A simple analytic method for cone beam calibration

In cone-beam tomography, for accurate image reconstruction to be achieved, the system first has to be calibrated. Few methods exist for direct cone-beam scanner calibration. The advantages of direct methods is that they do not need human intervention and can be very general with respect to the source/detector trajectory. With the assumption of a vertical scanner, Noo et al. obtained analytic equations for the calibration parameters with respect to the projected images of a calibration object. Without assumptions on the scanner geometry, a simple and direct method is described here, using a calibration object made of three orthogonal line segments with a common center. First, the projected center is identified. Then, three intermediate vectors are calculated from the data. Then, intrinsic (focal length and principal point) and extrinsic (rotation angles and translation vector from the calibration object to the scanner) parameters are obtained analytically from the three vectors