WO2011135917A1 - 放射線画像撮影装置 - Google Patents
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Definitions
- the present invention relates to a radiographic image capturing apparatus, and more particularly, to a radiographic image capturing apparatus capable of detecting the start of radiation irradiation by the apparatus itself.
- 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 types of so-called indirect radiographic imaging devices have been developed that convert charges into electromagnetic signals after they have been converted into electromagnetic waves of a wavelength, and then generated by photoelectric conversion elements such as photodiodes in accordance with the energy of the converted and irradiated electromagnetic waves. Yes.
- 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 device is known as an FPD (Flat Panel Detector) and has been conventionally formed integrally with a support base (or a bucky apparatus) (see, for example, Patent Document 1).
- FPD Full Panel Detector
- 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).
- a signal to irradiate radiation is transmitted from the radiation generation device that irradiates radiation to the radiographic imaging device, and radiation is emitted from the radiographic imaging device side.
- radiation is irradiated by transmitting a signal permitting irradiation to the radiation generator.
- each radiation detection element when radiation is started on the radiation imaging apparatus and charges are generated in each radiation detection element, each radiation detection element is connected to each radiation detection element. Based on the increase / decrease of the current value of the current flowing in the bias line by providing current detection means on the bias line by utilizing the fact that the electric charge flows out to the bias line and the current flowing through the bias line increases. It has been proposed to detect the start of radiation irradiation.
- JP-A-9-73144 JP 2006-058124 A Japanese Patent Laid-Open No. 6-342099 US Pat. No. 7,211,803 JP 2009-219538 A
- the bias line is usually connected to the electrode of each radiation detection element. Therefore, when the current detection means is provided in the bias line as described above, the noise generated in the current detection means is transmitted to each radiation detection element via the bias line, and the charge generated in each radiation detection element by radiation irradiation, that is, A noise component resulting from noise generated by the current detection means is superimposed on the image data.
- the current detection means is provided in the bias line, but is a current detection means newly provided in the radiographic imaging apparatus.
- the current value of the current flowing through each wiring in the radiographic imaging apparatus due to radiation irradiation is When configured to detect an increase, the above problem arises as an unavoidable problem.
- the image quality is usually deteriorated.
- the radiographic image becomes very difficult to see.
- a lesion portion where a doctor who viewed the radiographic image is captured in the image
- the present invention has been made in view of the above-described problems, and does not provide any new means in the apparatus, and accurately detects at least the start of radiation irradiation by the apparatus itself using each means already provided in the apparatus.
- An object of the present invention is to provide a radiographic imaging apparatus capable of performing the above-described operation. Moreover, it aims at providing the radiographic imaging apparatus which can make the image quality of the radiographic image produced
- 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; A detector comprising: A scanning driving means for applying an on-voltage while switching each of the scanning lines in sequence during an image data reading process of reading image data from the radiation detection element; When an on-voltage is applied to each scanning line and applied through the scanning line, charges accumulated in the radiation detection element are discharged to the signal line, and an off-voltage is applied through the scanning line.
- switch means for accumulating charges in the radiation detection element
- a read circuit that converts the charge emitted from the radiation detection element to the signal line and reads the image data
- Control means for controlling at least the scanning drive means and the readout circuit to perform a readout process of the data from the radiation detection element; With The control unit periodically performs a read operation on the read circuit in a state where an off voltage is applied to all the scan lines from the scan drive unit and the switch units are turned off before radiographic image capturing. And repeatedly performing a leak data reading process for converting the charge leaked from the radiation detection element into leak data via the switch means, and radiation irradiation is performed when the read leak data exceeds a threshold value. It is characterized by detecting that it has started.
- the radiographic imaging apparatus of the system as in the present invention using the readout circuit provided in the normal radiographic imaging apparatus, the charge leaked from the radiation detection element is read out as leak data via the switch means, Based on the increase in the leak data, it is detected that radiation irradiation has started. Therefore, the radiation imaging apparatus itself can at least irradiate the radiation by utilizing the characteristics of the switch means that increases the leakage current flowing inside due to the radiation irradiation without constructing an interface with the radiation generating apparatus. It is possible to accurately detect the start.
- FIG. 2 is a cross-sectional view taken along line XX in FIG. It is a top view which shows the structure of the board
- FIG. 5 is a cross-sectional view taken along line YY in FIG. It is a side view explaining the board
- 5 is a timing chart showing charge reset switches, pulse signals, and on / off timings of TFTs in image data read processing. It is a graph showing the change of the voltage value etc. in a correlated double sampling circuit.
- 10 is a timing chart showing charge reset switches, pulse signals, and TFT on / off timings in leak data read processing.
- 6 is a timing chart showing charge reset switch, pulse signal, and TFT on / off timing in leak data readout processing that is periodically repeated before radiographic imaging. It is a figure explaining each electric charge which leaks from each radiation detection element via each TFT, and is a figure explaining the relationship between them and leak data.
- 6 is a timing chart showing charge reset switches, pulse signals, and on / off timings of TFTs when reset processing of each radiation detection element is performed in leak data readout processing that is periodically repeated.
- 10 is a timing chart showing charge reset switches, pulse signals, and on / off timings of TFTs when performing image data read processing from each radiation detection element in periodically repeated leak data read processing. It is a graph showing the example of the leak data read by each leak data read-out process when very weak radiation is irradiated to a radiographic imaging device. It is a figure showing the example of the irradiation position with respect to the scintillator and detection part of the radiation by which the irradiation field was narrowed down, and each signal line.
- FIG. 10 is a timing chart showing charge reset switches, pulse signals, and on / off timings of TFTs when the start of radiation irradiation is detected in the fourth leak read process in the periodically repeated leak data read process. It is a figure explaining the line defect which arises on a radiographic image in the case of FIG. 10 is a timing chart showing charge reset switches, pulse signals, and on / off timings of TFTs when the start of radiation irradiation is detected in the fifth leak read process in the periodically repeated leak data read process. It is a figure explaining that a line defect appears continuously on a radiographic image in the case of FIG.
- FIG. 12 is a timing chart showing an example of on / off timing when the on-voltage is sequentially applied to scanning lines other than the adjacent scanning lines and reset processing of each radiation detection element is performed in the periodically repeated leak data reading processing.
- . 6 is a timing chart illustrating an example of on / off timing when performing on-off voltage application to a plurality of scanning lines and performing image data reading processing from each radiation detection element in leak data reading processing that is periodically repeated.
- 10 is a timing chart in charge accumulation mode and image data read processing, such as leak data read processing when the charge accumulation mode is performed by stopping the read operation by the read circuit.
- 6 is a timing chart in charge accumulation mode and image data read processing, such as leak data read processing when the charge accumulation mode is performed by continuing the read operation by the read circuit.
- FIG. 39 is a graph for explaining that leak data read in the case of FIG. 38 increases beyond the threshold at the start of radiation irradiation and decreases to a value equal to or less than the threshold at the end of radiation irradiation.
- 7 is a graph for explaining that leak data read in the next leak data read process returns to a value equal to or less than the original threshold when leak data becomes large due to large noise. It is a timing chart explaining the OFF time of TFT, and explaining that the OFF time of TFT becomes a different time interval for each line of the scanning line. It is a timing chart when reading the offset correction value by repeating the same processing sequence as the processing sequence for reading image data after the image data reading processing.
- FIG. 12 is a timing chart in charge accumulation mode and image data read processing, such as leak data read processing when image data read processing is performed by applying an on-voltage from a scanning line next to leak data read processing in which the start of radiation irradiation is detected.
- FIG. 44 is a timing chart showing the charge reset switch, pulse signal, and TFT on / off timing when on / off is performed at the same timing as the previous processing after the image data read processing in the case of FIG. 43.
- 10 is a timing chart in charge accumulation mode and image data read processing, such as leak data read processing when image data read processing is performed by applying an ON voltage from the first scanning line.
- FIG. 46 is a timing chart showing the charge reset switch, the pulse signal, and the on / off timing of the TFT when the on / off is performed at the same timing as the previous processing after the image data read processing in the case of FIG. 6 is a timing chart when the offset correction value readout process is performed so that the TFT off time before radiographic image capturing and the TFT off time from the image data readout process to the offset correction value readout process are the same.
- FIG. 48 is a timing chart in the case of performing reset processing of each radiation detection element after image data read processing in the case of FIG. 47.
- FIG. 6 is a timing chart when an offset correction value reading process is performed immediately after an image data reading process or after a predetermined time has elapsed.
- the radiographic imaging device is a so-called indirect radiographic imaging device that includes a scintillator or the like and converts the irradiated radiation into electromagnetic waves of other wavelengths such as visible light to obtain an electrical signal.
- the present invention can also be applied to a direct radiographic imaging apparatus.
- 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
- FIG. 2 is a cross-sectional view taken along line XX of FIG.
- the radiation image capturing apparatus 1 according to the present embodiment is configured by housing a scintillator 3, a substrate 4, and the like in a housing 2.
- the housing 2 is formed of a material such as a carbon plate or plastic that transmits at least the radiation incident surface R. 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.
- the side surface portion of the housing 2 can be opened and closed for replacement of a power switch 36, an indicator 37 composed of LEDs or the like, and a battery 41 (see FIG. 7 described later).
- the lid member 38 and the like are disposed.
- an antenna which is a communication means for transmitting and receiving information such as image data d, which will be described later, to and from an external device such as an image processing computer is provided on the side surface of the lid member 38.
- the device 39 is embedded.
- the installation position of the antenna device 39 is not limited to the side surface portion of the lid member 38, and the antenna device 39 can be installed at an arbitrary position of the radiographic image capturing apparatus 1.
- the number of antenna devices 39 to be installed is not limited to one, and a plurality of antenna devices 39 may be provided.
- a base 31 is disposed inside the housing 2 via a lead thin plate (not shown) on the lower side of the substrate 4, and an electronic component 32 and the like are disposed on the base 31.
- the PCB substrate 33, the buffer member 34, and the like are attached.
- 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 arranged so as to face a detection unit P described later of the substrate 4.
- the scintillator 3 is, for example, a phosphor whose main component is converted into an electromagnetic wave having a wavelength of 300 to 800 nm, that is, an electromagnetic wave centered on visible light when it receives radiation, and that is output.
- 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.
- the region is a detection unit P.
- 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 an on-voltage is applied to the connected scanning line 5 by the scanning driving means 15 described later and applied to the gate electrode 8g via the scanning line 5, and the radiation detection element The electric charge accumulated in 7 is emitted to the signal line 6.
- the TFT 8 is turned off when an off voltage is applied to the connected scanning line 5 and applied to the gate electrode 8 g via the scanning line 5, and the charge from the radiation detection element 7 to the signal line 6 is turned off. Is stopped, and the charge is held and accumulated in the radiation detection element 7.
- FIG. 5 is a sectional view taken along line YY 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).
- An upper portion of the gate electrode 8g on the gate insulating layer 81 made of SiN x ) or the like is connected to the first electrode 74 of the radiation detection element 7 via a 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 electrodes 8s and 8d from above.
- 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.
- 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.
- the auxiliary electrode 72 is not necessarily provided.
- 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.
- the radiation irradiated with respect to the radiographic imaging apparatus 1 injects from the radiation entrance surface R of the housing
- the electromagnetic wave reaches the i layer 76 of the radiation detection element 7, and electron-hole pairs are generated in the i layer 76.
- the radiation detection element 7 converts the electromagnetic waves irradiated from the scintillator 3 into electric charges (electron hole pairs).
- a second electrode 78 made of a transparent electrode such as ITO is laminated and formed so that the irradiated electromagnetic wave reaches the i layer 76 and the like.
- 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.
- 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. Further, each bias line 9 is bound to the connection 10 at a position outside the detection portion P of the substrate 4.
- 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.
- each input / output terminal 11 has an anisotropic COF (Chip On Film) 12 in which a chip such as a gate IC 12 a constituting a gate driver 15 b of the scanning drive means 15 described later is incorporated on a film. They are connected via an anisotropic conductive adhesive material 13 such as a conductive conductive adhesive 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.
- substrate 4 part of the radiographic imaging apparatus 1 is formed.
- illustration of the electronic component 32 and the like is omitted.
- FIG. 7 is a block diagram illustrating an equivalent circuit of the radiographic imaging apparatus 1 according to the present embodiment
- FIG. 8 is a block diagram illustrating an equivalent circuit for one pixel constituting the detection unit P.
- 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.
- the bias power supply 14 is connected to a control means 22 described later, and the control means 22 controls the bias voltage applied to each radiation detection element 7 from the bias power supply 14.
- the bias line 9 is connected via the second electrode 78 to the p-layer 77 side (see FIG. 5) of the radiation detection element 7.
- the bias power supply 14 supplies a voltage equal to or lower than a voltage applied to the second electrode 78 of the radiation detection element 7 via the bias line 9 as a bias voltage on the first electrode 74 side of the radiation detection element 7 (that is, a so-called reverse bias voltage). Is applied.
- 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 the 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.
- the scan driver 15 includes a power supply circuit 15a for supplying an on voltage and an off voltage to the gate driver 15b via the wiring 15c, and a voltage to be applied to each line L1 to Lx of the scan line 5 between the on voltage and the off voltage.
- a gate driver 15b that switches between the on state and the off state of each TFT 8 is provided.
- the scanning drive unit 15 applies an on-voltage sequentially to each of the lines L1 to Lx of the scanning line 5, or an off-voltage is applied to all the lines L1 to Lx of the scanning line 5. The applied state is maintained.
- image data read processing for reading out image data d from each radiological detection element 7, that is, generated and accumulated in each radiological detection element 7 by radiation irradiation to the radiographic imaging apparatus 1.
- the scanning driving unit 15 switches the voltage applied from the gate driver 15b between the on-voltage and the off-voltage for data reading.
- L1 to Lx are sequentially switched so that image data d is read from each radiation detection element 7 connected to each line L1 to Lx of the scanning line 5, respectively.
- the off-voltage is applied to all the lines L1 to Lx of the scanning line 5 from the scanning driving means 15 before the radiographic imaging, that is, before the radiation irradiation to the radiographic imaging apparatus 1 is started.
