WO2017006543A1

WO2017006543A1 - Radiation imaging apparatus, radiation imaging system, and method using radiation imaging apparatus

Info

Publication number: WO2017006543A1
Application number: PCT/JP2016/003120
Authority: WO
Inventors: Eriko Sato; Toshio Kameshima; Hideyuki Okada
Original assignee: Canon Kabushiki Kaisha
Priority date: 2015-07-09
Filing date: 2016-06-29
Publication date: 2017-01-12
Also published as: JP2017018283A; JP6552306B2

Abstract

A radiation imaging apparatus includes a pixel array, an output unit, a calculating unit, and a controller. The pixel array includes a plurality of pixels for outputting an image signal according to radiation emitted from a radiation generating apparatus. The output unit outputs a signal for calculating the irradiation dose of the radiation emitted to the pixel array. The calculating unit calculates an error due to a trailing edge waveform of data on the basis of a leading edge waveform of the data. The data indicates the waveform of the signal that is output from the output unit. The controller controls a timing at which a control signal for requesting the radiation generating apparatus to stop the emission of the radiation is output, on the basis of the error calculated by the calculating unit.

Description

RADIATION IMAGING APPARATUS, RADIATION IMAGING SYSTEM, AND METHOD USING RADIATION IMAGING APPARATUS

The present invention relates to a radiation imaging apparatus, a radiation imaging system, and a method using the radiation imaging apparatus.

Currently, radiation imaging apparatuses using flat panel detectors (hereinafter abbreviated as FRDs) formed of semiconductor material are being widely used as imaging apparatuses used in medical imaging diagnostics or nondestructive testing using radiation. For example, in medical imaging diagnostics, such radiation imaging apparatuses are used as digital imaging apparatuses for still-image capture such as radiography or for movie photographing such as fluoroscopy.

Some radiation imaging apparatuses monitor the irradiation dose of radiation and stop emission of the radiation when the irradiation dose reaches a target value (for example, outputs, to a radiation source, a signal for stopping emission of the radiation). This operation is called automatic exposure control (AEC), and, for example, enables excess emission of radiation to be prevented.

An example of such a radiation imaging apparatus is a radiation imaging apparatus which is disclosed in PTL 1 and in which a detector outputting an image signal according to radiation includes detection pixels for detecting the irradiation dose of the radiation. In PTL 1, a radiation detecting signal indicating that the irradiation dose of radiation is equal to or more than a predetermined value is generated on the basis of the signals from the detection pixels, and a timing of stopping emission of radiation emitted from a radiation source is controlled on the basis of the generated radiation detecting signal.

However, the technique disclosed in PTL 1 has an issue of accuracy of detection of an irradiation dose of radiation, and has an issue of accuracy of control of a radiation source based on the detection of an irradiation dose of radiation. Radiation emitted from a radiation source may fail to be stopped at once even when a stop instruction is received. In this case, a component for a delay in stopping radiation in response to a stop instruction may cause the actual irradiation dose of radiation emitted to the radiation imaging apparatus to be larger than the irradiation dose of radiation which is obtained at a timing at which the radiation detecting signal is generated.

Japanese Patent Laid-Open No. 2014-071034

The present invention provides a radiation imaging apparatus which enables an irradiation dose of radiation to be detected with higher accuracy. A radiation imaging apparatus includes a pixel array, an output unit, a calculating unit, and a controller. The pixel array includes a plurality of pixels for outputting an image signal according to radiation emitted from a radiation generating apparatus. The output unit outputs a signal for calculating the irradiation dose of the radiation emitted to the pixel array. The calculating unit calculates an error due to a trailing edge waveform of data on the basis of a leading edge waveform of the data. The data indicates the waveform of the signal that is output from the output unit. The controller controls a timing at which a control signal for requesting the radiation generating apparatus to stop the emission of the radiation is output, on the basis of the error calculated by the calculating unit.

Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

Fig. 1 is a schematic block diagram illustrating a radiation imaging system. Fig. 2A is a schematic equivalent circuit diagram for describing a detector. Fig. 2B is a schematic sectional view of a pixel included in a pixel array in the detector. Fig. 3 is a timing chart for describing operations performed by the detector. Fig. 4A illustrates time-change characteristics indicating a change to output time in radiation emitted from a radiation generating apparatus. Fig. 4B illustrates time-change characteristics of a signal that is output from dose detecting pixels. Fig. 5 includes (a) time-change characteristics of a signal which is output from the dose detecting pixels, and (b) time-change characteristics of the integrated value of the signal that is output from the dose detecting pixels. Fig. 6 is a flowchart for describing a process of calculating a dose of radiation. Fig. 7 includes (a) time-change characteristics of a signal that is output from the dose detecting pixels, and (b) time-change characteristics of the integrated value of the signal that is output from the dose detecting pixels.

Description of Embodiment

An embodiment of the present invention will be described below in detail with reference to the drawings. Typically, radiation may be X-rays, or may be α-rays, β-rays, or γ-rays.

A radiation imaging system will be described by using Fig. 1. Fig. 1 is a schematic block diagram illustrating the radiation imaging system.

The radiation imaging system may include an imaging apparatus 100, a control computer 109, a radiation control apparatus 110, a radiation generating apparatus 111, and a display unit 114. The imaging apparatus 100 may include a detector 104, a signal processor 105, a controller 106, and a communication unit 107. The detector 104 may include a pixel array 101 which includes multiple pixels converting radiation or light into electric signals, a driving circuit 102 which drives the pixel array 101, and a reading circuit 103 which outputs the electric signals from the driven pixel array 101 as an image signal. An example of the detector 104 will be described below in detail by using Figs. 2A and 2B. The signal processor 105 may include a calculating unit 116 for calculating the irradiation dose of radiation emitted to the detector 104. The control computer 109 may be provided with a communication unit 108 and a console 115. The radiation generating apparatus 111 may include a radiation source 112 and a radiation field narrowing mechanism 113.

The control computer 109 provides control signals to the imaging apparatus 100 and the radiation control apparatus 110 on the basis of photographing information that is input from a photographer (not illustrated) via the console 115 of the control computer 109. The radiation control apparatus 110 receiving a control signal from the control computer 109 controls an operation of emitting radiation from the radiation source 112 of the radiation generating apparatus 111 and an operation performed by the radiation field narrowing mechanism 113. The controller 106 of the imaging apparatus 100 which receives a control signal from the control computer 109 controls the units of the imaging apparatus 100. In accordance with radiation emitted from the radiation generating apparatus 111 controlled by the radiation control apparatus 110, the detector 104 of the imaging apparatus 100 outputs an image signal according to the radiation. The image signal that is output is subjected to image processing such as offset correction by the signal processor 105. Then, the resulting image signal is transmitted via the communication unit 107 and the communication unit 108 to the control computer 109. Known wireless or wired communication may be applied to the communication unit 107 and the communication unit 108. After being subjected to necessary image processing by the control computer 109, the transmitted image signal may be displayed on the display unit 114.

An example of the detector 104 will be described by using Figs. 2A and 2B. Fig. 2A is a schematic equivalent circuit diagram for describing the detector 104, and Fig. 2B is a schematic sectional view of a pixel included in the pixel array 101 of the detector 104. For the sake of simplicity of description, Fig. 2A illustrates the detector 104 having m × n pixels. However, an actual imaging apparatus has pixels more than these. For example, a 17-inch imaging apparatus has pixels with about 2800 rows and about 2800 columns.

The pixel array 101 has multiple pixels arranged in a matrix. Each of the pixels has a conversion device 201 that converts radiation to an electric signal, and a switching element 202 that outputs the electric signal. In the present embodiment, as illustrated in Fig. 2B, an indirect conversion device in which a wavelength converter 223 converting radiation to light is combined with a photoelectric conversion device 201' converting light into electric charge may be used as the conversion device. The wavelength converter 223 may be disposed above the photoelectric conversion device 201' with an interlayer insulating layer 222 interposed between the wavelength converter 223 and the photoelectric conversion device 201'. A PIN photodiode which is disposed on an insulating substrate such as a glass substrate and for which the main material is amorphous silicon is used as the photoelectric conversion device 201'. The photoelectric conversion device 201' may include an individual electrode 217, an n-type impurity semiconductor layer 218, an intrinsic semiconductor layer 219, a p-type impurity semiconductor layer 220, and a counter electrode 221. A direct conversion device which directly converts radiation into electric charge may be used as the conversion device. A transistor having a control terminal and two main terminals is desirably used as the switching element 202. In the present embodiment, a thin-film transistor (TFT) is used as the switching element 202. As illustrated in Fig. 2B, a TFT which is disposed on an insulating substrate such as a glass substrate and for which the main material is amorphous silicon is used as the switching element. The switching element 202 may include a gate electrode 211 that may serve as the control terminal, a gate insulating layer 212, an intrinsic semiconductor layer 213, an n-type impurity semiconductor layer 214, and a source or drain electrode 215 which serves as the two main terminals. The individual electrode 217 which is one of the electrodes of the conversion device 201 may be electrically connected to one of the two main terminals of the switching element 202 through a through hole of an interlayer insulating layer 216. The other electrode of the conversion device 201 is electrically connected to a bias power supply 116 via a common bias wiring line Bs. The other terminal of the two main terminals of the switching element 202 may be electrically connected to the reading circuit 103 via a corresponding one of signal wiring lines Sig1 to Sign.

