a registration method and an apparatus for navigation - guided interventions employing an x - ray device and a position acquisition system and avoid the use of patient - associated markers . by means of a defined arrangement of a carrying arm proceeding from a support mount at the x - ray device and a defined arrangement of an x - ray calibration phantom at the carrying arm , the coordinate transformation between a coordinate system allocated to the support mount and a coordinate system allocated to the x - ray calibration phantom is known . on the basis of the acquisition and evaluation of 2d projections of the x - ray calibration phantom with the x - ray device , a coordinate transformation between the coordinate system allocated to the support mount and a coordinate system allocated to a measurement volume of the x - ray device is produced . by arranging a device detectable by the position acquisition system at the support mount , a coordinate transformation between the coordinate system allocated to the measurement volume and a coordinate system allocated to the calibration phantom is determined for the navigation .