WO2017119251A1 - 放射線検出器 - Google Patents
放射線検出器 Download PDFInfo
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- WO2017119251A1 WO2017119251A1 PCT/JP2016/087259 JP2016087259W WO2017119251A1 WO 2017119251 A1 WO2017119251 A1 WO 2017119251A1 JP 2016087259 W JP2016087259 W JP 2016087259W WO 2017119251 A1 WO2017119251 A1 WO 2017119251A1
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- thin film
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- G01T1/16—Measuring radiation intensity
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- G01T1/20—Measuring radiation intensity with scintillation detectors
- G01T1/2018—Scintillation-photodiode combinations
- G01T1/20184—Detector read-out circuitry, e.g. for clearing of traps, compensating for traps or compensating for direct hits
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- G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
- G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
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- H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
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- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
- H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
- H01L27/144—Devices controlled by radiation
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- H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
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- H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
- H01L27/144—Devices controlled by radiation
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- H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
- H01L27/144—Devices controlled by radiation
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- H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
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Definitions
- Embodiments of the present invention relate to a radiation detector.
- the X-ray detector includes, for example, an array substrate having a plurality of photoelectric conversion units (also referred to as pixels) and a scintillator that is provided on the plurality of photoelectric conversion units and converts X-rays into fluorescence. ing.
- the photoelectric conversion unit is provided with a photoelectric conversion element that converts fluorescence from the scintillator into a signal charge, a thin film transistor that performs switching of signal charge accumulation and emission, a storage capacitor that accumulates signal charge, and the like.
- the X-ray detector reads the signal charge as follows. First, X-ray incidence is recognized from an externally input signal. Next, after the elapse of a predetermined time (the time necessary for accumulating the signal charge), the thin film transistor of the photoelectric conversion unit that performs reading is turned on, and the accumulated signal charge is converted into a voltage by an integrating amplifier. Convert to and read.
- the signal from the external device for example, X-ray irradiation from the X-ray source or the like has been performed
- the difference between the detected current integral value and the current integral value detected immediately before is obtained. If the current integration value detected immediately before is slightly lower than the threshold value, the difference between the current integration values flowing in the data line becomes small, and X-rays may not be detected. Also, when converting to voltage, if there is disturbance noise such as low frequency noise, the voltage value of each integrating amplifier is offset. Therefore, the influence of disturbance noise such as low-frequency noise is increased, and it may be difficult to accurately detect the start of X-ray incidence.
- the problem to be solved by the present invention is to provide a radiation detector capable of accurately detecting the start of radiation incidence.
- the radiation detector includes a substrate, a plurality of control lines provided on the substrate and extending in a first direction, and provided on the substrate and extending in a second direction intersecting the first direction.
- a photoelectric conversion unit including the thin film transistor and the photoelectric conversion element, a control circuit that is electrically connected to the plurality of control lines and switches an on state and an off state of the plurality of thin film transistors, and the plurality of data lines
- a signal detection circuit connected to the signal detection circuit; a reference potential unit electrically connected to the signal detection circuit; a determination unit electrically connected to the signal detection circuit; It is provided.
- the signal detection circuit detects a first current integration value via the data line and a second current integration value from the reference potential portion when the thin film transistor is in an OFF state.
- the determination unit determines the start of radiation incidence based on the difference between the detected first current integral value and the second current integral value.
- FIG. 1 is a schematic perspective view for illustrating an X-ray detector 1.
- FIG. 2 is a block diagram of the X-ray detector 1.
- FIG. 2 is a circuit diagram of the X-ray detector 1.
- FIG. It is a block diagram of the X-ray detector 101 which concerns on a comparative example. It is a graph for demonstrating the change of the difference of the current integral value in the detection method at the time of the X-ray incidence start which concerns on a comparative example.
- (A), (b) is a timing chart for illustrating the process in the X-ray detector 1.
- FIG. 6 is a flowchart for illustrating detection at the start of X-ray incidence. It is a block diagram for illustrating reference potential part 6a1 concerning other embodiments.
- FIG. 6 is a graph for illustrating the effect of the incident radiation detection unit 6. It is a graph for demonstrating the relationship between the sampling width
- the radiation detector according to the present embodiment can be applied to various types of radiation such as ⁇ rays in addition to X-rays.
- ⁇ rays in addition to X-rays.
- X-rays as a representative example of radiation will be described as an example. Therefore, by replacing “X-ray” in the following embodiments with “other radiation”, the present invention can be applied to other radiation.
- the X-ray detector 1 illustrated below is an X-ray plane sensor that detects an X-ray image that is a radiation image.
- X-ray flat sensors are roughly classified into direct conversion methods and indirect conversion methods.
- the direct conversion method is a method in which photoconductive charge (signal charge) generated inside the photoconductive film by incident X-rays is directly guided to a storage capacitor for charge storage by a high electric field.
- the indirect conversion method is a method in which X-rays are converted into fluorescence (visible light) by a scintillator, the fluorescence is converted into signal charges by a photoelectric conversion element such as a photodiode, and the signal charges are led to a storage capacitor.
- an indirect conversion type X-ray detector 1 is illustrated as an example, but the present invention can also be applied to a direct conversion type X-ray detector. That is, the X-ray detector only needs to have a detection unit that detects X-rays directly or in cooperation with the scintillator. Moreover, although the X-ray detector 1 can be used for general medical use etc., for example, there is no limitation in a use.
- FIG. 1 is a schematic perspective view for illustrating the X-ray detector 1.
- the bias line 2c3 and the like are omitted.
- FIG. 2 is a block diagram of the X-ray detector 1.
- FIG. 3 is a circuit diagram of the X-ray detector 1.
- the X-ray detector 1 includes an array substrate 2, a signal processing unit 3, an image processing unit 4, a scintillator 5, and an incident radiation detection unit 6.
- the array substrate 2 converts the fluorescence (visible light) converted from the X-rays by the scintillator 5 into an electrical signal.
- the array substrate 2 includes a substrate 2a, a photoelectric conversion unit 2b, a control line (or gate line) 2c1, a data line (or signal line) 2c2, and a bias line 2c3. Note that the numbers of photoelectric conversion units 2b, control lines 2c1, data lines 2c2, and bias lines 2c3 are not limited to those illustrated.
- the substrate 2a has a plate shape and is made of a translucent material such as non-alkali glass.
- a plurality of photoelectric conversion units 2b are provided on one surface of the substrate 2a.
- the photoelectric conversion unit 2b has a rectangular shape and is provided in a region defined by the control line 2c1 and the data line 2c2.
- the plurality of photoelectric conversion units 2b are arranged in a matrix.
- One photoelectric conversion unit 2b corresponds to one pixel.
- Each of the plurality of photoelectric conversion units 2b is provided with a photoelectric conversion element 2b1 and a thin film transistor (TFT) 2b2 which is a switching element. Further, as shown in FIG. 3, a storage capacitor 2b3 for storing the signal charge converted in the photoelectric conversion element 2b1 can be provided.
- the storage capacitor 2b3 has, for example, a rectangular flat plate shape and can be provided under each thin film transistor 2b2. However, depending on the capacitance of the photoelectric conversion element 2b1, the photoelectric conversion element 2b1 can also serve as the storage capacitor 2b3.
