Measurement accuracy in X-ray computed tomography metrology: Toward a systematic analysis of interference effects in tomographic imaging

• Step-by-step analysis of interaction effects resulting in systematic and random errors.
• Investigation of filtering effects (MTF) and its role in CT metrology.
• Surface characterization using CT data.
• The role of threshold determination strategies.

In this paper an investigation of interference effects leading to limitations of metrological performance of X-ray computed tomography (CT) used as a coordinate measuring technique is presented. Using reconstruction data, image quality metrics, and calculations of artifact formation, a deeper understanding and explanation of the physical and technical limitations of CT used in dimensional metrology is given. This is demonstrated in a case study using a simple hollow cylinder made of steel as a test object and calibration measurements from a tactile coordinate measuring machine (CMM). Two different threshold determination strategies for surface computation are applied. Within the study it is also shown that CT image properties, threshold determination strategies, and systematic and random measurement errors must have a definite correlation. As a conclusion it is recommended to focus more strongly on the correlation of local CT image quality and data evaluation operations in order to reduce systematic errors in surface computation and to increase repeatability of dimensional CT measurements.