JP2019088011A - Radiation imaging apparatus and radiation imaging system - Google Patents

Abstract

Kind Code: A1 A technique is provided that is advantageous for increasing the detection accuracy while increasing the detection frequency of radiation information. A radiation imaging apparatus has a plurality of pixels for acquiring a radiation image and a plurality of sensor units for detecting radiation. Each sensor unit includes a sensor that converts radiation into an electrical signal and accumulates the electrical signal in a signal accumulation period. The radiographic imaging apparatus further includes a signal accumulation period in the sensor of each of the plurality of sensor units having a first period of time and shifted from each other by a second period of time shorter than the first period of time. a control unit that controls a plurality of sensor units; and based on signals from the plurality of sensor units controlled by the control unit, information about radiation incident on the radiation imaging apparatus is obtained in cycles of the second time. , and a signal processing unit for outputting. [Selection drawing] Fig. 8

Description

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

  There is a radiation imaging apparatus having a conversion element that converts radiation into charge, and a pixel array in which pixels including switches such as thin film transistors are arranged. In recent years, multi-functionalization of such a radiation imaging apparatus has been studied. As one of them, incorporation of an automatic exposure control (AEC) function has attracted attention. The automatic exposure control in the radiation imaging apparatus can be used, for example, to detect the start of radiation irradiation from a radiation source, to determine the timing of stopping radiation irradiation, and to detect the radiation dose and the integrated dose.

  Patent Document 1 describes a radiation image capturing apparatus having pixels for radiation image capturing and pixels for radiation detection. Both the pixel for radiographic imaging and the pixel for radiation detection receive light to generate electric charge, and a sensor unit for accumulating the generated electric charge, and a TFT switch for reading out the electric charge accumulated in the sensor unit Including. In the pixel for radiographic imaging, the gate of the TFT switch is connected to the first scanning line, and in the pixel for radiation detection, the gate of the TFT switch is connected to the second scanning line. The source of the TFT switch is connected to the signal wiring for both the pixel for radiographic imaging and the pixel for radiation detection.

  In the passive pixel type conversion device as described in Patent Document 1, the signal stored in the sensor unit of the pixel is turned off by turning on the TFT switch to connect the sensor unit and the signal wiring and performing the readout operation. Do.

JP, 2012-015913, A

  In a radiation imaging apparatus, in order to accurately detect radiation information such as the intensity of radiation that changes from moment to moment, it is necessary to increase the readout frequency of signals from sensors that detect radiation information, that is, the detection frequency (time resolution). There is. However, if the detection frequency is increased, the accumulation period of signals in each sensor becomes short. As a result, the signal-to-noise ratio (SNR) at the time of reading out the signal from the sensor may decrease, and the detection accuracy of the radiation information may decrease. That is, the detection frequency of the radiation information and the detection accuracy are in a trade-off relationship.

  An object of the present invention is to provide an advantageous technique for enhancing detection accuracy while increasing the frequency of detection of radiation information.

  One aspect of the present invention is a radiation imaging apparatus having a plurality of pixels for acquiring a radiation image and a plurality of sensor units for detecting radiation, each sensor unit converting radiation into an electrical signal. The radiation imaging apparatus includes a sensor for converting and storing the electrical signal in a signal storage period, the radiation imaging device having a first time for the signal storage period in each of the plurality of sensor units, and The radiation imaging apparatus according to a control unit that controls the plurality of sensor units and signals from the plurality of sensor units controlled by the control unit so as to be mutually offset by a second time shorter than 1 hour A signal processing unit that outputs information on radiation incident on the light with the second time period as a cycle.

  According to the present invention, an advantageous technique is provided to increase the detection accuracy while increasing the detection frequency of radiation information.

FIG. 1 shows a radiation imaging system according to two embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS The figure which shows typically the radiation imaging device of embodiment of this invention. The figure which shows the more specific structural example of the radiation imaging device of embodiment of this invention. The figure which shows the structural example of a pixel and a sensor. The figure which shows the structural example of a signal processing part. FIG. 2 is a plan view (layout diagram) showing an example of the configuration of a pixel and a sensor. Sectional drawing which shows the structural example of a pixel and a sensor. The timing chart of the operation which detects the irradiation intensity of radiation. The timing chart of the operation which detects the irradiation intensity of radiation. The flowchart of the operation | movement which detects the irradiation intensity of a radiation. The timing chart of operation of the 1st modification. The figure which shows a 2nd modification. The figure which shows a 2nd modification. The figure which shows a 2nd modification. The figure which shows a 3rd modification. The figure which shows the modification of a sensor. The figure which shows the modification of a sensor. The figure which shows the modification of a sensor. The figure which shows the relationship of the sensor unit and sensor group in 2nd Embodiment. The timing chart which shows the operation | movement of 2nd Embodiment. The figure which shows the more specific structural example of a radiation imaging system.

  The invention will now be described through its exemplary embodiments with reference to the attached drawings.

First Embodiment
FIG. 1A schematically shows the configuration of a radiation imaging system according to an embodiment of the present invention. FIG. 1B schematically shows the configuration of a radiation imaging system according to another embodiment of the present invention. These radiation imaging systems include a radiation source 1 that emits radiation 3 such as X-rays, and a radiation imaging device 4. The radiation 3 emitted from the radiation source 1 passes through the subject 2 and enters the radiation imaging apparatus 4.

