolidating mammograms for teaching purposes. These techniques can be applied to any type of images where consolidation may be helpful. MATERIALS AND METHODS: Mammograms are digitized using a high optical density scanner. After the window and levels are adjusted, a four-view mammogram may be consolidated into a single image if desired. RESULTS: The high contrast of film screen mammograms is managed by using a high optical density scanner. Consolidation of image sets, such as a four-view mammogram, allows images to be easily inserted into text, slide, or poster documents. CONCLUSIONS: Digitizing mammograms for teaching purposes is facilitated by use of a high optical density scanner and consolidation of image sets into single images. The techniques described are also useful for other areas of radiology in which display of multiple images or modalities is desirable.     

Mammographic equipment, technique, and quality control

The most important improvements in mammographic technique were the introduction of single- or double-emulsion high-contrast film-screen combinations for mammography, the use of a specially designed low-kilovoltage Bucky grid to reduce scattered radiation, and the introduction of smaller focal spots to improve imaging geometry. Magnification techniques, especially the spot-film technique, yields clearer delineation of high-contrast microcalcifications. Dedicated mammographic equipment with specially designed x-ray tubes is necessary for modern high-quality mammography. However, in many modern mammographic units, the automatic exposure controller still fails to provide appropriate and constant optical film density over a wide range of tissue thickness and absorption. Extended-cycle processing of single-emulsion mammographic films can yield better image contrast and reduce exposure by up to 30%. Exposure times of less than 1 second are recommended to avoid the unnecessary higher doses caused by longer exposure times and reciprocity law failure. The wide dynamic range in mammography can be reduced by a beam equalization filter, and thus be better adapted to the decreased latitude of modern high-contrast mammographic screen-film systems. Mammographic film reading (detection of subtle microcalcifications) can be facilitated by modern computer evaluation of previously digitized mammograms. Standardization and assurance of image quality have been major challenges in the technical development of mammography. Different technical and anthropomorphic phantoms have been designed to measure and compare practical image quality. Detailed quality control measures have been developed. The benefit of a single or annual screening mammography, calculated in gained life expectancy, by far outweighs the relative risk for radiation-induced breast cancer.     

Digital full field mammography: comparison between radiographic direct magnification and digital monitor zooming

PURPOSE: Our goal was to compare digital magnification mammograms with images zoomed from the digital contact mammogram in patients with microcalcifications. PATIENTS AND METHODS: Fifty-five patients with 57 microcalcification clusters were evaluated with a FFDM system (Senographe 2000D, GE). In addition to a digital contact mammogram, a digital direct magnification mammogram (factor 1.8 [MAG1.8]) and an image zoomed from the contact mammogram with a magnification factor of 1.8 [ZOOM1.8] were obtained in each patient. The image quality (perfect = 5 points to inadequate = 1 point) and the characterization of microcalcifications (BI-RADS 2-5) were evaluated by 4 readers. The results were compared to histopathologic findings in 35 patients (37 lesions) and follow-up in 20 patients. RESULTS: Histopathology revealed 16 benign and 21 malignant lesions. 20 patients had benign changes verified by long-term follow-up. Image quality of direct magnification FFDM was assessed superior (4.44 points) to zoomed images (4.14 points). Sensitivity was superior for direct magnification (97.5%) in comparison to the zoomed images (96.3%). However, specificity (MAG1.8: 34.3%, ZOOM1.8: 40%), PPV (MAG1.8: 47.5%, ZOOM1.8: 49.8%) and accuracy (MAG1.8: 58.1%, ZOOM1.8: 61.2%) were better with zooming technique. Deviation steps from best BI-RADS assessment were 0.45 for MAG1.8 and 0.44 for ZOOM1.8. CONCLUSIONS: In patients with mammographic microcalcifications, monitor zooming of the digital contact mammogram is equivalent to direct magnification FFDM. Therefore, monitor zooming allows a reduction of the radiation exposure and an optimization of the work-flow.     

