Patent Number: 
Section: claims

1. An X-ray diagnostic apparatus comprising: an X-ray tube;  an X-ray detector;  a grid arranged on an image reception plane of said X-ray detector;  an arm configured to support said X-ray tube and said X-ray detector in such a manner that a distance between said X-ray tube and said image reception plane of said X-ray detector can be changed;  an arm support device configured to support said arm in such a manner that an angle of said arm can be changed;  a storage device configured to store moire image data files including moire fringes by said grid in association with at least one of said distance and said angle; and  a moire correction circuit configured to correct image data outputted from said X-ray detector based on moire image data file selectively read from said storage device in accordance with at least one of said distance and said angle. 2. The X-ray diagnostic apparatus according to  claim 1 , wherein said X-ray detector is a flat panel type detector adopting a direct conversion system or an indirect conversion system. claim 1 3. The X-ray diagnostic apparatus according to  claim 1 , further comprising a circuit configured to adjust the contrast or density of said moire image data selectively read from said storage device based on at least one of an X-ray tube voltage, an X-ray tube current of said X-ray tube, a gain of said X-ray detector and a radiography time. claim 1 4. The X-ray diagnostic apparatus according to  claim 1 , further comprising a circuit configured to dissolve or reduce the displacement of said moire image data selective read from said storage device with respect to image data outputted from said X-ray detector. claim 1 5. The X-ray diagnostic apparatus according to  claim 1 , wherein the moire image data files are obtained in a condition no top plate for mounting a patient is arranged between said X-ray tube and said X-ray detector. claim 1 6. The X-ray diagnostic apparatus according to  claim 1 , further comprising a circuit configured to generate a new moire image data file from moire image data files read from said storage device by a distance-linear interpolation. claim 1 7. The X-ray diagnostic apparatus according to  claim 1 , wherein when an examination radiography is effected with the grid being removed, said image data outputted from said X-ray detector substantially passes through said moire correction circuit. claim 1 8. An X-ray diagnostic apparatus comprising: an X-ray tube;  an X-ray detector;  a gird arranged on an image reception plane of said X-ray detector;  an arm configured to support said X-ray tube and said X-ray detector in such a manner that a distance between said X-ray tube and said image reception plane of said X-ray detector can be changed;  an arm support device configured to support said arm in such a manner that an angle of said arm can be changed;  a moire correction data generation circuit configured to perform frequency analysis of image data outputted from said X-ray detector, specifies a spatial frequency corresponding to a moire pattern, and generates moire correction data based on said specified spatial frequency; and  a moire correction circuit configured to correct image data outputted from said X-ray detector based on said generated moire correction data. 9. The X-ray diagnostic apparatus according to  claim 8 , wherein the spatial frequency corresponding to the moire pattern is a peak frequency in an analyzed spatial frequency distribution. claim 8 10. The X-ray diagnostic apparatus according to  claim 8 , wherein said moire correction data generation circuit generates moire correction data including a plurality of moire fringes having said specified spatial frequency. claim 8 11. The X-ray diagnostic apparatus according to  claim 8 , wherein said moire correction data generation circuit generates a one dimensional original image signal from image data outputted from said X-ray detector and subjects said one dimensional original image signal to frequency analysis. claim 8 12. The X-ray diagnostic apparatus according to  claim 8 , wherein said moire correction data generation circuit generates a plurality of one dimensional original image signals corresponding to a plurality of directions from image data outputted from said X-ray detector, individually performs frequency analysis of a plurality of said one dimensional original image signals, specifies a plurality of peak frequencies corresponding to said one dimensional original image signals respectively, and selects a highest peak frequency from a plurality of said peak frequencies. claim 8 13. The X-ray diagnostic apparatus according to  claim 12 , wherein said moire correction data generation circuit generates moire correction data including a plurality of moire fringes having said selected highest peak frequency as a spatial frequency in a direction corresponding to said selected highest peak frequency. claim 12 14. The X-ray diagnostic apparatus according to  claim 8 , wherein said X-ray