Patent Description:
Radiation imaging apparatuses having an automatic exposure control (AEC) function are known. Such a radiation imaging apparatus can measure a dose of radiation during emission, and based on a result of the measurement, the emission of radiation is terminated. For example, the radiation imaging apparatus monitors a dose of radiation by operating only pixels set for radiation detection at high speed during the emission of radiation.

Meanwhile, in X-ray imaging, scattered rays are generated when X-rays pass through an object. To remove the scattered rays, a grid is generally used. The grid has a structure in which an X-ray transmissive layer and an X-ray absorption layer each having a strip shape are alternately arranged, and the grid is disposed between the object and the imaging apparatus during image capturing.

Because of an overlap between the X-ray absorption layer of the grid and radiation detection pixels, some radiation detection pixels may detect a signal corresponding to an X-ray attenuated by the X-ray absorption layer. Depending on a pixel size, an arrangement of radiation detection pixels, and an array pitch of X-ray absorption layers of the grid, there may be a disproportionate influence on signals of the plurality of radiation detection pixels in a region of interest due to attenuation by the X-ray absorption layers of the grid. In this case, a discrepancy arises between an average dose of radiation in the region of interest and signals corresponding to a dose of radiation detected by the radiation detection pixels, which leads to deterioration of the accuracy of the automatic exposure control.

<CIT> discusses a radiation imaging apparatus in which periodicity in the arrangement of dose detection sensors and periodicity in the arrangement of radiation absorption portions of a grid are different from each other. This configuration is to suppress a disproportionate influence on the dose detection sensors due to dose attenuation by the grid even in a case where the positional relationship between the dose detection sensors and the grid changes. In the technique of <CIT>, however, there may be room for an improvement in the configuration to further decrease the disproportionate influence on the dose detection sensors due to the dose attenuation by the grid.

The present invention is directed to providing a technology for improving the accuracy of automatic exposure control, by reducing or suppressing a disproportionate influence on signals of a plurality of radiation detection pixels in a region of interest due to attenuation by an X-ray absorption layer of a grid.

According to a first aspect of the present invention, there is provided a radiation imaging apparatus as specified in claims <NUM> to <NUM>.

Exemplary embodiments of the present invention will be described below with reference to the attached drawings. Similar components are denoted by the same reference numerals through various exemplary embodiments, and the redundant descriptions will not be repeated. The exemplary embodiments can be modified and combined as appropriate.

<FIG> illustrates an example of a configuration of a radiation imaging apparatus <NUM> capable of performing radiography using a grid, according to a first exemplary embodiment of the present invention. The radiation imaging apparatus <NUM> has a plurality of pixels, which is arranged in an imaging region IR in a form of a plurality of rows and a plurality of columns, a plurality of driving lines <NUM>, and a plurality of signal lines <NUM>. The plurality of driving lines <NUM> is disposed to correspond to the plurality of rows of pixels, and each of the driving lines <NUM> corresponds to a different one of the pixel rows. The plurality of signal lines <NUM> is disposed to correspond to a plurality of columns of pixels, and each of the signal lines <NUM> corresponds to a different one of the pixel columns.

The plurality of pixels includes a plurality of imaging pixels <NUM>, which is used to acquire a radiation image, and one or more detection pixels <NUM> (hereinafter may also be referred to as the radiation detection pixels <NUM>), which is used to monitor a dose of radiation, and a pixel unit is formed of the imaging pixels <NUM> and the detection pixels <NUM>.

The imaging pixel <NUM> includes a conversion element <NUM> for converting radiation into an electrical signal and a switch element <NUM> for connecting the corresponding signal line <NUM> and the conversion element <NUM>. The detection pixel <NUM> includes a conversion element <NUM> for converting radiation into an electrical signal and a switch element <NUM> for connecting the corresponding signal line <NUM> and the conversion element <NUM>. The detection pixel <NUM> is disposed in a row and a column formed of the plurality of imaging pixels <NUM>. In <FIG> and subsequent figures, the conversion element <NUM> is not hatched and the conversion element <NUM> is hatched so as to be distinguishable between the imaging pixel <NUM> and the detection pixel <NUM>.