- the photoelectric conversion element 2b1 can be, for example, a photodiode.
- the thin film transistor 2b2 performs switching between accumulation and emission of electric charges generated when fluorescence enters the photoelectric conversion element 2b1.
- the thin film transistor 2b2 may include a semiconductor material such as amorphous silicon (a-Si) or polysilicon (P-Si).
- the thin film transistor 2b2 includes a gate electrode 2b2a, a source electrode 2b2b, and a drain electrode 2b2c. Gate electrode 2b2a of thin film transistor 2b2 is electrically connected to corresponding control line 2c1.
- the source electrode 2b2b of the thin film transistor 2b2 is electrically connected to the corresponding data line 2c2.
- the drain electrode 2b2c of the thin film transistor 2b2 is electrically connected to the corresponding photoelectric conversion element 2b1 and the storage capacitor 2b3.
- the anode side of the photoelectric conversion element 2b1 and the storage capacitor 2b3 are electrically connected to the corresponding bias line 2c3 (see FIG. 3).
- a plurality of control lines 2c1 are provided in parallel with each other at a predetermined interval.
- the control line 2c1 extends in the row direction (corresponding to an example of the first direction).
- One control line 2c1 is electrically connected to one of a plurality of wiring pads 2d1 provided near the periphery of the substrate 2a.
- One wiring pad 2d1 is electrically connected to one of a plurality of wirings provided on the flexible printed board 2e1.
- the other ends of the plurality of wirings provided on the flexible printed board 2e1 are electrically connected to the control circuit 31 provided on the signal processing unit 3, respectively.
- a plurality of data lines 2c2 are provided in parallel with each other at a predetermined interval.
- the data line 2c2 extends in the column direction (corresponding to an example of the second direction) orthogonal to the row direction.
- One data line 2c2 is electrically connected to one of a plurality of wiring pads 2d2 provided near the periphery of the substrate 2a.
- One wiring pad 2d2 is electrically connected to one of a plurality of wirings provided on the flexible printed board 2e2.
- the other ends of the plurality of wirings provided on the flexible printed circuit board 2e2 are electrically connected to the signal detection circuit 32 provided on the signal processing unit 3, respectively.
- the bias line 2c3 is provided in parallel with the data line 2c2 between the data line 2c2 and the data line 2c2.
- a bias power source (not shown) is electrically connected to the bias line 2c3.
- a bias power source (not shown) can be provided in the signal processing unit 3 or the like, for example.
- the bias line 2c3 is not necessarily required, and may be provided as necessary.
- the anode side of the photoelectric conversion element 2b1 and the storage capacitor 2b3 are electrically connected to the ground instead of the bias line 2c3.
- control line 2c1, the data line 2c2, and the bias line 2c3 can be formed using, for example, a low resistance metal such as aluminum or chromium.
- the protective layer 2f covers the photoelectric conversion unit 2b, the control line 2c1, the data line 2c2, and the bias line 2c3.
- the protective layer 2f includes, for example, at least one of an oxide insulating material, a nitride insulating material, an oxynitride insulating material, and a resin material.
- the oxide insulating material include silicon oxide and aluminum oxide.
- the nitride insulating material include silicon nitride and aluminum nitride.
- the oxynitride insulating material is, for example, silicon oxynitride.
- the resin material is, for example, an acrylic resin.
- the signal processing unit 3 is provided on the side of the array substrate 2 opposite to the scintillator 5 side.
- the signal processing unit 3 is provided with a control circuit 31 and a signal detection circuit 32.
- the control circuit 31 switches between the on state and the off state of the thin film transistor 2b2.
- the control circuit 31 includes a plurality of gate drivers 31a and a row selection circuit 31b.
- a control signal S1 is input to the row selection circuit 31b from the image processing unit 4 or the like.
- the row selection circuit 31b inputs the control signal S1 to the corresponding gate driver 31a according to the scanning direction of the X-ray image.
- the gate driver 31a inputs the control signal S1 to the corresponding control line 2c1.
- control circuit 31 sequentially inputs the control signal S1 for each control line 2c1 via the flexible printed board 2e1 and the control line 2c1.
- the thin film transistor 2b2 is turned on by the control signal S1 input to the control line 2c1, and the signal charge (image data signal S2) from the photoelectric conversion element 2b1 can be received.
- the signal detection circuit 32 detects the current integrated value via the data line 2c2, and also detects the current integrated value from the reference potential unit 6a.
- the signal detection circuit 32 reads the signal charge (image data signal S2) from the photoelectric conversion element 2b1 in accordance with the sampling signal from the image processing unit 4 when the thin film transistor 2b2 is in the on state.
- the image processing unit 4 is electrically connected to the signal detection circuit 32 via the wiring 4a and the determination unit 6b. Note that the image processing unit 4 may be integrated with the signal processing unit 3.
- the X-ray image is configured as follows. First, the thin film transistor 2b2 is sequentially turned on by the control circuit 31. When the thin film transistor 2b2 is turned on, a certain amount of charge is accumulated in the photoelectric conversion element 2b1 via the bias line 2c3. Next, the thin film transistor 2b2 is turned off. When X-rays are irradiated, the scintillator 5 converts the X-rays into fluorescence. When fluorescence enters the photoelectric conversion element 2b1, charges (electrons and holes) are generated by the photoelectric effect, and the accumulated charges are reduced by combining the generated charges with the accumulated charges (heterogeneous charges). . Next, the control circuit 31 sequentially turns on the thin film transistors 2b2. The signal detection circuit 32 reads the reduced charge (image data signal S2) accumulated in each photoelectric conversion element 2b1 through the data line 2c2 according to the sampling signal.
- image data signal S2 image data signal S2
- the image processing unit 4 receives the read image data signal S2, sequentially amplifies the received image data signal S2, and converts the amplified image data signal S2 (analog signal) into a digital signal. Then, the image processing unit 4 configures an X-ray image based on the image data signal S2 converted into a digital signal. The configured X-ray image data is output from the image processing unit 4 to an external device.
- the scintillator 5 is provided on the plurality of photoelectric conversion elements 2b1, and converts incident X-rays into visible light, that is, fluorescence.
- the scintillator 5 is provided so as to cover an area (effective pixel area) where a plurality of photoelectric conversion units 2b are provided on the substrate 2a.
- the scintillator 5 can be formed using, for example, cesium iodide (CsI): thallium (Tl) or sodium iodide (NaI): thallium (Tl). In this case, if the scintillator 5 is formed using a vacuum vapor deposition method or the like, the scintillator 5 composed of an aggregate of a plurality of columnar crystals is formed.
- the thickness dimension of the scintillator 5 can be set to about 600 ⁇ m, for example.
- the scintillator 5 can also be formed using, for example, gadolinium oxysulfide (Gd 2 O 2 S).
- the scintillator 5 can be formed as follows. First, particles made of gadolinium oxysulfide are mixed with a binder material. Next, the mixed material is applied so as to cover the effective pixel region. Next, the applied material is baked. Next, a groove is formed in the fired material using a blade dicing method or the like. At this time, a matrix-like groove portion can be formed so that the quadrangular columnar scintillator 5 is provided for each of the plurality of photoelectric conversion portions 2b.