- Leak data read processing for converting charges leaked from the radiation detection elements 7 through the TFTs 8 into leak data Dleak by periodically driving a read circuit 17 to be described later with the TFTs 8 turned off. This will be described in detail later.
- each signal line 6 is connected to each readout circuit 17 formed in each readout IC 16.
- the readout IC 16 is provided with one readout circuit 17 for each signal line 6.
- the readout circuit 17 includes an amplification circuit 18 and a correlated double sampling circuit 19.
- An analog multiplexer 21 and an A / D converter 20 are further provided in the reading IC 16. 7 and 8, the correlated double sampling circuit 19 is represented as CDS. In FIG. 8, the analog multiplexer 21 is omitted.
- 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, respectively.
- a power supply unit 18 d for supplying power to the amplifier circuit 18 is connected to the amplifier circuit 18.
- a switch 18e that opens and closes in conjunction with the charge reset switch 18c is provided between the operational amplifier 18a and the correlated double sampling circuit 19.
- 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.
- 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, and is controlled to be turned on / off by the control means 22, so that the charge reset switch 18c is turned on.
- the switch 18e is turned off in conjunction with it, and when the charge reset switch 18c is turned off, the switch 18e is turned on in conjunction with it.
- each radiation detection element is connected via each TFT 8 which is turned on while the charge reset switch 18c is turned off and the switch 18e is turned on. 7 is discharged to the signal line 6 (in the case of image data reading processing), or when the charge leaks from each radiation detection element 7 to the signal line 6 via each TFT 8 which is turned off (leakage).
- the charge flows through the signal line 6 and flows into the capacitor 18b of the amplifier circuit 18 and is accumulated.
- a voltage value corresponding to the amount of charge accumulated in the capacitor 18b is output from the output side of the operational amplifier 18a. In this way, the amplifier circuit 18 outputs a voltage value according to the amount of charge output from each radiation detection element 7 and converts the charge voltage.
- the amplifier circuit 18 may be configured to output a current in accordance with the charge output from the radiation detection element 7.
- the charge reset switch 18c is turned on, and when the switch 18e is turned off, the input side and the output side of the amplifier circuit 18 are short-circuited.
- the charge accumulated in 18b is discharged.
- the discharged electric charge passes through the operational amplifier 18a from the output terminal side of the operational amplifier 18a, goes out from the non-inverting input terminal and is grounded, or flows out to the power supply unit 18d, whereby the amplifier circuit 18 is reset. ing.
- a correlated double sampling circuit (CDS) 19 is connected to the output side of the amplifier circuit 18.
- 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.
- the charge reset switch 18c of the amplifier circuit 18 of each reading circuit 17 is controlled to be turned off.
- the so-called kTC noise is generated at the moment when the charge reset switch 18c is turned off, and the charge caused by the kTC noise accumulates in the capacitor 18b of the amplifier circuit 18.
- the voltage value output from the amplifier circuit 18 starts from the above-described reference potential V 0 at the moment when the charge reset switch 18c is turned off (indicated as “18coff” in FIG. 11). It changes by the amount of electric charge caused by kTC noise and changes to a voltage value Vin.
- the control means 22 transmits the first pulse signal Sp1 to the correlated double sampling circuit 19 as shown in FIG. 10, and at that time (shown as “CDS hold” (left side in FIG. 11)).
- the voltage value Vin output from the amplifier circuit 18 is held.
- an on-voltage is applied to one scanning line 5 (for example, line Ln of the scanning line 5) from the gate driver 15 b of the scanning driving unit 15, and the gate electrode 8 g is applied to the scanning line 5.
- the charges accumulated from the radiation detection elements 7 to which these TFTs 8 are connected are transferred to the signal lines 6.
- the voltage value output from the amplifier circuit 18 increases according to the amount of charge stored in the capacitor 18b.
- the control means 22 switches the on-voltage applied to the scanning line 5 from the gate driver 15b to the off-voltage and turns the gate electrode 8g on the scanning line 5 as shown in FIG. Is turned off (indicated as “TFToff” in FIG. 11), and at this stage, the second pulse signal Sp2 is transmitted to each correlated double sampling circuit 19, and at that time, the amplifier circuit 18 The output voltage value Vfi is held (displayed as “CDS hold” (right side) in FIG. 11).
- each correlated double sampling circuit 19 When each correlated double sampling circuit 19 holds the voltage value Vfi by the second pulse signal Sp2, it calculates the difference Vfi ⁇ Vin of the voltage value, and uses the calculated difference Vfi ⁇ Vin as the analog value image data d on the downstream side. To output.
- the image data d 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 d into digital values, outputs them to the storage means 40, and sequentially stores them.
- control means 22 applies the on-voltage from the gate driver 15b of the scanning drive means 15 as shown in FIG. 9, in the image data read processing for reading the image data d from each radiation detection element 7 as described above. This is performed each time the lines L1 to Lx of the scanning line 5 are sequentially switched.
- the readout circuit 17 is periodically driven in a state where each TFT 8 is in an OFF state, and the charge leaked from each radiation detection element 7 via each TFT 8 is leaked. Leak data reading processing for conversion into Dleak is performed.
- each TFT 8 Since the leak data reading process is performed in a state where each TFT 8 is turned off, an off voltage is applied to all the lines L1 to Lx of the scanning line 5 from the scanning driving means 15, as shown in FIG. That is, unlike the case of the image data reading process shown in FIG. 10, the on / off operation of each TFT 8 is not performed in the leak data reading process, and each TFT 8 is always in the off state at least during the leak data reading process. Is done.
- the on / off control of the charge reset switch 18c by the control means 22, the transmission of the pulse signals Sp1, Sp2 to the correlated double sampling circuit 19, and the like are the same as in the case of the image data reading process.
- the voltage output from the amplifier circuit 18 is equivalent to the amount of charge leaked from each radiation detection element 7 via each TFT 8 flowing into the capacitor 18b of the amplifier circuit 18 and accumulated. The value rises.
- the voltage value output from the amplifier circuit 18 increases.
- the increase in the voltage value in the case of the leak data reading process is usually higher than the degree of increase in the case of the image data reading process. The degree of is small.
- each correlated double sampling circuit 19 calculates the voltage value difference Vfi ⁇ Vin when holding the voltage value Vfi with the second pulse signal Sp2, and in the case of the leak data reading process.
- the calculated difference Vfi ⁇ Vin is output downstream as analog value leak data Dleak.
- the leak data Dleak output from the correlated double sampling circuit 19 is sequentially transmitted to the A / D converter 20 via the analog multiplexer 21, and is sequentially converted into leak data Dleak having a digital value.
- the control means 22 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a RAM (Random Access Memory), an input / output interface connected to the bus, an FPGA (Field Programmable Gate Array), etc. It is configured. It may be configured by a dedicated control circuit. And the control means 22 controls operation
- DRAM Dynamic RAM
- the above-described antenna device 39 is connected to the control unit 22, and each member such as the detection unit P, the scanning drive unit 15, the readout circuit 17, the storage unit 40, the bias power supply 14, and the like.
- a battery 41 for supplying electric power is connected.
- a connection terminal 42 for charging the battery 41 by supplying power to the battery 41 from a charging device (not shown) is attached to the battery 41.
- control unit 22 controls the bias power supply 14 to set or vary the bias voltage applied from the bias power supply 14 to each radiation detection element 7. It is designed to control the operation.
- the leakage data reading process is started before the radiation image capturing is started before the radiation image capturing apparatus 1 starts the radiation image capturing.
- the leak data reading process may be performed by pressing a power switch 36 (see FIG. 1) of the radiographic image capturing apparatus 1 by an operator such as a radiographer, the radiographic image capturing apparatus 1 being changed to an awake state, or The process is started when a signal indicating the start of the leak data reading process is received from the external device.
- control means 22 is configured to periodically repeat the leak data reading process shown in FIG. That is, as shown in FIG. 13, the charge reset switch 18c of the amplifier circuit 18 is applied in a state where the TFT 8 is turned off by applying the off voltage to all the lines L1 to Lx of the scanning line 5 from the scanning driving means 15. ON / OFF and transmission of pulse signals Sp1 and Sp2 to the correlated double sampling circuit 19 are periodically repeated.
- each TFT 8 is in an off state.
- each charge q is output from each radiation detection element 7 via each TFT 8. Leaks to the signal line 6 little by little.
- each charge q leaked from each radiation detection element 7 flows through the signal line 6 and flows into the capacitor 18b of the amplifier circuit 18 and is accumulated. Further, in the amplifier circuit 18, since a voltage value corresponding to the amount of charge accumulated in the capacitor 18b is output from the output side of the operational amplifier 18a, the charge reset switch 18c is turned off and then output from the amplifier circuit 18. As shown in FIG. 11, the correlated double sampling circuit 19 outputs the difference Vfi ⁇ Vin between the voltage values Vin and Vfi held in accordance with the pulse signals Sp1 and Sp2 as leak data Dleak.
- the leak data reading process the total value of each charge q leaking from each radiation detection element 7 connected to one signal line 6 through each TFT 8 is accumulated in the capacitor 18b of the amplifier circuit 18.
- the data corresponding to the total value of the leaked charges q is converted and read as leak data Dleak for each read circuit 18.
- the TFT 8 serving as a switch means leaks in the TFT 8 when irradiated with radiation or when irradiated with electromagnetic waves converted from radiation by the scintillator 3 (see FIG. 2 etc.) as in this embodiment. It is known that the amount of current increases. This is thought to be because electron-hole pairs are newly generated in the semiconductor layer 82 (see FIG. 5) of the TFT 8 when the TFT 8 is irradiated with electromagnetic waves.
- the amount of leakage current flowing in each TFT 8 is increased by irradiation of radiation (or irradiation of electromagnetic waves converted from radiation, the same applies hereinafter), and charge leakage from each radiation detection element 7 via each TFT 8. As the amount increases, the total value of the charges q leaking from each radiation detection element 7 connected to one signal line 6 increases, and the corresponding leak data Dleak also increases.
- the radiation image capturing apparatus 1 is irradiated with radiation.
- the value of the leak data Dleak increases at the start time t1.
- control means 22 is configured to monitor the leak data Dleak read in the periodically repeated leak data read processing shown in FIG. 13, and the read leak data Dleak is set to the set threshold value Dth (FIG. 15)), it is possible to detect that radiation irradiation has started.
- the control unit 22 applies the off voltage to all the lines L1 to Lx of the scan line 5 from the scan driving unit 15 before radiographic image capturing.
- Leak data read processing for converting the charge q leaked from each radiation detection element 7 through each TFT 8 into leak data Dleak by causing the read circuit 17 to perform a read operation periodically in a state where each TFT 8 is in an OFF state. Are repeatedly performed, and it is detected that radiation irradiation has started when the read leak data Dleak exceeds the threshold value Dth.
- the radiographic imaging apparatus 1 is not provided with new means, such as an electric current detection means, in the radiographic imaging apparatus 1 like invention in patent document 4 mentioned above and patent document 5.
- the radiation image capturing apparatus 1 itself can accurately detect at least the start of radiation irradiation using the existing readout circuit 17 or the like.
- the leak data Dleak for each read circuit 17 is output from each read circuit 17 as the leak data Dleak.
- One readout circuit 17 is provided for each signal line 6 provided in the detection unit P by several thousand to several tens of thousands. Therefore, in this embodiment, several thousand to several tens of thousands of leak data Dleak are output from each read circuit 17 in one leak data read process.
- the control means 22 extracts the maximum value from each of the leak data Dleak read for each leak data read process, and determines whether or not the maximum value of the leak data Dleak exceeds the threshold value Dth. It is supposed to be. If comprised in this way, for example, when radiation is irradiated only to the narrow range of the detection part P of the radiographic imaging device 1 (that is, when irradiation is performed with the irradiation field narrowed), the radiation is irradiated.
- the leak data Dleak does not increase in the portion that has not been subjected to the radiation, it is possible to accurately detect that the leak data Dleak has increased in the portion that has been irradiated with radiation, and to accurately detect the start of radiation irradiation.
- the noise generated in the readout circuit 17 is large, the leaked data Dleak on which the noise is superimposed exceeds the threshold value Dth and erroneously detects that radiation irradiation has started. There is a possibility that it may be.
- the total value (or average value) of the leak data Dleak is calculated for each read IC 16 provided with a predetermined number of read circuits 17, and the total value (or average value) is calculated. It is also possible to extract the maximum value from (1) and compare the maximum value with the threshold value Dth.
- the maximum value of the individual leak data Dleak is extracted, or the total value (or average value) of the leak data Dleak for each readout IC 16 is calculated, and the maximum value is extracted from the total value, and the threshold value Dth is extracted.
- the total value (or average value) of all the leak data Dleak read by each read circuit 17 during one leak data read process is calculated instead of the comparison with It is also possible to configure so that (or the average value) and the threshold value Dth are compared. If comprised in this way, the process which extracts a maximum value will become unnecessary.
- each radiation detecting element 7 When the state in which the TFT 8 is turned off by applying the off voltage to all the lines L1 to Lx of the scanning line 5 from the scanning driving unit 15 is continued, each radiation detecting element 7 The dark charge generated in the inside is accumulated in each radiation detection element 7, and a method for removing this will be described later.
- FIG. 16 is a graph showing how the leakage current Ioff flowing in the TFT 8 changes in accordance with the temperature change of the TFT 8 in a state where the TFT 8 is turned off (off voltage is applied to the gate electrode 8g of the TFT 8). is there.
- FIG. 16 also shows the temperature dependence of the current Ion flowing through the TFT 8 in a state where the TFT 8 is in an on state (a state where an on voltage is applied to the gate electrode 8g of the TFT 8).
- a reference potential V 0 of 0 [V] is applied from the amplifier circuit 18 to the drain electrode 8d (see FIGS. 7 and 8) of the TFT 8 via the signal line 6, and the gate electrode g of the TFT 8 is applied to the gate electrode g of the TFT 8.
- An off voltage of ⁇ 10 [V] is applied from the scanning drive means 15 via the scanning line 5, and a bias voltage (reverse bias voltage) of ⁇ 5 [V] is applied to the radiation detection element 7 via the bias line 9.
- the charge corresponding to the bias voltage is accumulated in the radiation detection element 7, that is, in this embodiment, the charge corresponding to the saturation charge amount of the photodiode that is the radiation detection element 7 is accumulated.
