JP2021078049A - Radiation imaging device and radiation imaging system - Google Patents

Abstract

To provide a technology advantageous to more accurately detect the presence/absence of irradiation with radiation.SOLUTION: A radiation imaging device includes: a plurality of pixel groups and a plurality of bias sources, the respective pixel groups corresponding to the bias sources on one-to-one basis; a drive circuit; and a detection unit. The pixel groups are constituted by pixels that include a conversion element for converting radiation to electric charge and a switch element for connecting the conversion element to a signal line. The bias sources supply bias potential to conversion elements of the pixels via bias lines. The drive circuit controls switch elements of the pixels. The detection unit acquires first signal values representing current flowing through a bias line connected to a pixel group including a pixel including a switch element turned on by the drive circuit and second signal values representing current flowing through a bias line connected to a pixel group whose switch elements are in an off state so that at least some of timings at which the first signal values are sampled overlap with timings at which the second signal values are sampled; and, on the basis of the first signal values and the second signal values, determines the presence/absence of irradiation with radiation.SELECTED DRAWING: Figure 1

Description

The present invention relates to a radiation imaging device and a radiation imaging system.

In medical image diagnosis and non-destructive inspection, a radiation imaging device using a plane detector (FPD) made of a semiconductor material is widely used. Patent Document 1 utilizes the fact that when a radiation imaging device is irradiated with radiation, a current (bias current) flows through a bias line that supplies a bias potential to a pixel in order to synchronize with a radiation generator. A radiation imaging device that detects the presence or absence of irradiation is shown. Further, the radiation imaging apparatus of Patent Document 1 acquires the bias current when the switch element is in the conductive state as an effective value and the bias current when the switch element is in the non-conducting state as a noise value from the same pixel, and obtains the effective value. The presence or absence of radiation is detected based on the noise value.

Japanese Unexamined Patent Publication No. 2014-168203

A current may flow through the bias line other than the irradiation of radiation, such as an impact being applied to the radiation imaging device. If the current flowing due to noise is large, there is a possibility that it will be erroneously detected as having been irradiated even though it has not been irradiated. Patent Document 1 shows that the influence of noise can be reduced by detecting the presence or absence of radiation irradiation based on an effective value and a noise value. However, it may not be possible to deal with noise having a high frequency component that occurs when an impact is applied to the radiation imaging device.

An object of the present invention is to provide a technique advantageous for detecting the presence or absence of radiation irradiation with higher accuracy.

In view of the above problems, the radiation imaging device according to the embodiment of the present invention includes a plurality of pixel groups and a plurality of bias sources in which one pixel group and one bias source are respectively arranged, and a drive circuit. , A detection unit, and each of the plurality of pixel groups is composed of a plurality of pixels including a conversion element for converting radiation into electric charges and a switch element for connecting the conversion element to a signal line. Each of the bias sources supplies a bias potential to the pixel conversion element via an electrically independent bias line for each bias source, the drive circuit controls the switch element of the pixel, and the detection unit is a plurality of pixels. The first signal value representing the current flowing through the bias line connected to the pixel group including the pixel whose drive circuit has the switch element turned on, and the pixel group in which the switch element is off among the plurality of pixel groups are connected. The second signal value representing the current flowing through the bias line is acquired so that at least a part of the sampling timing overlaps, and the presence or absence of irradiation is determined based on the first signal value and the second signal value. It is characterized by making a judgment.

By the above means, a technique advantageous for detecting the presence or absence of radiation irradiation with higher accuracy is provided.

The figure which shows the structural example of the radiation imaging system using the radiation imaging apparatus which concerns on this invention. The figure which shows the structural example of the radiation imaging apparatus of FIG. The flow chart explaining the operation of the radiation imaging apparatus of FIG. The schematic diagram of the drive timing of the radiation imaging apparatus of FIG. The schematic diagram of the drive timing which detects the radiation of the radiation image pickup apparatus of FIG. It is a detailed view of the drive timing which detects the radiation of the radiation image pickup apparatus of FIG. The schematic diagram of the drive timing of the radiation imaging apparatus of FIG. The figure which shows the modification of the structure of the radiation imaging apparatus of FIG. The schematic diagram of the drive timing which detects the radiation of the radiation image pickup apparatus of FIG. The figure which shows the modification of the detailed diagram of the drive timing of FIG.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. The following embodiments do not limit the invention according to the claims. Although a plurality of features are described in the embodiment, not all of the plurality of features are essential to the invention, and the plurality of features may be arbitrarily combined. Further, in the attached drawings, the same or similar configurations are designated by the same reference numbers, and duplicate explanations are omitted.

Further, the radiation in the present invention includes beams having the same or higher energy, for example, X, in addition to α rays, β rays, γ rays, etc., which are beams produced by particles (including photons) emitted by radiation decay. It can also include lines, particle beams, cosmic rays, etc.

The radiation imaging apparatus according to the present embodiment will be described with reference to FIGS. 1 to 10. FIG. 1 is a diagram showing a configuration example of a radiation imaging system SYS using the radiation imaging device 100 in the present embodiment. The radiation imaging system SYS of the present embodiment includes a radiation imaging device 100, a control computer 120, a radiation generator 130, and a radiation control device 140.

