JP2012247401A - Radiographic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress deterioration of characteristics of CMOS sensors due to X-ray radiation, and prevent an image sensor from being damaged because of weight added in imaging.SOLUTION: A radiographic apparatus 7 has a low-energy absorption member 20, a sensor panel 25, and a scintillator 26 disposed in this order below a top plate 13 which is irradiated with X-rays. The sensor panel 25 includes plural CMOS sensors 33 provided with signal output circuits on a substrate composed of a single crystal Si. The low-energy absorption member 20 absorbs a low-energy component that causes deterioration of characteristics of the signal output circuits from X-rays having passed through the top plate 13, and a cushioning material 20b housed at the center of the low-energy absorption member 20 protects the CMOS sensors 33 from being damaged because of an impact or a load applied to the top plate 13.

Description

  The present invention relates to a radiation imaging apparatus using a radiation detector that detects radiation and outputs image data of a radiation image. More specifically, the radiation imaging apparatus uses an image sensor made of a single crystal semiconductor for the radiation detector. About.

  In the medical field, a radiation imaging system that captures a subject using radiation, for example, X-rays, is known in order to perform image diagnosis. The radiation imaging system includes a radiation generation apparatus that irradiates an object with X-rays and a radiation imaging apparatus that receives an X-ray that has passed through the object and captures a radiation image of the object. The radiography system is a portable type with a flat-shaped casing in addition to a stationary type and a stationary type built in a standing-side imaging stand for imaging subjects in a standing position or a standing position. There is. The portable radiation imaging apparatus can also be used for an imaging method in which an image is taken by being inserted under a patient sleeping on a bed in a hospital room or the like.

  As a radiographic apparatus, a pixel unit that accumulates signal charges according to the amount of incident X-rays has a detection surface arranged in a matrix, and a signal charge is accumulated for each pixel unit on the detection surface, thereby A radiation detector that detects a radiation image representing the image information and outputs it as digital image data has been put into practical use.

  The radiation detector includes a TFT readout direct type, a TFT readout indirect type, and a CMOS readout indirect type. The TFT readout direct type receives X-rays with a photoelectric conversion layer made of a material that directly absorbs X-rays such as a-Se (amorphous selenium) and converts them into signal charges, and the generated signal charges are converted into TFT switches. This is a method of selectively reading out sequentially on a TFT panel using the. The TFT indirect type is a photoelectric conversion layer made of a material that converts X-rays into visible light by a scintillator and then absorbs visible light such as a-Si (amorphous silicon) and converts it into signal charges. Is received, and signal charges generated in the photoelectric conversion layer by this visible light are selectively read out sequentially by the TFT panel.

  In the CMOS readout indirect type, after converting X-rays into visible light by a scintillator, the visible light is photoelectrically converted by a CMOS image sensor (hereinafter referred to as a CMOS sensor), and a signal corresponding to visible light is read out. is there. A CMOS sensor made of a single crystal semiconductor such as silicon has a carrier mobility of 3 to 4 digits or more faster than a TFT panel made of a polycrystalline semiconductor such as a-Si, and peripheral circuits can be mounted together. Since variation in characteristics (for example, Vth) is small, it is suitable for high-quality shooting and moving image shooting that require high sensitivity, high S / N, and high-speed reading. In addition, since a CMOS sensor having a side of about 200 mm square from a 12-inch wafer can be manufactured at present, for example, there are four 17-inch square radiation detectors that are common as the size of a medical radiation detector. It can be configured by arranging the CMOS sensors.

JP 2005-249639 A JP 2010-077553 A

  In general, single crystal Si is used for the substrate of the CMOS sensor. However, since single crystal Si is brittle and easily broken, when a radiation detector comprising a CMOS sensor is used in a portable radiographic apparatus, it depends on the weight of the patient. A protection structure for preventing the CMOS sensor from being damaged is required, and the radiographic apparatus is increased in size.

  Further, it is known that a CMOS sensor made of single crystal Si undergoes characteristic degradation such as a change in the threshold voltage Vth of the MOS transistor and an increase in dark current due to X-ray irradiation. This is because in the MOS structure using single crystal Si, the charge at the boundary between the semiconductor and the oxide film (hereinafter referred to as interface charge) increases with the increase in absorbed dose. In addition, among the X-rays irradiated to the radiation imaging apparatus, it is considered that the low energy component of the X-rays that are not used for radiation imaging affects the characteristic deterioration of the CMOS sensor. That is, the high energy component of X-rays is transmitted through the CMOS sensor, but the low energy component of X-rays is absorbed by the CMOS sensor because there is not enough energy to pass through the CMOS sensor, and the interface charge is reduced. There is a possibility to increase.

  The characteristic deterioration due to the X-ray irradiation of the CMOS sensor is caused by X-rays in a so-called blank region where the detection surface of the radiation detector and the subject do not face each other when the size of the subject is smaller than the imaging range of the radiation imaging apparatus. Is particularly problematic because of direct irradiation.

