1. A method for removing artifacts from an EM field generator from a rotational 3D scan, comprising the steps of: preoperatively, characterizing the artifacts from the EM field generator over a range of rotational positions of an x-ray source and detector; intraoperatively, determining the position of the EM field generator relative to the x-ray source and detector; and removing the preoperatively characterized artifacts for the determined relative position of the EM field generator from a current x-ray image.