JP2016010066A - Radiation imaging apparatus and radiation imaging system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology that is advantageous for improving accuracy of detecting radiation information while improving a frequency of detecting the radiation information.SOLUTION: A radiation imaging apparatus includes: a plurality of pixels for acquiring a radiation image; and a plurality of sensor units for detecting a radiation. Each sensor unit includes a sensor that converts the radiation to an electric signal and stores the electric signal in a signal storage period. The radiation imaging apparatus also includes: a control unit for controlling the plurality of sensor units so that signal storage periods of respective sensors of the plurality of sensor units have a first time and mutually deviate from each other by a second time shorter than the first time; and a signal processing unit for outputting, on the basis of signals from the plurality of sensor units controlled by the control unit, information on a radiation incident on the radiation imaging apparatus in a period of the second time.

Description

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

  There is a radiation imaging apparatus having a pixel array in which pixels including a conversion element that converts radiation into electric charges and a switch such as a thin film transistor are arranged. In recent years, multi-functionalization of such a radiation imaging apparatus has been studied. As one of them, attention is focused on the incorporation of an automatic exposure control (AEC) function. 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 at which radiation irradiation should be stopped, and to detect the radiation dose or the cumulative dose.

  Patent Document 1 describes a radiographic imaging apparatus having radiographic imaging pixels and radiation detection pixels. Both the radiation image capturing pixel and the radiation detection pixel generate light when receiving light, store a generated charge, and a TFT switch for reading the charge stored in the sensor. Including. In the radiation image capturing pixel, the gate of the TFT switch is connected to the first scanning wiring, and in the radiation detecting pixel, the gate of the TFT switch is connected to the second scanning wiring. In both the radiation image capturing pixel and the radiation detection pixel, the source of the TFT switch is connected to the signal wiring.

  In the passive pixel conversion device described in Patent Document 1, the signal accumulated in the sensor unit of the pixel disappears when the TFT switch is turned on, the sensor unit and the signal wiring are connected and the reading operation is performed. To 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 every moment, it is necessary to increase the frequency of signal readout from a sensor that detects radiation information, that is, the detection frequency (time resolution). There is. However, when the detection frequency is increased, the signal accumulation period in each sensor is shortened. As a result, the signal-to-noise ratio (SNR) at the time of reading a signal from the sensor is lowered, and the detection accuracy of radiation information can be lowered. That is, the radiation information detection frequency and the detection accuracy are in a trade-off relationship.

  An object of this invention is to provide the technique advantageous in order to raise detection accuracy, raising the detection frequency 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, wherein each sensor unit converts radiation into an electrical signal. A sensor that converts and accumulates the electrical signal in a signal accumulation period, wherein the radiation imaging apparatus has a signal accumulation period in each of the sensors of the plurality of sensor units having a first time, and the first The radiation imaging apparatus based on a control unit that controls the plurality of sensor units and a signal from the plurality of sensor units controlled by the control unit so as to be shifted from each other by a second time shorter than one hour. And a signal processing unit that outputs information related to the radiation incident on the light source with the second time as a period.

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

The figure which shows the radiation imaging system of two embodiment of this invention. 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. The top view (layout figure) which shows the structural example 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 | movement which detects the irradiation intensity | strength of a radiation. The timing chart of the operation | movement which detects the irradiation intensity | strength of a radiation. The flowchart of the operation | movement which detects the irradiation intensity | strength 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 between the sensor unit in 2nd Embodiment, and a sensor group. The timing chart which shows operation | movement of 2nd Embodiment. The figure which shows the more specific structural example of a radiation imaging system.

  Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

[First Embodiment]
FIG. 1A schematically shows the configuration of a radiation imaging system according to one 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 apparatus 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 that are two-dimensionally arranged to form an array having a plurality of rows and a plurality of columns, and a substrate 100 that supports or holds 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 composed 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 that converts radiation into an electrical signal. The scintillator 190 can be shared by the plurality of conversion elements 12.