  The above problem is the ISS (Irradiation Side Sampling) method, that is, from the X-ray incident side in the housing so that the X-ray incident surface on which the X-ray of the scintillator is incident and the detection surface of the radiation detector face each other. This is more conspicuous when a system in which the radiation detector and scintillator are arranged in this order is adopted. In the ISS system, the radiation detector and the scintillator are arranged in this order from the X-ray incident side, so the scintillator and the radiation detector are arranged in this order, and the side opposite to the X-ray incident surface of the scintillator. This is because, compared with a PSS (Penetration Side Sampling) system that detects light on the surface, the X-ray dose irradiated to the radiation detector increases.

  In Patent Document 1, a scattered radiation absorption grid that absorbs X-rays scattered by the subject is disposed between the subject and the radiation imaging apparatus, and the background region is irradiated on the outer periphery of the scattered radiation absorption grid. Further, there is disclosed a device provided with an absorption part that absorbs X-rays. Patent Document 2 discloses disposing a filter that increases the amount of absorption of X-rays that are irradiated on the radiation-absent region in the radiation generator. However, both the absorption part of patent document 1 and the filter of patent document 2 do not absorb the low energy component of X-rays, but absorb the high energy component necessary for imaging. In addition, Patent Documents 1 and 2 do not disclose prevention of characteristics deterioration or damage prevention of the CMOS sensor.

  In order to solve the above-described problem, the present invention suppresses deterioration of characteristics in an unacceptable region of an image sensor made of a single crystal semiconductor such as a CMOS sensor, and prevents damage to the image sensor due to weight applied during photographing. Objective.

  In order to solve the above problems, a radiation imaging apparatus of the present invention includes a scintillator that converts radiation into light, a sensor panel, a housing, and a low energy absorbing member. The sensor panel has a plurality of pixel units including a photoelectric conversion layer that converts light converted by the scintillator into electric charge, and a signal output circuit that outputs a signal corresponding to the electric charge converted by the photoelectric conversion layer, and outputs a signal. The circuit is provided on a single crystal semiconductor substrate. The housing includes a housing main body that houses the scintillator and the sensor panel, and a top plate that is disposed on an incident surface on which radiation is incident on the scintillator. The low energy absorbing member is disposed between the top plate and the sensor panel and absorbs at least a low energy component of radiation transmitted through the top plate.

  In order to reinforce the sensor panel, the sensor panel and the scintillator may be sequentially bonded to the low energy absorbing member. In addition, the low energy absorption member absorbs the low energy component at the peripheral part of the irradiation surface rather than the central part in order to achieve both the maintenance of the image quality of the radiation image and the suppression of the deterioration of the characteristics of the signal output circuit. It is preferable to configure so as to be small.

  In order to provide an in-plane distribution in the amount of absorption of the low energy component of the low energy absorbing member, the thickness of the central portion of the irradiation surface of the low energy absorbing member and the peripheral portion thereof may be different. Moreover, you may provide a recessed part in the center part of the irradiation surface of a low energy absorption member. A buffer material may be accommodated in the recess of the low energy absorbing member to protect the sensor panel. The depth of the recess may be configured to gradually decrease from the central portion in the irradiation surface toward the peripheral portion, or may gradually decrease from the central portion in the irradiation surface toward the peripheral portion. It may be configured.

  As another method of providing an in-plane distribution in the amount of absorption of the low energy component of the low energy absorbing member, a radiation absorbing layer that absorbs the low energy component of radiation may be provided at the periphery of the irradiation surface of the low energy absorbing member. . In order to suppress deterioration of the radiation image due to the absorption distribution of the low energy component of the low energy absorbing member, the radiation image may be corrected according to the absorption distribution of the low energy absorbing member. Further, for example, a CMOS type image sensor may be used for the sensor panel. In order to allow the sensor panel to be irradiated with radiation from which low energy components have been removed, it is desirable that the low energy absorbing member be larger in size in a plane perpendicular to the radiation irradiation direction than the sensor panel. Furthermore, in order to reduce the thickness of the entire apparatus, the low energy absorbing member is preferably bonded to the top plate.

  It is preferable that the material of the low energy absorbing member includes the same material as that of the source filter that absorbs at least a low energy component from the radiation emitted from the radiation generating device. According to this, since the energy distribution of the radiation that has passed through the radiation source filter and the radiation that has passed through the low energy absorbing member becomes the same, the low energy component of the radiation that has passed through the subject is absorbed by the low energy absorbing member. Can be suppressed.

  The low energy component of radiation is an energy component that is not used for radiography, and is, for example, an energy component that is ½ or less of the energy distribution of radiation emitted from the radiation generation apparatus.

  According to the radiation imaging apparatus of the present invention, the low energy absorbing member absorbs at least a low energy component from the radiation irradiated to the sensor panel, thereby suppressing deterioration in characteristics of the signal output circuit provided on the single crystal semiconductor substrate. can do. In addition, since the sensor panel is bonded to the low energy absorbing member, it is possible to reinforce a single crystal semiconductor substrate that is easily broken.

  Further, in the irradiation surface irradiated with radiation of the low energy absorbing member, the absorption amount of the low energy component in the central portion is made smaller than the absorption amount in the peripheral portion. It is possible to suppress deterioration of characteristics when radiation is directly applied to the signal output circuit of the unit.

It is a block diagram of a radiography system. It is a perspective view which shows a radiation imaging device partially broken. It is sectional drawing of a radiography apparatus. It is a bottom view which shows the sensor panel bonded together by the low energy absorption member. It is sectional drawing which shows the structure of a radiation detector roughly. It is a graph which shows the sensitivity area | region of a photoelectric converting layer, and the light emission area | region of a scintillator. It is a circuit diagram which shows the structure of a signal output circuit. It is a perspective view which shows the state in which the imaging | photography site | part of a to-be-photographed object is mounted on the top plate. It is a block diagram which shows the principal part structure of the electric system of a radiography apparatus. It is a block diagram which shows the principal part structure of the electrical system of a console and a radiation generator. It is sectional drawing of the low energy absorption member which changed the depth of the recessed part in steps. It is sectional drawing of the low energy absorption member which changed the depth of the recessed part gradually. It is sectional drawing of the low energy absorption member which provided the X-ray absorption layer in the peripheral part.

  As shown in FIG. 1, a radiation imaging system 5 using the present invention includes a radiation generator 6 that irradiates a subject H with X-rays, and a radiation imaging device that captures a radiation image based on X-rays transmitted through the subject H. 7 and a console 8 for controlling the radiation generator 6 and the radiation imaging apparatus 7.

  The radiation generator 6 includes a radiation source 6a and a radiation source filter 6b. The radiation source 6a includes an X-ray tube 6c that emits X-rays and an irradiation field limiter (collimator) 6d that limits the irradiation field of the X-rays emitted by the X-ray tube 6c. The X-ray tube 6c has a cathode made of a filament that emits thermoelectrons, and an anode (target) that emits X-rays when the thermoelectrons emitted from the cathode collide. The irradiation field limiter 6d has, for example, a plurality of lead plates that shield X-rays arranged in a cross pattern, and an irradiation opening that transmits X-rays is formed in the center, and moves the position of the lead plate. By changing the size of the irradiation aperture, the irradiation field is limited.

  The radiation source filter 6b removes low energy components that are scattered during transmission of the subject H from the X-rays radiated from the radiation source 6a and tend to cause deterioration of the radiation image. For the radiation source filter 6b, a material having a property of transmitting a high energy component of X-rays used for radiography and absorbing only a low energy component is used. As such a material, for example, aluminum is suitable.

  In addition, the high energy component and low energy component of X-ray in this embodiment differ with X-ray energy distribution radiated | emitted from the X-ray tube 6c. For example, when the tube voltage of the X-ray tube 6c is 70 kV and the maximum energy of X-rays radiated from the X-ray tube 6c is about 70 KeV, the X-ray energy distribution is approximately 15 to 70 KeV. In the present embodiment, ½ or less of the X-ray energy distribution, for example, 15 to 40 KeV is set as the low energy component, and more than that is set as the high energy component.

  As shown in FIG. 2, the radiation imaging apparatus 7 according to the present invention includes a housing 12 whose overall shape is approximately box-shaped and whose rectangular upper surface is a radiation irradiation surface 11. The case 12 includes a top plate 13 provided with an irradiation surface 11 and a case main body 14 other than the top plate 13. For example, the case main body 14 is made of ABS resin or the like, and the top plate 13 is made of, for example, carbon. Etc. Thereby, the intensity | strength of the top plate 13 is ensured, suppressing the absorption of the radiation by the top plate 13. FIG. The casing 12 is the same size as a conventional cassette having a configuration for recording an image on a photosensitive material by radiation. Accordingly, the radiation imaging apparatus 7 is portable like the cassette, and can perform the same radiation imaging instead of the cassette.

  The irradiation surface 11 of the radiation imaging apparatus 7 includes a plurality of LEDs, and displays the operation mode (for example, “ready state” and “data transmitting”) of the radiation imaging apparatus 7 and the operation status such as the remaining capacity of the battery. A display unit 16 is provided. In addition, the display part 16 may be comprised by light emitting elements other than LED, and may be comprised by display means, such as a liquid crystal display and an organic EL display. Further, the display unit 16 may be provided at a site other than the irradiation surface 11.

  A panel-shaped radiation detector 19 that detects X-rays transmitted through the subject H is disposed in the housing 12 of the radiation imaging apparatus 7 so as to face the irradiation surface 11. Further, between the top plate 13 and the radiation detector 19, at least a low energy component of the X-rays transmitted through the top plate 13 is absorbed, and the radiation detector 19 is applied from a load or an impact applied to the top plate 13. The low energy absorption member 20 which protects is arrange | positioned.

  Inside the housing 12, a case 23 for accommodating various electronic circuits including a microcomputer and a rechargeable and detachable battery (secondary battery) is provided at one end along the short side of the irradiation surface 11. Has been placed. Various electronic circuits of the radiation imaging apparatus 7 including the radiation detector 19 are operated by electric power supplied from a battery accommodated in the case 23. A radiation shielding member made of a lead plate or the like on the irradiation surface 11 side of the case 23 in the housing 12 in order to prevent various electronic circuits accommodated in the case 23 from being damaged due to X-ray irradiation. Is arranged.

  As shown in FIG. 3, the low energy absorbing member 20 is bonded to the entire inner surface of the top plate 13 with an adhesive. A radiation detector 19 is bonded to the lower surface of the low energy absorbing member 20 with an adhesive. In this way, by attaching the low energy absorbing member 20 and the radiation detector 19 to the top plate 13, the radiation imaging apparatus 7 can be thinned and the radiation detector 19 can be reinforced by the low energy absorbing member 20. The low energy absorbing member 20 preferably has an outer size equal to or larger than that of the radiation detector 19 so that the radiation detector 19 can be attached.

  The radiation detector 19 has a configuration in which a sensor panel 25 and a scintillator 26 are stacked from the irradiation surface 11 side along the direction in which radiation is irradiated. On the lower surface of the scintillator 26, a vapor deposition substrate 27 used when the scintillator 26 is formed is disposed. A sealant 28 is provided on the outer periphery of the radiation detector 19 to protect the scintillator 26 from moisture and the like. A control board 29 is disposed on the bottom surface in the housing 12. The control board 29 and the sensor panel 25 are electrically connected via a flexible cable 30.

The scintillator 26 transmits the subject H and is irradiated onto the irradiation surface 11 of the housing 12, absorbs X-rays transmitted through the top plate 13 and the sensor panel 25, and emits light. The scintillator 26, for example, CsI: Tl and (cesium iodide was added thallium)), CsI: Na (sodium-activated cesium _{iodide), GOS (Gd 2 O 2} S: Tb) materials can be used such as . In this embodiment, as the scintillator 26, a plurality of columnar crystals are formed along the light emission direction from the vapor deposition substrate 27 toward the sensor panel 25 by vapor-depositing CsI: Tl on the vapor deposition substrate 27. The average diameter of the columnar crystal is approximately uniform along the longitudinal direction of the columnar crystal.

  The light generated in the scintillator 26 travels through the columnar crystal by the light guide effect of the columnar crystal and is emitted to the sensor panel 25. At this time, since diffusion of light emitted to the sensor panel 25 side is suppressed, blurring of the radiation image detected by the radiation imaging apparatus 7 is suppressed. Further, since the light reaching the deep part of the scintillator 26 is provided on the inner surface of the vapor deposition substrate 27 and reflected by the reflective layer to the sensor panel 25 side, the amount of light incident on the sensor panel 25 (the light emitted from the scintillator 26). Detection efficiency).

  In the present embodiment, the sensor panel 25 is disposed on the radiation irradiation surface side of the scintillator 26. However, a method for arranging the scintillator and the sensor panel in such a positional relationship is “surface reading method (ISS: Irradiation). Side Sampling) ”. Since the scintillator emits light more strongly on the X-ray incident side, the surface reading method (ISS) in which the sensor panel is disposed on the X-ray incident side of the scintillator has the sensor panel disposed on the side opposite to the X-ray incident side of the scintillator. Since the sensor panel and the light emission position of the scintillator are closer than the reading method (PSS: Penetration Side Sampling), the resolution of the radiographic image obtained by imaging is high, and the amount of light received by the sensor panel increases. As a result, the sensitivity of the radiation imaging apparatus is improved.

  As shown in FIG. 4, the sensor panel 25 includes a CMOS image sensor (hereinafter referred to as a CMOS sensor) 33 in which a plurality of pixel units that accumulate signal charges corresponding to the amount of incident X-rays are arranged in a matrix. The area is increased by arranging four sheets. The CMOS sensor 33 has a large rectangular shape with a side length of about 200 mm, for example, and a general 17-inch square radiation detector is constituted by four CMOS sensors 33 as the size of a medical radiation detector. be able to.

  For the substrate of the CMOS sensor 33, silicon which is a single crystal semiconductor is used. Therefore, compared to TFT panels made of a polycrystalline semiconductor such as a-Si, carrier mobility is 3 to 4 digits or more faster, peripheral circuits can be mixedly mounted, and variations in manufacturing characteristics (for example, Vth) are small. It is suitable for high-quality shooting and moving image shooting that require high sensitivity, high S / N, and high-speed reading.

  As shown in FIG. 5, the CMOS sensor 33 is divided into a signal output layer 34 made of a substrate made of single crystal Si and an insulating layer formed on the substrate, and a signal output layer 34 for each of a plurality of pixel portions. The formed first electrode 35, the photoelectric conversion layer 36 having a single configuration common to the plurality of pixel portions formed under the first electrode 35, and the plurality of pixel portions formed under the photoelectric conversion layer 36 And a common second electrode 37 having a single structure. The scintillator 26 is bonded to the lower surface of the second electrode 37 with an adhesive.

  A photoelectric conversion element 38 (see FIG. 7) is configured by the first electrode 35 included in the pixel portion, and the photoelectric conversion layer 36 and the second electrode 37 at a position overlapping the first electrode 35 in plan view. In this photoelectric conversion element 38, by applying a bias voltage between the first electrode 35 and the second electrode 37, the signal charge generated in the photoelectric conversion layer 36 is moved to the first electrode 35, from which the signal charge is transferred. The signal output layer 34 can be extracted.

  Visible light converted by the scintillator 26 enters the second electrode 37 from below. The second electrode 37 is made of a conductive material (for example, ITO) that is transparent to the incident light because the light (visible light in the present embodiment) incident thereon needs to be incident on the photoelectric conversion layer 36. The The second electrode 37 has a single configuration common to all the pixel portions, but may be divided for each pixel portion.