The conversion element <NUM> and the conversion element <NUM> can each be composed of a scintillator for converting radiation into light and a photoelectric conversion element for converting the light into an electrical signal. In general, the scintillator is formed in a sheet form covering the imaging region IR and shared by a plurality of pixels. Alternatively, the conversion element <NUM> and the conversion element <NUM> can each be configured of a conversion element that directly converts radiation into an electrical signal.

The switch element <NUM> and the switch element <NUM> can each include a thin-film transistor (TFT) in which an active region is formed of a semiconductor, such as an amorphous silicon or a polycrystalline silicon.

A first electrode of the conversion element <NUM> is connected to a first main electrode of the switch element <NUM>, and a second electrode of the conversion element <NUM> is connected to a bias line <NUM>. The bias line <NUM> extends in a column direction and is commonly connected to the second electrodes of the plurality of conversion elements <NUM> arranged in the column direction. The bias line <NUM> receives a bias voltage Vs from a power supply circuit <NUM>. Second main electrodes of the switch elements <NUM> of the one or more imaging pixels <NUM> included in one column are connected to the signal line <NUM>. Control electrodes of the switch elements <NUM> of the one or more imaging pixels <NUM> included in one row are connected to the driving line <NUM>.

The detection pixel <NUM> also has a pixel configuration similar to the configuration of the imaging pixel <NUM> and is connected to the corresponding driving line <NUM> and the corresponding signal line <NUM>. The imaging pixel <NUM> can be connected to the same signal line <NUM> as that of the detection pixel <NUM>.

A driving circuit <NUM> constituting a driving unit is configured to supply a driving signal to a driving target pixel, through each of the plurality of driving lines <NUM>, based on a control signal from a control unit <NUM>. In the present exemplary embodiment, the driving signal is a signal that turns on the switch element included in the driving target pixel. The switch element of each of the pixels is turned on by a signal at high level and turned off by a signal at low level. Thus, the signal at high level will be referred to as the driving signal. Supplying the driving signal to the pixel results in a state where signals accumulated in the conversion element of the pixel can be read out by a reading circuit <NUM>. Among the driving lines <NUM>, the driving line <NUM> connected to the detection pixel <NUM> will be referred to as a detection driving line <NUM>.

The reading circuit <NUM> is configured to read out signals from the plurality of pixels through the plurality of signal lines <NUM>. The reading circuit <NUM> includes a plurality of amplification units <NUM>, a multiplexer <NUM>, an analog-to-digital converter (hereinafter referred to as the A/D converter) <NUM>. Each of the plurality of signal lines <NUM> is connected to the corresponding amplification unit <NUM> among the plurality of amplification units <NUM> of the reading circuit <NUM>. The signal line <NUM> corresponds to the amplification unit <NUM> on a one-on-one basis. The multiplexer <NUM> selects the plurality of amplification units <NUM> in a predetermined order and supplies a signal from the selected amplification unit <NUM> to the A/D converter <NUM>. The A/D converter <NUM> converts the supplied signal into a digital signal and outputs the digital signal.

The signals read out from the imaging pixels <NUM> are supplied to a signal processing unit <NUM> and subjected to processing, such as calculation and storage, by the signal processing unit <NUM>. Specifically, the signal processing unit <NUM> includes a calculation unit <NUM> and a storage unit <NUM>, and the calculation unit <NUM> generates a radiation image based on the signals read out from the imaging pixels <NUM> and supplies the generated radiation image to the control unit <NUM>. The signals read out from the detection pixels <NUM> are supplied to the signal processing unit <NUM> and subjected to processing, such as calculation and storage, by the calculation unit <NUM>. Specifically, the signal processing unit <NUM> outputs information indicating emission of radiation to the radiation imaging apparatus <NUM>, based on the signals read out from the detection pixels <NUM>. For example, the signal processing unit <NUM> detects emission of radiation to the radiation imaging apparatus <NUM> and determines a dose and/or an integrated dose of radiation.

