JP2017046073A - Radiation imaging device, control method thereof, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a noise included in an offset image.SOLUTION: A radiation imaging device includes: a sensor part for generating a signal corresponding to a dose of incident radiation; a reading part for reading a signal from the sensor part; and a control part for causing the reading part to perform a first reading operation for reading a signal for generating a first image from the sensor part in a state that the radiation is not emitted and a second reading operation for reading a signal for generating a second image from the sensor part in a state that the radiation is emitted. The control part switches the driving operation of the reading part with the first reading operation and the second reading operation such that a noise included in the first image becomes smaller than a noise included in the second image.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a radiation imaging apparatus, a control method thereof, and a program.

  In the medical field or the like, a radiation imaging apparatus that generates a radiation image according to the amount of radiation that has passed through a subject has been put into practical use. Patent Document 1 describes a radiation imaging apparatus that corrects a subject image using an offset image acquired from a radiation detector in a state where radiation is not irradiated. The radiation imaging apparatus periodically updates the offset image, and when it is determined that noise from the outside of the radiation imaging apparatus is included in the offset image, the updating of the offset image at that time is stopped.

JP 2013-214793 A

  In the method described in Patent Literature 1, when the offset image is not updated, the subject image is corrected using the previously acquired offset image. Since the offset component included in the subject image can change over time, it is difficult to accurately correct the subject image using the old offset image. If there is little noise contained in the offset image, it is not necessary to stop updating the offset image. Accordingly, an object of the present invention is to provide a technique for reducing noise included in an offset image.

  In view of the above problems, a first image is obtained from a sensor unit that generates a signal according to the amount of incident radiation, a reading unit that reads a signal from the sensor unit, and the sensor unit that is not irradiated with radiation. A control unit that causes the reading unit to perform a first reading operation for reading a signal for generation and a second reading operation for reading a signal for generating a second image from the sensor unit irradiated with radiation. And the control unit performs the first reading operation and the second reading operation so that noise included in the first image is less than noise included in the second image. There is provided a radiation imaging apparatus characterized by switching a driving operation.

  The above means provides a technique for reducing noise included in the offset image.

The figure explaining the structure of the radiation imaging device of some embodiment. The figure explaining the structure of the column amplifier of some embodiment. The figure explaining the operation example of the radiation imaging device of FIG. The figure explaining the operation example of the radiation imaging device of FIG. The figure explaining the pass band of the filter circuit of the radiation imaging device of FIG. The figure explaining the operation example of the radiation imaging device of FIG. The figure explaining the operation example of the radiation imaging device of FIG. The figure explaining the operation example of the radiation imaging device of FIG. The figure explaining the structure of the radiation imaging system of some embodiment. The figure explaining the structure of the radiation imaging system of some embodiment.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. Throughout the various embodiments, similar elements are given the same reference numerals, and redundant descriptions are omitted. In addition, each embodiment can be appropriately changed and combined. In this specification, radiation includes X-rays, α-rays, β-rays, and γ-rays, and light includes visible light and infrared rays.

  With reference to FIG. 1, a configuration of a radiation imaging apparatus 100 according to some embodiments will be described. The radiation imaging apparatus 100 has each component shown in FIG. The sensor unit 105 has pixels arranged in a two-dimensional array. Each pixel includes a sensor S and a switch element T. In the example of FIG. 1, the case where the sensor unit 105 includes pixels of 3 rows and 3 columns is handled in order to simplify the description. The number of pixels included in the sensor unit 105 is not limited to this, and more pixels are generally included in the sensor unit 105. The horizontal arrangement of pixels is called a row, and the vertical arrangement is called a column. In FIG. 1, sensors S and switch elements T included in i rows and j columns (1 ≦ i ≦ 3, 1 ≦ j ≦ 3) are represented by Sij and Tij, respectively.

  The sensor S generates a signal corresponding to the amount of radiation incident on the sensor unit 105. For example, the sensor S may be a conversion element that converts radiation directly into electric charges. Alternatively, the sensor S may be a combination of a scintillator that converts radiation into light and a photoelectric conversion element that converts this light into electric charge. When the sensor S includes a scintillator, the scintillator may be disposed in common throughout the sensor unit 105. The sensor S further accumulates charges converted from radiation or light.

  The switch element T is, for example, a transistor. The sensor S and the switch element T may be mainly formed of amorphous silicon on a glass substrate. In this case, the switch element T may be a TFT (Thin Film Transistor).

  A drive line Vg is arranged for each of a plurality of pixels (pixel rows) arranged in the row direction. In FIG. 1, drive lines Vg included in i rows (1 ≦ i ≦ 3) are represented by Vgi. Each drive line Vg is commonly connected to the gates of the switch elements T of a plurality of pixels included in the same row. A signal line Sig is provided for each of a plurality of pixels (pixel columns) arranged in the column direction. In FIG. 1, signal lines Sig included in j rows (1 ≦ j ≦ 3) are represented by Sigj. Each signal line Sig is commonly connected to one main electrode of the switch elements T of a plurality of pixels included in the same column. The other main electrode of the switch element T is connected to one end of a sensor S included in the same pixel as the switch element T. A bias voltage Vs is supplied from the power supply circuit 104 to the other end of the sensor S.