  The photoelectric conversion layer 36 can generate signal charges corresponding to X-rays when used in combination with the scintillator 26. The photoelectric conversion layer 36 is made of an organic or inorganic photoelectric conversion material that absorbs visible light and generates a signal charge corresponding to the absorbed light amount. An example of the inorganic photoelectric conversion material is amorphous silicon (a-Si). Moreover, as an organic photoelectric conversion material, quinacridone is mentioned, for example. As shown in FIG. 6, the sensitivity of the organic photoelectric conversion material (OPC) made of quinacridone is higher than that of CsI: Na, single crystal Si (c-Si), etc., and the visible scintillator 26 made of CsI: Tl is generated. Since it is close to the wavelength range of light, high detection efficiency can be obtained. In order to enable high-quality image capturing and moving image capturing, it is preferable to use an organic photoelectric conversion material that has high carrier mobility and little manufacturing variation as the material of the photoelectric conversion layer 36.

  A signal output circuit 41 is provided in the signal output layer 34 corresponding to each photoelectric conversion element 38. The signal output circuit 41 converts the signal charge generated in the photoelectric conversion layer 36 of the corresponding photoelectric conversion element and moved to the first electrode 35 into a voltage signal corresponding to the amount of the signal charge, and is externally output by the signal output line S. For example, a known CMOS circuit is used. The signal output circuit 41 and the first electrode 35 are electrically connected by a contact wiring 42, and the signal charges collected by the first electrode 35 are transferred to the signal output circuit 41 through the contact wiring 42. Moved.

  As shown in FIG. 7, the signal output circuit 41 includes a reset transistor 44 that is a MOS transistor for resetting the accumulated signal charge, and a MOS transistor for converting the accumulated signal charge into a voltage signal and outputting the voltage signal. An output transistor 45, a row selection transistor 46 which is a MOS transistor for selectively outputting a voltage signal output from the output transistor 45 to the signal output line S, a reset line R for driving them, and a row selection Includes line L and the like.

  Of the signal output circuit 41, the reset line R, the row selection line L, and the signal output line S are generally made of aluminum and are not affected by the X-ray, but the reset transistor 44, the output transistor 45, and the row selection transistor 46 are not affected. Since it is formed of single crystal silicon, characteristic deterioration such as a change in threshold voltage Vth and an increase in dark current occurs due to X-ray irradiation. This is because in the MOS structure using single crystal Si, the charge at the boundary between the semiconductor and the oxide film (hereinafter referred to as interface charge) increases with the increase in absorbed dose. In this embodiment, the low energy absorbing member 20 is disposed so as to cover the sensor panel 25 in order to suppress the characteristic deterioration of the MOS transistor due to the X-ray irradiation.

  The low energy absorbing member 20 absorbs at least a low energy component that affects the characteristic deterioration of the MOS transistor from the X-rays transmitted through the top plate 13. The high energy component of the X-ray passes through the CMOS sensor 33, but the low energy component of the X-ray does not have enough energy to pass through the CMOS sensor 33 and is absorbed by the CMOS sensor 33. Therefore, the MOS transistor May increase the interfacial charge.

  The low energy absorbing member 20 is a plate-like body formed of a material that does not absorb much high energy components of X-rays used for radiography and absorbs a lot of low energy components. It is configured. The member of the low energy absorbing member 20 is preferably made of the same material as the above-described source filter 6b or a material containing the same material as the source filter 6b. By using the same material for the source filter 6b and the low energy absorbing member 20, the energy distribution of the X-rays transmitted through the source filter 6b and the X-rays transmitted through the low energy absorbing member 20 becomes the same. The low energy component of the X-ray that has passed through the subject H can be suppressed from being absorbed by the low energy absorbing member 20, and the loss of X-ray use is reduced.

  As shown in FIG. 8, in radiography using the radiographic apparatus 7, the imaging region of the subject H is often smaller than the imaging range of the radiation detector 19, and further, the imaging region of the subject H is the radiation detector 19. Most of the images are taken in the center of the shooting range. Therefore, the peripheral portion of the central portion where the imaging region of the subject H is arranged becomes a blank region where X-rays are directly irradiated without passing through the subject H, and the characteristic deterioration of the CMOS sensor 33 is likely to occur. Therefore, the X-rays irradiated to the radiation detector 19 are such that the central portion that affects the image quality of the radiation image has a small decrease in X-ray dose, and the peripheral portion corresponding to the blank region is less likely to deteriorate the characteristics of the CMOS sensor 33. It is desirable that at least the low energy component of X-rays is reduced.

  In order to solve the above problems, the low energy absorbing member 20 is provided with a concave portion 20a in the central portion of the surface on the top plate 13 side as shown in FIGS. By varying the thickness, the amount of X-ray absorption at the center is smaller than that at the periphery, and at least the low energy component of X-rays can be absorbed at the periphery so that the characteristics of the CMOS sensor 33 are not deteriorated. Yes. According to this, it is possible to simultaneously suppress the deterioration of the image quality of the radiation image and the characteristic deterioration of the CMOS sensor 33.

  As described above, when imaging is performed with the imaging region of the subject H placed on the top plate 13, the load of the subject H is applied to the top plate 13. The substrate of the CMOS sensor 33 constituting the sensor panel 25 is made of single crystal Si, which is a fragile material, and has a thickness of about several tens of μm. Therefore, depending on the load of the subject H applied to the top plate 13 A protective structure that does not break is required. In particular, in the sensor panel 25 using four CMOS sensors 33, if an impact or a load is applied to the center of the sensor panel 25, all four CMOS sensors 33 may be damaged, and the repair cost is very high. Become.

