Patent Number: 
Section: claims

1. A computed tomography scanner for performing a spiral scan, comprising:a rotatable X-ray emitter for generating a beam fan;an X-ray detector, positioned diametrically opposite to said rotatable X-ray emitter;an evaluation unit; andan X-ray filter, arranged downstream of the rotatable X-ray emitter, a position of the X-ray filter being correlated to a position of the X-ray detector and said X-ray filter being partly inserted into the beam fan only during operation for generating an unfiltered radiation component and, simultaneously, a filtered radiation component of the beam fan, wherein the radiation components have different X-ray spectra and wherein the evaluation unit is designed for separate evaluation of a measurement signal of the unfiltered radiation component and a measurement signal of the filtered radiation component, to obtain dual-energy images, wherein the X-ray filter is displaceably arranged in the beam fan and the X-ray filter is arranged in rotatable fashion. 2. The computed tomography scanner as claimed in claim 1, wherein the position of the X-ray filter is correlated to that of the X-ray detector such that, during the evaluation, there is an assignment of the portions on the X-ray detector the two filtered and unfiltered radiation components are incident. 3. The computed tomography scanner as claimed in claim 2, wherein the X-ray filter is made of tin, aluminum, copper, titanium or tungsten. 4. The computed tomography scanner as claimed in claim 2, wherein the X-ray filter covers a portion of the X-ray detector in a defined direction of extent of the X-ray detector. 5. The computed tomography scanner as claimed in claim 4, wherein the X-ray filter covers half of the X-ray detector in the defined direction of extent. 6. The computed tomography scanner as claimed in claim 1, wherein the X-ray filter is made of tin, aluminum, copper, titanium or tungsten. 7. The computed tomography scanner as claimed in claim 1, wherein the X-ray filter covers a portion of the X-ray detector in a defined direction of extent of the X-ray detector. 8. The computed tomography scanner as claimed in claim 7, wherein the X-ray filter covers half of the X-ray detector in the defined direction of extent. 9. The computed tomography scanner as claimed in claim 1, wherein the X-ray filter includes a plurality of different X-ray filters, displaceable into the beam fan. 10. The computed tomography scanner as claimed in claim 1, wherein the X-ray emitter comprises an emitter diaphragm, and wherein the X-ray filter is installed in the emitter diaphragm. 11. The computed tomography scanner as claimed in claim 1, wherein the computed tomography scanner is operateable in normal operation without the X-ray filter and in a dual-energy mode with the X-ray filter, and wherein a feed velocity of a patient couch relative to the X-ray emitter is reduced in the dual-energy mode in the case of a spiral scan. 12. A computed tomography scanner, for performing a spiral scan, comprising:a rotatable X-ray emitter for generating a beam fan;an X-ray detector, positioned diametrically opposite to said rotatable X-ray emitter;an evaluation unit; andan X-ray filter, arranged downstream of the rotatable X-ray emitter, a position of the X-ray filter being correlated to a position of the X-ray detector and said X-ray filter being partly inserted into the beam fan only during operation for generating an unfiltered and, simultaneously, a filtered radiation component of the beam fan, wherein the radiation components have different X-ray spectra, the evaluation unit is designed for separate evaluation of a measurement signal of the unfiltered radiation component and a measurement signal of the filtered radiation component, to obtain dual-energy images, the X-ray filter is displaceably arranged in the beam fan and the X-ray filter is displaceably arranged such that during a complete rotation of the X-ray emitter, the X-ray filter is adjustable at least between a cover position in which the X-ray filter completely covers the beam fan and a removed position in which the X-ray filter completely uncovers the beam fan. 13. A method for controlling a computed tomography scanner for performing a spiral scan, wherein the computed tomography scanner comprises a rotatable X-ray emitter for generating a beam fan, an X-ray detector positioned diametrically opposite to the rotatable X-ray emitter, and an evaluation unit, the method comprising:arranging an X-ray filter downstream of the X-ray emitter, a position of the X-ray filter being correlated to that of the X-ray detector;forming an unfiltered radiation component of the beam fan and, simultaneously, a filtered radiation component of the beam fan using the X-ray filter, the X-ray filter being only partly inserted into the beam fan, wherein the unfiltered and filtered radiation components have different X-ray spectra; andevaluating a measurement signal of the unfiltered radiation component, separate from an evaluation of a measurement signal of the filtered radiation component, to obtain dual-energy images, wherein the X-ray filter is displaceably arranged in the beam fan and the X-ray filter is arranged in rotatable fashion.