Pseudo‐CT generation from multi‐parametric MRI using a novel multi‐channel multi‐path conditional generative adversarial network for nasopharyngeal carcinoma patients

Purpose To develop and evaluate a novel method for pseudo‐CT generation from multi‐parametric MR images using multi‐channel multi‐path generative adversarial network (MCMP‐GAN). Methods Pre‐ and post‐contrast T1‐weighted (T1‐w), T2‐weighted (T2‐w) MRI, and treatment planning CT images of 32 nasopharyngeal carcinoma (NPC) patients were employed to train a pixel‐to‐pixel MCMP‐GAN. The network was developed based on a 5‐level Residual U‐Net (ResU‐Net) with the channel‐based independent feature extraction network to generate pseudo‐CT images from multi‐parametric MR images. The discriminator with five convolutional layers was added to distinguish between the real CT and pseudo‐CT images, improving the nonlinearity and prediction accuracy of the model. Eightfold cross validation was implemented to validate the proposed MCMP‐GAN. The pseudo‐CT images were evaluated against the corresponding planning CT images based on mean absolute error (MAE), peak signal‐to‐noise ratio (PSNR), Dice similarity coefficient (DSC), and Structural similarity index (SSIM). Similar comparisons were also performed against the multi‐channel single‐path GAN (MCSP‐GAN), the single‐channel single‐path GAN (SCSP‐GAN). Results It took approximately 20 h to train the MCMP‐GAN model on a Quadro P6000, and less than 10 s to generate all pseudo‐CT images for the subjects in the test set. The average head MAE between pseudo‐CT and planning CT was 75.7 ± 14.6 Hounsfield Units (HU) for MCMP‐GAN, significantly ( P ‐values < 0.05) lower than that for MCSP‐GAN (79.2 ± 13.0 HU) and SCSP‐GAN (85.8 ± 14.3 HU). For bone only, the MCMP‐GAN yielded a smaller mean MAE (194.6 ± 38.9 HU) than MCSP‐GAN (203.7 ± 33.1 HU), SCSP‐GAN (227.0 ± 36.7 HU). The average PSNR of MCMP‐GAN (29.1 ± 1.6) was found to be higher than that of MCSP‐GAN (28.8 ± 1.2) and SCSP‐GAN (28.2 ± 1.3). In terms of metrics for image similarity, MCMP‐GAN achieved the highest SSIM (0.92 ± 0.02) but did not show significantly improved bone DSC results in comparison with MCSP‐GAN. Conclusions We developed a novel multi‐channel GAN approach for generating pseudo‐CT from multi‐parametric MR images. Our preliminary results in NPC patients showed that the MCMP‐GAN method performed apparently superior to the U‐Net‐GAN and SCSP‐GAN, and slightly better than MCSP‐GAN.