The radiation generator 130 exposes the radiation imaging device 100 to radiation according to the control from the radiation control device 140. The control computer 120 can control the entire radiation imaging system SYS. Further, the control computer 120 acquires a radiation image generated by the radiation emitted from the radiation generator 130 to the radiation imaging device 100 via the subject.

The radiation imaging apparatus 100 includes a detection unit 110 including a pixel unit 101, a read circuit 102, a reference power supply 103, and a bias power supply unit 104, a power supply unit 105, a detection unit 106, and a control unit 107. A plurality of pixels for detecting radiation are arranged in the pixel unit 101 in a two-dimensional array. The read circuit 102 reads charge information from the pixel unit 101. The reference power supply 103 supplies a reference voltage to the read circuit 102. The bias power supply unit 104 supplies the bias potential to the pixel conversion element arranged in the pixel unit 101. The power supply unit 105 supplies electric power to each power source including the reference power supply 103 and the bias power supply unit 104. The detection unit 106 acquires current information from the bias power supply unit 104. More specifically, the detection unit 106 acquires information on the current flowing through the bias line for the bias power supply unit 104 to supply the bias potential to each pixel of the pixel unit 101 from the bias power supply unit 104. The detection unit 106 calculates the information of the current output from the bias power supply, and outputs the radiation information including the time variation of the intensity of the radiation incident on the pixel unit 101. As the detection unit 106, a digital signal processing circuit such as an FPGA, a DSP, or a processor can be used. Further, the detection unit 106 may be configured by using an analog circuit such as a sample hold circuit or an operational amplifier. Further, in the configuration shown in FIG. 1, the detection unit 106 is arranged in the radiation imaging device 100, but the control computer 120 may have the function of the detection unit 106. In this case, the radiation imaging device 100 shown in FIG. 1 and the portion of the control computer 120 that functions as the detection unit 106 are included, and can be said to be the “radiation imaging device” of the present embodiment. The detection unit 110 will be described in detail in the description of FIG. The control unit 107 controls the entire radiation imaging device 100, such as driving the radiation imaging device 100. The control unit 107 controls the detection unit 110 by a drive method transmitted from the control computer 120 according to a user setting or the like. Further, the driving method of the detection unit 110 may be changed by using the radiation information output by the detection unit 106.

FIG. 2 is an equivalent circuit diagram showing a configuration example of the detection unit 110 of the radiation imaging device 100. FIG. 2 shows a pixel portion 101 having pixel PIXs of 6 rows × 6 columns for the sake of simplicity of description. However, the pixel portion 101 of the actual radiation imaging device 100 may have more pixels, for example, a 17-inch radiation imaging device 100 may have a pixel PIX of about 2800 rows × about 2800 columns.

The pixel unit 101 is a two-dimensional detector having a plurality of pixels PIX arranged in a matrix. The pixel PIX includes a conversion element S (S11 to S66) that converts radiation into an electric charge, a switch element T (T11 to T66) that connects the conversion element S to a signal line Sigma and outputs an electric signal according to the electric charge. including. In the present embodiment, the conversion element S is an indirect type including a photoelectric conversion element and a wavelength converter that converts radiation into light in a wavelength band that can be detected by the photoelectric conversion element on the incident side of the radiation of the photoelectric conversion element. It is a conversion element. As a photoelectric conversion element that converts light into electric charges, a MIS-type photodiode that is arranged on an insulating substrate such as a glass substrate and whose main material is a semiconductor material such as amorphous silicon may be used. Further, as the photoelectric conversion element, not only a MIS type photodiode but also a PIN type photodiode, for example, may be used. Further, as the conversion element S, a direct type conversion element that directly converts radiation into electric charge may be used. A transistor having a control terminal and two main terminals may be used for the switch element T. In this embodiment, a thin film transistor (TFT) is used as the switch element T.

One electrode of the conversion element S is electrically connected to one of the two main terminals of the switch element T, and the other electrode of the conversion element S is connected to the bias power supply unit 104 via the bias wire Bs. It is electrically connected to the bias source 203. The control terminals of the plurality of switch elements T arranged in the row direction (horizontal direction in the drawing), for example, the switch elements T11, 13 and 15, are electrically connected in common to the drive line Vg1-1 in the first row. , A drive signal for controlling the conduction state of the switch element T is given from the drive circuit 214 via the drive line Vg. The drive circuit 214 controls the switch element T of the pixel PIX via a plurality of drive lines Vg arranged along the row direction. In a plurality of switch elements T arranged along the column direction (vertical direction in the drawing), for example, switch elements T11 to T61, the other main terminal of the two main terminals is charged with the signal line Sigma1 in the first row. While the switch element T is in a conductive state, an electric signal corresponding to the electric charge of the conversion element S is output to the read circuit 102 via the signal line. The signal lines Sigma1 to Sigma6 can transmit the electric signals output from the plurality of pixels PIX to the read circuit 102 in parallel for each row.

