CRF-EfficientUNet: An Improved UNet Framework for Polyp Segmentation in Colonoscopy Images With Combined Asymmetric Loss Function and CRF-RNN Layer

Colonoscopy is considered the gold-standard investigation for colorectal cancer screening. However, the polyps miss rate in clinical practice is relatively high due to different factors. This presents an opportunity to use AI models to automatically detect and segment polyps, supporting clinicians to reduce the number of polyps missed. Inspired by the success of UNets, a popular strategy for solving medical image segmentation tasks, this article proposes a novel framework for polyp segmentation called CRF-EfficientUNet, which enhances UNet using the EfficientNet encoder, a combined asymmetric loss function, and Conditional Random Field as a Recurrent Neural Network (CRF-RNN) layer on top. A novel loss function that combines pixel-wise cross-entropy loss and asymmetric similarity loss to solve the unbalanced imaging data problem is proposed. Training the proposed network with this loss function can achieve a considerably higher Dice score and better polyp segmentation prediction. In addition, we add the CRF-RNN layer to the proposed framework to improve the quality of semantic segmentation. Experimental results on popular benchmark datasets show that CRF-EfficientUNet achieves state-of-the-art accuracy compared to existing methods. The results of the experiments, which are performed on the CVC-ClinicDB dataset for training and testing, are 95.55% Dice and 92.23% IoU. While the experimental results on cross-dataset using Kvasir-SEG as the training set, CVC-ColonDB as the test set are 85.59% Dice and 76.19% IoU. These results indicate that the proposed method has high generalization capability and learning ability, and it can be a compelling choice for practical applications with considerable data variations. The source code is available at: https://github.com/lethithuhong1302/CRF-EfficientUNet