Gaussian sample model in in-line imaging

TL;DR

This paper explores how digital free-space propagation can enhance Shannon information in X-ray imaging, but questions whether the apparent gains reflect true resolution improvements or superficial high-frequency content.

Contribution

It demonstrates that simulated free-space propagation can increase formal information gain in X-ray imaging, highlighting the importance of evaluating image quality metrics.

Findings

Simulated free-space propagation yields higher formal information gain.

The increased information may be due to superficial high-frequency content.

Critical evaluation of image quality metrics is necessary.

Abstract

We investigate the gain in Shannon information that can be extracted from an X-ray image obtained after coherent free-space propagation of the transmitted beam and subsequent digital processing of the detected image. We show that simulated digital forward free-space propagation can produce a much higher formal information gain, both in projection imaging and in phase-contrast computed tomography, compared to conventional phase retrieval based on the Transport of Intensity equation. However, it appears that the extra information gained in the simulated free-space propagation may be due in part to superficial high-frequency content in the obtained images, rather than due to a genuine improvement of the spatial resolution. This points to the need to critically evaluate the performance of different types of image quality metrics and their relationship to the information content of the images.