JP5455312B2 - Radiation imaging apparatus, control method thereof, and program - Google Patents

Description

  The present invention relates to a radiation imaging apparatus and a radiation imaging system suitable for use in medical diagnosis and industrial nondestructive inspection. In this specification, it is assumed that electromagnetic waves such as X-rays and γ rays, α rays, and β rays are included in the radiation.

  In recent years, a digital radiation imaging apparatus that includes a non-single crystal semiconductor such as amorphous silicon or amorphous selenium as a main material and includes a conversion element that converts radiation or light into electric charges has been put into practical use. In addition, digital radiation imaging apparatuses having a conversion element that converts radiation or light into electric charges using a single crystal semiconductor as a main material such as a CCD or a CMOS sensor have been put into practical use. As a radiation imaging apparatus, there is an indirect system including a conversion element including a phosphor that converts radiation into visible light and a photoelectric conversion element mainly composed of amorphous silicon that converts the visible light into electric charge. There is also a direct method in which radiation is directly converted into electric charge by a conversion element mainly made of amorphous selenium or the like. Both of them are also called flat panel detectors (FPD) (flat detectors) because they can realize a large area and thin radiation imaging apparatus, and have a feature that the time from photographing to observing an image is very short.

  This radiation imaging apparatus is affected by the elapsed time from when the apparatus is turned on and the conversion element is biased, the time of the imaging operation, the amount of radiation applied to the apparatus, the amount of light, etc. There is a risk of fluctuations in the image characteristics and fluctuations in the acquired image signal. For example, the dangling bond or defect of the conversion element may act as a trap level, causing the dark current to fluctuate, or an afterimage (lag) may occur or fluctuate due to the influence of past radiation or light irradiation history. . In addition, due to at least one of these factors, there is a possibility that the sensitivity which is the input / output characteristic between the input of radiation or light and the output of the generated charge in the conversion element may fluctuate.

  Therefore, in the following Patent Document 1 and Patent Document 2, before irradiating the radiation imaging apparatus with radiation or light bearing subject information, the light source that does not bear subject information is irradiated from a separately prepared light source. And a fluctuation suppressing effect that suppresses fluctuations in the acquired image signal.

JP 2002-40144 A Japanese National Patent Publication No. 11-513221

  However, if the time until photographing after irradiating light that does not carry subject information as in Patent Document 1 or Patent Document 2 described above becomes longer, the above-described fluctuation suppressing effect becomes weaker as time elapses.

  Also, if the amount of light that does not carry subject information is large, or if the number of times of light emission is large, the load on the light source increases as the amount of current flowing through the light source that emits light increases. Further, as the amount of current increases, the power consumption of the light source increases and the heat generation of the light source also increases.

  In addition, when the amount of light irradiation from the light source or the number of times of light irradiation is large, element deterioration of the conversion element irradiated with light is promoted.

  The present invention provides a radiation imaging apparatus capable of stabilizing dark current, afterimage, and sensitivity of an imaging apparatus, reducing power consumption and heat generation of a light source, and suppressing the deterioration of a conversion element. It is for the purpose.

The radiation imaging apparatus of the present invention includes a flat panel detector including a conversion unit in which a plurality of pixels including conversion elements capable of converting radiation into electric charges are arranged in a matrix, and a light source capable of emitting light to the conversion unit when, and a control unit for controlling the flat panel detector and the light source, wherein, when it is determined that the dark output signal from the pixel of the flat panel detector to the predetermined reference value we were The light source is controlled so that the light source emits light.

Also, in the method for controlling a radiation imaging apparatus according to the present invention, a dark output signal from a pixel of a flat panel detector including a conversion unit in which a plurality of pixels including conversion elements capable of converting radiation into charges is arranged in a matrix is input. an input step, the control unit for controlling the flat panel detector and the light source is, when it is determined that the dark output signal us was the preset reference value, the light source to irradiate light to the converter unit And a control step for controlling.

The program of the present invention includes an input step of inputting the dark output signal from the pixel of the flat panel detector comprising a conversion unit pixels including conversion elements capable of converting radiation into electric charges are more arranged in a matrix, wherein control unit for controlling the flat panel detector and the light source is, and a control step of controlling the light source to irradiate light to the conversion unit when it is determined that the dark output signal to a predetermined reference value we were A program for causing a computer to execute.

  According to the present invention, it is possible to stabilize the dark current, the afterimage, and the sensitivity of the imaging device, to reduce the load, power consumption, and heat generation amount of the light source, and to suppress the deterioration of the conversion element. It becomes possible.

(First embodiment)
The components and functions of the radiation imaging apparatus according to the first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing a configuration example of a radiation imaging system according to the first embodiment of the present invention. The radiation imaging system of this embodiment is used especially for medical purposes. The flat detector in the present invention includes a wavelength converter 104 that converts the wavelength of irradiated radiation such as X-rays into visible light, and a sensor substrate 102 that outputs an electrical signal corresponding to the visible light. The flat detector according to the present invention further includes a drive circuit 110 that drives the sensor substrate 102 and a read circuit 108 that reads an electrical signal from the sensor substrate 102 and outputs a digital image signal. The radiation imaging apparatus according to the present embodiment includes a light source 105 that emits light that does not carry subject information to the sensor substrate 102 in order to suppress fluctuations in characteristics of the apparatus and acquired image signals. In the present embodiment, the radiation imaging apparatus has at least a flat detector and a light source 105 in a housing (not shown). The radiation imaging system includes at least a radiation source 103 that emits radiation, and a radiation imaging apparatus that acquires a digital image signal based on an electrical signal corresponding to the irradiated radiation. The radiation imaging system further includes an image processing circuit 122 that appropriately performs image processing on the acquired digital image signal, and a control unit 107 that controls the radiation source 103, the drive circuit 110, and the readout circuit 108. A specific method of image processing performed by the image processing circuit 122 uses a digital image signal, and any method can be used as long as it can solve the above-described problems. Here, the control unit 107 inputs the digital image signal image-processed by the image processing circuit 122 and controls the operation of the light source 105 based on the input digital image signal. Note that at least one of the image processing circuit 122 and the control unit 107 may be incorporated in the same IC or different IC as the readout circuit 108 and held in the housing, and may be included in the radiation imaging apparatus. The radiation imaging apparatus is installed such that the subject 101 exists between the radiation source 103 and a digital image signal based on an electrical signal corresponding to the radiation dose transmitted through the subject 101 that carries subject information is acquired. In this embodiment, the wavelength converter 104 is provided, and the indirect method is used in which visible light converted from radiation by the wavelength converter 104 is converted into an electrical signal by the sensor substrate 102. However, the present invention is not limited thereto. Is not to be done. Instead of using the wavelength converter 104, a direct system that directly converts radiation into an electrical signal by the sensor substrate 102 may be used. In addition, although the operation control of the light source in this invention is made by the control part 107, the detailed control operation of the control part 107 is mentioned later. In this embodiment, the radiation imaging apparatus, the image processing circuit 122, and the control unit 107 function as means for detecting information indicating the necessity of light irradiation from the light source 105 to the sensor substrate 102.