  The drive circuit 106 supplies a drive signal to the gate of the switch element T through the drive line Vg. When the drive signal is an on-voltage, the switch element T is turned on, and the sensor S and the signal line Sig are in a conductive state. Therefore, the electric charge accumulated in the sensor S is transferred to the signal line Sig through the switch element T. When the drive signal is an off voltage, the switch element T is turned off, and the sensor S and the signal line Sig are in a non-conductive state. Therefore, the sensor S accumulates electric charges generated by itself. The drive circuit 106 switches the voltage of the drive signal supplied to the drive line Vg in accordance with an instruction from the control circuit 102.

  The charge transferred from the sensor S to the signal line Sig is supplied to the readout circuit 101 connected to one end of the signal line Sig. The readout circuit 101 amplifies this charge, converts it into a digital signal, and then supplies it to the signal processing circuit 103. Specifically, the read circuit 101 includes a plurality of column amplifiers 107 to 109 individually connected to the signal line Sig, a multiplexer 110, a subtractor 111, and an AD converter 112.

  Each of the column amplifiers 107 to 109 converts the electric charge transferred from the sensor S to the signal line Sig into a voltage, and supplies this voltage to the multiplexer 110. Each of the column amplifiers 107 to 109 further supplies the multiplexer 110 with the output of the column amplifier in a state in which no charge is transferred from the sensor S to the signal line Sig. The column amplifiers 107 to 109 are supplied with the reference voltage Vref from the power supply circuit 104. The multiplexer 110 selects a signal from any one of the plurality of column amplifiers 107 to 109 in accordance with an instruction from the control circuit 102 and supplies the selected signal to the subtractor 111. The subtractor 111 supplies the AD converter 112 with the difference between the two outputs from any of the column amplifiers selected by the multiplexer 110. The AD converter 112 converts the supplied analog signal into a digital signal and supplies the digital signal to the signal processing circuit 103.

  The signal processing circuit 103 transmits data obtained by processing the supplied digital signal to a control system (not shown in FIG. 1). The power supply circuit 104 supplies power used by each component of the radiation imaging apparatus 100 in addition to the above-described bias voltage Vs and reference voltage Vref. The control circuit 102 supplies control signals to the reading circuit 101, the driving circuit 106, and the signal processing circuit 103, and controls these operations. At least one of the signal processing circuit 103 and the control circuit 102 is not realized by a dedicated circuit, but may be realized as a signal processing unit or a control unit by a general-purpose processing circuit such as a CPU executing a program. .

  Next, a configuration example of the column amplifier 107 in FIG. 1 will be described with reference to FIG. The other column amplifiers 108 and 109 may have the same configuration as the column amplifier 107. The column amplifier 107 includes an integrating amplifier 201, a sample hold circuit 202 (hereinafter, the sample hold circuit is referred to as an SH circuit), and a low pass filter 203. In the example of FIG. 2, the SH circuit 202 and the low-pass filter 203 share the same circuit element.

  The integrating amplifier 201 is an amplifier circuit that converts the charge supplied to the column amplifier 107 into a voltage. Specifically, the integrating amplifier has the circuit element shown in FIG. The signal line Sig1 is connected to the inverting input terminal of the operational amplifier OP, and the reference voltage Vref is supplied from the power supply circuit 104 to the non-inverting input terminal of the operational amplifier OP. Capacitance elements C_Cf1 and C_Cf2 are connected in parallel between the inverting input terminal and the output terminal of the operational amplifier OP via switch elements SW_Cf1 and SW_Cf2, respectively. On / off of the switch elements SW_Cf1 and SW_Cf2 is controlled by control signals Cf1 and Cf2 supplied from the control circuit 102, respectively. The control circuit 102 switches the gain of the integration amplifier 201 by switching on and off the switch elements SW_Cf1 and SW_Cf2.

  A switch element SW_RST is further connected between the inverting input terminal and the output terminal of the operational amplifier OP. The switching element SW_RST is turned on / off by a control signal RST supplied from the control circuit 102. When the switch element SW_RST is turned on, the inverting input terminal and the output terminal of the operational amplifier OP become conductive, and the integrating amplifier 201 is reset.

  The SH circuit 202 includes a first SH circuit 202a and a first SH circuit 202b, each performing a holding operation for holding an analog signal. The first SH circuit 202a includes a capacitive element C_SH1 and a switch element SW_CDS1 connected to one electrode of the capacitive element C_SH1. The first SH circuit 202b includes a capacitive element C_SH2 and a switch element SW_CDS2 connected to one electrode of the capacitive element C_SH2. On / off of the switch elements SW_CDS1 and SW_CDS2 is controlled by control signals CDS1 and CDS2 supplied from the control circuit 102, respectively. When the switch element SW_CDS1 is switched from OFF to ON, the first SH circuit 202a is switched from the hold mode to the sampling mode. During the sampling mode, an input signal to the first SH circuit 202a is charged in the capacitive element C_SH1. When the switch element SW_CDS1 is switched from on to off, the first SH circuit 202a is switched from the sampling mode to the hold mode. During the hold mode, the signal held in the capacitor C_SH1 is held (fixed). The same applies to the first SH circuit 202b.