  The radiation imaging apparatus 4 includes a plurality of photoelectric conversion elements PEC two-dimensionally arranged to form an array having a plurality of rows and a plurality of columns, and a substrate 100 for supporting or holding the plurality of photoelectric conversion elements PEC. , And a scintillator 190. The scintillator 190 converts radiation into light such as visible light. The photoelectric conversion element PEC is formed of, for example, a photodiode, and photoelectrically converts the light converted by the scintillator 190. The photoelectric conversion element PEC and the scintillator 190 constitute a conversion element 12 for converting radiation into an electric signal. The scintillator 190 can be shared by the plurality of conversion elements 12.

  In the embodiment shown in FIG. 1 (a), a scintillator 190 is directed to the side of the radiation source 1. In the embodiment shown in FIG. 1 (b), the substrate 100 is directed to the side of the radiation source 1, and the radiation 3 passes through the substrate 100 and an array composed of a plurality of photoelectric conversion elements PEC to form a scintillator It is incident on 190. Then, the light converted by the scintillator 190 is incident on the photoelectric conversion element PEC.

  One embodiment of the radiation imaging device 4 is schematically shown in FIG. 2 (a). The radiation imaging apparatus 4 shown in FIG. 2A has an imaging area 90. In the imaging region 90, a plurality of pixels for acquiring a radiation image and a plurality of sensor groups (a plurality of sensor units) for detecting radiation are arranged. Here, one or more radiation detection areas 80 are provided in the imaging area 90, and a plurality of sensor groups (a plurality of sensor units) are arranged in each radiation detection area 80. Pixels for acquiring a radiation image may also be arranged in the radiation detection area 80.

  Another embodiment of the radiation imaging apparatus 4 is schematically shown in FIG. In the radiation detection apparatus 4 shown in FIG. 2B, a plurality of radiation detection areas 80 are arranged so as to cover the entire area of the imaging area 90. In the radiation detection area 80, in addition to sensor groups (sensor units). , Pixels for acquiring a radiation image are arranged.

  FIG. 2C schematically shows an example of use of the radiation imaging apparatus 4 shown in FIG. In the example shown in FIG. 2C, radiation information (radiation imaging is performed using a radiation examination region 81 selected according to the subject 2 (for example, the human chest) among the plurality of radiation detection regions 80. Information on the radiation incident on the device 4 is detected.

  A more specific configuration example of the radiation imaging apparatus 4 shown in FIG. 2A is shown in FIG. 3. In the imaging region 90 of the radiation imaging apparatus 4, a plurality of pixels 11 for acquiring a radiation image, and a plurality of sensor groups SG1, SG2, SG3 and SG4 for detecting radiation are arranged. The plurality of pixels 11 are two-dimensionally arranged to form an array having a plurality of rows and a plurality of columns. In the imaging area 90, one or more radiation detection areas 80 are provided. In each radiation detection area 80, a plurality of sensor groups SG1, SG2, SG3 and SG4 are arranged. In the first embodiment, one sensor unit is configured by one sensor group. In the second embodiment described later, one sensor unit is configured by two sensor groups.

  As illustrated in FIG. 4A, each pixel 11 includes a conversion element 12 that converts radiation into an electrical signal, and a switch 13. As described above, the conversion element 12 may be configured by a photoelectric conversion element and a scintillator, or may be configured by an element that converts radiation directly into an electrical signal. The conversion element 12 can have a first electrode (also referred to as an individual electrode or readout electrode) and a second electrode (also referred to as a common electrode). The first electrode is connected to the column signal line 16 via the switch 13. The second electrode is connected to a bias line 19 for applying a bias potential to the conversion element 12.

  Each of the plurality of sensor groups SG1, SG2, SG3, and SG4 is configured of a plurality of sensors 111. As illustrated in FIG. 4B, each sensor 111 includes a conversion element 121 that converts radiation into an electrical signal, and a switch 131. The conversion element 121 may be configured by a photoelectric conversion element and a scintillator, or may be configured by an element that converts radiation directly into an electrical signal. In the former, the scintillator may be shared with the scintillator for the pixel 11. The conversion element 121 can have a first electrode (also referred to as an individual electrode or readout electrode) and a second electrode (also referred to as a common electrode). The first electrode is connected to the detection signal line 161 via the switch 131. The second electrode is connected to a bias line 19 for applying a bias potential to the conversion element 121.

  Description will be continued with reference to FIG. 3 again. SG <b> 1, SG <b> 2, SG <b> 3 and SG <b> 4 in FIG. 3 indicate the sensors 111. More specifically, SG1, SG2, SG3, and SG4 in FIG. 3 indicate sensor groups SG1, SG2, SG3, and SG4 to which the sensor 111 belongs. The imaging region 90 is configured, for example, by an array of pixels 11 in 1000 rows × 1000 columns to 3000 rows × 3000 columns. In the example shown in FIG. 3, the pixel 11 is not disposed at the position where the sensor 111 is disposed, but in another example, the pixel 11 may be disposed at the position where the sensor 111 is disposed. .

  The bias line 19 connected to the second electrode of the conversion element 12 of the pixel 11 and the second electrode of the conversion element 121 of the sensor 111 is connected to a bias power supply 50. The column signal line 16 connected to the source (or drain) of the switch 13 of the pixel 11 is connected to the reading unit 30. The detection signal line 161 connected to the source (or the drain) of the switch 131 of the sensor 111 is connected to the signal processing unit 40. The pixel control line 15 driven by the row selection unit 20 is connected to the gate of the switch 13 of the pixel 11. When the pixel control line 15 is driven to the active level, the conversion element 12 of the pixel 11 and the column signal line 16 are electrically connected by the switch 13. A sensor control line 411 driven by the sensor control unit 41 is connected to the gate of the switch 131 of the sensor 111. When the sensor control line 411 is driven to the active level, the conversion element 121 of the sensor 111 and the detection signal line 161 are electrically connected by the switch 131.