  In the embodiment shown in FIG. 1 (a), the scintillator 190 is directed towards the radiation source 1. In the embodiment shown in FIG. 1B, the substrate 100 is directed to the radiation source 1 side, and the radiation 3 passes through the substrate 100 and an array composed of a plurality of photoelectric conversion elements PEC and is used as a scintillator. Incident to 190. Then, the light converted by the scintillator 190 enters the photoelectric conversion element PEC.

  FIG. 2A schematically shows one embodiment of the radiation imaging apparatus 4. 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, the imaging region 90 is provided with one or a plurality of radiation detection regions 80, and a plurality of sensor groups (a plurality of sensor units) are arranged in each radiation detection region 80. Pixels for acquiring a radiation image can also be arranged in the radiation detection region 80.

  FIG. 2B schematically shows another embodiment of the radiation imaging apparatus 4. In the radiation detection apparatus 4 shown in FIG. 2B, a plurality of radiation detection regions 80 are arranged so as to cover the entire imaging region 90, and the radiation detection region 80 includes, in addition to sensor groups (sensor units). Pixels for acquiring a radiation image are arranged.

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

  FIG. 3 shows a more specific configuration example of the radiation imaging apparatus 4 shown in FIG. In the imaging area 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, 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 a plurality of radiation detection areas 80 are provided. In each radiation detection region 80, a plurality of sensor groups SG1, SG2, SG3, SG4 are arranged. In the first embodiment, one sensor unit is composed of one sensor group. In the second embodiment to be described later, one sensor unit is composed of 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 constituted by a photoelectric conversion element and a scintillator, or may be constituted by an element that directly converts radiation into an electric signal. The conversion element 12 may have a first electrode (which may also be referred to as an individual electrode or a readout electrode) and a second electrode (which may also be 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 includes 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 directly converts radiation into an electrical signal. In the former, the scintillator can be shared with the scintillator for the pixel 11. The conversion element 121 can have a first electrode (which can also be called an individual electrode or a readout electrode) and a second electrode (which can also be called 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.

  The description will be continued with reference to FIG. 3 again. SG1, SG2, SG3, and SG4 in FIG. 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 by an array of pixels 11 having, for example, 1000 rows × 1000 columns to 3000 rows × 3000 columns. In the example illustrated in FIG. 3, the pixel 11 is not disposed at the position where the sensor 111 is disposed. However, 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 the 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 readout unit 30. The detection signal line 161 connected to the source (or drain) of the switch 131 of the sensor 111 is connected to the signal processing unit 40. A 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 region 80 includes N sensor groups SG1, SG2, SG3, and SG4 (N sensor units), and each of the sensor groups SG1, SG2, SG3, and SG4 includes M pieces. Sensor 111 is included. In the example shown in FIG. 3, N = 4 and M = 4, but this is merely an example.

  In each radiation detection region 80, the detection signals in which the sources (or drains) of all the switches 131 of each of the M sensors 111 in the N sensor groups SG1, SG2, SG3, and SG4 (N sensor units) are common. It is connected to the line 161. On the other hand, a sensor control line 411 that is different for each sensor group (sensor unit) is connected to the gate of the switch 131 of the sensor 111. That is, the common kth sensor control line 411 is connected to the gate of the switch 131 of the sensor 111 of the kth 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.

  FIG. 5 shows a configuration example of the signal processing unit 40. In the example shown in FIG. 5, the signal processing unit 40 reads out the electric 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 detector 39 includes, for example, an integrating amplifier 31 and a reset switch 34. A detection signal line 161 is connected to the input of the integrating amplifier 31, and an AD converter 33 is connected to the output of the integrating amplifier 31. The reset switch 34 is arranged so that the input and output of the integrating amplifier 31 can be short-circuited. By making the reset switch 34 conductive, 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. When the current or voltage generated by the sensor 111 is read as a signal of the sensor 111, the signal processing unit 40 includes, for example, a non-inverting amplifier or an inverting amplifier. It may be configured to include.

  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 viewpoint, at least one of the row selection 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, the intensity of radiation, and the cumulative dose of radiation. Further, the control unit 49 is connected to the radiation source 1 and receives a signal indicating the start and / or stop of radiation irradiation from the radiation source 1 or starts and / or stops radiation irradiation to the radiation source 1. You can give instructions.

