DETERMINATION OF 3-DIMENSIONAL POSITIONS OF KNOWN SPARSE OBJECTS FROMA SINGLE PROJECTION

A new technique is developed for accurate determination of the three-d imensional position and orientation of known sparse objects, e.g., a c onfiguration of points, from a single-perspective projection. In this technique, a computer model of the known object is translated and rota ted so as to align it optimally in a least-squares sense with the proj ection lines connecting the image points with the focal spot by using a modification of the projection-Procrustes technique. The translation al and rotational adjustments are repeated iteratively until the angul ar change between iterations is less than 0.25 degrees. Simulations in dicate that, for rms input image errors of 0.03 cm, the three-dimensio nal positions and orientations can be determined to within approximate ly 0.2 cm and 0.3 degrees for a wide range of initially guessed positi ons and orientations, and positions can be determined with an accuracy of approximately 0.3 cm for objects having as few as four points. In phantom experiments, three-dimensional positions and orientations of a cube phantom were reproducibly determined to within 0.23 cm and 0.13 degrees. The entire calculation requires only 10 s on a VAX 3500 to co nverge to the solution. The accuracy, precision, and speed of the tech nique indicate that it will be a useful tool for determination of thre e-dimensional positions and orientations of known sparse objects. (C) 1997 American Association of Physicists in Medicine.