The control unit <NUM> controls the driving circuit <NUM> and the reading circuit <NUM>, based on information from the signal processing unit <NUM>. The control unit <NUM> controls, for example, a start and an end of exposure (accumulation of electric charges corresponding to emitted radiation in the imaging pixels <NUM>), based on the information from the signal processing unit <NUM>.

To determine a dose of radiation, the control unit <NUM> scans the detection driving line <NUM> by controlling the driving circuit <NUM>, so that only the signal of the detection pixel <NUM> can be read out. Next, the control unit <NUM> reads out signals of a column corresponding to the detection pixel <NUM> by controlling the reading circuit <NUM> and outputs the signals as information indicating the dose of radiation. Such operation makes it possible for the radiation imaging apparatus <NUM> to obtain emission information in the detection pixel <NUM> during emission of radiation.

<FIG> illustrates an example of a detailed circuit configuration of the amplification unit <NUM>. The amplification unit <NUM> includes a differential amplification circuit AMP and a sample hold circuit SH. The differential amplification circuit AMP amplifies a signal appearing on the signal line <NUM> and outputs the amplified signal. The control unit <NUM> can reset the potential of the signal line <NUM> by supplying a control signal φR to a switch element of the differential amplification circuit AMP. The output from the differential amplification circuit AMP can be held by the sample hold circuit SH. The control unit <NUM> causes the sample hold circuit SH to hold the signal by supplying a control signal φSH to a switch element of the sample hold circuit SH. The signal held by the sample hold circuit SH is read out by the multiplexer <NUM>.

An example of the structure of the pixel of the radiation imaging apparatus <NUM> will be described with reference to <FIG> and <FIG>. <FIG> is a plan view of a configuration of each of the imaging pixel <NUM> and the detection pixel <NUM> in the radiation imaging apparatus <NUM>. The plan view is equivalent to an orthographic projection on a plane parallel with the imaging region IR of the radiation imaging apparatus <NUM>.

<FIG> is a cross-sectional view of the imaging pixel <NUM> taken along a line A-A' in <FIG>. A cross sectional view of the detection pixel <NUM> is similar to the cross-sectional view of the imaging pixel <NUM>. The switch element <NUM> is disposed on a supporting substrate <NUM> of insulation, such as a glass substrate. The switch element <NUM> can be a TFT. An interlayer insulation layer <NUM> is disposed on the switch element <NUM>. The conversion element <NUM> is disposed on the interlayer insulation layer <NUM>. The conversion element <NUM> is a photoelectric conversion element that can convert light into an electrical signal. The conversion element <NUM> includes, for example, an electrode <NUM>, a PIN photodiode <NUM>, and an electrode <NUM>. Instead of the PIN-type photodiode, the conversion element <NUM> can be configured of a MIS-type sensor.

A protection film <NUM>, an interlayer insulation layer <NUM>, the bias line <NUM>, and a protection film <NUM> are disposed in this order on the conversion element <NUM>. A planarization film and a scintillator (neither is illustrated) are disposed on the protection film <NUM>. The electrode <NUM> is connected to the bias line <NUM> via a contact hole. As a material of the electrode <NUM>, indium tin oxide (ITO) having light transmission properties is used, and the electrode <NUM> can transmit light converted from radiation by the scintillator (not illustrated).

<FIG> illustrates an example of a configuration of a radiation imaging system <NUM> including the radiation imaging apparatus <NUM>. The radiation imaging system <NUM> includes the radiation imaging apparatus <NUM>, a radiation source <NUM>, a radiation source interface <NUM>, a communication interface <NUM>, a controller <NUM>, a grid <NUM>, and an object <NUM>.

The grid <NUM> is a sheet having a size close to the size of the radiation imaging apparatus <NUM> and is disposed between the object <NUM> and the radiation imaging apparatus <NUM>. The grid <NUM> is used to remove scattered rays that have passed through the object <NUM>. Preferably, the grid <NUM> is disposed immediately in front of the radiation imaging apparatus <NUM>.