The read circuit 102 is provided with an amplifier circuit 206 for amplifying an electric signal output in parallel from the pixel unit 101 corresponding to each signal line. The amplifier circuit 206 includes an integrator amplifier 205 that amplifies the output electric signal, a variable amplifier 204 that amplifies the electric signal output from the integrator amplifier 205, a sample hold circuit 207 that samples and holds the amplified electric signal, and a buffer amplifier. 209 is included. The integrating amplifier 205 includes an operational amplifier that amplifies and outputs an electric signal read from the pixel PIX, an integrating capacitance, and a reset switch. The integrating amplifier 205 can change the amplification factor by changing the value of the integrating capacitance. The electric signal output from the pixel PIX is input to the inverting input terminal of the integrating amplifier 205, the reference potential Vref is input from the reference power supply 103 to the forward rotation input terminal, and the amplified electric signal is output from the output terminal. To. Further, the integrated capacitance is arranged between the inverting input terminal and the output terminal of the operational amplifier. The sample hold circuit 207 is provided for each amplifier circuit 206, and is composed of a sampling switch and a sampling capacitance. Further, the reading circuit 102 includes a multiplexer 208 that sequentially outputs electric signals read in parallel from the amplifier circuit 206 and outputs them as an image signal of a series signal. The image signal Vout, which is an analog electric signal output from the buffer amplifier 209, is converted into digital image data by the A / D converter 210 and output to the control computer 120 shown in FIG.

The power supply unit 105 (omitted in FIG. 2) transforms the power from the battery and the outside into each power supply, and supplies power to the reference power supply 103, the bias power supply unit 104, and the like of the amplifier circuit shown in FIG. The reference power supply 103 supplies a reference voltage Vref to the forward rotation input terminal of the operational amplifier. The bias source 203 of the bias power supply unit 104 commonly supplies the bias potential Vs to the other electrode of the two electrodes of the conversion element S via the bias line Bs. Further, the bias source 203 of the bias power supply unit 104 outputs current information including time variation of the amount of current flowing through the bias line Bs to the detection unit 106. In the present embodiment, as a circuit for outputting current information, the bias source 203 includes a current-voltage conversion circuit 215 including an operational amplifier and a resistor, but is not limited to this configuration. For example, the bias source 203 may include a current-voltage conversion circuit using a shunt resistor. Further, the bias source 203 may further include an A / D conversion circuit that converts the output voltage of the current-voltage conversion circuit into a digital value, and may output current information as a digital value. Further, the bias source 203 may output an appropriate physical quantity corresponding to the amount of current supplied (flowed) to the bias line Bs to the detection unit 106.

The drive circuit 214 has a conduction voltage Vcom and non-conduction (off) that bring the switch element T into a conduction (on) state in response to the control signals D-CLK, OE, and DIO input from the control unit 107 shown in FIG. A drive signal including the non-conducting voltage Vss to be in the state is output to each drive line. As a result, the drive circuit 214 controls the on / off of the switch element T and drives the pixel unit 101. The control signal D-CLK is a shift clock of the shift register used as the drive circuit 214. The control signal DIO is a pulse transferred by the shift register, and the control signal OE is a signal that controls the output end of the shift register. The required driving time and scanning direction are set by the above control signals.

Further, the control unit 107 controls the operation of each component of the read circuit 102 by giving the control signals RC, SH, and CLK to the read circuit 102. Here, the control signal RC controls the operation of the reset switch of the integrating amplifier 205. The control signal SH controls the operation of the sample hold circuit 207. The control signal CLK controls the operation of the multiplexer 208.

FIG. 3 is a flow chart showing an operation example of the radiation imaging device 100 according to the present embodiment. As described above, each component of the radiation imaging apparatus 100 is controlled by the control unit 107. When the user sets the imaging conditions of the radiation image, first, in S301, the detection unit 106 acquires the radiation information from the information of the current flowing through the bias line Bs acquired from the bias source 203, and obtains the radiation information. Determine the start of irradiation. To determine the start of radiation irradiation, the amount of charge accumulated in the conversion element S of PIX is obtained from the radiation information, and when the intensity of radiation obtained from the amount of charge exceeds a predetermined threshold value, radiation is emitted. A method of determining that the irradiation of the above has been started may be used. When the detection unit 106 determines that the irradiation of radiation has not been started (NO in S301), the radiation imaging device 100 transitions to S302, and the control unit 107 tells the drive circuit 214 that the pixel PIX is converted by a dark current. A reset drive (hereinafter, may be referred to as blank reading) for removing the charge accumulated in S is performed. Blank reading is performed in order from the first line (0th line) to the last line (Y-1st line), and when the last line is reached, the process returns to the first line.

When the detection unit 106 determines that the irradiation of radiation has started (YES in S301), the radiation imaging device 100 transitions to S303, and the control unit 107 determines the end of irradiation of radiation. As a determination of the end of the irradiation of radiation, a method of determining that the irradiation of radiation has been completed may be used when a predetermined time has elapsed after the start of irradiation of radiation is determined. Further, the control unit 107 acquires the amount of electric charge accumulated in the conversion element S of the PIX from the radiation information acquired by the detection unit 106, and the radiation intensity obtained from the amount of electric charge is less than a predetermined threshold value. The end of radiation may be determined. When the end of radiation irradiation is not determined (NO in S303), in S304, the drive circuit 214 turns off the switch element T of the pixel PIX for acquiring a radiation image, and is converted from radiation. The drive for accumulating the signal (hereinafter, may be referred to as accumulating) is performed. When the end of radiation irradiation is determined (YES in S303), the radiation imaging device 100 transitions to S305, and the drive circuit 214 and the read circuit 102 are driven to read out the electric charge generated in the conversion element S of the pixel PIX (hereinafter,). , May be referred to as book reading.) The main reading can be performed in order from the first line to the last line of the pixel PIX arranged in the pixel unit 101. When the main reading reaches the last line, a series of shooting operations ends.

