A method and a CT system are disclosed for determining movement and rest phases of a partial object that moves at times in an examination object during a CT examination. In at least one embodiment, at least two different radiation sources are used for the comparative measurement, and a first radiation source emits a first fan beam at a specific rotation angle at a first instant, the absorption of said beam being measured in beamwise fashion, a second radiation source emits a second fan beam, at the same rotation angle at a second, later instant, the absorption of the beam likewise being measured in beamwise fashion, and the relative movement or relative rest of the partial object between the first and second instants is deduced by comparing deviating absorption values of a multiplicity of spatially equivalent and equidirectional fan beams proceeding from the same angular position of the radiation sources.