Breast dose from magnification films in mammography

In mammography, much attention has been given to estimating breast dose from exposures made in conventional "contact" geometry, but much less attention has been given to doses from magnification geometry. Estimation based on contact film dose is difficult because the grid is removed, the geometry is different, and calculation of scatter reaching the film is complex. In this paper, exposures of Perspex blocks of standard thickness to give the same film density in both geometries are compared on 20 X-ray sets of various designs with a nominal magnification 1.8. The ratio derived between doses in each geometry is 2.2+/-0.15, giving an average magnification film dose of 5.0+/-0.3 mGy.     

Image quality and dose in film-screen magnification mammography

Extended exposure times in magnification mammography are a result of the reduced X-ray tube currents required for a small focal spot. The consequences of this are the potential for reduced image quality through motion blur during exposure as well as the onset of film reciprocity law failure. Previous investigators have suggested increasing the X-ray tube potential as a practical mechanism for reducing exposure times in magnification mammography and have demonstrated negligible image quality degradation at least up to 32 kVp. This paper describes a film-screen magnification mammography study that expands upon this previous work to investigate the magnitude of the reduction of breast mean glandular dose and exposure time and the changes in subjective image quality (visibility of low contrast details in an RMI 152 phantom) with increases in tube potential between 28 kVp and 35 kVp. Measures of changes in the radiographic contrast and in the scatter-to-primary ratio (SPR) in magnification geometry as a function of tube potential were also obtained. Evidence for reciprocity law failure was also assessed. For a constant film optical density, increasing the X-ray tube potential from 28 kVp to 35 kVp reduced the mean glandular dose from 3.9 mGy to 2.7 mGy and reduced the exposure time from 3.2 s to 1.0 s. Over this range, the detection rate of fibrils and microcalcification-mimicking specks did not vary with tube potential at the 0.05 level of significance. It was found that only the low contrast mass detail detection rate at 35 kVp was significantly less than that at 28 kVp. The measured radiographic contrast decreased with tube potential and the SPR increased with tube potential. However, both changes were weak, and linear regressions determined that the 95% confidence intervals of the slopes relating both contrast and SPR with tube potential encompassed zero. It is concluded that magnification mammography performed at 34 kVp yields significant reductions in exposure time and mean glandular dose, with a detail detection capability similar to that at 28 kVp.     

Direct magnification in mammography with a 0.3 millimeter focus

The authors emphasize the value of mammography with a 0.3 millimetres microfocus-tube with a magnification system. This technique is limited to those large lesions increasing "twilight effect". For a better study of all breast's lesions the use of fine microfocus-tubes is suggested, as it results also from the latest literature.     

Focal spot size and scatter suppression in magnification mammography.

The improved image quality using magnification in film-screen mammography is related to a complicated interplay between focal spot size, x-ray tube output, detector resolution and sensitivity, air gap size, and target dimensions. Preliminary clinical evaluation of magnification mammography indicates that accuracy of diagnosis has been considerably enhanced. Additional technical and clinical evaluations are continuing, as suggested by mathematical modeling, in order to determine the best possible magnification protocols. While a small focal spot (less than 300 micrometers) is highly recommended for both contact and magnification with the film-screen systems, the smallest focal spot sizes (150 micrometers and smaller) may neither be necessary nor the best in all situations of reduced dose magnification mammography.     

Effects of a defective filter on magnification image quality in mammography.

A defective molybdenum filter in a dedicated mammographic unit was found to have a detrimental effect on image quality. The authors present a simple method for testing of molybdenum filters and suggest that it be incorporated into the acceptance testing routine for new mammographic units and that it be used in annual quality control checks.     