A dose, an emission upper limit time (millisecond (ms)), a tube current (milliampere (mA)), a tube voltage (kilovolt (kV)), a region of interest (ROI) that is an area where radiation is to be monitored, and the like are input into the controller <NUM>. When an exposure switch provided on the radiation source <NUM> is operated, the controller <NUM> transmits a start request signal to the radiation imaging apparatus <NUM>. The start request signal is a signal that requests a start of emission of radiation. In response to receipt of the start request signal, the radiation imaging apparatus <NUM> starts preparation to receive radiation that will be emitted by the radiation source <NUM>. When ready, the radiation imaging apparatus <NUM> transmits a start enable signal to the radiation source interface <NUM> via the communication interface <NUM>. The start enable signal is a signal notifying that emission of radiation can be started. In response to receipt of the start enable signal, the radiation source interface <NUM> causes the radiation source <NUM> to start emission of radiation.

When a threshold for an integrated value of a dose of emitted radiation is reached, the radiation imaging apparatus <NUM> transmits an end request signal to the radiation source interface <NUM> via the communication interface <NUM>. The end request signal is a signal requesting an end of the emission of radiation. In response to receipt of the end request signal, the radiation source interface <NUM> causes the radiation source <NUM> to end the emission of radiation. The control unit <NUM> determines the threshold for the dose, based on an input value of dose, a radiation emission intensity, a communication delay between units, a processing delay, and the like. Even in a case where the end request signal is not received, the radiation source <NUM> stops the emission of radiation when the radiation emission time reaches the input emission upper limit time.

Upon stopping the emission of radiation, the radiation imaging apparatus <NUM> sequentially scans the driving lines <NUM> (the driving lines <NUM> except for the detection driving lines <NUM>) to which the imaging pixels <NUM> are connected and reads out an image signal of each of the imaging pixels <NUM> using the reading circuit <NUM>, whereby a radiation image is acquired. Electric charges accumulated in the detection pixel <NUM> are read out during the emission of radiation, but the signals from these pixels cannot be used to form a radiation image. Thus, the signal processing unit <NUM> of the radiation imaging apparatus <NUM> performs interpolation processing using the pixel values of the imaging pixels <NUM> around the detection pixels <NUM>, whereby the pixel values at the positions of these pixels are interpolated.

<FIG> illustrate a detection area <NUM> in the radiation imaging apparatus <NUM>. The detection area <NUM> is an area where a dose of radiation during image capturing is detected, and the plurality of radiation detection pixels <NUM> disposed in the detection area <NUM> detects the dose of radiation. While there are various methods for arranging a plurality of the detection areas <NUM>, a symmetrical arrangement about the center of the radiation imaging apparatus <NUM> makes it possible to use the detection areas <NUM> in the same way irrespective of the orientation of the radiation imaging apparatus <NUM>. The shape of the detection area <NUM> can be a quadrangle, such as a square and rectangle, or can be a circle or an oval. Further, the detection area <NUM> can have an arbitrary shape contoured to correspond to the shape of an object. In the AEC, a dose of radiation emitted to a detection area is detected by reading out outputs of a plurality of radiation detection pixels in the detection area during emission of radiation. If an output of imaging pixels in the detection area approximately corresponds to an irradiated dose and the output of imaging pixels in the detection area is approximately equal to an output of the radiation detection pixels read out during the emission, it can be determined that the dose during image capturing is accurately detected, which means that the AEC can be accurately performed. However, depending on a pixel size, an arrangement of the radiation detection pixels, and a grid density (grid pitch), there may be a disproportionate influence of attenuation on the output of the plurality of radiation detection pixels in a region of interest due to an X-ray absorption layer of a grid. In this case, a difference arises between the output of the imaging pixels in the detection area and the output of the radiation detection pixels read out during the emission, which leads to deterioration of the accuracy of the AEC. The plurality of radiation detection pixels <NUM> in the detection area <NUM> is arranged in the entire detection area <NUM>, and while there are various arrangement methods, an arrangement method that improves the accuracy of the AEC by reducing or suppressing the disproportionate influence of attenuation due to the X-ray absorption layer of the grid will be described with reference to <FIG>.