  In the first embodiment, each radiation detection area 80 includes N sensor groups SG1, SG2, SG3, and SG4 (N sensor units), and each of the sensor groups SG1, SG2, SG3, and SG4 is M Sensor 111 of FIG. In the example shown in FIG. 3, N = 4 and M = 4, but this is merely an example.

  In each radiation detection area 80, a detection signal common to the sources (or drains) of all the switches 131 of M sensors 111 of N sensor groups SG1, SG2, SG3, and SG4 (N sensor units) It is connected to the line 161. On the other hand, different sensor control lines 411 are connected to the gate of the switch 131 of the sensor 111 for each sensor group (sensor unit). That is, a common k sensor control line 411 is connected to the gates of the switches 131 of the sensors 111 of the k sensor group. When the kth sensor control line 411 is driven to the active level, the signals of the M sensors 111 of the kth sensor group are output to the common detection signal line 161.

  A configuration example of the signal processing unit 40 is shown in FIG. In the example illustrated in FIG. 5, the signal processing unit 40 reads the charge generated by the sensor 111 as a signal of the sensor 111. The signal processing unit 40 can include, for example, a signal detection unit 39 and an AD converter 33. The signal detection unit 39 includes, for example, an integration amplifier 31 and a reset switch 34. The detection signal line 161 is connected to the input of the integration amplifier 31, and the AD converter 33 is connected to the output of the integration amplifier 31. The reset switch 34 is arranged to be able to short between the input and the output of the integrating amplifier 31. By turning on the reset switch 34, the potential of the output of the integrating amplifier 31 and the potential of the detection signal line 161 can be reset.

  The configuration of the signal processing unit 40 is not particularly limited, and when reading out the current or voltage generated by the sensor 111 as a signal of the sensor 111, the signal processing unit 40 may be, for example, a non-inverting amplifier or an inverting amplifier. It can be comprised.

  The row selection unit 20, the reading unit 30, the sensor control unit 41, and the signal processing unit 40 are controlled by the control unit 49. From a certain point of view, at least one of the row selecting unit 20, the reading unit 30, the sensor control unit 41, and the signal processing unit 40 can be understood as a part of the control unit 49.

  The control unit 49 can perform various processes based on the radiation information provided from the signal processing unit 40. The control unit 49 can detect, for example, that irradiation of radiation from the radiation source to the radiation detection apparatus 4 has been started, that irradiation of radiation has been stopped, intensity of radiation, integrated irradiation dose of radiation, and the like. Furthermore, the control unit 49 is connected to the radiation source 1 to receive a signal indicating start and / or stop of radiation irradiation from the radiation source 1 and to start and / or stop radiation irradiation to the radiation source 1. It can be instructed.

  FIG. 6 is a plan view (layout diagram) showing a configuration example of the pixel 11 and the sensor 111. As shown in FIG. 7 (a) is a cross-sectional view taken along line A-A 'in FIG. 6, and FIG. 7 (b) is a cross-sectional view taken along line B-B' in FIG. The switch 13 of the pixel 11 can be configured by a TFT (thin film transistor) as illustrated in FIG. 7A. The switch element 13 may be disposed on the substrate 100 and covered by the interlayer insulating layer 181. The conversion element 12 can be disposed on the interlayer insulating layer 181.

  The conversion element 12 is connected to the column signal line 16 via the switch 13. The conversion element 12 may include a first electrode 125, a PIN photodiode (photoelectric conversion element) 124, and a second electrode 126. A protective film 182, a second interphase insulating layer 183, a bias line 19, and a protective film 184 are sequentially disposed on the PIN photodiode. A planarization film (not shown) and a scintillator 190 are disposed on the protective film 184. The second electrode 126 is connected to the bias line 19 through the contact hole. As a material of the second electrode 126, ITO having a light transmitting property is used, and the light converted from the radiation by the scintillator 190 can be transmitted.

  Similarly, the switch 131 of the sensor 111 can be configured with a TFT (thin film transistor) as illustrated in FIG. 7B. The switch element 131 may be disposed on the substrate 100 and covered by the interlayer insulating layer 181. The conversion element 121 can be disposed on the interlayer insulating layer 181.

  The conversion element 121 is connected to the detection signal line 161 via the switch 131. The conversion element 121 may include a first electrode 125, a PIN photodiode (photoelectric conversion element) 124, and a second electrode 126. A protective film 182, a second interphase insulating layer 183, a bias line 19, and a protective film 184 are sequentially disposed on the PIN photodiode. A planarization film (not shown) and a scintillator 190 are disposed on the protective film 184.

  In the above example, a PIN photodiode is adopted as the photoelectric conversion element constituting the conversion elements 12 and 121, but the photoelectric conversion element may be, for example, a MIS type sensor.

  Hereinafter, a method of detecting radiation information based on a signal from the sensor 111 will be described. First, a method of detecting radiation intensity as radiation information will be described. The timing chart of the operation | movement which detects the irradiation intensity of a radiation is shown by FIG. At the top of FIG. 8, the intensity (“irradiation intensity”) of the radiation incident on the radiation detection area 80 is shown. In FIG. 8, the number of sensor groups is N, and the sensor groups are described as SG1, SG2,..., SGN. In the first embodiment, the sensor group and the sensor unit are equivalent, and the sensor units are described as SU1, SU2, ..., SUN.

  The sensor control unit 41 controls the first sensor group SG1 (first sensor unit SU1) to the kth sensor control line 411 (k = 1 to N) for individually controlling the Nth sensor group SGN (Nth sensor unit SUN). In response, voltage pulses (sensor control signals) are sequentially applied. Here, when the k-th sensor control line 411 is driven to the high level, the switch 131 of the sensor 111 of the k-th sensor group SGk becomes conductive.

