Patent Number: 
Section: claims

1. A collimator control method, comprising the steps of: forming X-rays emanating from a focus of an X-ray tube into a fan shaped beam by a collimator and projecting said fan shaped beam onto a detector element array comprising a plurality of detector element rows arranged side by side in a thickness direction of said fan shaped beam, each of said detector element rows comprising a plurality of X-ray detector elements disposed in an extent direction of said fan shaped beams;  detecting an error between an impingement position of said fan shaped beam and a predetermined impingement position in direction of said side by side arrangement of said detector element rows on said detector array;  controlling said collimator based on said detected error so that said impingement position of said ran shaped beam coincides with said predetermined impingement position; and  removing high frequency components in said detected error; and wherein  said collimator is controlled based on said error after removal of said high frequency components so that said impingement position of said fan shaped beam coincides with said predetermined impingement position. 2. The method of  claim 1 , further comprising the step of: claim 1 detecting said error based on ratio of difference between X-ray detected signals to a sum of said X-ray detected signals, said X-ray detected signals being detected by X-ray detector elements adjacent in direction of said side by side arrangement of said detector element rows. 3. The method of  claim 1 , wherein said high frequency components are removed by averaging. claim 1 4. The method of  claim 1 , wherein said high frequency components are removed by low pass filtering. claim 1 5. The method of  claim 1 , wherein claim 1 no control is performed when said error falls within a first range;  control is performed with a first proportional gain when said error exceeds said first range and falls within a second range larger than said first range; and  control is performed with a second proportional gain larger than said first proportional gain when said error exceeds said second range. 6. The method of  claim 5 , further comprising the step of: claim 5 detecting said error based on ratio of difference between X-ray detected signals to a sum of said X-ray detected signals, said X-ray detected signals being detected by X-ray detector elements adjacent in direction of said side by side arrangement of said detector element rows. 7. The method of  claim 5 , wherein said high frequency components are removed by averaging. claim 5 8. The method of  claim 5 , wherein said high frequency components are removed by low pass filtering. claim 5 9. A collimator control apparatus, comprising: an X-ray tube for generating X-rays emanating from a focus;  a collimator for forming said X-rays into a fan shaped beam;  a detector array comprising a plurality of detector element rows arranged side by side in a thickness direction of said fan shaped beam, each of said detector element rows comprising a plurality of X-ray detector elements disposed in an extent direction of said fan shaped beam;  error detecting means for detecting an error between an impingement position of said fan shaped beam and a predetermined impingement position in direction of said side by side arrangement of said detector element rows on said detector element array;  control means for controlling said collimator based on said detector error so that said impingement position on said fan shaped beam coincides with said predetermined impingement position; and  high frequency component removing means for removing high frequency components in said detected signal; and wherein  said control means comprises means for controlling said collimator based on said error after removal of said high frequency components so that said impingement position of said fan shaped beam coincides with said predetermined impingement position. 10. The apparatus of  claim 9 , wherein claim 9 said error detecting means comprises means for detecting said error based on ratio of difference between X-ray detected signals to a sum of said X-ray detected signals, said X-ray detected signals being detected by X-ray detector elements adjacent in direction of said side by side arrangement of said detector element rows. 11. The apparatus of  claim 9 , wherein claim 9 said high frequency component removing means comprises means for removing high frequency.components by averaging. 12. The apparatus of  claim 9 , wherein claim 9 said high frequency component removing means comprises means for removing high frequency components by low pass filtering. 13. The apparatus of  claim 9 , wherein claim 9 said control means comprises means for  performing no control when said error falls within a first range;  performing control with a first proportional gain when said error exceeds said first range and falls within a second range larger than said first range; and  performing control with a second proportional gain larger than said first proportional gain when said error exceeds said second range. 14. The apparatus of  claim 13 , wherein claim 13 said error detecting means comprises means for detecting said error based on ratio of difference between X-ray detected signals to a sum of said X-ray detected signals, said X-ray detected signals being detected by X-ray detector elements adjacent in direction of said side by side arrangement of said detector element rows. 15. The apparatus of  claim 13 , wherein claim 13 said high frequency component removing means comprises means for removing high frequency components by averaging. 16. The apparatus of  claim 13 , wherein claim 13 said high frequency component removing means comprises means for removing high frequency components by low pass filtering. 