A mobile radiography apparatus has radio-opaque markers, each marker coupled to a portion of the mobile radiography apparatus, wherein each of the markers is in a radiation path that extends from an x-ray source. A detector is mechanically uncoupled from the x-ray source for positioning behind a patient. Processing logic is configured to calculate a detector position with relation to the x-ray source according to identified marker positions in acquired projection images, and to reconstruct a volume image according to the acquired projection images.
