Patent Document ID: 20110135053
Application ID: 13058197
Patent Flag: 0

Claim One:
1. A calibration method for eliminating substantially circular ring artifacts (RA, RA 1 , RA 2 , RA 3 , RA 4 , RA 5 ) in a set of radiographic 2D projection images which are acquired from a number of distinct projection directions by a not perfectly isocentric 3D rotational X-ray scanner system equipped with at least one X-ray tube (S) and at least one associated X-ray detector (D) diametrically arranged with respect to said X-ray tube (S), said calibration method comprising the steps of scanning (S 2 ) a calibration phantom from each of said projection directions when moving each of said X-ray tube (S) and X-ray detector (D) along a circular trajectory (T F , T CD ) around an object to be visualized and tomographically reconstructed, for each projection direction, calculating (S 3 ) the 3D position (P F ) of the at least one X-ray tube's focal spot and the 3D center position (P CD ) of the associated at least one X-ray detector (D) from the acquired 2D projection images and determining (S 5 ) the 3D coordinates of the effective center of rotation (M RC , P Iso eff or P Iso eff ′) about which the not perfectly isocentric 3D rotational X-ray scanner system rotates from a set of geometrical calibration data which is obtained as a result of a 3D calibration procedure (S 4 ) executed on the basis of the calculated 3D position data.