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

Abstract

Long synonymous with medical imaging, x-ray computed tomography (CT) is proving its worth in industrial applications such as material characterization, defect analysis, and dimensional inspection e.g. of manufactured components. Since 2005, when the first purpose-built industrial x-ray CT instrument was made commercially available, there have been significant efforts to understand just how reliable x-ray CT dimensional measurements are. In metrology, the ultimate measure of confidence is metrological traceability—a clearly-defined but often not well-understood property of a measurement result. Metrological traceability places measurements on a comparable scale and provides a quantitative indication of measurement quality in the form of an uncertainty statement. From a practical perspective, achieving traceability can be divided into two tasks: (a) ensuring traceability of the scale with which the measurements are made and (b) assessing uncertainty in the resulting quantity assigned to the measurand. Based on this breakdown of the traceability problem, we provide a high-level discussion about traceability of x-ray CT dimensional measurements, review relevant work in understanding x-ray CT measurement uncertainty, and propose a framework for model-based uncertainty assessment per the Monte Carlo Simulation method and instrument scale calibration as a unified approach to traceability.