Breast density quantification in dual-energy mammography using virtual anthropomorphic phantoms

Abstract

Purpose: Breast density is a significant risk factor for breast cancer and can impact the sensitivity of screening mammography. Area-based breast density measurements may not provide an accurate representation of the tissue distribution, therefore volumetric breast density (VBD) measurements are preferred. Dual-energy mammography enables volumetric measurements without additional assumptions about breast shape. In this work we evaluated the performance of a dual-energy decomposition technique for determining VBD by applying it to virtual anthropomorphic phantoms.

Methods: The dual-energy decomposition formalism was used to quantify VBD on simulated dual-energy images of anthropomorphic virtual phantoms with known tissue distributions. We simulated 150 phantoms with volumes ranging from 50 to 709 mL and VBD ranging from 15% to 60%. Using these results, we validated a correction for the presence of skin and assessed the method's intrinsic bias and variability. As a proof of concept, the method was applied to 14 sets of clinical dual-energy images, and the resulting breast densities were compared to magnetic resonance imaging (MRI) measurements.

Results: Virtual phantom VBD measurements exhibited a strong correlation (Pearson's $r>0.95$ ) with nominal values. The proposed skin correction eliminated the variability due to breast size and reduced the bias in VBD to a constant value of -2%. Disagreement between clinical VBD measurements using MRI and dual-energy mammography was under 10%, and the difference in the distributions was statistically non-significant. VBD measurements in both modalities had a moderate correlation (Spearman's $\rho$ = 0.68).

Conclusions: Our results in virtual phantoms indicate that the material decomposition method can produce accurate VBD measurements if the presence of a third material (skin) is considered. The results from our proof of concept showed agreement between MRI and dual-energy mammography VBD. Assessment of VBD using dual-energy images could provide complementary information in dual-energy mammography and tomosynthesis examinations.

Keywords: clinical images; dual‐energy decomposition; dual‐energy mammography; magnetic resonance imaging; virtual phantoms; volumetric breast density.

FIGURE 1

(a) Schematic representation of the calibration phantom. (b) Cropped low‐energy image of the calibration array and a selected 70 × 70 px region of interest (ROI), indicated by an arrow.

FIGURE 2

Dual‐energy decomposition of a simulated dual‐energy image pair. From left to right: LE image, HE image, adipose tissue map, and fibroglandular tissue map. The nominal and quantified VBD for this phantom were 42.9% and 40.5%, respectively.

FIGURE 3

Simulated phantoms. (a) Measured VBD versus nominal VBD, no skin correction. The dashed black line is the identity. (b) Measured VBD versus nominal VBD, with skin correction. The dashed black line is the identity, the solid red line is the best fit of the data to a straight line, and the solid blue lines represent a ± 10% difference in VBD. Data are classified by phantom size: L, large, M, medium, S, small.

FIGURE 4

From left to right: LE and HE “for processing” mammograms, adipose tissue map, fibroglandular tissue map, MRI slice with a ROI delineating the analyzed breast (yellow rectangle). The measured VBD was 24.6% in mammograms and 29.0% in MRI. Hyper‐intense regions inside the MRI volumes of interest were considered adipose tissue.

FIGURE 5

VBD values obtained in clinical dual‐energy and MRI images. (a) Scatterplot of $VB{D}_{DEDM}$ and $VB{D}_{MRI}$. The black dashed line shows the identity and blue solid lines indicate the $\pm 10\%$ difference margin. (b) Bland‐Altman plot comparing $VB{D}_{DEDM}$ and ${VBD}_{MRI}$. The black dashed line corresponds to no difference between the values, the red line indicates the mean in $\mathrm{\Delta }VBD$, and blue solid lines show the 95% limits of agreement.