Improving Calibration and Out-of-Distribution Detection in Deep Models for Medical Image Segmentation

Convolutional neural networks (CNNs) have proved to be powerful medical image segmentation models. In this study, we address some of the main unresolved issues regarding these models. Specifically, training of these models on small medical image datasets is still challenging, with many studies promoting techniques such as transfer learning. Moreover, these models are infamous for producing overconfident predictions and for failing silently when presented with out-of-distribution (OOD) test data. In this article, for improving prediction calibration we advocate for multitask learning, i.e., training a single model on several different datasets, spanning different organs of interest and different imaging modalities. We show that multitask learning can significantly improve model confidence calibration. For OOD detection, we propose a novel method based on spectral analysis of CNN feature maps. We show that different datasets, representing different imaging modalities and/or different organs of interest, have distinct spectral signatures, which can be used to identify whether or not a test image is similar to the images used for training. We show that our proposed method is more accurate than several competing methods, including methods based on prediction uncertainty and image classification.