- the leakage current Ioff was actually measured while varying the temperature of the TFT 8.
- the reason why the leakage current Ioff flowing in the TFT 8 with the TFT 8 in the off state increases exponentially as the temperature of the TFT 8 increases is not necessarily clear, but at least the temperature of the TFT 8 This is considered to be because the vibration due to the heat of the atoms constituting the TFT 8 becomes intense due to the increase in the thickness of the TFT 8 and the carrier density in the semiconductor layer 82 (see FIG. 5) of the TFT 8 increases.
- the radiographic image capturing apparatus 1 formed integrally with the image forming apparatus 1 can be configured so that power is always supplied from a power supply external to the apparatus, and a readout IC 16 including a bias voltage 14, a scanning drive unit 15, and a readout circuit 17. If the device is operated for a long time, the temperature of the TFT 8 becomes stable and constant.
- the charge q leaked from the radiation detection element 7 through the TFT 8 at a constant temperature has a certain degree of fluctuation, but has a substantially constant value. Therefore, the leakage data Dleak corresponding to the total value of the charges q leaking from the radiation detecting elements 7 connected to the single signal line 6 through the TFTs 8 also has some fluctuations. It becomes a constant value. For this reason, the maximum value extracted from the leak data Dleak also has a certain amount of fluctuation, but is a substantially constant value.
- each charge q leaked through each TFT 8 increases, so that each leakage read by each readout circuit 17 as shown in FIG.
- the maximum value extracted from the data Dleak increases to a significantly large value.
- the radiographic imaging apparatus 1 in the case of the radiographic imaging apparatus 1 with a built-in battery as described above, the radiographic imaging apparatus 1 immediately before the radiographic imaging is performed in order to suppress the power consumption of the battery 41 (see FIG. 7) as much as possible.
- the power switch 36 (see FIG. 1) is pressed or the radiographic imaging apparatus 1 is shifted to the awake state to activate the bias voltage 14, the scanning drive means 15, the readout IC 16, and the like.
- the temperature of the TFT 8 rises as the temperature of the substrate 4 (see FIG. 3 and the like) rises when the bias voltage 14, the scanning drive means 15, the readout IC 16 and the like are activated. Therefore, for example, when the leak data reading process as shown in FIG. 13 is periodically repeated immediately after the power switch 36 of the radiographic imaging apparatus 1 is pressed, for example, as shown in FIG.
- the maximum value Dleak_max among the leak data Dleak read out at 17 gradually increases as the temperature of the TFT 8 increases.
- the threshold value Dth is configured to be set to a predetermined value Dth_pro in advance, for example, the radiation image capturing apparatus 1 is read by each readout circuit 17 due to the temperature rise of the TFT 8 even though no radiation is irradiated.
- the control means 22 may erroneously determine that radiation has been started.
- the radiographic image capturing apparatus 1 is a battery-embedded radiographic image capturing apparatus as described above, each leak data read out by the control means 22 in the leak data reading process that is periodically repeated. Based on the history of Dleak (in this case, the maximum value Dleak_max of each leak data Dleak), the threshold value Dth can be set while being updated.
- Every time leak data read processing is performed extraction is performed by past leak data read processing for a predetermined number of times such as 10 times or 100 times including leak data read processing immediately before the leak data read processing.
- An average value of the maximum value Dleak_max of the leaked data Dleak that is, an average value Dleak_ave of the moving average can be calculated, and a predetermined value set in advance can be added to the average value Dleak_ave to obtain a threshold value Dth. It is.
- the threshold value Dth can be set while being updated for each leak data reading process. And even if the value of each leak data Dleak read by each read circuit 17 increases due to the temperature rise of the TFT 8, the threshold value Dth also increases accordingly, and it is possible to prevent erroneous detection of the start of radiation irradiation. Is done.
- control means 22 is provided with a peak hold function or provided with a peak hold means, and every time leak data reading processing is performed, the maximum value Dleak_max of the leak data Dleak extracted this time is already held. If the value is larger than the value Dleak_max, the maximum value Dleak_max is updated to the maximum value Dleak_max extracted this time and held. Then, a predetermined value set in advance can be added to the stored maximum value Dleak_max to obtain the threshold value Dth.
- the threshold value Dth can be set while being updated for each leak data reading process. Even if the value of each leak data Dleak read by each read circuit 17 increases due to the temperature rise of the TFT 8, the past maximum value Dleak_max held is also updated to the large value, and the threshold value Dth is also correspondingly changed. growing. Therefore, it is possible to accurately prevent erroneous detection of the start of radiation irradiation.
- the current leak data read process It is possible to accurately detect that the irradiation of radiation has started at the point of time.
- the leak data reading process before the radiographic image capturing and the detection of the start of radiation irradiation according to the present invention are all performed from the scanning drive unit 15 to all the lines L1 to L1 as shown in FIG. This is performed in a state where each TFT 8 is turned off by applying an off voltage to Lx. However, if this state is continued, so-called dark charges generated by thermal excitation or the like due to the heat (temperature) of the radiation detection element 7 itself are accumulated in each radiation detection element 7, and the accumulated amount of dark charge increases. It is well known.
- the control unit 22 performs leak data in a state where an off voltage is applied to all the lines L1 to Lx of the scanning line 5 from the scanning driving unit 15 during the leakage data reading process.
- the scanning drive unit 15 performs the leak reading process between the leak data reading process and the next leak data reading process.
- An on-voltage is applied to each of the lines L1 to Lx of the scanning line 5 to perform a reset process for releasing and removing extra charges from each radiation detection element 7.
- the charge reset switch 18c of the amplifier circuit 18 of the readout circuit 17 is turned on, and although not shown, the switch 18e (see FIG. 8) is turned off in conjunction with this.
- the on-voltage is sequentially applied from the scanning drive unit 15 to each of the lines L1 to Lx of the scanning line 5.
- the TFTs 8 connected to the lines L1 to Lx of the scanning line 5 to which the ON voltage is applied are turned on, and extra charges are released from the radiation detection elements 7 to the signal lines 6 through the TFTs 8.
- the charge discharged to the signal line 6 passes through the charge reset switch 18c of the amplifier circuit 18, passes through the operational amplifier 18a from the output terminal side of the operational amplifier 18a of the amplifier circuit 18, exits from the non-inverting input terminal, and is grounded. Or flows out to the power supply unit 18 d and is removed from each radiation detection element 7 and the readout circuit 17.
- the leak data Dleak (more precisely, the maximum value Dleak_max of the leak data Dleak, the maximum value of the total value (or average value) of the leak data Dleak for each read IC 16, etc.).
- the leak data Dleak it is possible to accurately detect the start of radiation irradiation by monitoring the leakage data Dleak), and to allow the radiation generated in each radiation detection element 7 to be generated in a wide dynamic range. Therefore, it is possible to accurately acquire image data d corresponding to the dose of irradiated radiation.
- each radiation detection element 7 As a reset process for each radiation detection element 7, an ON voltage is sequentially applied from the scanning drive unit 15 to each line L1 to Lx of the scanning line 5 (that is, the ON voltage for each line of the scanning line 5). In the case of sequentially switching the line L of the scanning line 5 to which the ON voltage is applied), the leak data reading process and the next leak data reading are performed during the leak data reading process to be performed periodically. It is also possible to perform a reset process of each radiation detection element 7 by simultaneously applying an ON voltage to all the lines L1 to Lx of the scanning line 5 from the scanning driving unit 15 between the processes.
- the image data reading process is performed in the manner described with reference to FIG. Further, the read image data d is not used as a material for determining the start of radiation irradiation to the radiographic image capturing apparatus 1 by the control means 22, but the read image data d can be used effectively. Yes, in an appropriate manner.
- the leak data Dleak is generated by the power supply circuit 15a (see FIG. 7) of the scanning drive unit 15, and is caused by noise transmitted through the lines L1 to Lx of the scanning line 5 or noise generated by the readout circuit 17 or the like. It can be said that it is easily affected. That is, there may be a case where the S / N ratio of the leak data Dleak is not always good.
- Method 1 For example, the data shown in FIG. 21 is read by each leak data reading process when the radiation image capturing apparatus 1 is irradiated with a very low radiation dose per unit time, that is, a dose rate of about 0.5 [ ⁇ R / ms].
- a dose rate of about 0.5 [ ⁇ R / ms].
- 1-2 [ ⁇ R / ms] is generally said to be the lowest dose rate, and the above condition corresponds to the case of irradiation with a dose rate lower than that.
- the increase in the leak data Dleak due to radiation irradiation is buried in noise, and at least radiation irradiation start is performed. It cannot be detected.
- the noise derived from the power supply circuit 15a of the scanning drive means 15 is the noise generated in one power supply circuit 15a as shown in FIG.
- the signal is instantaneously transmitted to each TFT 8 via each line L1 to Lx of the scanning line 5 via the gate driver 15b. Therefore, the noise generated in the power supply circuit 15a is simultaneously transmitted to all the TFTs 8 and is superimposed on the read leak data Dleak.
- each radiation detection element 7 is in a state in which an i layer 76 (see FIG. 5) or the like is interposed between the first electrode 74 and the second electrode 78, and has a kind of capacitor-like structure. Have.
- the parasitic capacitance is C and the bias voltage is Vbias
- each readout IC 16 side noise caused by noise generated in each readout IC 16 etc. is superimposed on each TFT 8 etc. via each signal line 6. In this way, the same noise due to various noises generated in each functional unit in the apparatus is superimposed on the leak data Dleak read at the same timing.
- each leak data Dleak read by each read circuit 17 in one leak data read process includes various noises such as noise derived from the power supply circuit 15a of the scan driving unit 15 and noise derived from the bias power supply 14. Are simultaneously superimposed on each leak data Dleak.
- the following configuration is made.
- the S / N ratio of the leak data Dleak can be improved.
- the radiation imaging apparatus 1 when the radiation imaging apparatus 1 is irradiated with radiation at a low dose rate, such as in the case of Schuler imaging with a stethoscope, the radiation field F is often narrowed and irradiated.
- the signal line 6 is assumed to be extended in the vertical direction in the figure.
- each radiation detection provided at a position on the detection unit P corresponding to the radiation field F, that is, a position where an electromagnetic wave obtained by converting the irradiated radiation by the scintillator 3 can enter.
- the leakage data Dleak based on the charge q leaked through each TFT 8 as described above rises as shown in FIG.
- the radiation image capturing device 1 does not increase the leak current Dleak based on the charge q leaked through each TFT 8 because the leak current flowing in each TFT 8 does not increase.
- the noise generated in the power supply circuit 15a of the scanning drive unit 15 via the lines L1 to Lx of the scanning line 5 is different. Simultaneously transmitted to the TFT 8. Therefore, the noise generated in the power supply circuit 15a is simultaneously transmitted to all the TFTs 8 and is superimposed on the read leak data Dleak.
- each radiation at a position on the detection unit P where the electromagnetic wave emitted from the scintillator 3 can be incident by the control unit 22 that is, a position on the detection unit P corresponding to the radiation field F of radiation.
- the electromagnetic wave irradiated from the scintillator 3 does not enter the position on the detection unit P (that is, a position other than the position on the detection unit P corresponding to the radiation field F).
- a difference ⁇ D obtained by subtracting the leak data Dleak read from each radiation detection element 7 provided is calculated, and radiation irradiation starts when the calculated difference ⁇ D exceeds a threshold value ⁇ Dth set for the difference ⁇ D. It can be configured to detect that it has been done.
- the irradiation field F is narrowed so that the radiation is irradiated not on the entire area of the scintillator 3 or the detection unit P of the radiographic imaging apparatus 1 but on a part of the scintillator 3 or the detection unit P. It is premised on irradiation.
- the radiation field F of the radiation applied to the radiation image capturing apparatus 1 is normally set to the most suitable position on the radiation incident surface R for convenience of capturing for each capturing. Therefore, the irradiation field F may be set near the center of the radiation incident surface R as shown in FIG. 22, but may be set at a position corresponding to the vicinity of the periphery of the scintillator 3 or the detection unit P. For this reason, the signal line 6 is specified in advance, and each radiation detection element 7 connected to the signal line 6 cannot be specified in advance as a radiation detection element from which no electromagnetic wave is incident from the scintillator 3.
- control means 22 extracts the maximum value Dleak_max and the minimum value Dleak_min from each leak data Dleak read for each signal line 6, that is, for each read circuit 17, and the minimum value Dleak_min from the maximum value Dleak_max. It is possible to calculate the difference ⁇ D obtained by subtracting the difference ⁇ D, and detect that the radiation irradiation has started when the calculated difference ⁇ D exceeds the threshold value ⁇ Dth set for the difference ⁇ D.
- each leak data Dleak read for each read circuit 17 is usually overlaid with an offset due to the read characteristics of each read circuit 17, for example, the signal line 6 is connected. Even if the same amount of charge q leaks from each radiation detection element 7 connected to each readout circuit 17, each leak data Dleak read by each readout circuit 17 has a different value for each offset.
- leaks extracted by a predetermined number of past leak data read processing such as 5 times or 10 times including leak data read processing immediately before the leak data read processing.
- the moving average of the data Dleak is calculated for each readout circuit 17, the moving average is subtracted from the leak data Dleak read in the current leak data read process, and the subtracted value is used as the current leak data read process.
- the leak data Dleak read by the read circuit 17 is used.
- the value Dleak_min is extracted, the difference ⁇ D obtained by subtracting the minimum value Dleak_min from the maximum value Dleak_max is calculated, and radiation irradiation is started when the calculated difference ⁇ D exceeds the threshold value ⁇ Dth set for the difference ⁇ D.
- the signal line 6 disposed at the position on the detection unit P corresponding to the radiation irradiation field F when the radiation image capturing apparatus 1 is irradiated with radiation, as described above, the signal line 6 disposed at the position on the detection unit P corresponding to the radiation irradiation field F. Then, the leakage current flowing in each TFT 8 connected to the signal line 6 increases, and the leakage data Dleak read by the readout circuit 17 corresponding to the signal line 6 rises. In the signal line 6 arranged at a position other than the position on the detection unit P corresponding to F, the leakage current flowing in each TFT 8 connected to the signal line 6 does not increase, and corresponds to the signal line 6. The leak data Dleak read by the read circuit 17 does not rise.