<FIG> illustrates a configuration of the grid <NUM>. The grid <NUM> includes a radiation transmissive layer (hereinafter referred to as the X-ray transmissive layer) <NUM> and a radiation absorption layer (hereinafter referred to as the X-ray absorption layer) <NUM> each having a strip shape which is elongated in a first direction (i.e. each strip substantially extends along the first direction), and the X-ray transmissive layer <NUM> and the X-ray absorption layer <NUM> are alternately arranged in a second direction which is orthogonal to the first direction. A material easily transmitting X-rays, such as aluminum, is used for the X-ray transmissive layer <NUM>, and a material absorbing X-rays, such as lead, is used for the X-ray absorption layer <NUM>. For example, a grid density D which is the number of the X-ray absorption layers <NUM> per unit length is <NUM>/centimeter (cm) to <NUM>/cm, and a grid pitch is <NUM> micrometers (µm) to about <NUM>. Depending on a grid density (grid pitch), a pixel pitch, and an arrangement of the radiation detection pixels in the second direction, there may be variations in overlap degrees between the radiation detection pixel and the X-ray absorption layer <NUM>, and consequently the influence of attenuation due to the X-ray absorption layer <NUM> varies. Further, depending on a degree of the influence on the output of the plurality of radiation detection pixels due to the attenuation by the X-ray absorption layer <NUM>, the accuracy of the AEC changes.

<FIG> and <FIG> each illustrate an arrangement of the radiation detection pixels <NUM> of the grid in the second direction. <FIG> illustrates an arrangement and a pixel output of the radiation detection pixels <NUM> in a case where the pixel pitch is <NUM>, and the grid density is <NUM>/cm (the grid pitch is <NUM>). The pixel output indicates a ratio of an output of each of the pixels to an average output of the pixels in the detection area. An output of each of the pixels is affected by a grid disposed in front of the radiation imaging apparatus. The influence of the grid on a pixel output varies depending on a pixel pitch and a grid density (grid pitch). For example, output O which is affected by a grid of the pixels arranged in the second direction of the grid is expressed by the following equation (<NUM>): <MAT> where D represents a grid density (number/cm), P represents a pixel pitch (millimeter (mm)), and a represents a coordinate (integer) representing a position.

While the maximum value of the amplitude of the output O depends on a modulation transfer function (MTF) corresponding to the grid density (number/mm), the maximum value is fixed to <NUM> in the present invention for simplicity of description. In the case of this combination, the pixel pitch is half of the grid pitch, and thus, as the output of the pixels arranged in the second direction, an output (output -<NUM>) obtained with X-ray blocked by the X-ray absorption layer and an output (output <NUM>) obtained with X-ray passed through the X-ray transmissive layer alternately appear in a cycle. For example, in a case where the radiation detection pixel is disposed at each of coordinates <NUM>, <NUM>, <NUM>, and so on, an average output of the plurality of radiation detection pixels is -<NUM> with respect to a detection area pixel average output. In this case, a radiation detection pixel average output is small compared to the detection area pixel average output, and thus the threshold is reached later than the timing at which the threshold is supposed to be reached, which results in excessive emission, and consequently the accuracy of the AEC is deteriorated. In contrast, in a case where the radiation detection pixel is disposed at each of coordinates <NUM>, <NUM>, <NUM>, and so on, the radiation detection pixel average output is <NUM>, which is large compared to the detection area pixel average output. Thus, the threshold is reached before the timing at which the threshold is supposed to be reached, which results in insufficient emission, and consequently the accuracy of the AEC is deteriorated. To address this issue, for example, for the radiation detection pixel having an output (output <NUM>) which is obtained with X-ray passed through the X-ray transmissive layer at the coordinate <NUM>, another radiation detection pixel is disposed at a position having an output (output -<NUM>) which is obtained with X-ray blocked in the X-ray absorption layer at the coordinate <NUM>. In this way, two detection pixels are disposed at different positions in the second direction to form a pair. Output signal values of the pair of the two radiation detection pixels are averaged, so that each other's grid influences are canceled, and the detection area pixel average output and the radiation detection pixel average output value become approximately equal, and thus the accuracy of the AEC can be improved by reducing or suppressing the influence of the grid. In other words, the output signal values of the pair of the detection pixels are offset by each other in terms of the influence of the attenuation by the grid and become approximately equal to a detection area pixel average value. Here, being approximately equal to the average value means that differences of about <NUM>% of the average value are included as an allowable range. The outputs of the radiation detection pixels can be used for the total value, instead of the average value.