  A variable resistance element R_LPF is connected between the integrating amplifier 201 and the SH circuit 202. The variable resistance element R_LPF changes its resistance value according to the control signal supplied from the control circuit 102. When the switch element SW_CDS1 is turned on, the variable resistance element R_LPF and the capacitive element C_SH1 are brought into conduction, and the variable resistance element R_LPF and the capacitive element C_SH1 form a low-pass filter. The low pass filter is a filter circuit for filtering the signal obtained from the integrating amplifier 201. The signal filtered by the low pass filter is held in the capacitive element C_SH1. When the switch element SW_CDS1 is turned off in this state, the voltage signal held in the capacitor element C_SH1 is held and is supplied to the multiplexer 110 thereafter. Similarly, when the switch element SW_CDS2 is turned on, the voltage signal is held in the capacitor element C_SH2, and then supplied to the multiplexer 110.

  Next, an operation example of the radiation imaging apparatus 100 will be described with reference to the timing chart of FIG. “Radiation” in FIG. 3 indicates whether the radiation imaging apparatus 100 is irradiated with radiation. When the radiation level is low, the radiation is not irradiated and when the radiation level is high, the radiation is irradiated. “Operation” in FIG. 3 indicates an operation performed by the radiation imaging apparatus 100. “R_LPF” indicates a change in the resistance value of the variable resistance element R_LPF according to some embodiments.

  The radiation imaging apparatus 100 mainly performs an offset signal readout operation (time T1 to T2), a standby operation (time T2 to T3), and a radiation signal readout operation (time T3). The offset signal readout operation is an operation of reading out from the sensor unit 105 a charge signal generated by the sensor unit 105 in a state where radiation is not irradiated. The signal processing circuit 103 generates an offset image based on a signal read by the offset signal reading operation (hereinafter referred to as an offset signal). The standby operation is an operation of resetting the charge accumulated in the sensor unit 105 while waiting for the radiation signal readout operation to start. The radiation signal readout operation is an operation of reading out from the sensor unit 105 a charge signal generated by the sensor unit 105 in a state where radiation is irradiated. The signal processing circuit 103 generates an offset image based on a signal read by the radiation signal reading operation (hereinafter referred to as a radiation signal). In FIG. 3, one offset signal reading operation (that is, an operation of reading one offset signal from each pixel of the sensor unit 105) is indicated by F [i]. One reset operation (that is, an operation of resetting each pixel of the sensor unit 105) is indicated by R [i]. One radiation signal reading operation (that is, an operation of reading one radiation signal from each pixel of the sensor unit 105) is denoted by X [i].

  The radiation image includes not only information related to radiation but also information that is derived from the characteristics of the sensor S and the readout circuit 101 and is irrelevant to radiation. Information derived from the characteristics of the sensor S and the readout circuit 101 and unrelated to radiation is hereinafter referred to as offset information. The offset information includes, for example, information related to the dark current generated in the sensor S, the offset of the readout circuit 101, and the like. The offset information may vary from pixel to pixel even in the same image, and may vary from timing to image acquisition even in the same pixel. Therefore, the radiation imaging apparatus 100 reduces such variation by acquiring an offset image including offset information separately from the radiation image and subtracting the offset image from the radiation image. The radiation imaging apparatus 100 stores the offset image in the signal processing circuit 103, for example.

  The offset information changes depending on the temperature in the radiation imaging apparatus 100, aging of circuit elements of the radiation imaging apparatus 100, and the like. Therefore, the radiation imaging apparatus 100 appropriately acquires an offset image and corrects the radiation image using the newly acquired offset image. The radiation imaging apparatus 100 may start the offset signal reading operation when a preset time has elapsed since the previous offset image acquisition, or may start the offset signal reading operation in response to an instruction from the user. Also good. Since the offset signal cannot be acquired during the radiation signal readout operation, the radiation imaging apparatus 100 finishes the radiation signal readout operation when it is determined that the offset signal should be acquired during the radiation signal readout operation. Hold until

  The radiation imaging apparatus 100 continuously performs 30 offset signal read operations F [1] to F [30] 30 times when newly acquiring an offset image as in the operation example illustrated in FIG. Get the offset image. The radiation imaging apparatus 100 (specifically, the signal processing circuit 103) calculates one offset image used for correcting the radiation image by averaging the 30 offset images. The number of offset images acquired by the radiation imaging apparatus 100 to calculate one offset image used for correction is not limited to 30 and may be any number of 1 or more.

  The offset information can include various noises in addition to the information derived from the characteristics of the sensor S and the readout circuit 101. Such noise includes, for example, electromagnetic waves radiated to the radiation imaging apparatus 100 from other devices, noise generated by the circuit itself mounted on the radiation imaging apparatus 100, noise mixed in the power supply circuit 104, and the like. . Since such noise can take different values between the offset image and the radiation image, the noise of the offset image may appear as an artifact in the image obtained by subtracting the offset image from the radiation image.