- the maximum value Dleak_max of the leak data Dleak calculated by subtracting the moving average from the leak data Dleak read by each readout circuit 17 is used.
- the difference ⁇ D obtained by subtracting the minimum value Dleak_min is a positive value that is significantly different from zero.
- the threshold value ⁇ Dth is set to an appropriate value with respect to the difference ⁇ D, for example, even when very weak radiation as shown in FIG. As shown in the above, it is possible to accurately detect the start and end of radiation irradiation.
- the data shown in FIG. 21 is the data when the radiation image capturing apparatus 1 is irradiated with radiation at an extremely low dose rate that cannot be obtained by normal radiation image capturing, as described above. Since the result as shown in FIG. 23 is obtained for such data, the difference ⁇ D becomes clearer when the radiation image capturing apparatus 1 is irradiated with radiation having a higher dose rate. Needless to say that will rise.
- the irradiation field F is not narrowed and the entire radiation incident surface R (see FIG. 1 and the like) of the radiographic imaging apparatus 1 is covered. In some cases, radiation is emitted. In such a case, the start and end of radiation irradiation cannot be detected by the method of [Method 1-1] described above.
- the method shown in the explanation of the above principle and the method shown in [Method 1-1] are used in combination, and both methods can start radiation irradiation simultaneously.
- the start or end of radiation irradiation can be detected when the start or end of radiation irradiation is detected by any of these methods. desirable.
- the read IC 16 (see FIG. 7 and the like) is formed with a predetermined number of read circuits 17 such as 128 and 256, respectively.
- 128 readout circuits 17 are formed in one readout IC 16 and 1024 signal lines 6 are wired, at least 8 readout ICs 16 are provided.
- each radiation detection element 7 connected via each signal line 6 is located at a position other than the position on the detection unit P corresponding to the radiation field F, that is, the detection unit P where the electromagnetic wave from the scintillator 3 is not incident. It is considered that there is a readout IC 16 that becomes each radiation detection element 7 provided in the upper position.
- the radiation field F since the radiation field F is narrowed, the radiation reaches all the radiation detection elements 7 connected to a certain readout IC 16 even though the radiation imaging apparatus 1 is irradiated with radiation. No (accurately, no electromagnetic wave converted from radiation by the scintillator 3 is incident), it is considered that such a readout IC 16 exists.
- the maximum value and the minimum value are extracted from each leak data Dleak calculated by subtracting the moving average from each leak data Dleak read for each read circuit 17.
- an average value for each read IC 16 of each leak data Dleak calculated by subtracting the moving average from each leak data Dleak read for each read circuit 17 is calculated, and each read IC 16 The maximum value and the minimum value can be extracted from the average value for each.
- each read circuit 17 is formed in the read IC 16 by a predetermined number, for example, 128 or 256, for each read circuit 17 as described above. For example, instead of subtracting the moving average from each leaked data Dleak read out, the 128 leaked data Dleak output from each read circuit 17 for one read IC 16 in one leak data read process, for example.
- the average value for each read IC 16 can be calculated first.
- the average number of leak data Dleak for each read IC 16 for each leak data read process is eight, which is equal to the number of read ICs 16 in the above example.
- a moving average is calculated for each of the average values of the leak data Dleak for each of the eight read ICs 16, the moving average is subtracted from each average value, and each average value obtained by subtracting the moving average is compared. A maximum value and a minimum value are extracted from them, a difference ⁇ D obtained by subtracting the minimum value from the maximum value is calculated, and it is detected that radiation irradiation has started when the calculated difference ⁇ D exceeds a threshold value ⁇ Dth. It can be configured as follows.
- the electric noise generated for each of the multiple read circuits 17 in the read IC 16 calculates the average value of the leak data Dleak. Since they cancel each other out, there is also an advantage that it is possible to reduce the influence of the electrical noise generated in each readout circuit 17 on the leak data Dleak and its moving average.
- the scintillator 3 may be originally formed smaller than the detection unit P provided on the substrate 4 as schematically shown in FIG. In FIG. 25, it is assumed that the signal line 6 is wired so as to extend in the vertical direction in the figure.
- each radiation detection element 7 provided in the position under the scintillator 3 on the detection part P, ie, the position in which the electromagnetic wave which the irradiated radiation converted by the scintillator 3 can inject is in.
- the leak data Dleak based on the charge q leaked through each TFT 8 as described above rises as shown in FIG.
- the radiation image capturing apparatus 1 is irradiated with radiation at each radiation detection element 7 provided at a position other than immediately below the scintillator 3 on the detection unit P, that is, a position on the detection unit P where the electromagnetic wave from the scintillator 3 does not enter.
- the leak current flowing through each TFT 8 does not increase, the leak data Dleak based on the charge q leaked through each TFT 8 does not rise.
- the power supply circuit 15a of the scanning drive unit 15 and the bias power supply 14 are provided via the lines L1 to Lx of the scanning line 5.
- the generated noise is simultaneously transmitted to each TFT 8 and each radiation detection element 7. Therefore, noise generated in the power supply circuit 15a and the like is transmitted to all the TFTs 8 at the same time and is superimposed on the read leak data Dleak.
- the leakage read out from each radiation detection element 7 at the position on the detection unit P where the electromagnetic wave irradiated from the scintillator 3 can enter (that is, the position immediately below the scintillator 3) is used by the control means 22.
- the difference obtained by subtracting the leak data Dleak read from each radiation detection element 7 provided at a position on the detection part P where the electromagnetic wave irradiated from the scintillator 3 is not incident (that is, a position other than immediately below the scintillator 3) from the data Dleak It is possible to calculate ⁇ D and detect the start of radiation irradiation when the calculated difference ⁇ D exceeds the threshold value ⁇ Dth in the same manner as described above.
- leak data Dleak read for each signal line 6 at this position B that is, for each read circuit 17 provided for each signal line 6, is received from each radiation detection element 7 at a position immediately below the scintillator 3.
- the contribution due to the leaked charge q is not mixed, and from each of these readout circuits 17, leak data Dleak that is not related to the irradiated radiation or the electromagnetic waves irradiated from the scintillator 3, that is, the power supply circuit 15a of the scanning drive means 15
- the leak data Dleak resulting from the noise generated in step S1 is read out.
- the signal lines 6 wired at these positions B are read out by the respective readout circuits 17.
- the leak data Dleak is each of the latter provided at a position on the detection portion P where the electromagnetic wave irradiated from the scintillator 3 is not incident (that is, a position other than immediately below the scintillator 3).
- the leakage data Dleak read from the radiation detection element 7 can be handled.
- each radiation provided at the position on the detection unit P where the electromagnetic wave irradiated from the scintillator 3 is not incident that is, a position other than immediately below the scintillator 3.
- the leak data Dleak read from the detection element 7 for example, one leak of the leak data Dleak read by each read circuit 17 provided in each signal line 6 wired at the position B described above.
- the data Dleak can be selected and used, and the average value of the leak data Dleak can be calculated and used as the latter leak data Dleak.
- the power supply circuit 15a When configured as described above, for example, when the difference ⁇ D is calculated as described above based on the data illustrated in FIG. 21, the power supply circuit 15a superimposed on the leak data Dleak as illustrated in FIG. The noise component derived from is accurately removed from the leak data Dleak. Then, an increase in leak data Dleak due to radiation irradiation can be extracted as an increase in difference ⁇ D.
- the radiographic imaging device 1 when configured as shown in FIG. 25, at least the leak data Dleak is obtained by performing the respective processes as described above and calculating the difference ⁇ D. It is possible to remove noise components derived from the superimposed power supply circuit 15a, and to improve the S / N ratio of the leak data Dleak. Then, by setting the threshold value ⁇ Dth to an appropriate value and detecting the start of radiation irradiation based on the calculated difference ⁇ D, it is possible to accurately detect the start of radiation irradiation. It becomes.
- each leak data Dleak read for each read circuit 17 is overlaid with the offset due to the read characteristics of each read circuit 17, As in [Method 1-1], each time a leak data read process is performed, a predetermined number of past leak data read processes including the leak data read process immediately before the leak data read process are read.
- the moving average of the leak data Dleak read by each readout circuit 17 provided in each signal line 6 wired to the position A and the position B is calculated for each readout circuit 17, This moving average is subtracted from the leak data Dleak read in the leak data read processing, and this subtracted value is applied in the current leak data read processing. It is preferable that the processing such as the leak data Dleak read by the reading circuit 17 is performed.
- a process of subtracting the moving average from the leak data Dleak read by each readout circuit 17 to make the leak data Dleak is always performed, or the dose rate of the irradiated radiation It is determined as appropriate whether or not it is configured to be performed only when the value is very low.
- the capacitance of the capacitor 18b of the amplifier circuit 18 composed of the above-described charge amplifier circuit is variable, and is repeatedly performed before radiographic imaging.
- the capacitor cf of the capacitor 18b of the amplifier circuit 18 may be variable so as to be smaller than the capacity in the image data reading process.
- the amplifying circuit 18 leaks from the radiation detection element 7 and outputs a voltage value corresponding to the charge q accumulated in the capacitor 18b, but it is variable so that the capacitance cf of the capacitor 18b becomes small.
- V q / cf
- the noise component originally superimposed on the charge q leaked from the radiation detection element 7 that is, for example, the noise component derived from the power supply circuit 15a as described above
- the voltage value V output from the amplifier circuit 18 is large.
- the noise component also increases and the S / N ratio is not improved, but at least the noise component generated in the readout circuit 17 including the amplifier circuit 18 does not increase even if the voltage value V increases.
- the capacitance cf of the capacitor 18b is too low, the capacitor 18b is likely to be saturated with each charge q leaked from each radiation detection element 7. However, if the capacitor 18b is saturated, the capacitor 18b in the readout circuit 17 having the capacitor 18b is saturated. Since reading may be adversely affected after the next time, the capacitance cf of the capacitor 18b is adjusted to be lowered to an appropriate value. In addition, when the image data reading process is performed after the radiation imaging apparatus 1 is irradiated with radiation, the capacity cf of the capacitor 18b is returned to a normal predetermined capacity.
- the capacitance of the capacitor 18b of the amplifier circuit 18 can be varied.
- the capacitors C1 to C4 are connected in parallel. Connect to. Then, the switches Sw1 to Sw3 are connected in series to the capacitors C2 to C4, respectively. Note that a switch may be connected to the capacitor C1 in series.
- the capacitance cf of the capacitor 18b is the total value of the capacitance of the capacitor C1 and the capacitances of the capacitors C2 to C4 connected in series to the switches that are turned on among the switches Sw1 to Sw3. .
- the leak data Dleak is derived from the leak current Ioff flowing in the TFT 8 in the off state.
- the off voltage is applied to the gate electrode 8 g of the TFT 8, so the gate electrode 8 g side of the semiconductor layer 82 of the TFT 8. (Lower in FIG. 27) is in a state where the density of electrons is small.
- a leak current Ioff flows through the TFT 8 in the off state when holes flow in a region where the electron density on the gate electrode 8g side of the semiconductor layer 82 is small.
- the leakage current Ioff since the reverse bias voltage is applied to the second electrode 78 (not shown in FIG. 27) of the radiation detection element 7 connected to the source electrode 8s, the leakage current Ioff is It flows from the drain electrode 8d side having a relatively high potential through the region on the gate electrode 8g side of the semiconductor layer 82 to the source electrode 8s side having a relatively low potential.
- the scintillator 3 is provided on the upper side in the drawing.
- the electron-hole pairs are mainly generated on the scintillator 3 side (the upper side in FIG. 27) of the semiconductor layer 82 of the TFT 8.
- the electron density is relatively high on the scintillator 3 side of the semiconductor layer 82, the probability that the generated holes recombine with the electrons increases. Therefore, as described above, when the electromagnetic wave is irradiated from the scintillator 3 by irradiation of the radiation, an electron-hole pair is generated in the semiconductor layer 82 of the TFT 8, and the amount of the leakage current Ioff flowing in the TFT 8 in the off state is reduced. Although it increases, some of the holes that are carriers are recombined with electrons, so that the increase rate of the leakage current Ioff is reduced.
- the scintillator 3 of each TFT 8 (not shown in FIG. 28) It is possible to arrange the wiring 85 on the side and apply a negative voltage to the wiring 85 at the time of leak data reading processing repeatedly performed at least before radiographic image capturing. is there.
- the wiring 85 is formed of a conductive material that transmits electromagnetic waves irradiated from the scintillator 3 such as ITO, and is provided in the same number as each signal line 6 in parallel with each signal line 6, for example. Then, at least in the case of leak data reading processing that is repeatedly performed before radiographic imaging, for example, a negative voltage that is the same as the off-voltage applied to each scanning line 5 from the scanning drive unit 15 is applied.
- a negative voltage that is the same as the off-voltage applied to each scanning line 5 from the scanning drive unit 15 is applied.
- the negative voltage applied to each wiring 85 is not necessarily a negative voltage having the same value as the off voltage. As described above, a region having a low electron density is formed on the scintillator 3 side of the semiconductor layer 82 of the TFT 8. It is set to a voltage that can be accurately formed. Further, it is possible to apply a turn-off voltage to each wiring 85 from the power supply circuit 15a of the scanning drive means 15, and it is also possible to apply a negative voltage from another power supply circuit. Is possible.
- each wiring 85 in order to avoid adversely affecting the reading of the image data d from each radiation detection element 7 at least in the image data reading process performed after radiation irradiation to the radiation image capturing apparatus 1, to each wiring 85.
- the application of the negative voltage is stopped (that is, in a floating state), or a predetermined voltage such as 0 [V] is applied.
- the wiring 85 and the bias line 9 are formed on the upper surface (that is, the surface on the scintillator 3 side not shown) of the first planarizing layer 80a formed by being stacked above the radiation detection element 7 and the TFT 8.
- the form of forming the wiring 85 is not limited to this form, and the electron density is low on the scintillator 3 side of the semiconductor layer 82 of the TFT 8. If the region can be formed, the wiring 85 can be arranged at an appropriate position.
- the leak data reading process has been described as an image data reading process.
