Learning a Loss Function for Segmentation: A Feasibility Study

When training neural networks for segmentation, the Dice loss is typically used. Alternative loss functions could help the networks achieve results with higher user acceptance and lower correction effort, but they cannot be used directly if they are not differentiable. As a solution, we propose to train a regression network to approximate the loss function and combine it with a U-Net to compute the loss during segmentation training. As an example, we introduce the contour Dice coefficient (CDC) that estimates the fraction of contour length that needs correction. Applied to CT bladder segmentation, we show that a weighted combination of Dice and CDC loss improves segmentations compared to using only Dice loss, with regard to both CDC and other metrics.