Multiple pixels in the pixel array 101 according to the present embodiment include photographing pixels P1 which output signals for generating an image signal according to radiation, and dose detecting pixels P2 which output signals for calculating the irradiation dose of radiation emitted to the pixel array 101. The signals which are output by the dose detecting pixels P2 may be used as signals for generating an image signal. The control terminals of the switching elements 202 of the photographing pixels P1 may be electrically connected to a driving circuit 102a which is used for photographing and which is included in the driving circuit 102, via driving wiring lines G1 to Gm for photographing. The driving circuit 102a for photographing is used to drive the photographing pixels P1. In contrast, the control terminals of the switching elements 202 of the dose detecting pixels P2 may be electrically connected to a driving circuit 102b which is used for dose detection and which is included in the driving circuit 102, via driving wiring lines G1' to Gm' for detection. The driving circuit 102b for dose detection is used to drive the dose detecting pixels P2. The driving circuit 102a for photographing and the driving circuit 102b for dose detection may be independently or synchronously operated by using control signals which may be received by the respective driving circuits.

The reading circuit 103 is used to read electric signals which are output in parallel from the pixel array 101. In the reading circuit 103, amplifying circuits 203 which amplify electric signals which are output in parallel from the pixel array 101 are provided for the respective signal wiring lines. Each of the amplifying circuits 203 includes an integrating amplifier 207 which amplifies an output electric signal, a variable amplifier 204 which amplifies the electric signal from the integrating amplifier 207, a sample and hold circuit 205 which samples and holds the amplified electric signal, and a buffer amplifier 206. The integrating amplifier 207 includes an operational amplifier which amplifies and outputs the read electric signal, an integral capacity, and a reset switch. In the integrating amplifier 207, the amplification factor may be changed by changing the integral capacity value. The inverting input terminal of the operational amplifier receives the output electric signal; the non-inverting input terminal receives a reference voltage Vref from a reference power supply 107b; and an amplified electric signal is output from the output terminal. The integral capacity is disposed between the inverting input terminal and the output terminal of the operational amplifier. The sample and hold circuit 205 which is provided for a corresponding one of the amplifying circuits includes a sampling switch and a sampling capacity. The reading circuit 103 includes a multiplexer 208 which sequentially outputs electric signals which are read in parallel from the amplifying circuits 203, as a serial image signal, and a buffer amplifier 209 which performs impedance conversion on the image signal and which outputs the resulting signal. An analog image signal Vout which is output from the buffer amplifier 209 is converted into a digital image signal ADOUT by an analog-to-digital (A/D) converter 210, and the resulting signal is output to the signal processor 105 illustrated in Fig. 1. A power supply unit (not illustrated) includes the reference power supply 107b for the amplifying circuits 203, and the bias power supply 116. The reference power supply 107b supplies the reference voltage Vref to the non-inverting input terminal of each operational amplifier. The bias power supply 116 supplies, as a common voltage, a bias voltage Vs to the other electrode of each conversion device via the bias wiring line Bs. This enables the conversion device to convert radiation into electric charge.