- the description is based on the premise that it is performed at the same timing. That is, during the leak data reading process, the time interval from the transmission of the first pulse signal Sp1 to the correlated double sampling circuit 19 from the control means 22 to the transmission of the second pulse signal Sp2 is the image data reading. The case where it is performed at the same time interval as the case of processing has been described.
- the pulse signal is sent from the control means 22 to the correlated double sampling circuit 19 during the leak data reading process. It is possible to improve the S / N ratio of leak data Dleak by controlling the time intervals for transmitting Sp1 and Sp2 to be longer than the time intervals for the image data reading process. .
- the noise component superimposed on the leak data Dleak does not increase with time, and the voltage value from the amplifier circuit 18 held when the first pulse signal Sp1 is transmitted to the correlated double sampling circuit 19. Since the difference between the noise component superimposed on Vin and the noise component superimposed on the voltage value Vfi from the amplification circuit 18 held when the second pulse signal Sp2 is transmitted, the pulse signal Sp1, Even if the time interval of each transmission of Sp2 is increased, it does not increase.
- the leak data Dleak indicates that the charge q leaked from each radiation detection element 7 as the time interval for transmitting the pulse signals Sp1 and Sp2 from the control means 22 to the correlated double sampling circuit 19 becomes longer. Since the amount of storage in the capacitor 18b of the amplifier circuit 18 increases, the voltage value output from the amplifier circuit 18 rises, and the difference between the voltage value Vin and the voltage value Vfi increases more greatly, so the value increases.
- the noise component superimposed on the leak data Dleak can be expressed as a vibration component in which the voltage value that increases with time increases or decreases with time.
- the noise component expressed as the vibration component does not increase the width of the vibration (that is, the vibration width in the vertical direction in FIG. 30) depending on time, and is almost constant regardless of time. Is superimposed on a voltage value that rises with time (that is, a voltage value read out as leak data Dleak).
- the noise component superimposed on the leak data Dleak does not increase even if the time interval between the transmissions of the pulse signals Sp1 and Sp2 is increased.
- each leak data readout is performed.
- the image data reading process is configured to be performed during the leak data reading process shown in FIG. Similarly, the time interval of transmission of the pulse signals Sp1 and Sp2 at the time of each leak data reading process can be lengthened.
- the first leak data read process is performed after applying the ON voltage to the line L1 of the scanning line 5
- the second leak data reading process is performed after the on-voltage is applied to the line L2 of the scanning line 5.
- the numbers above the timing chart of the charge reset switch 18c in FIG. 31 and the like indicate the number of leak data reading processes.
- the start of radiation irradiation was not detected based on the leak data Dleak read out in the third leak data read process, but the leak data Dleak read out in the fourth leak data read process Is detected from the radiation detection elements 7 connected to the line L4 of the scanning line 5 to which the on-voltage is applied in the reset process immediately before the fourth leak data reading process.
- a part of useful charge generated in each radiation detecting element 7 due to radiation irradiation is emitted to the signal line 6 through each TFT 8.
- each image data d read from each radiation detection element 7 connected to the line L4 of the scanning line 5 in the image data readout process performed after radiation irradiation to the radiation image capturing apparatus 1 is not necessarily effective. It may be difficult to say that it is data.
- the ON voltage is set in the reset process immediately before the leak data read process (in the above example, the fourth leak data read process) in which the start of radiation irradiation is detected based on the leak data Dleak. May be configured to invalidate the image data d read from each radiation detection element 7 connected to the scanning line 5 to which is applied (in the above example, the line L4 of the scanning line 5).
- the invalidated image data d along the scanning line 5 is linearly formed on the radiation image p generated based on the read image data d. Therefore, a so-called line defect occurs. Therefore, in such a case, for example, for each radiation detection element 7 connected to the line L4 of the scanning line 5 in which the image data d is invalidated, the invalidated image data d is discarded and the scanning is performed.
- the image data d is calculated by linear interpolation, for example, with each image data d read from each radiation detection element 7 connected to the line L3 and the line L5 of the scanning line 5 adjacent to the line 5. Configured.
- the start of radiation irradiation can be detected based on the leak data Dleak read in the first leak data read process (in the above example, the fourth leak data read process) after the start of irradiation.
- the irradiation of radiation is actually started when the fourth leak data reading process is performed.
- the leak data Dleak read in the fourth leak data read process does not exceed the threshold value Dth described above, and the reset process for each radiation detection element 7 is performed.
- the start of radiation irradiation is detected for the first time when the leak data Dleak read in the reading process exceeds the threshold value Dth.
- the line L5 of the scanning line 5 to which the ON voltage is applied not only in the reset process immediately before the fourth leak data read process as described above but also in the reset process immediately before the fifth leak data read process.
- charges generated in each radiation detection element 7 due to radiation irradiation are emitted to the signal line 6 through each TFT 8. Therefore, not only each radiation detection element 7 connected to the line L4 of the scanning line 5, but also each image data d read from each radiation detection element 7 connected to the line L5 of the scanning line 5 is effective. It is hard to say that the data is invalid and must be invalidated.
- each radiation connected to the lines L3 and L6 of the scanning lines 5 adjacent to the scanning lines 5 in the same manner as described above.
- the image data d of each radiation detection element 7 connected to the lines L4 and L5 of the scanning line 5 is calculated, for example, by linear interpolation with each image data d read from the detection element 7, for example. It is not unthinkable to do.
- the reason that the line defect may appear continuously on the radiation image p is that the reset process of each radiation detection element 7 performed during the leak data reading process, for example, as shown in FIG. This is also because the on-voltage is sequentially applied while shifting the lines L1 to Lx of the scanning line 5 line by line.
- the on-voltage is applied while shifting the lines L1 to Lx of the scanning line 5 line by line.
- the on-voltage is applied during the last reset process. It is possible to perform a reset process for each radiation detection element 7 by applying an on-voltage to the scanning lines 5 other than the scanning line 5 adjacent to the scanning line 5 to which is applied.
- the line of the scanning line 5 that performs the reset process by applying the on-voltage is the line of the scanning line 5 that has been subjected to the reset process by applying the on-voltage immediately before the line.
- the reset processing of each radiation detection element 7 is performed so as not to be adjacent lines.
- the example shown in FIG. 35 is not necessarily preferable because the line defect appears on the radiation image p in an adjacent position. Therefore, in practice, the interval between the line L of the scanning line 5 to which the reset process is performed by applying the on-voltage and the line L of the scanning line 5 to which the on-voltage is applied immediately after that is configured to be wide. It is preferable.
- the scanning drive unit 15 described above is configured by connecting the scanning lines 5 to, for example, 128 terminals of each gate IC 12a (see FIG. 6) constituting the gate driver 15b, first, The on-voltage is applied to the scanning line 5 connected to the first terminal of the first gate IC 12a to reset each radiation detection element 7, and in the next reset process, the first of the second gate IC 12a.
- a reset process is performed by applying an on-voltage to the scanning line 5 connected to the terminal.
- processing 1 and processing 2 can be combined and performed.
- the reset process of each radiation detection element 7 and the image data read process from each radiation detection element 7 at the time of the periodically performed leak data reading process are performed from the scanning drive unit 15 to the scanning line 5.
- the on-voltage is sequentially applied to each of the lines L1 to Lx.
- the on-voltage is simultaneously applied to the plurality of lines L of the scanning line 5 to reset the radiation detection elements 7 and detect each radiation. It is also possible to configure to perform image data read processing from the element 7.
- each gate IC 12a constituting the gate driver 15b of the scanning drive means 15 as described above, as shown in FIG.
- the on-voltage is simultaneously applied to each scanning line 5 connected to the first terminal of the IC 12a to perform reset processing of each radiation detection element 7, etc., and in the next reset processing, the second terminal of each gate IC 12a is connected.
- a reset process or the like is performed by simultaneously applying an on-voltage to the connected scanning lines 5.
- the plurality of lines L of the scanning lines 5 to which the ON voltage is applied simultaneously are not adjacent on the detection unit P in order to prevent the line defects on the radiation image p from appearing continuously as described above.
- a plurality of scanning lines 5 are provided.
- each radiation detection element 7 is reset by sequentially applying an ON voltage while shifting each line L1 to Lx of the scanning line 5 line by line.
- the on-voltage is set so that the lines L1 to Lx of the scanning line 5 to which the on-voltage is applied are not adjacent to each other as shown in FIG. It is also possible to perform a reset process or the like of each radiation detection element 7 by sequentially applying.
- This charge accumulation mode is a mode in which charges generated in each radiation detection element 7 by radiation irradiation are accumulated in each radiation detection element 7.
- the readout operation by the readout circuit 17 is stopped and the charge reset switch 18c of the amplifier circuit 18 is turned on, as in the case of normal radiographic imaging. In this state, it is possible to configure to wait for a predetermined time set in advance.
- the readout circuit 17 is configured to periodically perform the readout operation to repeatedly perform the leakage data readout process and to continue monitoring the readout leakage data Dleak. It is also possible.
- the leak data Dleak read at time t1 (that is, the fourth leak data read process shown in FIG. 38, which is the same as time t1 shown in FIG. 15) is the threshold value.
- the start of radiation irradiation is detected, and after the transition to the charge accumulation mode, while the radiation imaging apparatus 1 is irradiated with radiation, every leak data read process after the radiation irradiation start detection
- the leak data Dleak read out in the above (exactly, the maximum value Dleak_max in each leak data Dleak read out by each read circuit 17 for each leak data read process as described above) is a high value exceeding the threshold Dth. become.
- the leak data Dleak read out in the leak reading process (see ⁇ in FIG. 38) that is first performed after the radiation irradiation to the radiation image capturing apparatus 1 is completed is that each TFT 8 Since the amount of leak current flowing inside returns to the original dark amount, the value drops to a value equal to or less than the threshold value Dth at time t2 when the ⁇ -th leak data read process is performed.
- the radiation image capturing apparatus 1 is configured such that the leak data reading process is periodically repeated even after the start of radiation irradiation is detected and the mode is shifted to the charge accumulation mode, and the read leak data Dleak is monitored. It is possible to detect the end of irradiation of the radiation.
- the control means 22 is configured to detect the end of radiation irradiation by determining that the radiation irradiation has ended when the read leak data Dleak becomes equal to or less than the threshold value Dth. .
- a preview image is created before full-scale image processing is performed on the image data d by an external computer or the like to generate a diagnostic radiographic image.
- Display, and a radiographer or the like looks at the preview image and confirms whether or not the subject is photographed on the radiation image and whether or not the subject is photographed at an appropriate position on the radiation image. Often done.
- the readout operation by the readout circuit 17 is stopped and the system waits for a predetermined time as in the case of normal radiographic imaging. For example, there is an advantage that it is not necessary to perform the leak data reading process in the charge accumulation mode, and the power consumption of the radiation image capturing apparatus 1 can be suppressed. Further, since the off voltage is applied to all the lines L1 to Lx of the scanning line 5 and the differential of each readout circuit 17 is stopped, there is an advantage that the control configuration is simplified.
- FIG. 39 shows a case in which the leak data reading process is continued to read out the leak data Dleak even after the end of radiation irradiation is detected at time t2, but this is only due to the radiation exposure.
- This is an experimental example to show how the data Dleak changes. Actually, when the end of radiation irradiation is detected at time t2, the leak data reading process is stopped and the image data reading process is started immediately. Is done.
- the scanning driving means 15 and the reading circuit 17 are operated, and the read image data d are sequentially stored in the storage means 40 (see FIG. 7 and the like). Is done.
- the scanning line 5 in which the on-voltage is finally applied and the reset process of each radiation detection element 7 is performed in the leak data reading process before radiographic image capturing.
- the image data d is sequentially read from the line L5 next to the line L4 and the reading process of the last line Lx of the scanning line 5 is completed, the reading process is performed up to the line L4 after returning to the first line L1 of the scanning line 5.
- the image data d can be read sequentially from the first line L1 of the scanning line 5.
- the leak data Dleak read in the next leak data reading process shifted to the charge accumulation mode returns to a value equal to or lower than the original threshold value Dth.
- the image data reading process starts immediately.
- the image data reading process is automatically started after a predetermined time has elapsed from time t1.
- each radiation detection element 7 reads only the charges that carry no information about the subject (that is, unnecessary charges such as dark charges) as image data d. Therefore, useless processing is performed.
- the leak data Dleak is monitored by periodically repeating the leak data reading process, it is detected that the read leak data Dleak has exceeded the threshold value Dth and radiation irradiation has started.
- the transition to the charge accumulation mode is canceled and the state before radiographic image capturing is set. It can be configured to return.
- the leaked data Dleak that has been read out in the leaked data reading process immediately after the leaked data reading process in which it has been detected that the read out leakage data Dleak has exceeded the threshold value Dth and radiation irradiation has started is detected.
- it becomes Dth or less it is configured to cancel the transition to the charge accumulation mode and return to the state before radiographic image capturing. And it becomes possible to acquire the effect similar to the above by comprising in this way.
- each radiation detection element 7 and the image data readout process from each radiation detection element 7 are performed during the leak data readout process, and the radiation detection process is performed within each radiation detection element 7 during that time. There is a risk that useful charges generated may be lost.
- the leak data Dleak detects the start of radiation irradiation exceeding the threshold value Dth and immediately falls to a value equal to or less than the threshold value Dth in the next leak data read processing, Rather than canceling the transition to the charge accumulation mode, the leak data reading process is continuously performed, and the process in which the read leak data Dleak becomes a value equal to or smaller than the threshold value Dth is set to an appropriate number of times of two or more. It is possible to configure so as to cancel the transition to the charge accumulation mode and return to the state before radiographic image capture when it is repeated a predetermined number of times.
- the leak data reading process is performed even after the start of the radiation irradiation is detected, and the leak data reading is performed after the leak data reading process is detected to detect the start of the radiation irradiation.
- the leak data Dleak read out by the process within a time period that can be clearly determined not to be radiation irradiation (that is, a predetermined number of times including the leak data read process immediately after the leak data read process in which the start of radiation irradiation is detected)
- the leakage circuit 17 leaks from the radiation detecting element 7 via the TFT 8 serving as a switch unit using the readout circuit 17 provided in the normal radiographic image capturing apparatus.
- the charge q to be read is read out as leak data Dleak, and it is detected that radiation irradiation has started based on the increase in the leak data Dleak.