  Next, the radiation imaging apparatus of this embodiment will be described in detail with reference to FIG. FIG. 2 is a circuit diagram illustrating a schematic configuration example of the radiation imaging apparatus according to the present embodiment. In FIG. 2, the number of pixels is 9 in 3 rows and 3 columns for convenience of explanation. However, the present invention is not limited to this, and the number of pixels can be appropriately determined as necessary. is there.

The sensor substrate 102 of the radiation imaging apparatus according to the present embodiment includes a conversion unit in which a plurality of pixels S11 to S33 are arranged in a matrix on an insulating substrate such as a glass substrate. Each of the pixels S11 to S33 includes conversion elements D1 to D9 that convert radiation or light into electric charges, and switch elements T11 to T33 that output electric signals based on the converted electric charges. Each of the conversion elements D1 to D9 has a capacitor C1 for accumulating detected charges inside or separately. The conversion elements D1 to D9 in the present embodiment are composed of a wavelength converter (not shown) that converts radiation into light that can be sensed by the photoelectric conversion element, and a photoelectric conversion element that converts light into electric charge. As the wavelength converter, CsI: Tl, Gd ₂ O ₂ S: Tb, or the like is preferably used. As the photoelectric conversion element, an MIS type photoelectric conversion element mainly composed of amorphous silicon is used. However, the present invention is not limited to this, and a PIN type photodiode may be used. Moreover, you may use the element which can convert the radiation which made amorphous selenium etc. the main material directly into an electric charge as conversion element D1-D9. The conversion elements D1 to D9 have at least two electrodes and a semiconductor layer provided between the two electrodes. The switch elements T11 to T33 in the present embodiment use thin film transistors (TFTs) whose main material is amorphous silicon. However, the present invention is not limited thereto, and TFTs whose main material is polysilicon are used. It may be used. In this embodiment, a three-terminal active element is used. However, the present invention is not limited to this, and a two-terminal active element such as a switching diode may be used. In this embodiment, one electrode of the conversion element is connected to one of the source and drain which are the two main electrodes of the switch element. However, the present invention is not limited to this, and the source and follow amplifiers may be configured by connecting the gates of the conversion element and the switch element. In that case, a switch element for initializing the potential of the connection portion between the conversion element and the gate of the switch element may be provided separately. The drive lines G1 to G3 are connected in common to the gates, which are the control terminals of the switch elements of a plurality of pixels in the row direction, in units of rows, and transmit drive signals from the drive circuit 110 to the switch elements. The signal wirings M1 to M3 are connected in common to the other of the sources or drains of the switch elements of a plurality of pixels in the column direction, and transmit electric signals output by the switch elements to the readout circuit 108. is there. In addition, a bias wiring (not shown) is connected to the other electrode of the conversion element in common to a plurality of pixels, and a bias for the conversion element to convert radiation or light into electric charge is supplied to the conversion element. The sensor substrate 102 includes pixels S11 to S33 provided on an insulating substrate, drive wirings G1 to G3, signal wirings M1 to M3, and a bias wiring.

  The drive circuit 110 is electrically connected to the drive wirings G1 to G3, and applies a drive signal in units of rows to the switch elements of a plurality of pixels connected to the drive wirings G1 to G3 via the drive wirings G1 to G3. Then, the sensor substrate 102 is driven by controlling the conduction state and the non-passage state of the switch element. The drive signal output from the drive circuit 110 has a pulsed conduction voltage that brings the switch element into a conduction state. For example, the switch elements T11 to T13 to which the drive signal is applied from the drive circuit 110 via the drive wiring G1 in the first row are turned on, and electrical signals corresponding to the charges of the conversion elements D1 to D3 are applied to the signal wirings M1 to M3. Output in parallel in units of lines. Similarly, the switch elements in the second row and the switch elements in the third row are sequentially driven, and an electrical signal output from the pixel in units of rows is converted into a digital image signal of one frame by the readout circuit 108 and output.

  The readout circuit 108 is electrically connected to the signal wirings M1 to M3, reads the electrical signals output via the signal wirings M1 to M3 in parallel in units of rows, converts the parallel signals into serial signals, and analog Is converted into a digital signal and a digital image signal is output. The readout circuit 108 has an operational amplifier (A1 to A3) that is electrically connected to the signal wiring and amplifies and outputs the electrical signal from the signal wiring, and a sample hold circuit that samples and holds the electrical signal from the operational amplifier. ing. The sample and hold circuit includes switches (Sr1 to Sr3) that sample electric signals and capacitors (CL1 to CL3) that hold the sampled electric signals. The operational amplifiers (A1 to A3) and the sample hold circuit are provided for each of the signal wirings M1 to M3. The electrical signals output in parallel are processed in parallel up to the sample and hold circuit. The readout circuit 108 sequentially outputs an electrical signal held in a sample and hold circuit prepared for each signal wiring and converts it into a serial image signal, and an amplifier B that converts an impedance of the image signal output from the multiplexer. Further, it has. The readout circuit 108 further includes an analog / digital converter (A / D converter) 121 that converts an analog image signal output from the amplifier A4 into a digital image signal. In this embodiment, the A / D converter 121 is provided at the subsequent stage of the multiplexer Sr4. However, the present invention is not limited to this, and the A / D converter is provided for each of the signal wirings M1 to M3. It may be provided in the previous stage. The configuration in the readout circuit 108 is an example, and various forms are conceivable. Analog signals from the signal wirings M1 to M3 are input, amplified, multiplexed, A / D converted, and output as digital image signals. As long as there is a function, it may be other than the above example.

  Although not shown in FIG. 2, in the radiation imaging apparatus of the present embodiment, a light source 105 is disposed between the front surface (back surface) opposite to the light receiving surface of the sensor substrate 102 and the housing. . Here, the light receiving surface of the sensor substrate 102 is a surface on which pixels are formed, is opposed to the wavelength converter 104, and is a surface on the side irradiated with radiation at the time of imaging. As the light source 105, an organic EL panel, an LED, a cold cathode tube, or the like is preferably used, or may be used in combination with a known light guide. The light emission wavelength of the light source 105 is desirably in a band that can be absorbed by the conversion elements D1 to D3. The light emitted from the light source 105 is directly incident from the back surface of the sensor substrate 102 and is absorbed by the semiconductor layers of the conversion elements D1 to D3.

