Current and Future Methods for Measuring Breast Density: A Brief Comparative Review

Abstract

Breast density is one of the strongest predictors of breast cancer risk. Women with the densest breasts are 4 to 6 times more likely to develop cancer compared with those with the lowest densities. Breast density is generally assessed using mammographic imaging; however, this approach has limitations. Magnetic resonance imaging and ultrasound tomography are some alternative imaging modalities that can aid mammography in patient screening and the measurement of breast density. As breast density becomes more commonly discussed, knowledge of the advantages and limitations of breast density as a marker of risk will become more critical. This review article discusses the relationship between breast density and breast cancer risk, lists the benefits and drawbacks of using multiple different imaging modalities to measure density and briefly discusses how breast density will be applied to aid in breast cancer prevention and treatment.

Keywords: Breast cancer risk; Breast density; Mammography; Ultrasound tomography.

Figure 1

Examples of the BI-RADS categories for density measurements made on mammography.

Figure 2

An example of the CUMULUS software measuring mammographic percent density in a mammogram. A user selects the edge threshold (red) that separates the breast tissue from the background and the density threshold (green) that separates dense tissue from non-dense tissue. MPD can be calculated by taking the number of pixels estimated by the density threshold (dense area) and dividing by the number of pixels estimated by the edge threshold (total breast area)[46].

Figure 3

(Left) Example of a pre-contrast T1 weighted coronal MRI image. (Right) The same image with a user defined threshold used to separate dense tissue (yellow) from fatty tissue.

Figure 4

Examples of sound speed images created from an Ultrasound Tomgraphy device. Each image represents one slice in a stack of images corresponding to a single breast. Image slices are obtained moving from the chest wall to past the nipple to image the entire volume of the breast. The images are roughly organized according to the BI-RADS mammographic density categories. Top Left is a fatty breast (BI-RADS category a), Top Right is a breast with scattered densities (b), Bottom Left is a heterogeneously dense breast (c) and Bottom Right is a dense breast (d).