New CR system with pixel size of 50 microm for digital mammography: physical imaging properties and detection of subtle microcalcifications

PURPOSE: To investigate the physical imaging properties and detection of simulated microcalcifications of a new computed radiography (CR) system with a pixel size of 50 microm for digital mammography. MATERIALS AND METHODS: New and conventional CR were employed in this study. The new CR system included a high-resolution imaging plate coupled with the FCR5000MA (50 microm pixel pitch) including transparent support and a dual-sided reader. The conventional CR system was coupled with the FCR9000 (100 microm pixel pitch). Modulation transfer functions (MTFs) and Wiener spectra (WS) of the new and conventional CR systems were measured. Observer performance tests were conducted to compare the effects of pixel size (50 microm vs. 100 microm) on the diagnostic accuracy of CR systems in the detection of simulated microcalcifications. RESULTS: The presampling MTF of the new CR system was higher at high frequencies than the conventional CR system. The WS of the new CR system was comparable to that of the conventional CR system at all frequencies. The area under the receiver operating characteristic (ROC) curve (Az) obtained with the new CR and the conventional CR systems were 0.84 and 0.79, respectively. Results showed that the detection of simulated clustered microcalcifications was significantly improved by use of the new CR system compared with the conventional CR system (p<0.05). CONCLUSION: The new CR mammography system improved physical imaging properties and detection of simulated microcalcifications over conventional CR mammography.     

Digital mammography: observer performance study of the effects of pixel size on the characterization of malignant and benign microcalcifications

RATIONALE AND OBJECTIVES: The authors performed this study to evaluate the effects of pixel size on the characterization of mammographic microcalcifications by radiologists. MATERIALS AND METHODS: Two-view mammograms of 112 microcalcification clusters were digitized with a laser scanner at a pixel size of 35 microm. Images with pixel sizes of 70, 105, and 140 microm were derived from the 35-microm-pixel size images by averaging neighboring pixels. The malignancy or benignity of the microcalcifications had been determined with findings at biopsy or 2-year follow-up. Region-of-interest images containing the microcalcifications were printed with a laser imager. Seven radiologists participated in a receiver operating characteristic (ROC) study to estimate the likelihood of malignancy. The classification accuracy was quantified with the area under the ROC curve (Az). The statistical significance of the differences in the Az values for different pixel sizes was estimated with the Dorfman-Berbaum-Metz method and the Student paired t test. The variance components were analyzed with a bootstrap method. RESULTS: The higher-resolution images did not result in better classification; the average Az with a pixel size of 35 microm was lower than that with pixel sizes of 70 and 105 microm. The differences in Az between different pixel sizes did not achieve statistical significance. CONCLUSION: Pixel sizes in the range studied do not have a strong effect on radiologists' accuracy in the characterization of microcalcifications. The low specificity of the image features of microcalcifications and the large interobserver and intraobserver variabilities may have prevented small advantages in image resolution from being observed.     

Digital gastrointestinal imaging: the effect of pixel size on detection of subtle mucosal abnormalities

Five radiographs of double-contrast colon examinations demonstrating subtle mucosal changes of inflammatory bowel disease and five radiographs of healthy colonic mucosa were selected and digitized to four levels of resolution. Pixel sizes of 0.1 mm, 0.2 mm, 0.4 mm, and 0.8 mm were used. Ten radiologists interpreted the images, which were displayed on laser-printed film. Analysis of variance with repeated measures was performed and receiver operator characteristic curves were determined. The results demonstrate that the sensitivity in detecting subtle mucosal abnormalities improved as the resolution improved, with the best sensitivity at the highest resolution; more experienced readers detected details well even at the poorer levels of resolution; the resolution necessary for successfully evaluating the colonic mucosa was lower than expected; and given low noise levels, the matrix size used in conventional television fluoroscopy would be adequate for mucosal evaluation.     

Digital radiography of subtle pulmonary abnormalities: an ROC study of the effect of pixel size on observer performance

Forty conventional radiographs with examples of mild interstitial infiltrates and subtle pneumothoraces and 40 normal studies of the chest were selected and digitized, with pixel sizes of 1.0, 0.5, 0.2, and 0.1 mm. Observer performance tests were carried out using receiver operating characteristic analysis. Conventional radiographs and digitized images were compared. The results indicate that, in such cases, diagnostic accuracy increases significantly as the pixel size is reduced, at least to the 0.1-mm level. We conclude that, for digital systems using screen-film or similar image receptors, use of a pixel size substantially larger than 0.1 mm may result in some loss of diagnostic accuracy.     

