Brain MRI Super-Resolution Using 3D Dilated Convolutional Encoder–Decoder Network

The spatial resolution of magnetic resonance images (MRI) is limited by the hardware capacity, sampling time, signal-to-noise ratio (SNR), and patient comfort. Recently, deep convolutional neural networks (CNN) have achieved impressive success in MRI super-resolution (SR) reconstruction. Increasing network depth or width can enlarge the receptive field to improve SR accuracy, however, it is impractical for MRI reconstruction in clinical applications because of high computational loads. To address this issue, we propose a novel dilated convolutional encoder-decoder (DCED) network to improve the resolution of MRI. We exploit three-dimensional (3D) dilated convolutions as encoders to extract high-frequency features. The dilated encoders capture wider contextual information by exponentially enlarging the receptive field, without introducing additional parameters or layers. Then we decode the features using deconvolution operations to alleviate gridding artifacts and restore fine details. To improve information flow, the encoders and decoders are aggregated into symmetrically connected blocks. The output of each block is passed to the final convolution layer, which facilitates to extract hierarchical features. In addition, we also exploit a geometric self-ensemble 3D wavelet fusion method to improve the potential performance of MRI SR. Experimental results on four public available brain datasets show that our proposed method outperforms NLM (non-local means), LRTV (low-rank and total variation) and current CNN-based SR methods, which demonstrates that our method achieves a new state-of-the-art performance in MRI SR task.