- At least radiation irradiation can be performed in the radiation imaging apparatus 1 itself by utilizing the characteristics of the TFT 8 in which a leakage current flowing inside due to radiation irradiation increases without constructing an interface with the radiation generation apparatus. It is possible to accurately detect the start.
- the offset correction value O is also referred to as a dark read value, and is the charge generated and accumulated in each radiation detection element 7 by irradiation of radiation while the TFT 8 is in the OFF state after shifting to the charge accumulation mode. Apart from this, dark charges or the like generated by thermal excitation or the like due to the heat (temperature) of the radiation detection element 7 itself corresponds to the offset of the image data d accumulated in each radiation detection element 7. As described above, the offset correction value O is read out in a state of being included in the image data d read out in the image data read-out process after radiographic imaging.
- the radiographic imaging apparatus 1 is not irradiated with radiation, and the radiographic imaging apparatus 1 is left in a state where each TFT 8 is turned off, and then the same as the image data reading process.
- the offset correction value O is acquired for each radiation detection element 7 by reading out the dark charge and the like accumulated from each radiation detection element 7, and each image data d is obtained by a radiation image generation process performed by an external computer or the like. Then, the offset correction value O is subtracted from each of them to calculate the true image data d * derived only from the charges generated by the radiation irradiation, and a radiation image is generated based on the true image data d * .
- the true image data d * obtained by subtracting the offset correction value O from each image data d is not a normal value, and is generated based on it.
- the radiographic image becomes abnormal or the image quality deteriorates.
- the process of reading the offset correction value O from each radiation detection element 7 is performed in the same manner as the image data reading process shown in FIG. 10 or FIG. This is called value read processing.
- the offset correction value O corresponds to the charge (dark charge) generated and accumulated in the radiation detection element 7 while each TFT 8 is in the OFF state as described above, but more accurately.
- the reset process of each radiation detection element 7 (or the image data read process from each radiation detection element 7 in the leak data readout process before radiographic imaging). .))
- the on-voltage applied to a line Ln of the scanning line 5 is switched to the off-voltage, and then the on-voltage applied to the line Ln of the scanning line 5 is switched to the off-voltage in the image data reading process after radiographic image capturing. This corresponds to the electric charge generated and accumulated in the radiation detection element 7.
- the on-voltage applied to the line Ln of the scanning line 5 is switched to the off-voltage, and then the on-voltage applied to the line Ln of the scanning line 5 is turned off in the image data reading process after radiographic imaging.
- the time interval until switching to the voltage is referred to as the TFT 8 off time.
- the off time of the TFT 8 is a time interval represented by T1 to T4 in the lines L1 to L4 of the scanning line 5 in FIG.
- each processing is actually performed by applying an on voltage and an off voltage to each of the lines L1 to Lx of the scanning line 5, respectively.
- the offset correction value O does not necessarily increase linearly (that is, proportionally) with the off time of the TFT 8. This is considered to be because the generation rate of dark charges generated in each radiation detection element 7 when the radiation imaging apparatus 1 is left without irradiation with radiation as described above is non-linear with respect to time changes. .
- the offset correction value O is the same value if the TFT 8 has the same off time.
- the process for obtaining the offset correction value O can be configured as in the following configuration examples.
- the offset correction value O does not increase in a form proportional to the off time of the TFT 8, but becomes the same value if the off time of the TFT 8 is the same. Therefore, for example, the off time of the TFT 8 for each line L of the scanning line 5 can be configured to be the same off time in the image data reading process and the offset correction value reading process as follows.
- the voltage applied to each line L1 to Lx of the scanning line 5 from the scanning driving means 15 at the same timing as those processes is set between the on voltage and the off voltage.
- the readout circuit 17 sequentially performs a readout operation to perform a leak data readout process, a reset process for each radiation detection element 7, a transition to a charge accumulation mode (however, no radiation is irradiated), and an offset correction value readout process. I do.
- the same processing sequence as the processing sequence for reading the image data d (that is, the leakage data reading processing, the transition to the charge accumulation mode, and the image data reading processing) is repeated after the image data reading processing, Read the offset correction value O.
- the offset correction value O is read out in the same processing sequence as that when reading out the image data d, the lines L1 to L4 (in reality, the scanning line 5) of the scanning lines as described above. Even if the off times T1 to T4 of the TFTs 8 for the respective lines L1 to Lx are different from each other), the image data d is obtained when viewed for each of the lines L1 to L4 of the scanning line.
- the off time of the TFT 8 at the time of reading and the off time of the TFT 8 at the time of reading the offset correction value O thereafter are the same time interval.
- the offset correction value O is read by the image data reading process.
- the offset included in the image data d thus obtained and the offset correction value O read out by the offset correction value reading process are the same value.
- the offset included in the image data d read from the radiation detection element 7 in the image data reading process and the radiation detection element in the offset correction value reading process thereafter 7 is the same value as the offset correction value O read from 7.
- the offset correction value O read out in the offset correction value read process is subtracted from each image data d read out in the image data read process, thereby irradiating with radiation.
- True image data d * derived only from the generated charges can be accurately calculated for each radiation detection element 7.
- a radiographic image can be accurately generated based on the true image data d * .
- the control means 22 of the radiographic image capturing apparatus 1 causes the storage means 40 (see FIG. 7 and the like) to sequentially store the image data d read from each radiation detection element 7 in the image data read processing. After that, when another image is not taken continuously, the same processing sequence is automatically repeated to perform the offset correction value reading process, and the read offset correction value O is sequentially stored in the storage unit 40.
- each image data d and each offset correction value O are sequentially read out from the storage means 40 at an appropriate timing, and these data are subjected to image processing via the antenna device 39 (see FIGS. 1 and 7, etc.). It is configured to transmit to an external computer or the like.
- the leak data reading process (“4” in FIG. 41, that is, “4” in FIG.
- the start of radiation irradiation is detected based on the leak data Dleak read in the second leak read process), and the image data d is read from the first line L1 of the scanning line 5 in the image data read process. Shown about the case.
- the data is read in the leak data reading process immediately after the on-voltage is applied to the line L2 in the middle of the scanning line 5 and the reset process of each radiation detection element 8 is performed.
- the reading process of the image data d is performed from the next line L3 of the scanning line 5. can do. This is a case where processing is performed in the same manner as the case shown in FIG.
- each radiation detection element 7 after radiographic imaging is taken.
- the voltage applied to each of the lines L1 to Lx of the scanning line 5 from the scanning drive means 15 is switched between the on-voltage and the off-voltage at the same timing as each processing up to the image data reading processing in FIG.
- the image data read process reads the image data d from the first line L1 of the scanning line 5. It is also possible to configure.
- the off times T1 to T4 of the TFT 8 are relatively different values for the lines L1 to L4 of the scanning line 5, and in particular, the TFTs 8 between the lines L2 and L3 of the adjacent scanning line 5 on the detection unit P. The off times T2 and T3 are greatly different.
- image data readout processing from each radiation detection element 7 after radiographic imaging is performed.
- the voltage applied to each of the lines L1 to Lx of the scanning line 5 from the scanning driving unit 15 at the same timing as each of the above processes is switched between the on-voltage and the off-voltage, and the reading circuit 17 sequentially performs the reading operation, Leak data reading processing, reset processing of each radiation detection element 7, transition to the charge accumulation mode (however, no radiation is irradiated), and offset correction value reading processing are performed.
- each process after the image data reading process is performed as shown in FIGS.
- the off times T1 to T4 of the TFTs 8 for the respective scanning lines L1 to L4 are different from each other,
- the off time of the TFT 8 when reading the image data d and the off time of the TFT 8 when reading the offset correction value O thereafter are the same time interval.
- the offset included in the image data d read by the image data reading process and the offset correction value read by the offset correction value reading process Even when O is the same value and viewed for each radiation detection element 7, the offset amount included in the image data d read from the radiation detection element 7 in the image data reading process and the subsequent offset correction value reading are performed.
- the offset correction value O read from the radiation detection element 7 in the process becomes the same value.
- the offset correction value O read out in the offset correction value read process is subtracted from each image data d read out in the image data read process, thereby irradiating with radiation.
- True image data d * derived only from the generated charges can be accurately calculated for each radiation detection element 7.
- a radiographic image can be accurately generated based on the true image data d * .
- the time interval from the reset process of each radiation detection element 7 before the radiographic image capture to the image data read process that is, the off time T1 to T4 of the TFT 8.
- the offset correction value reading process so that the time interval (off time) from the image data reading process to the offset correction value reading process is the same.
- the reset process of each radiation detection element 7 is performed, and thereafter, from the reset process of each radiation detection element 7 to the offset correction value reading process. It is also possible to perform the offset correction value reading process so that the time interval becomes the same as the time interval from the reset process of each radiation detection element 7 before the radiographic image capturing to the image data read process. is there.
- the TFT 8 OFF times T1 to T4 in the image data reading process and the TFT 8 OFF times T1 to T4 in the offset correction value reading process have the same time interval.
- the offset included in the image data d read by the image data reading process and the offset correction value O read by the offset correction value reading process have the same value.
- the offset correction value O read out in the offset correction value read process is subtracted from each image data d read out in the image data read process.
- True image data d * derived only from the generated charges can be accurately calculated for each radiation detection element 7.
- a radiographic image can be accurately generated based on the true image data d * .
- the scanning drive unit 15 scans the scanning line 5 at the same timing as the image data reading process in a state where no radiation is irradiated. It is also possible to perform an offset correction value reading process by sequentially applying an ON voltage to each of the lines L1 to L4. As in the case shown in FIG. 48, it is possible to perform a reset process for each radiation detection element 7 once after the image data read process is completed, and then perform an offset correction value read process. is there.
- the time interval from the image data reading process to the offset correction value reading process (that is, the off time of the TFT 8) is the same time interval Ta for all the lines L1 to L4 of the scanning line 5.
- the TFT 8 OFF time T1 to T4 for each line L1 to L4 of the scanning line 5 from the reset process at the time of the leak data read process before radiographic image capture to the image data read process, and the image data read process Since the time interval Ta until the offset correction value reading process is not the same as the time interval Ta, when viewed for each of the scanning lines L1 to L4, the offset amount included in the image data d read out in the image data reading process. And the offset correction value O read in the offset correction value reading process are not the same value.
- the true image data d * can be accurately calculated even if the offset correction value O read by the offset correction value reading process is subtracted from each image data d read by the image data reading process. Can not. That is, the value is different from the original true image data d * .
- the table and the relational expression are held in advance in an external computer or the like that performs image processing based on the image data d and the offset correction value O transmitted from the radiation image capturing apparatus 1.
- the experiment is performed in a state where the temperature of each functional unit, the substrate 4 and the like is stabilized by energizing each functional unit including the readout circuit 17 of the radiographic imaging device 1 for a long time, for example. .
- an offset amount (hereinafter referred to as an offset amount O1) included in the image data d read from each radiation detection element 7 connected to the line L1 of the scanning line 5 in the image data reading process is calculated.
- the computer or the like first reads or calculates the offset correction value O1 * (see FIG. 50) as a reference corresponding to the off time T1 with reference to the above table or according to the above relational expression. .
- the set reference offset correction value O1 * cannot be used as the offset O1 as it is.
- an offset correction value Oa * (see FIG. 50) serving as a reference in the off time Ta is obtained, and the offset correction value O1 * serving as the reference and the offset O1 are calculated.
- the offset O1 is calculated from the read offset correction value O according to the following equation (2) derived from the following equation (1).
- O1 O ⁇ O1 * / Oa * (2)
- the processing for acquiring the offset correction value O including the offset correction value reading processing is performed only once after the image data reading processing has been described.
- the offset correction value O obtained in each process is averaged for each radiation detection element 7 and the average value is offset correction for each radiation detection element 7. It can also be configured to be used as the value O.
- the image data The readout circuit 17 and the scanning drive means 15 are driven at the same ON / OFF operation timing as in the case of the readout process (see FIG. 10) to perform the leak data readout process, or as shown in FIG. 29, the control means
- the leak data reading process is performed by transmitting the time intervals at which the pulse signals Sp1 and Sp2 are transmitted from 22 to the correlated double sampling circuit 19 so as to be longer than those in the case of the image data reading process.
- the reading process is performed at the same timing as the normal image data reading process.
- the on-voltage is sequentially applied from the line Ln + 1 to read out the image data d from each radiation detection element 7 (see FIGS. 37, 38, 43, etc.) or the first line of the scanning line 5
- the on-voltage is sequentially applied from L1 to read out the image data d from each radiation detection element 7 (see FIG. 45 and the like).
- the TFTs 8 from when the TFTs 8 are turned off to the off state by the reset process performed in the leak data read process before radiographic image capturing until the TFTs 8 are turned from the on state to the off state by the image data read process.
- the off times T1 to T4 are different from each other in the scanning lines L1 to L4.
- the off times T1 to T4 of the TFT 8 until the image data reading process are different from each other in the scanning lines L1 to L4.
- the off time of the TFT 8 until the image data reading process and the off time of the TFT 8 until the offset correction value reading process thereafter have the same time interval.
- the offset correction value O having the same value as the offset due to dark charges or the like included in the image data d read by the image data reading process is read by the offset correction value reading process. .
- the offset correction value reading process is performed by sequentially applying the ON voltage to L1 to L4, and the offset correction value O read by the offset correction value reading process in the subsequent calculation process is used to perform the image data reading process.
- the offset O1 included in the read image data d is calculated.
- the image data d is read from each radiation detection element 7 and then offset as described above.
- the correction value O is read out, not only the offset due to the dark charge generated by the thermal excitation by the heat (temperature) of the radiation detecting element 7 itself as described above but also a so-called lag other than that. It is known that the offset is read out.
- the offset due to dark charges or the like is relatively easily removed by repeating the reset process of each radiation detection element 7, for example, but the offset due to the lag repeats the reset process of each radiation detection element 7. It is known that there is a feature that even if it goes, it does not disappear easily.
- the offset due to the dark charge or the like decreases to a value close to 0 relatively quickly when the reset processing of each radiation detection element 7 is repeated.
- the offset due to the lag cannot be easily removed even if the reset process of each radiation detection element 7 is repeated, and the offset after the radiation imaging apparatus 1 is left in a state where no radiation is irradiated even if the reset process is repeated.
