Patent Number: 
Section: claims

1. A computer tomography medical examination device, comprising:a radiation source for x-raying an object being medically examined from a projection direction with a radiation energy associated to the projection direction;a detector for detecting a radiation from the radiation source and recording a projection image of the object;a data memory for storing a predetermined correction value; andan evaluation unit connected downstream of the detector for correcting a radiation hardening of the projection image,wherein an operating parameter of the radiation source is applied to determine the radiation energy associated to the projection direction which depends on an absorption characteristics of the object,wherein the evaluation unit is provided with the operating parameter and reads the predetermined correction value allocated to the operating parameter and corrects a radiation hardening on the projection image. 2. The device as claimed in claim 1, wherein the radiation source is an x-ray tube and the detector is an x-ray detector. 3. The device as claimed in claim 1, wherein a variable of the operating parameter is an x-ray tube voltage. 4. The device as claimed in claim 1, wherein the evaluation unit reads the predetermined correction value relative to the x-ray tube voltage from the data memory and carries out a water correction on the projection image by the predetermined correction value. 5. The device as claimed in claim 1, wherein the evaluation unit performs a post-reconstructive correction of an hardening on the projection image that is caused by an attenuation which is different than a water-equivalent material in the object. 6. The device as claimed in claim 5, wherein the post-reconstructive correction of the hardening of the projection image is carried out iteratively by the evaluation unit. 7. The device as claimed in claim 5, wherein the post-reconstructive correction of the hardening of the projection image is carried out by the evaluation unit with a spatial resolution that is less than a spatial resolution of the projection image. 8. The device as claimed in claim 1,wherein an object model differentiated according to the absorption characteristics of the object is determined by the evaluation unit from the projection image,wherein an object data record derived from the object model is allocated by the evaluation unit to a pixel of the projection image,wherein the correction value for the projection image is determined by the evaluation unit using the object data record and the x-ray tube voltage. 9. The device as claimed in claim 1, wherein the object is a live animal or human patient. 10. A method for correcting a radiation hardening on a projection image of an object being medically examined, comprising:x-raying the object by a radiation source from a projection direction with a radiation energy associated to the projection direction;detecting a radiation from the radiation source and recording a projection image of the object by a detector;storing a predetermined correction value in a data memory;correcting the radiation hardening of the projection image by an evaluation unit connected downstream of the detector; andproviding a corrected projection image,wherein an operating parameter of the radiation source is applied to determine the radiation energy associated to the projection direction which depends on an absorption characteristics of the object,wherein the evaluation unit is provided with the operating parameter and reads the predetermined correction value allocated to the operating parameter and corrects a radiation hardening on the projection image. 11. The method as claimed in claim 10, wherein the radiation source is an x-ray tube and the detector is an x-ray detector and the projection image is generated by the x-ray tube and the x-ray detector. 12. The method as claimed in claim 10, wherein the tube voltage is used as a variable of the operating parameter. 13. The method as claimed in claim 10, wherein a water correction on the projection image is carried out by the evaluation unit by reading a predetermined correction value from the data memory relative to the tube voltage applied. 14. The method as claimed in claim 10, wherein a post-reconstructive correction of the radiation hardening on the projection image is performed by the evaluation unit relative to the tube voltage, the hardening caused by a material having a different attenuating effect than a water-equivalent material. 15. The method as claimed in claim 14, wherein the post-reconstructive correction of the hardening is performed iteratively by the evaluation unit. 16. The method as claimed in claim 14, wherein the post-reconstructive correction of the hardening is performed with a spatial resolution that is less than a spatial resolution of the project image data. 17. The method as claimed in claim 10,wherein a three-dimensional object model differentiated according to an absorption characteristics of the object is determined by the evaluation unit from the projection image,wherein an object data record is derived from the object model and is allocated to the project image,wherein the object data record and the tube voltage are used to determine a correction value for the projection image from the data memory. 18. The method as claimed in claim 10, wherein the object is a live animal or human patient.