Judging X-ray Source Performance in CT Applications

The performance of the X-ray source plays a critical role in the quality of a computed tomography (CT) imaging system. In the pursuit of standardizing source performance evaluation in CT, this work identifies and develops unique methods and metrics designed to target X-ray source performance independently of confounding system effects—an important consideration for high-resolution sources that may outperform other system components, such as rotation stages. These methods and metrics are validated through simulations and applied to assess and compare two X-ray sources. To quantify achievable resolution, a copper wire with a diameter of 120 μm is scanned without rotation to reduce interference from other system components. By analysing the extent of edge blurring in the reconstruction, the in-plane modulation transfer function (MTF) is obtained. Additionally, two signal-to-noise ratio (SNR) metrics are introduced, combining MTF and noise power spectrum (NPS) data to estimate the smallest detectable feature size within an in-plane slice of the reconstructed volume. Simulation results demonstrate a strong correlation between one of these metrics and human visual assessment. Experimental results show that both sources can achieve sub-micron resolution, with one consistently outperforming the other in this regard. Although the proposed SNR metrics have not yet been experimentally validated or applied, they show potential for guiding source selection by identifying performance across a wide range of imaging conditions and purposes. By providing a standardized and quantitative assessment framework, this work enables more informed selection and optimization of X-ray sources—both for users and manufacturers—ultimately improving CT imaging performance.