Conventionally, the measurement of breast density has relied on a visual assessment by the radiologist reviewing the mammogram. The American College of Radiology (ACR) devised the Breast Imaging Reporting and Data System (BI-RADS®) breast composition descriptions to standardize the description of breast density. The 5th edition of BI-RADS issued by the ACR clarified the breast composition descriptions further and states that density "...is an overall assessment of the volume of attenuating tissues in the breast, to help indicate the relative possibility that a lesion could be obscured by normal tissue..." The BI-RADS Breast Composition Categories are:
A. The breasts are almost entirely fatty;
B. There are scattered areas of fibroglandular density;
C. The breasts are heterogeneously dense, which may obscure small masses; and
D. The breasts are extremely dense, which lowers the sensitivity of mammography.
Categories A and B are considered "non-dense" or "fatty", while categories C and D are considered "dense".
The next step in breast density measurement
BI-RADS scoring is subjective and varies between physicians (and even within the same physician). To help address the subjectivity associated with the assessment of breast density, there are now commercial products cleared by the U.S. Food & Drug Administration (FDA) which measure breast density directly from the mammogram. One such software—Volpara—does not involve any additional testing or radiation dose and generates mathematical, computer-driven breast density measures based on the true 3D properties of a woman’s breasts. Known as volumetric breast density, this can be determined using the calculation of the volume of fibroglandular tissue divided by the total volume of tissue within the breast. This method provides reproducible measurements which show excellent calibration MRI (considered the “gold standard” of volumetric breast density measurement). Such measurements are designed to help physicians assess breast density more objectively and helping them better manage the breast care of their patients’ breast care.
Following are examples of images by breast composition with software generated breast density measurements:
VolparaDensity corresponds to the gold standard measurement of breast density, as well as clinical outcomes: