Equivariance2Inverse: A Practical Self-Supervised CT Reconstruction Method Benchmarked on Real, Limited-Angle, and Blurred Data

TL;DR

This paper introduces Equivariance2Inverse, a self-supervised CT reconstruction method that is robust to scintillator blurring and limited-angle data, benchmarked on real and synthetic datasets.

Contribution

It combines concepts from Robust Equivariant Imaging and Sparse2Inverse to improve robustness in self-supervised CT reconstruction, especially under real-world conditions.

Findings

Methods assuming pixel-wise independent noise perform poorly with scintillator blurring.

Rotational invariance of object distribution helps reduce artifacts in limited-angle reconstructions.

Equivariance2Inverse outperforms existing methods on real-world and synthetic datasets.

Abstract

Deep learning has shown impressive results in reducing noise and artifacts in X-ray computed tomography (CT) reconstruction. Self-supervised CT reconstruction methods are especially appealing for real-world applications because they require no ground truth training examples. However, these methods involve a simplified X-ray physics model during training, which may make inaccurate assumptions, for example, about scintillator blurring, the scanning geometry, or the distribution of the noise. As a result, they can be less robust to real-world imaging circumstances. In this paper, we review the model assumptions of six recent self-supervised CT reconstruction methods. Based on this, we combined concepts of the Robust Equivariant Imaging and Sparse2Inverse methods in a new self-supervised CT reconstruction method called Equivariance2Inverse that is robust to scintillator blurring and limited-angle data. We benchmarked Equivariance2Inverse and the existing methods on the real-world 2DeteCT dataset and on synthetic data with and without scintillator blurring and a limited-angle scanning geometry. The results of our benchmark show that methods that assume that the noise is pixel-wise independent do not perform well on data with scintillator blurring. Moreover, they show that when the distribution of objects is rotationally invariant, this invariance can be used to reduce artifacts in limited-angle reconstructions.