JP2010263517A - Radiographic image photographing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiographic image photographing apparatus capable of obtaining an appropriate radiographic image by accurately reducing influences of noise caused by a current detecting means. <P>SOLUTION: The radiographic image photographing apparatus 1 includes: a plurality of radiation detecting elements 7 arrayed in a two-dimensional shape in each of regions (r) defined with scan lines 5 and signal lines 6 disposed to cross each other; switch means 8 each of which is disposed for each radiation detecting element 7 and switched between OFF state and ON state according to voltages impressed on the scan lines 5, in which a charge Q in the radiation detecting element 7 is held during an OFF state and the charge Q is discharged from the radiation detecting element 7 during an ON state; an amplifier circuit 18 for converting the charge Q discharged from the radiation detecting element 7 into a voltage; a power supply section 41 for supplying power to the amplifier circuit 18; a current detecting means 42 for detecting a current that flows from the power supply section 41 to the amplifier circuit 18; and a control means 22 for detecting at least start of irradiation with radiation according to the value of the current detected by the current detecting means 42. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a radiographic imaging apparatus, and more particularly to a radiographic imaging apparatus capable of detecting at least the start of radiation irradiation.

  A so-called direct type radiographic imaging device that generates electric charges by a detection element in accordance with the dose of irradiated radiation such as X-rays and converts it into an electrical signal, or other radiation such as visible light with a scintillator or the like. Various so-called indirect radiographic imaging devices have been developed that convert charges to electromagnetic waves after being converted into electrical signals by generating electric charges with photoelectric conversion elements such as photodiodes in accordance with the energy of the converted and irradiated electromagnetic waves. Yes. In the present invention, the detection element in the direct type radiographic imaging apparatus and the photoelectric conversion element in the indirect type radiographic imaging apparatus are collectively referred to as a radiation detection element.

  This type of radiographic imaging apparatus is known as an FPD (Flat Panel Detector), and conventionally formed integrally with a support base (or a bucky apparatus) (see, for example, Patent Document 1). A portable radiographic imaging device in which an element or the like is housed in a housing has been developed and put into practical use (see, for example, Patent Documents 2 and 3).

  By the way, in these radiographic imaging apparatuses, particularly portable radiographic imaging apparatuses, information on the start and end of radiation irradiation is transmitted to the radiographic imaging apparatus from an external device such as a computer that manages the radiation irradiation apparatus and system. Accordingly, the radiation image capturing apparatus may be configured to read image data from each radiation detection element after the radiation irradiation ends.

  However, for that purpose, an interface between the radiation irradiating apparatus and the computer and the radiation imaging apparatus must be established, and a control configuration must be constructed in the entire system including the radiation irradiating apparatus and the computer. The configuration for recognizing the start and end of irradiation is large. For this reason, it is desirable that the radiation imaging apparatus itself can detect the start and end of radiation irradiation.

  At that time, it is possible to arrange a sensor or the like in the radiographic imaging apparatus so that the start or end of radiation irradiation is detected by the sensor, but the sensor is arranged in the radiographic imaging apparatus. Space is required, and the apparatus becomes large. Further, when the sensor is provided, there is a problem that a large amount of electric power is consumed for driving the sensor, and in particular, a portable radiographic imaging apparatus consumes a built-in battery.

  Therefore, as shown in FIG. 11 to be described later, it is possible to detect a current flowing through a bias line for applying a bias voltage to each radiation detection element, and to detect the start or end of radiation irradiation by increasing or decreasing the current value. It has been proposed (see Patent Document 4). If comprised in this way, it will become possible to detect the start and completion | finish of radiation irradiation easily in the state which suppressed power consumption by providing an electric current detection means in the existing wiring etc.

JP-A-9-73144 JP 2006-058124 A JP-A-6-342099 US Pat. No. 7,211,803

  However, in the radiographic imaging apparatus as described above, each radiation detection element is formed to be small in order to increase the resolution of the obtained radiographic image. Thus, compared with the switch element (TFT) 8 etc. which are formed by a fine process, the radiation detection element 7 has a wider light collection area in order to increase the light collection rate. Therefore, the parasitic capacitance of the radiation detection element 7 is relatively large.

  When a current detection unit is provided on the bias line 9 for applying a bias voltage (reverse bias voltage) to the radiation detection element 7 as described above, a radiation detection element having a relatively large parasitic capacitance according to noise generated by the current detection unit. Charges with relatively large noise superimposed on 7 are accumulated. In addition, since noise is further superimposed when reading out the charge on which relatively large noise is superimposed as described above from each radiation detection element 7, the image quality of the finally obtained radiographic image due to the influence of noise, in particular, In some cases, the graininess deteriorates.

  When the image quality of radiographic images deteriorates, especially when the granularity deteriorates, for example, when making a diagnosis using such radiographic images, the lesion may be overlooked or the normal part may be mistaken for the lesion. There is a risk of inconvenience such as misdiagnosis. For this reason, it is desirable for the radiographic imaging apparatus to obtain a radiographic image with an appropriate image quality in which the influence of noise is eliminated as much as possible.

  The present invention has been made in view of the above-mentioned problems, and appropriately reduces the influence of noise generated by current detection means for detecting a current for detecting the start of radiation irradiation or the like. An object of the present invention is to provide a radiographic imaging apparatus capable of obtaining an image.