  Next, the image acquisition operation of the radiation imaging apparatus will be described with reference to FIG. Radiation emitted from the radiation source and transmitted through the subject is irradiated to the radiation imaging apparatus. The irradiated radiation is wavelength-converted by the wavelength converter 104 into light in a wavelength band that can be detected by the conversion elements D1 to D9, and the converted light is irradiated to the conversion elements D1 to D9. The conversion elements D1 to D9 generate electric charges according to the amount of irradiated light, and the generated electric charges are accumulated in the capacitor C1. The operation so far is referred to as an accumulation operation.

  Next, a drive signal is applied from the drive circuit 110 to the drive wirings G1 to G3, and the read operation is performed in which the switch elements T11 to T33 are turned on to output electric signals based on charges from the pixels. In the present embodiment, the drive signal from the drive circuit 110 is sequentially applied in the order of the drive wiring G1 in the first row, the drive wiring G2 in the second row, and the drive wiring G3 in the third row. As a result, the switch elements for the reading operation are controlled in units of rows, and electrical signals are output in parallel from the pixels in units of rows. First, a drive signal is applied from the drive circuit 110 to the drive wiring G1 in the first row, and a conduction voltage is applied to the control terminals of the switch elements T11 to T13 in the first row. As a result, the switch elements T11 to T13 in the first row are turned on, and electric signals based on the charges accumulated in the capacitors C1 of the pixels S11 to S13 in the first row are output in parallel to the signal wirings M1 to M3. Is done. The electrical signals output to the signal wirings M1 to M3 are read by the reading circuit 108. The electric signal read out to the reading circuit 108 is amplified by the operational amplifiers A1 to A3. Here, the reset switches Sw1 to Sw4 connected to the operational amplifiers A1 to A3 are opened when the electric signal is read. Subsequently, the switches Sr1 to Sr3 of the sample and hold circuit are turned on, and the electric signals amplified by the operational amplifiers A1 to A3 are accumulated in the capacitors CL1 to CL3 of the sample and hold circuit. After the electrical signals are accumulated in the capacitors CL1 to CL3, the switches Sr1 to Sr3 are made non-conductive, and the electrical connection between the capacitors CL1 to CL3 and the signal wirings M1 to M3 is cut off. Thereafter, the operational amplifiers A1 to A3 and the signal wirings M1 to M3 are reset using the reset switches Sw1 to Sw4 to prepare for output of electric signals from the next row. The operation so far is referred to as a read operation.

  The electric signals sampled and held in the capacitors CL1 to CL3 are sequentially output by the multiplexer Sr4, converted in parallel and serially, and sequentially read out to the amplifier B. As a result, the stored electrical signals can be sequentially output in the order of the capacitors CL1, CL2, and CL3. At this time, since the amount of charge accumulated in the capacitor Cf4 of the amplifier B changes every time it is output, it is necessary to short-circuit the switch Sw4 and return the capacitor Cf4 to the initial state every time the capacitors CL1 to CL3 are selected by the multiplexer Sr4. There is. As a result, electrical signals based on the charges of the pixels S11 to S13 in the first row are sequentially output to the amplifier B as analog electrical signals by the multiplexer Sr4. The analog electrical signal is impedance-converted by the amplifier B, converted from digital to analog by the A / D converter 121, and output as a digital image signal for one row. The operation so far is referred to as an output operation.

  The readout operation and the output operation are sequentially performed in the second and third rows in the same manner, whereby a digital image signal for one row is output from the readout circuit 108. Further, in the present embodiment, for example, the output operation of the first row and the read operation of the second row are performed by overlapping in time within the same period. As a result, it is possible to shorten the time of the photographing operation for acquiring the image signal for one image, as compared with the mode in which the read operation for the second row is performed after the output operation for the first row.

  Next, a method for controlling the radiation imaging apparatus and the radiation imaging system in the present embodiment will be described.

  Radiation imaging apparatuses and radiation imaging systems are affected by the time elapsed since the apparatus was turned on and the conversion element was biased, the time taken for imaging, the amount of radiation or the amount of light irradiated to the apparatus, etc. As a result, fluctuations in the characteristics of the apparatus and fluctuations in the acquired image signal occur. In order to solve this problem, the radiation imaging apparatus and radiation imaging system of the present invention irradiate the sensor substrate 102 with light that does not carry image information emitted from the light source 105, separately from radiation or light having image information. Thus, fluctuations in device characteristics and fluctuations in image signals are suppressed. However, irradiating light that does not carry image information at every photographing operation causes deterioration of the conversion element and light source 105 that performs light irradiation. For this reason, it is desirable to temporarily stop the emission of light from the light source 105 after irradiating a necessary dose.