Direct magnification mammography in combination with computed radiography. First clinical results

Summary Introduction: The combination of direct magnification mammography and computed radiography provides an improvement in spatial resolution of storage phosphor-based digital systems. A clinical study comparing conventional and digital direct magnification mammograms was performed. Methods: 100 survey mammograms in 1.5- or 1.7-fold magnification and 50 4-fold spot magnification views were obtained with a prototype direct magnification mammography system and a storage phosphor-based digital system. An intraindividual comparison of these with previous conventional radiograms of the same patients was carried out. Results: The diagnostic value of digital survey mammograms using the direct magnification technique is comparable to that of conventional radiograms of the breast, especially with regard to the identification of microcalcifications and lesions and the clinical consequences. Spot magnification views performed with this combination of techniques allowed improvement in the evaluation of microcalcifications. In 15 % of cases, diagnostic procedures were adjusted accordingly. Conclusion: The combination of the direct magnification technique with digital storage phosphor radiography systems allows the performance of digital mammography by improving the overall spatial resolution. The diagnostic value of digital direct magnification survey mammograms was comparable to that of conventional mammograms. Digital 4-fold spot magnification views improved visualisation of the morphologic aspects of microcalcifications.      

Effects of breast thickness and lesion location on resolution in digital magnification mammography

This study aimed to examine the resolution effects of breast thickness and lesion location in magnification mammography by evaluating generalized modulation transfer function (GMTF) including the effect of focal spot, effective pixel size, and the scatter. Polymethyl methacrylate (PMMA) thicknesses ranging from 10 to 40 mm were placed on a standard supporting platform that was positioned to achieve magnification factors ranging from 1.2 to 2.0. As the magnification increased, the focal spot MTF degraded, while the detector MTF improved. The GMTF depended on the trade-off between the focal spot size and effective pixel size. Breast thickness and lesion location had little effect on the resolution at high frequencies. The resolution of small focal spot did improve slightly with increasing PMMA thickness for magnification factors less than 1.8. In contrast, system resolution decreased with increasing PMMA thickness for magnification factors greater than 1.8 since focal spot blur begins to dominate spatial resolution. In particular, breast thickness had a large effect on the resolution at lower frequencies. A low-frequency drop effect increased with increasing PMMA thickness because of the increase in scatter fraction. Hence, the effect of compressed breast thickness should be considered for the standard magnification factor of 1.8 that is most commonly used in clinical practice. Our results should provide insights for determining optimum magnification in clinical application of digital mammography, and our approaches can be extended to a wide diversity of radiological imaging systems.     

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.     

Comparison of two screen-film combinations in contact and magnification mammography: detectability of microcalcifications

A new dual-screen, dual-emulsion-film combination that allows a decrease in radiation dose of approximately 66% was compared with a widely used single-screen, single-emulsion-film system in contact and magnification mammography. Clustered microcalcifications randomly superimposed on a breast phantom were detected, and the location and number of individual calcifications were determined by four observers. The detectability of calcifications, determined with a receiver operating characteristic (ROC) analysis area, was 0.92 for magnification and 0.82 for contact mammography with the single-emulsion-film system, compared with 0.84 and 0.72, respectively, with the dual-emulsion-film system. More clusters were correctly located and more individual calcifications were counted with magnification than with contact mammography. The dual-emulsion-film system with the magnification technique performs as well as the single-emulsion-film system with the contact technique, while retaining a decrease in required dose of approximately 40%.     

Magnification mammography using 0.1 mm microfocus. Comparison of grid and spot-view magnification

Phantom measurements of resolution and dosimetry of 0.1 mm microfocus spot magnification mammography and 0.3 mm grid technique using different film-screen systems form the basis of this study. The diagnostic efficiency of spot views with these methods is evaluated according to the detection and analysis of microcalcifications, and the assessment of tumor margins.     

Image quality in mammography with special reference to anti-scatter grids and the magnification technique