  First, during the period from time t11 to t12, the sensor control line 411 of the first sensor group SG1 (SU1) is driven to the high level, and the switch 131 of the sensor 111 of the first sensor group SG1 is changed from the nonconductive state to the conductive state. Ru. Thereafter, in the period from time t21 to t22, the switch 131 of the sensor 111 of the second sensor group SG2 (SU2) is changed from the non-conduction state to the conduction state. Hereinafter, the sensor 111 of the Nth sensor group SGN (SUN) is similarly controlled. Thereafter, the process returns to the first sensor group SG1 (SU1), and the sensor control line 411 of the first sensor group SG1 (SU1) is driven to the high level in the period from time t13 to t14. As a result, the switch 131 of the sensor 111 of the first sensor group SG1 (SU1) is changed from the non-conductive state to the conductive state.

  Hereinafter, operations of the sensor 111 and the signal processing unit 40 will be described. The switch 131 of the sensor 111 of the first sensor group SG1 is in a non-conductive state in the period from time t12 to t13. The charge generated by the irradiation of radiation during this period is accumulated in the conversion element 121 of the sensor 111 of the first sensor group SG1. That is, the period from time t12 to t13 is the signal accumulation period SAP. A signal corresponding to the charge accumulated in the conversion element 121 of the sensor 111 of the first sensor group SG1 is sent to the signal processing unit 40 at time t13. Specifically, at time t13, the switch 131 of the sensor 111 of the first sensor group SG1 is switched to the conductive state, whereby the signal of the sensor 111 of the first sensor group SG1 is transmitted through the detection signal line 161 to the signal processing unit Sent to 40

  The signal processing unit 40 detects a signal output from the sensor 111 of the first sensor group SG1 as a signal amount (irradiation intensity) m (1) of the sensor 111 of the first sensor group SG1 at time t111 immediately after time t13. And outputs the signal amount m (1) to the control unit 49.

  Similarly, at time t112 immediately after time t23, the signal processing unit 40 detects the signal amount m (2) of the sensor 111 of the second sensor group SG2 and outputs the signal amount m (2) to the control unit 49. . Similarly, the signal processing unit 40 similarly detects the signal amounts m (3) to m (N) of the sensors 111 of the third to N-th sensor groups SG3 to SGN and outputs them to the control unit 49. Thereafter, the signal processing unit 40 repeats the above process in order from the first sensor group SG1. Thereby, a signal sequence (numerical value sequence) including signal amounts m (1), m (2),..., M (N), m (1), m2 (2). The signal processing unit 40 outputs the signal amounts m (1), m (2), ..., m (N), m (1), m2 (2), ... with the sampling interval SI as a cycle. .

  The signal quantities m (1), m (2), ..., m (N) differ from each other in the sensor group used to acquire them, but the error due to that is the sensor of a plurality of sensor groups It can be reduced by arranging 111 in a distributed manner.

  Here, the interval between the timing of detecting m (k) and the timing of detecting m (k + 1) (for example, the interval between t111 and t112) is the sampling interval (second time) SI. The signal accumulation period SAP in each sensor group corresponds to the product of the sampling interval SI and the number N of sensor groups. The frequency (times / second) at which the signal processing unit 40 detects the signal amount (irradiation intensity of radiation) from any of the plurality of sensor groups is the reciprocal of the sampling interval SI.

  The control unit 49 causes the signal accumulation period SAP in each of the plurality of sensor units SU1 to SUN to have a first time, and to be mutually offset by a second time that is the length of the sampling period SI. A plurality of sensor units SU1 to SUN are controlled. Here, the second time which is the length of the sampling period SI is shorter than the first time which is the length of the signal accumulation period SAP. The control of the plurality of sensor units SU1 to SUN by the control unit 49 can be performed through the control of the row selection unit 20.

  The control unit 49 can detect the start and end timings of radiation irradiation based on the radiation information (in this case, the irradiation amount m (k)) provided from the signal processing unit 40. For example, the control unit 49 determines the time (t114) when the signal amount m (k) (or the value of the numerical value string generated by interpolation from the signal string consisting of the signal amount m (k)) exceeds the threshold Th1. It can be detected as the timing when irradiation of radiation is started. Similarly, the control unit 49 determines the time at which the signal amount m (k) (or a value sequence generated by interpolation from a signal sequence consisting of the signal amount m (k)) falls below a threshold. It can be detected as the timing at which the irradiation was stopped.

  Alternatively, as described below, the control unit 49 can also detect the integrated irradiation amount of radiation based on the radiation information (here, the irradiation amount m (k)) provided from the signal processing unit 40. FIG. 9 shows a timing chart of an operation of detecting the integrated irradiation amount based on the irradiation intensity of the radiation.

  Similarly to the operation shown in FIG. 8, the signal processing unit 40 measures the signal amounts m (1), m (2),..., M (N), m (1), m2 (2),. Output a signal sequence consisting of The control unit 49 receives the signal amount m (1) of the first sensor group SG1 (SU1) at time t111. Then, the control unit 49 sets a value obtained by adding m (1) to the integrated signal amount m '(1) held in the control unit 49 as a new m' (1), and the next first sensor group It holds up to detection of the signal amount m (1) of SG1 (SU1). Similarly, the control unit 49 calculates and holds the integrated signal amount m '(k) for other sensor groups, that is, the k-th sensor group SGk as needed. As a result, a signal sequence including integrated signal amounts m '(1), m' (2), ..., m '(N), m' (1), m'2 (2), ... is obtained. .