  Therefore, the control circuit 102 of the radiation imaging apparatus 100 performs the driving operation of the readout circuit 101 in the offset signal readout operation and the radiation signal readout operation so that the noise contained in the offset image is less than the noise contained in the radiation image. Switch. Here, the driving operation is an operation in which the control circuit 102 controls the driving of the reading circuit 101. For example, the control circuit 102 supplies a control signal to the reading circuit 101 or the control circuit 102 reads the reading circuit 101. Including the operation to set For example, the control circuit 102 switches the driving operation of the column amplifiers 107 to 109 included in the reading circuit 101. More specifically, the control circuit 102 switches the driving operation of at least one of the SH circuit 202 and the low-pass filter 203 of the column amplifiers 107 to 109. As described above, the control circuit 102 switches the driving operation of the readout circuit 101, whereby noise included in the offset image is reduced, and as a result, the image quality of the radiation image after correction using the offset image is improved. Further, since it is not necessary to cancel the acquisition of the offset image, the radiation image can be corrected using the offset image corresponding to the most recent situation of the radiation imaging apparatus 100.

  Subsequently, an operation example of the radiation imaging apparatus 100 according to the first embodiment will be described with reference to FIGS. 4 and 5. In the first embodiment, the control circuit 102 switches the setting of the low-pass filter 203 between the offset signal readout operation and the radiation signal readout operation. Other settings and driving operations may be the same. Specifically, as shown in FIG. 4, the control circuit 102 drives each circuit element at the same timing described below in the offset signal readout operation and the radiation signal readout operation. As shown in FIG. 3, the control circuit 102 makes the resistance value of the variable resistance element R_LPF during the offset signal readout operation higher than the resistance value of the variable resistance element R_LPF during the radiation signal readout operation.

  Hereinafter, one offset signal reading operation F [1] will be described, but the control circuit 102 performs the same driving operation even in one radiation signal reading operation X [1]. As shown in FIG. 3, the difference between the two operations is that the radiation imaging apparatus 100 is not irradiated with radiation in the offset signal readout operation F [1], whereas the radiation imaging apparatus 100 in the radiation signal readout operation X [1]. 100 is irradiated with radiation.

  When the offset signal read operation F [1] starts, the control circuit 102 starts an accumulation operation. In the accumulation operation, the control circuit 102 maintains the control signals RST, CDS1, and CDS2 at the off voltage for a predetermined period, and also maintains the drive signals that the drive circuit 106 supplies to the drive lines Vg1 to Vg3 at the off voltage. During this accumulation operation, charges corresponding to the dark current are accumulated in the sensor S.

  When the accumulation operation ends, the control circuit 102 shifts to a read operation. In the reading operation, the control circuit 102 controls the driving circuit 106 and the reading circuit 101 so as to read the offset signal from each sensor S of the sensor unit 105 for each pixel row. First, as indicated by F [1] [1] in FIG. 4, the control circuit 102 reads an offset signal from the sensor S included in the first pixel row. Specifically, the control circuit 102 turns on the switch element SW_RST and the switch element SW_CDS1. As a result, the voltage signal when the integrating amplifier 201 is reset is held in the capacitive element C_SH1. Thereafter, the control circuit 102 turns off the switch element SW_RST, and then turns off the switch element SW_CDS1. As a result, the voltage signal held in the capacitor C_SH1 is held.

  Subsequently, the control circuit 102 switches the drive signal that the drive circuit 106 supplies to the drive line Vg1 in the first row to an on voltage. Thereby, the electric charge accumulated in the sensor S included in the first row is transferred to each signal line Sig. Subsequently, the control circuit 102 turns on the switch element SW_CDS2. Accordingly, a voltage signal corresponding to the electric charge accumulated in the sensor S is held in the capacitive element C_SH2. Thereafter, the control circuit 102 turns off the switch element SW_CDS2. As a result, the voltage signal held in the capacitor C_SH2 is held. The read circuit 101 reads the difference between the two signals held by the SH circuit 202 at F [1] [1] as an offset signal.

  Subsequently, the control circuit 102 reads out an offset signal in the same manner from the sensor S included in the second pixel row as indicated by F [1] [2], and thereafter, indicated by F [1] [3]. Similarly, the offset signal is read out from the sensor S included in the third pixel row. As described above, the offset signal from each pixel for generating one offset image is acquired.

  In the reset operation R [i], the control circuit 102 sequentially removes the electric charge accumulated in the sensor S by switching the driving signal supplied to each driving signal Vg to the on voltage. The control circuit 102 may not perform the driving operation of the reading circuit 101 during the reset operation.

  With reference to FIG. 5A, the relationship between the variable resistance element R_LPF and the pass characteristic of the low-pass filter 203 will be described. The horizontal axis of the graph in FIG. 5A indicates the frequency, and the vertical axis indicates the gain (G) by the low-pass filter 203. 5A indicates the frequency characteristics of the low-pass filter 203 in the offset signal readout operation F [1], and the broken line 502 in FIG. 5A indicates the low-pass filter 203 in the radiation signal readout operation X [1]. The frequency characteristics of are shown. As shown in FIG. 5A, the control circuit 102 sets the low pass filter 203 so that the pass band of the low pass filter 203 in the offset signal readout operation is narrower than the pass band of the low pass filter 203 in the radiation signal readout operation. Switch.