Detection of simulated microcalcifications in a phantom with digital mammography: effect of pixel size

PURPOSE: To evaluate the effect of pixel size on the detection of simulated microcalcifications in a phantom with digital mammography. MATERIALS AND METHODS: A high-spatial-resolution prototype imager that yields variable pixel size (39 and 78 microm) and a clinical full-field digital mammography (FFDM) system that yields a 100-microm pixel size were used. Radiographic images of a contrast-detail (CD) phantom were obtained to perform four-alternative forced-choice observer experiments. Polymethylmethacrylate was added to obtain phantom thicknesses of 45 and 58 mm, which are typical breast thicknesses encountered in mammography. Phantom images were acquired with both systems under nearly identical exposure conditions by using an antiscatter grid. Twelve images were acquired for each phantom thickness and pixel size (for a total of 72 images), and six observers participated in this study. Observer responses were used to compute the fraction of correctly detected disks. A signal detection model was used to fit the recorded data from which CD characteristics were obtained. Repeated-measures analyses with mixed-effects linear models were performed for each of the six observers. All statistical tests were two sided and unadjusted for multiple comparisons. A P value of .05 or less was considered to indicate a significant difference. RESULTS: Statistical analysis revealed significantly better CD characteristics with 39- and 78-microm pixel sizes compared with 100-microm pixel size for all disk diameters and phantom thicknesses (P<.001). Increase in phantom thickness degraded CD characteristics regardless of pixel size (P<.001). CONCLUSION: On the basis of the conditions of this study, reducing pixel size below 100 mum with low imaging system noise enhances the visual perception of small objects that correspond to typical microcalcifications.     

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.     

The effect of digital unsharp-mask filtering on the signal-to-noise ratio in computed radiography.

The effect of image processing in computed radiography (CR) has been analyzed in many ROC studies. The results have not shown great diagnostic improvements, except in some special occasions. The theoretical effect of image enhancement on the signal-to-noise ratio in CR images has so far not been assessed. Concerning the previous results, the changes induced in the signal-to-noise ratio by digital image processing are certainly of interest. We calculated the signal-to-noise ratio in various conditions according to the principles of the Rose model, using the computerized image data of storage phosphor radiography. Seventy-seven computed radiographs processed by Gaussian unsharp-mask filtering using different kernel widths were analyzed. The signal-to-noise ratio was reduced in all images by more than 40% when the smallest kernels were used, and increased slowly towards the original value with greater kernel sizes. In no conditions did the ratio exceed the original one. The results show that although edges and signal contrast can be enhanced by unsharp-mask filtering, this happens at the cost of increased noise. This might at least in part explain why image processing does not significantly improve the diagnostic information content of a computed radiograph.     

A comparison of digitized storage phosphors and conventional mammography in the detection of malignant microcalcifications

The detectability of malignant tumor-derived microcalcifications with conventional mammography was compared to that with digital images (2000 X 2510 pixels by 10 bits) derived from a storage phosphor-based digital radiography system capable of 5 line pair/mm resolution at identical exposure factors (30 kVp, 250 mAs, 65 cm film-focus distance). Microcalcifications (50-800 microns in diameter) were randomly superimposed on a preserved human breast specimen. ROC analysis based on 480 observations made by four readers indicated that the ability to detect the calcifications with digital images (ROC area = 0.871 +/- 0.066) was equivalent to conventional mammography (ROC area = 0.866 +/- 0.075) despite lower spatial resolution. With digital mammography, 62% of all clusters were correctly localized, but only 23.6% of the individual calcifications were counted. With conventional mammography 61% of all clusters were correctly localized, but significantly more of the individual calcifications (31.5%) were counted.     

Real-time US elastography in the differentiation of suspicious microcalcifications on mammography

The purpose of this study was to retrospectively evaluate the use of US elastography in the differentiation of mammographically detected suspicious microcalcifications, using histology as the reference standard. Between May 2006 and April 2007, real-time US elasticity images were obtained in 77 patients (age range, 24–67 years; mean, 46 years) with 77 mammographically detected areas of microcalcifications (42 benign and 35 malignant lesions) prior to needle biopsy. Two experienced radiologists reviewed cine clips of elasticity and B-mode images and assigned an elasticity score of 1 to 3 in consensus, based on the degree of strain in the hypoechoic lesion without information of mammography and histology. For the elasticity score, the mean ± standard deviation was 1.5 ± 0.7 for benign and 2.7 ± 0.7 for malignant lesions (P < 0.001). When a cutoff point between elasticity scores of 1 and 2 was used, US elastography showed 97% (34/35) sensitivity, 62% (26/42) specificity, 68% (34/50) PPV, and 96% (26/27) NPV with an Az value of 0.852 (0.753–0.923, 95% confidence interval) in the differentiation of benign and malignant microcalcifications. Our results suggest that US elastography has the potential to differentiate benign and malignant lesions associated with microcalcifications detected at screening mammography.     

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.     

Use of artificial neural networks (computer analysis) in the diagnosis of microcalcifications on mammography.

