Pincushion correction techniques and their effects on calculated 3D positions and imaging geometries

Two techniques for pincushion correction are evaluated based on their effect on calculation of the image geometry and 3D positions of object points. Images of a uniform wire mesh and a calibration phantom containing lead beads in its surface were acquired on the image intensifier TV systems in our catheterization labs. The radial mapping functions relating points in the original images and in the corrected images were determined using the mesh image. The undistorted mesh model was also used to determine and correct the distortions locally, i.e., for each square region between the mesh points. Thus, two corrected images were obtained. Images of the calibration phantom before and after correction were analyzed to determine the 3D position of the lead beads and the imaging geometry, using a calibration algorithm and the enhanced Metz-Fencil technique. In comparing the 3D positions calculated from the radially corrected and locally corrected images, the calculated 3D positions using the calibration technique vary by less than 0.6 mm in the x and y direction and less than 5.0 mm in the z direction. The uncorrected data yields differences of over 1 cm in the z direction. The 3D positions calculated using the enhanced Metz-Fencil technique appear to be more accurate when pincushion correction is applied.