  However, as a result of sincere examination, the inventor of the present application has found that the effect of suppressing the above-described fluctuation is weakened with the lapse of time after the end of light irradiation. Here, using FIGS. 14A to 14C, an experiment example in which the change in sensitivity of the radiation imaging apparatus is verified (change in output when light of a constant intensity is continuously captured) is shown. Here, the sensitivity is input / output characteristics of the conversion element obtained based on an output obtained by irradiating the conversion element with radiation or light having a certain intensity. In this experiment, a bias is applied to the conversion element to stand by, and after irradiating light that does not carry image information, the conversion element is repeatedly irradiated with radiation or light of a certain intensity to perform an imaging operation, and output at that time Was observed as a sensitivity change. FIG. 14A shows a timing chart of the radiation imaging system in this experiment. In FIG. 14A, the horizontal axis represents time. On the vertical axis, in order from the top, imaging operations (continuous imaging), sensitivity, and dark output value (FPN value) for irradiation of light not carrying image information, radiation of a certain intensity or irradiation of light are shown. Here, the dark output value in the present invention is an output in the dark that is acquired from the imaging device in a dark state where light or radiation is not input to the imaging device, and includes the amount of fixed pattern noise of the imaging device. . This dark output value is acquired in the same operation sequence as the accumulation operation without irradiation with radiation in the imaging operation described above. FIG. 14B shows the time T1 from the start of the first image signal photographing operation after the irradiation of light not carrying image information and the stable sensitivity after the start of the first image signal readout operation. It is the graph which showed the change of time T2 until it is made. In FIG. 14B, the horizontal axis indicates time, and the vertical axis indicates time T2 from the start of the first image signal reading operation until stable sensitivity is obtained. In FIG. 14B, the longer the time T1 from the irradiation of light not carrying image information to the start of the first image signal readout operation, the longer the time T2 until stable sensitivity is obtained. In other words, it can be understood that the fluctuation suppressing effect obtained by irradiating light that does not carry image information becomes weaker as time passes. As a result, it is understood that output fluctuation may occur and usability may deteriorate when continuous shooting is performed without irradiating light that does not carry image information during continuous shooting. Further, as the time T1 becomes longer, the dark current fluctuates, and the dark output value fluctuates in the same way as the time T2 until the sensitivity is stabilized. FIG. 14C is a graph showing the variation in the time T1 and the dark output value from when the light not carrying image information is irradiated until the first image signal photographing operation is started. In FIG. 14C, it can be seen that the dark output value decreases as the time T1 increases. That is, it can be seen from FIG. 14B and FIG. 14C that the change in sensitivity correlates with the change in dark output value. From FIG. 14B and FIG. 14C, if the time T1 is short, the time T2 until the sensitivity is stabilized becomes short and the fluctuation suppressing effect becomes high, but the dark output value becomes large. If the time T1 becomes longer, the time T2 until the sensitivity is stabilized becomes longer and the fluctuation suppressing effect is lowered, but the dark output value becomes smaller. That is, the time T2 at which the sensitivity variation stabilizes is correlated with the dark output value variation, and the degree of stabilization of the sensitivity variation can be determined by observing the dark output value variation. Then, it can be determined that the required fluctuation suppressing effect can no longer be obtained when the dark output value becomes a predetermined value. By setting the predetermined value as the reference value and comparing the reference value with the dark output value, it is possible to determine that the required fluctuation suppressing effect cannot be obtained. If instability of the sensitivity becomes a problem when evaluating the image quality, the dark output value is large immediately after the light irradiation, but the fluctuation of the sensitivity is quickly stabilized and the image can be taken in a stable state. However, depending on the type and structure of the conversion element, there is a form in which the dark output value increases when irradiated with light, and even in this case, a state immediately after light irradiation in which the dark output value increases and the sensitivity is stabilized quickly is preferable. Note that the above-described experiment is an example, and in addition to the above-described changes in sensitivity and dark current, afterimage generation and the like vary with time after irradiation with light that does not carry image information. As described above, the inventor of the present application, in the above-mentioned experiment, that the effect of suppressing the fluctuation is weakened with the lapse of time after the end of the irradiation of the light that does not bear the image information, and the time when the fluctuation of the sensitivity is stabilized and the fluctuation observed thereby. It was found that there is a correlation between the suppression effect and the fluctuation of the dark output value.

  In the present embodiment, control by the control unit 107 is performed based on dark output values acquired in advance focusing on dark output values or information on dark output images based on dark output values for one image. In the present invention, a dark output image based on a dark output value or a dark output value for one image is used as a dark output signal. As for the output of the sensor substrate 102, when the conversion elements D1 to D9 are irradiated with light that does not bear image information emitted from the light source 105 after a bias is applied to the conversion elements D1 to D9, an effect of suppressing variation in sensitivity is obtained. However, the sensitivity fluctuation suppressing effect is weakened with the passage of time from the irradiation of light that does not carry image information. The photographer and the observer of the photographed image may feel uncomfortable with the image acquired due to the reduction in the sensitivity fluctuation suppression effect. For this reason, it is necessary to suppress the decrease in the sensitivity fluctuation suppressing effect to such an extent that the image observer does not feel uncomfortable. Further, when the sensitivity fluctuation suppressing effect is reduced, the amount of afterimages is also increased. These also give the image observer a sense of incongruity.

  How much the sensitivity fluctuation suppression effect is reduced to give the image viewer a sense of incongruity, or what percentage of the sensitivity changes between shots, and the image observer feels strange It is difficult to define whether to give it because it involves subjective evaluation, but it is necessary to draw a tolerance line. In the present embodiment, control is performed using a dark output value or a dark output image (dark output signal) when an uncomfortable image is generated as a reference value. This reference value is determined by measuring and evaluating an image acquired in advance by an image observer or image processing software.

  Next, a radiation imaging apparatus and a radiation imaging system and an operation thereof in the present embodiment for solving the above problems will be described. FIG. 3 is a schematic configuration diagram of the radiation imaging apparatus and the radiation imaging system in the present embodiment, and FIG. 4 is a timing chart at the time of subject photographing of the radiation imaging apparatus and the radiation imaging system.

  In FIG. 3, a C-arm 118 that performs medical X-ray imaging and fluoroscopy includes a flat panel detector (imaging unit) 119 and a radiation source (X-ray source) 103. As in FIG. 1, the flat detector 119 houses the wavelength converter 104, the sensor substrate 102, the drive circuit 110, the readout circuit 108, and the light source 105 in a housing (not shown). The radiation source 103 is attached at a position facing the flat detector 119 of the C arm 118. Moreover, although the form in which the flat detector 119 is attached to the C arm 118 has been described in the present embodiment, the present invention is not limited thereto. For example, it may be provided at a fixed position such as a table, or may be in a form that can be freely carried as a cassette.

  The flat panel detector 119 held by the C arm 118 is connected to a PC (personal computer) 111 by a cable or wireless communication, and is synchronized with the radiation source 103 via the PC 111. The PC 111 includes the control unit 107 shown in FIG. The photographer (engineer or doctor) can check the photographed image through the display of the PC 111.

  The PC 111 also includes the image processing circuit 122 of FIG. 1, acquires an output from the sensor substrate 102 as a digital image signal through the reading circuit 108, and performs image processing. In this embodiment, the PC 111 performs the light emission operation of the light source 105 based on the obtained dark output value, information after the arithmetic processing using the dark output image corresponding to one image, and the operation state of the radiation source 103. Control. Conditions for causing the light source 105 to emit light will be described later. Next, an example of driving including shooting timing will be described.