- the groove portion can be filled with air (air) or an inert gas such as nitrogen gas for preventing oxidation. Moreover, you may make it a groove part be in a vacuum state.
- a reflection layer (not shown) can be provided so as to cover the surface side (X-ray incident surface side) of the scintillator 5 in order to improve the use efficiency of fluorescence and improve sensitivity characteristics.
- a moistureproof body (not shown) that covers the scintillator 5 and the reflective layer (not shown) can be provided.
- a general X-ray detector reads signal charges as follows. First, it recognizes that X-rays have entered from a signal from an external device such as an X-ray source. Next, after the elapse of a predetermined time (the time necessary for accumulating signal charges), the thin film transistor 2b2 of the photoelectric conversion unit 2b that performs reading is turned on to read the accumulated signal charges. In other words, a general X-ray detector does not detect that X-rays are actually incident on the X-ray detector. Therefore, it is necessary to provide a predetermined time between the time when the signal from the external device is input and the time when the reading operation is started.
- an external circuit that synchronizes with a signal from an external device (for example, a signal notifying that X-ray irradiation from an X-ray source or the like has been performed) is required. If an external circuit is provided, it is easily affected by noise and the like, and if the circuit cannot be synchronized with X-ray irradiation, there is a possibility that an X-ray image cannot be acquired.
- the thin film transistor 2b2 which is a semiconductor element is irradiated with X-rays
- a current flows between the drain electrode 2b2c and the source electrode 2b2b by the photoelectric effect. That is, when the thin film transistor 2b2 is irradiated with X-rays, the resistance value decreases, and the thin film transistor 2b2 is apparently turned on. Therefore, if this is used, it is possible to directly detect the start of X-ray incidence.
- FIG. 4 is a block diagram of the X-ray detector 101 according to the comparative example.
- the X-ray detector 101 is provided with an array substrate 2 and a signal processing unit 3. Although not shown, an image processing unit 4 and a scintillator 5 are also provided. However, the X-ray detector 101 is not provided with the incident radiation detection unit 6.
- the X-ray detector 101 detects the start of X-ray incidence as follows. First, each thin film transistor 2b2 is turned off.
- the signal processing unit 3 or the like detects the current integrated value of each data line 2c2.
- the current integration value is sequentially detected for each of the plurality of photoelectric conversion units 2b electrically connected to the data line 2c2. Such detection of the current integration value is repeatedly performed.
- the difference between the detected current integrated value and the current integrated value detected immediately before is obtained by a comparison circuit, etc., the time when the difference in the current integrated value changes is detected, and the difference in the current integrated value changes.
- This time is determined as the X-ray incidence start time. In this way, it is possible to directly detect the start of X-ray incidence.
- disturbance noise such as low-frequency noise during the period in which the current integration value from the photoelectric conversion unit 2b is detected (in the period in which the signal charge is read)
- the current integration value in which the disturbance noise is detected Overlap.
- the influence of disturbance noise appears on a row pixel basis on an X-ray image, for example. Such influence of disturbance noise is called lateral noise.
- the difference between the detected current integrated value and the current integrated value detected immediately before is obtained.
- an offset is further superimposed on the detected current integrated value.
- an erroneous determination occurs in the determination at the start of X-ray incidence.
- the difference between the current integration values obtained to increase the signal is integrated, the influence of lateral noise increases, and the possibility of erroneous determination further increases.
- FIG. 5 is a graph for illustrating the change in the difference between the current integral values in the detection method at the start of X-ray incidence according to the comparative example.
- X1 in FIG. 5 is the pulse width of the incident X-ray.
- N1 is noise.
- S1 is an effective electrical signal that can be used for determination at the start of X-ray incidence.
- the difference between the current integration values increases. Therefore, when the change in the difference between the current integral values is detected, the X-ray incidence start time can be detected.
- the influence of disturbance noise increases.
- the difference between the current integration values in the same photoelectric conversion unit 2b is obtained, the difference between the obtained current integration values becomes small. For this reason, the value of the effective electrical signal S1 is likely to be small, so that erroneous determination is more likely to occur in the determination at the start of X-ray incidence.
- the X-ray detector 1 is provided with an incident radiation detection unit 6.
- the incident radiation detection unit 6 includes a reference potential unit 6a and a determination unit 6b.
- the reference potential unit 6a can be electrically connected to a power source such as a constant voltage power source or a constant current power source.
- the reference potential portion 6a can be electrically connected to a float potential without being electrically connected to a power source or the like.
- the determination unit 6b is electrically connected to the reference potential unit 6a via the signal detection circuit 32.
- the reference potential unit 6a and the determination unit 6b can be provided in a region where X-rays do not enter.
- the reference potential unit 6a and the determination unit 6b can be provided, for example, in a region where the signal processing unit 3 or the image processing unit 4 is provided.
- the reference potential unit 6 a and the determination unit 6 b can be integrated with the signal processing unit 3 or the image processing unit 4.
- FIGS. 6A and 6B are timing charts for illustrating processing steps in the X-ray detector 1.
- FIG. 6A is a timing chart for illustrating detection at the start of X-ray incidence.
- FIG. 6B is a timing chart for illustrating a processing step after the start of X-ray incidence.
- FIG. 7 is a flowchart for illustrating detection at the start of X-ray incidence.
- the control circuit 31 when detecting the start of X-ray incidence, first, the control circuit 31 does not input the control signal S1 (voltage) to all the control lines 2c1. To do. That is, all the thin film transistors 2b2 are turned off. Subsequently, sampling signals are sequentially input from the image processing unit 4 to the signal processing unit 3 to start sampling. As described above, when X-rays are irradiated onto the photoelectric conversion unit 2b, a current flows between the drain electrode 2b2c and the source electrode 2b2b due to the photoelectric effect. The detection of the current integration value from each photoelectric conversion unit 2b is terminated within each sampling width. Further, the integrated current value from the reference potential portion 6a is detected within each sampling width (step ST1 in FIG. 7).
- the determination unit 6b obtains a difference between the current integration value from each photoelectric conversion unit 2b and the current integration value from the reference potential unit 6a (step ST2 in FIG. 7).
- the determination unit 6b determines whether or not the obtained difference in current integral value satisfies a predetermined determination criterion (step ST3 in FIG. 7). When the determination criterion is satisfied, the determination unit 6b determines that X-rays have entered. When the determination criterion is not satisfied, the determination unit 6b determines that X-rays are not incident.
- step ST4 in FIG. 7 processing for constructing an X-ray image illustrated in FIG. 6B is performed (step ST4 in FIG. 7). For example, as shown in FIG. 6B, sampling signals are sequentially input from the image processing unit 4 to the signal processing unit 3, and sampling is started. Next, the control circuit 31 inputs the control signal S1 to the control line 2c1 within the respective sampling widths after a lapse of a certain period. That is, the control circuit 31 turns on the thin film transistor 2b2 that performs sampling after a certain period.
- the “certain period” can be a time determined in advance by experiments or simulations.
- the “predetermined period” can be fixedly set or can be set each time before the X-ray irradiation. Further, the “certain period” may be a time when the detected value exceeds the first threshold and falls below the second threshold.
