Regularization with optimal space-time priors

TL;DR

This paper introduces a novel variational regularization method for dynamic imaging, leveraging cylindrical shearlets to achieve sparse representations and improve reconstruction quality in dynamic tomography.

Contribution

It develops a new regularization framework using cylindrical shearlets, including theoretical analysis and convergence guarantees, specifically tailored for spatio-temporal data in dynamic tomography.

Findings

The method provides stable reconstructions under noise.

Theoretical convergence rates are established.

Numerical experiments confirm improved reconstruction quality.

Abstract

We propose a variational regularization approach based on a multiscale representation called cylindrical shearlets aimed at dynamic imaging problems, especially dynamic tomography. The intuitive idea of our approach is to integrate a sequence of separable static problems in the mismatch term of the cost function, while the regularization term handles the nonstationary target as a spatio-temporal object. This approach is motivated by the fact that cylindrical shearlets provide (nearly) optimally sparse approximations on an idealized class of functions modeling spatio-temportal data and the numerical observation that they provide highly sparse approximations even for more general spatio-temporal image sequences found in dynamic tomography applications. To formulate our regularization model, we introduce cylindrical shearlet smoothness spaces, which are instrumental for defining suitable embeddings in functional spaces. We prove that the proposed regularization strategy is well-defined, and the minimization problem has a unique solution (for $ p > 1$). Furthermore, we provide convergence rates (in terms of the symmetric Bregman distance) under deterministic and random noise conditions, within the context of statistical inverse learning. We numerically validate our theoretical results using both simulated and measured dynamic tomography data, showing that our approach leads to an efficient and robust reconstruction strategy.