Patent Number: 
Section: claims

1. A radiation image acquisition apparatus, comprising: a sensor for spatially sampling a radiation transmission distribution of an object to be imaged at a spatial sampling interval and acquiring an image of said object; and  a scattered ray removing grid for removing scattered rays from said object,  wherein an interval of elements of said scattered ray removing grid is set such that a spatial frequency of a stripe pattern, in said image, which originates from said scattered ray removing grid becomes not less than ⅓ and not greater than 40% of a sampling frequency that is a reciprocal of said spatial sampling interval. 2. The apparatus according to  claim 1 , wherein said scattered ray removing grid is used without being moved during acquisition of said image by said sensor. claim 1 3. The apparatus according to  claim 1 , further comprising an image processing unit for removing said stripe pattern which originates from said scattered ray removing grid by filtering said image. claim 1 4. The apparatus according to  claim 3 , wherein said image processing unit performs said removing in accordance with operation performed by an operator. claim 3 5. The apparatus according to  claim 3 , wherein said image processing unit performs said removing in accordance with an application purpose of said image. claim 3 6. The apparatus according to  claim 5 , wherein said image processing unit performs said removing if the purpose is to perform spatial frequency emphasis processing for said image. claim 5 7. The apparatus according to  claim 5 , wherein said image processing unit performs no said removing if the purpose is to perform display or hard copy operation of said image on a scale not less than 100%. claim 5 8. The apparatus according to  claim 5 , wherein said image processing unit performs said removing if the purpose is to perform display or hard copy operation of said image upon reduction of said image. claim 5 9. The apparatus according to  claim 5 , wherein said image processing unit performs no said removing if the purpose is to store said image. claim 5 10. The apparatus according to  claim 3 , wherein said image processing unit performs said removing in accordance with a portion to be imaged of said object. claim 3 11. The apparatus according to  claim 10 , wherein said image processing unit performs no said removing if the portion is a bone portion. claim 10 12. The apparatus according to  claim 10 , wherein said image processing unit performs no said removing if the portion is a pelvis or joint portion. claim 10 13. The apparatus according to  claim 10 , wherein said image processing unit performs said removing if the portion is a chest or abdominal portion. claim 10 14. The apparatus according to  claim 3 , wherein said image processing unit performs said removing in accordance with an amplitude of said stripe pattern. claim 3 15. The apparatus according to  claim 14 , wherein said image processing unit performs said removing if the amplitude of said stripe pattern is larger than a predetermined threshold. claim 14 16. A radiation image acquisition method of spatially sampling a radiation transmission distribution of an object to be imaged at a spatial sampling interval and acquiring an image of said object using a sensor and a scattered ray removing grid for removing scattered rays from said object, comprising: setting an interval of elements of said scattered ray removing grid such that a spatial frequency of a stripe pattern, in said image, which originates from said scattered ray removing grid becomes not less than ⅓ and not greater than 40% of a sampling frequency that is a reciprocal of said spatial sampling interval. 17. The method according to  claim 16 , wherein said scattered ray removing grid is used without being moved during acquisition of said image by said sensor. claim 16 18. A radiation image acquisition apparatus, comprising: a sensor for spatially sampling a radiation transmission distribution of an object to be imaged at a spatial sampling interval and acquiring an image of said object; and  a scattered ray removing grid for removing scattered rays from said object,  wherein an interval of elements of said scattered ray removing grid is set such that a spatial frequency that is a reciprocal of said interval of elements of said scattered ray removing grid is within fs(n+1/3)xcx9cfs(n+0.4) or fs(n+0.6)xcx9cfs(n+2/3), where 1/fs is said spatial sampling interval and n is an integer not less than 0. 19. The apparatus according to  claim 18 , wherein said scattered ray removing grid is used without being moved during acquisition of said image by said sensor. claim 18 20. A radiation image acquisition method of spatially sampling a radiation transmission distribution of an object to be imaged at a spatial sampling interval and acquiring an image of said object using a sensor and a scattered ray removing grid for removing scattered rays from said object, comprising: setting an interval of elements of said scattered ray removing grid such that a spatial frequency that is a reciprocal of said interval of elements of said scattered ray removing grid is within fs(n+1/3)xcx9cfs(n+0.4) or fs(n+0.6)xcx9cfs(n+2/3), where 1/fs is said spatial sampling interval and n is an integer not less than 0. 21. The method according to  claim 20 , wherein said scattered ray removing grid is used without being moved during acquisition of said image by said sensor. claim 20 22. A design method of designing at least one of a sensor and a scattered ray removing grid used for an apparatus for spatially sampling a radiation transmission distribution of an object to be imaged at a spatial sampling interval and acquiring an image of said object using said sensor and said scattered ray removing grid for removing scattered rays from said object, comprising: determining at least one of an interval of elements of said scattered ray removing grid and said spatial sampling interval of said sensor such that a spatial frequency of a stripe pattern, in said image, which originates from said scattered ray removing grid becomes not less than ⅓ and not greater than 40% of a sampling frequency that is a reciprocal of said spatial sampling interval. 