Voxel Size Calibration for High-resolution CT

Abstract

In cone-beam X-ray computed tomography (CT), distances between the source, object, and detector influence the visual fidelity and voxel size of a reconstructed volume. Calibration using reference objects is an appropriate tool for preventing errors in the estimates of these distances. There is, however, a lack of such objects for high-resolution systems with a small field of view (FoV). In this work, we propose a method to measure the distances mentioned above, improving the determination of voxel size. We use a custom reference object suitable for a FoV of around one millimeter. Many approaches have been developed for this calibration task and discussed in the literature, but none apply to CT scanners with a small FoV and a cone-beam magnification close to one. The proposed method thus aims to provide a calibration procedure for such devices. A Rigaku Nano3DX CT scanner has been calibrated through this method and used for practical validation of the method's accuracy. Results have shown that this approach allows for accurate calibration, which leads to improvements in reconstruction quality and accuracy of voxel size determination.

Charting the course towards dimensional measurement traceability by x-ray computed tomography

“…Zemek et al [85] propose determining SRD and SDD for small measurement volumes from projections of a reference object, comprising two spheres with calibrated centerto-center distance, acquired at multiple SDDs. The parameters of a line fit to the observed projected center-to-center distances as a function of detector displacement is used to determine SRD and SDD.…”