JP2021129209A - Radiation imaging apparatus and radiation imaging system - Google Patents

Abstract

To provide a technique advantageous in improving the degree of freedom of control in detecting the presence or absence of irradiation of a radiation.SOLUTION: A radiation imaging apparatus includes a plurality of pixel groups and a plurality of bias lines in each of which one pixel group and one bias line are arranged in correspondence with each other, a driving circuit, and a detection unit. The plurality of pixel groups are formed of pixels each including a conversion element that converts a radiation into an electric charge and a switching element that transfers the electric charge to a column signal line. The plurality of bias lines are electrically independent of each other and supply a bias potential to the conversion elements in the pixels. In detecting the presence or absence of irradiation of a radiation, the driving circuit operates to turn on the switching elements in the pixels included in each pixel group of the plurality of pixel groups in parallel in predetermined order, and the detection unit detects the presence or absence of irradiation of a radiation based on a plurality of signal values indicating currents flowing in the plurality of bias lines.SELECTED DRAWING: Figure 7

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 discloses a radiation imaging apparatus that detects the presence or absence of radiation irradiation from a current flowing through a bias line for applying a bias voltage to a radiation detection element.

Japanese Unexamined Patent Publication No. 2010-268171

When capturing a radiation image, there are various irradiation conditions such as the intensity and irradiation range of the radiation applied to the FPD. In the configuration shown in Patent Document 1, since the irradiation of radiation is detected using one system of bias lines, the irradiation is detected according to the irradiation conditions of radiation, such as shortening the sampling cycle when strong radiation is irradiated. It is necessary to set the operation to do. However, if the dose of radiation incident on the radiation imaging device is smaller than expected due to the structure of the subject, the amount of charge generated by the irradiation of radiation for one sampling will be smaller, and the irradiation of radiation will be detected. It can be difficult. The method of detecting the presence or absence of radiation irradiation using one system has a low degree of freedom of control when detecting the presence or absence of radiation irradiation, and may not be able to cope with various radiation irradiation conditions and subjects.

An object of the present invention is to provide a technique advantageous for improving the degree of freedom of control when detecting the presence or absence of radiation irradiation.

In view of the above problems, the radiation imaging apparatus according to the embodiment of the present invention includes a plurality of pixel groups and a plurality of bias lines in which one pixel group and one bias line 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 that converts an electric charge into an electric charge and a switch element that transfers the electric charge to a column signal line. Each of the bias lines supplies a bias potential to the pixel conversion element electrically independently of each other, and when detecting the presence or absence of irradiation of radiation, the drive circuit is included in each pixel group of the plurality of pixel groups. The switch elements of the pixels are turned on in parallel in a predetermined order, and the detection unit detects the presence or absence of irradiation based on a plurality of signal values indicating the currents flowing through each of the plurality of bias lines. It is a feature.

The above means provides an advantageous technique for improving the degree of freedom of control when detecting the presence or absence of radiation irradiation.

The figure which shows the configuration example of the radiation imaging system using the radiation imaging apparatus which concerns on this disclosure. The figure which shows the structural example of the comparative example of the radiation imaging apparatus of FIG. The schematic diagram of the drive timing 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 which detects the radiation of the radiation image pickup 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 structural example 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 of the radiation imaging apparatus of FIG. The figure which shows the structural example of the radiation imaging apparatus of FIG. The schematic diagram of the drive timing of the radiation imaging apparatus 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 given 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 11. FIG. 1 is a diagram showing a configuration example of a radiation imaging system SYS using the radiation imaging device 100 in this 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 device 100 includes an imaging unit 110 including a pixel unit 101, a reading 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 imaging unit 110 will be described later. 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 image pickup 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 imaging unit 110 may be changed by using the radiation information output by the detection unit 106.