  When the low-pass filter 203 is formed by the variable resistance element R_LPF and the capacitance element C_SH1, the cutoff frequency Fc is 1 / {2π × (resistance value of the variable resistance element R_LPF) × (capacitance value of the capacitance element C_SH1). }. Therefore, the larger the resistance value of the variable resistance element R_LPF, the narrower the pass band of the low-pass filter 203. Therefore, the control circuit 102 switches the resistance value of the variable resistance element R_LPF so that the resistance value of the variable resistance element R_LPF in the offset signal readout operation is larger than the resistance value of the variable resistance element R_LPF in the radiation signal readout operation. As a result, the amount of noise included in the signal passing through the low-pass filter 203 in the offset signal reading operation F [1] is reduced, and the noise included in the offset image is also reduced accordingly.

  The low-pass filter 203 mainly removes noise superimposed on the signal passing through the signal line and periodic noise superimposed on the reference voltage Vref of the integrating amplifier 201. Such noise causes artifacts extending in the row direction in the radiographic image (so-called horizontal noise). In the present embodiment, such lateral noise can be effectively reduced.

  In the operation example shown in FIG. 3, the resistance value of the variable resistance element R_LPF is kept constant during the operation of reading 30 offset signals (time T1 to T2). However, instead of this, the control circuit 102 may change the resistance value of the variable resistance element R_LPF for each offset signal read operation. In the operation example shown in FIG. 3, the control circuit 102 changes the resistance value of the variable resistance element R_LPF at time T2, but changes the resistance value at any timing before the radiation signal reading operation X [1] starts. May be.

  Subsequently, an operation example of the radiation imaging apparatus 100 according to the second embodiment will be described with reference to FIG. In the second embodiment, the control circuit 102 switches the driving operation of the SH circuit 202 between the offset signal readout operation and the radiation signal readout operation. The driving operation of other circuits and the setting of the reading circuit 101 may be the same. Specifically, as illustrated in FIG. 6, the control circuit 102 switches the driving timing of the SH circuit 202 between an offset signal readout operation and a radiation signal readout operation. As shown in FIG. 6, the driving content of the SH circuit 202 may be equal between the offset signal reading operation and the radiation signal reading operation.

  The control circuit 102 makes the duration T_F1 of the sampling mode of the first SH circuit 202a in the offset signal readout operation longer than the duration T_X1 of the sampling mode of the first SH circuit 202a in the radiation signal readout operation. Further, the control circuit 102 makes the sampling mode duration T_F2 of the first SH circuit 202b in the offset signal readout operation longer than the sampling mode duration T_X2 of the first SH circuit 202b in the radiation signal readout operation.

  During the sampling mode durations T_F1 and T_F2, the capacitive elements C_SH1 and C_SH2 are charged by the voltage signal from the integrating amplifier 201. The longer the sampling mode durations T_F1 and T_F2, the higher the accuracy of signals charged in the capacitive elements C_SH1 and C_SH2. For example, the durations T_F1 and T_F2 of the sampling mode may be a time that is five times or more the time constant of the low-pass filter 203.

  In the second embodiment, the control circuit 102 may make the resistance value of the variable resistance element R_LPF equal to each other in the offset signal reading operation and the radiation signal reading operation. In this case, the low-pass filter 203 may include a fixed resistance element instead of the variable resistance element R_LPF. Instead of this, the control circuit 102 may switch the resistance value of the variable resistance element R_LPF as in the first embodiment. In this case, the time constant of the low-pass filter 203 during the offset signal reading operation increases. Accordingly, the control circuit 102 accordingly sets the sampling mode durations T_F1 and T_F2 during the offset signal readout operation to be longer than the durations T_X1 and T_X2 during the radiation signal readout operation.

  When the control circuit 102 does not change the resistance value of the variable resistance element R_LPF, the control circuit 102 may set the sampling mode duration T_F1 longer or shorter than the sampling mode duration T_X1. May be. Furthermore, the control circuit 102 may make the duration T_F2 of the above-described sampling mode longer or shorter than T_X2 of the above-described sampling mode. FIG. 5B shows the frequency characteristics of the low-pass filter 203. When the duration of the sampling mode of the SH circuit 202 is T_SH, the gain of the low-pass filter 203 is minimal at a frequency where the frequency is 1 / (T_SH × n). Therefore, by making the sampling mode duration different between the offset signal readout operation and the radiation signal readout operation, the influence of external noise of a specific frequency is reduced.

  As shown in FIG. 6, in the second embodiment, the time related to the read operation during the offset signal read operation is longer than the time related to the read operation during the radiation signal read operation. Therefore, the control circuit 102 may adjust the time related to the accumulation operation to make the time related to one offset signal read operation coincide with the time related to one radiation signal read operation. In other words, the control circuit 102 may match the frame rate for acquiring the offset image with the frame rate for acquiring the radiation image. As a result, the net charge accumulation time until the signal is read from the sensor S is equal between the offset signal reading operation and the radiation signal reading operation.