  First, the radiation imaging apparatus is turned on to apply a bias to the conversion elements D1 to D9. Next, light that does not bear image information emitted from the light source 105 is irradiated to the conversion elements D1 to D9 of the sensor substrate 102. Thereafter, in the imaging operation described above, the accumulation operation is performed without being irradiated with radiation, and the dark output value is periodically acquired in the same operation sequence for the other operations. In this embodiment, a dark output value is acquired every minute. At this time, the radiation emitted from the radiation source 103 and the light not carrying the image information emitted from the light source 105 are not irradiated to the sensor substrate 102. The obtained dark output value and the dark output image (dark output signal) based on the dark output value are output to the PC 111 including the control unit 107 and processed to obtain an average value. The control unit 107 compares the acquired dark output value or dark output image with a reference value acquired and set in advance. When it is determined that the acquired dark output value or the average value of the dark output image is lower than the reference value acquired in advance, the control unit 107 of the PC 111 operates the light source 105 to emit light that does not carry image information from the light source 105. Let The emitted light is irradiated to the conversion elements D1 to D9, and the trap levels in the conversion elements are filled, thereby enabling measurement with stable characteristics such as dark current, afterimage generation, suppression of sensitivity change, and the like. The electric charge in the trap level returns to the state before light irradiation with the passage of time due to excitation by heat or the like. For this reason, a dark output value or a dark output image is always acquired and compared with a reference value to determine whether light emission from the light source 105 and irradiation of the conversion element are necessary. However, when the timing for acquiring the dark output image and the timing for acquiring the radiographic image overlap, acquisition of the radiographic image has priority. As a result, the throughput of radiological image acquisition is not reduced. When the photographer presses the photographing button 115, the radiation source 103 emits radiation, the radiation imaging apparatus performs a photographing operation, and a subject image is generated.

  In the present embodiment, when a dark output value or a reference value of a dark output image is acquired, or when a bias is applied to a conversion element in a photographing operation, a dark output value or a dark output image is acquired every minute. . However, when acquiring the dark output value or the dark output image reference value, it is possible to determine whether the dark output value or dark output image that has been obtained causes a sense of incongruity. Good. There may be a case where the interval for acquiring the dark output value or the dark output image is too long and when the first dark output value or the dark output image is acquired, the image is already uncomfortable. On the other hand, there are cases where an interval between acquisitions is too short, and a huge number of dark output values or dark output images must be discriminated in order to find dark output values or dark output images that cause discomfort. The former may not be able to meet the problem, and the latter is not preferable because of poor work efficiency.

  In this embodiment, light irradiation is performed when the dark output value or the dark output image falls below the reference value. However, depending on the type of sensor, the dark output value or the dark output value is reduced when the effect obtained by irradiating the light source 105 is weakened. In some cases, the output image becomes high and some kind of image discomfort may occur. In such a case, light irradiation may be performed when the dark output value or the dark output image exceeds the reference value. In this embodiment, the dark output value or the average of the dark output image is used. However, a part of the dark output value or the dark output image in the sensor substrate 102 may be used, or the dark output value or the maximum value or the minimum of the dark output image may be used. A value or the like may be used.

  In this embodiment, only the dark output value or the average of the dark output image is used, but the dark output value or the dark output image also depends on the temperature. Therefore, the control unit 107 may have a temperature sensor as a component, and the dark output value or the dark output image serving as a reference value for irradiating light may be changed depending on the temperature detected by the temperature sensor. Further, instead of emitting light that does not carry image information from the light source 105 without the light source 105, radiation that does not carry image information may be emitted from the radiation source 103.

  As described above, a photographed image with improved characteristics can be obtained almost simultaneously with the photographer's intention to photograph. Specifically, the dark current, afterimage, and sensitivity of the imaging device can be stabilized. In addition, it is possible to expect the effects of suppressing the light irradiation time to the conversion element, reducing the power consumption and heat generation amount of the light source, and suppressing the deterioration of the conversion element.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 5 is a schematic diagram showing a configuration example of a radiation imaging system according to the second embodiment of the present invention. The difference between the present embodiment and the first embodiment is that a timer 106 is added. In this embodiment, the dark output value or dark output image from the image processing circuit 122 is not directly used for control. Similar to the first embodiment, a dark output value or a dark output image from the radiation imaging apparatus is used to determine image discomfort, and a timer is used with a reference time as a time from when light that does not carry image information is irradiated. 106 stores. The timer 106 outputs time information to the control unit 107 in the radiographic image capturing operation, and the control unit 107 determines whether or not the light source 105 needs to emit light and irradiate the conversion element based on the time information. Judgment is made and emission of light not carrying image information from the light source 105 is controlled. Specifically, in the radiographic image capturing operation, the timer 106 measures the time after the light that does not carry image information is emitted from the light source 105. The timer 106 gives a signal as time information to the control unit 107 when the measured time reaches a reference value, which is a preliminarily stored image disagreement determination time. Based on the signal, the control unit 107 emits light that does not carry image information from the light source 105 and irradiates the conversion element with light. Since other configurations are the same as those of the first embodiment, a detailed description thereof is omitted.

  Next, a radiation imaging apparatus and a radiation imaging system in this embodiment will be described with reference to FIG. FIG. 6 is a schematic configuration diagram of a radiation imaging apparatus and a radiation imaging system in the present embodiment. The radiation imaging system may be other than this configuration example. The difference from the first embodiment shown in FIG. 3 is that the stand 113 supports the flat detector 119 instead of the C-arm 118, and the radiation source 103 is fixed to the ceiling. A photographer (engineer or doctor) can also print a radiographic image acquired by the printer 112 via the PC 111. Since the other configuration is the same as that of the first embodiment, the detailed description is omitted.

  Although the timer 106 in this embodiment is provided in the flat detector 119, the present invention is not limited thereto, and may be provided in the PC 111, for example.

  In the present embodiment, the elapsed time when a sense of incongruity occurs may be recorded by observing the corrected image. For example, the user may determine whether or not there is a sense of discomfort by observing the difference between the acquired image and the image acquired one sheet before.

  Next, operations of the radiation imaging apparatus and the radiation imaging system in this embodiment will be described with reference to FIG. FIG. 7 is a timing chart at the time of subject photographing of the radiation imaging apparatus and the radiation imaging system.

  First, the radiation imaging apparatus is turned on to apply a bias to the conversion elements D1 to D9. Next, the timer 106 once outputs the irradiation command 1 to the control unit 107 in the PC 111, and the control unit 107 causes the light source 105 to emit light that does not carry image information, and causes the conversion elements D1 to D9 of the sensor substrate 102 to emit the light source 105. Irradiate light that does not carry image information emitted from the camera. At that time, the timer 106 starts measuring the time after the light source 105 emits light that does not carry image information. When the measured time reaches a reference value that is a preliminarily stored image disagreement, the timer 106 outputs the irradiation command 1 to the control unit 107 in the PC 111 as time information. Then, the control unit 107 in the PC 111 emits light that does not carry image information from the light source 105 based on the irradiation command 1 and irradiates the conversion element with light. If the radiation is emitted from the radiation source 103 before the measured time reaches the reference value, the timer 106 starts measuring the time after the radiation is emitted. The timer 106 compares the time after irradiation with the radiation with the reference value, and outputs the irradiation command 1 when the time exceeds the reference value.

