1. A method for geometric calibration of a CT scanner having at least one row of detector cells, the method comprising: executing the following for each row of the at least one row of detector cells: establishing a complete geometric description of the CT scanner, wherein the complete geometric description comprises at least one unknown geometric parameter; establishing a description of a forward projection function using the complete geometric description; acquiring actual projection coordinates of a calibration phantom placed in a scanning field of view (SFOV) on a current row of detector cells and corresponding to a plurality of angles; acquiring calculated projection coordinates of the calibration phantom on the current row of detector cells and corresponding to the plurality of angles using the description of the forward projection function; and acquiring a calibrated value for the at least one unknown geometric parameter by evaluating said at least one unknown geometric parameter based on the acquired actual projection coordinates and calculated projection coordinates using a nonlinear least square fitting algorithm.