The driving circuit 102a for photographing outputs driving signals to the driving wiring lines G1 to Gm in accordance with control signals (D-CLK, OE, and DIO) received from the controller 106 illustrated in Fig. 1. Each of the driving signal has a conducting voltage for turning the switching element 202 to the conductive state, and a non-conducting voltage for turning the switching element 202 to the non- conductive state. The driving circuit 102b for detection outputs driving signals to each of the driving wiring lines G1' to Gm' in accordance with control signals (D-CLK', OE', and DIO') received from the controller 106. Each of the driving signal has the conducting voltage and the non-conducting voltage. Thus, the driving circuit 102 drives the pixel array 101. The control signals D-CLK and D-CLK' are shift clocks of shift registers used as driving circuits. The control signals DIO and DIO' are pulses transferred by the shift registers. The control signals OE and OE' are signals for controlling the output ends of the shift registers. As described above, the required time and the scanning direction of the driving are set. The controller 106 provides a control signal RC, a control signal SH, and a control signal CLK for the reading circuit 103, thereby controlling operations of the components of the reading circuit 103. The control signal RC is used to control operations of the reset switches of the integrating amplifiers; the control signal SH, operations of the sample and hold circuits 205; the control signal CLK, operations of the multiplexer 208; and the control signal ADCLK, operations of the A/D converter 210. In the present embodiment, an output unit provided by the present invention includes the dose detecting pixels P2, the driving wiring lines G1' to Gm' for detection, the driving circuit 102b for detection, and the reading circuit 103, and outputs a signal for calculating the irradiation dose of radiation emitted to the pixel array 101.

An automatic exposure control (AEC) operation in the present embodiment will be described by using Fig. 3. Fig. 3 is a timing chart for describing operations performed by the detector 104. Fig. 3 illustrates an example of the pixel array 101 with three rows and three columns (m = 3 and n = 3). Digital signals Vg1 to Vg3 are supplied to the driving wiring lines G1 to G3 for photographing, and Driving signals Vg1' to Vg3' are supplied to the driving wiring lines G1' to G3' for detection.

At t11, when the bias voltage Vs is supplied to the conversion devices 201, the detector 104 starts an idling operation. The idling operation is an operation for decreasing dark current which may occur in the conversion devices 201, by repeatedly performing an initialization operation in which the switching elements 202 of the pixels are sequentially turned to the conductive state line by line. In the idling operation, during a period (t11 to t12) until time t12 at which a signal (irradiation signal) for transmitting notification about start of emission of radiation is detected, the controller 106 controls the driving circuit 102 so that the initialization operation is repeatedly performed. In this period, in the case where an image signal does not need to be output, the controller 106 may control the reading circuit 103 so that generation of heat and power consumption in the reading circuit 103 are suppressed. At that time, it is desirable that the reset switches of the integrating amplifiers 207 be turned to the conductive state, and that drifting of output due to input offset current in the integrating amplifiers 207 be suppressed.

At time t12, when an irradiation signal is detected, the supply of the conducting voltage which is performed by the driving circuit 102a for photographing is stopped, and the switching elements 202 of the photographing pixels P1 remain in the non-conductive state. This operation is called an accumulating operation. During the period (accumulation period) in which the accumulating operation is performed, when the detector 104 is irradiated with radiation, electric signals according to the emitted radiation may be accumulated in the photographing pixels P1. In contrast, the driving circuit 102b for detection sequentially supplies the conducting voltage line by line, whereby signals of the dose detecting pixels P2 are sequentially output. At that time, the controller 106 controls the reading circuit 103 so that the reading circuit 103 outputs a signal obtained to calculate the irradiation dose of radiation, on the basis of the received signals. In the present embodiment, during a period from t12 to t13, an offset reading operation for obtaining signals according to offset components of the dose detecting pixels P2 is performed. Signals which are output in the offset reading operation may be used in offset correction of signals that are output from the dose detecting pixel P2. During a period from t13 to t14, the driving circuit 102b for detection sequentially supplies the conducting voltage to the switching elements 202 of the dose detecting pixels P2 line by line, whereby a detection-signal reading operation in which signals of the dose detecting pixels P2 are sequentially read line by line is performed. The signals that are output from the dose detecting pixels P2 are output via the reading circuit 103, and may be used as a signal obtained to calculate the irradiation dose of radiation. For example, by integrating the signal, the calculating unit 116 may calculate the irradiation dose of radiation emitted to the detector 104. The signal processor 105 determines whether or not an appropriate irradiation dose is obtained, on the basis of the irradiation dose calculated by the calculating unit 116. The controller 106 controls the detector 104 and the signal processor 105 so that the detection-signal reading operation and the calculation are repeatedly performed until it is determined that the appropriate irradiation dose is obtained. When the signal processor 105 determines that the appropriate irradiation dose is obtained, the controller 106 may output, via the control computer 109 to the radiation control apparatus 110, a control signal for exerting control so that the irradiation of radiation which is performed by the radiation generating apparatus 111 is stopped. The above-described determination will be described in detail below. The detection-signal reading operation, the calculation, and the determination are called an AEC operation. In this example, the calculating unit 116 may be included in the signal processor 105. The above-described determination may be performed by the calculating unit 116.

After the AEC operation, during a period from t14 to t15, a known method may be used to output, from the photographing pixels P1, signals used as an image signal according to radiation emitted during the accumulating operation, and may be used to output the image signal via the reading circuit 103 to the detector 104.

By using Figs. 4A and 4B, principles leading to the present invention will be described. Fig. 4A illustrates time-change characteristics indicating a change to output time in radiation emitted from the radiation generating apparatus 111. Fig. 4B illustrates time-change characteristics of a signal that is output from the dose detecting pixels P2. Herein, a change to output time is referred to as a waveform. The output may be the output of one dose detecting pixel P2, or may be the average of the outputs of the dose detecting pixels P2.

Ideally, it is desirable that radiation be emitted from the radiation generating apparatus 111 in a so-called rectangular waveform in which radiation instantaneously rises up when the irradiation is started, and instantaneously falls down in response to the end of the irradiation. However, as illustrated in Fig. 4A, various factors actually cause the rising up and the falling down not to be instantaneously made. In many cases, a certain degree of time is required until a desired output is obtained in the leading edge and the trailing edge of radiation, and a delay occurs. Such a delay may differ depending on a radiation generating apparatus. As illustrated in Fig. 4A, a delay time Ta in the leading edge of radiation a emitted from a certain radiation generating apparatus may be different from a delay time Tb in the leading edge of radiation b emitted from another radiation generating apparatus. The same is true for delay times Ta' and Tb' in the trailing edge. When such a delay occurs, for example, the delay Ta in the leading edge may be calculated by the calculating unit 116 during the AEC operation. However, for the trailing edge, if an irradiation dose is calculated on the basis of only a signal obtained by the calculating unit 116 during the AEC operation, the amount of radiation emitted to the detector 104 during the delay time Ta' in the trailing edge causes an error.

As a result of serious consideration, the inventor has found that the leading edge of a waveform of radiation has a correlation with the trailing edge. That is, the inventor has found that a more appropriate irradiation dose may be calculated in the following manner: a trailing edge waveform of data indicating a waveform of radiation is calculated on the basis of the leading edge waveform; a value corresponding to the error is calculated on the basis of the calculated trailing edge waveform; and the calculated value is used to calculate a more appropriate irradiation dose. Such calculation is performed by the calculating unit 116, enabling calculation of a more appropriate irradiation dose in which an error due to a delay time in the trailing edge is suppressed.

For example, when an indirect conversion device is used as the conversion device, conversion characteristics of the wavelength converter are desirably considered. As illustrate in Fig. 4B, even when the same radiation is emitted, time-change characteristics, such as start of emission of light and afterglow characteristics, may differ depending on the type of a wavelength converter. Fig. 4B illustrates time-change characteristics of thallium doped caesium iodide (CsI:Tl) and gadolinium oxysulfide (GOS) as typical examples of the wavelength converter. A delay time in the leading edge (start of emission of light) of CsI:Tl is represented by Tc; a delay time in the trailing edge (afterglow) of CsI:Tl is represented by Tc'; a delay time in the leading edge (start of emission of light) of GOS is represented by Tg; and a delay time in the trailing edge (afterglow) of GOS is represented by Tg'. Even when such delays occur, for example, the delay Tc in the leading edge may be calculated by the calculating unit 116 during the AEC operation. However, for the trailing edge, if an irradiation dose is calculated on the basis of only a signal obtained by the calculating unit 116 during the AEC operation, the amount of afterglow emitted to the detector 104 during the delay time Tc' in the trailing edge causes an error. Therefore, as a result of serious consideration, the inventor has found that the leading edge of the emission waveform of a wavelength converter has a correlation with the trailing edge. That is, in an indirect radiation imaging apparatus, a leading edge waveform of the output from a pixel includes a delay in the leading edge of radiation and a delay of emission of light of the wavelength converter. This is not limited to an indirect conversion device. For example, even in a direct conversion device, this may occur depending on the conversion characteristics of the conversion device. That is, the inventor has found that the leading edge in conversion characteristics of a conversion device has a correlation with the trailing edge.

