Dr. Hixson is a Women's Imaging Specialist in Chattanooga, TN.

Mammography is the most effective screening modality for detecting early breast cancer. A landmark study by Tabár et al ¹ demonstrated a 42% reduction in breast cancer deaths in women who were screened versus those who were not screened. Dr. Tabár states, our goal is to detect invasive tumor masses when they are as small as possible, preferably <10 mm in diameter. Women with mammographically detected 1- to 10- mm invasive breast carcinoma have a 93% 16-year survival. ²

Breast cancer is a heterogeneous disease with many histologic subtypes. Even if mammography is the best proven method for finding breast cancer in its early stages, it is only natural that a single method will never be able to detect all of the subtypes. In addition, the composition of the breast tissue surrounding the lesion(s) will significantly influence our ability to demonstrate the presence of a benign or malignant lesion. It has long been recognized that a cancer is more likely to be missed if it is located in a dense breast.

Kolb et al ³ have performed an important study of 27,825 mammographic examinations and 13,547 bilateral whole-breast screening ultrasound examinations in conjunction with the mammograms. Ultrasound was able to detect cancers missed the same day by mammography, and these were most frequently in dense breasts. Their results showed a mammographic sensitivity of 78% for all breast density categories. The sensitivity for mammography was 98% for BIRADS density category 1, breast composed almost entirely of fat. However, the sensitivity was only 48% for BIRADS density category 4, extremely dense breast. This is a useful study that documents the progressive decrease in mammographic sensitivity as the breast density increases. However, well-trained radiologists using state-of-the-art film screen mammography should achieve higher sensitivities than reported in this study.

Birdwell et al ⁴ studied 115 cancers missed by screening mammography. The majority of missed cancers (57%) were located in the middle of the breast where compression is suboptimal with a conventional horizontally oriented compression paddle. A total of 28% of the missed cancers were located in the posterior third of the breast, and 11% were missed in the anterior third of the breast, which receives negligible compression with a conventional paddle.

The American College of Radiology (ACR) is striving to improve mammographic image quality so suboptimal images will not cause cancer to be missed. The ACR reports that common causes for failure of the clinical imaging evaluation process are unsharpness, poor contrast, and failure to spread apart the fibroglandular tissues. ⁵ Inadequate compression is usually the underlying cause for all of these deficiencies. Better compression prevents motion unsharpness by reducing breast thickness to allow shorter exposure times and by immobilizing the breast. Patient motion is the most common cause of readily detectable image unsharpness. ⁵

The previous limitations of film-screen mammography led to a search for alternative screening modalities. Whole-breast digital mammographic units have been developed and are now available. However, no studies to date have demonstrated any increased sensitivity of whole-breast digital mammography. Furthermore, the performance of film-screen mammography has significantly improved due to the recent introduction of several new products.

Improved compression paddles

A standard screening mammogram is obtained by compressing a cone-shaped structure between two flat, parallel surfaces. It is not possible to achieve uniform compression from the chest wall to the nipple with a conventional compression paddle. Images obtained by expert mammographers commonly exhibit subtle motion blur in the mid-breast and anterior breast. Conventional screening paddles are oriented horizontally and produce optimum compression of only the thick posterior portion of the breast. The middle third of the breast is incompletely compressed, and the anterior breast receives negligible compression.

Compression paddles have recently been developed that produce increased compression of the anterior half of the breast. These paddles typically rotate as compression is applied, causing the nipple end of the paddle to go downward and the chest wall end to go upward. As the compression force increases, there is increasing compression of the breast anteriorly with a corresponding decrease in compression applied posteriorly. However, this can be detrimental since most cancers are located in the posterior half of the breast, which is also the most common location for a cancer to be missed.