  In order to solve such a problem, in the present embodiment, the sensor panel 25 is reinforced by the low energy absorbing member 20 disposed between the top plate 13 and the sensor panel 25, and the inside of the recess 20a of the low energy absorbing member 20 is provided. By accommodating the cushioning material 20b, the load and impact applied to the central portion of the top plate 13 are absorbed. As the buffer material, sponge, rubber or the like can be used.

  FIG. 9 is a block diagram illustrating a configuration of the radiation imaging apparatus 7. The radiation imaging apparatus 7 includes a signal processing unit 50, an image memory 51, a control unit 52, a wireless communication unit 53, a power supply unit 54, and the like, in addition to the radiation detector 19 described above. The signal processing unit 50 includes an amplifier that amplifies the voltage signal output from each pixel unit of the sensor panel 25, a multiplexer, an A / D (analog / digital) converter, and the like, and the voltage output from the sensor panel 25. The signal is converted into digital image data.

  In addition, the signal processing unit 50 includes an image correction unit 50 a that corrects a radiation image in accordance with an absorption distribution of a low energy component of X-rays by the low energy absorption member 20. Since the low energy absorption member 20 has different thicknesses at the central portion and the peripheral portion, the low energy absorption amount differs between the central portion and the peripheral portion. The effect appears. The image correction unit 50a corrects the image data according to the absorption distribution of the low energy component of the low energy absorbing member 20, thereby removing the influence of the absorption distribution of the low energy absorbing member 20 from the radiation image represented by the image data. .

  An image memory 51 is connected to the signal processing unit 50, and the image data output from the image correction unit 50 a of the signal processing unit 50 is stored in order in the image memory 51. The image memory 51 has a storage capacity capable of storing image data for a plurality of frames, and image data obtained by imaging is sequentially stored in the image memory 51 every time a radiographic image is captured.

  The image memory 51 is connected to a control unit 52 that controls the overall operation of the radiation imaging apparatus 7. The control unit 52 includes a microcomputer, and includes a CPU 52a, a memory 52b including a ROM and a RAM, a nonvolatile storage unit 52c including an HDD (Hard Disk Drive), a flash memory, and the like.

  In addition, a wireless communication unit 53 is connected to the control unit 52. The wireless communication unit 53 is compatible with a wireless local area network (LAN) standard represented by IEEE (Institute of Electrical and Electronics Engineers) 802.11a / b / g / n, etc. Control the transmission of various information between them. The control unit 52 can wirelessly communicate with the console 8 (see FIG. 10) via the wireless communication unit 53, and can transmit and receive various types of information to and from the console 8.

  Further, the radiation imaging apparatus 7 is provided with a power supply unit 54, and the various electronic circuits (signal processing unit 50, image memory 51, control unit 52, wireless communication unit 53, etc.) described above are connected to the power supply unit 54. (Not shown), it is operated by the power supplied from the power supply 54. The power supply unit 54 incorporates the above-described battery (secondary battery) so as not to impair the portability of the radiation imaging apparatus 7, and supplies power from the charged battery to various electronic circuits. The signal processing unit 50, the image memory 51, the control unit 52, and the wireless communication unit 53 are provided in the case 23 described above or on the control board 29.

  As shown in FIG. 10, the console 8 is composed of a computer, a CPU 57 that controls the operation of the entire apparatus, a ROM 58 that stores various programs including a control program in advance, a RAM 59 that temporarily stores various data, and various data Are connected to each other via a bus. Further, a communication I / F unit 61 and a wireless communication unit 62 are connected to the bus, a display 63 is connected via a display driver 64, and an operation panel 65 is further connected via an operation input detection unit 66. .

  The communication I / F unit 61 is connected to the communication I / F unit 70 of the radiation generation apparatus 6 via the connection terminal 61 a, the communication cable 69, and the connection terminal 70 a of the radiation generation apparatus 6. The console 8 (the CPU 57) transmits / receives various information such as exposure conditions to / from the radiation generating apparatus 6 via the communication I / F unit 61. The wireless communication unit 62 has a function of performing wireless communication with the wireless communication unit 53 of the radiation imaging apparatus 7, and the console 8 (the CPU 57) transmits / receives various information such as image data to / from the radiation imaging apparatus 7. This is performed via the wireless communication unit 62. The display driver 64 generates and outputs a signal for displaying various information on the display 63, and the console 8 (the CPU 57) displays an operation menu, a captured radiation image, and the like on the display 63 via the display driver 64. Display. The operation panel 65 includes a plurality of keys, and various information and operation instructions are input. The operation input detection unit 66 detects an operation on the operation panel 65 and notifies the CPU 57 of the detection result.

  The radiation generator 6 includes a communication I / F unit 70 that transmits and receives various information such as an exposure condition between the radiation source 6 a and the console 8, and an exposure condition received from the console 8 (the exposure condition is changed to this exposure condition). Includes a tube voltage and tube current information), and a radiation source controller 72 for controlling the radiation source 6a.