- an offset correction value O having a larger value than that in the case of only the offset due to dark charge or the like is read.
- the reason why the offset due to the lag cannot be easily removed is that some of the electrons and holes generated in the radiation detection element 7 due to irradiation of strong radiation are This is considered to be because a state in which a transition to a kind of metastable energy state (metastable state) is lost and mobility in the radiation detection element 7 is lost is maintained for a relatively long time.
- the electrons and holes in this metastable energy state transition to a conduction band at an energy level considered to be higher than this metastable energy with a certain probability by thermal energy, and mobility is restored. For this reason, even if the reset processing of each radiation detection element 7 is repeated after radiographic imaging, for example, the offset due to the lag cannot be easily removed, and the offset correction value readout processing after radiographic imaging is reduced to the offset due to dark charges or the like. It is considered that the offset due to the lag is superimposed and read as the offset correction value O.
- Olag the offset due to the lag is represented as Olag.
- the offset Olag due to this lag occurs not only when strong radiation is irradiated, but also when a normal dose of radiation including weak radiation is irradiated. However, when radiation that is not so strong is irradiated, the ratio of the offset Olag due to the lag included in the offset correction value O is often small enough to be ignored.
- the radiation detection element 7 such as a photodiode used in the radiographic image capturing apparatus 1 that the offset amount Olag due to the lag increases to a level that cannot be ignored when the radiation is irradiated. Therefore, how much dose of radiation is used in the method of the third embodiment described below is appropriately determined for each radiographic imaging apparatus 1. It is also possible to always perform the image data reading process and the offset correction value reading process by the method of the third embodiment.
- an on-voltage is sequentially applied to each line Ln of the scanning line 5 as shown in FIG. 51 in the image data reading process after the radiation image capturing apparatus 1 is irradiated with radiation.
- an offset Olag due to a lag occurs immediately after the voltage applied to each line Ln of the scanning line 5 is switched from the on voltage to the off voltage.
- the offset Olag due to the lag generated per unit time is expressed as ⁇ Olag
- the offset ⁇ Olag due to the lag per unit time is the voltage applied to each line Ln of the scanning line 5 as shown in FIG. Is largest at the time when the on-voltage is switched to the off-voltage, and then gradually decreases. Therefore, the offset amount Olag due to the lag, which can be expressed as an integral value per unit time of the offset amount ⁇ Olag per unit time, increases with time as shown in FIG.
- the data for each radiation detection element 7 finally obtained should have the same value.
- the abnormality of the radiation detection element 7 and the offset for each readout circuit 17 are not considered.
- the true image data d * derived from the charges generated in each radiation detection element 7 due to radiation irradiation have the same value.
- the off time T1 to T4 of the TFT 8 is different for each of the lines L1 to L4 of the scan line 5, and therefore, as shown in FIG.
- the values of offset Olag (1) to Olag (4) due to the lag for each of the five lines L1 to L4 are different from each other.
- the off time T2 of the TFT 8 is the shortest in the line L2 of the scanning line 5 among the lines L1 to L4 of the scanning line 5, and the adjacent scanning is performed.
- the off time T3 of the TFT 8 is the longest in the line L3 of the line 5. Therefore, as shown in FIG. 52A, in the offset amount Olag (1) to Olag ⁇ ⁇ (4) due to lag, the offset amount Olag (2) due to lag is the smallest value, and the offset amount Olag (3) due to lag is The largest value.
- the entire radiographic image should have the same brightness (luminance) because the radiographic image capturing apparatus 1 is uniformly irradiated with strong radiation. Nevertheless, the brightness of the radiographic image is slightly different in each region of the image, and further, there is a step difference in brightness at positions corresponding to the lines L2 and L3 of the scanning line 5 on the radiographic image. Can do.
- each line L1 to L4 (scanning line 5) of the scanning line 5 in the image data reading process after radiographic imaging is performed.
- the timing at which the turn-on voltage is sequentially applied to all the lines L1 to L4 of the scanning line 5 is the same time interval Tc. It is possible to make it variable so that
- the processing sequence for reading the image data d and the processing until the offset correction value O is read after the image data reading processing are performed.
- the sequence is the same processing sequence, or as in [Configuration Example 2] for each line L1 to L4 of the scanning line 5, the TFT 8 off time T1 to T4 and the offset correction value reading processing until the image data reading processing
- the offset correction value reading process is performed so that the OFF times T1 to T4 of the TFTs 8 are the same, the OFF times T1 to T4 of the TFTs 8 before and after the image data reading process are all the same time interval Tc.
- the offset amount Olag (1) ⁇ All Olag (4) values are the same. Since the true image data d * derived from the charges generated in each radiation detection element 7 due to radiation irradiation have the same value, the value d ⁇ O calculated according to the above equation (5) is the scanning line 5. All the lines L1 to L4 have the same value.
- the entire radiographic image has the same brightness when the radiographic image capturing apparatus 1 is imaged by irradiating strong radiation uniformly. . In this way, it is possible to prevent a step in the brightness on the radiation image as described above.
- the image data read process is configured to perform the read process of the image data d from the first line L1 of the scanning line 5.
- the off time T1 to T4 of the TFT 8 cannot be set to the same time interval Tc for each of the lines L1 to L4 of the scanning line 5.
- the off-times T1 to T4 of the TFT 8 are set to the same time interval Tc for each of the lines L1 to L4 of the scanning line 5 as described above, for example, as shown in FIG.
- the start of radiation irradiation is detected based on the leak data Dleak read in the leak data read process immediately after the on-voltage is applied to the line L2 in the middle of the line 5 and the reset process of each radiation detection element 8 is performed.
- the image data reading process is configured to read the image data d from the next line L3 of the scanning line 5.
- the time interval Ta from the image data reading process to the offset correction value reading process is set to the same time interval as the time interval Tc.
- the off times T1 to T4 of the TFTs 8 before and after the image data reading process are all the same time interval Tc. Therefore, based on the above table and the relational expression, the offset caused by the dark charge according to the above expression (2). It is not necessary to calculate the minute Od (O1 in the formula).
- the offset Olag due to this lag becomes a problem when strong radiation is irradiated, and often does not become a problem when weak radiation or a normal dose of radiation is irradiated.
- the timing of applying the on voltage and the off voltage to each of the lines L1 to Lx of the scanning line 5 in the image data reading process after the radiation image capturing is normally set. It is also possible to configure so that the mode can be switched between the mode (in the case of the second embodiment) that is performed at the timing of (2) and the mode (in the case of the third embodiment) that is performed by varying the timing. is there.
- It may be used in the field of radiographic imaging (especially in the medical field).
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Abstract
Description
互いに交差するように配設された複数の走査線および複数の信号線と、前記複数の走査線および複数の信号線により区画された各領域に二次元状に配列された複数の放射線検出素子とを備える検出部と、
前記放射線検出素子から画像データを読み出す画像データ読み出し処理の際に、オン電圧を印加する前記各走査線を順次切り替えながら印加する走査駆動手段と、
前記各走査線に接続され、前記走査線を介してオン電圧が印加されると前記放射線検出素子に蓄積された電荷を前記信号線に放出させ、前記走査線を介してオフ電圧が印加されると前記放射線検出素子内に電荷を蓄積させるスイッチ手段と、
前記画像データ読み出し処理の際には、前記放射線検出素子から前記信号線に放出された前記電荷を前記画像データに変換して読み出す読み出し回路と、
少なくとも前記走査駆動手段および前記読み出し回路を制御して前記放射線検出素子からの前記データの読み出し処理を行わせる制御手段と、
を備え、
前記制御手段は、放射線画像撮影前に、前記走査駆動手段から全ての前記走査線にオフ電圧を印加して前記各スイッチ手段をオフ状態とした状態で、前記読み出し回路に周期的に読み出し動作を行わせて、前記スイッチ手段を介して前記放射線検出素子からリークした前記電荷をリークデータに変換するリークデータ読み出し処理を繰り返し行わせ、読み出した前記リークデータが閾値を越えた時点で放射線の照射が開始されたことを検出することを特徴とする。
図1は、本実施形態に係る放射線画像撮影装置の外観斜視図であり、図2は、図1のX-X線に沿う断面図である。本実施形態に係る放射線画像撮影装置1は、図1や図2に示すように、筐体2内にシンチレータ3や基板4等が収納されて構成されている。