FIG. 4 is a schematic view of the drive timing of the radiation imaging device 100. The control unit 107 drives the switch element S to conduct in order from the first row (0th row) to the last row (Y-1st row) of the pixel unit 101 until the irradiation of radiation is started (blank reading). ) Is repeated in the drive circuit 214. If the blank reading reaches the last line until the irradiation of radiation is started, the blank reading is repeated by returning to the first line.

When the detection unit 106 detects (determines) the start of irradiation of radiation, the control unit 107 transmits the switch element T in the row to which all the pixels PIX for acquiring the radiation image are connected via the drive circuit 214. Shift to drive (accumulation) to turn off. Details of the determination of the presence or absence of radiation will be described later. Accumulation continues until it is determined that the irradiation of radiation is complete. When the irradiation of radiation is completed, the control unit 107 controls the drive circuit 214 and the read circuit 102, sequentially conducts the switch element T from the first row to the last row, and performs a main reading to read a signal from the pixel PIX.

Next, FIG. 5A shows the drive timing when the start of irradiation of the radiation of the radiation imaging device 100 in the present embodiment is detected. Further, as a comparative example, FIG. 5B shows the drive timing when a malfunction occurs due to an impact or the like. Here, the line in which the start of irradiation of radiation is determined in the radiation imaging apparatus 100 will be described as line Ys.

FIG. 5A is an enlarged view of the vicinity of the Ys line, which is the line for determining the start of radiation irradiation shown in FIG. FIG. 5A shows information on the current output from the bias source 203 for the detection unit 106 to output radiation information including the time variation of the intensity of the radiation incident on the pixel unit 101. The detection unit 106 acquires radiation information from the information of the current flowing through the bias line Bs acquired from the bias source 203, and determines the start of radiation irradiation. In FIG. 5A, irradiation of radiation is started between the scans of the Ys-1 row and the Ys row, the information of the current flowing through the bias line Bs during the scan of the Ys row exceeds the determination threshold value, and the detection unit 106 , It is determined that the irradiation of radiation has started. According to the result of this determination, the control unit 107 shifts the pixel unit 101 to the storage operation for acquiring the radiographic image.

On the other hand, FIG. 5B is an enlarged view of the vicinity of the Ys line in FIG. 4 when an impact is applied during scanning of the Ys line in the radiographic imaging apparatus of the comparative example. Generally, in a radiation imaging device, weight reduction of the radiation imaging device is required in order to improve portability and usability. For the housing of the radiation imaging device, there is a tendency to select a lighter material such as carbon from the metal that has been used so far. As a result, the rigidity of the housing is reduced, and impact and pressure are easily transmitted to the internal circuit board. Similarly, circuit boards are also miniaturized and densified, and for example, there is a tendency to adopt small and large-capacity ceramic capacitors or to integrate a plurality of circuits on a small number of boards. As a result, when an impact or pressure is transmitted to the circuit board, the ceramic capacitor generates voltage noise due to the piezoelectric effect, and the noise is transmitted to various circuits due to interference between the circuits, and malfunctions are likely to occur. That is, the circuit of the radiation imaging device can be more susceptible to impact and pressure. Therefore, in the example shown in FIG. 5B, an impact is applied during scanning of the Ys line in the blank reading, the information of the current flowing through the bias line Bs exceeds the determination threshold value, and the detection unit 106 is irradiated with radiation. It makes a false judgment that it has started. According to this determination, the control unit 107 shifts the pixel unit 101 to the storage operation.

Next, with reference to FIG. 6, the detailed operation in which the detection unit 106 in the present embodiment determines the start of radiation irradiation will be described. In the present embodiment, the radiation imaging apparatus 100 may have the following characteristics with respect to the bias current flowing through the bias line Bs.
(1) During irradiation of radiation, a current proportional to the irradiation amount of radiation per unit time flows in the bias line Bs. This current is shown as the "first signal" in FIG. This current can flow more when the switch element T of the pixel PIX is in the on (conducting) state than when it is in the off (non-conducting) state, but in the figure, it is represented by a constant value for simplicity.
(2) When the switch element T of the pixel PIX irradiated with radiation is conducted, a current proportional to the amount of electric charge accumulated in the conversion element S of the pixel PIX before conducting the switch element T flows in the bias line Bs. .. This current is shown as the "second signal" in FIG.
(3) When the switch element T of the pixel PIX is switched on / off, a current flows through the bias line Bs. This current can be called switching noise (not shown).
(4) When an impact or a magnetic field is applied to the radiation imaging device 100, a current corresponding to the frequency of noise applied to the bias line Bs can flow. This current is called external noise and is shown as "external noise" in FIG. For example, due to the influence of an electromagnetic field generated from a commercial power source, a current of about 50 to 60 Hz can flow through the bias line Bs. Further, when an impact is input to the radiation imaging device, a current of several Hz to several kHz can flow through the bias line Bs.
(5) Even when a magnetic field or an impact is not applied to the radiation imaging device 100, a current flows through the bias line Bs due to electromagnetic waves generated by the radiation imaging device 100 itself or internal noise of the detection unit 106 or the like. This current is called system noise (not shown).