  FIG. 6 is a plan view (layout diagram) illustrating a configuration example of the pixel 11 and the sensor 111. 7A is a cross-sectional view taken along line A-A ′ in FIG. 6, and FIG. 7B is a cross-sectional view taken along line B-B ′ in FIG. 6. The switch 13 of the pixel 11 can be composed of a TFT (Thin Film Transistor) as illustrated in FIG. The switch element 13 is disposed on the substrate 100 and can be covered with an interlayer insulating layer 181. The conversion element 12 may 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 can include a first electrode 125, a PIN photodiode (photoelectric conversion element) 124, and a second electrode 126. On the PIN photodiode, a protective film 182, a second interphase insulating layer 183, a bias line 19, and a protective film 184 are arranged in this order. A planarizing 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 a contact hole. The material of the second electrode 126 is made of ITO having optical transparency, so that light converted from radiation by the scintillator 190 can be transmitted.

  Similarly, the switch 131 of the sensor 111 can be configured by a TFT (Thin Film Transistor) as illustrated in FIG. 7B. The switch element 131 may be disposed on the substrate 100 and covered with the interlayer insulating layer 181. A conversion element 121 may 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 can include a first electrode 125, a PIN photodiode (photoelectric conversion element) 124, and a second electrode 126. On the PIN photodiode, a protective film 182, a second interphase insulating layer 183, a bias line 19, and a protective film 184 are arranged in this order. A planarizing film (not shown) and a scintillator 190 are disposed on the protective film 184.

  In the above example, a PIN photodiode is employed 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 for detecting radiation information based on a signal from the sensor 111 will be described. First, a method for detecting radiation intensity as radiation information will be described. FIG. 8 shows a timing chart of the operation for detecting the irradiation intensity of radiation. In the uppermost part of FIG. 8, the intensity of radiation incident on the radiation detection region 80 (“radiation irradiation intensity”) is shown. In FIG. 8, the number of sensor groups is N, and the sensor groups are described as SG1, SG2,. In the first embodiment, the sensor group and the sensor unit are equivalent, and the sensor unit is described as SU1, SU2,..., SUN.

  The sensor control unit 41 moves from 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). On the other hand, voltage pulses (sensor control signals) are sequentially applied. Here, it is assumed that the switch 131 of the sensor 111 of the kth sensor group SGk is turned on when the kth sensor control line 411 is driven to a high level.

  First, during a period from time t11 to t12, the sensor control line 411 of the first sensor group SG1 (SU1) is driven to a high level, and the switch 131 of the sensor 111 of the first sensor group SG1 is changed from a non-conductive state to a conductive state. The Thereafter, during a 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-conductive state to the conductive state. Thereafter, the control is similarly performed up to the sensor 111 of the Nth sensor group SGN (SUN). After that, returning to the first sensor group SG1 (SU1), the sensor control line 411 of the first sensor group SG1 (SU1) is driven to a high level during the period from time t13 to t14. Thereby, 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-conducting state from time t12 to t13. Charges generated by radiation irradiation during this period are 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 electric 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 t <b> 13, the switch 131 of the sensor 111 of the first sensor group SG <b> 1 transitions to a conductive state, so that the signal of the sensor 111 of the first sensor group SG <b> 1 passes through the detection signal line 161. 40.

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

  Similarly, the signal processing unit 40 detects the signal amount m (2) of the sensor 111 of the second sensor group SG2 at time t112 immediately after time t23, and outputs the signal amount m (2) to the control unit 49. . Similarly, the signal processing unit 40 detects the signal amounts m (3) to m (N) of the sensors 111 of the third to Nth sensor groups SG3 to SGN and outputs them to the control unit 49. Thereafter, the signal processing unit 40 repeats the above processing in order from the first sensor group SG1. As a result, a signal sequence (numerical sequence) composed of signal quantities 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). .

  The signal amounts m (1), m (2),..., M (N) are different from each other in the sensor group used to acquire them, and the error due to this is the sensor of the plurality of sensor groups. It can be reduced by disposing 111 in a distributed manner.

  Here, the interval between the timing for detecting m (k) and the timing for 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 matches 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 (radiation intensity) from any of the plurality of sensor groups is the reciprocal of the sampling interval SI.