  Next, the operation of this embodiment will be described. When a radiographic image is captured using the radiographic apparatus 7, a photographer (for example, a radiographer or the like) emits radiation with the irradiation surface 11 facing upward between the imaging target region of the subject H and the imaging table. The photographing device 7 is inserted, and a preparatory work for adjusting the orientation, position, etc. is performed.

  As shown in FIG. 8, when the imaging part of the subject H is directly placed on the top plate 13, an impact and a load when the imaging part of the subject H is placed are applied to the top plate 13. Since the impact and load are absorbed by the low energy absorbing member 20 and the buffer material 20b, the CMOS sensor 33 of the sensor panel 25 is not damaged.

  When the preparatory work is completed, the photographer operates the operation panel 65 to instruct the start of photographing. As a result, the console 8 transmits an instruction signal for instructing the start of exposure to the radiation generation apparatus 6, and the radiation generation apparatus 6 emits radiation from the radiation source 6a. The X-rays emitted from the radiation source 6a have low energy components absorbed by the radiation source filter 6b, are transmitted through the imaging region of the subject H, and are irradiated onto the irradiation surface 11 of the radiation imaging apparatus 7. The scintillator 26 is irradiated through the absorbing member 20 and the sensor panel 25.

  Since the low energy component of the X-rays transmitted through the top plate 13 is absorbed by the low energy absorbing member 20, the characteristic deterioration of each CMOS sensor 33 due to the absorption of the low energy component of the X-rays by the sensor panel 25 is suppressed. can do. In particular, since the low energy absorbing member 20 has a thicker peripheral edge than the central part, it can effectively suppress deterioration of characteristics due to direct irradiation of the X-rays to the blank region of the peripheral part. it can. Moreover, since the thickness of the center part of the low energy absorbing member 20 is thinner than that of the peripheral part, X-rays transmitted through the imaging region of the subject H are not absorbed more than necessary, and the radiation image is deteriorated. Do not generate.

  Most of the X-rays irradiated to the scintillator 26 are converted to light in the vicinity of the X-ray incident surface of the scintillator 26, that is, in the vicinity of the sensor panel 25, and travel toward the sensor panel 25. Of the light generated by the scintillator 26, the light directed toward the vapor deposition substrate 27 is reflected by the reflective layer of the vapor deposition substrate 27 and travels toward the sensor panel 25. Thereby, the resolution of the radiographic image obtained by imaging is high, and the amount of light received by the sensor panel 25 is increased. As a result, the sensitivity of the radiographic apparatus 7 is improved. Moreover, since the light which goes to the sensor panel 25 from the scintillator 26 is guided by the columnar crystal of the scintillator 26 made of CsI: Tl, image blurring is suppressed.

  The visible light converted by the scintillator 26 passes through the second electrode 37 and enters the photoelectric conversion layer 36, where it is converted into signal charges. After the exposure is completed, the signal charge generated in the photoelectric conversion layer 36 is converted into a voltage signal by the signal output circuit 41, and this voltage signal is sequentially output from each pixel. The output voltage signal is converted into image data by the signal processing unit 50. The image correcting unit 50 a corrects the image data according to the absorption distribution of the low energy component of the X-rays by the low energy absorbing member 20 and stores the corrected image data in the image memory 51. The CPU 52 a transmits the image data stored in the image memory 51 to the console 8 through the wireless communication unit 53. The CPU 57 of the console 8 stores the image data received from the radiation imaging apparatus 7 in the HDD 60 via the RAM 59. In addition, the CPU 57 causes the display 63 to display a radiation image composed of image data stored in the HDD 60 via the display driver 64.

  As described above, since the low energy absorbing member 20 absorbs at least a low energy component from the X-rays irradiated to the sensor panel 25, the characteristic deterioration of the CMOS sensor 33 can be suppressed. Further, since the absorption amount of the low energy component is made different between the central portion and the peripheral portion of the low energy absorbing member 20, the characteristic deterioration of the CMOS sensor 33 in the unexposed region is suppressed while maintaining the image quality of the radiation image. be able to. Furthermore, since the impact and load applied to the top plate 13 can be received by the low energy absorbing member 20 and the buffer material 20b, the sensor panel 25 can be prevented from being damaged. These effects can be particularly remarkable in the ISS type radiation detector 19 in which the sensor panel 25 is disposed on the X-ray irradiation side.

  In the above embodiment, the low energy absorbing member 20 is provided with the concave portion 20a having a constant depth. However, as shown in FIG. 11, the concave portion 20d whose depth gradually decreases as it approaches the peripheral portion, As shown in FIG. 12, a recess 20e whose depth gradually decreases as it approaches the peripheral edge may be used. Further, as shown in FIG. 13, an X-ray absorption layer 20f may be provided on one surface of the low energy absorption member 20 so as to cover the peripheral portion. The X-ray absorption layer 20f is preferably a metal layer that is excellent in absorbing low-energy components of X-rays. For example, a metal having an atomic number of about 20 to 31 is applicable.

  Moreover, although the recessed part 20a of the low energy absorption member 20 was provided in the top plate 13 side, you may provide in the sensor panel 25 side. Further, when the image quality of the radiation image does not deteriorate due to the X-ray absorption of the low energy absorbing member 20, the recess may be omitted from the low energy absorbing member 20. In this case, the cushioning material housed in the recess is also omitted, but the sensor panel 25 can be prevented from being damaged by the low energy absorbing member 20 alone.