In order to solve the above-described problem, the radiographic imaging device of the present invention includes:
A plurality of scanning lines and a plurality of signal lines arranged so as to intersect with each other; a plurality of radiation detecting elements arranged in a two-dimensional manner in each region partitioned by the plurality of scanning lines and the plurality of signal lines; ,
An off state and an on state are switched according to a voltage applied to the connected scanning line, arranged for each radiation detection element, and in the off state, the charge generated in the radiation detection element is retained, Switch means for releasing the charge from the radiation detection element in the ON state;
An amplifier circuit for converting the electric charge emitted from the radiation detection element into a voltage;
A power supply for supplying power to the amplifier circuit;
Current detection means for detecting a current flowing from the power supply unit to the amplifier circuit;
Control means for detecting at least the start of radiation irradiation based on the value of the current detected by the current detection means;
It is characterized by providing.

  According to the radiographic imaging apparatus of the system of the present invention, the current flowing from the power supply unit to the amplifier circuit increases when the apparatus is irradiated with radiation. Therefore, it is possible to accurately detect the start of radiation irradiation at least by providing the current detection means on the wiring connecting the power supply unit and the amplifier circuit and detecting the increase in current detected by the current detection means. Become.

  In this way, the current detection means is provided not on the bias line connecting the radiation detection element and the bias power supply as in the prior art but on the wiring connecting the power supply unit and the amplifier circuit. For this reason, in the conventional radiographic imaging apparatus, noise generated by the current detection means may be amplified by a large parasitic capacitance of the radiation detection element, further superimposed at the time of resetting and reading, and amplified by an amplifier circuit to increase. However, according to the radiographic imaging apparatus of the system as in the present invention, it is possible to suppress amplification of noise from the current detection means by the radiation detection element and the amplification circuit, and further attenuate and compress by the characteristics of the amplification circuit. Therefore, it is possible to reduce noise superimposed on the voltage value output from the amplifier circuit.

  For this reason, the influence of noise on the charge accumulated in each radiation detection element is reduced according to the dose of the irradiated radiation, and further, the charge is read by the amplification circuit in the reading process of the charge (image data) from each radiation detection element. When amplified, the noise generated by the current detection means is not amplified as in the conventional case, so that the influence of noise on the quality of the finally obtained radiographic image is reduced, and in particular, the granularity of the radiographic image is accurately deteriorated. Therefore, it is possible to obtain an appropriate radiation image in which the influence of noise is accurately reduced.

It is a perspective view which shows the radiographic imaging apparatus which concerns on each embodiment. It is sectional drawing which follows the AA line in FIG. It is a top view which shows the structure of the board | substrate which concerns on this embodiment. It is an enlarged view which shows the structure of the radiation detection element, TFT, etc. which were formed in the small area | region on the board | substrate of FIG. It is sectional drawing which follows the XX line in FIG. It is a side view explaining the board | substrate with which COF, a PCB board | substrate, etc. were attached. It is a block diagram showing the equivalent circuit of the radiographic imaging apparatus which concerns on this embodiment. It is a block diagram showing the equivalent circuit about 1 pixel which comprises a detection part. It is a graph showing the example of the voltage value corresponded to the electric current detected by an electric current detection means, (A) represents the state which started irradiation of a radiation, (B) represents the state which turned off TFT. It is a graph showing the example of the voltage value equivalent to the electric current detected with an electric current detection means, (A) represents the state which turned off TFT, (B) represents the state by which irradiation of the radiation was complete | finished. It is a block diagram showing the equivalent circuit about 1 pixel in the conventional radiographic imaging apparatus which provided the electric current detection means in the bias line. It is a figure explaining the noise and noise charge which are superimposed by each process in the conventional radiographic imaging apparatus. It is a figure explaining the noise and noise charge which are superimposed by each process in the radiographic imaging device concerning this embodiment.

  Embodiments of a radiographic image capturing apparatus according to the present invention will be described below with reference to the drawings.

  In the following description, the radiographic imaging apparatus is a so-called indirect radiographic imaging apparatus that includes a scintillator and the like, converts irradiated radiation into electromagnetic waves of other wavelengths such as visible light, and obtains an electrical signal with a photoelectric conversion element. Although a case will be described, the present invention can also be applied to a direct type radiographic imaging apparatus. Although the case where the radiographic image capturing apparatus is portable will be described, the present invention is also applicable to a radiographic image capturing apparatus formed integrally with a support base or the like.

  FIG. 1 is an external perspective view of the radiographic image capturing apparatus according to the present embodiment, and FIG. 2 is a cross-sectional view taken along line AA in FIG. As shown in FIGS. 1 and 2, the radiographic imaging apparatus 1 according to the present embodiment is configured as a portable (cassette type) apparatus in which a scintillator 3, a substrate 4, and the like are housed in a housing 2. .

  The housing 2 is formed of a material such as a carbon plate or plastic that transmits radiation at least on a surface R (hereinafter referred to as a radiation incident surface R) that receives radiation. 1 and 2 show a case in which the housing 2 is a so-called lunch box type formed by the frame plate 2A and the back plate 2B. However, the housing 2 is integrally formed in a rectangular tube shape. It is also possible to use a so-called monocoque type.

  As shown in FIG. 1, the side surface of the housing 2 is opened and closed to replace a power switch 36, an indicator 37 composed of LEDs and the like, and a battery 40 (not shown) (see FIG. 7 described later). A possible lid member 38 and the like are arranged. In the present embodiment, an antenna device 39 that is a communication unit for wirelessly communicating with the outside is embedded in the side surface of the lid member 38.

  As shown in FIG. 2, a base 31 is disposed inside the housing 2 via a thin lead plate or the like (not shown) on the lower side of the substrate 4. The disposed PCB substrate 33, the buffer member 34, and the like are attached. In the present embodiment, a glass substrate 35 for protecting the substrate 4 and the radiation incident surface R of the scintillator 3 is disposed.

  The scintillator 3 is attached to a detection unit P, which will be described later, of the substrate 4. As the scintillator 3, for example, a scintillator 3 that has a phosphor as a main component and converts it into an electromagnetic wave having a wavelength of 300 to 800 nm, that is, an electromagnetic wave centered on visible light when it receives incident radiation, is used.

  In the present embodiment, the substrate 4 is formed of a glass substrate. As shown in FIG. 3, a plurality of scanning lines 5 and a plurality of signal lines are provided on a surface 4 a of the substrate 4 facing the scintillator 3. 6 are arranged so as to cross each other. In each small region r defined by the plurality of scanning lines 5 and the plurality of signal lines 6 on the surface 4 a of the substrate 4, radiation detection elements 7 are respectively provided.

  Thus, the entire region r in which a plurality of radiation detection elements 7 arranged in a two-dimensional manner are provided in each small region r partitioned by the scanning line 5 and the signal line 6, that is, shown by a one-dot chain line in FIG. The region is a detection unit P.

  In the present embodiment, a photodiode is used as the radiation detection element 7, but other than this, for example, a phototransistor or the like can also be used. Each radiation detection element 7 is connected to the source electrode 8s of the TFT 8 serving as a switch means, as shown in the enlarged views of FIGS. The drain electrode 8 d of the TFT 8 is connected to the signal line 6.

  The TFT 8 is turned on when a turn-on voltage is applied to the connected scanning line 5 by the scanning drive means 15 described later and applied to the gate electrode 8g, and is generated and accumulated in the radiation detection element 7. The charged electric charge is discharged to the signal line 6. The TFT 8 is turned off when the off voltage is applied to the connected scanning line 5 and the off voltage is applied to the gate electrode 8g, and the discharge of the charge from the radiation detecting element 7 to the signal line 6 is stopped. Electric charges generated in the radiation detection element 7 are held and accumulated in the radiation detection element 7.

  Here, the structure of the radiation detection element 7 and the TFT 8 in this embodiment will be briefly described with reference to the cross-sectional view shown in FIG. FIG. 5 is a sectional view taken along line XX in FIG.

A gate electrode 8g of a TFT 8 made of Al, Cr or the like is formed on the surface 4a of the substrate 4 so as to be integrally laminated with the scanning line 5, and silicon nitride (laminated on the gate electrode 8g and the surface 4a). The first electrode 74 of the radiation detecting element 7 is connected to the upper portion of the gate electrode 8g on the gate insulating layer 81 made of SiN _x ) or the like via the semiconductor layer 82 made of hydrogenated amorphous silicon (a-Si) or the like. The formed source electrode 8s and the drain electrode 8d formed integrally with the signal line 6 are laminated.

The source electrode 8s and the drain electrode 8d are divided by a first passivation layer 83 made of silicon nitride (SiN _x ) or the like, and the first passivation layer 83 covers both the electrodes 8s and 8d from above. In addition, ohmic contact layers 84a and 84b formed in an n-type by doping hydrogenated amorphous silicon with a group VI element are stacked between the semiconductor layer 82 and the source electrode 8s and the drain electrode 8d, respectively. The TFT 8 is formed as described above.

  In the radiation detecting element 7, an auxiliary electrode 72 is formed by laminating Al, Cr, or the like on the insulating layer 71 formed integrally with the gate insulating layer 81 on the surface 4 a of the substrate 4. A first electrode 74 made of Al, Cr, Mo or the like is laminated on the auxiliary electrode 72 with an insulating layer 73 formed integrally with the first passivation layer 83 interposed therebetween. The first electrode 74 is connected to the source electrode 8 s of the TFT 8 through the hole H formed in the first passivation layer 83.

  On the first electrode 74, an n layer 75 formed in an n-type by doping a hydrogenated amorphous silicon with a group VI element, an i layer 76 which is a conversion layer formed of hydrogenated amorphous silicon, and a hydrogenated amorphous A p layer 77 formed by doping a group III element into silicon and forming a p-type layer is formed by laminating sequentially from below.

  When radiation enters from the radiation incident surface R of the housing 2 of the radiographic imaging apparatus 1 and is converted into an electromagnetic wave such as visible light by the scintillator 3, and the converted electromagnetic wave is irradiated from above in the figure, the electromagnetic wave is detected by radiation. The electron hole pair is generated in the i layer 76 by reaching the i layer 76 of the element 7. In this way, the radiation detection element 7 converts the electromagnetic waves irradiated from the scintillator 3 into electric charges.

  Further, a second electrode 78 made of a transparent electrode such as ITO is laminated on the p layer 77, and the irradiated electromagnetic wave is configured to reach the i layer 76 and the like. In the present embodiment, the radiation detection element 7 is formed as described above. The order of stacking the p layer 77, the i layer 76, and the n layer 75 may be reversed. Further, in the present embodiment, a case where a so-called pin-type radiation detection element formed by sequentially stacking the p layer 77, the i layer 76, and the n layer 75 as described above is used as the radiation detection element 7. However, it is not limited to this.

