JP2011232278A - Radiation imaging apparatus - Google Patents

Abstract

Provided is a radiation imaging apparatus that prevents image deterioration due to external light and suppresses deterioration of yield in a manufacturing process.
An electronic cassette (20) includes a substrate (120), a pixel (72) formed on the substrate, and a scintillator (122) that converts radiation into light having sensitivity to the pixel (72). The pixel 72 has a filter characteristic that restricts transmission of light in a wavelength band in which the pixel 72 has sensitivity. As a result, the manufacturing process is simplified, deterioration of the yield in the manufacturing process can be suppressed, and deterioration of the radiation image due to the influence of external light can be suppressed.
[Selection] Figure 5

Description

  The present invention relates to a radiation imaging apparatus that captures light by converting radiation into visible light.

  In the medical field, a radiation imaging apparatus is used that images a human body by irradiating the human body with radiation and detecting the intensity of the radiation transmitted through the human body. In the radiation imaging apparatus, there are a direct conversion type that converts radiation directly into an electric signal and an indirect conversion type that converts radiation into visible light and converts the converted visible light into an electric signal.

  In an indirect conversion type radiation imaging apparatus, external light such as sunlight or fluorescent light is incident on the photoelectric conversion element, and the radiation image is deteriorated. Conventionally, external light is incident on the photoelectric conversion element. In Patent Document 1 shown below, it is described that a light absorption layer is provided on the back side of a substrate provided with a photoelectric conversion portion.

JP 2003-303945 A

  However, as described in Patent Document 1 described above, when a light-absorbing layer that shields external light is provided in a separate process on a substrate on which a photoelectric conversion unit and a TFT are formed, not only the manufacturing process increases, but also due to an additional process. There is a concern that defects may occur, which causes a deterioration in manufacturing yield. In addition, since a light absorption layer is provided on the back side of the substrate, when external light is incident from a region where the light absorption layer is not provided, such as a side surface of the substrate, the external light passes through the substrate and enters the photoelectric conversion element. Light is received, and the radiographic image deteriorates.

  Therefore, the present invention has been made in view of such conventional problems, and an object of the present invention is to provide a radiation imaging apparatus that suppresses image deterioration due to external light and suppresses deterioration in yield in the manufacturing process.

  In order to achieve the above object, the present invention provides a radiation imaging apparatus comprising: a substrate; a pixel formed on the substrate; and a light conversion unit that converts radiation into light having sensitivity to the pixel. In the radiation imaging apparatus, the substrate has a filter characteristic that restricts transmission of light in a wavelength band in which the pixel has sensitivity.

  The substrate may have a filter characteristic that most restricts transmission of light having a wavelength at which the sensitivity of the pixel reaches a peak.

  The substrate may have a filter characteristic that restricts transmission of light other than a wavelength band of light converted by the light conversion unit.

  The light conversion unit may be provided on a side where radiation is incident on the pixel formed on the substrate.

  The light conversion unit may be provided on a side opposite to a side on which radiation is incident on a pixel formed on the substrate.

  According to the present invention, the substrate on which the pixel is formed has a function as a filter that restricts the transmission of light in a wavelength band in which the pixel has sensitivity, so that the manufacturing process is simplified and the yield in the manufacturing process is reduced. Deterioration can be suppressed and deterioration of the radiation image due to the influence of external light can be suppressed.

  Since the substrate on which the pixel is formed most restricts the transmission of light having a wavelength at which the sensitivity of the pixel reaches its peak, it is possible to further prevent deterioration of the radiation image due to the influence of external light.

  Since the substrate on which the pixels are formed restricts the transmission of light outside the wavelength band of the light converted by the light conversion unit, the light conversion unit is formed on the side of the substrate where the pixels are not formed. In addition, it is possible to suppress deterioration of the radiation image due to the influence of external light.

It is a block diagram of the radiation imaging system of this Embodiment. It is a perspective view of the electronic cassette shown in FIG. It is a figure which shows typically the arrangement | sequence of the pixel in a radiation conversion panel, and the electrical connection between a pixel and a cassette control part. It is a figure which shows the circuit structure of the electronic cassette shown in FIG. It is a figure which shows an example of the state when external light injects into the schematic cross section of the radiation conversion panel shown in FIG.3 and FIG.4, and the board | substrate of a radiation conversion panel. It is a figure which shows an example of the sensitivity characteristic of a pixel, and the filter characteristic of a board | substrate. FIG. 6 is a diagram showing a state of external light incident on a substrate of the radiation conversion panel shown in FIG. 5 when the pixel does not have a function as a filter that restricts transmission of light in a wavelength band with sensitivity. . FIG. 5 is a schematic cross-sectional view of the radiation conversion panel shown in FIGS. 3 and 4 when a scintillator is formed on the side where no pixel is provided on the substrate, and an example of a state when external light is incident on the substrate of the radiation conversion panel. is there.