- the input control signal S1 is terminated within the sampling width.
- the signal charge (image data signal S2) from the photoelectric conversion element 2b1 can be received.
- the image data signal S2 read by the signal detection circuit 32 passes through the determination unit 6b and is input to the image transmission unit 4.
- the image transmission unit 4 sequentially amplifies the input image data signal S2 and converts it into a digital signal.
- the image transmission part 4 comprises an X-ray image based on the image data signal S2 converted into the digital signal.
- the configured X-ray image data is output from the image transmission unit 4 to an external device.
- the determination unit 6b determines that X-rays are not incident, it detects at least one of the number of times (the number of determinations) that the process up to the determination (step ST1 to step ST3) is repeated and the elapsed time (Step ST5 in FIG. 7). Next, it is determined whether or not at least one of the detected number of times and the elapsed time exceeds a specified value (step ST6 in FIG. 7). If the detected number of determinations does not exceed the specified value, the process returns to step ST1 and the above-described process is performed again. That is, the control circuit 31 maintains the plurality of thin film transistors 2b2 in the off state.
- the signal detection circuit 32 detects again the current integration value from each photoelectric conversion unit 2b and the current integration value from the reference potential unit 6a.
- the determination unit 6b determines again the X-ray incidence start time based on the difference between the current integration value from each photoelectric conversion unit 2b and the current integration value from the reference potential unit 6a. If the detected number of determinations exceeds a specified value, the data related to the determination (data regarding the number of determinations, elapsed time, detected current integrated value, etc.) is initialized (erased), and the process returns to step ST1 and described above. Repeat the process.
- FIG. 8 is a block diagram for illustrating a reference potential unit 6a1 according to another embodiment.
- the reference potential portion 6a1 is provided with a thin film transistor 2b2 and a storage capacitor 2b3. That is, the reference potential unit 6a1 has a configuration in which the photoelectric conversion element 2b1 is removed from the photoelectric conversion unit 2b.
- the reference potential portion 6a1 may include only the thin film transistor 2b2.
- the reference potential portion 6a1 may be one in which the drain electrode 2b2c and the bias line 2c3 are not electrically connected and an insulator is formed instead of the photoelectric conversion element 2b1.
- the reference potential portion 6a1 is provided in a region defined by the control line 2c1 and the data line 2c2 in the peripheral region of the array substrate 2.
- the plurality of reference potential portions 6a1 are provided side by side in the direction in which the control lines 2c1 are arranged.
- the electrical connection between the thin film transistor 2b2 and the storage capacitor 2b3 can be the same as in the photoelectric conversion unit 2b.
- the thin film transistor 2b2 when the thin film transistor 2b2 is irradiated with X-rays, a current flows between the drain electrode 2b2c and the source electrode 2b2b due to the photoelectric effect. In this case, if the photoelectric conversion element 2b1 is not provided, the current flowing between the drain electrode 2b2c and the source electrode 2b2b is substantially constant.
- the reference potential portion 6a1 utilizes this phenomenon.
- the reference potential unit 6a1 Since the only difference in configuration between the reference potential unit 6a1 and the photoelectric conversion unit 2b is the presence or absence of the photoelectric conversion element 2b1, the reference potential unit 6a1 can be formed in the step of forming the photoelectric conversion unit 2b. Therefore, it is possible to reduce manufacturing costs and improve productivity.
- the reference potential portion 6a1 can be provided on the array substrate 2. Therefore, it is possible to save space and to downsize the X-ray detector 1.
- a plurality of photoelectric conversion units 2b provided in an arbitrary column can be used as a reference potential unit. That is, the reference potential unit can be a plurality of photoelectric conversion units 2b arranged in a row in the direction in which the plurality of control lines 2c1 are arranged among the plurality of photoelectric conversion units 2b arranged in a matrix.
- the photoelectric conversion unit 2b for detecting the X-ray image is different from the photoelectric conversion unit 2b serving as the reference potential unit, the detection method at the start of X-ray incidence according to the comparative example described above. As described above, the detection time of the current integral value does not shift.
- the photoelectric conversion unit 2b for detecting the X-ray image and the photoelectric conversion unit 2b serving as the reference potential unit have the same configuration, thereby further reducing the manufacturing cost and improving the productivity. be able to.
- FIG. 9 is a block diagram for illustrating a reference potential unit 6a2 according to another embodiment.
- the reference potential unit 6a2 includes a plurality of photoelectric conversion units 2b serving as the above-described reference potential units and a shielding member 6a2a that covers them.
- the shielding member 6a2a is formed of a material having a high X-ray absorption rate.
- the material having a high X-ray absorption rate can be, for example, a heavy metal such as lead, copper, or iron.
- the shielding member 6a2a made of a material having a high X-ray absorption rate can be provided on the X-ray incident side of the scintillator 5.
- the shielding member 6a2a can be formed of a material capable of shielding the fluorescence from the scintillator 5.
- a material capable of shielding fluorescence can be appropriately selected from, for example, a metal material, an inorganic material, and an organic material.
- shielding member 6a2a which covers photoelectric conversion part 2b was illustrated, shielding member 6a2a which covers reference potential part 6a1 illustrated in Drawing 8 can also be provided.
- the shielding member 6a2a If the shielding member 6a2a is provided, X-rays or fluorescence will not enter the photoelectric conversion unit 2b below the shielding member 6a2a. Alternatively, X-rays do not enter the reference potential portion 6a1 below the shielding member 6a2a. Therefore, when X-rays are irradiated to the X-ray detector 1, it is possible to suppress the generation of current in the photoelectric conversion unit 2b and the reference potential unit 6a1 provided under the shielding member 6a2a. That is, the reference potential can be made substantially zero.
- the reference potential portion on the array substrate 2 it is preferable to provide the reference potential portion in the peripheral region of the array substrate 2 in consideration of the influence on the obtained X-ray image. This is because, in X-ray image capturing, the central region is used for capturing a more important portion, and the peripheral region is used for capturing relatively low importance such as positioning.
- FIG. 10 is a graph for illustrating the effect of the incident radiation detection unit 6.
- FIG. 10 shows the case where the reference potential portion 6a2 illustrated in FIG. 9, that is, the shielding member 6a2a is provided.
- X2 in FIG. 10 is the pulse width of the incident X-ray.
- N2 is noise.
- S2 is an effective electrical signal that can be used for determination at the start of X-ray incidence.
- FIG. 10 when the X-rays are incident, the difference between the current integrated values increases. Therefore, when the change in the difference between the current integral values is detected, the X-ray incidence start time can be detected.
- the difference between the detected current integrated value and the current integrated value detected immediately before is obtained. For this reason, the influence of disturbance noise due to horizontal noise or the like is increased.
- the incident radiation detection unit 6 reference potential units 6a, 6a1, 6a2
- the current integration value from the photoelectric conversion unit 2b detected almost simultaneously and the current from the reference potential unit 6a are detected. The difference from the integral value can be obtained. If the current integrated value is detected almost at the same time, the disturbance noise included in the detected current integrated value becomes equal, so that the disturbance noise can be canceled when the difference between the current integrated values is obtained. That is, in-phase noise can be removed.
