PIViT: Large Deformation Image Registration with Pyramid-Iterative Vision Transformer

Large deformation image registration is a challenging task in medical image registration. Iterative registration and pyramid registration are two common CNN-based methods for the task. However, these methods usually consume more parameters and time. Additionally, the existing CNN-based registration methods mainly focus on local feature extraction, limiting their ability to capture the long-distance correlation between image pairs. In this paper, we propose a fast and accurate learning-based algorithm, Pyramid-Iterative Vision Transformer (PIViT), for 3D large deformation medical image registration. Our method constructs a novel pyramid iterative composite structure to solve large deformation problem by using low-scale iterative registration with a Swin Transformer-based long-distance correlation decoder. Furthermore, we exploit pyramid structure to supplement the detailed information of the deformation field by using high-scale feature maps. Comprehensive experimental results implemented on brain MRI and liver CT datasets show that the proposed method is superior to the existing registration methods in terms of registration accuracy, training time and parameters, especially of a significant advantage in running time. Our code is available at https://github.com/Torbjorn1997/PIViT.