The present invention relates to an X-ray exposure control device having the function of controlling the exposure to X-rays, an X-ray image detection apparatus including the same, and an X-ray imaging system including the same.
In medical imaging using X-rays, there have conventionally been used, in general, an X-ray film method which utilizes a screen-film radiographic system in which a fluorescent screen is combined with an X-ray film and which involves directly recording an X-ray image on an X-ray film and developing the recorded X-ray image; a computed radiography (CR) method which involves recording an X-ray image on a storage phosphor sheet called imaging plate (IP) as a latent image and then reading photostimulated luminescence through laser scanning to acquire X-ray image data as digital data; and a digital radiography (DR) method which involves directly and instantaneously reading an X-ray image with an X-ray detection element such as a flat panel detector (FPD) having an X-ray sensitive layer disposed on a thin film transistor (TFT) substrate to directly acquire X-ray image data as digital data.
Any X-ray imaging system adopting any of the foregoing methods is provided with an automatic exposure control (AEC) mechanism to stop X-ray radiation in a case where X-ray radiation from an X-ray source is detected and a proper X-ray radiation dose is reached. Since the foregoing X-ray imaging system is provided with the AEC mechanism, an X-ray image of proper density can be acquired at all times in the same radiographic environment even in radiographing a variety of different sites.
Such conventional AEC is called phototimer using a so-called ionization chamber or an ion chamber having a photoelectric conversion element.
A conventional X-ray imaging system having such conventional AEC is shown in FIGS. 21A, 21B and 21C.
As shown in these drawings, an X-ray imaging system 200 includes an X-ray source 202, a dedicated device for X-ray image detection (hereinafter referred to as “X-ray detection device”) 206 provided so as to be opposed to the X-ray source 202 and receiving an image of X-rays having passed through a subject 204 (radiographic site), a dosimeter 210 disposed between the position where the subject 204 is radiographed and the X-ray detection device 206, and provided with X-ray sensors 208 at a plurality of positions constituting a lighting field, and an AEC section 212 which controls the stop of the X-ray source 202 according to the X-ray integrated dose (exposure dose) as detected by the X-ray sensors 208 in the lighting field of the dosimeter 210. Here, the dosimeter 210 and the AEC section 212 constitute the AEC mechanism. A plurality of X-ray sensors, and in the illustrated case, three X-ray sensors 208 (suffixed by R, G and B symbols) are attached to the dosimeter 210. Since the X-ray sensors are fixed with respect to the X-ray detection device 206, the lighting field is fixed. For instance, the lighting field includes “blue (B)” and “green (G)” corresponding to the lung field in the front chest and “red (R)” in the abdomen.
In the X-ray imaging system 200 as described above, X-rays are radiated from the X-ray source 202 toward the subject 204 (radiographic site); the X-rays radiated to the lighting field of the subject 204 are detected by the X-ray sensors 208 of the dosimeter 210; the detection signals are integrated in the AEC section 212; when the X-ray dose detected by the X-ray sensors 208 and integrated in the AEC section 212 reaches an X-ray radiation dose (exposure dose) suitable to the subject 204, a stop signal Sp for stopping the X-ray source 202 is generated in the AEC section 212 and transmitted from the AEC section 212 to the X-ray source 202 to stop the X-ray source 202.
In recent years, in order to reduce the dose loss due to the dosimeter 210 shown in FIG. 21B and to reduce the cost (cut down the cost) involved in separately providing the dosimeter 210, an attempt is also made to integrate the dosimeter 210 with the X-ray detection device 206 (see JP 7-2014901 A and JP 2011-174908 A (hereinafter referred to as Patent Literatures 1 and 2)).
In Patent Literatures 1 and 2, some pixels of the X-ray image detection device are used as pixels for detecting the X-ray dose.
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