INTRODUCTION/OBJECTIVE: The purpose of this study was to evaluate a computer based method for differentiating malignant from benign clustered microcalcifications, comparing it with the performance of three physicians. METHODS AND MATERIAL: Materials for the study are 240 suspicious microcalcifications on mammograms from 220 female patients who underwent breast biopsy, following hook wire localization under mammographic guidance. The histologic findings were malignant in 108 cases (45%) and benign in 132 cases (55%). Those clusters were analyzed by a computer program and eight features of the calcifications (density, number, area, brightness, diameter average, distance average, proximity average, perimeter compacity average) were quantitatively estimated by a specific artificial neural network. Human input was limited to initial identification of the calcifications. Three physicians-observers were also evaluated for the malignant or benign nature of the clustered microcalcifications. RESULTS: The performance of the artificial network was evaluated by receiver operating characteristics (ROC) curves. ROC curves were also generated for the performance of each observer and for the three observers as a group. The ROC curves for the computer and for the physicians were compared and the results are:area under the curve (AUC) value for computer is 0.937, for physician-1 is 0.746, for physician-2 is 0.785, for physician-3 is 0.835 and for physicians as a group is 0.810. The results of the Student's t-test for paired data showed statistically significant difference between the artificial neural network and the physicians' performance, independently and as a group. DISCUSSION AND CONCLUSION: Our study showed that computer analysis achieves statistically significantly better performance than that of physicians in the classification of malignant and benign calcifications. This method, after further evaluation and improvement, may help radiologists and breast surgeons in better predictive estimation of suspicious clustered microcalcifications and reduce the number of biopsies for non-palpable benign lesions.     

ROC analysis of mammography and palpation for breast screening

Receiver operating characteristic curves (ROCs) for mammography and clinical palpation individually and in combination are generated using screening data from Breast Cancer Detection Demonstration Project (BCDDP) No. 25. Detailed standard records of disease features observed on screening were kept by all examiners. And actual disease states at examination were determined for each case by pathology or follow-up. The ROCs are produced from these objective data without the usual concern for examiners' ultimate diagnostic conclusions. Comparative analysis of the ROCs illustrates the clear superiority of mammography over clinical palpation as an individual screening modality as well as the further superiority of the combined use of both modalities.     

Mucinous breast carcinoma showing as a cluster of suspicious microcalcifications on mammography

We report a case of mucinous breast carcinoma whose mammographic features consisted of a suspicious cluster of microcalcifications as the unique sign of malignancy. The lesion was non-palpable and measured approximately 2 cm at the greatest diameter. The microcalcifications showed several morphologies: round, pleomorphic, and fine shapes were identified. The total number of microcalcifications was > 30 and the number per square centimeter varied from 10 to 20. The histological calcifications showed good correlation with the mammographic ones and were localized predominantly at the periphery of the tumor inside ducts with ductal carcinoma in situ or in the acellular mucin. Two types were observed: psammomatous and gross-irregular calcifications. To our knowledge, only one case with similar findings has been reported previously. Received 10 November 1997; Revision received 3 April 1998; Accepted 2 June 1998     

Breast pilomatrixoma manifested as microcalcifications on mammography: report of two cases

Pilomatricoma is a benign tumor of hair follicule origin corresponding to a firm subcutaneous nodule requiring histology for diagnosis. Only few breast pilomatricomas have been reported, with imaging showing well defined nodules with microcalcifications. We report two cases of intra-mammary pilomatricomas presenting as ACR BI-RADS 4 and 5 microcalcifications, suspicious for malignant tumors. Percutaneous biopsy confirmed the histological diagnosis. Malignant pilomatricomas have been reported, suggesting that all pilomatricomas should be resected.     

Digital mammography: effects of reduced radiation dose on diagnostic performance

PURPOSE: To experimentally determine the relationship between radiation dose and observer accuracy in the detection and discrimination of simulated lesions for digital mammography. MATERIALS AND METHODS: This HIPAA-compliant study received institutional review board approval; the informed consent requirement was waived. Three hundred normal craniocaudal images were selected from an existing database of digital mammograms. Simulated mammographic lesions that mimicked benign and malignant masses and clusters of microcalcifications (3.3-7.4 cm in diameter) were then superimposed on images. Images were rendered without and with added radiographic noise to simulate effects of reducing the radiation dose to one half and one quarter of the clinical dose. Images were read by five experienced breast imaging radiologists. Results were analyzed to determine effects of reduced dose on overall interpretation accuracy, detection of microcalcifications and masses, discrimination between benign and malignant masses, and interpretation time. RESULTS: Overall accuracy decreased from 0.83 with full dose to 0.78 and 0.62 with half and quarter doses, respectively. The decrease associated with transition from full dose to quarter dose was significant (P < .01), primarily because of an effect on detection of microcalcifications (P < .01) and discrimination of masses (P < .05). The level of dose reduction did not significantly affect detection of malignant masses (P > .5). However, reduced dose resulted in an increased mean interpretation time per image by 28% (P < .0001). CONCLUSION: These findings suggest that dose reduction in digital mammography has a measurable but modest effect on diagnostic accuracy. The small magnitude of the effect in response to the drastic reduction of dose suggests potential for modest dose reductions in digital mammography.