3D Axial-Attention for Lung Nodule Classification

Purpose: In recent years, Non-Local based methods have been successfully applied to lung nodule classification. However, these methods offer 2D attention or a limited 3D attention to low-resolution feature maps. Moreover, they still depend on a convenient local filter such as convolution as full 3D attention is expensive to compute and requires a big dataset, which might not be available. Methods: We propose to use 3D Axial-Attention, which requires a fraction of the computing power of a regular Non-Local network. Additionally, we solve the position invariant problem of the Non-Local network by proposing adding 3D positional encoding to shared embeddings. Results: We validated the proposed method on the LIDC-IDRI dataset by following a rigorous experimental setup using only nodules annotated by at least three radiologists. Our results show that the 3D Axial-Attention model achieves state-of-the-art performance on all evaluation metrics including AUC and Accuracy. Conclusions: The proposed model provides full 3D attention effectively, which can be used in all layers without the need for local filters. The experimental results show the importance of full 3D attention for classifying lung nodules.