Before explaining the image pickup unit 110 of the radiation imaging apparatus 100 of the present embodiment, the image pickup unit 110'of the comparative example will be described. FIG. 2 is an equivalent circuit diagram showing a configuration example of an imaging unit 110'of a comparative example of the radiation imaging apparatus 100. FIG. 2 shows a pixel portion 101 having a pixel PIX of 6 rows × 6 columns for the sake of simplicity of description. However, the pixel portion 101 of the actual radiation imaging apparatus 100 may have more pixels. For example, a 17-inch radiation imaging device 100 may have a pixel PIX of about 2800 rows x 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 is a conversion element S (S11 to S66) that converts radiation into an electric charge, and a switch element T (T11) that transfers the electric charge generated by the conversion element S to a signal line Sigma and outputs an electric signal according to the electric charge. ~ T66) and. In the present embodiment, the conversion element S includes a photoelectric conversion element and a wavelength converter such as a scintillator 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 an indirect type 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 line 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 to the drive line G1 in the first row and are driven. A drive signal for controlling the conduction state of the switch element T is given from the circuit 214 via the drive line G1. The drive circuit 214 controls the switch element T of the pixel PIX via a plurality of drive lines G arranged along the row direction. In the plurality of switch elements T arranged along the column direction (vertical direction in the drawing), for example, the switch elements T11 to T61, the other main terminal of the two main terminals is on the row signal line Sig1 in the first row. While electrically connected and the switch element T is in a conductive state, an electric signal corresponding to the charge of the conversion element S is output to the read circuit 102 via the column signal line Sigma1. 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. NS. 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 electrical 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 a time variation of the amount of the current flowing through the bias line Bs to the detection unit 106. In the present embodiment, the bias source 203 includes, but is not limited to, a current-voltage conversion circuit 215 including an operational amplifier and a resistor as a circuit for outputting current information. 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 a non-conducting state (on operation) that causes the switch element T to be in a conductive state (ON operation) in response to the control signals D-CLK, OE, and DIO input from the control unit 107 shown in FIG. A drive signal including a non-conducting voltage Vss to be turned off) 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 shows the basic drive timing of the radiation imaging apparatus 100 including the imaging unit 110'of the comparative example. FIG. 4 is a flow chart of the basic operation of the radiation imaging apparatus 100 regardless of the imaging units 110 and 110'. In FIG. 3, Vg1, Vg2, Vg3, VgYs, and VgY indicate drive signals supplied to the respective drive lines G of the first row to the Yth row of the pixel unit 101. Here, the row in which the start of irradiation of radiation is detected in the radiation imaging apparatus 100 will be described as row Ys.

When the user sets the imaging conditions for the radiographic image, the control unit 107 first resets the drive circuit 214 to remove the charges accumulated in the conversion element S of the pixel PIX due to the dark current (hereinafter, reset drive). (Sometimes referred to as blank reading)) is performed (S401). 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.

While performing blank reading, 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 detects the presence or absence of radiation irradiation (S402). To detect the start of radiation irradiation, it is determined that radiation irradiation has started when the cumulative value of the time variation of the current flowing through the bias line Bs exceeds a predetermined threshold value within a predetermined period. The method of If the detection unit 106 does not detect the start of radiation irradiation (NO in S402), the blank reading is continued.

When the detection unit 106 detects the start of irradiation of radiation (YES in S402), the radiation imaging device 100 transitions to S403, the control unit 107 ends the blank reading operation in the drive circuit 214, and then all of them. The switch element T is made non-conducting with respect to the drive lines G1 to GY. In S403, the electric charge generated in response to the incident radiation is accumulated in the conversion element S.

Next, the control unit 107 determines the end of radiation irradiation (S404). 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 may determine that the radiation has ended when the cumulative value of the time variation of the current flowing through the bias line Bs is less than the predetermined threshold value within a predetermined period. When the end of radiation irradiation is not determined (NO in S404), the drive circuit 214 continues to turn off the switch element T of the pixel PIX for acquiring the radiation image, and drives to accumulate the signal converted from the radiation (hereinafter, , May be referred to as accumulation.) Is performed. When the end of radiation irradiation is determined (YES in S404), the radiation imaging device 100 transitions to S405, 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. 5 shows the drive timing when the start of radiation irradiation is detected. In FIG. 5, VgYs-2, VgYs-1, VgYs, and VgYs + 1 indicate drive signals supplied to the drive lines G from the Ys-2 line to the Ys + 1 line of the pixel unit 101. Row Ys is the row that detects the start of radiation irradiation as described above.

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.
(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.
(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 order to detect the presence / absence (start) of radiation irradiation, the signal value of the signal caused by the current flowing through the bias line Bs as the detection signal may be used as it is. However, when external noise due to the influence of an impact or a magnetic field cannot be ignored, the signal caused by the current flowing through the bias line Bs may be processed to detect the irradiation of radiation.

For example, as shown in FIG. 5, the current flowing through the bias line Bs is sampled when the switch element T of the pixel PIX is turned on (conducting state), and this is used as an S signal. Further, when the switch element T is turned off (non-conducting state), the current flowing through the bias line Bs is sampled and used as an N signal. External noise can be removed by taking the difference between the S signal and the N signal. However, since the external noise fluctuates with the passage of time, the S signal and the N signal sampled at times close to each other may be used. For example, assuming that the signal value of the S signal sampled at the yth time is S (y), the signal value of the N signal sampled at the yth time is N (y), and the signal value from which external noise is removed is X (y), the following is assumed. The signal value X (y) is obtained by the calculation as shown in the equation (1) shown in. Equation (1) is a signal caused by a current flowing through the bias line Bs when the switch element T is operating on and a signal caused by a current flowing through the bias line Bs when the switch element T is operating off. And means the difference operation of.
X (y) = S (y)-{N (y) + N (y-1)} / 2 ... (1)

Such a method of reducing external noise is called correlated double sampling (CDS). The CDS is not limited to the method represented by the formula (1). For example, for the calculation of the signal value X (y), only one of the signal value N (y) and the signal value N (y-1) may be used as the signal value of the N signal, or the signal value S ( Signal values that are not adjacent to each other, such as y-1) and signal value N (y-2), may be used. Further, as the signal value S (y) of the S signal sampled at the yth time, a value obtained by adding or averaging the values sampled a plurality of times during the period may be used. The detection unit 106 detects, for example, the presence or absence of radiation irradiation when the cumulative value of the signal value X (y) exceeds a predetermined threshold value.

In addition, switching noise generated when the switch element T is switched on / off may not be ignored. In this case, it is necessary to process the signal caused by the current flowing through the bias line Bs so that the influence of the switching noise is reduced. As a process for reducing the switching noise, for example, it is conceivable to perform a process of subtracting the value of the switching noise sampled in advance from the value of the signal caused by the current flowing through the bias line Bs.

Here, although the magnitude of the switching noise differs for each row, it has been confirmed that the magnitude of the switching noise in the same row has high reproducibility. Therefore, as shown in FIG. 6, the signal value of the signal caused by the current flowing through the current bias line Bs is subtracted from the signal value of the signal caused by the current flowing through the bias line Bs one frame before the same line. .. This makes it possible to reduce switching noise. When the pixel PIX is arranged in the pixel section 101 over Y rows in the column direction, the signal value of the S signal one frame before is S (yy), and the signal value of the N signal one frame before is N (y−y−. Y). Therefore, the signal value X (y) is obtained by the calculation as shown in the following equation (2).
X (y) = [S (y)-{N (y) + N (y-1)} / 2]
-[S (y-Y)-{N (y-Y) + N (y-1-Y)} / 2] ... (2)

The first term of the equation (2) describes the current flowing through the bias line Bs when the switch element T is operating on and the current flowing through the bias line Bs when the switch element T is operating off for the y row. It means to calculate the difference with. The second term of the equation (2) is the current flowing through the bias line Bs when the switch element T is operating on and the bias line when the switch element T is operating off for the y line one frame before. It means that the difference between the current flowing through Bs and the current is calculated. The whole of the equation (2) means to obtain the amount of change of the difference between the latest S signal and the N signal and the difference between the S signal and the N signal one frame before for the same line.

The processing method shown in FIG. 6 is called frame correction. The frame correction is not limited to the method of the equation (2). For example, the difference between the latest S signal and the signal value of the N signal may be frame-corrected by using the difference between the signal values of the S signal and the N signal two frames or two frames or more before. Further, the amount of change between frames may be obtained by using only one of the S signal and the N signal.

Here, a problem when the imaging unit 110'of the comparative example shown in FIG. 2 is used will be described. The electric charge generated by irradiation of radiation in the conversion element S is determined by the product of the intensity of the irradiated radiation and the irradiation time. The irradiation time of this radiation is generally in the range of 1 ms to several hundred ms. For example, in a round-trip car or a portable radiation generator 130, the irradiation time tends to be long because the radiation output is weak due to the available power source. On the other hand, in the stationary radiation generator 130, the degree of freedom in supplying power is high, and the irradiation time tends to be shortened in order to prevent image blurring due to the movement of the subject. When detecting the presence or absence of radiation irradiation using a signal caused by the time fluctuation of the current flowing through the bias line Bs, if the measurement period of the time fluctuation is lengthened, the time required to detect the radiation irradiation becomes long. Therefore, when strong radiation is irradiated in a short irradiation time, it takes a long time to detect the irradiation of the radiation, so that an artifact is likely to occur in the obtained radiation image. On the other hand, if the time variation measurement period is shortened, it may be difficult to detect the presence or absence of irradiation when weak radiation is irradiated over a long irradiation time.