The New S.O.F.T. Paddle™

The S.O.F.T. Paddle™ developed by American Mammographics (Chattanooga, TN) is different. It has a gently curved compression surface that slopes downward toward the nipple. It does not rotate. As the paddle is lowered, there is almost simultaneous contact with the breast from the chest wall to the nipple. Table 1 shows the benefits of S.O.F.T. Paddle™. Optimum compression of all areas of the breast is achieved. S.O.F.T. Paddle™ produces a significant improvement in image quality, particularly in dense breasts (Figures 1 and 2). Dr. László Tabár is now using the S.O.F.T. Paddle™ for screening mammograms interpreted at Falun Central Hospital in Falun, Sweden. Dr. Tabár says of the S.O.F.T. Paddle™, the image details that are so essential in making the first and most important decision (callback or normal) are visualized so well and with such a sharpness as I have never experienced it previously. (L. Tabar, personal communication).

Other helpful tools

The use of darker films and brighter view boxes is now recommended, and this is essential for proper interpretation of dense breasts. The ACR QC Manual recommends an optical density (OD) of at least 1.40 for the background density for the phantom image. ⁵ A background OD of 1.80 is much better and is optimal for dense breasts. The OD should be set high enough to prevent the OD from falling below 1.0 in the densest area of any breast. The ACR requires a minimum viewbox luminance of 3000 nits. ⁵ However, a luminance of at least 5000 nits is necessary to evaluate the darker peripheral areas of a film. The cones in the retina are responsible for perceiving fine details, and they function best at high light levels.

Mammographic films and screens have significantly improved in the last several years. For example, the Kodak MIN-R 2000 film and MIN-R 2000 screens produce very high-quality images. The MIN-R 2190 screen is 25% faster. It can be used routinely or only selectively for dense breasts to improve contrast and reduce motion blur. Contrast is further increased with Kodak X-OMAT EX II developer and companion fixer. The use of the 2190 screen and the S.O.F.T. Paddle™ together can produce considerable improvement in image quality, especially with dense breasts (Figure 2).

There have been many significant improvements in mammographic equipment. For example, the Diamond Unit (Instrumentarium Imaging, Milwaukee, WI) incorporates numerous technological advances. This unit was selected as the best new product at RSNA 2000. It contains the Diamond X-ray tube with a special microfocusing cup that improves spatial resolution. It also utilizes a proprietary grid (ROC Grid) with a 6:1 ratio and a low radiation absorption interspace material, which provides the same X-ray transmission as a 5:1 grid. Figure 3 illustrates the improved image quality when the Instrumentarium Diamond X-ray tube, the ROC grid, and the S.O.F.T. Paddle™ are used together.

Discussion

Early detection by mammographic screening is a proven method of decreasing mortality from breast cancer. The present generation of physicians is the first to offer a significantly better outcome for cancer patients, by significantly decreasing the rate of advanced cancers through early detection and treatment in an early stage. Yet, paradoxically, there is a growing shortage of radiologists who are expert in mammography, and many radiologists would prefer not to have to read mammograms. The reasons are probably reflected in the results of a recent survey of radiology residents from 211 accredited radiology residencies in the U.S. and Canada by Bassett et al. ⁶ Their results showed that 63% of the residents would not want to spend one-fourth or more of their time interpreting mammograms. The most common reasons were: not interesting enough, fear of lawsuits, and too much stress. One surprising result was that 87% of the residents rated interpretation of mammograms as being more stressful than other types of imaging. This is partly understandable, taking the complexity of breast diseases into account, the need for learning histopathologic-mammographic correlation, the need for interdisciplinary cooperation, the steady demand for making perfect decisions, and because of the need for continuous quality and product control. There are a few solutions to this problem. One is continuous, high-quality training and further education. In addition, improvement in image quality and standardization of the method would help to make mammography more attractive for the future generation of professionals.

Conclusion

Simple, cost-effective tools and inventions have recently become available that can significantly improve image quality, particularly in dense breasts. The use of these products should result in fewer missed cancers and fewer callbacks for supplemental imaging. Better quality images also should reduce the time for interpretations.