Microcalcifications of breast tissue: appearance on synchrotron radiation imaging with 6-microm resolution

OBJECTIVE: The purpose of this study was to use synchrotron radiation imaging with 6-microm resolution to evaluate amorphous and pleomorphic breast tissue microcalcifications. CONCLUSION: Synchrotron radiation imaging depicted microcalcifications as small as 24 microm. Imaging with this technique revealed that most amorphous and pleomorphic calcifications on conventional mammograms are clusters of fine specks and that in addition to the shape or density of a speck, the distribution density of clustered specks is a factor determining the apparent shape.     

Storage phosphor and film-screen mammography: performance with different mammographic techniques

The aim of this study was to compare the image quality of storage phosphor plates with that in screen-film radiograms in mammography. Two anode/filter combinations were also compared – Mo/Mo and W/Rh. S Storage phosphor plates, generation IIIN (Fuji, Tokyo, Japan) and a conventional screen-film system (Kodak, Rochester, N. Y.) were evaluated using two mammographic units. One unit had a 0.6-mm focal spot, an anode/filter combination of Mo/Mo and no grid (A_Mo); the other had a 0.3-mm focal spot, a grid, and two possible combinations of anode/filter Mo/Mo (B_Mo) and W/Rh (B_W). Simulated tumours and microcalcifications were randomly positioned in an anthropomorphic breast phantom (RMI model 165, no. 210–009, Radiation Measurements Inc., Middleton, Wisconsin). The image quality was evaluated using a modified version of receiver operating characteristics analysis. Five observers evaluated 300 films and 300 hard copy images each. Radiation doses were also determined. The image quality of the conventional screen-film images was significantly better than that for the storage phosphor plate mammograms. The B_Mo system rated best, for the detection of both tumours and microcalcifications, although it was not significantly different from the B_W system. Systems B_Mo and B_W rated significantly better than the A_Mo system for both image receptors studied. The mean absorbed dose was twice as high for the B_Mo system as for the A_Mo and B_W systems for both conventional and digital technique. The mammograms produced with the screen-film combination gave a significantly better detectability than the storage phosphor plates used in this study. Substantial dose reduction could be achieved using an anode/filter combination of W/Rh instead of Mo/Mo with no significant loss of information in the images. Received 6 June 1997; Revision received 22 August 1997; Accepted 10 July 1998     

Spectral phase based medical image processing

RATIONALE AND OBJECTIVES: To exploit the spectral phase characteristics of digital or digitized mammograms for early detection of microcalcifications, shape, and sizes of suspected lesions and to demonstrate its use for training radiologists to discriminate signal features in different spatially varying backgrounds. MATERIALS AND METHODS: We propose two algorithms: in the phase-only image (POI) reconstruction algorithm the spectral phase of the digital mammogram is extracted from its Fourier spectrum. This is coupled with unit magnitude and inverse Fourier transformed to reconstruct the POI thus enhancing the features of interest such as microcalcifications, shape, and sizes of suspected lesions. In the algorithm for image reconstruction from a priori phase-only information, spectral phase is used to extract signal features of the digital mammogram and then this is combined with spectral magnitude that is extracted and averaged over an ensemble of unrelated digital mammograms. RESULTS: The results for several digital phantoms and mammograms show that POI reconstructs only high spatial frequencies related to the features such as microcalcifications, shape, and size of masses like cysts and tumors. The results on image reconstruction from a priori phase-only information demonstrate the changes in the visibility of signal features when buried in a wide variety of real world mammogram backgrounds with different densities. CONCLUSION: The POI can aid radiologists in early detection of microcalcifications, lesions, and other masses of interest in digital mammograms. This reconstruction method is self-adaptive to changes in the background. The image reconstruction from a priori phase-only information can help the radiologist as a training tool in his decision-making process. Preliminary experiments indicate the potential of the techniques for early diagnosis of breast cancer. Clinical studies on these algorithm procedures are in progress for application as a diagnostic CAD tool in digital mammography. These methods can in general be applied to other medical images such as CT and MRI images.