Therefore, the inventor has found that an error due to a trailing edge waveform of data indicating a waveform of a signal that is output from the output unit may be calculated on the basis of the data indicating a leading edge waveform of the signal that is output from the output unit, and that the calculated error may be used to calculate a more appropriate irradiation dose. Such calculation is performed by the calculating unit 116, enabling calculation of a more appropriate irradiation dose in which an error in the irradiation dose is suppressed. In particular, this enables a radiation imaging apparatus using indirect conversion devices to calculate a more appropriate irradiation dose in which an error in the irradiation dose is suppressed and in which a delay time in the trailing edge of a wavelength converter is considered in addition to a delay time in the trailing edge of radiation. The irradiation dose thus calculated may be used as data, for example, for exposure dose management of an object. In addition, when the irradiation dose thus calculated is used in the AEC, the output timing for a control signal that is used to request the radiation generating apparatus 111 to stop emission of radiation and that is output from the controller 106 is adjusted. That is, the controller 106 controls a timing for outputting a control signal for requesting the radiation generating apparatus 111 to stop emission of radiation, on the basis of the calculated error.

By using Figs. 5A and 5B, a calculating method performed by the calculating unit 116 will be described. Fig. 5 includes (a) time-change characteristics which are characteristics of a signal that is output from the dose detecting pixels P2 and which are used to describe the calculating method performed by the calculating unit 116. Fig. 5 also includes (b) time-change characteristics of an integrated value of a signal that is output from the dose detecting pixels P2.

The waveform of radiation emitted to the pixel array 101 is ideally a rectangular wave y(t), and its integrated value Y(t) increases in proportion to time. When the waveform is an ideal rectangular wave, the calculating unit 116 calculates an integrated value obtained by integrating a signal that is output from the dose detecting pixels P2, and compares the integrated value with a threshold B that is an indicator of an adequate dose. When the integrated value reaches the threshold B, the calculating unit 116 determines that radiation emitted to the pixel array 101 reaches the adequate dose. On the basis of the determination, the controller 106 transmits an irradiation stopping signal to the radiation control apparatus 110, and causes the radiation generating apparatus 111 to stop emission of radiation which is made by the radiation source 112. When radiation emitted at time t0 forms an ideal rectangular wave, the integrated value calculated by the calculating unit 116 at time t2 is equal to a dose of emission to the pixel array 101. However, as illustrated in (a) in Fig. 5, a delay is actually present in the waveform of radiation emitted to the pixel array 101 as illustrated in the waveform x(t) of a signal that is output from the output unit. A delay causes the waveform of radiation emitted to the pixel array 101 to rise up during a period T₁ between time t0 to time t1, and to fall down during a period T₂ from time t3 to time t4. That is, as illustrated in (b) in Fig. 5, at time t3 at which it is determined that the integrated value exceeds the threshold B, even if the radiation generating apparatus 111 is instructed to stop emission of radiation, the component falling down between time t3 and time t4 is emitted to the pixel array 101. Therefore, radiation, the amount of which is more than the threshold B, is emitted.

When an error in an integrated value of radiation which may be emitted during the period T₂ is represented by S₂, S₂ may be obtained from the waveform for the leading edge period from t0 to t1 of a signal that is output from the output unit. This is because the leading edge waveform of a signal that is output from the output unit has a correlation with the trailing edge waveform. Therefore, an error due to the trailing edge waveform may be obtained from the difference from the ideal rectangular leading edge waveform. When the calculating unit 116 determines that radiation has risen up at time t1, the calculating unit 116 calculates the difference S₁ between the integrated value of the waveform of the ideal rectangular wave and that of the actual leading edge waveform of a signal that is output from the output unit, on the basis of the leading edge period T₁, the maximum value A of a signal that is output from the output unit, and the waveform x(t) of a signal that is output from the output unit at time t.

That is, an error S₂ which is an integrated value of radiation which may be emitted during a period T₂ is similar to the difference S₁ in the integrated value of the leading edge waveform. Therefore, assume that S₁ is nearly equal to S₂. The integrated value S₂ of radiation emitted during the period T₂ may be calculated on the basis of the leading edge waveform. To obtain a more correct correlation between the leading edge waveform and the trailing edge waveform, waveforms may be obtained in advance, and a coefficient K is obtained from the obtained waveforms as information about the difference between the leading edge and the trailing edge. Then, Expression (2) described below may be obtained. When S₁ = S₂, the coefficient K = 1.

By using Figs. 6, 7A, and 7B, the way in which the calculating unit 116 calculates the dose of radiation will be described. Fig. 6 is a flowchart for describing the process. Figs. 7A and 7B illustrate time-change characteristics which are characteristics of a signal and the integrated value of the signal that is output from the dose detecting pixels P2, and which are used to describe the way in which the calculating unit 116 calculates the irradiation dose.

As illustrated in Fig. 6, in step S601, when the controller 106 receives, from the control computer 109, a control signal for requesting irradiation, the calculating unit 116 starts monitoring the signal from the output unit (step S602). The calculating unit 116 uses Expression (1) to calculate the difference (error) S₁ between the integrated value of the ideal waveform and that of the actual leading edge waveform, from the signal from the output unit during the period T₁ (step S603). The calculating unit 116 uses Expression (2) to calculate the integrated value S₂ of radiation which may be emitted during the period T₂, from the calculated value S₁ (step S604), and monitors the calculated value S₂ (S605).

By using Figs. 7A and 7B, methods of calculating the irradiation dose which are performed in step S604 will be described. In the method illustrated in (a) in Fig. 7, the threshold B is changed to a corrected threshold B' on the basis of the calculated value S₂, whereby the calculating unit 116 calculates an irradiation dose in consideration of the calculated value S₂. In contrast, in the method illustrated in (b) in Fig. 7, the calculated value S₂ is added to the integrated value of a signal from the output unit, and a corrected integrated value Z(t) is obtained. In this example, the integrated value of a signal from the output unit is processed. The present invention is not limited to this. For example, signal intensity differences or a histogram of signals may be used.

Thus, the calculating unit 116 determines whether or not the irradiation dose calculated by the calculating unit 116 exceeds the threshold B or the corrected threshold B' (step 606). If the calculating unit 116 determines that the irradiation dose does not exceed the thresholds B and B' (NO), the monitoring is continuously performed. In contrast, if the calculating unit 116 determines that the irradiation dose exceeds the threshold B or B' (YES), the controller 106 outputs a control signal for requesting the radiation generating apparatus 111 to stop emission of radiation, to the radiation control apparatus 110 via the control computer 109 (step 607). After that, the calculation performed by the calculating unit 116 is ended, and the monitoring is ended (S608).

In the embodiment, the example in which the signal processor 105 includes the calculating unit 116, that is, in which the imaging apparatus 100 includes the calculating unit 116 is described. The present invention is not limited to this. For example, the calculating unit 116 may be included in the control computer 109. In this case, the radiation imaging apparatus provided by the present invention may correspond to a unit including the imaging apparatus 100 and the control computer 109. In contrast, when the imaging apparatus 100 includes the calculating unit 116 as in the embodiment, the radiation imaging apparatus provided by the present invention may correspond to the imaging apparatus 100. In addition, a computer included in the calculating unit 116 may execute programs, whereby the embodiment may be achieved. Further, a unit for supplying programs to a computer, for example, a computer-readable recording medium such as a compact disc-read-only memory (CD-ROM) in which the programs are recorded, or a transmission medium such as the Internet which transmits the programs, may be applied as an embodiment of the present invention. Furthermore, the programs may be applied as an embodiment of the present invention. The recording medium, the transmission medium, and the programs are included in the scope of the present invention. An invention using a combination that may be easily conceived from the embodiment of the present invention is included in the scope of the present invention.

Other Embodiments

Embodiment(s) of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a 'non-transitory computer-readable storage medium') to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD) (trade mark)), a flash memory device, a memory card, and the like.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2015-138110, filed July 9, 2015, which is hereby incorporated by reference herein in its entirety.

