Improved volumetric breast density assessment in dense breasts

K. Holland, A. Gubern-Mérida, R. Mann and N. Karssemeijer

7th International Workshop on Breast Densitometry and Cancer Risk Assessment 2015.

To personalize screening procedures, volumetric percent density (VPD) may be used to stratify risk groups. To obtain VPD, the glandular tissue volume (GTV) is estimated in unprocessed mammograms using a physics-based method which relies on an internal reference value (RV) representing the projection of fat only. However, pure fat pixels are rare in dense breasts, causing an underestimation of GTV and VPD. The purpose of this work is to improve the VPD estimate in dense breasts. We collected 43 paired FFDM and MRI examinations. Mammographic VPD was estimated in different ways using three different reference values and compared to estimations based on MRI data. Pearson correlation coefficients were calculated with estimations averaged over both breasts and both mammographic views. The first two RVs are percentiles (0.99) of the pixel value distribution in the breast interior (BI). RV1 was obtained with a small BI. For RV2, a larger BI was used. Especially in dense breasts this may facilitate the identification of a pure fat pixel, that may not be present in the small BI. RV3 was defined by estimating the proportion of dense tissue in the densest location in the larger BI, using the maximum fraction of dense tissue projected on a line crossing the BI. Additionally we investigated a combination of the three estimations, by taking estimations of RV1 for nondense breasts and a combination of the results of RV2 and RV3 for dense breasts, using the estimation with RV1 to determine if the breast is dense. We found correlations of 0.89, 0.87 and 0.76 using RV1, RV2 and RV3 respectively. This improved to 0.91 when combining the three estimations. The reference value determination is crucial for calculation of VPD. The combination of three different methods yields the best result as different breasts density patterns require different approaches.