Patent Number: 046882421
Section: summary

BACKGROUND OF THE INVENTION The present invention relates to an X-ray imaging system which irradiates an object with X-rays, and detects X-rays transmitted through the object to obtain transmission X-ray data, thereby forming a visible image based on the transmission X-ray data and, more particularly, to a scattered X-ray elimination technique suitable for a so-called digital radiography apparatus which converts an X-ray image into digital data. In conventional X-ray imaging systems, a detector for detecting X-rays receives direct X-rays transmitted through an object without being scattered, as well as scattered X-rays scattered by the object. The scattered X-rays are a major factor contributing to the degradation of contrast and sharpness of an X-ray image obtained through the detector. For this reason, in X-ray imaging systems, it is very important to eliminate scattered X-rays. In order to eliminate scattered X-rays, a grid is usually used in conventional systems. However, since the grid itself generates scattered X-rays, it cannot perform satisfactory elimination of scattered X-rays. If scattered X-rays can be eliminated, a contrast and sharpness of an X-ray image can be improved, thus providing a good X-ray image. In addition, if an image based on direct X-rays can be obtained, attenuation of the X-rays by the object can be accurately calculated by logarithmic conversion of the image data. Therefore, it is very desirable to eliminate scattered X-rays. Although various studies have been made on the nature of these scattered X-rays, since X-ray scattering involves complicated phenomena, many aspects thereof still remain unsolved. SUMMARY OF THE INVENTION It is an object of the present invention to provide an X-ray imaging system which effectively eliminates scattered X-ray components contained in image data, and which can form an X-ray image of high contrast and sharpness without blurring. In order to achieve the above object of the present invention, there is provided an X-ray imaging system comprising: an X-ray source for emitting X-rays to be radiated on an object; an X-ray image detection section for detecting an X-ray image emitted from the X-ray source and transmitted through the object; an X-ray mask member, having a plurality of X-ray shielding regions distributed in a predetermined pattern, for locally shielding X-rays with the plurality of X-ray shielding regions; a drive unit for moving the X-ray mask member so that the X-ray mask member is inserted or removed with respect to an X-ray radiation field between the X-ray image detection section and the X-ray source and is sequentially positioned at a plurality of predetermined positions in the X-ray radiation field; a storage section for storing X-ray image data; a first calculating section, associated with the storage section, for calculating scattered X-ray intensity distribution data associated with the object, based on a plurality of transmission X-ray data obtained by irradiating the object with X-rays when the X-ray mask member is located at different positions in the X-ray radiation field, and on transmission X-ray data obtained by irradiating the object with X-rays when the X-ray mask member is located outside the X-ray radiation field; a second calculating section, associated with the storage section, for calculating X-ray image data, from which the influence of scattered X-rays is eliminated, in accordance with the scattered X-ray intensity distribution data obtained by the first calculating section and transmission X-ray data obtained by irradiating the object with X-rays when the X-ray mask member is located outside the X-ray radiation field; and an image output unit for outputting the X-ray image data calculated by the second calculating section as a visible image. The present invention provides an X-ray imaging system, which can sufficiently eliminate scattered X-ray components contained in the image data and can form an X-ray image of high contrast and sharpness without blurring. More specifically, in the X-ray imaging system of this invention, a plurality of masked X-ray data, produced by an X-ray mask member displaced to different positions in an X-ray radiation field, are subjected to calculation of scattered X-ray intensity distribution, thus greatly improving calculation precision of the scattered X-ray components contained in the image data. Therefore, the scattered X-ray components contained in the image data can be effectively eliminated.