Massimiliano Ferrucci

Towards geometrical calibration of x-ray computed tomography systems - A review

Industrial x-ray computed tomography (XCT) is seen as a potentially effective tool for the industrial inspection of complex parts. In particular, XCT is an attractive solution for the measurement of internal geometries, which are inaccessible by conventional coordinate measuring systems. While the technology is available and the benefits are recognized, methods to establish the measurement assurance of XCT systems are lacking. More specifically, the assessment of measurement uncertainty and the subsequent establishment of measurement traceability is a largely unknown process. This paper is a review of research that contributes to the development of a geometrical calibration procedure for XCT systems. A brief introduction to the geometry of cone-beam tomography systems is given, after which the geometrical influence factors are outlined. Mathematical measurement models play a significant role in understanding how geometrical offsets and misalignments contribute to error in measurements; therefore, the application of mathematical models in simulating geometrical errors is discussed and the corresponding literature is presented. Then, the various methods that have been developed to measure certain geometrical errors are reviewed. The findings from this review are discussed and suggestions are provided for future work towards the development of a comprehensive and practical geometrical calibration procedure.

Towards Traceability of CT Dimensional Measurements

There can be no discussion on the accuracy of a measurement result without its proven traceability. Traceability is a fundamental property of a measurement that ensures the measured quantity is comparable to the international definition of the unit with which it is expressed. The task of achieving traceability requires a thorough understanding of the measurement procedure and, in particular, the operating principle of the measuring instrument. In this chapter, the concept of traceability is introduced as it applies to dimensional measurements. The role of instrument calibration in establishing traceability of its measurements is presented for earlier coordinate measuring systems, to serve as a precursor to the discussion on how CT instruments can be calibrated. Finally, methods for assessing task-specific measurement uncertainty are discussed.