Spiral X-ray computed tomography of long wooden samples: Influence of pitch and geometric calibration on reconstruction quality

Abstract

X-ray computed tomography (XCT) is widely used for three-dimensional characterization of material microstructure. In wood science, XCT increasingly serves as a tool for quantitative analysis of annual rings, porosity, and other structural features requiring high reconstruction fidelity, and geometrical consistency. Spiral XCT enables scanning of samples exceeding the detector field of view in height by combining continuous sample rotation with synchronized axial translation during acquisition. This work investigates the influence of mechanical alignment, motion synchronization, geometric calibration, and spiral pitch on the reconstruction quality of long wooden specimens.
Reconstruction fidelity depends on the agreement between the assumed spiral trajectory and the actual coupled rotational and axial motion during acquisition. Misalignment of the rotation axis with respect to the source–detector geometry, together with inaccuracies in axial translation or magnification calibration, may introduce geometric distortions, blurring, and loss of structural fidelity. The effect of spiral pitch, defined as the axial displacement per full rotation, was experimentally investigated by performing scans with different predefined pitch values. Increasing the spiral pitch reduced axial sampling density and projection overlap, resulting in progressively stronger interpolation artefacts and degradation of reconstruction quality.
The study further demonstrates the sensitivity of cone-beam spiral XCT reconstruction to accurate magnification calibration, as even small scaling errors lead to cumulative misregistration along the reconstructed volume. Reliable spiral XCT of long wooden samples therefore requires accurate geometric calibration, stable synchronization of the rotational and axial motions, and an appropriately selected spiral pitch.