The present invention relates to a radiographic imaging system whereby a subject is irradiated with radiation, and the radiation that has penetrated the subject is detected and converted into an electric signal to produce a radiographic image based upon the electric signal obtained by the conversion.
Radiographic imaging systems are used in a variety of fields for such applications as medical diagnoses in medicine and nondestructive tests in industry. Presently, some radiographic imaging systems use a flat panel detector (FPD) for converting radiation into an electric signal as a radiographic image information detector (radiation detector) for detecting the radiation that has penetrated a subject (e.g., X-ray, alpha ray, beta ray, gamma ray, electron beam, and ultraviolet ray).
In a radiographic imaging system using an FPD, a subject is irradiated with radiation emitted from a radiation source, and the radiation that has penetrated the subject is converted into an electric signal to read out an electric signal corresponding to image data of the subject from the FPD, thus producing a radiographic image.
When acquiring a radiographic image, scatter radiation component occurring when radiation penetrates the subject also reaches the FPD in addition to the linear penetration component that has penetrated the subject. The scatter radiation component reaching the FPD causes the image to blur.
To address this problem, a proposal was made in JP 10-305030 A and JP 10-262961 A suggesting placement of a grid between the FPD and the radiation source (specifically, on the side of the FPD closer to the radiation source) to eliminate scatter radiation. This grid generally has a configuration such that a radiation shielding substance and a radiotransparent substance are disposed alternately. Examples thereof include a grid secured in a given position (referred to also as “stationary grid” below) as described in JP 10-305030 A and a grid that moves as radiation is emitted from the radiation source toward the FPD (referred to also as “moving grid” below) as described in JP 10-262961 A.
While such a grid eliminates scatter radiation, it in turn causes the image of the grid to be produced in the radiographic image.
To address this problem, the system described in JP 10-305030 A acquires a radiographic image through the grid without a subject and uses acquired radiographic image data together with the imaging conditions to predict a grid image in the radiographic image and remove the grid image.
JP 2005-284873 A describes a detection method of detecting defective pixels attributable to defects in the FPD itself. According to that method, a radiographic image is acquired without a subject and used to detect defective pixels.
Where a stationary grid is used, the position of the grid image can be determined and, therefore, the grid image can be removed appropriately by calculating the grid image in the radiographic image from a grid image measured without a subject and the imaging conditions as in the case of the system described in JP 10-305030 A.
On the other hand, where a moving grid is used as described in JP 10-262961 A, no grid image is basically formed in any particular position because the grid is moved when an image is taken. Thus, there is no need to remove any grid image unlike where a stationary grid is used.
However, even in a case where the grid is moved when an image is taken, artifacts can occur as dust attaches to the grid or a moving grid develops operation failure. Thus, where a moving grid is used, artifacts can cause image failure. Further, inconsistency in the grid itself can cause image failure.
Another problem is that image failure attributable to the moving grid changes with irradiation time and other factors.