A PyTorch implementation of the gradient consistency loss function, based on:

Penney, G.P., et al.: A comparison of similarity measures for use in 2-D-3-D medical image registration. IEEE transactions on medical imaging 17(4) (1998) 586–595

and

Hiasa Y, Otake Y, Takao M, et al. Cross-modality image synthesis from unpaired data using CycleGAN. Springer; 2018:31-41.