# Comparing Image Quality in Phase Contrast sub$\mu$ X-Ray Tomography -- A Round-Robin Study

## TL;DR

This study develops a comprehensive method to evaluate and compare image quality in sub-micrometer CT scans using a phantom, modeling SNR spectra and transfer functions to assess detection effectiveness across different scanners.

## Contribution

Introduces a novel detection effectiveness (DE) metric that normalizes volume SNR with respect to the object’s power spectrum, enabling comparison of scan quality across various subμ CT systems.

## Key findings

- Volume SNR can be normalized to reveal detection effectiveness.
- DE allows comparison of source-based and detector-based CT scanners.
- The method highlights the influence of technical and operator choices on scan quality.

## Abstract

How to evaluate and compare image quality from different sub-micrometer (sub$\mu$) CT scans? A simple test phantom made of polymer microbeads is used for recording projection images as well as 13 CT scans in a number of commercial and non-commercial scanners. From the resulting CT images, signal and noise power spectra are modeled for estimating volume signal-to-noise ratios (3D SNR spectra). Using the same CT images, a time- and shape-independent transfer function (MTF) is computed for each scan, including phase contrast effects and image blur ($\mathrm{MTF_{blur}}$). The SNR spectra and MTF of the CT scans are compared to 2D SNR spectra of the projection images. In contrary to 2D SNR, volume SNR can be normalized with respect to the object's power spectrum, yielding detection effectiveness (DE) a new measure which reveals how technical differences as well as operator-choices strongly influence scan quality for a given measurement time. Using DE, both source-based and detector-based sub$\mu$ CT scanners can be studied and their scan quality can be compared. Future application of this work requires a particular scan acquisition scheme which will allow for measuring 3D signal-to-noise ratios, making the model fit for 3D noise power spectra obsolete.