detector is a flat panel type detector adopting a direct conversion system or an indirect conversion system. claim 8 15. An X-ray diagnostic apparatus comprising: an X-ray tube;  an X-ray detector;  a grid arranged on an image reception plane of said X-ray detector;  an arm configured to support said X-ray tube and said X-ray detector in such a manner that a distance between said X-ray tube and said image reception plane of said X-ray detector can be changed;  an arm support device configured to support said arm in such a manner that an angle of said arm can be changed;  a frequency analysis circuit configured to subject image data outputted from said X-ray detector to frequency analysis and specify a spatial frequency corresponding to a moire pattern; and  a moire correction circuit configured to attenuate a component of said specified spatial frequency included in image data outputted from said X-ray detector. 16. The X-ray diagnostic apparatus according to  claim 15 , wherein the spatial frequency corresponding to the moire pattern is a peak frequency in an analyzed spatial frequency distribution. claim 15 17. The X-ray diagnostic apparatus according to  claim 15 , wherein said frequency analysis circuit generates a one dimensional original image signal from image data outputted from said X-ray detector and subjects said one dimensional original image signal to frequency analysis. claim 15 18. The X-ray diagnostic apparatus according to  claim 15 , wherein said frequency analysis circuit generates a plurality of one dimensional original image signals corresponding to a plurality of directions from image data outputted from said X-ray detector, individually subjects a plurality of said primary image signals to frequency analysis, specifies a plurality of peak frequencies, and selects a highest peak frequency from a plurality of said peak frequencies. claim 15 19. X-ray diagnostic apparatus according to  claim 18 , wherein said moire correction circuit attenuates a spatial frequency component of said selected highest peak frequency in a direction corresponding to said selected highest peak frequency. claim 18 20. The X-ray diagnostic apparatus according to  claim 15 , wherein said X-ray detector is a flat panel type detector adopting a direct conversion system or an indirect conversion system. claim 15 21. An X-ray diagnostic apparatus comprising: an X-ray tube;  an X-ray detector;  a grid arranged on an image reception plane of said X-ray detector;  an arm configured to support said X-ray tube and said X-ray detector in such a manner that a distance between said X-ray tube and said image reception plane of said X-ray detector can be changed;  a sensor configured to detect a distance between said X-ray tube and said image reception plane of said X-ray detector;  an arm support device configured to support said arm in such a manner that an angle of said arm can be changed;  a storage device configured to store moire image data when a distance between said X-ray tube and said image reception plane of said X-ray detector is a reference distance;  a moire image enlargement circuit which is configured to enlarge said moire image data based on said distance detected by said sensor and said reference distance; and  a moire correction circuit which corrects image data outputted from said X-ray detector based on said enlarged moire image data. 22. An X-ray diagnostic apparatus according to  claim 21 , wherein said moire image enlargement circuit enlarges said moire image data in accordance with a magnification C 1 /C 0  represented by the following expression: claim 21 C 1 / C 0 =( Ppxe2x88x92Pg )/(( Pp/M 1 )xe2x88x92 Pg )  where C 0  is a pattern cycle of moire fringes corresponding to said reference distance; C 1  is a pattern cycle of moire fringes corresponding to said distance detected by said sensor;  Pp is a pixel pitch of said X-ray detector;  Pg is a grid plate projected image of said grid on said image reception plane of said detector corresponding to said reference distance; and  M 1  is a ratio of a magnification of a grid projected image on said image reception plane of said detector with respect to said grid corresponding to said reference distance and a magnification of a grid projected image on said image reception plane of said detector with respect to said grid corresponding to said distance detected by said sensor. 23. The X-ray diagnostic apparatus according to  claim 22 , wherein said moire image enlargement circuit calculates said ratio M 1  in accordance with the following expression: claim 22 M 1 =( S 1 /( S 1 xe2x88x92 D 0 ))/( S 0 /( S 0 xe2x88x92 D 0 ))  where D 0  is a physical distance between said grid and said image reception plane of said detector; S 0  is said reference distance; and  S 1  is a distance detected by said sensor. 24. The X-ray diagnostic apparatus according to  claim 21 , wherein said X-ray detector is a flat panel type detector adopting a direct conversion system or an indirect conversion system. claim 21