  When the irradiation command 1 and the timing for acquiring the radiation image overlap, acquisition of the radiation image has priority. As a result, the throughput of radiological image acquisition is not reduced. As described above, as in the first embodiment, the dark current, the afterimage, and the sensitivity of the imaging device can be stabilized. In addition, it is possible to expect the effects of suppressing the light irradiation time to the conversion element, reducing the power consumption and heat generation amount of the light source, and suppressing the deterioration of the conversion element. In addition, it is possible to perform control without periodically acquiring a dark output value or a dark output image as compared with the first embodiment, and an effect of reducing the load on the system can be obtained.

(Third embodiment)
Next, a third embodiment of the present invention will be described with reference to FIGS. FIGS. 8A and 8B are schematic views showing a configuration example of a radiation imaging system according to the third embodiment of the present invention. In addition to the configuration of the second embodiment, a subject detection sensor ( Contact sensor) 116 is provided. The subject detection sensor 116 functions as means for detecting information indicating the necessity of light irradiation, and is controlled by the control unit 107 to notify the control unit 107 of the presence or absence of human contact or approach. Specifically, a pressure sensor that can detect pressure, a sensor that detects a current change in contact with a human body, a temperature sensor that can detect a human body temperature, and the like are applicable. The subject detection sensor 116 is attached to a part where the chin is placed on the table 113 that the subject touches at the time of photographing. The subject detection sensor 116 detects the pressure when the subject (patient) 114 places his / her chin before photographing, and outputs a subject detection signal to the control unit 107 in the PC 111. In the present embodiment, the control unit 107 in the PC 111 emits light that does not carry image information from the light source 105 based on the signal from the timer 106, the subject detection signal of the subject detection sensor 116, and the state of the radiation source 103. Control whether or not to perform. Since other configurations are the same as those of the second embodiment, detailed description thereof is omitted.

  Next, the control method of the radiation imaging system of this embodiment is demonstrated using FIG. FIG. 9 is a timing chart at the time of subject photographing of the radiation imaging apparatus and the radiation imaging system.

  First, the radiation imaging apparatus is turned on to apply a bias to the conversion elements D1 to D9. Next, the timer 106 once outputs the irradiation command 1 to the control unit 107 in the PC 111, and the control unit 107 causes the light source 105 to emit light that does not carry image information, and causes the conversion elements D1 to D9 of the sensor substrate 102 to emit the light source 105. Irradiate light that does not carry image information emitted from the camera. At that time, as in the second embodiment, the timer 106 starts measuring the time after the light source 105 emits light that does not carry image information. When the measured time reaches a reference value that is a preliminarily stored image disagreement, the timer 106 outputs the irradiation command 1 to the control unit 107 in the PC 111 as time information. Further, when the subject detection sensor 116 detects that the jaw of the subject (patient) 114 has touched the subject detection sensor 116 of the table 113, it outputs an irradiation command 2 as a subject detection signal to the control unit 107 in the PC 111. To do. When the irradiation command 2 is input after the irradiation command 1 is input, the control unit 107 in the PC 111 causes the light source 105 to emit light that does not carry image information, and irradiates the conversion element with light. If the radiation is emitted from the radiation source 103 before the measured time reaches the reference value, the timer 106 starts measuring the time after the radiation is emitted. The timer 106 compares the time after irradiation with the radiation with the reference value, and outputs the irradiation command 1 when the time exceeds the reference value. Thereafter, the light source 105 does not emit light regardless of the input of the irradiation command 2 until the next irradiation command 1 is output. In the photographing operation, when the photographer presses the photographing button 115, the photographing operation is started immediately, and the radiation source 103 exposes the radiation. When the irradiation command 2 from the subject detection sensor 116 and the timing for acquiring the radiographic image overlap, acquisition of the radiographic image has priority. As a result, the throughput of radiological image acquisition is not reduced. When the irradiation command 1 from the timer 106 is output, the light irradiation is performed when the irradiation command 2 is output again after the photographing period is completed.

  FIG. 10 is a flowchart showing the control method according to the present embodiment. In step S1201, when a predetermined time as a reference value elapses from power-on or light irradiation of the light source 105, the process proceeds to step S1202. Next, in step S1202, the timer 106 outputs an irradiation command 1 to the control unit 107 in the PC 111. Next, in step S1203, the control unit 107 in the PC 111 determines whether or not the irradiation command 2 is input from the subject detection sensor 116. When there is an input of irradiation command 2, the process proceeds to step S1205, and when there is no input of irradiation command 2, the process proceeds to step S1204. The irradiation command 3 will be described later in a fourth embodiment. In step S1204, the control unit 107 in the PC 111 causes the flat panel detector to wait until an irradiation command 2 is input. If the input of the irradiation command 2 is detected by the control unit 107, the process proceeds to step S1205. In step S1205, the control unit 107 in the PC 111 determines whether or not it is during the shooting operation. If it is during the shooting operation, the process proceeds to step S1207, and if it is not during the shooting operation, the process proceeds to step S1206. In step S1207, the control unit 107 in the PC 111 waits until the photographing period ends, and returns to step S1203. In step S1206, the control unit 107 in the PC 111 irradiates the light source 105 with light.

  As described above, in the present embodiment, the dark current, the afterimage, and the sensitivity of the imaging device can be stabilized as in the first embodiment. In addition, it is possible to expect the effects of suppressing the light irradiation time to the conversion element, reducing the power consumption and heat generation amount of the light source, and suppressing the deterioration of the conversion element. In addition, it is possible to perform control without periodically acquiring a dark output value or a dark output image as compared with the first embodiment, and an effect of reducing the load on the system can be obtained. Further, by using the subject detection sensor 116, it is possible to reduce the number of times of light irradiation by the light source 105 when the subject does not exist at a position where the subject can be photographed, as compared with the second embodiment.

