A method and a CT system are disclosed for detecting and differentiating plaque in vessel structures of a patient. In at least one embodiment, a computed tomography system that is equipped with at least one focus detector system and, per focus detector system, with at least one transradiated x-ray/optical grating, is used to reconstruct the spatial distribution of the refractive index in the region of vessel structures of the patient from detected projection data. Further, at least one plaque form is highlighted in a pictorial display on the basis of a previously known value range of the refractive index for at least one plaque form.