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

Abstract

This paper is about calibration of cone-beam (CB) scanners for both x-raycomputed tomography and single-photon emission computed tomography. Scannercalibration refers here to the estimation of a set of parameters which fullydescribe the geometry of data acquisition. Such parameters are needed for thetomographic reconstruction step. The discussion is limited to the usual casewhere the cone vertex and planar detector move along a circular path relativeto the object. It is also assumed that the detector does not have spatialdistortions. We propose a new method which requires a small set ofmeasurements of a simple calibration object consisting of two sphericalobjects, that can be considered as `point' objects. This object traces twoellipses on the detector and from the parametric description of theseellipses, the calibration geometry can be determined analytically usingexplicit formulae. The method is robust and easy to implement. However, it isnot fully general as it is assumed that the detector is parallel to therotation axis of the scanner. Implementation details are given for anexperimental x-ray CB scanner.