<FIG> illustrates an arrangement and a pixel output of the radiation detection pixels <NUM> in a case where the pixel pitch is <NUM>, and the grid density is <NUM>/cm (the grid pitch is about <NUM>). In the case of this combination, the pixel pitch and the grid pitch are not integer multiples, and thus, different degrees of influences due to the grid periodically appear as the output of the pixels arranged in the second direction of the grid. Based on the periodicity of the grid influence, for example, for the radiation detection pixel at the coordinate <NUM>, the radiation detection pixel is disposed at the position of the coordinate <NUM>, so that the grid influence can be canceled by an average output of the pair of the two radiation detection pixels. The following equation (<NUM>) can express the position of a radiation detection pixel by which the grid influence can be canceled, for a certain radiation detection pixel, based on the periodicity of the grid influence which varies depending on the pixel pitch and the grid density: <MAT>.

In the case of the pixel pitch of <NUM> and the grid density of <NUM>/cm (the grid pitch of <NUM>) in <FIG>, k = <NUM> is established, and C = <NUM>, <NUM>, <NUM>, and so on is established when n = <NUM>, <NUM>, <NUM>, and so on. Thus, the position by which the grid influence can be canceled for the radiation detection pixel at the coordinate <NUM> is each of the coordinates <NUM>, <NUM>, <NUM>, and so on. In the case of the pixel pitch of <NUM> and the grid density of <NUM>/cm (the grid pitch of about <NUM>) in <FIG>, k = <NUM> is established, and C = <NUM>, <NUM>, <NUM>, and so on is established when n = <NUM>, <NUM>, <NUM>, and so on. Thus, the position by which the grid influence can be canceled for the radiation detection pixel at the coordinate <NUM> is each of the coordinates <NUM>, <NUM>, <NUM>, and so on. In this way, the arrangement of the radiation detection pixels can be determined in accordance with a grid density to be combined with the pixel pitch of the radiation imaging apparatus, based on the equation (<NUM>). The radiation detection pixels can be arranged by selecting n so that C becomes an integer, or can be disposed at positions each obtained by rounding off C in a case where C is not an integer. Further, the radiation detection pixel for readout can be selected so that the grid influence can be reduced or suppressed, by changing the detection driving line <NUM> for driving in image capturing, in accordance with the grid density to be combined with the pixel pitch. In this way, the arrangement of the pair of radiation detection pixels to reduce or suppress the grid influence is determined in accordance with the pixel pitch and the grid density with respect to the periodic grid influence, and thus the grid influence can be canceled even in a case where the output has changed because of a shift of the grid in the second direction. For example, in a case where the grid shifts in the second direction by one pixel in <FIG>, the output at the coordinates <NUM> and <NUM> in <FIG> becomes the output of the two radiation detection pixels. In this case as well, the grid influence can be canceled by averaging the output of the two radiation detection pixels. The pair of the two radiation detection pixels can similarly cancel the grid influence, with respect to any shift amount of the grid.

<FIG> illustrates a configuration of a second exemplary embodiment in which a plurality of pairs of radiation detection pixels <NUM> to reduce or suppress a grid influence is disposed in a detection area. <FIG> illustrates an arrangement and a pixel output of radiation detection pixels <NUM> in a case where a pixel pitch is <NUM> and a grid density is <NUM>/cm (a grid pitch is <NUM>). In <FIG>, a pair of radiation detection pixels <NUM> are disposed based on the equation (<NUM>), and a plurality of pairs of radiation detection pixels <NUM> is disposed at regular intervals. In a case where there is a plurality of pairs of radiation detection pixels <NUM> as well, the influence of the grid is canceled by each pair of radiation detection pixels <NUM> (coordinates <NUM> and <NUM>, coordinates <NUM> and <NUM>, and coordinates <NUM> and <NUM>), in accordance with the periodicity of the grid influence. Therefore, the grid influence on the output of the plurality of radiation detection pixels <NUM> in the detection area can be reduced or suppressed, whereby the accuracy of AEC can be improved.

