Convolutional neural network‐based model observer for signal known statistically task in breast tomosynthesis images

Abstract

AbstractBackgroundSince human observer studies are resource‐intensive, mathematical model observers are frequently used to assess task‐based image quality. The most common implementation of these model observers assume that the signal information is exactly known. However, these tasks cannot thoroughly represent situations where the signal information is not exactly known in terms of size and shape.PurposeConsidering the limitations of the tasks for which signal information is exactly known, we proposed a convolutional neural network (CNN)‐based model observer for signal known statistically (SKS) and background known statistically (BKS) detection tasks in breast tomosynthesis images.MethodsA wide parameter search was conducted from six different acquisition angles (i.e., 10°, 20°, 30°, 40°, 50°, and 60°) within the same dose level (i.e., 2.3 mGy) under two separate acquisition schemes: (1) constant total number of projections, and (2) constant angular separation between projections. Two different types of signals: spherical (i.e., SKE tasks) and spiculated (i.e., SKS tasks) were used. The detection performance of the CNN‐based model observer was compared with that of the Hotelling observer (HO) instead of the IO. Pixel‐wise gradient‐weighted class activation mapping (pGrad‐CAM) map was extracted from each reconstructed tomosynthesis image to provide an intuitive understanding of the trained CNN‐based model observer.ResultsThe CNN‐based model observer achieved a higher detection performance compared to that of the HO for all tasks. Moreover, the improvement in its detection performance was greater for SKS tasks compared to that for SKE tasks. These results demonstrated that the addition of nonlinearity improved the detection performance owing to the variation of the background and signal. Interestingly, the pGrad‐CAM results effectively localized the class‐specific discriminative region, further supporting the quantitative evaluation results of the CNN‐based model observer. In addition, we verified that the CNN‐based model observer required fewer images to achieve the detection performance of the HO.ConclusionsIn this work, we proposed a CNN‐based model observer for SKS and BKS detection tasks in breast tomosynthesis images. Throughout the study, we demonstrated that the detection performance of the proposed CNN‐based model observer was superior to that of the HO.