MRLN: Multi-Task Relational Learning Network for MRI Vertebral Localization, Identification, and Segmentation.

Magnetic resonance imaging (MRI) vertebral localization, identification, and segmentation are important steps in the automatic analysis of spines. Due to the similar appearances of vertebrae, the accurate segmentation, localization, and identification of vertebrae remain challenging. Previous methods solved the three tasks independently, ignoring the intrinsic correlation among them. In this paper, we propose a multi-task relational learning network (MRLN) that utilizes both the relationships between vertebrae and the relevance of the three tasks. A dilation convolution group is used to expand the receptive field, and LSTM(Long Short-Term Memory) to learn the prior knowledge of the order relationship between the vertebral bodies. We introduce a co-attention module to learn the correlation information, localization-guided segmentation attention(LGSA) and segmentation-guided localization attention(SGLA), in the decoder stage of segmentation and localization tasks. Learning two tasks simultaneously as well as the correlation between tasks can not only avoid the overfitting of a single task but also correct each other. To avoids the cumbersome weight adjustment for different tasks loss functions, we formulated a novel XOR loss that provides a direct evaluation criterion for the localization relationship of the semantic location regression and semantic segmentation. This method was evaluated on a dataset which includes multiple MRI modalities (T1 and T2), various fields of view. Experimental results demonstrate that both of the co-attention and XOR loss work outperforms the most recent state of art.