  Subsequently, an operation example of the radiation imaging apparatus 100 according to the third example will be described with reference to FIG. In the third embodiment, the control circuit 102 switches the driving operation of the SH circuit 202 between the offset signal readout operation and the radiation signal readout operation. The driving operation of other circuits and the setting of the reading circuit 101 may be the same. Specifically, as illustrated in FIG. 7, the control circuit 102 switches the driving content of the SH circuit 202 between an offset signal reading operation and a radiation signal reading operation.

  In the third embodiment, the radiation signal readout operation X [i] is the same as that in the first embodiment, but the offset signal readout operation F [i] is different from the first embodiment. Hereinafter, the first offset signal read operation F [1] will be described as an example, but the same applies to other offset signal read operations F [i].

  First, as described above, the control circuit 102 reads an offset signal from the sensor S included in the first pixel row in F [1] [1]. Specifically, the readout circuit 101 reads out the difference between the two signals held in the SH circuit 202 at F [1] [1] as an offset signal. In reading the offset signal, the control circuit 102 turns on the drive signal that the drive circuit 106 supplies to the drive line Vg1 in the first row between the sampling mode of the first SH circuit 202a and the sampling mode of the first SH circuit 202b. Switch to voltage.

  Thereafter, in N [1] [1], the control circuit 102 causes the readout circuit 101 to output a signal while maintaining the drive signal supplied to the drive line Vg1 of the first row by the drive circuit 106 at the off voltage. Specifically, the control circuit 102 turns on the switch element SW_RST and the switch element SW_CDS1. As a result, the voltage signal when the integrating amplifier 201 is reset is held in the capacitive element C_SH1. Thereafter, the control circuit 102 turns off the switch element SW_RST, and then turns off the switch element SW_CDS1. As a result, the voltage signal held in the capacitor C_SH1 is held. Subsequently, the control circuit 102 turns on the switch element SW_CDS2. Thus, after the integration amplifier 201 is reset, a voltage signal corresponding to the potential of the signal line Sig to which no signal is transferred from the sensor S is held in the capacitor C_SH2. Thereafter, the control circuit 102 turns off the switch element SW_CDS2. As a result, the voltage signal held in the capacitor C_SH2 is held. The read circuit 101 outputs the difference between the two signals held by the SH circuit 202 at N [1] [1]. This difference is called a noise signal. Thereafter, the control circuit 102 performs the same process for the second pixel row and the third pixel row.

  The control circuit 102 continuously performs the sampling mode of the first SH circuit 202a and the sampling mode of the first SH circuit 202b at N [1] [1], during which the driving circuit 106 applies the driving line Vg1 of the first row. The drive signal to be supplied is not switched to the on voltage. The signal processing circuit 103 generates an offset image by subtracting the noise signal from the offset signal for each pixel.

  The noise signal includes noise generated in the readout circuit 101 and does not include a component corresponding to the charge from the sensor S. Therefore, the noise generated in the readout circuit 101 can be removed from the offset signal by subtracting the noise signal acquired continuously from the offset signal from the offset signal. By generating the offset image in this way, low frequency noise can be removed from the offset image. Specifically, the frequency is longer than the reciprocal of the time from the start of the sampling mode of the first SH circuit 202b in F [1] [1] to the start of the sampling mode of the first SH circuit 202b in N [1] [1]. Noise is removed. For example, when the time related to the reading operation for one pixel row is several tens of microseconds to several hundreds of microseconds, relatively low frequency noise of 10 kHz to 100 kHz is removed.

  Furthermore, in this embodiment, artifacts (so-called vertical noise) extending in the column direction in the radiographic image can be effectively reduced. This is because the noise appearing in the column direction is mainly due to the fact that a signal having variation is given to the plurality of integrating amplifiers 201 as a result of the electromagnetic noise having spatial variation acting on the signal line Sig.

  The noise signal includes not only noise generated in the readout circuit 101 but also an offset component of the readout circuit 101. Here, the offset component is a component that does not change over time, and the noise is a component that changes over time. Therefore, the offset image generated by subtracting the noise signal from the offset signal does not include the offset component of the readout circuit 101. Therefore, even if the radiographic image is corrected using the offset image, the offset component of the readout circuit 101 included in the radiographic image may not be removed.

  Therefore, in this embodiment, after N [1] [3] is finished, the control circuit 102 continuously performs sampling by the first SH circuit 202a and sampling by the first SH circuit 202b while the integrating amplifier 201 is reset. May be. Thereby, the offset component of the readout circuit 101 is acquired. This operation is represented by RST [1] in FIG. Specifically, with the start of RST [1], the control circuit 102 turns on the switch element SW_RST and the switch element SW_CDS1. As a result, the voltage signal when the integrating amplifier 201 is reset is held in the capacitive element C_SH1. Thereafter, the control circuit 102 turns off the switch element SW_CDS1 while keeping the switch element SW_RST on. As a result, the voltage signal held in the capacitor C_SH1 is held. Subsequently, the control circuit 102 turns on the switch element SW_CDS2. As a result, the voltage signal when the integrating amplifier 201 is reset is held in the capacitive element C_SH2. Thereafter, the control circuit 102 turns off the switch element SW_RST and the switch element SW_CDS2. As a result, the voltage signal held in the capacitor C_SH2 is held. The read circuit 101 reads the difference between the two signals held by the SH circuit 202 during resetting of the integrating amplifier 201 as an offset signal at RST [1]. The signal processing circuit 103 subtracts the noise signal (the signal obtained from N [1] [j]) from the offset signal (the signal obtained from F [1] [j]) for each pixel, and uses RST [1]. An offset image is generated by adding the acquired signal.