次に、本発明におけるリークデータ読み出し処理と、リークデータ読み出し処理により読み出されたリークデータDleakに基づく放射線画像撮影装置1に対する放射線の照射開始の検出について説明する。
次に、放射線画像撮影装置1に対する放射線の照射が開始されたか否かの判断の基準となる上記の閾値Dthの決め方について説明する。
前述したように、本発明に係る放射線画像撮影前のリークデータ読み出し処理や放射線の照射開始の検出は、図13等に示したように、走査駆動手段15から走査線5の全てのラインL1~Lxにオフ電圧を印加して各TFT8をオフ状態とした状態で行われる。しかし、この状態を継続すると、放射線検出素子7自体の熱(温度)による熱励起等によって発生したいわゆる暗電荷が、各放射線検出素子7内に蓄積され、暗電荷の蓄積量が増加していくことがよく知られている。
ここで、リークデータDleakのS/N比の改善について説明する。走査駆動手段15から走査線5の全てのラインL1~Lxにオフ電圧を印加した状態で各TFT8を介して各放射線検出素子7からリークした電荷q(図14参照)に起因するリークデータDleakは、図16に示したように、オフ状態のTFT8内を流れるリーク電流Ioffがオン状態のTFT8内を流れる電流Ionに比べて桁違いに小さいことからも分かるように、通常、小さい値になる。
例えば図21に示すデータは、単位時間当たりの線量すなわち線量率が約0.5[μR/ms]の非常に低い放射線を放射線画像撮影装置1に照射した場合に各リークデータ読み出し処理で読み出されたリークデータDleakの例であり、時刻t1に放射線の照射が開始され、時刻t2に照射を終了した場合の例である。
放射線画像撮影装置1に放射線を照射する際、放射線画像撮影装置1の放射線入射面R(図1、図2参照)側から見た場合、図22に示すように、放射線画像撮影装置1のシンチレータ3や検出部Pの全域ではなく、シンチレータ3や検出部Pの一部に照射野Fが絞られて放射線が照射される場合がある。
一方、放射線画像撮影装置1によっては、図25に模式的に示すように、もともとシンチレータ3が基板4上に設けられた検出部Pより小さく形成される場合がある。なお、図25においても、信号線6は図中の上下方向に延在するように配線されているものとする。
また、リークデータDleakのS/N比を改善する手法として、前述したチャージアンプ回路で構成された増幅回路18のコンデンサ18bの容量を可変できるように構成しておき、放射線画像撮影前に繰り返し行われるリークデータ読み出し処理の際には、増幅回路18のコンデンサ18bの容量cfが、画像データ読み出し処理の際の容量よりも小さくなるように可変するように構成することも可能である。
また、リークデータDleakは、前述したように、オフ状態のTFT8内を流れるリーク電流Ioffに由来する。その際、図5に示したTFT8の断面構造を模式的に表した図27に示すように、TFT8のゲート電極8gにオフ電圧が印加されているため、TFT8の半導体層82のゲート電極8g側(図27中では下側)は電子の密度が小さい状態になっている。
また、図12に示したリークデータ読み出し処理と、図10に示した画像データ読み出し処理とを比較して分かるように、本実施形態では、これまで、リークデータ読み出し処理を、画像データ読み出し処理と同じタイミングで行うことを前提として説明した。すなわち、リークデータ読み出し処理の際に、制御手段22から相関二重サンプリング回路19に1回目のパルス信号Sp1を送信してから2回目のパルス信号Sp2を送信するまでの時間間隔が、画像データ読み出し処理の場合と同じ時間間隔で行われる場合について説明した。
図19や図20に示したように、放射線画像撮影前に周期的に繰り返し行われるリークデータ読み出し処理や、読み出されたリークデータDleakに基づく放射線の照射開始の検出を行う際に、各放射線検出素子7内で発生する暗電荷等の余分な電荷を除去するために、リークデータ読み出し処理と次のリークデータ読み出し処理との間に、各放射線検出素子7のリセット処理や各放射線検出素子7からの画像データ読み出し処理を行う場合、以下のような問題が生じる虞れがある。
放射線画像p上で線欠陥が連続して現れないようにするための処理として、例えば、前述したリークデータのS/N比を改善するための手法4(図29参照)のように、例えば、リークデータ読み出し処理の際に、制御手段22から相関二重サンプリング回路19にパルス信号Sp1、Sp2をそれぞれ送信する時間間隔が画像データ読み出し処理の際の時間間隔よりも長い時間間隔になるように構成することが可能である。
また、放射線画像p上で線欠陥が連続して現れる可能性を生じさせている理由は、リークデータ読み出し処理の間に行う各放射線検出素子7のリセット処理において、例えば図33に示したように、走査線5の各ラインL1~Lxを1ラインずつシフトさせながらオン電圧を順次印加しているためであるとも考えられる。
また、上記の各例では、周期的に行われるリークデータ読み出し処理の際の各放射線検出素子7のリセット処理や各放射線検出素子7からの画像データ読み出し処理を、走査駆動手段15から走査線5の各ラインL1~Lxに順次オン電圧を印加して行う場合について説明したが、走査線5の複数のラインLに同時にオン電圧を印加して、各放射線検出素子7のリセット処理や各放射線検出素子7からの画像データ読み出し処理を行うように構成することも可能である。
次に、上記のようにして制御手段22が周期的に繰り返し行われるリークデータ読み出し処理で読み出されたリークデータDleakに基づいて、すなわちリークデータDleakが閾値Dthを越えたと判断して、放射線の照射が開始されたことを検出した後の各処理について説明する。なお、以下では、放射線画像撮影前の処理として、図31に示したような処理を行う場合について説明するが、上記の各手法や各処理を行うことが可能であることは言うまでもない。
制御手段22は、上記のようにして放射線の照射が開始されたことを検出すると、走査駆動手段15から走査線5の全てのラインL1~Lxにオフ電圧を印加して、各TFT8をオフ状態とした状態を維持して電荷蓄積モードに移行する。この電荷蓄積モードとは、放射線の照射により各放射線検出素子7内で発生する電荷を各放射線検出素子7内に蓄積させるモードのことである。
図37に示した場合には所定時間が経過した時点で、また、図38に示した場合には放射線の照射の終了を検出した時点で、制御手段22は、図37や図38に示したように、続いて、走査駆動手段15から走査線5の各ラインL1~Lxにオン電圧を順次印加させ、読み出し回路17に順次読み出し動作を行わせて、各放射線検出素子7からそれぞれ画像データdを読み出す画像データ読み出し処理を行わせる。
ここで、放射線の照射開始の誤検出を防止する処理について説明する。例えば、上記のように、ある時刻t1にリークデータDleakの値が大きくなって閾値Dthを越えたとしても、瞬間的に大きなノイズが乗る等して何らかの原因でたまたまリークデータDleakが大きくなったような場合もあり得る。
以上の第1の実施形態では、上記のように、放射線画像撮影前のリークデータ読み出し処理(その間に行われる各放射線検出素子7のリセット処理や各放射線検出素子7からの画像データ読み出し処理を含む。)や、放射線画像撮影時の電荷蓄積モード、放射線画像撮影後の画像データ読み出し処理までの各処理について説明した。
オフセット補正値Oは、上記のように、各TFT8がオフ状態とされていた間に放射線検出素子7内で発生して蓄積された電荷(暗電荷)に相当するものであるが、より正確に言えば、本実施形態や第1の実施形態では、放射線画像撮影前のリークデータ読み出し処理の際の各放射線検出素子7のリセット処理(或いは各放射線検出素子7からの画像データ読み出し処理。以下同じ。)で走査線5のあるラインLnに印加したオン電圧をオフ電圧に切り替えてから、放射線画像撮影後の画像データ読み出し処理で走査線5の当該ラインLnに印加したオン電圧をオフ電圧に切り替えるまでの間に、放射線検出素子7内で発生して蓄積された電荷に相当するものである。
一方、第1の実施形態で示したように、放射線画像撮影前のリークデータ読み出し処理の間に各放射線検出素子7のリセット処理や各放射線検出素子7からの画像データ読み出し処理を行う場合(図37、図38参照)や、リークデータ読み出し処理の際に相関二重サンプリング回路19へのパルス信号Sp1、Sp2の各送信の時間間隔を長くする場合(図29参照)等には、TFT8のオフ時間は、図41等にT1、T2、T3、T4で示すように、走査線5の各ラインL1~Lxごとにそれぞれ異なる時間間隔になる。
本発明者らが行った実験では、オフセット補正値Oは、TFT8のオフ時間には必ずしも線形に(すなわち比例して)増加するものではないことが分かっている。これは、上記のように放射線を照射しない状態で放射線画像撮影装置1を放置した場合に各放射線検出素子7内で発生する暗電荷の発生速度が時間変化に対して非線形であるためと考えられる。なお、オフセット補正値Oは、TFT8のオフ時間が同じであれば、同じ値になる。
[構成例1]
上記の前提3で述べたように、オフセット補正値Oは、TFT8のオフ時間に比例する形では増加しないが、TFT8のオフ時間が同じであれば同じ値になる。そこで、例えば、以下のようにして、走査線5の各ラインLごとのTFT8のオフ時間を、画像データ読み出し処理とオフセット補正値読み出し処理とで同じオフ時間になるように構成することができる。
また、電荷リセット用スイッチ18cやパルス信号Spの図示を省略するが、例えば、図47に概略的に示すように、画像データ読み出し処理が終了した後、放射線が照射されない状態で、走査線5の各ラインL1~L4ごとに、画像データ読み出し処理で走査線5に印加したオン電圧をオフ電圧に切り替えてからオフセット補正値読み出し処理で走査線5に印加したオン電圧をオフ電圧に切り替えるまでのTFT8のオフ時間が、図41に示したTFT8のオフ時間T1~T4とそれぞれ同じになるようなタイミングでオフセット補正値読み出し処理を行うように構成することが可能である。
一方、図49に示すように、画像データ読み出し処理を終了した後、すぐに、或いは所定時間経過後に、放射線が照射されない状態で、画像データ読み出し処理と同じタイミングで走査駆動手段15から走査線5の各ラインL1~L4にオン電圧を順次印加させてオフセット補正値読み出し処理を行うように構成することも可能である。なお、図48に示した場合と同様に、画像データ読み出し処理が終了した後で一旦各放射線検出素子7のリセット処理を行い、その後、オフセット補正値読み出し処理を行うように構成することも可能である。
O1*:O1=Oa*:O …(1)
が成り立つことを利用して、下記(1)式から導出される下記(2)式に従って、読み出されたオフセット補正値Oから上記のオフセット分O1を算出する。
O1=O×O1*/Oa* …(2)
上記の第2の実施形態では、各TFT8をオフ状態としている間に各放射線検出素子7内で発生し蓄積される、放射線検出素子7自体の熱(温度)による熱励起等によって発生した暗電荷等に起因するオフセット補正値Oを取得する場合の種々の構成例について説明した。
d=d*+Od …(3)
の関係が成り立つ。
O=Od+Olag …(4)
の関係が成り立つ。
d-O=(d*+Od)-(Od+Olag)
∴d-O=d*-Olag …(5)
となる。
3 シンチレータ
5、L1~Lx 走査線
6 信号線
7 放射線検出素子
8 TFT(スイッチ手段)
15 走査駆動手段
16 読み出しIC
17 読み出し回路
18 増幅回路
18a オペアンプ
18b、C1~C4 コンデンサ
19 相関二重サンプリング回路
22 制御手段
85 配線
cf 容量
d 画像データ
Dleak リークデータ
Dth 閾値
O オフセット補正値
P 検出部
q 電荷
r 領域
T1~T4 TFTのオフ時間(時間間隔)
Tc 同じ時間間隔
V 電圧値
Vfi-Vin 差分
Vin、Vfi 電圧値
ΔD 差分
ΔDth 閾値
Claims (13)
- 互いに交差するように配設された複数の走査線および複数の信号線と、前記複数の走査線および複数の信号線により区画された各領域に二次元状に配列された複数の放射線検出素子とを備える検出部と、
前記放射線検出素子から画像データを読み出す画像データ読み出し処理の際に、オン電圧を印加する前記各走査線を順次切り替えながら印加する走査駆動手段と、
前記各走査線に接続され、前記走査線を介してオン電圧が印加されると前記放射線検出素子に蓄積された電荷を前記信号線に放出させ、前記走査線を介してオフ電圧が印加されると前記放射線検出素子内に電荷を蓄積させるスイッチ手段と、
前記画像データ読み出し処理の際には、前記放射線検出素子から前記信号線に放出された前記電荷を前記画像データに変換して読み出す読み出し回路と、
少なくとも前記走査駆動手段および前記読み出し回路を制御して前記放射線検出素子からの前記データの読み出し処理を行わせる制御手段と、
を備え、
前記制御手段は、放射線画像撮影前に、前記走査駆動手段から全ての前記走査線にオフ電圧を印加して前記各スイッチ手段をオフ状態とした状態で、前記読み出し回路に周期的に読み出し動作を行わせて、前記スイッチ手段を介して前記放射線検出素子からリークした前記電荷をリークデータに変換するリークデータ読み出し処理を繰り返し行わせ、読み出した前記リークデータが閾値を越えた時点で放射線の照射が開始されたことを検出することを特徴とする放射線画像撮影装置。 - 前記制御手段は、放射線画像撮影前に繰り返し行わせる前記リークデータ読み出し処理の際に、前記リークデータ読み出し処理と次の前記リークデータ読み出し処理との間に、前記走査駆動手段から前記各走査線にオン電圧を印加させて前記各放射線検出素子から余分な電荷を除去するリセット処理を行わせることを特徴とする請求の範囲第1項に記載の放射線画像撮影装置。
- 前記制御手段は、前記各放射線検出素子から余分な電荷を除去するために、放射線画像撮影前に繰り返し行わせる前記リークデータ読み出し処理の際に、前記リークデータ読み出し処理と次の前記リークデータ読み出し処理との間に、前記走査駆動手段から前記各走査線にオン電圧を印加させて前記画像データ読み出し処理を行わせることを特徴とする請求の範囲第1項に記載の放射線画像撮影装置。
- 前記走査駆動手段は、前記各走査線に順次オン電圧を印加する際、直前のリセット処理または直前の画像データ読み出し処理の際にオン電圧を印加した前記走査線に前記検出部上で隣接する走査線以外の走査線にオン電圧を印加するようにして、前記リセット処理または前記画像データ読み出し処理を行うことを特徴とする請求の範囲第2項または第3項に記載の放射線画像撮影装置。
- 前記走査駆動手段は、前記各走査線に順次オン電圧を印加する際、前記検出部上で隣接しない複数の前記走査線に同時にオン電圧を印加して前記リセット処理または前記画像データ読み出し処理を行うことを特徴とする請求の範囲第2項から第4項のいずれか一項に記載の放射線画像撮影装置。
- 前記制御手段は、周期的に繰り返し行われる前記リークデータ読み出し処理で読み出された前記各リークデータの履歴に基づいて、前記閾値を更新させながら設定することを特徴とする請求の範囲第1項から第5項のいずれか一項に記載の放射線画像撮影装置。
- 前記制御手段は、同一の前記リークデータ読み出し処理で読み出された前記リークデータの中から最大値と最小値とを抽出し、前記最大値から前記最小値を差し引いた差分を算出し、算出した前記差分が閾値を越えた時点で放射線の照射が開始されたことを検出することを特徴とする請求の範囲第1項から第6項のいずれか一項に記載の放射線画像撮影装置。
- 所定個数の前記読み出し回路が形成された複数の読み出しICを備え、
前記制御手段は、前記同一のリークデータ読み出し処理で読み出された前記リークデータの代わりに、同一の前記リークデータ読み出し処理で読み出された前記各リークデータの前記各読み出しICごとの平均値をそれぞれ算出し、前記各リークデータの前記各読み出しICごとの平均値の中から最大値と最小値とを抽出することを特徴とする請求の範囲第7項に記載の放射線画像撮影装置。 - 前記制御手段は、今回の前記リークデータ読み出し処理の直前の前記リークデータ読み出し処理を含む所定回数分の過去の前記各リークデータ読み出し処理で読み出された前記各リークデータの移動平均をそれぞれ算出し、前記各リークデータから前記移動平均をそれぞれ減算した値の中から最大値と最小値とを抽出し、前記最大値から前記最小値を差し引いた差分を算出し、算出した前記差分が閾値を越えた時点で放射線の照射が開始されたことを検出することを特徴とする請求の範囲第1項から第6項のいずれか一項に記載の放射線画像撮影装置。
- 所定個数の前記読み出し回路が形成された複数の読み出しICを備え、
前記制御手段は、
前記同一のリークデータ読み出し処理で読み出された前記リークデータの代わりに、同一の前記リークデータ読み出し処理で読み出された前記各リークデータの前記各読み出しICごとの平均値をそれぞれ算出し、
今回の前記リークデータ読み出し処理の直前の前記リークデータ読み出し処理を含む所定回数分の過去の前記各リークデータ読み出し処理で読み出された前記各リークデータの前記平均値の移動平均をそれぞれ算出し、
前記各リークデータの前記各読み出しICごとの平均値から前記平均値の移動平均をそれぞれ減算した値の中から最大値と最小値とを抽出することを特徴とする請求の範囲第9項に記載の放射線画像撮影装置。 - 前記読み出し回路は、
前記放射線検出素子から放出された前記電荷または前記スイッチ手段を介して前記放射線検出素子からリークした前記電荷を電圧値に変換して出力する増幅回路と、
前記増幅回路に前記電荷が流入する前に前記増幅回路が出力する前記電圧値を保持し、前記増幅回路に前記電荷が流入した後に前記増幅回路が出力する前記電圧値を保持して、前者の前記電圧値と後者の前記電圧値との差分を前記画像データまたは前記リークデータとして出力する相関二重サンプリング回路と、
を備え、
前記相関二重サンプリング回路は、前記リークデータ読み出し処理の際の前記2回の保持動作の間の時間間隔が、前記画像データ読み出し処理の際の前記2回の保持動作の間の時間間隔よりも長い時間間隔になるように制御されることを特徴とする請求の範囲第1項から第10項のいずれか一項に記載の放射線画像撮影装置。 - 前記制御手段は、放射線の照射が開始されたことを検出すると、前記走査駆動手段から全ての前記走査線にオフ電圧を印加して前記各スイッチ手段をオフ状態とした状態を維持して電荷蓄積モードに移行し、前記読み出し回路に周期的に読み出し動作を行わせて前記リークデータ読み出し処理を繰り返し行わせ、読み出した前記リークデータが前記閾値以下になった時点で放射線の照射が終了したことを検出すると、前記走査駆動手段から前記各走査線にオン電圧を順次印加させ、前記読み出し回路に順次読み出し動作を行わせて、前記各放射線検出素子からそれぞれ画像データを読み出す画像データ読み出し処理を行わせることを特徴とする請求の範囲第1項から第11項のいずれか一項に記載の放射線画像撮影装置。
- 前記制御手段は、前記画像データ読み出し処理を終了した後、放射線が照射されない状態で、前記放射線画像撮影前のリークデータ読み出し処理、前記電荷蓄積モードへの移行、および前記画像データ読み出し処理と同じタイミングで前記走査駆動手段から前記各走査線に印加する電圧をオン電圧とオフ電圧との間で切り替え、前記読み出し回路に順次読み出し動作を行わせて、リークデータ読み出し処理、前記電荷蓄積モードへの移行、および前記各放射線検出素子からそれぞれオフセット補正値を読み出すオフセット補正値読み出し処理を行わせることを特徴とする請求の範囲第12項に記載の放射線画像撮影装置。
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US20130032696A1 (en) | 2013-02-07 |
JPWO2011135917A1 (ja) | 2013-07-18 |
EP2564779A1 (en) | 2013-03-06 |
CN102933146A (zh) | 2013-02-13 |
EP2564779A4 (en) | 2015-05-20 |
JP5737286B2 (ja) | 2015-06-17 |
CN102933146B (zh) | 2015-02-25 |
EP2564779B1 (en) | 2017-08-30 |
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