A bias line 9 for applying a bias voltage to the radiation detection element 7 is connected to the upper surface of the second electrode 78 of the radiation detection element 7 via the second electrode 78. The second electrode 78 and the bias line 9 of the radiation detection element 7, the first electrode 74 extended to the TFT 8 side, the first passivation layer 83 of the TFT 8, that is, the upper surfaces of the radiation detection element 7 and the TFT 8 are A second passivation layer 79 made of silicon nitride (SiN _x ) or the like is covered from above.

  As shown in FIGS. 3 and 4, in this embodiment, one bias line 9 is connected to a plurality of radiation detection elements 7 arranged in rows, and each bias line 9 is connected to a signal line 6. Are arranged in parallel with each other. In addition, each bias line 9 is bound to one connection 10 at a position outside the detection portion P of the substrate 4.

  In this embodiment, as shown in FIG. 3, each scanning line 5, each signal line 6, and connection 10 of the bias line 9 are input / output terminals (also referred to as pads) provided near the edge of the substrate 4. 11 is connected. As shown in FIG. 6, a COF (Chip On Film) 12 in which a chip such as a gate IC 12a functioning as a gate driver 15b of a scanning drive unit 15 described later is incorporated in each input / output terminal 11 is anisotropically conductively bonded. They are connected via an anisotropic conductive adhesive material 13 such as a film (Anisotropic Conductive Film) or an anisotropic conductive paste (Anisotropic Conductive Paste).

  The COF 12 is routed to the back surface 4b side of the substrate 4 and connected to the PCB substrate 33 described above on the back surface 4b side. Thus, the board | substrate 4 part of the radiographic imaging apparatus 1 is formed. In FIG. 6, illustration of the electronic component 32 and the like is omitted.

  Here, the circuit configuration of the radiation image capturing apparatus 1 will be described. FIG. 7 is a block diagram illustrating an equivalent circuit of the radiographic imaging apparatus 1 according to the present embodiment, and FIG. 8 is a block diagram illustrating an equivalent circuit for one pixel constituting the detection unit P.

  As described above, each radiation detection element 7 of the detection unit P of the substrate 4 has the bias line 9 connected to the second electrode 78, and each bias line 9 is bound to the connection 10 to the bias power supply 14. It is connected. The bias power supply 14 applies a bias voltage to the second electrode 78 of each radiation detection element 7 via the connection 10 and each bias line 9.

  In the present embodiment, as can be seen from the fact that the bias line 9 is connected to the p-layer 77 side (see FIG. 5) of the radiation detection element 7 via the second electrode 78, A voltage lower than the voltage applied to the first electrode 74 side of the radiation detection element 7 (that is, a so-called reverse bias voltage) is applied to the second electrode 78 of the radiation detection element 7 as a bias voltage via the bias line 9. Yes. The bias power supply 14 is supplied with power from the battery 40.

  The first electrode 74 of each radiation detection element 7 is connected to the source electrode 8s of the TFT 8 (indicated as S in FIGS. 7 and 8), and the gate electrode 8g of each TFT 8 (FIGS. 7 and 8). Are respectively connected to the lines L1 to Lx of each scanning line 5 extending from a gate driver 15b of the scanning driving means 15 described later. Further, the drain electrode 8 d (denoted as D in FIGS. 7 and 8) of each TFT 8 is connected to each signal line 6.

  In this embodiment, the scanning drive unit 15 includes a power supply circuit 15a and a gate driver 15b. In this embodiment, the gate driver 15b is formed by arranging a plurality of the gate ICs 12a described above in parallel. Further, the scanning drive means 15 controls the voltage applied to the gate electrode 8g of the TFT 8 via each scanning line 5 connected to the gate driver 15b.

  Each signal line 6 is connected to each readout circuit 17 formed in the readout IC 16. Note that a predetermined number of readout circuits 17 are provided in the readout IC 16, and by providing a plurality of readout ICs 16, readout circuits 17 corresponding to the number of signal lines 6 are provided.

  The readout circuit 17 includes an amplifier circuit 18, a correlated double sampling circuit 19, an analog multiplexer 21, and an A / D converter 20. 7 and 8, the correlated double sampling circuit 19 is represented as CDS. In FIG. 8, the analog multiplexer 21 is omitted.

In the present embodiment, the amplifier circuit 18 is configured by a charge amplifier circuit, and is configured by connecting a capacitor 18b and a charge reset switch 18c in parallel to the operational amplifier 18a and the operational amplifier 18a. Further, the signal line 6 is connected to the inverting input terminal on the input side of the operational amplifier 18 a of the amplifier circuit 18, and the reference potential V ₀ is applied to the non-inverting input terminal on the input side of the amplifier circuit 18. ing. Note that the reference potential V ₀ is set to an appropriate value, and in this embodiment, for example, 0 [V] is applied.

  The charge reset switch 18c of the amplifier circuit 18 is connected to the control means 22 described later, and is controlled to be turned on / off by the control means 22. When the charge reset switch 18c is off and the TFT 8 of the radiation detection element 7 is turned on (that is, when an on-voltage is applied to the gate electrode 8g of the TFT 8 via the scanning line 5), the radiation The electric charge discharged from the detection element 7 flows into the capacitor 18b and is accumulated, and a voltage value corresponding to the accumulated electric charge is output from the output terminal of the operational amplifier 18a.

  In this way, the amplifier circuit 18 outputs a voltage in accordance with the amount of charge output from each radiation detection element 7, converts the charge voltage, and amplifies it. When the charge reset switch 18c is turned on, the input side and the output side of the amplifier circuit 18 are short-circuited, and the charge accumulated in the capacitor 18b is discharged to reset the amplifier circuit 18. ing. Note that the amplifier circuit 18 may be configured to output a current in accordance with the charge output from the radiation detection element 7.

