Obtaining regionally comparable anatomical as well as functional (perfusion/ventilation) in-formation of a respiratory system via computed tomography (CT) is a time-consuming task and often associated with a high radiation dose for the subject. In order to solve these problems, a method for processing CT imaging data is provided which comprises the steps of providing CT imaging data obtained at least at two x-ray energy levels in a first respiratory phase, preferably in an inhalation phase, of the subject and providing second CT imaging data obtained at least at two x-ray energy levels in a second respiratory phase, preferably in an exhalation phase, of the subject. The method further comprises reconstructing first regional perfusion blood volume (PBV) imaging data from the provided first CT imaging data, reconstructing second regional PBV imaging data from the provided second CT imaging data, reconstructing first virtual non-contrast (VNC) imaging data from the provided first CT im- aging data, and reconstructing second VNC imaging data from the provided second CT imaging data. The method further comprises determining a transformation function T for registering the first and second reconstructed VNC imaging data； registering the first and second reconstructed VNC imaging data by applying said transformation function T. The same transformation function T can also be applied to register the first and second PBV imaging data. Further the method comprises calculating regional ventilation imaging data using the registered first and second reconstructed VNC imaging data and/or the determined transformation function T.