In the "bias current" of FIG. 6, these first and second signals, external noise (and switching noise, system noise) are shown to be constant over time. However, FIG. 6 only conceptually shows when these signals and noise appear, and is not always constant over time.

In order to detect the irradiation of radiation, more specifically, the start of irradiation of radiation, the sample value of the signal caused by the current flowing through the bias line Bs as the detection signal may be used as it is. b) There is a case where a misjudgment is made as shown in. Therefore, in order to reduce the influence of external noise due to an impact, a magnetic field, or the like, the radiation imaging apparatus 100 of the present embodiment uses the method described below, and the detection unit 106 calculates radiation information and irradiates the radiation. Is detected.

In the present embodiment, as shown in FIG. 2, the bias power supply unit 104 includes a plurality of bias sources 203. Further, the pixel PIX arranged in the pixel unit 101 constitutes a plurality of pixel groups. More specifically, one pixel group and one bias source 203 are arranged correspondingly to each other, and each of the plurality of bias sources 203 is provided via electrically independent bias lines Bs for each bias source 203. A bias potential is supplied to the conversion element S of the pixel PIX. In the configuration shown in FIG. 2, the bias source 203a supplies the bias potential to the pixel group including the pixel PIXa via the bias line Bsa, and the bias source 203b supplies the bias potential to the pixel group including the pixel PIXb via the bias line Bsb. It supplies a bias potential. The detection unit 106 acquires radiation information based on the signals of the currents flowing through the bias line Bsa and the bias line Bsb output from the bias source 203a and the bias source 203b, and detects the irradiation of radiation. For example, the detection unit 106 determines that radiation is being emitted when the radiation information or the integral value of the radiation information exceeds a predetermined threshold value.

As shown in FIG. 6, the drive cycle of the drive circuit 214 is represented by a time TI. That is, the radiation imaging apparatus 100 performs a reset operation (blank reading) once every time TI. Of the time TI, the time during which the drive circuit 214 supplies a high-level drive signal (hereinafter, may be referred to as on time) is represented by time TH, and the time during which the drive circuit 214 supplies a low-level drive signal (hereinafter, off). (Sometimes called time) is expressed in time TL. In the present embodiment, as an example, the control unit 107 controls the drive circuit 214 so that time TH = time TL. That is, with the start of one reset operation, the drive circuit 214 switches the drive signal of a certain drive line Vg from the low level to the high level, and returns the drive signal of the drive line Vg to the low level after the time TH has elapsed. Then, after the TL of the same length has elapsed, the next reset operation is started. For example, time TH = time TL = 16 μsec may be set.

Further, as shown in FIG. 6, the period in which the detection unit 106 samples the current flowing through the bias lines Bsa and Bsb from the bias sources 203a and 203b is represented by the time TS. In the present embodiment, the detection unit 106 is biased from the bias sources 203a and 203b during a period in which a high-level drive signal is supplied to the switch element T of the pixel PIX having the drive line Vg as time TH = time TS. The signal value representing the current flowing through Bsa and Bsb is sampled. In the timing diagram shown in FIG. 6, time TH = time TL = time TS = TI / 2, but the value is not limited to this, and time TH and time TL are set to arbitrary time and ratio. Good. Further, the time TH and the time TS do not have to be the same time, and the detection unit 106 may perform the sampling operation a plurality of times during the time TH period, with the time TS as a period shorter than the time TH. ..

In the present embodiment, as described above, the bias power supply unit 104 is provided with two bias sources 203a and 203b. Therefore, the detection unit 106 can simultaneously acquire two signals of the current flowing through the bias line Bsa and the bias line Bsb output from the bias source 203a and the bias source 203b in one time TS. Here, of the two pixel groups, the signal value representing the current flowing through the bias line Bs connected to the pixel group including the pixel PIX in which the drive circuit 214 has the switch element T turned on is referred to as an effective value S. Further, of the two pixel groups, a signal value representing a current flowing through the bias line Bs connected to the pixel group in which the switch element T is in the off state is referred to as an N value.

The detection unit 106 may sample the effective value S and the noise value N at the same timing as shown in FIG. Since the effective value S and the noise value N are acquired without a time difference, the above-mentioned second signal is included only in the effective value S in which the switch element T is in a conductive state with respect to the effective value S and the noise value N. .. On the other hand, the first signal and the external noise are included in substantially the same amount in the effective value S and the noise value N regardless of the conduction state of the switch element T. Therefore, the detection unit 106 can remove external noise based on the effective value S and the noise value N, more specifically, based on the difference between the effective value S and the noise value N, and can be used as radiation information. Only the second signal can be taken out.