Further, it is conceivable that the radiation irradiation area is small, or the radiation does not easily reach the peripheral portion of the pixel portion 101 due to the structure of the subject or the like. In this case, when the switch element T of the connected pixel PIX is sequentially turned on from the drive line G arranged at one end of the pixel unit 101 toward the other end, many until the presence or absence of radiation irradiation is detected. It may take some time. That is, it is necessary to always set an appropriate accumulation time, sampling period, order of driving the pixel PIX to detect radiation irradiation, and the like according to the radiation irradiation conditions.

Therefore, the configuration of the imaging unit 110 of the present embodiment will be described with reference to FIG. 7. The difference from the imaging unit 110 of the comparative example shown in FIG. 2 is as follows.

The conversion elements S arranged in the row direction, for example, the conversion elements S11, S13, and S15, have control terminals connected to the drive wiring Ga1 in the first row via the switch elements T11, T13, and T15, respectively. Further, the other electrodes of the conversion elements S11, S13, and S15 are connected to the bias source 203a of the bias power supply unit 104 via a common bias line Bsa. The conversion elements S12, S14, and S16 arranged in the same row as the switch elements S11, S13, and S15 have control terminals connected to the drive wiring Gb1 in the first row via the switch elements T12, T14, and T16, respectively. Further, the other electrodes of the conversion elements S12, S14, and S16 are connected to the bias source 203b of the bias power supply unit 104 via a common bias line Bsb. Hereinafter, the conversion elements S arranged in the other row directions are also connected in the same manner.

The bias wiring Bsa is electrically connected to the bias source 203a, and the bias wiring Bsb is electrically connected to the bias source 203b. Further, the switch element T of the pixel PIX included in the pixel group composed of the pixels (for example, the pixel PIXa) connected to the bias line Bsa is controlled by the drive circuit 214a via the drive line group Ga. Similarly, the switch element T of the pixel PIX included in the pixel group composed of the pixels (for example, the pixel PIXb) connected to the bias line Bsb is controlled by the drive circuit 214b via the drive line group Gb. That is, there are two electrically independent paths for driving the switch element T and acquiring information on the current flowing through the bias line Bs in order to detect the presence or absence of radiation irradiation. In the configuration shown in FIG. 7, the drive circuit is divided into two, a drive circuit 214a and a drive circuit 214b, for the sake of simplicity, but one drive circuit 214 controls two pixel groups respectively. It may be configured to be used.

In the configuration shown in FIG. 7, two pixel groups are arranged, but bias lines Bs that supply a bias potential to three or more pixel groups and the conversion element S of the pixel PIX included in each pixel group are arranged. It may have been done. That is, the imaging unit 110 of the radiation imaging apparatus 100 may include a plurality of pixel groups and a plurality of bias lines Bs in which one pixel group and one bias line Bs are arranged so as to correspond to each other. Each of the plurality of bias lines Bs may electrically supply the bias potential to the conversion element S of the pixel PIX independently of each other.

Next, the drive timing of the radiation imaging apparatus 100 including the imaging unit 110 will be described with reference to FIG. As shown in FIG. 8, the drive circuit 214 turns on the switch elements S of the pixel PIX included in each pixel group of the plurality of pixel groups in parallel in a predetermined order. Here, as shown in FIG. 7, a case where two sets of pixel groups and bias lines Bs are arranged will be described. In FIG. 8, Vga1 to VgaY are drive line groups Ga for driving a pixel group (hereinafter, may be referred to as a first pixel group) including the pixel PIXa among the pixel PIX arranged in the pixel unit 101. The drive signals supplied to the respective drive lines Ga1 to GaY of the first line to the Yth line are shown. Further, Vgb1 to VgbY are the first of the drive line group Gb for driving the pixel group including the pixel PIXb (hereinafter, may be referred to as the second pixel group) among the pixel PIX arranged in the pixel unit 101. The drive signals supplied to the respective drive lines Gb1 to GbY from the row to the Yth row are shown.

As shown in FIG. 8, when detecting the presence or absence of radiation irradiation, the drive circuit 214 is set to the second pixel group rather than the time for turning on the switch element S of the pixel PIX included in the first pixel group. The time for turning on the switch element S of the included pixel PIX may be lengthened. Further, the drive circuit 214 periodically turns on the switch element S of the pixel PIX included in the second pixel group rather than periodically turning on the switch element S of the pixel PIX included in the first pixel group. The cycle of causing may be lengthened.

Since the amount of current flowing through the bias line Bs increases in proportion to the time when the switch element S is turned on, the S / N ratio of the signal caused by the current flowing through the bias line Bs can be improved, and the presence or absence of irradiation can be detected. It is possible to improve the sensitivity of the current. On the other hand, if the time during which the switch element S is turned on is lengthened, the sampling cycle (period of one frame) may become long. Therefore, the delay time from the actual irradiation to the detection of the start of the irradiation can be long. Since the electric charge generated by the radiation incident during the delay time is discarded without being used for the generation of the radiation image by the blank reading operation, it can be obtained when a large dose of radiation is irradiated in a short time. There is a high possibility that an artifact will occur in the radiographic image. However, in the present embodiment, the on-operation period of the switch element S is short, and the first pixel group that operates the switch element S with a short sampling cycle accurately determines the presence or absence of irradiation when strong radiation is irradiated in a short time. It can be detected well. Further, the second pixel group that operates the switch element S with a long on-operation period and a long sampling cycle can accurately detect the presence or absence of irradiation when weak radiation is irradiated.

As described above, in the present embodiment, a plurality of (two sets) of pixel groups and bias lines Bs are arranged, and the drive circuit 214 is operated to turn on the conversion element S of the pixel PIX of the plurality of (two) pixel groups. Drive differently. At this time, the detection unit 106 detects the presence or absence of radiation irradiation based on a plurality of (two) signal values indicating currents flowing through each of the plurality (two) bias lines Bs. More specifically, the presence or absence of radiation irradiation can be detected when at least one of the cumulative values of the plurality of (two) signal values X (y) exceeds a predetermined threshold value. In the present embodiment, the radiation imaging apparatus 100 arranges a plurality of (two) pixel groups and bias lines Bs having different detection characteristics in one imaging unit 110. This makes it possible to detect the presence or absence of radiation irradiation with high accuracy regardless of the intensity of the irradiated radiation.

As shown in FIG. 7, pixel PIXa and pixel PIXb adjacent to each other in the row direction may be included in different pixel groups among a plurality of pixel groups. Since the pixels PIX included in different pixel groups are adjacent to each other, it is possible to detect the presence or absence of radiation irradiation with different detection characteristics regardless of the position where the radiation is irradiated.

FIG. 9 is a diagram showing a modified example of the drive timing of the radiation imaging apparatus 100 described with reference to FIG. FIG. 9 is an operation for improving the S / N ratio of the signal caused by the current flowing through the bias line Bs in the pixel group in which the switch element T is operated for a short time. When detecting the presence or absence of radiation irradiation, the drive circuit 214a may supply a signal for turning on the switch element T to a plurality of drive lines G in the drive line group Ga at the same time. In the configuration shown in FIG. 9, the drive circuit 214a supplies signals to the four drive lines G (for example, drive lines Ga1 to Ga4) of the drive line group Ga to simultaneously turn on the switch element T. As a result, in one blank reading operation, a current proportional to the electric charge accumulated in the pixel PIX included in the first pixel group for four lines flows through the bias wiring Bsa. As a result, the S / N ratio of the signal caused by the current flowing through the bias line Bs can be improved, and the sensitivity for detecting the presence or absence of radiation irradiation can be improved. In the configuration shown in FIG. 9, the drive circuit 214a supplies signals for turning on the switch element T to the four drive lines G at the same time, but the present invention is not limited to this. The drive circuit 214a may supply a signal for simultaneously turning on the switch element T to an arbitrary number of two or more.

Further, as shown in FIGS. 8 and 9, during the main reading, a signal for simultaneously turning on the switch element T is supplied to the drive line G connected to the pixel PIX of the first pixel group and the second pixel group. You may. For example, the control unit 107 controls the drive circuit 214 so that signals are simultaneously read from the pixels PIX arranged in the same row of the first pixel group and the second pixel group. As a result, the increase in the main reading time accompanying the increase in the drive line G is suppressed. Specifically, as shown in FIG. 2, the column signal line Sigma is shared by the pixels arranged for each column among the plurality of pixel PIXs. Therefore, when the radiographic image data is acquired, the drive circuits 214a and 214b can suppress the increase in the main reading time by simultaneously turning on the switch element T of the pixel PIXa and the pixel PIXb.

Further, as shown in FIG. 10, two pixels included in the first pixel group and the second pixel group and adjacent to each other may be connected to one column signal line Sigma. In other words, two pixels of the pixel PIX that are adjacent to each other in the row direction and are included in different pixel groups among the plurality of pixel groups may share the column signal line Sigma. For example, the pixel PIXa and the pixel PIXb may share the column signal line Sigma2. In this case, at the time of the main reading, the switch element T is alternately turned on by the drive line group Ga and the drive line group Gb, such as drive line Ga1 → drive line Gb1 → drive line Ga2 → drive line Gb2. Supply the signal of. The signals of two pixels PIX adjacent to each other can be output to the same column signal line Sigma in a time-division manner. As a result, the time required for the main reading is doubled, but the number of parts of the reading circuit 102 is reduced, so that the cost increase can be suppressed, the wiring pattern in the pixel portion 101 can be reduced, and the opening of the conversion element S can be reduced. The rate can be increased.

In the above-described embodiment, the case where two sets of pixel groups and bias lines Bs are arranged has been described, but the present invention is not limited to this. Radiation may be detected with different detection characteristics by arranging three or more sets of pixel groups and bias lines Bs and driving them differently.

FIG. 11 is a diagram showing a further modification of the drive timing of the radiation imaging apparatus 100 described with reference to FIGS. 8 and 9. FIG. 11 is an example of the drive timing of the radiation imaging device 100 including the imaging unit 110 shown in FIG. 7. As shown in FIG. 11, the drive circuits 214a and 214b have a row in which the blank reading operation is started in the first pixel group and a blank reading drive in the second pixel group when the detection of the presence or absence of radiation irradiation is started. Start the line starting with a different line.

For example, the drive circuit 214a supplies a signal for turning on the switch element T in a predetermined order from the drive line Ga1 to which the pixel PIXa is connected among the drive lines G included in the drive line group Ga. On the other hand, the drive circuit 214b is in a predetermined order from the drive line G (for example, the drive line Gb2) different from the drive line Gb1 to which the pixel PIXb is connected among the drive lines G included in the drive line group Gb. , A signal for turning on the switch element T may be supplied. Further, for example, in the drive circuit 214a, the switch elements are sequentially switched from the drive line G (for example, the drive line Ga1) arranged at one end in the row direction of the drive lines G included in the drive line group Ga toward the other end. The operation of supplying a signal for turning on T is started. On the other hand, in the drive circuit 214b, among the drive lines G included in the drive line group Gb, the drive lines G (for example, drive lines Gb3 and Gb4) arranged in the center in the row direction are sequentially arranged toward the other end. The operation of supplying a signal for turning on the switch element T may be started. Here, the drive line G arranged in the center in the column direction is a drive line within a range of 1/3 from one end in the column direction and 1/3 from the other end of the drive lines G arranged in the pixel portion 101. It can be a drive line excluding the drive line in the range of. Further, here, the drive line G arranged in the center in the column direction is a drive line G arranged in the pixel portion 101, which is in the range of 1/4 from one end in the column direction and 1 from the other end. It may be a drive line excluding the drive line in the range of / 4.

At this time, at this time, as shown in FIG. 11, the drive circuits 214a and 214b are used to turn on the switch element T on each drive line G of the drive line group Ga and the drive line group Gb in the same cycle. Supply a signal. That is, in the first pixel group and the second pixel group, the time for reading a signal from the pixel PIX and the sampling cycle may be the same. In this case, the pixel PIX including the switch element T connected to the drive line G to which the signal for turning on the switch element T in the drive line group Ga is supplied, and the switch element T in the drive line group Gb. The pixel PIX including the switch element T connected to the drive line G to which the signal for on operation is supplied is scanned separated by a predetermined row in the column direction. Here, an example in which two sets of pixel groups and bias lines Bs are arranged has been described, but as described above, a plurality of pixel groups may exist. For example, consider a case where n groups of pixels exist and pixel PIXs are arranged over Y rows in the column direction. At this time, among the plurality of drive lines G, the pixel PIX including the switch element T connected to the drive line G to which the signal for operating the switch element T is simultaneously supplied is only Y / n rows in the column direction. It may be separated.

Further, in the first pixel group and the second pixel group, the time for reading a signal from the pixel PIX and the sampling period are not limited to the same. As described with reference to FIGS. 8 and 9, the time for reading a signal from the pixel PIX and the sampling period may be different in the first pixel group and the second pixel group. At this time, when the detection of the presence or absence of radiation irradiation is started, the pixel including the switch element T connected to the drive line G to which the signal for turning on the switch element T in the drive line group Ga is supplied. The PIX and the pixel PIX including the switch element T connected to the drive line G to which the signal for operating the switch element T of the drive line group Gb is supplied are separated by a predetermined row in the column direction. You may be.

In the drive shown in FIG. 11, the time interval in which the conversion elements S of the pixel PIX arranged in the row of the pixel unit 101 are blank-read is halved from the case where the blank-reading operation is sequentially performed from the first row. For example, even when radiation is irradiated only to the central portion of the pixel portion 101, the time until the presence or absence of radiation irradiation can be detected can be shortened as compared with the case where the blank reading operation is sequentially performed from the first row. .. That is, the responsiveness when detecting the irradiation of radiation can be improved. Even when the radiation irradiation area is small or the radiation does not easily reach the peripheral part of the pixel portion 101 due to the structure of the subject, the responsiveness when detecting the radiation irradiation is improved and unnecessary exposure is performed. Can be suppressed.

In the above-described embodiment, the case where two sets of pixel groups and bias lines Bs are arranged has been described, but the present invention is not limited to this. For example, when four sets of pixel groups and bias lines Bs are arranged, the sampling cycle for reading a signal from the conversion element S of each pixel PIX is 1/4 of the case where the blank reading operation is sequentially performed from the first row. become. That is, the responsiveness to detect radiation is further increased. However, if the number of pixel groups is increased, the number of pixel PIXs connected to the same bias line Bs is reduced, and as a result, the S / N ratio of the signal due to the current flowing through the bias line Bs is lowered. sell. This means a decrease in sensitivity when detecting the presence or absence of radiation. Therefore, the number of pixel groups to be arranged and the number of sets of bias lines Bs may be appropriately determined in consideration of the balance between the responsiveness of detection of the presence or absence of radiation irradiation and the sensitivity.

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.

100: Radiation imaging device, 106: Detection unit, 214: Drive circuit, Bs: Bias line, PIX: Pixel, S: Conversion element, Sigma: Column signal line, T: Switch element

Claims (15)