(Fourth embodiment)
The radiation imaging apparatus and radiation imaging system in this embodiment will be described with reference to FIG. FIG. 11 is a schematic diagram illustrating a configuration example of a radiation imaging system according to the fourth embodiment of the present invention. The difference between the fourth embodiment and the third embodiment of the present invention is that a position detection sensor (position sensor) 117 is added instead of the subject detection sensor 116. The position detection sensor 117 functions as a means for detecting information indicating the necessity of light irradiation, is controlled by the control unit 107, and transmits information related to the position of the sensor to the control unit 107. Specifically, an infrared sensor, a gyro sensor, or the like is applicable as the position detection sensor 117, but any sensor that can detect position information including the inclination and direction of the sensor substrate 102 may be used. Further, the position information transmitted to the control unit 107 may be a binary value indicating a position where the image can be captured or a position where the image cannot be captured, or may be a digital value or an analog value representing information such as an angle or a position. In the case of the latter information, the control unit 107 determines whether the photographing position or the non-capturing position according to a preset condition at the time of shipment or by the operator. Since other configurations are the same as those of the third embodiment, detailed description thereof is omitted.

  FIG. 12 is a schematic configuration diagram of a radiation imaging apparatus and a radiation imaging system in the present embodiment. FIG. 12 is an external view showing a configuration example of the radiation imaging system according to the present embodiment. The radiation imaging system of this embodiment is obtained by adding a position detection sensor 117 to the flat panel detector of the radiation imaging system described in the first embodiment of the present invention shown in FIG. Since it is the same as that of embodiment, detailed description is omitted. The position detection sensor 117 of the present embodiment is an infrared sensor and can detect whether the bed 120 is in the vicinity. When the position detection sensor 117 in the C-arm 118 approaches the bed 120 and becomes ready for photographing, a signal is output to the PC 111. In the present embodiment, an infrared sensor is used as the position detection sensor 117, but other sensors may be used as long as information about the position can be transmitted to the control unit 107 in the PC 111. Based on the signal from the timer 106, the position detection signal from the position detection sensor 117, and the state of the radiation source 103, the control unit 107 in the PC 111 determines whether to emit light that does not carry image information from the light source 105. Take control.

  Next, the control method of the radiation imaging system of this embodiment is demonstrated using FIG. FIG. 13 is a timing chart at the time of subject photographing of the radiation imaging apparatus and the radiation imaging system. In the present embodiment, the irradiation command 2 from the subject detection sensor 116 in the third embodiment is replaced with an irradiation command 3 that is a position detection signal from the position detection sensor 117. The rest is the same as the control method of the third embodiment, and a detailed description is omitted.

  As described above, in the present embodiment, the dark current, the afterimage, and the sensitivity of the imaging device can be stabilized as in the first embodiment. In addition, it is possible to expect the effects of suppressing the light irradiation time to the conversion element, reducing the power consumption and heat generation amount of the light source, and suppressing the deterioration of the conversion element. In addition, it is possible to perform control without periodically acquiring a dark output value or a dark output image as compared with the first embodiment, and an effect of reducing the load on the system can be obtained. Similarly to the third embodiment, by using the position detection sensor 117, it is possible to reduce the number of times of light irradiation by the light source 105 when the subject does not exist at a position where photographing is possible, as compared with the second embodiment. Is possible.

  FIG. 15 is a block diagram illustrating a hardware configuration example of the PC (personal computer) 111 according to the first to fourth embodiments. A central processing unit (CPU) 1802, ROM 1803, RAM 1804, network interface 1805, input device 1806, output device 1807 and external storage device 1808 are connected to the bus 1801. The CPU 1802 performs data processing or calculation and controls various components connected via the bus 1801. The CPU 1802 corresponds to the control unit 107. The ROM 1803 stores a control procedure (computer program) of the CPU 1802 in advance, and is started when the CPU 1802 executes this computer program. A computer program is stored in the external storage device 1808, and the computer program is copied to the RAM 1804 and executed. A RAM 1804 is used as a work memory for data input / output, transmission / reception, and temporary storage for control of each component. The external storage device 1808 is, for example, a hard disk storage device or a CD-ROM, and the stored content does not disappear even when the power is turned off. The CPU 1802 executes the computer program in the RAM 1804 to perform the processes of the first to fourth embodiments. A network interface 1805 is an interface for connecting to a network, and inputs and outputs signals and data to and from the radiation source 103, the flat panel detector 119, and the imaging button 115. The input device 1806 is, for example, a keyboard and a mouse, and can perform various designations or inputs. The output device 1807 is a display, a printer, or the like, and can display and print a subject image.

  As described above, the first to fourth embodiments can be realized by the computer 111 executing a program. Also, means for supplying a program to a computer, for example, a computer-readable recording medium such as a CD-ROM recording such a program, or a transmission medium such as the Internet for transmitting such a program is also applied as an embodiment of the present invention. Can do. A computer program product such as a computer-readable recording medium in which the above program is recorded can also be applied as an embodiment of the present invention. The above program, recording medium, transmission medium, and computer program product are included in the scope of the present invention. As the recording medium, for example, a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

  As described above, according to the first to fourth embodiments, the information from the detection unit provided in the radiation imaging system is obtained after the photoelectric conversion element is irradiated with light that does not carry the subject information in advance before photographing the subject. Then, an appropriate timing for irradiating light to the conversion element is determined again and irradiation is performed.

  The dark current, afterimage, and sensitivity of the imaging device can be stabilized. In addition, it is possible to expect the effects of suppressing the light irradiation time to the conversion element, reducing the power consumption and heat generation amount of the light source, and suppressing the deterioration of the conversion element.

  The flat panel detector 119 of the present invention includes a conversion unit in which a plurality of pixels including conversion elements D1 to D3 capable of converting radiation into charges are arranged in a matrix. The conversion element includes a wavelength converter 104 that converts radiation into light, and a photoelectric conversion element that converts the converted light into electric charges. The photoelectric conversion element has an amorphous semiconductor on an insulating substrate. The light source 105 can irradiate the conversion unit with light in a wavelength band that can be detected by the conversion element. The control unit 107 controls the flat detector 119 and the light source 105. Specifically, the control unit 107 inputs a signal from the flat detector 119 in the input step, and controls irradiation of the light source 105 based on the input signal in the control step.

  The flat detector 119 of the present invention includes a drive circuit 110, a readout circuit 108, and an image processing circuit 122. The drive circuit 110 controls the conduction and non-conduction states of the switch elements T11 to T33 of the pixels in units of rows in order to output electric signals based on the charges converted by the conversion elements to the signal wirings M1 to M3. The substrate 102 is driven. The readout circuit 108 reads out electrical signals output to the signal wirings M1 to M3 and converts them from analog signals to digital image signals. The signal processing circuit 122 processes the converted digital image signal.

  In the first embodiment, the control unit 107 compares the dark output signal acquired from the flat detector 119 at a predetermined cycle with a reference value, and the light source 105 is turned on when (dark output signal) falls below the reference value. The light source 105 is controlled to emit light.

