Measurement of sample stage error motions in cone-beam X-ray computed tomography instruments by minimization of reprojection errors

Abstract

Reconstruction algorithms in X-ray computed tomography assume a particular geometrical alignment of the instrument components: X-ray source, sample stage, and detector. Motion errors and misalignments in the actual instrument contribute to errors in the reconstruction. In previous work, we presented an object-based procedure to measure the instrument geometrical alignment at a single position of the sample rotation stage along its linear translation axes. Here, we present an object-based method to determine error motions of the sample stage manipulator in cone-beam X-ray computed tomography instruments. The proposed method is applied with a reference object comprising calibrated sphere center positions to determine error motions of the stage as it is translated along the nominal magnification axis from the X-ray source towards the detector. Results agree with previous reference measurements performed using laser interferometers and electronic levels, albeit at a loss of sensitivity at lower imaging magnifications when the projected object occupies progressively smaller areas of the detector image. To compensate for the lower sensitivity, we propose a solution based on having a limited set of reference objects of various sizes to be used along the entire magnification range of the sample stage.