Morphological Simplification of Brain MR Images by Deep Learning for Facilitating Deformable Registration

Brain MR image registration is challenging due to the large inter-subject anatomical variation. Especially, the highly convoluted brain cortex makes it difficult to accurately align the corresponding structures of the underlying images. In this paper, we propose a novel deep learning strategy to simplify the image registration task. Specifically, we train a morphological simplification network (MS-Net), which can generate a simplified image with fewer anatomical details given a complex input image. With this trained MS-Net, we can reduce the complexity of both the fixed and the moving images and iteratively derive their respective trajectories of gradually simplified images. The generated images at the ends of the two trajectories are so simple that they are very similar in appearance and morphology and thus easy to register. In this way, these two trajectories can act as a bridge to link the fixed and the moving images and guide their registration. Our experiments show that the proposed method can achieve more accurate registration results than state-of-the-art methods. Moreover, the proposed method can be generalized to the unseen dataset without the need for re-training or domain adaptation.