  In the example of FIG. 7, the example in which the offset component of the readout circuit 101 is obtained by performing RST [1] only once. Alternatively, one offset component may be obtained by averaging a plurality of offset components obtained by performing RST [1] a plurality of times. Furthermore, instead of the above example, an offset image may be generated as follows. Obtained from an offset signal (F [1] [j-1] for pixels in a row and the same column adjacent to the pixel from an offset signal (signal obtained by F [1] [j]) for a certain pixel. Signal). Thereafter, the signal acquired by RST [1] is added. Furthermore, in this example, instead of subtracting the offset signal (the signal obtained with F [1] [j-1]), the offset signal obtained with F [1] [j-1] and F [1] [ j] may be subtracted from the average of the offset signal obtained in step [j].

  In the third embodiment, the control circuit 102 may match the frame rate for acquiring the offset image with the frame rate for acquiring the radiation image. Further, in the example of FIG. 7, the offset signal read operation F [1] does not include the accumulation operation, but the control circuit 102 may perform the accumulation operation before the read operation. Further, in the third embodiment, setting switching as in the first embodiment and driving timing switching as in the second embodiment may be used in combination.

  In the first to third embodiments described above, the type of noise reduced from the offset image can be different. Further, depending on the setting of the radiation imaging apparatus 100, it may be difficult to execute any of the first to third embodiments described above. For example, in the third embodiment, since the number of times of signal readout is large in the offset signal readout operation, it may not be suitable for high frame rate imaging. Therefore, the control circuit 102 may determine which one of these embodiments should be performed instead of performing only one of the first to third embodiments. An example of a determination method performed by the control circuit 102 will be described with reference to FIG. The operation of FIG. 8 is started at the timing of acquiring the offset image.

  In step 801, the control circuit 102 acquires two offset images for determination. The driving operation of the readout circuit 101 when acquiring the determination offset image may be the offset signal readout operation of any of the first to third embodiments described above, or may be a radiation signal readout operation. May be.

  In step 802, the control circuit 102 determines whether or not the amount of noise included in the determination offset image is equal to or less than a threshold value. The amount of noise is calculated as follows, for example. The control circuit 102 takes the difference between the two offset images. An image obtained by this difference is called a difference image. The control circuit 102 averages the pixel values in the row direction and the column direction of the difference image, and obtains the standard deviation of the row and the column. The control circuit 102 uses this standard deviation as the amount of noise included in the determination offset image.

  If the amount of noise is equal to or less than the threshold (“YES” in step 802), the control circuit 102 acquires a correction offset image in step 804 using the same drive operation settings as in step 801. Since the method of acquiring the offset image for correction is as described above, it will not be repeated here. If the amount of noise is not less than or equal to the threshold (“NO” in step 802), the control circuit 102 switches the drive operation setting of the readout circuit 101 in step 803. The setting of the driving operation after switching may be a setting for the offset signal reading operation in any of the first to third embodiments described above, or a setting for the radiation signal reading operation. However, the setting of the driving operation already used for the determination is not selected. The order of setting of the drive circuits selected by the control circuit 102 in step 803 may be defined in advance or may be random. Thereafter, the control circuit 102 performs the processing from step 801 to determine the amount of noise using the new setting of the driving operation.

  If the amount of noise does not fall below the threshold value using any setting, the control circuit 102 acquires a correction offset image using the setting with the smallest amount of noise among the settings determined so far. When the radiation imaging apparatus 100 has a plurality of driving methods, the control circuit 102 may acquire an offset image for determination by the method of FIG. 8 for each driving method. Further, the control circuit 102 may determine the number of offset signal read operations F [i] to be performed to generate a correction offset image by analyzing the determination offset image.

  Next, a configuration example of a radiation imaging system including the radiation imaging apparatus 100 of FIG. 1 will be described with reference to FIG. The radiation imaging apparatus 100 in FIG. 9 is a portable radiation imaging apparatus, and includes a wireless communication unit 901 and a battery 902 in addition to the components described in FIG. The wireless communication unit 901 transmits the image generated by the signal processing circuit 103 to an external device and supplies an instruction from the external device to the control circuit 102. The battery 902 supplies power to the power supply circuit 104.

  The radiation imaging system further includes a control system 903 and a radiation generator 907. The control system 903 includes a wireless communication unit 905 that transmits and receives data to and from the radiation imaging apparatus 100, a computer 904 for the user to control the radiation imaging apparatus 100, and a display 906 for the user to check images and settings. Prepare. The radiation generation apparatus 907 includes a radiation control unit 908 that controls radiation exposure, a tube 909 that generates radiation, and an exposure switch 910.

