Weakly Supervised Captioning of Ultrasound Images
Alsharid M., Sharma H., Drukker L., Papageorgiou AT., Noble JA.
Medical image captioning models generate text to describe the semantic contents of an image, aiding the non-experts in understanding and interpretation. We propose a weakly-supervised approach to improve the performance of image captioning models on small image-text datasets by leveraging a large anatomically-labelled image classification dataset. Our method generates pseudo-captions (weak labels) for caption-less but anatomically-labelled (class-labelled) images using an encoder-decoder sequence-to-sequence model. The augmented dataset is used to train an image-captioning model in a weakly supervised learning manner. For fetal ultrasound, we demonstrate that the proposed augmentation approach outperforms the baseline on semantics and syntax-based metrics, with nearly twice as much improvement in value on BLEU-1 and ROUGE-L. Moreover, we observe that superior models are trained with the proposed data augmentation, when compared with the existing regularization techniques. This work allows seamless automatic annotation of images that lack human-prepared descriptive captions for training image-captioning models. Using pseudo-captions in the training data is particularly useful for medical image captioning when significant time and effort of medical experts is required to obtain real image captions.