Claims

A radiation imaging apparatus comprising:
a pixel array configured to include a plurality of pixels for outputting an image signal according to radiation emitted from a radiation generating apparatus;
an output unit configured to output a signal for calculating the irradiation dose of the radiation emitted to the pixel array;
a calculating unit configured to calculate an error due to a trailing edge waveform of data on the basis of a leading edge waveform of the data, the data indicating a waveform of the signal that is output from the output unit; and
a controller configured to control a timing at which a control signal for requesting the radiation generating apparatus to stop the emission of the radiation is output, on the basis of the error calculated by the calculating unit.
The radiation imaging apparatus according to Claim 1,
wherein the calculating unit calculates the irradiation dose on the basis of the error.
The radiation imaging apparatus according to Claim 1 or 2,
wherein, in the calculation performed by the calculating unit, the error S₂ satisfies

where a waveform of the signal from the output unit during a period T₁ between time t0 and time t1 is represented by x(t), a maximum value of the signal from the output unit is represented by A, a difference between an integrated value of a waveform of an ideal rectangular wave and an integrated value of the actual leading edge waveform of the signal that is output from the output unit is represented by S₁, and a coefficient is represented by K.
The radiation imaging apparatus according to Claim 3,
wherein the calculating unit calculates the irradiation dose by adding the error to the signal from the output unit.
The radiation imaging apparatus according to Claim 3,
wherein the calculating unit calculates the irradiation dose by changing a threshold on the basis of the error, the threshold being used to determine whether or not the irradiation dose of the radiation emitted to the pixel array reaches an adequate irradiation dose on the basis of comparison with the signal from the output unit.
The radiation imaging apparatus according to any one of Claims 1 to 5,
wherein each of the plurality of pixels includes a conversion device and a switching element, the conversion device converting radiation into an electric signal, the switching element outputting the electric signal.
The radiation imaging apparatus according to Claim 6,
wherein the plurality of pixels include a photographing pixel and a dose detecting pixel, the photographing pixel outputting a signal used to generate the image signal according to the radiation, the dose detecting pixel outputting a signal used to calculate the irradiation dose of the radiation emitted to the pixel array.
The radiation imaging apparatus according to Claim 7, further comprising:
a driving circuit for photographing configured to drive the photographing pixel;
a driving circuit for dose detection configured to drive the dose detecting pixel; and
a reading circuit configured to read electric signals that are output in parallel from the pixel array,
wherein the output unit includes the dose detecting pixel, the driving circuit for dose detection, and the reading circuit.
A radiation imaging system comprising:
the radiation imaging apparatus according to any one of Claims 1 to 8; and
the radiation generating apparatus configured to emit radiation to the radiation imaging apparatus.
A method for, by using a radiation imaging apparatus, controlling stopping of emission of radiation, the radiation imaging apparatus including an output unit outputting a signal for calculating the irradiation dose of the radiation emitted to a pixel array, the pixel array including a plurality of pixels for outputting an image signal according to the radiation, the radiation being emitted from a radiation generating apparatus, the stopping being performed by the radiation generating apparatus, the method comprising:
by using an error, controlling a timing of outputting a control signal, the error occurring due to a trailing edge waveform of data and being calculated on the basis of a leading edge waveform of the data, the data indicating a waveform of the signal that is output from the output unit, the control signal being used to request the radiation generating apparatus to stop the emission of the radiation.
A radiation imaging apparatus comprising:
a pixel array configured to include a plurality of pixels for outputting an image signal according to radiation emitted from a radiation generating apparatus;
an output unit configured to output a signal for calculating the irradiation dose of the radiation emitted to the pixel array; and
a calculating unit configured to calculate the irradiation dose on the basis of the signal that is output from the output unit,
wherein the calculating unit calculates an error due to a trailing edge waveform of data on the basis of a leading edge waveform of the data, the data indicating a waveform of the signal that is output from the output unit, and calculates the irradiation dose on the basis of the calculated error.
A method for, by using a radiation imaging apparatus, calculating an irradiation dose, the radiation imaging apparatus including an output unit outputting a signal for calculating the irradiation dose, the irradiation dose being the dose of radiation emitted to a pixel array, the pixel array including a plurality of pixels for outputting an image signal according to the radiation, the radiation being emitted from a radiation generating apparatus, the method comprising:
calculating the irradiation dose by using a value calculated on the basis of a leading edge waveform of data indicating a waveform of the signal that is output from the output unit.