Analytic method based on identification of ellipse parameters for scanner calibration in cone-beam tomography

This paper is about calibration of cone-beam (CB) scanners for both x-ray c omputed tomography and single-photon emission computed tomography. Scanner calibration refers here to the estimation of a set of parameters which full y describe the geometry of data acquisition. Such parameters are needed for the tomographic reconstruction step. The discussion is limited to the usua l case where the cone vertex and planar detector move along a circular path relative to the object. It is also assumed that the detector does not have spatial distortions. We propose a new method which requires a small set of measurements of a simple calibration object consisting of two spherical ob jects, that can be considered as 'point' objects. This object traces two el lipses on the detector and from the parametric description of these ellipse s, the calibration geometry can be determined analytically using explicit f ormulae. The method is robust and easy to implement. However, it is not ful ly general as it is assumed that the detector is parallel to the rotation a xis of the scanner. Implementation details are given for an experimental x- ray CB scanner.