  In the second embodiment, the control unit 107 includes a timer 106 in which a time is stored and set in advance until the (dark output signal) of the flat detector 119 falls below a reference value after the flat detector 119 is irradiated by the light source 105. Have The control unit 107 controls the light source 105 so that the light source 105 emits light when the time set by the timer 106 elapses.

  In the third embodiment, the subject detection sensor 116 detects the presence of a subject and outputs a subject detection signal. The control unit 107 controls the irradiation of the light source 105 based on at least the signal from the flat detector 119 and the subject detection signal from the subject detection sensor 116.

  In the fourth embodiment, the position detection sensor 117 detects whether the flat detector 119 is disposed at a position where photographing can be performed and outputs a position detection signal. The control unit 107 controls irradiation of the light source 105 based on at least the signal from the flat detector 119 and the position detection signal from the position detection sensor 117.

  The first to fourth embodiments have been described above. However, as other embodiments, for the purpose of solving the problems of the present invention, when the combination of the first to fourth embodiments is performed, it is easily imagined. Even if it is applied, it is within the scope of the present invention. The above-described embodiments are merely examples of implementation in carrying out the present invention, and the technical scope of the present invention should not be construed as being limited thereto. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.

It is a schematic diagram which shows the structural example of the radiation imaging system by the 1st Embodiment of this invention. It is a circuit diagram which shows the schematic structural example of the radiation imaging device of this invention. 1 is a schematic configuration diagram of a radiation imaging apparatus and a radiation imaging system in a first embodiment of the present invention. It is a timing chart at the time of the object imaging | photography of the radiation imaging device and radiation imaging system in the 1st Embodiment of this invention. It is a schematic diagram which shows the structural example of the radiation imaging system by the 2nd Embodiment of this invention. It is a schematic block diagram of the radiation imaging device and radiation imaging system in the 2nd Embodiment of this invention. It is a timing chart at the time of subject photography of a radiation imaging device and a radiation imaging system in a 2nd embodiment. It is a schematic diagram which shows the structural example of the radiation imaging system by the 3rd Embodiment of this invention. It is a timing chart at the time of the object imaging | photography of the radiation imaging device and radiation imaging system in the 3rd Embodiment of this invention. It is a flowchart which shows the control method by 3rd Embodiment. It is a schematic diagram which shows the structural example of the radiation imaging system by the 4th Embodiment of this invention. It is a schematic block diagram of the radiation imaging device and radiation imaging system in the 4th Embodiment of this invention. It is a timing chart at the time of the object imaging | photography of the radiation imaging device and radiation imaging system in the 4th Embodiment of this invention. FIG. 14A is a timing chart of the radiation imaging system in the experiment, and FIG. 14B shows the time T1 from the irradiation of light not carrying image information to the start of the first image signal imaging operation and the first time. FIG. 14C is a graph showing a change in time T2 from the start of the reading operation of the image signal until a stable sensitivity is obtained, and FIG. 14C shows the first image after irradiation with light that does not carry image information. It is a graph which shows fluctuation | variation of time T1 and dark output value until it starts the imaging | photography operation | movement of a signal. It is a block diagram which shows the hardware structural example of the personal computer of 1st-4th embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Subject 102 Sensor board 103 Radiation source 104 Wavelength conversion body 105 Light source 106 Timer 107 Control unit 108 Reading circuit 110 Driving circuit 115 Shooting button 116 Subject detection sensor 117 Position detection sensor 119 Planar detector 121 A / D converter 122 Image processing circuit S11 to S33 Pixels T11 to T33 Switch elements D1 to D9 Conversion elements G1 to G3 Drive lines M1 to M3 Signal lines A1 to A3 Operational amplifier B Amplifiers Sw1 to Sw4 Reset switches CL1 to CL3 Sample hold capacitors Sr1 to Sr3 For sample hold Switch Sr4 multiplexer

Claims (11)

A flat panel detector including a conversion unit in which a plurality of pixels including conversion elements capable of converting radiation into charges are arranged in a matrix;
A light source capable of emitting light to the converter;
A controller for controlling the flat detector and the light source,
The control unit is characterized in that said light source when it is determined that the dark output signal from the pixel of the flat panel detector to the predetermined reference value we were to control the light source to emit light Radiation imaging device.   The radiation imaging apparatus according to claim 1, wherein the dark output signal is acquired from the flat detector at a predetermined cycle.   The control unit includes a timer in which a time from when the light is emitted to the flat detector by the light source until the dark output signal reaches a reference value is set in advance, and at the time set by the timer 3. The radiation imaging apparatus according to claim 2, wherein the light source is controlled so that the light source emits light when the light reaches the light source. And a subject detection sensor that detects the presence of the subject and outputs a subject detection signal.
The radiation imaging apparatus according to claim 2, wherein the control unit controls light emission of the light source based on at least the dark output signal and a subject detection signal from the subject detection sensor. Furthermore, it has a position detection sensor that detects whether the flat detector is arranged at a position where photographing can be performed and outputs a position detection signal,
The radiation imaging apparatus according to claim 2, wherein the control unit controls light emission of the light source based on at least the dark output signal and a position detection signal from the position detection sensor. The flat panel detector
A drive circuit for outputting an electric signal based on the electric charge converted by the conversion element to a signal wiring;
A readout circuit that reads out the electrical signal output to the signal wiring and converts it from an analog signal to a digital signal;
The radiation imaging apparatus according to claim 1, further comprising a processing circuit that processes the converted digital signal. The conversion element is:
A wavelength converter for converting radiation into light;
The radiation imaging apparatus according to claim 1, further comprising a photoelectric conversion element that converts the converted light into an electric charge.   The radiation imaging apparatus according to claim 7, wherein the photoelectric conversion element includes an amorphous semiconductor on an insulating substrate. A radiation imaging apparatus according to claim 1;
A radiation imaging system comprising: a radiation source for irradiating radiation. An input step of inputting a dark output signal from a pixel of a flat panel detector including a conversion unit in which a plurality of pixels including a conversion element capable of converting radiation into electric charge are arranged in a matrix;
Control step the control unit, for controlling the light source so if it is determined that the dark output signal us was a preset reference value, for irradiating light to said converter for controlling the flat panel detector and the light source A control method for a radiation imaging apparatus. An input step of inputting a dark output signal from a pixel of a flat panel detector including a conversion unit in which a plurality of pixels including a conversion element capable of converting radiation into electric charge are arranged in a matrix;
Control unit for controlling the flat panel detector and the light source, and a control step of controlling the light source to irradiate light to the conversion unit when it is determined that the dark output signal us was the preset reference value A program that causes a computer to execute.

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