Resolution-invariant measurements of small objects in polychromatic CT data

Richard A. Ketcham

doi:10.1117/12.2532082

10 September 2019 Resolution-invariant measurements of small objects in polychromatic CT data

Richard A. Ketcham

Proceedings Volume 11113, Developments in X-Ray Tomography XII; 111130B (2019) https://doi.org/10.1117/12.2532082
Event: SPIE Optical Engineering + Applications, 2019, San Diego, California, United States

Abstract

Features such as particles, pores, or cracks are challenging to measure accurately in CT data when they are small relative to the data resolution, characterized as a point-spread function (PSF). These challenges are particularly acute when paired with segmentation, as the PSF distributes some of the signal from a voxel among neighboring ones; effectively dispersing some of the signal from a given object to a region outside of it. Any feature of interest with one or more dimensions on the order of the PSF will be impacted by this effect, and measurements based on global thresholds necessarily fail. Measurements of the same features should be consistent across different instruments and data resolutions. The PVB (partial volume and blurring) method successfully compensates by quantifying features that are small in all three dimensions based on their attenuation anomaly. By calibrating the CT number of the phase of interest (in this case, gold) it is possible to accurately measure particles down to <6 voxels in data acquired on two instruments, 14 years apart, despite severe artifacts. Altogether, the PVB method is accurate, reproducible, resolution-invariant, and objective; it is also notable for its favorable error structure. The principal challenge is the need for representative effective CT numbers, which reflect not only the features of interest themselves, but also the X-ray spectrum, the size, shape and composition of the enclosing sample, and processing details such as beam-hardening correction. Empirical calibration is the most effective approach.

Conference Presentation

Citation Download Citation

Richard A. Ketcham "Resolution-invariant measurements of small objects in polychromatic CT data", Proc. SPIE 11113, Developments in X-Ray Tomography XII, 111130B (10 September 2019); https://doi.org/10.1117/12.2532082

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