1. A method for generating a tomographic temperature map in a patient using a CT device, the method comprising: sampling and tomographically reconstructing attenuation values of tissue based on at least two mutually different X-ray energies or X-ray energy spectra relative to at least two sets of energy-dependent image data; performing a rho/Z decomposition of the tomographic image data, and ascertaining a current local density and a current local mean Z value for each location; ascertaining a local temperature distribution in the tissue, current local temperature values being determined from previously experimentally determined or theoretically calculated relations between Z values, density and temperature; and at least one of outputting and visualizing a spatial temperature distribution.