Some of the parameters determining image quality in mammography are analyzed: the effects of primary photon spectra, focal spot size and screen-film systems on spatial resolution are discussed as are scattered radiation, development temperature and absorbed dose. The parameters limiting spatial resolution and contrast are evaluated for the standard and magnification techniques. Methods of reducing scattered radiation to improve contrast are evaluated. Scatter to primary ratios for different scatter reducing methods are compared, using the physical quantity energy imparted. For the standard technique the spatial resolution has been found to be limited by the fluorescent screen. With magnification technique the focal spot is the weakest link for the spatial resolution. The contrast is mainly set by the amount of scatter using the standard technique considering the use of a low tube potential (approximately 25 kVp). Using the magnification technique the amount of scatter is so small, that the tube potential is the limiting factor. We have found the optimized standard mammographic technique to be achieved under the following conditions: 25 kVp, 0.3 to 0.6 mm focal spot, film-focus distance 500 mm, anti-scatter grid, developing temperature 36 to 38 degrees C and 4 minutes total processing time with the screen-film system we have used. In magnification technique an air gap of at least 20 mm is desired. With an FFD of about 500 mm this will give a magnification ratio of 1.8 to 2.0 and a 0.1 mm X 0.1 mm focus spot is mandatory. With this technique, it is necessary to use a faster screen-film system than that used in standard mammography.     

0.1 mm超微焦点放大摄影诊断未触及肿块的乳腺癌

目的研究０．１ｍｍ超微焦点钼靶Ｘ线放大摄影对临床未触及肿块的乳腺癌的诊断价值。方法３５例乳腺癌病例均经手术病理证实，所有病例术前临床均未触及肿块。所有病例术前都进行了普通钼靶摄影（以下简称普通摄影）与０．１ｍｍ超微焦点钼靶Ｘ线放大摄影（以下简称放大摄影），并选择检出率及分辨率为观察指标。结果放大摄影的图像质量明显优于普通摄影，且在统计学上有非常显著性差异。结论应把放大摄影列为检查未触及肿块而临床或普通钼靶摄影疑诊乳腺癌病例的常规手段。     

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.     

全数字乳腺摄影机最佳曝光条件的探讨

目的 探讨并找出全数字乳腺摄影机(FFDM)的最佳曝光条件。方法 用全数字乳腺X 线摄影机对Fluke NA 18-220 乳腺模体进行自动曝光控制(AEC)摄影,记录曝光条件为29kV、40mAs,用手动调整不同的mAs值(24、28、32、36和45mAs)和kV (22、23、25、27和31kV)对模体曝光,由4位影像学家在相同条件下进行软阅读,并按照美国放射学会(ACR)的评分标准对模体中的钙化点、尼龙纤维、肿块灶进行打分,对所得数据进行方差分析(ANOVA)。结果 在相同的摄影电压29 kV下,手动曝光条件下32mAs和AEC的40mAs的影像信息的评价分值差异没有统计学意义(P>0.05),说明这2种摄影条件对乳腺摄影体模内容物的显示基本相同,但二者的辐射剂量确有明显的不同。在相同的摄影电流40mAs下,27kV和29kV的影像信息的评价分值没有统计学意义(P>0.05),说明这2种摄影条件对乳腺摄影体模内容物的显示基本相同,但二者的辐射剂量不相同。结论 在保证影像质量的前提下,自动曝光控制摄影条件初始设定水平的合理性应进行必要的检测来验证。     

Short communication: anomalous image quality phantom scores in magnification mammography: evidence of phase contrast enhancement

Anomalously high image quality scores were noted for images of the Leeds TORMAM phantom obtained using magnification mammography. Comparison of optical density profiles of fibre features in the images with non-magnified images and images previously obtained using an in-line phase contrast geometry showed the presence of phase contrast enhancement in the magnification images. The effect on the phantom score is particularly marked for this design of phantom owing to its use of fibres, which tend to enhance well. A large proportion of the phantom score is associated with fibrous features. It is concluded that direct comparison of TORMAM phantom scores from magnified images with those from non-magnified images is not valid due to the different balance of physical mechanisms forming the two kinds of image.     

乳腺摄片普查过程中漏误诊的相关因素

乳腺摄片为乳腺癌普查的重要手段，但部分患者乳腺片存在着假阴性与假阳性的不足，为临床漏误诊埋下了隐患。为减少漏误诊，本文搜集近年来国内外部分有关乳腺摄片普查方而的资料进行分析总结认为，乳腺摄片技术方面导致乳腺癌普查摄片假阴性与假阳性的因素可为：乳腺摄影器械质量性能及其相关因素、乳腺摄片投照位置的选择与胶片质量方面的因素以及受检者乳腺密度与年龄方而的因素等。