17. An X-ray CT apparatus, comprising: an X-ray tube for generating X-rays emanating from a focus;  a collimator for forming said X-rays into a fan shaped beam;  a detector element array comprising a plurality of detector element rows arranged side by side in a thickness direction of said fan shaped beam, each of said detector element rows comprising a plurality of X-ray detector elements disposed in line in an extent direction of said fan shaped beam;  an error detecting means for detecting an error between an impingement position of said fan shaped beam and a predetermined impingement position in direction of said side by side arrangement of said detector element rows on said detector element array;  a control means for controlling said collimator based on said detected error so that said impingement position of said fan shaped beam coincides with said predetermined impingement position;  a signal acquiring means for acquiring X-ray detected signals for a plurality of views with an X-ray emitting/detecting system including said X-ray tube, said collimator and said detector element array, being rotated around an axis parallel with a thickness direction of said fan shaped beam;  a tomographic image producing means for producing tomographic images for slices crossed by said fan shaped beam on said X-ray detected signals; and  means for removing high frequency components in said detected error; and wherein  said control means comprises means for controlling said collimator based on said error after removal of said high frequency components so that impingement position of said fan shaped beam coincides with said predetermined impingement position. 18. The apparatus of  claim 17 , wherein claim 17 said error detecting means comprises means for detecting said error based on ratio of difference between X-ray detected signals to a sum of said X-ray detected signals, said X-ray detected signals being detected by X-ray detector elements adjacent in direction of said side by side arrangement of said detector element rows. 19. The apparatus of  claim 17 , wherein said means for removing high frequency components comprises means for removing high frequency components by averaging. claim 17 20. The apparatus of  claim 17 , wherein said means for removing high frequency components comprises means for removing high frequency components by low pass filtering. claim 17 21. The apparatus of  claim 17 , wherein claim 17 said control means comprises means for  performing no control when said error falls within a first range;  performing control with a first proportional gain when said error exceeds said first range and falls within a second range larger than said first range; and  performing control with a second proportional gain larger than said first proportional gain when said error exceeds said second range. 22. The apparatus of  claim 21 , wherein claim 21 said error detecting means comprises leans for detecting said error based on ratio of difference between X-ray detected signals to a sum of said X-ray detected signals, said X-ray detected signals being detected by X-ray detector elements adjacent in direction of said side by side arrangement of said detector element rows. 23. The apparatus of  claim 21 , wherein claim 21 said means for removing high frequency components comprises means for removing high frequency components by averaging. 24. The apparatus of  claim 21 , wherein claim 21 said means for removing high frequency components comprises means for removing high frequency components by low pass filtering. 25. A collimator control method, comprising the steps of: forming X-rays emanating from a focus of an X-ray tube into a fan shaped beam by a collimator and projecting said fan shaped beam unto a detector element array comprising a plurality of detector element rows arranged side by side in a thickness direction of said fan shaped beam, each of said detector element rows comprising a plurality of X-ray detector elements disposed in an extent direction of said fan shaped beam;  detecting an error between an impingement position of said fan shaped beam and a predetermined impingement position in direction of said side by side arrangement of said detector element rows on said detector array, said error being based on a ratio of difference between X-ray detected signals to sum of said X-ray detected signals; and  controlling said collimator based on said detected error so that said impingement position of said fan shaped beam coincides with said predetermined impingement position, wherein  no control is performed when said error falls within a first range,  control is performed with a first proportional gain when said error exceeds said first range and falls within a second range larger than said first range, and  control is performed with a second proportional gain larger than said first proportional gain when said error exceeds said second range, whereby control is stable and rapid. 26. A collimator control apparatus comprising: means for forming X-rays emanating from a focus of an X-ray tube into a fan shaped beam by a collimator and projecting said fan shaped beam onto a detector element array comprising a plurality of detector element rows arranged side by side in a thickness direction of said fan shaped beam, each of said detector element rows comprising a plurality of X-ray detector elements disposed in an extent direction of said fan shaped beam;  means for detecting an error between an impingement position of said fan shaped beam and a predetermined impingement position in direction of said side by side arrangement of said detector element rows on said detector array, said error being based on a ratio of difference between X-ray detected signals to sum of said X-ray detected signals; and  means for controlling said collimator based on said detected error so that said impingement position of said fan shaped beam coincides with said predetermined impingement position, wherein  no control is performed when said error falls within a first range,  control is performed with a first proportional gain when said error exceeds said first range and falls within a second range larger than said first range, and  control is performed with a second proportional gain larger than said first proportional gain when said error exceeds said second range, whereby control is stable and rapid.