- the noise N2 is smaller than the noise N1. Therefore, it is possible to increase the value of the effective electrical signal S2.
- the S / N ratio is five times that of the example illustrated in FIG. 10.
- FIG. 11 is a graph for illustrating the relationship between the sampling width and the difference between the obtained current integration values in the step of detecting the current from the photoelectric conversion unit 2b with the thin film transistor 2b2 turned off.
- the horizontal axis represents the sampling width
- the vertical axis represents the difference between the obtained current integration values.
- Condition 2 in FIG. 11 is a case where an X-ray tube current twice the X-ray tube current in Condition 1 is passed through the X-ray source.
- the difference between the current integral values obtained in proportion to the X-ray tube current increases. Further, the difference in the obtained current integrated value can also be increased by increasing the sampling width.
- the signal detection circuit 32 changes the sampling width when the thin film transistor 2b2 is on and the sampling width when the thin film transistor 2b2 is off. In this case, the signal detection circuit 32 causes the sampling width when the thin film transistor 2b2 is turned off to be longer than the sampling width when the thin film transistor 2b2 is turned on.
- this phenomenon is a change in the floating coupling capacitance between the drain electrode 2b2c and the source electrode 2b2b. That is, the change in the floating coupling capacitance when X-rays are irradiated is detected as a voltage, and the difference in current integral value obtained at this time is electrically applied to the control line 2c1 irradiated with X-rays. It is assumed that the number increases in proportion to the number of connected photoelectric conversion units 2b.
- the difference between the current integral values obtained in proportion to the sampling width increases. This is because when the thin film transistor 2b2 is irradiated with X-rays even when the thin film transistor 2b2 is turned off, a current flows between the drain electrode 2b2c and the source electrode 2b2b due to the photoelectric effect, and a current continues to flow through the data line 2c2. It can be understood that the difference in the current integral value obtained in proportion to the width increases.
- FIG. 12 is a graph for illustrating the relationship between the sampling width and the difference between the obtained current integration values in the step of detecting the current from the photoelectric conversion unit 2b with the thin film transistor 2b2 turned off.
- Condition 3 in FIG. 12 is a case where the drain electrode 2b2c and the bias line 2c3 are not electrically connected in the reference potential portion 6a1 illustrated in FIG. In this case, the reference potential portion 6a1 is formed by depositing an insulator instead of the photoelectric conversion element 2b1.
- Condition 4 is a case where a plurality of photoelectric conversion units 2b arranged in a line in the direction in which the plurality of control lines 2c1 are arranged are used as a reference potential unit. Note that the X-ray irradiation conditions are the same.
- the difference in the current integration value obtained also varies depending on the configuration of the element connected to the drain electrode 2b2c. Under the condition 3 in which the drain electrode 2b2c and the bias line 2c3 are not electrically connected, the difference between the obtained current integration values becomes very small. This is presumably because current did not flow easily because no voltage was applied from the bias line 2c3. As described above, when the reference potential portion 6a1 in which the photoelectric conversion element 2b1 is not provided is used, the level of the difference between the obtained current integration values is hardly changed, and in-phase noise can be removed. Therefore, it is possible to improve the S / N ratio and to suppress erroneous detection.
- the X-ray intensity tends to decrease from the central region toward the peripheral region. Therefore, if the row of photoelectric conversion units 2b in the peripheral region is used as the reference potential unit, the effect illustrated in FIG. 12 can be obtained. Further, when the row of photoelectric conversion units 2b in the central region is used as the reference potential unit, it is sufficiently possible to obtain the same effect by devising the determination criterion. Also, the common-mode noise can be removed as the reference potential portion 6a.
- the difference between the obtained current integrated values is proportional to the sampling width. Therefore, if the sampling width is increased, the difference between the obtained current integrated values can be increased, so that the S / N ratio can be further improved.
- the current integrated value may be different for each data line 2c2.
- the determination unit 6b averages the current integration value for each of the plurality of data lines 2c2, and determines the X ray incidence start time based on the difference between the averaged current integration value and the current integration value from the reference potential unit. Make a decision.
- the X-ray detector 1 since the X-ray detector 1 according to the present embodiment includes the incident radiation detection unit 6, the integrated current value from the photoelectric conversion unit 2b detected almost simultaneously and the reference potential unit The difference from the current integrated value from 6a can be obtained. If the detection is performed almost simultaneously, the disturbance noise included in the detected current integrated value becomes equal, so that the disturbance noise can be canceled when the difference between the current integrated values is obtained. That is, in-phase noise can be removed. Therefore, since the S / N ratio can be greatly improved, erroneous determination can be suppressed.
Abstract
Description
しかしながら、この様にすると、X線検出器の動作の開始が外部機器からの信号に依存することになるので、外部機器からの信号(例えば、X線源などからのX線照射がされたことを知らせる信号)と同期させる外部回路が必要になる。外部回路を設けるとノイズなどの影響を受けやすくなり、X線照射との回路同期できない場合には、X線画像を取得できなくなるおそれがある。
前記信号検出回路は、前記薄膜トランジスタがオフ状態の時に、前記データラインを介して第1の電流積分値を検出するとともに、前記基準電位部からの第2の電流積分値を検出する。前記判定部は、検出された前記第1の電流積分値と前記第2の電流積分値との差に基づいて放射線の入射開始時を判定する。
本実施の形態に係る放射線検出器は、X線のほかにもγ線などの各種放射線に適用させることができる。ここでは、一例として、放射線の中の代表的なものとしてX線に係る場合を例にとり説明をする。したがって、以下の実施形態の「X線」を「他の放射線」に置き換えることにより、他の放射線にも適用させることができる。
直接変換方式は、入射X線により光導電膜内部に発生した光導電電荷(信号電荷)を高電界により電荷蓄積用の蓄積キャパシタに直接導く方式である。
間接変換方式は、X線をシンチレータにより蛍光(可視光)に変換し、蛍光をフォトダイオードなどの光電変換素子により信号電荷に変換し、信号電荷を蓄積キャパシタに導く方式である。
以下においては、一例として、間接変換方式のX線検出器1を例示するが、本発明は直接変換方式のX線検出器にも適用することができる。
すなわち、X線検出器は、X線を直接的またはシンチレータと協働して検出する検出部を有するものであれば良い。
また、X線検出器1は、例えば、一般医療用途などに用いることができるが、用途に限定はない。
なお、図1においては、バイアスライン2c3などを省いて描いている。
図2は、X線検出器1のブロック図である。
図3は、X線検出器1の回路図である。
図1~図3に示すように、X線検出器1には、アレイ基板2、信号処理部3、画像処理部4、シンチレータ5、および入射放射線検出部6が設けられている。
アレイ基板2は、基板2a、光電変換部2b、制御ライン(又はゲートライン)2c1、データライン(又はシグナルライン)2c2、およびバイアスライン2c3を有する。
なお、光電変換部2b、制御ライン2c1、データライン2c2、およびバイアスライン2c3の数などは例示をしたものに限定されるわけではない。
光電変換部2bは、基板2aの一方の表面に複数設けられている。
光電変換部2bは、矩形状を呈し、制御ライン2c1とデータライン2c2とにより画された領域に設けられている。複数の光電変換部2bは、マトリクス状に並べられている。
なお、1つの光電変換部2bは、1つの画素(pixel)に対応する。
また、図3に示すように、光電変換素子2b1において変換した信号電荷を蓄積する蓄積キャパシタ2b3を設けることができる。蓄積キャパシタ2b3は、例えば、矩形平板状を呈し、各薄膜トランジスタ2b2の下に設けることができる。ただし、光電変換素子2b1の容量によっては、光電変換素子2b1が蓄積キャパシタ2b3を兼ねることができる。
薄膜トランジスタ2b2は、蛍光が光電変換素子2b1に入射することで生じた電荷の蓄積および放出のスイッチングを行う。薄膜トランジスタ2b2は、アモルファスシリコン(a-Si)やポリシリコン(P-Si)などの半導体材料を含むものとすることができる。薄膜トランジスタ2b2は、ゲート電極2b2a、ソース電極2b2b及びドレイン電極2b2cを有している。薄膜トランジスタ2b2のゲート電極2b2aは、対応する制御ライン2c1と電気的に接続される。薄膜トランジスタ2b2のソース電極2b2bは、対応するデータライン2c2と電気的に接続される。薄膜トランジスタ2b2のドレイン電極2b2cは、対応する光電変換素子2b1と蓄積キャパシタ2b3とに電気的に接続される。また、光電変換素子2b1のアノード側と蓄積キャパシタ2b3は、対応するバイアスライン2c3と電気的に接続される(図3を参照)。
1つの制御ライン2c1は、基板2aの周縁近傍に設けられた複数の配線パッド2d1のうちの1つと電気的に接続されている。1つの配線パッド2d1には、フレキシブルプリント基板2e1に設けられた複数の配線のうちの1つが電気的に接続されている。フレキシブルプリント基板2e1に設けられた複数の配線の他端は、信号処理部3に設けられた制御回路31とそれぞれ電気的に接続されている。
1つのデータライン2c2は、基板2aの周縁近傍に設けられた複数の配線パッド2d2のうちの1つと電気的に接続されている。1つの配線パッド2d2には、フレキシブルプリント基板2e2に設けられた複数の配線のうちの1つが電気的に接続されている。フレキシブルプリント基板2e2に設けられた複数の配線の他端は、信号処理部3に設けられた信号検出回路32とそれぞれ電気的に接続されている。
バイアスライン2c3には、図示しないバイアス電源が電気的に接続されている。図示しないバイアス電源は、例えば、信号処理部3などに設けることができる。
なお、バイアスライン2c3は、必ずしも必要ではなく、必要に応じて設けるようにすればよい。バイアスライン2c3が設けられない場合には、光電変換素子2b1のアノード側と蓄積キャパシタ2b3は、バイアスライン2c3に代えてグランドに電気的に接続される。
保護層2fは、例えば、酸化物絶縁材料、窒化物絶縁材料、酸窒化物絶縁材料、および樹脂材料の少なくとも1種を含む。
酸化物絶縁材料は、例えば、酸化シリコン、酸化アルミニウムなどである。
窒化物絶縁材料は、例えば、窒化シリコン、窒化アルミニウムなどである。
酸窒化物絶縁材料は、例えば、酸窒化シリコンなどである。
樹脂材料は、例えば、アクリル系樹脂などである。
信号処理部3には、制御回路31と、信号検出回路32とが設けられている。
制御回路31は、薄膜トランジスタ2b2のオン状態とオフ状態を切り替える。
図2に示すように、制御回路31は、複数のゲートドライバ31aと行選択回路31bとを有する。
行選択回路31bには、画像処理部4などから制御信号S1が入力される。行選択回路31bは、X線画像の走査方向に従って、対応するゲートドライバ31aに制御信号S1を入力する。
ゲートドライバ31aは、対応する制御ライン2c1に制御信号S1を入力する。
例えば、制御回路31は、フレキシブルプリント基板2e1と制御ライン2c1とを介して、制御信号S1を各制御ライン2c1毎に順次入力する。制御ライン2c1に入力された制御信号S1により薄膜トランジスタ2b2がオン状態となり、光電変換素子2b1からの信号電荷(画像データ信号S2)が受信できるようになる。
信号検出回路32は、薄膜トランジスタ2b2がオン状態の時に、画像処理部4からのサンプリング信号に従って光電変換素子2b1から信号電荷(画像データ信号S2)を読み出す。
画像処理部4は、配線4aおよび判定部6bを介して、信号検出回路32と電気的に接続されている。なお、画像処理部4は、信号処理部3と一体化されていてもよい。
まず、制御回路31によって薄膜トランジスタ2b2が順次オン状態となる。薄膜トランジスタ2b2がオン状態となることで、バイアスライン2c3を介して一定の電荷が光電変換素子2b1に蓄積される。次に、薄膜トランジスタ2b2をオフ状態にする。X線が照射されると、シンチレータ5によりX線が蛍光に変換される。蛍光が光電変換素子2b1に入射すると、光電効果によって電荷(電子およびホール)が発生し、発生した電荷と、蓄積されている電荷(異種電荷)とが結合して蓄積されている電荷が減少する。次に、制御回路31は、薄膜トランジスタ2b2を順次オン状態にする。信号検出回路32は、サンプリング信号に従って各光電変換素子2b1に蓄積されている減少した電荷(画像データ信号S2)をデータライン2c2を介して読み出す。
シンチレータ5は、例えば、ヨウ化セシウム(CsI):タリウム(Tl)、あるいはヨウ化ナトリウム(NaI):タリウム(Tl)などを用いて形成することができる。この場合、真空蒸着法などを用いて、シンチレータ5を形成すれば、複数の柱状結晶の集合体からなるシンチレータ5が形成される。
シンチレータ5の厚み寸法は、例えば、600μm程度とすることができる。
また、空気中に含まれる水蒸気により、シンチレータ5の特性と図示しない反射層の特性が劣化するのを抑制するために、シンチレータ5と図示しない反射層を覆う図示しない防湿体を設けることができる。
すなわち、一般的なX線検出器の場合は、X線が実際にX線検出器に入射したのを検出しているわけではない。
そのため、外部機器からの信号が入力された時点と、読み出し動作を開始する時点との間に所定の時間を設ける必要がある。またさらに、外部機器からの信号(例えば、X線源などからのX線照射がされたことを知らせる信号)と同期させる外部回路が必要になる。外部回路を設けるとノイズなどの影響を受けやすくなり、X線照射との回路同期できない場合には、X線画像を取得できなくなるおそれがある。
図4に示すように、X線検出器101には、アレイ基板2および信号処理部3が設けられている。また、図示は省略するが、画像処理部4およびシンチレータ5も設けられている。ただし、X線検出器101には、入射放射線検出部6が設けられていない。
X線検出器101においては、以下のようにしてX線の入射開始時を検出する。
まず、各薄膜トランジスタ2b2をオフ状態にする。信号処理部3などにより、各データライン2c2の電流積分値を検出する。電流積分値は、データライン2c2に電気的に接続された複数の光電変換部2b毎に順次検出する。この様な電流積分値の検出を反復して行う。そして、検出された電流積分値と、一つ前に検出された電流積分値との差を比較回路などにより求め、電流積分値の差が変化した時点を検出し、電流積分値の差が変化した時点をX線の入射開始時と判定する。この様にすれば、X線の入射開始時を直接検出することができる。
ところが、光電変換部2bからの電流積分値を検出している期間に(信号電荷を読み出している期間に)、低周波ノイズなどの外乱ノイズがあると、外乱ノイズが検出された電流積分値に重なる。外乱ノイズの影響は、例えば、X線画像上において行画素単位で現れる。この様な外乱ノイズの影響は、横引きノイズと呼ばれている。
図5中のX1は、入射したX線のパルス幅である。N1は、ノイズである。S1はX線の入射開始時の判定に用いることができる有効電気信号である。
図5から分かるように、X線が入射すると、電流積分値の差が増加する。そのため、電流積分値の差の変化を検出すればX線の入射開始時を検出することができる。
ところが、前述したように、外乱ノイズの影響が大きくなる。この場合、同じ光電変換部2bにおける電流積分値同士の差を求めるため、求められた電流積分値の差が小さくなる。そのため、有効電気信号S1の値が小さくなりやすくなるので、X線の入射開始時の判定において誤判定がさらに生じやすくなる。
図1および図2に示すように、入射放射線検出部6は、基準電位部6aおよび判定部6bを有する。
基準電位部6aは、例えば、定電圧電源や定電流電源などの電源と電気的に接続されたものとすることができる。基準電位部6aは、電源などと電気的に接続せず、フロート電位と電気的に接続することもできる。
判定部6bは、信号検出回路32を介して基準電位部6aと電気的に接続されている。
基準電位部6aおよび判定部6bは、X線が入射しない領域に設けることができる。基準電位部6aおよび判定部6bは、例えば、信号処理部3または画像処理部4が設けられる領域に設けることができる。基準電位部6aおよび判定部6bは、信号処理部3または画像処理部4と一体化することもできる。
図6(a)は、X線の入射開始時の検出を例示するためのタイミングチャートである。
図6(b)は、X線の入射が開始された後の処理工程を例示するためのタイミングチャートである。
図7は、X線の入射開始時の検出を例示するためのフローチャートである。
次に、判定部6bは、求められた電流積分値の差が所定の判定基準を満たしているか否かを判定する(図7のステップST3)。
判定基準を満たしている場合には、判定部6bは、X線が入射したと判定する。判定基準を満たしていない場合には、判定部6bは、X線が入射していないと判定する。
例えば、図6(b)に示すように、画像処理部4から信号処理部3に順次サンプリング信号を入力し、サンプリングを開始する。
次に、制御回路31は、一定期間経過後に、それぞれのサンプリング幅内において、制御ライン2c1に制御信号S1を入力する。すなわち、制御回路31は、一定期間経過後に、サンプリングを行う薄膜トランジスタ2b2をオン状態にする。
なお、「一定期間」は、実験やシミュレーションにより予め求められた時間とすることができる。この場合、「一定期間」は、固定的に設定することもできるし、X線の照射の前にその都度設定することもできる。
また、「一定期間」は、検出値が第1の閾値を超え、第2の閾値を下回った時とすることもできる。
入力された制御信号S1は、サンプリング幅内において終了させる。制御信号S1により薄膜トランジスタ2b2がオン状態となると、光電変換素子2b1からの信号電荷(画像データ信号S2)が受信できるようになる。信号検出回路32により読み出された画像データ信号S2は、判定部6bを通過して、画像伝送部4に入力される。画像伝送部4は、入力された画像データ信号S2を順次増幅し、デジタル信号に変換する。そして、画像伝送部4は、デジタル信号に変換された画像データ信号S2に基づいて、X線画像を構成する。構成されたX線画像のデータは、画像伝送部4から外部の機器に向けて出力される。
次に、検出された判定の回数および経過時間の少なくともいずれかが規定値を超えているか否かを判定する(図7のステップST6)。
検出された判定の回数などが規定値を超えていなければ、ステップST1に戻り前述した工程を再度行う。
すなわち、制御回路31は、複数の薄膜トランジスタ2b2をオフ状態に維持する。
信号検出回路32は、各光電変換部2bからの電流積分値と、基準電位部6aからの電流積分値とを再度検出する。
判定部6bは、各光電変換部2bからの電流積分値と、基準電位部6aからの電流積分値との差に基づいてX線の入射開始時を再度判定する。
検出された判定の回数などが規定値を超えていれば、判定にかかわるデータ(判定の回数、経過時間、検出した電流積分値などに関するデータ)を初期化(消去)し、ステップST1に戻り前述した工程を再度行う。
図8に示すように、基準電位部6a1には、薄膜トランジスタ2b2と、蓄積キャパシタ2b3が設けられている。すなわち、基準電位部6a1は、光電変換部2bから光電変換素子2b1を除いた構成を有している。
なお、基準電位部6a1は、薄膜トランジスタ2b2のみを有するものであってもよい。
また、基準電位部6a1は、ドレイン電極2b2cとバイアスライン2c3を電気的に接続せず、光電変換素子2b1の代わりに絶縁物を成膜したものとすることもできる。
また、基準電位部6a1は、アレイ基板2に設けることができる。そのため、省スペース化、ひいてはX線検出器1の小型化を図ることができる。
すなわち、基準電位部は、マトリクス状に並べられた複数の光電変換部2bのうち、複数の制御ライン2c1が並ぶ方向に並べて設けられた一列の複数の光電変換部2bとすることができる。
この場合、X線画像を検出するための光電変換部2bと、基準電位部となる光電変換部2bとが異なるものとなるので、前述した比較例に係るX線の入射開始時の検出方法のように、電流積分値の検出時期がずれることがない。そのため、外乱ノイズの影響が大きくなることはない。
この様にすれば、X線画像を検出するための光電変換部2bと、基準電位部となる光電変換部2bとが全く同じ構成となるので、製造コストの低減や生産性の向上をさらに図ることができる。
図9に示すように、基準電位部6a2は、前述した基準電位部となる複数の光電変換部2bと、それらを覆う遮蔽部材6a2aを有する。
基準電位部6a2となる光電変換部2bの上にシンチレータ5が設けられない場合には、遮蔽部材6a2aは、X線吸収率が高い材料から形成される。X線吸収率が高い材料は、例えば、鉛、銅、鉄等の重金属とすることができる。基準電位部6a2となる光電変換部2bの上にシンチレータ5が設けられる場合には、X線吸収率が高い材料からなる遮蔽部材6a2aをシンチレータ5のX線の入射側に設けることができる。遮蔽部材6a2aがシンチレータ5とアレイ基板2との間に設けられる場合には、遮蔽部材6a2aはシンチレータ5からの蛍光を遮光することができる材料から形成することができる。蛍光を遮光することができる材料は、例えば、金属材料、無機材料、有機材料などから適宜選択することができる。
なお、光電変換部2bを覆う遮蔽部材6a2aを例示したが、図8に例示をした基準電位部6a1を覆う遮蔽部材6a2aを設けることもできる。
なお、図10は、図9に例示をした基準電位部6a2、すなわち、遮蔽部材6a2aを設けた場合である。
図10中のX2は、入射したX線のパルス幅である。N2は、ノイズである。S2はX線の入射開始時の判定に用いることができる有効電気信号である。
図10から分かるように、X線が入射すると、電流積分値の差が増加する。そのため、電流積分値の差の変化を検出すればX線の入射開始時を検出することができる。
これに対して、入射放射線検出部6(基準電位部6a、6a1、6a2)を設けるようにすれば、ほぼ同時に検出された光電変換部2bからの電流積分値と、基準電位部6aからの電流積分値との差を求めることができる。ほぼ同時に電流積分値を検出するようにすれば、検出された電流積分値に含まれる外乱ノイズが同等となるので、電流積分値の差を求めた際に外乱ノイズを相殺することができる。すなわち、同相ノイズを除去することができる。
その結果、例えば、図10と図5とを比較すれば明らかな様に、ノイズN2はノイズN1にくらべて小さくなる。そのため、有効電気信号S2の値を大きくすることが可能となる。図5に例示をしたものの場合には、図10に例示をしたものと比較するとS/N比が5倍になった。
また、横軸はサンプリング幅、縦軸は求められた電流積分値の差を表している。
図11中の条件2は、条件1におけるX線管電流の2倍のX線管電流をX線源に流した場合である。
図11から分かるように、X線管電流に比例して求められた電流積分値の差が増加する。また、サンプリング幅を大きくすることによっても求められた電流積分値の差を増加させることができる。
そのため、信号検出回路32は、S/N比を向上させるために、薄膜トランジスタ2b2がオン状態の時のサンプリング幅と、薄膜トランジスタ2b2がオフ状態の時のサンプリング幅とを変更する。
この場合、信号検出回路32は、薄膜トランジスタ2b2がオフ状態の時のサンプリング幅が、薄膜トランジスタ2b2がオン状態の時のサンプリング幅よりも長くなるようにする。
図12中の条件3は、図8に例示をした基準電位部6a1において、ドレイン電極2b2cとバイアスライン2c3を電気的に接続しない場合である。この場合、基準電位部6a1は、光電変換素子2b1の代わりに絶縁物を成膜したものとしている。条件4は、複数の制御ライン2c1が並ぶ方向に並べて設けられた一列の複数の光電変換部2bを基準電位部とした場合である。
なお、X線の照射条件は同じとしている。
このように、光電変換素子2b1が設けられていない基準電位部6a1を用いれば、求められた電流積分値の差のレベルはほとんど変わらず、かつ、同相ノイズを除去することができる。そのため、S/N比の向上を図ることができ、ひいては誤検出を抑制することができる。
また、中央領域にある光電変換部2bの列を基準電位部とする場合には、判定基準を工夫することによって同様の効果を得ることは十分可能である。
また、基準電位部6aとしても同相ノイズを除去することができる。
この場合、判定部6bは、複数のデータライン2c2毎の電流積分値を平均し、平均された電流積分値と基準電位部からの電流積分値との差に基づいてX射線の入射開始時を判定するようにする。
Claims (11)
- 基板と、
前記基板に設けられ、第1の方向に延びる複数の制御ラインと、
前記基板に設けられ、前記第1の方向に交差する第2の方向に延びる複数のデータラインと、
前記複数の制御ラインと、前記複数のデータラインと、により画された複数の領域のそれぞれに設けられ、対応する前記制御ラインと対応する前記データラインとに電気的に接続された薄膜トランジスタおよび光電変換素子を有する光電変換部と、
前記複数の制御ラインと電気的に接続され、複数の前記薄膜トランジスタのオン状態とオフ状態を切り替える制御回路と、
前記複数のデータラインと電気的に接続された信号検出回路と、
前記信号検出回路と電気的に接続された基準電位部と、
前記信号検出回路と電気的に接続された判定部と、
を備え、
前記信号検出回路は、前記薄膜トランジスタがオフ状態の時に、前記データラインを介して第1の電流積分値を検出するとともに、前記基準電位部からの第2の電流積分値を検出し、
前記判定部は、検出された前記第1の電流積分値と前記第2の電流積分値との差に基づいて放射線の入射開始時を判定する放射線検出器。 - 前記基準電位部は、前記制御ラインと前記データラインとに電気的に接続された前記薄膜トランジスタを有する請求項1記載の放射線検出器。
- 前記基準電位部は、マトリクス状に並べられた前記複数の光電変換部のうち、前記複数の制御ラインが並ぶ方向に並べて設けられた一列の前記複数の光電変換部を有する請求項1記載の放射線検出器。
- 前記基準電位部は、前記基準電位部に設けられた前記薄膜トランジスタ、または前記基準電位部に設けられた前記複数の光電変換部を覆う遮蔽部材をさらに有する請求項2または3に記載の放射線検出器。
- 前記基準電位部は、電源、または、フロート電位と電気的に接続されている請求項1記載の放射線検出器。
- 前記信号検出回路は、前記薄膜トランジスタがオン状態の時のサンプリング幅と、前記薄膜トランジスタがオフ状態の時のサンプリング幅とを変更する請求項1~5のいずれか1つに記載の放射線検出器。
- 前記薄膜トランジスタがオフ状態の時のサンプリング幅は、前記薄膜トランジスタがオン状態の時のサンプリング幅よりも長い請求項6記載の放射線検出器。
- 前記判定部により前記放射線の入射が開始されたと判定された場合には、
前記制御回路は、一定期間経過後に前記複数の薄膜トランジスタをオン状態にする請求項1~7のいずれか1つに記載の放射線検出器。 - 前記判定部により前記放射線の入射が開始されていないと判定された場合には、
前記制御回路は、前記複数の薄膜トランジスタをオフ状態に維持し、
前記信号検出回路は、前記第1の電流積分値と、前記第2の電流積分値とを再度検出し、
前記判定部は、前記第1の電流積分値と前記第2の電流積分値との差に基づいて放射線の入射開始時を再度判定する請求項1~7のいずれか1つに記載の放射線検出器。 - 前記判定部は、前記判定の回数および経過時間の少なくともいずれかを検出し、検出された前記判定の回数および前記経過時間の少なくともいずれかが規定値を超えた場合には、
前記判定の回数、前記経過時間、前記第1の電流積分値、および前記第2の電流積分値に関するデータを初期化する請求項9記載の放射線検出器。 - 前記判定部は、前記複数のデータライン毎の前記第1の電流積分値を平均し、前記平均された前記第1の電流積分値と前記第2の電流積分値との差に基づいて前記放射線の入射開始時を判定する請求項1~10のいずれか1つに記載の放射線検出器。
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JP2013157793A (ja) * | 2012-01-30 | 2013-08-15 | Fujifilm Corp | 放射線照射開始判定装置、放射線画像撮影装置、放射線画像撮影制御装置、放射線照射開始判定方法、及び放射線照射開始判定プログラム |
JP2014526178A (ja) | 2011-07-13 | 2014-10-02 | トリクセル | 入射放射を自動検出することによって光検出器を制御する方法 |
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JP2013157793A (ja) * | 2012-01-30 | 2013-08-15 | Fujifilm Corp | 放射線照射開始判定装置、放射線画像撮影装置、放射線画像撮影制御装置、放射線照射開始判定方法、及び放射線照射開始判定プログラム |
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