  The control unit 49 can determine that the integrated irradiation amount has reached the appropriate amount at a time (t114) when the integrated signal amount m '(k) of any of the sensor groups exceeds the threshold value Th2. As the information indicating the irradiation intensity, the signal amount m (k) at each time point may be used as described with reference to FIG. 8, or the difference between the sensor groups of the integrated signal amount m ′ (k) m '(2) -m' (1) etc. may be used.

  FIG. 10 shows a flowchart of the operation described with reference to FIG. This operation may include a preparation step (S1010 to S1014), an operation step (S1016 to S1020), and a control step (S1024, S1026).

  First, the preparation steps (S1010 to S1014) will be described. In S1010, the control unit 49 resets the sensors 111 of the sensor groups SG1 to SGN. Specifically, the control unit 49 causes the switch 131 of the sensor 111 of the sensor groups SG1 to SGN to be in a conductive state, and removes the charge (such as dark charge) stored in the conversion element 121. In S1012, the control unit 49 clears the integrated signal amount m ′ (k) (k = 1 to N) held in the memory in the control unit 49. In S1014, a variable k that specifies a sensor group is set to 1. In the preparation step, offset correction and / or sensitivity correction may also be performed among the sensor groups SG1 to SGN.

  Next, the calculation steps (S1016 to S1020) will be described. In S1016, the control unit 49 obtains the signal amount m (k) of the k-th sensor group SGk (k-th sensor unit SUk) from the signal processing unit 40. In S1018, the control unit 49 adds the signal amount m (k) to the integrated signal amount m '(k) of the k-th sensor group SGk held in the control unit 49, and adds a new integrated signal amount m' (k). And the value of In S1020, control unit 49 determines whether integrated signal amount m '(k) exceeds threshold value Th2, and in the case of exceeding, the process proceeds to S1024, and in the case of not exceeding, the value of k in S1022 Is changed by 1 and the process returns to S1016.

  Next, control steps (S1024, S1026) will be described. In S1024, the control unit 49 causes the radiation source 1 to stop the radiation irradiation. In S1026, the control unit 49 controls the row selection unit 20 and the reading unit 30 to read an image.

  Instead of the above processing, the signal processing unit 40 may be provided with an integration circuit, and the integration dose may be obtained by the integration circuit.

  Hereinafter, the effects of the first embodiment will be exemplarily described, but this is not intended to control the present invention. When detecting radiation information such as radiation intensity and integrated irradiation dose based on a signal from the sensor 111 having the conversion element 121 and the switch 131, the detection accuracy of the radiation information depends on the signal-to-noise ratio (SNR). The SNR is a ratio of a signal value (signal amount) to random noise generated in the conversion element 121, the switch 131, the signal processing unit 40, and the like.

  When the detection frequency (or signal accumulation period) of the radiation information is determined, reading out the signals from all the M × N sensors 111 at the same time makes the signal amount smaller than when reading out the signal from one detection pixel. It will be M × N times. Further, of the random noise, a component (kTC noise) proportional to the capacitance of the conversion element 121 is √ (M × N) times, and the other components are the same.

  On the other hand, in the first embodiment, M signals are simultaneously read out for every N sensor groups (sensor units). Further, the signal accumulation period in the sensor 111 of each sensor group (sensor unit) is N times that in the case where signals are simultaneously read from all the M × N sensors 111, so the signal amount is also N times. Therefore, in the first embodiment, the signal amount obtained in one read operation is M × N times that in the case of reading a signal from one sensor 111. In the first embodiment, kTC noise of random noise is √M times, and the other components are the same. Therefore, according to the first embodiment, the SNR, that is, the detection accuracy can be enhanced as compared with the case where signals are simultaneously read from all the M × N sensors 111.

  In the first embodiment, the signal of M sensors 111 out of the M × N sensors 111 is read out in one read operation, and this signal is used as a representative value of the output values of the M × N sensors 111. To change the sensor group (sensor unit). By this, the detection frequency (time resolution) of radiation information can be raised.

  Hereinafter, the arrangement, shape, and size of the radiation detection area 80 will be supplemented. In radiography with a human subject, etc., to obtain an image of appropriate brightness, monitor the integrated radiation dose at the position corresponding to the lung field, abdominal cavity, spine, joints, etc. and adjust the radiation dose. It is widely done. Generally, in such a method, in consideration of the ease of positioning between the subject and the radiation imaging apparatus, the radiation detection area can be an area where the radiation intensity can be regarded as substantially uniform. For example, in radiation imaging of a human chest, when the subject 2 is disposed relative to the imaging region 90 as shown in FIG. 2C, the radiation intensity is approximately one in the region corresponding to the lung field (about 5 cm square) You can think of it as Generally, the arrangement, shape, and size of the radiation detection area 80 can be determined according to the shape and size of the central part (lumbar spine, pelvis, joints, breast, etc.) in radiation imaging. The shape of the radiation detection area 80 may be square, or may be another shape such as a circle. The size of the radiation detection area 80 is preferably about 3 to 5 cm for imaging centered on human lung field, abdominal cavity, spine, and joints, and about 0.5 to 1 cm for imaging of a breast.