  The control unit 49 has a signal accumulation period SAP in each of the sensors 111 of the plurality of sensor units SU1 to SUN having a first time and is shifted from each other by a second time that is the length of the sampling period SI. The plurality of sensor units SU1 to SUN are controlled. Here, the second time that is the length of the sampling period SI is shorter than the first time that is the length of the signal accumulation period SAP. The control unit 49 can control the plurality of sensor units SU <b> 1 to SUN 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 (here, the dose 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 a numerical sequence generated by interpolation from the signal sequence including the signal amount m (k)) exceeds the threshold Th1. It can be detected as the timing when radiation irradiation is started. Similarly, the control unit 49 determines the time when the signal amount m (k) (or the value of a numerical sequence generated by interpolation from the signal sequence consisting of the signal amount m (k)) falls below the threshold value. It can be detected as the timing when irradiation is stopped.

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

  Similarly to the operation shown in FIG. 8, the signal processing unit 40 has signal amounts m (1), m (2),..., M (N), m (1), m2 (2). A signal sequence consisting of is output. 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 accumulated signal amount m ′ (1) held in the control unit 49 as a new m ′ (1), and sets the next first sensor group. This holds until the detection of the signal amount m (1) of SG1 (SU1). Similarly, the control unit 49 calculates and holds the accumulated signal amount m ′ (k) as needed for other sensor groups, that is, the k-th sensor group SGk. As a result, a signal string composed of integrated signal amounts m ′ (1), m ′ (2),..., M ′ (N), m ′ (1), m′2 (2). .

  The control unit 49 can determine that the integrated irradiation amount has reached an appropriate amount at the time (t114) when the integrated signal amount m ′ (k) of any sensor group exceeds the threshold Th2. As 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 process (S1010 to S1014), a calculation process (S1016 to S1020), and a control process (S1024, S1026).

  First, the preparation process (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 turns on the switches 131 of the sensors 111 of the sensor groups SG1 to SGN and removes charges (such as dark charges) accumulated in the conversion element 121. In S1012, the control unit 49 clears the accumulated signal amount m ′ (k) (k = 1 to N) held in the memory in the control unit 49. In S1014, the variable k that identifies the sensor group is set to 1. In addition, in the preparation process, offset correction and / or sensitivity correction between the sensor groups SG1 to SGN may be performed.

  Next, the calculation process (S1016 to S1020) will be described. In S1016, the control unit 49 acquires the signal amount m (k) of the kth sensor group SGk (kth 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 a new integrated signal amount m ′ (k ) Value. In S1020, the control unit 49 determines whether or not the integrated signal amount m ′ (k) exceeds the threshold Th2, and if so, the process proceeds to S1024, and if not, the value of k is determined in S1022. Is changed by 1, and the process returns to S1016.

  Next, the control process (S1024, S1026) will be described. In S1024, the control unit 49 causes the radiation source 1 to stop emitting radiation. In step 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 integrating circuit, and the integrated irradiation amount may be obtained by the integrating circuit.

  Hereinafter, the effects of the first embodiment will be described by way of example, but this is not intended to control the present invention. When detecting radiation information such as radiation intensity and integrated dose based on a signal from a sensor 111 having a conversion element 121 and a switch 131, detection accuracy of the radiation information depends on a 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, the signal amount when reading signals from all the M × N sensors 111 simultaneously is larger than when reading signals from one detection pixel. M × N times. Moreover, the component (kTC noise) proportional to the capacity | capacitance of the conversion element 121 among random noise becomes (root) (MxN) times, and another component is the same.

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

  In the first embodiment, signals of M sensors 111 out of M × N sensors 111 are read out in one reading operation, and this signal is used as a representative value of output values of M × N sensors 111. This operation is performed while changing the sensor group (sensor unit). Thereby, the detection frequency (time resolution) of radiation information can be increased.

