Super-resolution reconstruction of single anisotropic 3D MR images using residual convolutional neural network

Abstract

High-resolution (HR) magnetic resonance (MR) imaging is an important diagnostic technique in clinical practice. However, hardware limitations and time constraints often result in the acquisition of anisotropic MR images. It is highly desirable but very challenging to enhance image spatial resolution in medical image analysis for disease diagnosis. Recently, studies have shown that deep convolutional neural networks (CNN) can significantly boost the performance of MR image super-resolution (SR) reconstruction. In this paper, we present a novel CNN-based anisotropic MR image reconstruction method based on residual learning with long and short skip connections. The proposed network can effectively alleviate the vanishing gradient problem of deep networks and learn to restore high-frequency details of MR images. To reduce computational complexity and memory usage, the proposed network utilizes cross-plane self-similarity of 3D T1-weighted (T1w) MR images. Based on experiments on simulated and clinical brain MR images, we demonstrate that the proposed network can significantly improve the spatial resolution of anisotropic MR images with high computational efficiency. The network trained on T1w MR images is able to effectively reconstruct both SR T1w and T2-weighted (T2w) images, exploiting image features for multi-modality reconstruction. Moreover, the experimental results show that the proposed method outperforms classical interpolation methods, non-local means method (NLM), and sparse coding based algorithm in terms of peak signal-to-noise-ratio, structural similarity image index, intensity profile, and small structures. The proposed method can be efficiently applied to SR reconstruction of thick-slice MR images in the out-of-plane views for radiological assessment and post-acquisition processing.