Dynamic Multi-scale Feature Integration Network for unsupervised MR-CT synthesis.

Abstract

Unsupervised MR-CT synthesis presents a significant opportunity to reduce radiation exposure from CT scans and lower costs by eliminating the need for both MR and CT imaging. However, many existing unsupervised methods face limitations in capturing different anatomical structures due to their inability to model features with large receptive fields, and the receptive fields of different structures can vary. To address this challenge, we propose a novel Dynamic Multi-scale Feature Integration Network (DMFI-Net) tailored for unsupervised MR-CT synthesis. Our DMFI-Net dynamically adjusts its receptive field to extract multi-scale receptive field features, effectively capturing intricate anatomical details to enhance the synthesis performance. Specifically, we present a Global Context-enhanced Kernel Selection (GCKS) module, which intelligently modulates the receptive fields of convolutions for capturing fine-grained details essential to image transformation. By incorporating global cues, the module enriches multi-scale receptive features with comprehensive semantic information, which is crucial for synthesizing globally distributed target regions or organs. Additionally, a Scale Enhancement Module (SEM) is proposed to integrate features extracted with different scales, preserving richer spatial information. Furthermore, we present a scale-aware reconstruction branch to bolster the encoder's feature extraction capability and improve model generalization. This branch is capable of reconstructing downsampled input images that have undergone random masking, underscoring the model's robust feature extraction ability. Extensive experimental results on one private and two public MR-CT datasets demonstrate that our model significantly outperforms state-of-the-art MR-CT synthesis methods in both qualitative and quantitative evaluations. The implementation code will be released upon acceptance of this manuscript at https://github.com/taozh2017/DMFINet.