A method and device generating a computer tomography data set CT* of an object, wherein a nuclear spin tomography recording MR of said object is obtained, and a transformation or mapping protocol f(MR.sub.R) for a nuclear spin tomography reference data set MR.sub.R is ascertained. The nuclear spin tomography reference data set MR.sub.R can be mapped onto said recorded nuclear spin tomography data set MR, wherein said ascertained transformation or mapping protocol f is applied to a computer tomography reference data set CT.sub.R corresponding to the nuclear spin tomography reference data set MR.sub.R to determine a virtual computer tomography data set CT*=f(CT.sub.R).