Evaluation of Subtraction Processing for Mammograms Analyzed by Breast Density and Thickness

In recent years, with the development of digital technology, radiologists compare bilateral and temporal mammograms easily to use the findings of difference as references for diagnosis. In this study, we examined the potential for clinical effectiveness of a subtraction processing system for mammograms in the comparative interpretation. We aimed to evaluate subgroup analysis on right and left subtraction-processed mammograms using VoxelMorph for registration. Breast density and thickness were used for subgroup analysis, which affected the depiction of the mammogram's mammary glands. We used normal mammograms with mediolateral oblique view divided into 1,000 cases for training, 100 cases for validation, and 500 cases for testing. The horizontally flipped left mammogram was aligned with the right mammogram using VoxelMorph. The 500 cases for testing were classified into four groups equally using the breast density and thickness determined from right mammograms. Based on the evaluation using the average sum of absolute difference (hereafter “SAD”) between the right mammogram and the transformed left mammogram as the objective index, it turned out that the highest density group had the lowest average of SAD (0.0482) and the thinnest compressed breast thickness group had the lowest average of SAD (0.0381). The results of this study showed that the accuracy of subtraction processing was high, especially in dense breasts. The high accuracy in dense breasts, where false-negative findings are common, suggests the potential for clinical effectiveness of the subtraction processing system for mammograms.