Mutual information neural estimation in CNN-based end-to-end medical image registration

Image registration is one of the most underlined processes in medical image analysis. Recently, convolutional neural networks (CNNs) have shown significant potential in both affine and deformable registration. However, the lack of voxel-wise ground truth challenges the training of an accurate CNN-based registration. In this work, we implement a CNN-based mutual information neural estimator for image registration that evaluates the registration outputs in an unsupervised manner. Based on the estimator, we propose an end-to-end registration framework, denoted as MIRegNet, to realize one-shot affine and deformable registration. Furthermore, we propose a weakly supervised network combining mutual information with the Dice similarity coefficients (DSC) loss. We employed a dataset consisting of 190 pairs of 3D pulmonary CT images for validation. Results showed that the MIRegNet obtained an average Dice score of 0.960 for registering the pulmonary images, and the Dice score was further improved to 0.963 when the DSC was included for a weakly supervised learning of image registration.