In the configuration of FIG. 2, the current information output from the two bias sources 203a and 203b is an analog value obtained by converting the current flowing through the bias lines Bsa and Bsb into a voltage. Therefore, the detection unit 106 calculates radiation information for determining the presence or absence of radiation irradiation based on the digital value obtained by analog-to-digital conversion of the difference between the analog values of the effective value S and the noise value N, respectively. It is supposed to be. However, the present invention is not limited to this, and for example, an A / D converter that A / D-converts the outputs of the current-voltage conversion circuit 215 arranged in the bias source 203 includes the bias source 203 and the detection unit 106. It may be arranged in between. In this case, the detection unit 106 may calculate the radiation information based on the difference between the effective value S output from the bias sources 203a and 203b and the A / D-converted digital value of the noise value N.

Here, the two sample values acquired in the reset operation (blank reading) of the y-th time (y is an arbitrary natural number) are used as the effective value S (y) and the noise value N (y) for detecting the radiation signal, respectively. Let X (y) be the radiation information. The detection unit 106 may calculate the radiation information X (y) by the calculation as shown in the equation (1).
X (y) = S (y) -N (y) ... (1)

In the equation (1), the current flowing through the bias line Bs connected to the pixel group including the pixel PIX with the switch element T turned on and the current flowing through the bias line Bs connected to the pixel group with the switch element T turned off And means the difference processing. When the output characteristics of each pixel PIX are different, radiation information is calculated using signal values weighted to S (y) and N (y) according to the variation of each pixel PIX as shown in equation (2). You may.
X (y) = a × S (y) −b × N (y) ・ ・ ・ (2)

When the detection unit 106 detects the start of radiation irradiation, the control unit 107 causes all the switch elements T to be in a non-conducting state, and stores the radiation signal in the pixel PIX. After that, the control unit 107 performs the main reading according to the completion of the irradiation of radiation. In the configuration shown in FIG. 2, two drive lines for dividing into each pixel group are connected to the pixel PIX arranged in the row direction. In the configuration shown in FIG. 2, the pixel PIX includes pixel PIXa and pixel PIXb adjacent to each other in the row direction. Further, the pixel PIXa and the pixel PIXb are included in different pixel groups among the plurality of pixel groups, and are connected to different drive lines among the plurality of drive lines Vg. Here, in the circuit diagram shown in Patent Document 1, there are Y drive lines Vg, whereas in the present embodiment, there are 2 Y drive lines Vg. Therefore, when the switch element T is sequentially conducted from the first line (0 line) to the last line (Y-1 line) and the main reading is performed, if the drive cycle time TI is the same as in Patent Document 1, all the lines It takes twice as long to read the signal. Therefore, as shown in FIG. 7, during the main reading, the control unit 107 controls the drive circuit 214 so that the drive lines Vg for two lines are conducted together, and the main reading time due to the increase in the drive line Vg is increased. Suppress the increase. Specifically, as shown in FIG. 2, the signal line Sigma is shared by the pixels arranged in each row among the plurality of pixel PIXs. Therefore, when the radiographic image data is acquired, the drive circuit 214 can suppress an increase in the main reading time by simultaneously turning on the switch element T of the pixel PIXa and the pixel PIXb.

In the present embodiment, the effective value S and the noise value N are sampled at the same timing by arranging the two bias sources 203. As a result, the radiation imaging device 100 is highly resistant to noise generated when pressure or impact is applied to the housing without requiring a synchronization signal with the radiation generator 130, and can obtain high-quality image information. And the radiation imaging system SYS can be provided.

Although it has been described that the two bias sources 203 are arranged in the present embodiment, three or more bias sources 203 may be arranged. In this case, the effective value S and the noise value N may be appropriately sampled from the currents flowing through the three or more bias lines Bs. Further, in the configuration shown in FIG. 2, pixel PIXs belonging to the two pixel groups are alternately arranged in the row direction, and pixel PIXs adjacent to each other in the column direction are included in the same pixel group among the two pixel groups. However, it is not limited to this. Pixels PIX belonging to each pixel group may be arranged in an appropriate order.

Further, in the present embodiment, as shown in FIG. 6, the effective value S and the noise value N are sampled at the same timing, but the present invention is not limited to this. When there is one bias source 203, the effective value S and the noise value N can be sampled only at different timings. Therefore, the detection unit 106 acquires the effective value S and the noise value N so that at least a part of the sampling timings overlap, so that the influence of the external noise is affected as compared with the case where the bias source 203 is one. It becomes possible to suppress it.

Further, the difference in the number of pixel PIXs included in each pixel group of the plurality of pixel groups may be within 10% for each pixel group. Further, for example, the number of pixel PIX included in each pixel group may be the same. By aligning the number of pixel PIX included in the pixel group, the amounts of external noise, switching noise, system noise, etc. flowing through the bias line Bs are aligned, and the noise when the detection unit 106 detects the presence or absence of radiation irradiation The effect can be suppressed.

Next, a modified example of the configuration example of the detection unit 110 of the radiation imaging apparatus 100 shown in FIG. 2 will be described with reference to FIG. FIG. 8 is an equivalent circuit diagram showing a configuration example of the detection unit 110 of the radiation imaging device 100. The configuration of the detection unit 110 of FIG. 8 is different from the configuration of the pixel unit 101 and the configuration of the amplifier circuit 206 of the reading circuit 102 as compared with the configuration of FIG. Specifically, the pixel PIXa and the pixel PIXb, which are included in different pixel groups and are connected to different drive lines Vg and are adjacent to each other in the row direction, share a signal line Sigma. Therefore, the number of signal line sigs is halved as compared with the configuration shown in FIG. Along with this, the number of amplifier circuits 206 arranged in the read circuit 102 is halved as compared with the configuration shown in FIG. As a result, in the configuration shown in FIG. 2, the amplifier circuit 206 of the read circuit 102 can be reduced to solve the problem that the scale of the drive circuit 214 increases as compared with the configuration of Patent Document 1. As a result, it is possible to suppress an increase in cost due to an increase in the number of ICs in the entire radiation imaging device 100 including the drive circuit 214 and the read circuit 102, and to reduce the wiring in the pixel unit 101.

As described above with reference to FIG. 6, the detection of the presence or absence of radiation irradiation is connected to different bias sources 203 via bias lines Bs that are electrically independent of each other, so that the effective value S and noise are detected at the same timing. The value N can be sampled. Further, similarly to the configuration shown in FIG. 2 described above, the pixel PIXs for acquiring the effective value S and the noise value N are arranged adjacent to each other. Therefore, even if a local impact is applied to the housing of the radiation imaging apparatus 100 as noise, the same noise is applied at the same timing with respect to the pitch on which the pixel PIX is arranged. Can be regarded as. Therefore, by the operation described with reference to FIG. 6, noise can be removed even in the configuration shown in FIG. 8, and the start of radiation irradiation can be detected more accurately.

FIG. 9 is a schematic view showing the drive timing of the detection unit 110 shown in FIG. The drive for detecting the presence or absence of irradiation of radiation during blank reading is the same as the drive described with reference to FIG. 6, and is therefore omitted. In the present embodiment, since the pixels PIXa and the pixels PIIXb that are adjacent to each other are connected to the same signal line Sigma, it is read that the switch element T is turned on at the time of the main reading as described above. This is not possible because the signals for only two pixels are added. Therefore, as shown in FIG. 9, when acquiring the radiographic image data, the drive circuit 214 turns on the switch element T of the pixel PIX connected to the same signal line Sigma at different timings. As a result, the electric charge accumulated in each pixel PIX can be read out.

Also in this embodiment, the effective value S and the noise value N are sampled at the same timing by arranging the two bias sources 203. As a result, the radiation imaging device 100 is highly resistant to noise generated when pressure or impact is applied to the housing without requiring a synchronization signal with the radiation generator 130, and can obtain high-quality image information. And the radiation imaging system SYS can be provided. Further, the number of amplifier circuits 206 of the read circuit 102 can be reduced by sharing the signal line Sigma for outputting signals by the pixels PIX adjacent to each other in the row direction. This makes it possible to offset the cost increase due to the increase in the circuit scale of the drive circuit 214.

Next, with reference to FIG. 10, a method of suppressing a decrease in the frame rate of blank reading due to an increase in the number of drive lines Vg will be described. As described above with reference to FIG. 3, the drive cycle TI of the drive circuit 214 has two periods, an on time (time TH) and an off time (time TL). That is, the plurality of drive lines Vg include a first drive line (for example, drive line Vg1-1) and a second drive line (for example, Vg1-2) different from the first drive line, and are irradiated with radiation. When determining the presence or absence of the drive circuit 214, the drive circuit 214 is a switch connected to the drive line Vg1-2 after a predetermined time has elapsed from turning the switch element T connected to the drive line Vg1-1 from on to off. Turn on the element T.

On the other hand, since the detection unit 110 of the radiation imaging apparatus 100 of the present embodiment includes a plurality of bias sources 203 (two systems in the present embodiment), the effective value S and the noise value N can be sampled at the same time during the time TH. .. In other words, in the configuration of this embodiment, it is not always necessary to provide an off time (time TL). Therefore, when determining the presence or absence of radiation irradiation, the drive circuit 214 uses the timing of turning the switch element T connected to the drive line Vg1-1 from on to off and the switch connected to the drive line Vg1-2. The timing of turning the element T from off to on is controlled so as to overlap.

Generally, it is known that a current flows through the bias line Bs when the switch element T is switched on and off. This current is called switching noise. As shown in FIG. 10, switching noise is canceled by superimposing the falling edge of the drive signal to the switch element T of one pixel row and the rising edge of the drive signal to the switch element T of the next pixel row. Can be done. That is, the driving of the detection unit 110 shown in FIG. 10 is effective when the switching noise of the switch element T is large.

Further, in the drive shown in FIG. 10, the off time (time TL) during blank reading becomes unnecessary, and the drive cycle per line can be shortened as time TI = time TH. In the configuration of the radiation imaging apparatus 100 of the present embodiment, the drive line Vg is increased as compared with the configuration shown in Patent Document 1. However, by arranging the plurality of bias sources 203, it is possible to shorten the time TI which is the drive cycle at the time of blank reading, and it is possible to maintain the read time of one frame for each line.