  The amplifier circuit 18 is supplied with electric power for driving the amplifier circuit 18 from a power supply unit 41 connected to the battery 40. The power supply unit 41, each amplifier circuit 18, and Is provided with current detection means 42 for detecting a current flowing from the power supply unit 41 to each amplifier circuit 18.

  In the present embodiment, as shown in FIG. 8, the current detection means 42 includes a resistor 42 a having a predetermined resistance value connected in series to a wiring connecting the power supply unit 41 and each amplifier circuit 18, and a resistor 42 a in parallel thereto. 42d and a differential amplifier 42b for measuring the voltage V between both terminals of the resistor 42a. The differential amplifier 42b generates the voltage V between both terminals of the resistor 42a. By measuring, the current flowing through the wiring is converted into a voltage value V and detected.

  As the resistor 42a provided in the current detection means 42, a resistor having a resistance value capable of converting a current flowing in the wiring into an appropriate voltage value V is used. The current detection means 42 outputs the voltage value V detected by converting the current in this way from the differential amplifier 42b to the control means 22. Moreover, the detection accuracy in the case of a low dose is improved by connecting the diode 42d in parallel with the resistor 42a. It is also possible to connect the diode 42d in series with the wiring without using the resistor 42a and measure the voltage V between both terminals with the differential amplifier 42b.

  As will be described later, the control unit 22 detects the start and end of radiation irradiation on the radiographic imaging device 1 based on the current value detected by the current detection unit 42. In this case, since the power supply efficiency is improved by supplying power directly from the power supply unit 41 to each amplifier circuit 18 without passing through the resistor 42a of the current detection unit 42, the current detection unit 42 includes A switch 42c is provided for short-circuiting between both terminals of the resistor 42a when it is not necessary to detect this.

  A correlated double sampling circuit (CDS) 19 is connected to the output side of the amplifier circuit 18. In this embodiment, the correlated double sampling circuit 19 has a sample and hold function. The sample and hold function in the correlated double sampling circuit 19 is turned on / off by a pulse signal transmitted from the control means 22. To be controlled.

  That is, in the correlated double sampling circuit 19, after the amplifier circuit 18 is reset, the charge reset switch 18c is turned off, and before the image data is read from each radiation detection element 7, the control means 22 performs the first time. When the pulse signal is received, the voltage value output from the amplifier circuit 18 at that time is held.

  Then, the gate driver 15b is controlled to apply an on-voltage to the gate electrode 8g of each TFT 8 to turn on the TFT 8, and when the charge discharged from the radiation detecting element 7 flows into the capacitor 18b and is accumulated, the control means When the second pulse signal from 22 is received, the voltage value output from the amplifier circuit 18 is held again at that time, and the difference value between these voltage values is output downstream as image data. Yes.

  The image data of each radiation detection element 7 output from the correlated double sampling circuit 19 is transmitted to the analog multiplexer 21 and sequentially transmitted from the analog multiplexer 21 to the A / D converter 20. Then, the A / D converter 20 sequentially converts the image data into digital values, which are output to the storage means 43 and sequentially stored.

  The control means 22 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an input / output interface, etc., not shown, and a microcomputer or FPGA (Field Programmable Gate Array). It is configured. It may be configured by a dedicated control circuit. And the control means 22 controls operation | movement etc. of each member of the radiographic imaging apparatus 1. The control means 22 is connected to a storage means 43 composed of a DRAM (Dynamic RAM) or the like.

  In the present embodiment, the control unit 22 is connected to the antenna device 39 described above, and further includes the detection unit P, the bias power source 14, the scanning drive unit 15, the readout circuit 17, the power supply unit 41, and the storage unit. A battery 40 for supplying power to each member such as 43 is connected. As described above, the battery 40 is built in the housing 2 of the radiographic image capturing apparatus 1, and the battery 40 has a connection terminal 44 when the battery 40 is charged by supplying power from the external device to the battery 40. It is attached.

  As described above, the control means 22 controls the bias power supply 14 to set a bias voltage to be applied to each radiation detection element 7 from the bias power supply 14, or the charge reset switch 18 c of the amplification circuit 18 of the readout circuit 17. Various processes such as on / off control and transmission of a pulse signal to the correlated double sampling circuit 19 to control on / off of the sample hold function are executed.

  Further, the control means 22 performs scanning from the scanning driving means 15 to the scanning driving means 15 at the time of reset processing of each radiation detecting element 7 or reading of image data from each radiation detecting element 7 after radiographic imaging. A pulse signal for switching the voltage applied to the gate electrode 8g of each TFT 8 between the on voltage and the off voltage via the line 5 is transmitted.

  Furthermore, the control means 22 detects at least the start of radiation irradiation to the radiation imaging apparatus 1 based on the value of the current flowing from the power supply unit 41 detected by the current detection means 42 to each amplifier circuit 18. ing.

  Hereinafter, detection of the start of radiation irradiation in the control unit 22 will be described.

  In the radiographic imaging device 1, before radiographic imaging is performed, reset processing is performed to release extra charges such as dark charges accumulated in each radiation detection element 7 and unread charges of previous radiographic imaging. Is done. In the present embodiment, the control unit 22 applies an on-voltage to each scanning line 5 from the scanning driving unit 15 and applies an on-voltage to the gate electrode 8g of each TFT 8 connected to each scanning line 5. The TFT 8 is turned on. That is, the gates of all the TFTs 8 are in an open state, which also serves as a reset process.