  Hereinafter, the arrangement of the sensor 111 will be supplemented. Under the imaging conditions illustrated in FIG. 2C, since the subject 2 is not uniform, the distribution of the radiation intensity transmitted through the subject 2 in the radiation detection region 80 is not uniform. For example, in the human chest, ribs are present at intervals of 2 to 3 cm, and the radiation transmittance of this portion is low. Other parts of the human also have bones and soft tissues periodically located at intervals of about 1 to several cm. For this reason, it is preferable that the arrangement pitch of the sensor 111 in each sensor group (sensor unit) be equal to or less than half of the minimum value (about 1 cm) of the period in the portion consisting of bone and soft tissue, ie about 5 mm or less . By arranging the plurality (M) of sensors 111 constituting each sensor group (sensor unit) equally in the radiation detection area 80, the obtained radiation information can be sufficiently averaged. This can reduce the number of sensor groups (sensor units). As the number (M) of sensors 111 per sensor group (sensor unit) is increased, the averaging effect is enhanced.

Since the signal accumulation period in each sensor group (sensor unit) is the product of the sampling interval and the number (N) of sensor groups (sensor units), the number (N) of sensor groups (sensor units) can be increased. It is advantageous. In practice, N may be determined according to the response time constant of the signal processing unit 40, the frequency of detection of the required radiation information, and the like. Note that if the values of N and M are too large, an adverse effect (dropout of pixels) occurs on the image acquired by the pixel 11, so N and M take into consideration the balance between the above-described effect and the adverse effect on the image. Can be determined. When the radiation detection area 80 is a square of 5 cm on a side, for example, N = 25 and M = 100, it is possible to obtain a high averaging effect within a range where there is no adverse effect on the image. When arranging each sensor group (sensor unit) in a two-dimensional matrix in the radiation detection area 80, the arrangement pitch is 5 cm // (100) = 5 mm
It is preferable in order to satisfy the above-mentioned condition regarding the arrangement interval.

  The radiation irradiation period needs to be controlled with an error of 1% (0.01 to 10 ms) in order to prevent useless exposure of the subject to the general radiation irradiation period (about 1 to 1000 ms). At this time, the sampling interval by the signal processing unit 40 may be 0.01 to 10 ms or less, and the signal processing unit 40 can be configured by a general circuit (such as an integrating amplifier). Further, since N = 25, the signal accumulation period in the sensor of each sensor group (sensor unit) is about 0.25 ms to 250 ms, and a sufficient signal amount can be obtained. The number N of sensor groups (sensor units) may be different for each radiation detection area according to the object to be inspected.

  Hereinafter, some modifications of the first embodiment will be described. A first modification is described in FIG. It is useful when the radiation imaging apparatus 4 has a function of detecting the start of radiation irradiation. The start of the radiation irradiation can be detected by, for example, a notification from the radiation source 1 or the irradiation of the radiation by a detection unit provided in the radiation imaging apparatus 4. When the control unit 49 detects the start of radiation irradiation at time t00, it turns on the switches 131 of the sensors 111 of all the sensor groups SG1 to SGN (sensor units SU1 to SUN) in the period from time t00 to t01. These sensors 111 are thereby reset. This reset removes excess charge (such as dark charge). Next, the control unit 49 returns the switches 131 of the sensors 111 of all the sensor groups SG1 to SGN (sensor units SU1 to SUN) to the non-conductive state to start signal accumulation. After that, the operation shown in FIG. 8 or FIG. 9 is the same. According to the first modification, it is possible to accurately detect radiation information after the start of radiation irradiation.

  The second modified example is shown in FIG. 12, FIG. 13 and FIG. In the second modification, the sensor 111 is replaced by the sensor 111 ′, and only the sensor 111 ′ is disposed in the radiation detection area 80. The sensor 111 'also functions as a pixel. That is, the sensor 111 ′ includes the conversion element 121 that converts radiation into an electrical signal, the switch 131, and the conversion element 12 that converts radiation into an electrical signal, and the switch 13. That is, the sensor 111 ′ has a configuration in which the pixel 11 and the sensor 111 are combined. In the second modification, in the imaging region 90, the plurality of pixels 11 and the plurality of sensors 111 'are arranged so as to configure a plurality of rows and a plurality of columns. The number of pixels in each of the plurality of rows (the number of pixels 11 and the number of sensors 111 ') is equal to one another.

  According to the second modification, since the loss of radiation image information due to the loss of the pixels 11 due to the arrangement of the sensor 111 ′ does not occur, the quality of the obtained radiation image can be improved. Further, since loss of radiation image information due to loss of the pixels 11 due to the arrangement of the sensors 111 ′ does not occur, it is advantageous for increasing the number of sensors 111 ′. This is advantageous for the improvement of the detection frequency of radiation information and the detection accuracy.

  A third modification is shown in FIG. Here, in FIG. 15, the sensor 111 is illustrated as SG1, SG2, SG3, and SG4 indicating the sensor group to which it belongs. In the third modification, detection signal lines 161 arranged in different columns are separated from each other. Further, in the third modification, a plurality of signal detection units 39 are provided such that one signal detection unit 39 corresponds to each detection signal line 161, and a plurality of signal detection units 39 and AD converters 33 are provided. A multiplexer 32 is disposed between them. The multiplexer 32 selects the outputs of the plurality of signal detection units 39 in a predetermined order, and supplies the same to the AD converter 33. Each signal detection unit 39 can have the configuration illustrated in FIG. The integrating amplifier 31 may be replaced by another amplifier such as a non-inverting amplifier or an inverting amplifier.

  In the example shown in FIG. 15, only one sensor 111 of one sensor group (sensor unit) is connected to one detection signal line 161, but sensors 111 of different sensor groups (sensor units) are connected to each other. It may be done.

