Reconstructing invariances of CT image denoising networks using invertible neural networks

Elias Eulig, Björn Ommer, Marc Kachelriess

Abstract: Long lasting efforts have been made to reduce radiation dose and thus the potential radiation risk to the patient for CT acquisitions without severe deterioration of image quality. To this end, different reconstruction and noise reduction algorithms have been developed, many of which are based on iterative reconstruction techniques, incorporating prior knowledge in the image domain. Recently, deep learning-based methods have shown impressive performance, outperforming many of the previously proposed CT denoising approaches both visually and quantitatively. However, with most neural networks being black boxes they remain notoriously difficult to interpret and concerns about the robustness and safety of such denoising methods have been raised. In this work we want to lay the fundamentals for a post-hoc interpretation of existing CT denoising networks by reconstructing their invariances.