  Hereinafter, the arrangement, shape, and size of the radiation detection region 80 will be supplemented. In radiography of subjects such as human subjects, in order to obtain images with appropriate brightness, the integrated dose is monitored at positions corresponding to the lung field, abdominal cavity, spinal column, joints, etc., and the radiation dose is adjusted. It is widely done. In general, in such a method, considering the ease of positioning between the subject and the radiation imaging apparatus, the region where the radiation is detected can be a region where the radiation intensity can be regarded as being substantially uniform. For example, in radiographic imaging of a human chest, when the subject 2 is arranged with respect to the imaging area 90 as shown in FIG. 2C, the radiation intensity is generally one in the area corresponding to the lung field (about 5 cm square). Can be considered. In general, the arrangement, shape, and size of the radiation detection region 80 can be determined according to the shape and size of a central portion (lumbar vertebra, pelvis, joint, breast, etc.) in radiation imaging. The shape of the radiation detection region 80 may be a square or other shapes such as a circle. The size of the radiation detection region 80 is preferably about 3 to 5 cm for imaging centered on the human lung field, abdominal cavity, spinal column, and joints, and about 0.5 to 1 cm for imaging the breast.

  Hereinafter, the arrangement of the sensor 111 will be supplemented. Under the imaging conditions illustrated in FIG. 2C, the subject 2 is not uniform, and the distribution of the radiation intensity transmitted through the subject 2 in the radiation detection region 80 is not uniform. For example, ribs are present in the human chest at intervals of 2 to 3 cm, and the radiation transmittance of this portion is low. In other parts of humans, bones and soft tissues are periodically present at intervals of about 1 to several centimeters. For this reason, the arrangement pitch of the sensors 111 in each sensor group (sensor unit) is preferably less than half of the minimum value (about 1 cm) in the portion composed of the bone and soft tissue, that is, about 5 mm or less. . By arranging a plurality (M) of sensors 111 constituting each sensor group (sensor unit) evenly dispersed in the radiation detection region 80, the obtained radiation information can be sufficiently averaged. Thereby, it is possible to reduce between a plurality of sensor groups (sensor units). As the number (M) of sensors 111 per sensor group (sensor unit) is increased, the averaging effect increases.

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. Actually, N can be determined according to the response time constant of the signal processing unit 40, the required detection frequency of radiation information, and the like. If the values of N and M are too large, the image acquired by the pixel 11 will be adversely affected (missing pixels). Therefore, N and M take into account the balance between the effects described above and the adverse effect on the image. Can be determined. When the radiation detection region 80 is a square having a side of 5 cm, for example, if N = 25 and M = 100, a high averaging effect can be obtained within a range where there is no adverse effect on the image. When each sensor group (sensor unit) is arranged in a two-dimensional matrix within the radiation detection region 80, the arrangement pitch is 5 cm / √ (100) = 5 mm.
This is preferable because the above-described conditions regarding the arrangement interval are satisfied.

  In order to prevent unnecessary exposure of the subject to a general radiation irradiation period (about 1 to 1000 ms), the radiation irradiation period needs to be controlled with an error of 1% (0.01 to 10 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). Since N = 25, the signal accumulation period in the sensors 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 region in accordance with the object to be protected.

  Hereinafter, some modified examples of the first embodiment will be described. FIG. 11 shows a first modification. This is useful when the radiation imaging apparatus 4 has a function of detecting the start of radiation irradiation. The start of radiation irradiation can be detected, for example, by a notification from the radiation source 1 or by a detection unit provided in the radiation imaging apparatus 4. When detecting the start of radiation irradiation at time t00, the controller 49 turns on the switches 131 of the sensors 111 of all the sensor groups SG1 to SGN (sensor units SU1 to SUN) during the period from time t00 to t01. As a result, these sensors 111 are reset. This reset removes extra charges (such as dark charges). Subsequently, the control part 49 returns the switch 131 of the sensor 111 of all the sensor groups SG1-SGN (sensor unit SU1-SUN) to a non-conduction state, and starts accumulation | storage of a signal. Thereafter, the operation shown in FIG. 8 or 9 is the same. According to the first modification, radiation information after the start of radiation irradiation can be detected accurately.

