Virtual alignment of x-ray cone-beam tomography system using two calibration aperture measurements

Abstract

In cone-beam tomography, relatively small misalignment of the imaging system is geometrically magnified and may cause severe distortion of the reconstructed image. We describe a method for align- ment of a cone-beam tomography system built on an x-ray microfocus tube, an image intensifier, and a high-resolution CCD camera. To obtain geometrical parameters of system misalignment, we suggest measuring two 180-deg-opposed cone-beam radiographs of a specially manufac- tured calibration aperture. An advantage of the aperture over other cali- bration objects is that we can easily restore its idealized picture by ap- plying a certain threshold to the measured data. The method permits the lateral displacement vector and lateral tilt angle to be accurately found. Unlike other alignment methods, our approach enables virtual system alignment by using mathematical processing of the measured data, rather than moving the parts of the system. The virtually aligned system data are used for 3-D image reconstruction by a standard filtered back- projection algorithm. Experimental results demonstrate considerable im- provement of the image quality after applying the alignment method sug- gested. © 1999 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(99)00802-8)