Author:

Keywords:

X-ray computed tomography, magnification axis, calibration, scale error, dimensional metrology

Abstract:

For high measurement accuracy with X-ray computed tomography (CT), that requires no scale calibration afterwards, due to incorrect assessment of voxel size during a CT scan, object magnification needs to be precisely calculated in order to minimize scale error of the reconstructed volume. Magnification, which is given by the z-axis of the machine’s coordinate system, is defined by the ratio between the source-detector (SDD) and source-rotation axis distances (SRD). An inaccurate definition of either thereof distances leads to error in voxel size which by itself results in scale error of the reconstructed volume. A correct assessment of these distances is therefore of paramount importance. In this work, a new methodology to correctly assess SDD and SRD is presented. The procedure bases itself in the use of radiographs acquired along the magnification axis rather than whole 3D scans. The newly developed method provides an accurate and fast way of calibrating both distances, improving dimensional metrology and quality control by X-ray CT. Boundary conditions, that enable the new methodology to work, were studied, tested and validated with both simulation and real data sets. Preliminary results indicate that the proposed calibration methodology reduces length error deviations in the measurements of a calibrated test object