Patent Number: 
Section: claims

1. A filter assembly intended for use in a computed tomography system having an x-ray source for projecting an x-ray beam along a projection axis, said filter assembly comprising:a filter element for attenuating the x-ray beam and having a center axis parallel to the projection axis;a first support plate, on which the filter element is mounted, for positioning the filter element within the x-ray beam; wherein the filter element and the first support plate are notch-shaped in the center part of the filter assembly along a direction perpendicular to the projection axis; anda second support plate having a shape similar to that of the first support plate and cooperating with the first support plate so as to sandwich the filter element(20). 2. The filter assembly as claimed in claim 1, further comprising at least one additional filter element and a support plate having a shape similar to that of the filter element and the first support plate, respectively. 3. The filter assembly as claimed in claim 2, wherein each filter element is sandwiched by two support plates. 4. The filter assembly as claimed in claim 2, wherein the support plates are shaped in such a way that they completely cover the side surfaces of the filter element facing the support plates. 5. The filter assembly as claimed in claim 4, wherein the notch is a saddle notch. 6. The filter assembly as claimed in claim 4, further comprising a fastening means for fastening the support plates so as to form a cassette. 7. The filter assembly as claimed in claim 6, wherein the fastening means comprises spacer bushes for adjusting the distance between the support plates. 8. The filter assembly as claimed in claim 7, wherein the filter element comprises some protrusions cooperating with recesses placed in the support plates so as to mount the filter element on the support plates. 9. A filter assembly, comprising:a filter element for attenuating the x-ray beam and having a center axis parallel to the projection axis;a first support plate, on which the filter element is mounted, for positioning the filter element within the x-ray beam; wherein the filter element and the first support plate are notch-shaped in the center part of the filter assembly along a direction perpendicular to the projection axis; andat least one additional filter element and a support plate having a shape similar to that of the filter element and the first support plate, respectively. 10. The filter assembly as claimed in claim 9, further comprising a second support plate having a shape similar to that of the first support plate and cooperating with the first support plate so as to sandwich the filter element. 11. The filter assembly as claimed in claim 9, wherein each filter element is sandwiched by two support plates. 12. The filter assembly as claimed in claim 9, wherein the support plates are shaped in such a way that they completely cover the side surfaces of the filter element facing the support plates. 13. The filter assembly as claimed in claim 12, wherein the notch is a saddle notch. 14. The filter assembly as claimed in claim 12, further comprising a fastening means for fastening the support plates so as to form a cassette. 15. The filter assembly as claimed in claim 14, wherein the fastening means comprises spacer bushes for adjusting the distance between the support plates. 16. The filter assembly as claimed in claim 15, wherein the filter element comprises some protrusions cooperating with recesses placed in the support plates so as to mount the filter element on the support plates. 17. A method, comprising:attenuating an x-ray beam with a filter element, of a filter assembly, that is sandwiched between two support plates that position the filter element within the x-ray beam, wherein the filter element and the support plates are notch-shaped in the center part of the filter assembly along a direction perpendicular to the projection axis. 18. The method of claim 17, further comprising:positioning the filter element within the x-ray beam by positioning the two support plates within the x-ray beam. 19. The method of claim 17, wherein the filter assembly includes at least one additional filter element and a support plate having a shape similar to that of the filter element and the first support plate, respectively. 20. The method of claim 17, wherein the notch is a saddle shaped notch.