Method for preparing reconstructed CT image data records and CT system

A method for preparing reconstructed CT image data records from N≧2 projection data records, recorded with N different spectral weightings, defined as a product function of the energy-dependent weighting of a radiation spectrum used and a spectral sensitivity of a detector that is used, the method comprising:

• CT scanning an examination object and generating N projection data records, each measured with different spectral weightings;
• reconstructing N CT image data records, each with a large number of local image values, which reflect local mean attenuation values at a location of the examination object and of a measurement field depending on respective energy-dependent spectral weightings used for the CT scanning;
• establishing a first list of reference materials with known mean attenuation values, which permit an initial approximate calculation of beam hardening in the examination object;
• establishing a second list of reference materials with known mean attenuation values, which may be present in the examination object;
• calculating an initial approximate distribution of reference materials in the examination object by comparing the previously calculated local mean attenuation values with the mean attenuation values from the first list of reference materials;
• determining a distribution of local energy-dependent attenuation functions in the examination object on the basis of the last known distribution of reference materials and previously known material-specific energy-dependent attenuation functions;
• calculating local measurement-spectrum-dependent weighting functions at the locations of the examination object on the basis of the last known material distribution in the examination object with the with the associated material-specific energy-dependent attenuation functions;
• determining the distribution of reference materials from the second list of reference materials according to plausibility principles over at least one specified region of interest in the examination object on the basis of previously calculated local energy-dependent attenuation functions;
• and
• displaying the determined distribution of reference materials from the second list at least in the specified region of interest in the examination object.