Performance evaluation of an image-based measurement method used to determine the geometric errors of cone-beam CT instruments

Computed Tomography (CT) has been used in an upward trend to inspect dimensional and geometric characteristics of manufactured parts. The complexity of the measurement chain, however, gives rise to many influence factors that affect the measurement accuracy. Some of these factors are under the control of the user, who needs to properly set some CT instrument parameters for a specific measurement task. Over other influence factors, the user may have some degree of control, such as the interaction of the x-rays with the physical matter, which produces image discrepancies. Finally, there are some influence factors over which the user may have no control at all, such as misalignments resulted from imperfections of the CT instrument hardware. In this regard, this paper describes the experimental evaluation of the geometric errors of a cone-beam CT instrument using an image-based method to map them. The experiments were performed under different test conditions, designed with the main purpose of understanding the behavior of the geometric errors in time and space, as well as assisting the appropriate actions to be taken for e.g. error correction by software. Special attention was given to the evaluation of the effectiveness of the measurement method itself to detect the geometric errors.