Rethinking Multi-Contrast MRI Super-Resolution: Rectangle-Window Cross-Attention Transformer and Arbitrary-Scale Upsampling

Recently, several methods have explored the potential of multi-contrast magnetic resonance imaging (MRI) super-resolution (SR) and obtain results superior to single-contrast SR methods. However, existing approaches still have two shortcomings: (1) They can only address fixed integer upsampling scales, such as 2×, 3×, and 4×, which require training and storing the corresponding model separately for each upsampling scale in clinic. (2) They lack direct interaction among different windows as they adopt the square window (e.g., 8×8) transformer network architecture, which results in inadequate modelling of longer-range dependencies. Moreover, the relationship between reference images and target images is not fully mined. To address these issues, we develop a novel network for multi-contrast MRI arbitrary-scale SR, dubbed as McASSR. Specifically, we design a rectangle-window cross-attention transformer to establish longer-range dependencies in MR images without increasing computational complexity and fully use reference information. Besides, we propose the reference-aware implicit attention as an upsampling module, achieving arbitrary-scale super-resolution via implicit neural representation, further fusing supplementary information of the reference image. Extensive and comprehensive experiments on both public and clinical datasets show that our McASSR yields superior performance over SOTA methods, demonstrating its great potential to be applied in clinical practice. Code will be available at https://github.com/GuangYuanKK/McASSR.