  Next, another configuration example of the radiation imaging system including the radiation imaging apparatus 100 of FIG. 1 will be described with reference to FIG. A radiation imaging apparatus 100 in FIG. 10 is a stationary radiation imaging apparatus, and includes a wireless communication unit 901 and a battery 902 in addition to the components described in FIG. A description of components common to the radiation imaging system of FIG. 9 is omitted. The power supply circuit 104 receives power from a wall outlet outside the radiation imaging apparatus 100. The radiation imaging apparatus 100 and the control system 903 are connected with priority.

  The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

DESCRIPTION OF SYMBOLS 100 Radiation imaging device, 101 Reading circuit, 102 Control circuit, 105 Sensor part, 106 Drive circuit

Claims (13)

A sensor unit that generates a signal according to the amount of incident radiation;
A reading unit for reading a signal from the sensor unit;
A first read operation for reading a signal for generating a first image from the sensor unit that is not irradiated with radiation, and a second image for generating a second image from the sensor unit that is irradiated with radiation. A control unit that causes the reading unit to perform a second reading operation of reading a signal,
The control unit switches the driving operation of the reading unit between the first reading operation and the second reading operation so that noise included in the first image is less than noise included in the second image. A radiation imaging apparatus. The readout unit includes a filter circuit for filtering a signal obtained in the first readout operation and the second readout operation,
The radiation imaging apparatus according to claim 1, wherein the control unit switches setting of the filter circuit between the first readout operation and the second readout operation. The said control part switches the setting of the said filter circuit so that the pass band of the said filter circuit in the said 1st read-out operation may become narrower than the pass band of the said filter circuit in the said 2nd read-out operation | movement. Item 3. The radiation imaging apparatus according to Item 2. The filter circuit is a low-pass filter having a variable resistance element,
The control unit switches the resistance value of the variable resistance element so that a resistance value of the variable resistance element in the first read operation is larger than a resistance value of the variable resistance element in the second read operation. The radiation imaging apparatus according to claim 3, wherein the radiation imaging apparatus is characterized. The read unit includes a sample hold circuit for holding signals obtained in the first read operation and the second read operation,
5. The radiation imaging apparatus according to claim 1, wherein the control unit switches a driving operation of the sample hold circuit between the first reading operation and the second reading operation. 6. The said control part drives the said sample hold circuit so that the continuation time of the sampling mode in the said 1st read-out operation may become longer than the continuation time of the sampling mode in the said 2nd read-out operation. The radiation imaging apparatus described in 1. The sample and hold circuit includes a first sample and hold circuit and a second sample and hold circuit,
In each of the first read operation and the second read operation, a signal obtained by the read circuit is held in the first sample hold circuit in a state where a signal from the sensor unit is not transferred to the read unit. And a first holding operation for holding the signal obtained by the readout circuit in the second sample and hold circuit in a state where the signal from the sensor unit is transferred to the readout unit,
The first readout operation is further performed by holding the signal obtained by the readout circuit in the first sample and hold circuit in a state where the signal from the sensor unit is not transferred to the readout unit, and then from the sensor unit. Including a second holding operation for holding the signal obtained by the readout circuit in the second sample and hold circuit in a state where the signal is not transferred to the readout unit;
The radiation imaging according to claim 5 or 6, wherein the first image is generated based on a signal held by the first holding operation and a signal held by the second holding operation. apparatus. The readout circuit includes an amplifier circuit,
In the second holding operation, holding of the signal to the second sample and hold circuit is performed after resetting the amplifier circuit,
The first readout operation may further include a signal obtained by the readout circuit in a state where a signal from the sensor unit is not transferred to the readout unit during the reset of the amplification circuit, and the first readout operation during the reset of the amplification circuit. After being held in one sample and hold circuit, the signal obtained by the readout circuit is held in the second sample and hold circuit while the signal from the sensor unit is not transferred to the readout unit during reset of the amplifier circuit Including a third holding action
The radiation imaging apparatus according to claim 7, wherein the first image is generated further based on a signal held by the third holding operation.   2. The time required for reading a signal for generating one first image and the time required for reading a signal for generating one second image are equal to each other. The radiation imaging apparatus of any one of thru | or 8. When the amount of noise included in the first image exceeds a threshold, the control unit performs the first reading operation on the reading unit by a driving operation different from the driving operation used for acquiring the first image. The radiation imaging apparatus according to claim 1, wherein: The radiation imaging apparatus generates the first image based on a signal read from the sensor unit by the first reading operation, and based on a signal read from the sensor unit by the second reading operation. The radiation imaging apparatus according to claim 1, further comprising a signal processing unit that generates the second image. A sensor unit that generates a signal according to the amount of incident radiation;
A method for controlling a radiation imaging apparatus comprising a reading unit that reads a signal from the sensor unit,
A step of causing the reading unit to perform a first reading operation of reading a signal for generating a first image from the sensor unit in a state where radiation is not irradiated;
A step of causing the readout unit to perform a second readout operation of reading out a signal for generating a second image from the sensor unit in a state of being irradiated with radiation,
The drive operation of the read unit is switched between the first read operation and the second read operation so that noise included in the first image is less than noise included in the second image. Control method.   The program for making a computer perform each process of the control method of Claim 12.

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