In a method for reconstructing a CT image from data acquired from an examination subject, a reconstruction algorithm is employed that is based on an ideal short-scan circle-and-line trajectory. To adapt the reconstruction algorithm to a "real world" scan trajectory, data are acquired with a C-arm CT apparatus wherein the focus is moved through an actual short-scan circle-and-line trajectory. For each position of the focus in the actual trajectory, a projection matrix is electronically generated and the reconstruction algorithm with the ideal trajectory is adapted to the actual trajectory using the projection matrices.