Examples of mammographic density. (a) 0% mammographic density, (b) less than 10%, (c) less than 25%, (d) less than 50%, (e) less than 75%, and (f) greater than 75%. On the right is an illustration of Cumulus in the measurement of mammographic density. The red line outlines the breast, and the green line outlines the area of density. Republished with permission from .