  The signal detection unit 39 can have a function (reset switch 34) for resetting the detection signal line 161. In the third modification, since the detection signal lines 161 arranged in different columns are separated from each other, the capacitance of the detection signal line 161 viewed from each signal detection unit 39 is small. Therefore, the time required to reset the detection signal line 161 by the signal detection unit 39 is shortened. Therefore, the time required for the read operation and the sampling interval can be shortened. This is advantageous for increasing the frequency of detection of radiation information.

  Alternatively, for example, a low pass filter may be provided on the input side of the signal detection unit 39 to reduce the influence of noise from the external electromagnetic field while maintaining the detection frequency of the radiation information.

  Alternatively, the signal processing unit 40 may be configured by a combination of the plurality of techniques described above. For example, the start of radiation irradiation can be detected by a circuit in which the time required to read out a signal is short, and the integrated irradiation amount can be measured by a circuit in which noise is eliminated.

  Furthermore, when the signal processing unit 40 includes the reset switch 34 for each detection signal line 161, as shown in FIG. 16, the conversion element 121 of the sensor 111 is connected to the detection signal line 161 without passing through the switch 131. It is also good. The signal accumulation time of the sensor 111 of each sensor group (sensor unit) can be determined by the opening / closing timing of the reset switch 34, and can perform the same operation as the operation shown in FIG. A plan view (layout view) of the sensor 111 shown in FIG. 16 is shown in FIG. A cross-sectional view taken along the line B-B 'of FIG. 17 is shown in FIG. The omission of the switch 131 simplifies the structure of the sensor 111. This is advantageous for improving the yield.

Second Embodiment
In the second embodiment, as shown in FIG. 19, each sensor unit is composed of two sensor groups. For example, the first sensor unit SU1 is composed of a first sensor group SG1 and a second sensor group SG2. In other words, the first sensor unit SU1 includes the sensor (first sensor) 111 of the first sensor group SG1 and the sensor (second sensor) 111 of the second sensor group SG2. The second sensor unit SU2 is configured of a third sensor group SG3 and a fourth sensor group SG2. In other words, the second sensor unit SU2 includes the sensor (third sensor) 111 of the third sensor group SG3 and the sensor (fourth sensor) 111 of the fourth sensor group SG4. The radiation imaging apparatus 4 of the second embodiment may have the same configuration as that of the first embodiment as to the configuration of the imaging region 90.

  FIG. 20 shows the operation of the radiation imaging apparatus 4 of the second embodiment. Here, a method of detecting radiation intensity as radiation information will be described by way of example. The sensor control unit 41 controls the voltage pulse (sensor control signal) according to a predetermined procedure for the kth sensor control line 411 (k = 1 to N) for individually controlling the first sensor group SG1 to the Nth sensor group SGN. Apply.

  Specifically, the first sensor control line 411 that controls the sensor 111 of the first sensor group SG1 that constitutes a part of the first sensor unit SU1 is driven to the high level in the period from t11 to t12. The second sensor control line 411 that controls the sensor (second sensor) 111 of the second sensor group SG2 that constitutes another part of the first sensor unit SU1 has a period from time t11 to t12 and time t21. It is driven to high level in the period up to t22.

  Similarly, the third sensor control line 411 that controls the sensor 111 of the third sensor group SG3 that constitutes a part of the second sensor unit SU2 is driven to the high level in the period from t31 to t32. The fourth sensor control line 411 that controls the sensor (second sensor) 111 of the fourth sensor group SG4 that constitutes another part of the second sensor unit SU2 has a period from time t31 to t32 and time t41. It is driven to high level in the period up to t42.

  As described above, after the first sensor unit SU1 to the (N / 2) th sensor unit SU (N / 2) are driven, the first sensor unit SU1 to the (N / 2) th sensor unit SU (again N / 2) is similarly driven.

  Specifically, the first sensor control line 411 that controls the sensor 111 of the first sensor group SG1 that constitutes a part of the first sensor unit SU1 is driven to the high level in the period from t13 to t14. The second sensor control line 411 that controls the sensor (second sensor) 111 of the second sensor group SG2 that constitutes another part of the first sensor unit SU1 has a period from time t13 to t14 and time t23. It is driven to high level in the period up to t24.

  Similarly, the third sensor control line 411 that controls the sensor 111 of the third sensor group SG3 that constitutes a part of the second sensor unit SU2 is driven to the high level in the period from t33 to t34. The fourth sensor control line 411 that controls the sensor (second sensor) 111 of the fourth sensor group SG4 that constitutes another part of the second sensor unit SU2 has a period from time t33 to time t34 and time t43. It is driven to the high level in the period up to t44.

  On the other hand, the signal processing unit 40 sets the signal amount m (1) to the signal accumulated in the conversion element 121 of the sensor 111 of the first sensor group SG1 that constitutes a part of the first sensor unit SU1 in the period from time t12 to t13. As detected. The signal processing unit 40 also converts the signal accumulated in the conversion element 121 of the sensor (second sensor) 111 of the second sensor group SG2 that constitutes another part of the first sensor unit SU1 in the period from time t12 to t21. It is detected as the signal amount m (2). Then, the signal processing unit 40 calculates m (1) -m (2), and outputs m (1) -m (2) to the control unit 49 at time t211. Here, the period from time t12 to t21 is a third time shorter than the first time which is the length of the signal accumulation period SAP of the sensor 111 of the first sensor group SG1.

  Similarly, the signal processing unit 40 sets the signal amount m (3 (3)) to the signal accumulated in the conversion element 121 of the sensor 111 of the third sensor group SG3 that constitutes a part of the second sensor unit SU2 in the period from time t32 to t33. Detect as). The signal processing unit 40 also converts the signal accumulated in the conversion element 121 of the sensor 111 of the fourth sensor group SG4 that constitutes another part of the second sensor unit SU2 in the period (third time) from time t32 to t41. It is detected as the signal amount m (4). Then, the signal processing unit 40 calculates m (3) -m (4), and outputs m (3) -m (4) to the control unit 49 at time t212.