A radiation imaging device including a plurality of pixel groups and a plurality of bias lines in which one pixel group and one bias line are respectively arranged, a drive circuit, and a detection unit.
Each of the plurality of pixel groups is composed of pixels including a conversion element that converts radiation into an electric charge and a switch element that transfers the electric charge to a column signal line.
Each of the plurality of bias lines electrically independently supplies a bias potential to the conversion element of the pixel.
When detecting the presence or absence of radiation
In the drive circuit, the switch elements of the pixels included in each pixel group of the plurality of pixel groups are turned on in parallel in a predetermined order.
The detection unit is a radiation imaging device that detects the presence or absence of radiation irradiation based on a plurality of signal values indicating currents flowing through each of the plurality of bias lines. The radiation imaging according to claim 1, wherein the detection unit detects the presence or absence of radiation irradiation when at least one of the cumulative values of the plurality of signal values exceeds a predetermined threshold value. Device. The plurality of pixel groups include a first pixel group and a second pixel group.
When detecting the presence or absence of radiation, the drive circuit causes the pixel included in the second pixel group to be turned on rather than the time required to turn on the switch element of the pixel included in the first pixel group. The radiation imaging apparatus according to claim 1 or 2, wherein the time for turning on the switch element is lengthened. The drive circuit periodically turns on the switch element of the pixel included in the second pixel group rather than periodically turning on the switch element of the pixel included in the first pixel group. The radiation imaging apparatus according to claim 3, wherein the period of making the radiation is lengthened. A plurality of drive lines for the drive circuit to control the switch element are arranged along the row direction in the pixel portion in which the pixels forming the plurality of pixel groups are arranged in a matrix.
The pixels include a first pixel and a second pixel that are adjacent to each other in the row direction.
The radiation imaging apparatus according to any one of claims 1 to 4, wherein the first pixel and the second pixel are included in different pixel groups among the plurality of pixel groups. A plurality of drive lines for the drive circuit to control the switch element are arranged along the row direction in the pixel portion in which the pixels forming the plurality of pixel groups are arranged in a matrix.
The pixels include a first pixel included in the first pixel group and a second pixel included in the second pixel group that are adjacent to each other in the row direction.
The plurality of drive lines are a first drive line group that controls the switch element of the pixel included in the first pixel group, and a second drive line group that controls the switch element of the pixel included in the second pixel group. Including drive line group,
The first pixel is connected to the first drive line in the first drive line group, and is connected to the first drive line.
The radiation imaging apparatus according to claim 3 or 4, wherein the second pixel is connected to a second drive line in the second drive line group. A plurality of drive lines for the drive circuit to control the switch element are arranged along the row direction in the pixel portion in which the pixels forming the plurality of pixel groups are arranged in a matrix.
The plurality of pixel groups include a first pixel group and a second pixel group.
The plurality of drive lines are a first drive line group that controls the switch element of the pixel included in the first pixel group, and a second drive line group that controls the switch element of the pixel included in the second pixel group. Including drive line group,
When detecting the presence or absence of radiation irradiation, the drive circuit sends a signal for turning on the switch element to each drive line of the first drive line group and the second drive line group in the same cycle. The radiation imaging device according to claim 1 or 2, wherein the radiation imaging device is provided. The pixels include a first pixel included in the first pixel group and a second pixel included in the second pixel group that are adjacent to each other in the row direction.
The first pixel is connected to the first drive line in the first drive line group, and is connected to the first drive line.
The second pixel is connected to the second drive line in the second drive line group, and is connected to the second drive line.
When detecting the presence or absence of radiation, the drive circuit
Among the drive lines included in the first drive line group, signals for turning on the switch element are supplied in a predetermined order from the first drive line.
The claim is characterized in that signals for turning on the switch element are supplied in a predetermined order from a drive line different from the second drive line among the drive lines included in the second drive line group. 7. The radiation imaging device according to 7. When detecting the presence or absence of radiation, the drive circuit
Among the drive lines included in the first drive line group, the operation of sequentially supplying a signal for turning on the switch element is started from the drive line arranged at one end in the row direction toward the other end.
Among the drive lines included in the second drive line group, an operation of sequentially supplying a signal for turning on the switch element is started from the drive line arranged at the center in the row direction toward the other end. The radiation imaging device according to any one of claims 6 to 8, wherein the radiation imaging device is characterized. When the detection of the presence or absence of irradiation of radiation is started, the pixel including the switch element connected to the drive line to which the signal for turning on the switch element is supplied in the first drive line group. , The pixel including the switch element connected to the drive line to which the signal for operating the switch element is supplied in the second drive line group is separated by a predetermined row in the column direction. The radiation imaging device according to any one of claims 6 to 9, wherein the radiation imaging device is provided. There are n groups of the plurality of pixel groups, and there are n groups.
The pixels are arranged in the column direction over Y rows.
When the detection of the presence or absence of irradiation of radiation is started, the pixel including the switch element connected to the drive line to which the signal for turning on the switch element is simultaneously supplied among the plurality of drive lines The radiation imaging device according to any one of claims 6 to 10, wherein the radiation imaging apparatus is separated by Y / n rows in the column direction. The claim is characterized in that, when detecting the presence or absence of irradiation of radiation, the drive circuit supplies a signal for simultaneously turning on the switch element to a plurality of drive lines in the first drive line group. The radiation imaging device according to any one of 6 to 11. The radiation imaging apparatus according to any one of claims 5 to 12, wherein the column signal line is shared by pixels arranged for each column among the pixels. 5. A aspect of claim 5, wherein two pixels of the pixels that are adjacent to each other in the row direction and are included in different pixel groups among the plurality of pixel groups share the column signal line. The radiation imaging apparatus according to any one of 13 to 13. 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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