Double U-Net CycleGAN for 3D MR to CT image synthesis.

PURPOSE

CycleGAN and its variants are widely used in medical image synthesis, which can use unpaired data for medical image synthesis. The most commonly used method is to use a Generative Adversarial Network (GAN) model to process 2D slices and thereafter concatenate all of these slices to 3D medical images. Nevertheless, these methods always bring about spatial inconsistencies in contiguous slices. We offer a new model based on the CycleGAN to work out this problem, which can achieve high-quality conversion from magnetic resonance (MR) to computed tomography (CT) images.

METHODS

To achieve spatial consistencies of 3D medical images and avoid the memory-heavy 3D convolutions, we reorganized the adjacent 3 slices into a 2.5D slice as the input image. Further, we propose a U-Net discriminator network to improve accuracy, which can perceive input objects locally and globally. Then, the model uses Content-Aware ReAssembly of Features (CARAFE) upsampling, which has a large field of view and content awareness takes the place of using a settled kernel for all samples.

RESULTS

The mean absolute error (MAE), peak-signal-to-noise ratio (PSNR), and structural similarity index measure (SSIM) for double U-Net CycleGAN generated 3D image synthesis are 74.56±10.02, 27.12±0.71 and 0.84±0.03, respectively. Our method achieves preferable results than state-of-the-art methods.

CONCLUSION

The experiment results indicate our method can realize the conversion of MR to CT images using ill-sorted pair data, and achieves preferable results than state-of-the-art methods. Compared with 3D CycleGAN, it can synthesize better 3D CT images with less computation and memory.