  The radiation imaging apparatus according to the present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments.

  FIG. 1 is a configuration diagram of the radiation imaging system of the present embodiment. The radiation imaging system 10 includes a radiation source 18 for irradiating a patient 16 as a subject 14 lying on an imaging stand 12 such as a bed with radiation 16 having a dose according to imaging conditions, and radiation 16 transmitted through the subject 14. An electronic cassette (radiation imaging device) 20 that detects and converts to a radiographic image, a console 24 that controls the radiation source 18 and the electronic cassette 20, and a display device 26 that displays the radiographic image are provided.

  Between the console 24, the radiation source 18, the electronic cassette 20, and the display device 26, for example, UWB (Ultra Wide Band), IEEE802.11. Signals are transmitted and received by wireless LAN using a / g / n or wireless communication using millimeter waves or the like. Note that signals may be transmitted and received by wired communication using a cable.

  The console 24 is connected to a radiology information system (RIS) 28 for comprehensively managing radiographic images and other information handled in the radiology department in the hospital. The RIS 28 is used for comprehensive management of medical information in the hospital. A medical information system (HIS) 30 to be managed is connected.

  FIG. 2 is a perspective view of the electronic cassette shown in FIG. 1, and the electronic cassette 20 includes a panel unit 32 and a control unit 34 disposed on the panel unit 32. The thickness of the panel unit 32 is set to be thinner than the thickness of the control unit 34.

  The panel unit 32 includes a substantially rectangular casing 40 made of a material that can transmit the radiation 16, and the imaging surface 42 of the panel unit 32 is irradiated with the radiation 16. A guide line 44 indicating the imaging area and imaging position of the subject 14 is formed at a substantially central portion of the imaging surface 42. The outer frame of the guide line 44 becomes an imageable region 36 indicating the irradiation field of the radiation 16. The center position of the guide line 44 (intersection where the guide line 44 intersects in a cross shape) is the center position of the imageable area 36 and the geometric center position of the electronic cassette 20.

  The control unit 34 has a substantially rectangular casing 50 made of a material that is impermeable to the radiation 16. The housing 50 extends along one end of the imaging surface 42, and the control unit 34 is disposed outside the imageable region 36 on the imaging surface 42. In this case, inside the housing 50, there is a cassette control unit 80 that controls a panel unit 32, which will be described later, a power supply unit 108 such as a battery, and a communication unit 110 that can transmit and receive signals wirelessly between the console 24. Etc. are arranged (see FIGS. 3 and 4). The power supply unit 108 supplies power to the panel unit 32, and also supplies power to the cassette control unit 80 and the communication unit 110.

  On the side surface 52 in the short direction of the control unit 34, as an interface means capable of transmitting and receiving information between the input terminal 54 of the AC adapter for charging the power source unit 108 from an external power source and an external device. USB terminal 56 and a card slot 58 for loading a memory card such as a PC card.

  The panel unit 32 includes a radiation conversion panel and a drive circuit unit which will be described later. The radiation conversion panel converts the radiation 16 transmitted through the subject 14 into fluorescence contained in the visible light region by a scintillator (light conversion unit), and converts the converted fluorescence into a photoelectric comprising a substance such as amorphous silicon (a-Si). It is an indirect conversion type radiation conversion panel that converts an electrical signal by a conversion element.

  FIG. 3 is a diagram schematically illustrating an arrangement of pixels in the radiation conversion panel and an electrical connection between the pixels and the cassette control unit. In the radiation conversion panel 70, a large number of pixels 72 are arranged on a substrate (not shown), and a plurality of gate lines 76 for supplying a control signal from the drive circuit unit 74 to the pixels 72 and a plurality of pixels 72. A plurality of signal lines 78 for reading out the output electric signals and outputting them to the drive circuit unit 74 are arranged. The pixel 72 has a photoelectric conversion element. The cassette control unit 80 of the control unit 34 controls the drive circuit unit 74 by supplying a control signal to the drive circuit unit 74.

  FIG. 4 is a diagram illustrating a circuit configuration of the electronic cassette. In the radiation conversion panel 70, a photoelectric conversion layer in which each pixel 72 having a photoelectric conversion element made of a substance such as a-Si that converts visible light into an electrical signal is arranged on an array of matrix-like TFTs 82. It has a structure. In this case, in each pixel 72 to which a bias voltage is supplied from the bias circuit 84 constituting the drive circuit unit 74, charges generated by converting visible light into an electrical signal (analog signal) are accumulated, and each column is stored. By sequentially turning on the TFTs 82, the charge can be read out as an image signal.

  A gate line 76 extending in parallel to the column direction and a signal line 78 extending in parallel to the row direction are connected to the TFT 82 connected to each pixel 72. Each gate line 76 is connected to a gate drive circuit 86, and each signal line 78 is connected to a multiplexer 92 constituting the drive circuit unit 74. A control signal for controlling on / off of the TFTs 82 arranged in the column direction is supplied from the gate drive circuit 86 to the gate line 76. In this case, the gate drive circuit 86 is supplied with an address signal from the cassette control unit 80, and the gate drive circuit 86 performs on / off control of the TFT 82 in accordance with the address signal.

  The current held in each pixel 72 flows out to the signal line 78 through the TFTs 82 arranged in the row direction. This charge is amplified by the amplifier 88. A multiplexer 92 is connected to the amplifier 88 via a sample and hold circuit 90. The multiplexer 92 includes an FET switch 94 that switches a signal line 78 that outputs a signal, and a multiplexer driving circuit 96 that turns on one FET switch 94 and outputs a selection signal. The multiplexer drive circuit 96 is supplied with an address signal from the cassette control unit 80, and turns on one FET switch 94 in accordance with the address signal. An A / D converter 98 is connected to the FET switch 94, and a radiation image converted into a digital signal by the A / D converter 98 is supplied to the cassette control unit 80 via the flexible substrate 112. The flexible substrate 112 electrically connects the cassette control unit 80 and the drive circuit unit 74.

  The TFT 82 functioning as a switching element may be realized in combination with another imaging element such as a CMOS (Complementary Metal-Oxide Semiconductor) image sensor. Furthermore, it can be replaced with a CCD (Charge-Coupled Device) image sensor that transfers charges while shifting them with a shift pulse corresponding to a gate signal referred to as a TFT.

  The cassette control unit 80 includes an address signal generation unit 100 that generates an address signal to be supplied to the gate drive circuit 86 and the multiplexer drive circuit 96, and an image memory 102 that stores a radiation image detected by the radiation conversion panel 70. Prepare. The radiographic image stored in the image memory 102 is transmitted to the console 24 or the like by the communication unit 110.

  FIG. 5 is a diagram showing an example of a schematic cross section of the radiation conversion panel shown in FIGS. 3 and 4 and a state when external light is incident on the substrate of the radiation conversion panel. The radiation conversion panel 70 shown in FIG. 5 includes a substrate 120, a pixel 72 that converts light formed on the substrate 120 into an electric signal, and light that is formed on the pixel 72 and has sensitivity to radiation. And a scintillator 122 for converting into The scintillator 122 has a light emitter that absorbs incident radiation and emits fluorescence. For example, cesium iodide (CsI) or gadolinium sulfate (GOS) may be used as the light emitter. The emission spectrum of the illuminant using CsI when irradiated with radiation is, for example, 420 nm to 600 nm. Further, the emission spectrum of the illuminant using GOS upon irradiation with radiation has a steep peak near 550 nm. The fluorescence emitted by the scintillator is within the wavelength band (visible light wavelength band) in which the pixel 72 is sensitive. Although not shown, the TFT is also formed on the substrate 120.

  The substrate 120 has a filter characteristic that restricts transmission of light (visible light) in a wavelength band in which the pixel 72 has sensitivity. When the substrate 120 is made of a glass-based material, a metal, a pigment, or the like is kneaded into the glass-based material. When the substrate 120 is made of a plastic-based material, the metal, the pigment, the dye, or the like is made into a plastic-based material. By kneading, the substrate 120 can function as a filter that restricts transmission of light in a wavelength band in which the pixel 72 has sensitivity.

  For example, the substrate 120 may be configured by kneading a material used in a general optical filter (for example, a bandpass filter) that is a general-purpose product into plastic. When a photoelectric conversion element is formed using an organic photoelectric conversion material having a sharp absorption spectrum for visible light compared to amorphous silicon (a-Si) and used in combination with the substrate 120 functioning as a filter, the effect as a filter is further increased. Becomes higher. In addition, the substrate 120 may have a filter characteristic that restricts transmission of light in a wavelength band where the pixel 72 is not sensitive.

  FIG. 6 is a diagram showing the sensitivity characteristics of the pixels and the filter characteristics of the substrate. 6 indicates the sensitivity characteristic of the pixel 72, and the dotted line indicates the filter characteristic of the substrate 120. The pixel 72 has the highest sensitivity at the wavelength a (becomes peak sensitivity), and the sensitivity decreases as the wavelength becomes smaller and larger than the wavelength a. A wavelength with high sensitivity refers to a wavelength at which an output electric signal becomes large when light of the same intensity is incident on the pixel 72.

  Further, it is preferable that the substrate 120 at least restricts transmission of light in a wavelength band in which the pixel 72 has sensitivity, and most restricts transmission of light of the wavelength a at which the pixel 72 has peak sensitivity. Note that the substrate 120 may have a structure that does not completely transmit light in the wavelength band in which the pixel 72 has sensitivity or light in the wavelength a.

  FIG. 7 shows the state of external light incident on the substrate when the substrate of the radiation conversion panel shown in FIG. FIG. When radiation enters the scintillator 122, the scintillator 122 absorbs the incident radiation and emits fluorescence. That is, radiation is converted into fluorescence. The pixel 72 receives the converted fluorescence. On the other hand, when external light is incident on the substrate 120, the substrate 120 functions as a guide light, and the external light incident on the substrate 120 is received by the pixel 72 through the substrate 120. As a result, the captured radiation image is deteriorated.

  However, in the present embodiment, the substrate 120 functions as a substrate that restricts the transmission of light in the wavelength band in which the pixel 72 has sensitivity, so that most of the external light incident on the substrate 120 is shown in FIG. Is absorbed by the substrate 120 and can significantly suppress external light incident on the pixel 72. Thereby, deterioration of a radiographic image can be prevented.

  In FIG. 5, front surface imaging is taken as an example, but the same applies to backside imaging. Backside imaging refers to imaging by making radiation incident on the radiation conversion panel 70 from the side where the pixels 72 of the substrate 120 are not provided (the side where the scintillator 122 of the radiation conversion panel 70 shown in FIG. 5 is not provided). It refers to the method. In this case, the incident radiation passes through the substrate 120 and enters the scintillator 122, and the scintillator 122 converts the incident radiation into fluorescence. The pixel 72 receives the fluorescence converted by the scintillator 122.

  FIG. 8 shows an example of a schematic cross section of the radiation conversion panel shown in FIGS. 3 and 4 when the scintillator is formed on the side of the substrate where no pixels are provided, and a state when external light is incident on the substrate of the radiation conversion panel. FIG. The radiation conversion panel 70 shown in FIG. 8 differs from the radiation conversion panel 70 shown in FIG. 5 in that the scintillator 122 is formed not on the pixel 72 but on the side where the pixel 72 of the substrate 120 is not formed. . Further, the substrate 120 shown in FIG. 8 has a filter characteristic that transmits light in the fluorescent wavelength band emitted from the scintillator 122 and restricts transmission of light in the fluorescent wavelength band. For example, when GOS is used for the scintillator 122, the substrate 120 is a filter (band pass filter) that has high transmittance of several tens of nm in the vicinity including 550 nm and cuts other wavelength bands or has low transmittance. Preferably there is. 8 transmits light in the wavelength band of the fluorescence emitted by the scintillator 122 out of light in the wavelength band in which the pixel 72 has sensitivity, and restricts transmission of light other than the wavelength band of the fluorescence. It may have filter characteristics.

  The radiation incident on the pixel 72 and the substrate 120 shown in FIG. 8 passes through the pixel 72 and the substrate 120 and enters the scintillator 122. The scintillator 122 converts incident radiation into fluorescence. The pixel 72 receives fluorescence converted by the scintillator 122 and transmitted through the substrate 120. On the other hand, out of the external light incident on the substrate 120 via the scintillator 122 and the external light directly incident on the substrate 120, the external light included in the fluorescence wavelength band emitted by the scintillator 122 passes through the substrate 120 and passes through the pixel. Most of the external light that is incident on 72 but not included in the fluorescence wavelength band emitted by the scintillator 122 is absorbed by the substrate 120. Thereby, since the substrate 120 transmits only a part of the incident external light, it is possible to suppress degradation of the radiation image due to the influence of the external light.

  In FIG. 8, front surface imaging is taken as an example, but back surface imaging may be used. The back side imaging is a method of performing imaging by making radiation incident on the radiation conversion panel 70 from the side where the pixels of the substrate 120 are not provided (the side where the scintillator 122 shown in FIG. 8 is provided) as described above. . In this case, the incident radiation is converted into fluorescence by the scintillator 122, and the converted fluorescence passes through the substrate 120 and enters the pixel 72.

  As described above, since the substrate 120 on which the pixel 72 is formed has a function as a filter that transmits light in a wavelength band in which the pixel 72 has sensitivity, the manufacturing process is simplified, and the yield in the manufacturing process is deteriorated. Can be suppressed, and deterioration of the radiation image due to external light can be suppressed.

  Further, the substrate 120 on which the pixel 72 is formed has a function as a filter that most restricts the transmission of light having a wavelength at which the sensitivity of the pixel 72 reaches a peak, thereby further degrading the radiation image due to the influence of external light. Can be prevented.

  Further, the substrate 120 on which the pixel 72 is formed has a function as a filter that restricts transmission of light other than the wavelength band of light converted by the scintillator 122, so that the side of the substrate 120 on which the pixel 72 is not formed. Even when the scintillator 122 is formed (on the side opposite to the side where the radiation enters the pixel 72), deterioration of the radiation image due to the influence of external light can be suppressed.

  In the above embodiment, the substrate 120 of the radiation conversion panel 70 shown in FIG. 5 has the filter characteristics shown in FIG. 6, but transmits light in the fluorescent wavelength band emitted by the scintillator 122. Filter characteristics that limit transmission of the fluorescence wavelength band, or light in a wavelength band in which the pixel 72 has sensitivity, light that passes through the fluorescence wavelength band emitted by the scintillator 122 and that is not in the fluorescence wavelength band It may be possible to provide a filter characteristic that restricts the transmission of light. Even in this case, deterioration of the radiation image due to the influence of external light can be suppressed.

  In the above embodiment, the wavelength band in which the pixel 72 is sensitive is the visible light wavelength band. However, the wavelength band in which the pixel 72 is sensitive is the wavelength band other than the visible light wavelength band (for example, infrared Or ultraviolet light).

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above-described embodiment. It is apparent from the scope of the claims that the embodiments added with such changes or improvements can be included in the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 10 ... Radiation imaging system 12 ... Imaging stand 14 ... Subject 16 ... Radiation 18 ... Radiation source 20 ... Electronic cassette 24 ... Console 26 ... Display apparatus 28 ... Radiology information system 30 ... Medical information system 32 ... Panel part 34 ... Control part 70 ... Radiation conversion panel 72 ... Pixel 82 ... TFT 120 ... Substrate 122 ... Scintillator

Claims (5)

A substrate,
Pixels formed on the substrate;
A light conversion unit that converts radiation into light having sensitivity to the pixels;
A radiation imaging apparatus comprising:
The radiation imaging apparatus, wherein the substrate has a filter characteristic that restricts transmission of light in a wavelength band in which the pixel has sensitivity. The radiation imaging apparatus according to claim 1,
The radiation imaging apparatus, wherein the substrate has a filter characteristic that most restricts transmission of light having a wavelength at which the sensitivity of the pixel reaches a peak. The radiation imaging apparatus according to claim 1,
The radiation imaging apparatus according to claim 1, wherein the substrate has a filter characteristic that restricts transmission of light other than a wavelength band of light converted by the light conversion unit. The radiation imaging apparatus according to any one of claims 1 to 3,
The radiation conversion device, wherein the light conversion unit is provided on a side where radiation is incident on the pixel formed on the substrate. The radiation imaging apparatus according to claim 1,
The radiation conversion device, wherein the light conversion unit is provided on a side opposite to a side on which radiation is incident on a pixel formed on the substrate.

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