  Thereafter, the signal processing unit 40 executes the same processing until the (N / 2) th sensor unit SU (N / 2), and thereafter, performs the same processing from the first sensor unit to the (N / 2) th sensor unit SU. Repeat until (N / 2).

  As a result, a numerical value sequence of M (k) = m (k-1) -m (k) is obtained with the period from time t211 to t212 as the sampling interval (period = second time). By handling the numerical sequence of M (k) in the same manner as m (k) in the first embodiment, it is possible to detect the start and end timings of radiation irradiation and the integrated irradiation dose.

  An offset component can be superimposed on the signal output from the sensor 111 due to disturbance (external electromagnetic field, temperature change, etc.) received by the conversion element 121 and the switch 131 of the sensor 111 and the signal processing unit 40. According to the second embodiment, the offset component can be removed by computing m (k-1) -m (k). Thus, radiation information can be detected more accurately.

[Application example]
A more specific configuration example of the radiation imaging system is shown in FIG. The X-ray 6060 generated by the X-ray tube 6050 which is a radiation source passes through the chest 6062 of the patient or subject 6061 and enters each of the conversion elements 12 included in the radiation imaging apparatus 6040. The incident X-ray includes information on the inside of the body of the subject 6061. The radiation is converted into charge by the conversion element 12 in response to the incidence of X-rays to obtain electrical information. This information is converted into digital data and image processed by an image processor 6070 as signal processing means and can be observed on a display 6080 as display means in the control room.
Further, this information can be transferred to a remote place by a transmission processing means such as a telephone line 6090, and can be displayed on a display 6081 serving as a display means such as a doctor room at another place or can be stored in a recording means such as an optical disc. It is also possible for doctors to diagnose. Further, the film can be recorded on a film 6110 as a recording medium by a film processor 6100 as a recording means.

1: radiation source 100: substrate 11: pixel 111: sensor 12: conversion element 121: conversion element 15: pixel control line 16: column signal line 161: detection signal line 40: signal processing unit , 41: sensor control unit, 411: sensor control line, SG1 to SG4: sensor group

  One aspect of the present invention relates to a radiation imaging apparatus having a plurality of pixels for acquiring a radiation image and a plurality of sensor units for detecting radiation, each sensor unit converting the radiation into an electrical signal The radiation imaging device includes a sensor that accumulates the electrical signal in a signal accumulation period, the radiation imaging device having a first time period in which the signal accumulation period in each of the plurality of sensor units has a first time; Based on signals from a control unit that controls the plurality of sensor units and the plurality of sensor units controlled by the control unit so as to be mutually offset by a second time that is shorter than the time, the radiation imaging apparatus Detection of start of irradiation, determination of timing to stop irradiation, detection of integrated irradiation dose, and / or Is utilized, the information on radiation, a cycle of the second time, and a signal processing unit for outputting.

Claims (9)

A radiation imaging apparatus comprising: a plurality of pixels for acquiring a radiation image; and a plurality of sensor units for detecting radiation,
Each sensor unit includes a sensor that converts radiation into an electrical signal and stores the electrical signal in a signal accumulation period,
The radiation imaging apparatus is
Control for controlling the plurality of sensor units such that the signal accumulation period in each of the plurality of sensor units has a first time and is mutually offset by a second time shorter than the first time Department,
A signal processing unit that outputs information on radiation incident on the radiation imaging apparatus as the second time period based on signals from the plurality of sensor units controlled by the control unit;
A radiation imaging apparatus comprising: The signal processing unit includes an amplifier that amplifies signals from the plurality of sensor units, and outputs the signal amplified by the amplifier as the information.
The radiation imaging apparatus according to claim 1, The signal processing unit outputs, as the information, a value obtained by integrating the signal from each of the plurality of sensor units for each sensor unit.
The radiation imaging apparatus according to claim 1, The control unit resets the plurality of sensor units in response to the start of irradiation of radiation to the radiation imaging apparatus, and thereafter, each signal accumulation period of the plurality of sensor units has the first time And control the plurality of sensor units to be mutually offset by the second time,
The radiation imaging apparatus according to any one of claims 1 to 3, characterized in that: The plurality of pixels are arranged to form a plurality of rows and a plurality of columns, and the number of pixels in each of the plurality of rows is equal to each other.
The radiation imaging apparatus according to any one of claims 1 to 4, characterized in that: The control unit controls the plurality of sensor units such that a signal accumulation period is repeated in each of the plurality of sensor units.
The radiation imaging device according to any one of claims 1 to 5, characterized in that: Each sensor unit includes a plurality of sensors including the sensor, and each sensor includes a conversion element that converts radiation into an electric signal and stores the same, and a switch disposed between the conversion element and a detection signal line. The switches of each of the plurality of sensors constituting each sensor unit are controlled by a common control line;
A signal from each sensor unit is sent to the signal processing unit via the detection signal line.
The radiation imaging device according to any one of claims 1 to 6, characterized in that: Each sensor unit further includes a second sensor,
The signal accumulation period in the second sensor of each of the plurality of sensor units has a third time shorter than the first time,
The signal processing unit outputs, as the information, a signal corresponding to a difference between a signal from the sensor in each sensor unit and a signal from the second sensor.
The radiation imaging device according to any one of claims 1 to 6, characterized in that: A radiation source generating radiation,
A radiation imaging apparatus according to any one of claims 1 to 8,
A radiation imaging system comprising: