New reconstruction algorithm for digital breast tomosynthesis: better image quality for humans and computers

Background: The image quality of digital breast tomosynthesis (DBT) volumes depends greatly on the reconstruction algorithm. Purpose: To compare two DBT reconstruction algorithms used by the Siemens Mammomat Inspiration system, filtered back projection (FBP), and FBP with iterative optimizations (EMPIRE), using qualitative analysis by human readers and detection performance of machine learning algorithms. Material and Methods: Visual grading analysis was performed by four readers specialized in breast imaging who scored 100 cases reconstructed with both algorithms (70 lesions). Scoring (5-point scale: 1=poor to 5=excellent quality) was performed on presence of noise and artifacts, visualization of skin-line and Cooper's ligaments, contrast, and image quality, and, when present, lesion visibility. In parallel, a three-dimensional deep-learning convolutional neural network (3D-CNN) was trained (n=259 patients, 51 positives with BI-RADS 3, 4, or 5 calcifications) and tested (n=46 patients, nine positives), separately with FBP and EMPIRE volumes, to discriminate between samples with and without calcifications. The partial area under the receiver operating characteristic curve (pAUC) of each 3D-CNN was used for comparison. Results: EMPIRE reconstructions showed better contrast (3.23 vs. 3.10, P=0.010), image quality (3.22 vs. 3.03, P<0.001), visibility of calcifications (3.53 vs. 3.37, P=0.053, significant for one reader), and fewer artifacts (3.26 vs. 2.97, P<0.001). The 3D-CNN-EMPIRE had better performance than 3D-CNN-FBP (pAUC-EMPIRE=0.880 vs. pAUC-FBP=0.857; P<0.001). Conclusion: The new algorithm provides DBT volumes with better contrast and image quality, fewer artifacts, and improved visibility of calcifications for human observers, as well as improved detection performance with deep-learning algorithms.