<FIG> illustrates a configuration in which a plurality of pairs of radiation detection pixels <NUM> to reduce or suppress a grid influence is disposed in a detection area. <FIG> illustrates an arrangement and a pixel output of radiation detection pixels <NUM> in a case where a pixel pitch is <NUM> and a grid density is <NUM>/cm (a grid pitch is <NUM>). In <FIG>, a pair of radiation detection pixels <NUM> are disposed based on the equation (<NUM>), and a plurality of pairs of radiation detection pixels <NUM> is disposed at different intervals. In a case where pairs of radiation detection pixels <NUM> are disposed at irregular intervals, the influence of the grid is canceled by each pair of radiation detection pixels <NUM> (coordinates <NUM> and <NUM>, coordinates <NUM> and <NUM>, and coordinates <NUM> and <NUM>), in accordance with the periodicity of the grid influence. Therefore, the grid influence on the output of the plurality of radiation detection pixels <NUM> in the detection area can be reduced or suppressed, whereby the accuracy of AEC can be improved. The case where the pairs of radiation detection pixels <NUM> are disposed at irregular intervals means a case where pairs of detection pixels are aperiodically arranged.

An example in which the radiation imaging apparatus <NUM> is applied to a radiation detection system will be described below with reference to <FIG>. An X-ray <NUM> generated by an X-ray tube <NUM> that is a radiation source passes through a chest <NUM> of a patient or subject <NUM> and is incident on a radiation imaging apparatus <NUM> represented by the radiation imaging apparatus <NUM> described above. The incident X-ray includes information about the inside of the body of the subject <NUM>. The scintillator emits light in response to the incidence of the X-ray, and the photoelectric conversion element photoelectrically converts the light, whereby electrical information is obtained. The information is converted into digital information, and the digital information is subjected to image processing by an image processor <NUM> that is a signal processing unit. The processed information is displayed on a display <NUM> of a display unit in a control room, whereby the user can observe the image.

In addition, the information can be transferred to a remote location by a transmission processing unit using, for example a telephone line <NUM>, and the transferred information can be displayed on a display <NUM> of a display unit or saved into a recording unit, such as an optical disc, in an examination room at another place, which can allow a doctor to make diagnosis at the remote location. The information can also be recorded in a film <NUM> that is a recording medium recorded by a film processor <NUM> serving as a recording unit.

Claim 1:
A radiation imaging apparatus (<NUM>) for performing radiography using a grid in which a radiation transmissive layer and a radiation absorption layer each having a strip shape and extending in a first direction are alternately arranged in a second direction, the radiation imaging apparatus comprising:
pixel means including a plurality of imaging pixels (<NUM>) for acquiring a radiation image and a plurality of detection pixels (<NUM>) for detecting a dose of radiation that are disposed in an imaging region;
driving means (<NUM>) for driving the plurality of imaging pixels (<NUM>) and the plurality of detection pixels (<NUM>);
reading means (<NUM>) for reading out a signal from each of the plurality of imaging pixels (<NUM>) and the plurality of detection pixels (<NUM>); and
control means (<NUM>) for determining an amount of radiation being emitted to the radiation imaging apparatus,
wherein the plurality of detection pixels includes a first detection pixel and a second detection pixel that are in a pair in the second direction, an output signal value of the first detection pixel is larger than an average value of output signal values of the plurality of imaging pixels and the plurality of detection pixels, and an output signal value of the second detection pixel is smaller than the average value, characterized in that
a plurality of pairs of the first detection pixel and the second detection pixel is disposed in an aperiodic arrangement.