  In addition, the charge reset switch 18c of each amplifier circuit 18 is also turned on, and the switch 42c of the current detection means 42 is switched to the off state so that the current flows through the resistor 42a and waits until radiation is applied. . In the present embodiment, as described above, a case where all the TFTs 8 are turned on in the reset process will be described. However, the radiation detection element 7 that is not used for radiographic imaging, that is, the radiation detection element 7 that is not irradiated with radiation. In some cases, the reset process is not performed. In such a case, all the TFTs 8 that form an image other than the radiation detection element 7 are turned on.

  When radiation image capturing is started and radiation irradiation is started from a radiation irradiation apparatus (not shown) to the radiation incident surface R (see FIG. 1) of the radiation image capturing apparatus 1, in the present embodiment, the irradiated radiation is converted into the scintillator 3. Is incident on. Then, the electromagnetic waves converted into other wavelengths such as visible light by the scintillator 3 enter each radiation detection element 7 immediately below, and electron-hole pairs are generated in each radiation detection element 7. In this embodiment, The holes move to the second electrode 78 side of the radiation detection element 7 and flow out to the bias power source 14 through the bias line 9.

  The generated electrons move to the first electrode 74 side of the radiation detection element 7 and flow out to the signal line 6 through the TFT 8. Then, the electrons flow through the signal line 6, flow through the charge reset switch 18c in which the amplifier circuit 18 is turned on, and output to the output terminal of the operational amplifier 18a (that is, the correlated double sampling circuit (CDS) 19 in FIG. 8). Flows through the current detection means 42 through the operational amplifier 18a.

  As described above, since the switch 42c of the current detection means 42 is switched to the OFF state, electrons flow through the resistor 42a and flow out to the power supply unit 41. That is, a current is supplied from the power supply unit 41 and flows through the resistor 42a. Then, the voltage V between both terminals of the resistor 42 a generated by the current flowing through the resistor 42 a is detected by the differential amplifier 42 b, and the voltage value V is output to the control means 22.

  At that time, the voltage value V corresponding to the current output from the differential amplifier 42b changes, for example, as shown in FIG. That is, before the start of radiation irradiation, a voltage value V corresponding to a so-called dark current that is generated by thermal excitation or the like due to heat of each radiation detection element 7 itself and flows out from each radiation detection element 7 is detected. When radiation irradiation is started at t1 and electron-hole pairs start to be generated in each radiation detection element 7, electrons flow as described above, and the voltage value V output from the differential amplifier 42b of the current detection means 42. Increases rapidly.

  Therefore, in the present embodiment, the control unit 22 increases the voltage value V corresponding to the current detected by the current detection unit 42. For example, the control unit 22 increases the voltage value V when the voltage value V exceeds a preset threshold. When a preset threshold value is exceeded, it is detected that radiation irradiation has started.

  However, if the TFT 8 is kept in the ON state as it is, the charges (electron hole pairs) generated in each radiation detection element 7 flow out, and the charges cannot be accumulated and read out as image data. Therefore, when the control means 22 detects that the voltage value V has increased and radiation irradiation has started, the control means 22 applies an off voltage to each scanning line 5 from the scanning driving means 15 and is connected to each scanning line 5. An off voltage is applied to the gate electrode 8g of each TFT 8 so that all TFTs 8 are turned off and the gates of all TFTs 8 are closed.

  When the gates of the TFTs 8 are closed, charge does not flow out through the TFTs 8, so that the current detection means 42 corresponds to the current detected at time t2 when the gates of all the TFTs 8 are closed as shown in FIG. 9B. The voltage value V to be rapidly decreased. In the state where the gate of the TFT 8 is closed, charges generated by radiation irradiation are accumulated in each radiation detecting element 7.

  Normally, the TFTs 8 are formed so that the leakage current is very low. Therefore, when all the TFTs 8 are turned off at the time t2, the voltage value V from the current detection means 42 as shown in FIG. 9B. As shown in FIG. 10 (A), the number of radiation detecting elements 7 and TFTs 8 is enormous, and leakage currents through these TFTs 8 are collected. The voltage value V from the means 42 may then be maintained at a higher value than the voltage value produced by the dark current.

  In such a case, when the radiation irradiation is finished and the generation of electric charges in each radiation detection element 7 is stopped, the voltage value V output from the current detection means 42 as shown in FIG. May decrease further. Therefore, in such a case, the control means 22 is configured to detect that radiation irradiation has been completed at the time t3 when the voltage value V corresponding to the current detected by the current detection means 42 has decreased. Is possible.

  Further, as shown in FIG. 9B, when the voltage value V from the current detection means 42 decreases and no further decrease in the voltage value V can be detected even after the radiation irradiation is completed, the control is performed. The means 22 increases the voltage value V corresponding to the current detected by the current detection means 42 at the time t1 and detects the start of radiation irradiation. It can be configured to determine that it has ended.

  When the control means 22 detects the end of radiation irradiation or determines that the irradiation of radiation has ended after a predetermined time has elapsed after the start of radiation irradiation, the control means 22 continues from the power supply unit 41 to the amplifier circuit 18. Therefore, the switch 42c of the current detection means 42 is switched to the on state, the two terminals of the resistor 42a are short-circuited, and the power is smoothly supplied from the power supply unit 41 to the amplifier circuit 18. It is supposed to be in a state to be done.