  A second modification is shown in FIGS. 12, 13, and 14. In the second modification, the sensor 111 is replaced by the sensor 111 ′, and only the sensor 111 ′ is disposed in the radiation detection region 80. The sensor 111 'also functions as a pixel. That is, the sensor 111 ′ includes a conversion element 121 that converts radiation into an electrical signal and a switch 131, and includes a conversion element 12 that converts radiation into an electrical signal and a 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, the imaging region 90 includes a plurality of pixels 11 and a plurality of sensors 111 ′ so as to form a plurality of rows and a plurality of columns. The number of pixels in each of the plurality of rows (the sum of the number of pixels 11 and the number of sensors 111 ') is equal to each other.

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

  FIG. 15 shows a third modification. Here, in FIG. 15, the sensor 111 is illustrated as SG1, SG2, SG3, and SG4 indicating the sensor group to which the sensor 111 belongs. In the third modification, the 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 so that one signal detection unit 39 corresponds to each detection signal line 161, and a plurality of signal detection units 39 and the AD converter 33 are connected to each other. A multiplexer 32 is disposed between them. The multiplexer 32 selects the outputs of the plurality of signal detectors 39 according to a predetermined order and supplies them to the AD converter 33. Each signal detection unit 39 may have the configuration illustrated in FIG. The integrating amplifier 31 may be replaced with another amplifier such as a non-inverting amplifier or an inverting amplifier.

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

  The signal detection unit 39 may have a function of resetting the detection signal line 161 (reset switch 34). In the third modified example, 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 for resetting 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 detection frequency of radiation information.

  Alternatively, while maintaining the detection frequency of radiation information, 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.

  Or you may comprise the signal processing part 40 by the combination of said several technique. For example, it is possible to detect the start of radiation irradiation with a circuit that takes a short time to read out a signal, and to measure the integrated dose with a circuit that takes noise countermeasures.

  Further, when the signal processing unit 40 includes the reset switch 34 for each detection signal line 161, the conversion element 121 of the sensor 111 is connected to the detection signal line 161 without passing through the switch 131, as shown in FIG. 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 the same operation as that shown in FIG. FIG. 17 is a plan view (layout diagram) of the sensor 111 shown in FIG. FIG. 18 is a sectional view taken along line B-B ′ of FIG. 17. By omitting the switch 131, the structure of the sensor 111 is simplified. 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 includes 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 includes 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. In the radiation imaging apparatus 4 of the second embodiment, the configuration of the imaging region 90 can be the same as that of the first embodiment.

  FIG. 20 shows the operation of the radiation imaging apparatus 4 of the second embodiment. Here, as an example, a method for detecting radiation intensity as radiation information will be described. The sensor control unit 41 applies voltage pulses (sensor control signals) according to a predetermined procedure to the k-th sensor control line 411 (k = 1 to N) for individually controlling the first sensor group SG1 to the N-th sensor group SGN. Apply.

  Specifically, the first sensor control line 411 that controls the sensors 111 of the first sensor group SG1 constituting a part of the first sensor unit SU1 is driven to a high level during a period from t11 to t12. In addition, the second sensor control line 411 that controls the sensor (second sensor) 111 of the second sensor group SG2 constituting another part of the first sensor unit SU1 has a period from time t11 to t12 and from time t21. Driven to a high level during the period up to t22.

  Hereinafter, similarly, the third sensor control line 411 that controls the sensor 111 of the third sensor group SG3 constituting a part of the second sensor unit SU2 is driven to a high level in a period from t31 to t32. Further, the fourth sensor control line 411 for controlling the sensor (second sensor) 111 of the fourth sensor group SG4 constituting the other part of the second sensor unit SU2 has a period from time t31 to t32 and from time t41. It is driven to the high level during the period up to t42.

  As described above, after the first sensor unit SU1 to the (N / 2) th sensor unit SU (N / 2) is driven, the first sensor unit SU1 to the (N / 2) th sensor unit SU ( N / 2) is driven in the same way.

  Specifically, the first sensor control line 411 that controls the sensors 111 of the first sensor group SG1 constituting a part of the first sensor unit SU1 is driven to a high level during a period from t13 to t14. In addition, 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 from time t23. It is driven to the high level during the period up to t24.

  Hereinafter, similarly, the third sensor control line 411 that controls the sensor 111 of the third sensor group SG3 constituting a part of the second sensor unit SU2 is driven to the high level in the period from t33 to t34. Further, the fourth sensor control line 411 for controlling the sensor (second sensor) 111 of the fourth sensor group SG4 constituting the other part of the second sensor unit SU2 has a period from time t33 to t34 and from time t43. It is driven to the high level during the period up to t44.

  On the other hand, the signal processing unit 40 outputs the signal accumulated in the conversion element 121 of the sensor 111 of the first sensor group SG1 constituting a part of the first sensor unit SU1 during the period from time t12 to t13 as a signal amount m (1). Detect as. The signal processing unit 40 also outputs the signal accumulated in the conversion element 121 of the sensor (second sensor) 111 of the second sensor group SG2 constituting another part of the first sensor unit SU1 during the period from time t12 to t21. It is detected as a 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 that is the length of the signal accumulation period SAP of the sensors 111 of the first sensor group SG1.

  Similarly, the signal processing unit 40 outputs the signal accumulated in the conversion element 121 of the sensor 111 of the third sensor group SG3 constituting a part of the second sensor unit SU2 during the period from time t32 to t33 as a signal amount m (3 ) To detect. The signal processing unit 40 also outputs 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 during the period from time t32 to t41 (third time). It is detected as a 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 performs the same processing up to 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).

  Thereby, a numerical sequence of M (k) = m (k−1) −m (k) is obtained with the period from time t211 to t212 as the sampling interval (cycle = second time). By handling this numerical sequence of M (k) in the same way as m (k) in the first embodiment, the start and end timing of radiation irradiation and the integrated dose can be detected.

  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, the switch 131, and the signal processing unit 40 of the sensor 111. According to the second embodiment, the offset component can be removed by calculating m (k−1) −m (k). Therefore, radiation information can be detected more accurately.

[Application example]
FIG. 21 shows a more specific configuration example of the radiation imaging system. X-rays 6060 generated by an X-ray tube 6050 serving as a radiation source pass through the chest 6062 of the patient or subject 6061 and enter each conversion element 12 included in the radiation imaging apparatus 6040. This incident X-ray includes information inside the body of the subject 6061. Corresponding to the incidence of X-rays, the conversion element 12 converts the radiation into electric charges to obtain electrical information. This information is converted into digital data, image-processed by an image processor 6070 as a signal processing means, and can be observed on a display 6080 as a display means in a control room.
Further, this information can be transferred to a remote place by 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 in another place or stored in a recording means such as an optical disk. It is also possible for a doctor to make a diagnosis. Moreover, it can also record on the film 6110 used as a recording medium by the film processor 6100 used 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

Claims (9)

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 includes a sensor that converts radiation into an electrical signal and accumulates the electrical signal in a signal accumulation period;
The radiation imaging apparatus includes:
Control for controlling the plurality of sensor units such that signal accumulation periods in the sensors of the plurality of sensor units have a first time and are shifted from each other by a second time shorter than the first time. And
Based on signals from the plurality of sensor units controlled by the control unit, a signal processing unit that outputs information on the radiation incident on the radiation imaging apparatus with the second time as a cycle;
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 signals 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 radiation irradiation to the radiation imaging apparatus, and thereafter, each signal accumulation period of the plurality of sensor units has the first time. And controlling the plurality of sensor units so as to be shifted from each other by the second time.
The radiation imaging apparatus according to claim 1, wherein: 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 claim 1, wherein: The control unit controls the plurality of sensor units so that a signal accumulation period is repeated in each of the plurality of sensor units.
The radiation imaging apparatus according to claim 1, wherein: Each sensor unit includes a plurality of sensors including the sensor, and each sensor includes a conversion element that converts and stores radiation into an electrical signal, and a switch disposed between the conversion element and the detection signal line. The switches 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 apparatus according to claim 1, wherein the radiation imaging apparatus is a radiation imaging apparatus. Each sensor unit further includes a second sensor,
A signal accumulation period in each of the second sensors 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 and a signal from the second sensor in each sensor unit.
The radiation imaging apparatus according to claim 1, wherein the radiation imaging apparatus is a radiation imaging apparatus. A radiation source that generates radiation; and
The radiation imaging apparatus according to any one of claims 1 to 8,
A radiation imaging system comprising: