ReviewWhat effect does mammographic breast density have on lesion detection in digital mammography?
Introduction
High mammographic breast density (MBD) has been shown to be a significant predictor of breast cancer risk, having been linked with a four- to sixfold increase in lifetime risk.1, 2, 3, 4 Byrne et al.2 found that more than 18% (66 of 354) of cancerous lesions occurred in women with more than 75% MBD and 44.1% occurred in women with more than 50% MBD. Women with low MBD had a lower rate of breast cancer (3.5 cases per 1000 women) than women with high MBD (11.5 cases per 1000 women).5 The majority of previously published studies has used breast images that have been acquired using conventional screen-film mammographic systems, which has been the primary imaging technique for the breast since the introduction of screening programmes in the early 1970s, although it has been used for many decades.6 However, the advent of digital mammography in January 20007 has introduced many changes to the screening environment, and today in many countries, including Australia, all screening is carried out in a complete digital environment. Given this shift, it is important to ask whether the evidence compiled using analogue technology is still valid in the digital domain, particularly considering emerging new evidence that the limitations faced by radiologists when examining dense breast tissue may not now hold true.
This review addresses the question of whether radiologists face the same set of challenges when reading digital mammograms as they did when reading screen-film, and whether the association of mammographic breast density and risk has to be reassessed in the light of modern digital technology.
Section snippets
Background
The mammographic appearance of breast tissue varies between women according to the differences in breast tissue composition and their x-ray attenuation coefficient.8 Basically, the breast consists of two types of tissue, fat and fibroglandular, which are represented by light and dark areas on a mammogram. MBD is a term used to define the portion of a standard mammographic view that comprises fibroglandular tissue. Examples of breasts with different mammographic densities are shown in Fig 1.
Assessment methods for MBD
Many breast density measurement methods have been introduced, however, some are subjective and qualitative, and others are quantitative measures. This review will cite the most common breast density measurements.
Subjective methods include Wolfe's grading, Tabar, Breast Imaging Reporting and Data System (BIRADS), and visual estimation. Wolfe's grading includes four breast density categories: N pattern (fatty radiolucent breast), P1 and P2 (fibroglandular tissue prominence in less than or more
Radiologists' performance and MBD
A number of studies have shown that the sensitivity of the radiologist to detect breast cancer decreases with increasing MBD,24, 25, 26 with cancer detection decreasing to between 30% and 64.4% in high-density breasts compared to 80–98% in low-density breasts.27, 28 Studies have examined the combined effect of age and breast density on mammographic sensitivity and have generally shown better performance in low MBD images compared with high MBD images in both young and old age groups. Rosenberg
Clinical indicators of reduced mammographic efficacy
As well as examining the sensitivity and specificity of imaging systems, there are clinical outcomes, which have been assessed as a way of showing that increased mammographic density has an effect on cancer detection.
Digital mammography performance and MBD
Digital mammography is now replacing conventional screen-film mammography in most countries. In digital mammography the process of image acquisition, display, and storage are performed independently and each function is optimized individually.57 Unlike screen film mammography, where intensifying screens are used to amplify the exposure and convert x-ray to light photons to form the mammographic image on a film, in digital mammography, images are captured as electrical signals that are converted
Conclusion
High MBD has been found to lead to lower sensitivity in breast cancer detection. Recent studies suggest that an increased performance can be achieved using digital mammography compared with screen-film technology in women with high MBD breasts. Therefore, there seems to be a possibility that the determined effect of high MBD could be overcome with the sophisticated post-processing and increased image quality that digital technology can provide. Hence, the impact of digital technology on
Acknowledgment
The authors thank Dr Warwick B. Lee, Mariusz W. Pietrzyk, Warren M. Reed, and Yanpeng Li for their invaluable editorial and writing assistance. D. S. AL Mousa was sponsored by Jordan University of Science and Technology.
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