23. A design method of designing at least one of a sensor and a scattered ray removing grid used for an apparatus for spatially sampling a radiation transmission distribution of an object to be imaged at a spatial sampling interval and acquiring an image of said object using said sensor and said scattered ray removing grid for removing scattered rays from said object, comprising: determining at least one of an interval of elements of said scattered ray removing grid and said spatial sampling interval of said sensor such that a spatial frequency that is a reciprocal of said interval of elements of said scattered ray removing grid is within fs(n+1/3)xcx9cfs(n+0.4) or fs(n+0.6)xcx9cfs(n+2/3), where 1/fs is said spatial sampling interval and n is an integer not less than 0. 24. A radiographic apparatus, comprising: a sensor for spatially sampling a radiation transmission distribution of an object to be imaged at a spatial sampling interval and acquiring an image of said object; and  a grid for reducing scattered radiation from said object,  wherein a sampling frequency Fs of said sensor as a reciprocal of the spatial sampling interval and a spatial frequency Fg of said grid as a reciprocal of an interval of shades of elements of said grid on an image-receiving surface of said sensor substantially satisfy Fg=jxc2x7Fs/3, where j is a positive integer except for multiples of three. 25. The apparatus according to  claim 24 , wherein the frequency Fs falls within a range of 5 to 10 cyc/mm, and j is two. claim 24 26. The apparatus according to  claim 24 , further comprising an image processing unit for removing an image component originating from said grid from the image. claim 24 27. The apparatus according to  claim 24 , wherein said sensor has a pixel adding function of multiplying the spatial sampling interval by a natural number except for a multiple of three. claim 24 28. The apparatus according to  claim 24 , wherein said sensor is a direct sensor for directly converting the radiation transmission distribution into a charge distribution. claim 24 29. The apparatus according to  claim 24 , wherein said sensor is an indirect sensor for converting the radiation transmission distribution into a light intensity distribution by using a phosphor and converting the light intensity distribution into a charge distribution. claim 24 30. The apparatus according to  claim 24 , wherein the frequency Fs and the frequency Fg substantially satisfy  claim 24 with j 1  and j 2  being so selected as to satisfy |j 1 Fsxe2x88x92Fg| less than Fs/2 and |j 2 Fsxe2x88x922Fg| less than Fs/2. 31. A radiographic method of spatially sampling a radiation transmission distribution of an object to be imaged at a spatial sampling interval by using a sensor and a grid for reducing scattered radiation from said object, and acquiring an image of said object, comprising: acquiring an image of said object such that a sampling frequency Fs of said sensor as a reciprocal of the spatial sampling interval and a spatial frequency Fg of said grid as a reciprocal of an interval of shades of elements of said grid on an image-receiving surface of said sensor substantially satisfy Fg=jxc2x7Fs/3, where j is a positive integer except for multiples of three. 32. The method according to  claim 31 , wherein the frequency Fs falls within a range of 5 to 10 cyc/mm, and j is two. claim 31 33. The method according to  claim 31 , wherein the frequency Fs and the frequency Fg substantially satisfy  claim 31 with j 1  and j 2  being so selected as to satisfy |j 1 Fsxe2x88x92Fg| less than Fs/2 and |j 2 Fsxe2x88x922Fg| less than Fs/2. 34. A design method of designing at least one of a sensor and a grid used for a radiographic apparatus for spatially sampling a radiation transmission distribution of an object to be imaged at a spatial sampling interval and acquiring an image of said object using said sensor and said grid for reducing scattered rays from said object, comprising: determining at least one of the spatial sampling interval of said sensor and an interval of elements of said grid such that a sampling frequency Fs of said sensor as a reciprocal of the spatial sampling interval and a spatial frequency Fg of said grid as a reciprocal of an interval of shades of elements of said grid on an image-receiving surface of said sensor substantially satisfy Fg=jxc2x7Fs/3, where j is a positive integer except for multiples of three. 35. A radiation image acquisition apparatus, comprising: a sensor for spatially sampling a radiation transmission distribution of an object to be imaged at a spatial sampling interval and acquiring an image of said object; and  a scattered ray removing grid for removing scattered rays from said object,  wherein an interval of elements of said scattered ray removing grid is set such that a spatial frequency of a stripe pattern, in said image, which originates from said scattered ray removing grid becomes not greater than 40% of a sampling frequency that is a reciprocal of said spatial sampling interval. 36. The apparatus according to  claim 35 , wherein the spatial frequency of the stripe pattern becomes not less than 25% of the sampling frequency. claim 35 37. The apparatus according to  claim 35 , wherein the spatial frequency of the stripe pattern becomes not less than 30% of the sampling frequency. claim 35 38. A radiation image acquisition method of spatially sampling a radiation transmission distribution of an object to be imaged at a spatial sampling interval and acquiring an image of said object using a sensor and a scattered ray removing grid for removing scattered rays from said object, comprising: setting an interval of elements of said scattered ray removing grid such that a spatial frequency of a stripe pattern, in said image, which originates from said scattered ray removing grid becomes not greater than 40% of a sampling frequency that is a reciprocal of said spatial sampling interval. 