  Then, the charge reset switch 18c of the amplifier circuit 18 is turned off in order to perform a reading process for reading out the charge accumulated from each radiation detection element 7, and the charge released from the radiation detector element 7 to the capacitor 18b of the amplifier circuit 18 is turned off. Is ready to accumulate.

  Next, the operation of the radiation image capturing apparatus 1 according to this embodiment will be described.

  When detecting the start of radiation irradiation by detecting the current flowing through the bias line 9 connected to each radiation detection element 7 as in the conventional radiographic imaging apparatus described above, for example, as shown in FIG. The current flowing through the bias line 9 can be detected by providing the same current detection means 42 as in the present embodiment at the portion where the connection 10 of the bias line 9 is connected to the bias power supply 14.

In the radiation detection element 7, as an initial state, that is, a state before radiation is applied, Cp obtained by multiplying the above-described difference V ₀ -Vbias between the reference potential V ₀ and the bias voltage Vbias by the parasitic capacitance Cp of the radiation detection element 7 is used. A charge Q of (V ₀ −Vbias) is generated. At this time, as described above, since the radiation detection element 7 has a relatively large parasitic capacitance Cp in order to increase the condensing area, the charge Q = Cp (V ₀ − generated in the radiation detection element 7 in the initial state. Vbias) also increases the sensitivity of the charge change to the voltage change. The parasitic capacitance Cp includes a characteristic that can be regarded as a capacitance of a photodiode that is the radiation detection element 7 and equivalently converted into a capacitance.

  Further, in the conventional radiographic imaging apparatus 100, noise is generated in the current detection means 42 provided in the bias line 9 (connection 10) connecting the radiation detection element 7 and the bias power source 14, as shown in FIG. In addition, the noise N42 generated by the current detection means 42 is superimposed on the noise Nbias generated in the bias voltage Vbias by the bias power supply 14 itself.

  Then, when the control means 22 detects the start of radiation irradiation and closes the gates of all the TFTs 8, these noises Nbias and N42 are caused by the charge Q at both ends of the radiation detection element 7 as shown in FIG. Are superimposed and held as noise charges Qnbias and Qn42.

  Next, in the readout process for reading out the accumulated charges from each radiation detecting element 7 after the radiation irradiation is completed, the noise charges Qnbias and Qn42 that are superposed and held when the gate is closed as described above are applied. Further, since noise Nbias generated in the bias power supply 14 and noise charge caused by the noise N42 generated in the current detecting means 42 when the gate of the TFT 8 is opened in the reading process are superimposed, as shown in FIG. Thus, the noise charges Qnbias and Qn42 increase.

  In the reading process, noise N41 is generated in the voltage supplied to the operational amplifier 18a by the power supply unit 41 (see FIG. 11), and the noise N41 is attenuated by 1 / α times due to the PSRR (Power Supply Rejection Ratio) characteristic of the operational amplifier 18a. . Therefore, as shown in FIG. 12C, the noise charges corresponding to the product of the increased noise charges Qnbias and Qn42, and the attenuated noise N41 and the capacitance set in the operational amplifier 18a and the parasitic capacitance inside the operational amplifier 18a. Qn41 is superimposed.

  Also in this case, the parasitic capacitance includes a characteristic that can be regarded as a capacitance of the operational amplifier 18a and equivalently converted into a capacitance. Further, the operational amplifier 18a of the amplifier circuit 18 has a high PSRR characteristic α of several tens of times, and usually has a characteristic that the influence of the noise N41 from the power supply unit 41 is suppressed to 1 / α times. Yes. Since the noise N41 from the power supply unit 41 is attenuated by 1 / α times in the amplifier circuit 18 and transmitted, a small noise charge Qn41 is superimposed as shown in FIG.

  On the other hand, in the radiographic image capturing apparatus 1 according to the present embodiment, as shown in FIG. 8 and the like, the current detection unit 42 is provided on the wiring connecting the power supply unit 41 and each amplifier circuit 18.

  As described above, due to the PSRR characteristic of the operational amplifier 18a of the amplifier circuit 18, the noise N42 from the current detection means 42 is attenuated 1 / α times in the amplifier circuit 18 and transmitted, so to speak, a small compressed noise charge Qn42 is superimposed. The

  Similarly to the description of the conventional radiographic imaging apparatus 100 described above, when the generation of noise N from the bias power supply 14 side is seen, in the radiographic imaging apparatus 1 according to the present embodiment, only the noise Nbias generated by the bias power supply 14 is detected. However, the charge noise Qnbias is retained by the relatively large parasitic capacitance Cp of the radiation detection element 7 when the start of radiation irradiation is detected and the gates of all the TFTs 8 are closed (see A in FIG. 13).

  Next, in the readout process in which the radiation irradiation is completed and the charge accumulated from each radiation detection element 7 is read, the noise Nbias generated in the bias voltage Vbias by the bias power supply 14 itself is further superimposed on the held noise Qnbias. Therefore, as shown in FIG. 13B, the noise charge Qnbias increases and is output.

  Then, as shown in FIG. 13C, the noise N41 of the power supply unit 41 and the noise N42 of the current detection means 42 are superimposed by being multiplied by 1 / α by the PSRR characteristic of the operational amplifier 18a. Therefore, as can be seen by comparing C in FIG. 12 and C in FIG. 13, in this embodiment, it is possible to reduce the noise N superimposed on the voltage value output from the operational amplifier 18 a of the amplifier circuit 18. Become.

  That is, in this embodiment, the noise Nbias generated by the bias power supply 14 is amplified, but the noise N42 generated by the current detection means 42 is relatively high in the radiation detection element 7 as in the conventional radiographic imaging apparatus 100. The noise N42 and the noise N41 attenuated by the PSRR characteristic of the amplifier circuit 18 are not superimposed through the large parasitic capacitance Cp.

  As described above, in the radiographic imaging apparatus 1 according to the present embodiment, the noise N42 generated by the current detection unit 42 is amplified and enlarged by the large parasitic capacitance Cp of the radiation detection element 7 as in the conventional radiographic imaging apparatus 100. In contrast, instead of being superimposed, the voltage value is finally output from the operational amplifier 18a to the correlated double sampling circuit 19 because it is superimposed and attenuated by the PSRR characteristic of the amplifier circuit 18. It is possible to reduce the noise N superimposed on the.

  As described above, according to the radiographic imaging apparatus 1 according to the present embodiment, the current flowing from the power supply unit 41 to the amplifier circuit 18 increases when the apparatus is irradiated with radiation. Therefore, the current detection means 42 is provided on the wiring connecting the power supply unit 41 and the amplifier circuit 18, and by detecting an increase in current detected by the current detection means 42, at least the start of radiation irradiation is accurately detected. It becomes possible.

  Further, in the radiographic image capturing apparatus 1 according to the present embodiment, the current detection unit 42 is not the bias line 9 that connects the radiation detection element 7 and the bias power supply 14 as in the prior art, but the power supply unit 41. It was provided on the wiring connecting the amplifier circuit 18.

  Therefore, in the conventional radiographic imaging apparatus 100, the noise N42 generated by the current detection means 42 is amplified by the large parasitic capacitance Cp of the radiation detection element 7, and further, the noise N42 is superimposed and increased at the time of resetting and reading. In this embodiment, amplification of the noise N42 from the current detection means 42 by the radiation detection element 7 and the amplifier circuit 18 can be suppressed, and the noise N42 is attenuated by the PSRR characteristic of the operational amplifier 18a of the amplifier circuit 18. Therefore, the noise N superimposed on the voltage value output from the amplifier circuit 18 can be reduced.

  For this reason, the influence of the noise N on the charge Q accumulated in each radiation detection element 7 is reduced according to the dose of the irradiated radiation, and further, the noise N42 generated in the current detection means 42 is reduced by the operational amplifier 18a. The influence of the noise N on the image quality of the finally obtained radiographic image is reduced, and in particular, deterioration of the granularity of the radiographic image can be prevented accurately, and an appropriate radiographic image can be obtained.

  And since it becomes possible to improve the granularity etc. of a radiographic image, it becomes possible to obtain the radiographic image of the suitable image quality in which the influence of noise was reduced exactly, for example, such a radiographic image is obtained. In the case of making a diagnosis using this method, it is possible to significantly reduce the possibility of inconveniences such as overlooking a lesion or mistaking a normal part as a lesion and causing a misdiagnosis.

  The current detecting means 42 may be, for example, the resistor 42a shown in FIG. 8 or the differential circuit as long as it can accurately detect the current flowing from the power supply unit 41 to the amplifier circuit 18 or the voltage value corresponding thereto. The configuration is not limited to the configuration of the present embodiment including the amplifier 42b, the switch 42c, and the like, and an appropriate configuration may be used.

DESCRIPTION OF SYMBOLS 1 Radiographic imaging device 5 Scanning line 6 Signal line 7 Radiation detection element 8 TFT (switch means)
18 Amplifier 22 Control means 41 Power supply section 42 Current detection means 42a Resistor 42c Switch Q Charge r Region V Voltage value (voltage value corresponding to current)

Claims (6)

A plurality of scanning lines and a plurality of signal lines arranged so as to intersect with each other; a plurality of radiation detecting elements arranged in a two-dimensional manner in each region partitioned by the plurality of scanning lines and the plurality of signal lines; ,
An off state and an on state are switched according to a voltage applied to the connected scanning line, arranged for each radiation detection element, and in the off state, the charge generated in the radiation detection element is retained, Switch means for releasing the charge from the radiation detection element in the ON state;
An amplifier circuit for converting the electric charge emitted from the radiation detection element into a voltage;
A power supply for supplying power to the amplifier circuit;
Current detection means for detecting a current flowing from the power supply unit to the amplifier circuit;
Control means for detecting at least the start of radiation irradiation based on the value of the current detected by the current detection means;
A radiographic imaging apparatus comprising:   The current detection means includes a resistor connected in series to a wiring connecting the power supply unit and the amplifier circuit, and a switch capable of short-circuiting between both terminals of the resistor, and at least the start of radiation irradiation 2. The device according to claim 1, wherein the short circuit of the switch is released when detecting the switch, and the other terminals of the resistor are short-circuited by the switch in other cases. Radiographic imaging device.   The radiographic imaging apparatus according to claim 1, wherein the control unit detects the start of radiation irradiation when the value of the current detected by the current detection unit increases.   The control means determines that the irradiation of radiation has been completed when a predetermined time has elapsed after the value of the current detected by the current detection means has increased and the start of irradiation has been detected. The radiographic imaging device according to claim 3.   The radiation according to any one of claims 1 to 3, wherein the control means detects the end of radiation irradiation when the value of the current detected by the current detection means decreases. Image shooting device.   The switch means is turned on when detecting the start of radiation irradiation, and after the control means detects the start of radiation irradiation, the switch means is turned off, and the charge generated in the radiation detection element is detected. 6. The radiographic image capturing apparatus according to claim 1, wherein accumulation in the radiation detection element is started.

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