A method of generating a three-dimensional representation of a region of interest on a target object, comprising the steps of: a) identifying a fiducial marker of known geometry in a region of interest of the target object or on a moveable surface which is fixed relative to the region of interest; b) creating a first image of the fiducial marker and first image of the region of interest by detecting radiation from a radiation source with a detector when the region of interest and fiducial marker are in a first position relative to the radiation source and the detector is in a first detector position relative to the radiation source; c) moving the fiducial marker and region of interest relative to the radiation source to a second position relative to the radiation source and moving the detector to a second detector position relative to the radiation source; d) creating a second image of the fiducial marker and a second image of the region of interest by detecting radiation from the radiation source with the detector when the region of interest and fiducial marker are in the second position relative to the radiation source and the detector is in the second detector position relative to the radiation source; e) calculating an expected second image of the fiducial marker based on an intended spatial relationship between the radiation source, region of interest and fiducial marker and the detector in the second position, the geometry of the fiducial marker and the first position of the fiducial marker; f) generating corrected second image data for the region of interest utilising a comparison of the second image of the fiducial marker with the expected second image of the fiducial marker; and g) generating a three-dimensional representation of the region of interest utilising the first image, or a corrected first image data, and the corrected second image data for the region of interest. a) identifying a fiducial marker of known geometry in a region of interest of the target object or on a moveable surface which is fixed relative to the region of interest; b) creating a first image of the fiducial marker and first image of the region of interest by detecting radiation from a radiation source with a detector when the region of interest and fiducial marker are in a first position relative to the radiation source and the detector is in a first detector position relative to the radiation source; c) moving the fiducial marker and region of interest relative to the radiation source to a second position relative to the radiation source and moving the detector to a second detector position relative to the radiation source; d) creating a second image of the fiducial marker and a second image of the region of interest by detecting radiation from the radiation source with the detector when the region of interest and fiducial marker are in the second position relative to the radiation source and the detector is in the second detector position relative to the radiation source; e) calculating an expected second image of the fiducial marker based on an intended spatial relationship between the radiation source, region of interest and fiducial marker and the detector in the second position, the geometry of the fiducial marker and the first position of the fiducial marker; f) generating corrected second image data for the region of interest utilising a comparison of the second image of the fiducial marker with the expected second image of the fiducial marker; and g) generating a three-dimensional representation of the region of interest utilising the first image, or a corrected first image data, and the corrected second image data for the region of interest.