Even with the drive shown in FIG. 10, the effective value S and the noise value N are sampled at the same timing by arranging the two bias sources 203. As a result, the radiation imaging device 100 is highly resistant to noise generated when pressure or impact is applied to the housing without requiring a synchronization signal with the radiation generator 130, and can obtain high-quality image information. And the radiation imaging system SYS can be provided. Further, as described above, in blank reading, switching noise associated with on / off of the switch element T can be reduced, and the accuracy of determining the start of radiation irradiation can be improved. Further, in the blank reading, by omitting the time TL, the sampling rate for acquiring the current flowing through the bias line Bs for determining the presence or absence of radiation irradiation can be improved, and the determination of the presence or absence of radiation irradiation can be performed. Time resolution is improved.

The invention is not limited to the above embodiments, and various modifications and modifications can be made without departing from the spirit and scope of the invention. Therefore, a claim is attached to make the scope of the invention public.

106: Detector unit, 203: Bias source, 214: Drive circuit, Bs: Bias line, PIX: Pixel, S: Conversion circuit, T: Switch element

Claims (15)

A radiation imaging device including a plurality of pixel groups and a plurality of bias sources in which one pixel group and one bias source are respectively arranged, a drive circuit, and a detection unit.
Each of the plurality of pixel groups is composed of a pixel including a conversion element that converts radiation into an electric charge and a switch element that connects the conversion element to a signal line.
Each of the plurality of bias sources supplies a bias potential to the conversion element of the pixel via electrically independent bias lines for each bias source.
The drive circuit controls the switch element of the pixel and
The detection unit
Among the plurality of pixel groups, the first signal value representing the current flowing through the bias line connected to the pixel group including the pixel whose drive circuit has the switch element turned on, and the plurality of pixel groups. The second signal value representing the current flowing through the bias line connected to the pixel group in the off state of the switch element is acquired so that at least a part of the sampling timing overlaps.
A radiation imaging device characterized in that the presence or absence of irradiation of radiation is determined based on the first signal value and the second signal value. The radiation imaging apparatus according to claim 1, wherein the detection unit samples the first signal value and the second signal value at the same timing. The pixel portion in which the plurality of pixel groups are arranged is composed of the plurality of the pixels arranged in a matrix.
A plurality of drive lines for the drive circuit to control the switch element are arranged along the row direction.
The plurality of pixels include a first pixel and a second pixel that are adjacent to each other in the row direction.
The first pixel and the second pixel are included in different pixel groups among the plurality of pixel groups, and are connected to different drive lines among the plurality of drive lines. The radiation imaging apparatus according to claim 1 or 2. The signal line is shared by the pixels arranged in each row among the plurality of the pixels.
The radiation imaging apparatus according to claim 3, wherein the drive circuit simultaneously turns on the switch elements of the first pixel and the second pixel when acquiring the radiation image data. The radiation imaging apparatus according to claim 3, wherein the first pixel and the second pixel share the signal line. The fourth or fifth aspect of claim 4 or 5, wherein when acquiring radiographic image data, the drive circuit turns on the switch element of a pixel connected to the same signal line among the plurality of pixels at different timings. Radiation imaging device. The radiation imaging apparatus according to any one of claims 3 to 6, wherein the pixels adjacent to each other in the column direction among the plurality of the pixels are included in the same pixel group among the plurality of pixel groups. The plurality of drive lines include a first drive line and a second drive line different from the first drive line.
When determining the presence or absence of radiation, the drive circuit sets the timing of turning the switch element connected to the first drive line from on to off and the switch element connected to the second drive line. The radiation imaging apparatus according to any one of claims 3 to 7, wherein the timing of turning from off to on is controlled so as to overlap. The plurality of drive lines include a first drive line and a second drive line different from the first drive line.
When determining the presence or absence of radiation, the drive circuit is connected to the second drive line after a predetermined time has elapsed from turning the switch element connected to the first drive line from on to off. The radiation imaging apparatus according to any one of claims 3 to 7, wherein the switch element is turned on. The pixel including the switch element connected to the first drive line and the pixel including the switch element connected to the second drive line are in different pixel groups from the plurality of pixel groups. The radiation imaging device according to claim 8 or 9, wherein the radiation imaging device is included. The radiation imaging apparatus according to any one of claims 1 to 10, wherein the plurality of pixel groups are two pixel groups. The radiation according to any one of claims 1 to 11, wherein the detection unit determines the presence or absence of radiation irradiation based on the difference between the first signal value and the second signal value. Imaging device. The first signal value and the second signal value are analog values, respectively, and are
The detection unit is characterized in that it determines the presence or absence of radiation irradiation based on a digital value obtained by analog-to-digital conversion of the difference between the analog values of the first signal value and the second signal value. The radiation imaging apparatus according to. The radiation imaging apparatus according to any one of claims 1 to 13, wherein the difference in the number of pixels included in each of the plurality of pixel groups is within 10%. The radiation imaging apparatus according to any one of claims 1 to 14,
A radiation generator that irradiates the radiation imaging device with radiation,
A radiation imaging system characterized by being equipped with.

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