1. A method, comprising: using a CT scan of a patient with at least two different x-ray energy regions, so that separate projection data exist for each x-ray energy region; generating volume displays for bone material and at least one further material composition; calculating two simulated dual energy x-ray absorptiometry (DEXA) projection recordings, each with a respectively different x-ray energy spectrum, using the volume displays for bone material and the at least one further material composition; using the two simulated DEXA projection recordings to determine a specific bone mass occupancy; and generating and outputting at least one projection recording using at least one of the simulated DEXA projection recordings and at least one average, specific bone mass occupancy in at least one region of the at least one projection recording.