Resolve slow mixing in the phase posterior under angular undersampling

Resolve the unresolved slow mixing of the phase posterior produced by angular undersampling in Bayesian multi-contrast CT, including under combined angular and phase-step undersampling.

Background

Posterior sampling with NUTS showed substantially poorer convergence and effective sample sizes for the phase channel under sparse-angle and combined undersampling than for attenuation and dark-field channels. The joint total-variation prior improved some diagnostics but did not eliminate the problem, especially under combined undersampling. Because slow mixing affects the reliability of posterior uncertainty summaries, improving or validating inference for this phase posterior remains an unresolved methodological issue.

References

Slow phase mixing persists, however, and under combined undersampling the phase $99$th percentile of $\hat R$ remains approximately $1.18$ for both priors.

— Bayesian Joint Reconstruction and Uncertainty Quantification for Limited-Data Multi-Contrast X-Ray CT  (2610.21406 - Yazdanian et al., 15 Oct 2026) in Section 5, Discussion, paragraph beginning “Sampling cost and convergence limit quantitative UQ”