39. The method according to  claim 38 , wherein the spatial frequency of the stripe pattern becomes not less than 25% of the sampling frequency. claim 38 40. The method according to  claim 38 , wherein the spatial frequency of the stripe pattern becomes not less than 30% of the sampling frequency. claim 38 41. A radiation image acquisition apparatus, comprising: a sensor for spatially sampling a radiation transmission distribution of an object to be imaged at a spatial sampling interval and acquiring an image of said object; and  a scattered ray removing grid for removing scattered rays from said object,  wherein an interval of elements of said scattered ray removing grid is set such that a spatial frequency that is a reciprocal of said interval of elements of said scattered ray removing grid is within fs(n+0.25)xcx9cfs(n+0.4) or fs(n+0.6)xcx9cfs(n+0.75), where 1/fs is said spatial sampling interval and n is an integer not less than 0. 42. A radiation image acquisition apparatus, comprising: a sensor for spatially sampling a radiation transmission distribution of an object to be imaged at a spatial sampling interval and acquiring an image of said object; and  a scattered ray removing grid for removing scattered rays from said object,  wherein an interval of elements of said scattered ray removing grid is set such that a spatial frequency that is a reciprocal of said interval of elements of said scattered ray removing grid is within fs(n+0.3)xcx9cfs(n+0.4) or fs(n+0.6)xcx9cfs(n+0.7), where 1/fs is said spatial sampling interval and n is an integer not less than 0. 43. A radiation image acquisition method of spatially sampling a radiation transmission distribution of an object to be imaged at a spatial sampling interval and acquiring an image of said object using a sensor and a scattered ray removing grid for removing scattered rays from said object, comprising: setting an interval of elements of said scattered ray removing grid such that a spatial frequency that is a reciprocal of said interval of elements of said scattered ray removing grid is within fs(n+0.25)xcx9cfs(n+0.4) or fs(n+0.6)xcx9cfs(n+0.75), where 1/fs is said spatial sampling interval and n is an integer not less than 0. 44. A radiation image acquisition method of spatially sampling a radiation transmission distribution of an object to be imaged at a spatial sampling interval and acquiring an image of said object using a sensor and a scattered ray removing grid for removing scattered rays from said object, comprising: setting an interval of elements of said scattered ray removing grid such that a spatial frequency that is a reciprocal of said interval of elements of said scattered ray removing grid is within fs(n+0.3)xcx9cfs(n+0.4) or fs(n+0.6)xcx9cfs(n+0.7), where 1/fs is said spatial sampling interval and n is an integer not less than 0. 45. A design method of designing at least one of a sensor and a scattered ray removing grid used for an apparatus for spatially sampling a radiation transmission distribution of an object to be imaged at a spatial sampling interval and acquiring an image of said object using said sensor and said scattered ray removing grid for removing scattered rays from said object, comprising: determining at least one of an interval of elements of said scattered ray removing grid and said spatial sampling interval of said sensor such that a spatial frequency of a stripe pattern, in said image, which originates from said scattered ray removing grid becomes not greater than 40% of a sampling frequency that is a reciprocal of said spatial sampling interval. 46. The method according to  claim 45 , wherein the spatial frequency of the stripe pattern becomes not less than 25% of the sampling frequency. claim 45 47. The method according to  claim 45 , wherein the spatial frequency of the stripe pattern becomes not less than 30% of the sampling frequency. claim 45 48. A design method of designing at least one of a sensor and a scattered ray removing grid used for an apparatus for spatially sampling a radiation transmission distribution of an object to be imaged at a spatial sampling interval and acquiring an image of said object using said sensor and said scattered ray removing grid for removing scattered rays from said object, comprising: determining at least one of an interval of elements of said scattered ray removing grid and said spatial sampling interval of said sensor such that a spatial frequency that is a reciprocal of said interval of elements of said scattered ray removing grid is within fs(n+0.25)xcx9cfs(n+0.4) or fs(n+0.6)xcx9cfs(n+0.75), where 1/fs is said spatial sampling interval and n is an integer not less than 0. 49. A design method of designing at least one of a sensor and a scattered ray removing grid used for an apparatus for spatially sampling a radiation transmission distribution of an object to be imaged at a spatial sampling interval and acquiring an image of said object using said sensor and said scattered ray removing grid for removing scattered rays from said object, comprising: determining at least one of an interval of elements of said scattered ray removing grid and said spatial sampling interval of said sensor such that a spatial frequency that is a reciprocal of said interval of elements of said scattered ray removing grid is within fs(n+0.3)xcx9cfs(n+0.4) or fs(n+0.6)xcx9cfs(n+0.7), where 1/fs is said spatial sampling interval and n is an integer not less than 0.