  In addition, the low energy component absorbing member 20 absorbs the low energy component of the X-ray. However, when the characteristic deterioration of the CMOS sensor is caused by the high energy component of the X ray, the low energy component absorbing member 20 High energy components may also be absorbed.

  In order to give flexibility to the CMOS sensor, the CMOS sensor may be composed of an organic thin film transistor formed on a plastic film. The organic thin film transistor is described in detail in “Tsuyoshi Sekitani,“ Flexible organic transistors and circuits with extreme bending stability ”, Nature Materials 9, November 7, 2010, p.1015-1022”. Detailed description is omitted.

  In order to give flexibility to the CMOS sensor, a structure in which a photodiode and a transistor formed of single crystal Si are arranged on a flexible plastic substrate may be used. For the placement of photodiodes and transistors on a plastic substrate, for example, Fluidic Self-, which is a technology that disperses device blocks of about several tens of microns in a solution and places them at a required position on an arbitrary substrate. Assembly (FSA) method can be used. As for the FSA method, “Koichi Maezawa,“ Resonant Tunnel Device Block Fabrication Technology for Fluidic Self-Assembly ””, IEICE Technical Report ED, Electronic Devices, The Institute of Electronics, Information and Communication Engineers, June 2008 6th, 108, 87, p.67-71 ", detailed description will be omitted.

  In the above embodiment, the CMOS sensor has been described as an example. However, the present invention uses a single crystal semiconductor substrate as in the CMOS sensor, and performs radiography using a CCD image sensor in which characteristic deterioration occurs due to X-ray irradiation. It can also be applied to devices. Further, although an ISS type radiation detector has been described as an example, the present invention is also applicable to a PSS type radiation detector. Furthermore, the present invention can also be applied to a direct conversion type radiation detector that converts X-rays into electric charges by a photoelectric conversion layer.

  In addition, although the example in which the radiation detector is incorporated in the cassette-size housing has been described, it is also possible to incorporate the radiation detector in a standing type or a standing type imaging apparatus or a mammography apparatus. Moreover, although X-rays have been described as an example of radiation, the present invention may use radiation other than X-rays, such as γ-rays. In addition, it is needless to say that the configuration of the radiation imaging apparatus according to the present invention described in the above embodiment is an example, and can be appropriately changed without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 5 Radiation imaging system 6 Radiation generator 6b Radiation source filter 7 Radiography apparatus 19 Radiation detector 20 Low energy absorption member 20a Recess 20b Buffer material 25 Sensor panel 26 Scintillator 33 CMOS sensor 41 Signal output circuit 36 Photoelectric conversion layer

Claims (15)

A scintillator that converts radiation into light;
A plurality of pixel units each including a photoelectric conversion layer that converts light converted by the scintillator into electric charge, and a signal output circuit that outputs a signal corresponding to the electric charge converted by the photoelectric conversion layer; A sensor panel provided on a single crystal semiconductor substrate;
A housing having a housing main body for housing the scintillator and the sensor panel, and a top plate disposed on an incident surface on which radiation is incident on the scintillator;
A low energy absorbing member disposed between the top plate and the sensor panel and absorbing at least a low energy component of radiation transmitted through the top plate;
A radiation imaging apparatus comprising:   The radiation imaging apparatus according to claim 1, wherein the sensor panel and the scintillator are sequentially bonded to the low energy absorbing member.   The radiographic apparatus according to claim 2, wherein the low energy absorbing member has a smaller amount of absorption of the low energy component in the peripheral portion than in the central portion of the irradiation surface irradiated with radiation.   The radiation imaging apparatus according to claim 3, wherein the low energy absorbing member has different thicknesses at a central portion and a peripheral portion of the irradiation surface.   The radiation imaging apparatus according to claim 4, wherein the low energy absorbing member is provided with a recess in a central portion of the irradiation surface.   The radiation imaging apparatus according to claim 5, wherein a buffer material is accommodated in the recess.   The radiation imaging apparatus according to claim 5 or 6, wherein a depth of the concave portion is gradually reduced from a central portion in the irradiation surface toward a peripheral portion.   The radiation imaging apparatus according to claim 5, wherein a depth of the concave portion is gradually shallower from a central portion in the irradiation surface toward a peripheral portion.   The radiation imaging apparatus according to claim 3, wherein the low energy absorbing member is provided with a radiation absorbing layer that absorbs a low energy component of radiation at a peripheral portion of the irradiation surface.   The radiation imaging apparatus according to claim 2, further comprising an image correction unit that corrects a radiation image according to an absorption distribution of a low energy component of the low energy absorbing member.   The radiation imaging apparatus according to claim 1, wherein the sensor panel is a CMOS image sensor.   The radiation imaging apparatus according to claim 1, wherein the low energy absorbing member has a size in a plane orthogonal to a radiation irradiation direction larger than that of the sensor panel.   The radiation imaging apparatus according to claim 1, wherein the low energy absorbing member is bonded to the top plate.   The material of the said low energy absorption member contains the same material as the radiation source filter which absorbs at least a low energy component from the radiation radiated | emitted from the radiation generator, The one of Claims 1-13 characterized by the above-mentioned. Radiography equipment.   The low-energy component of the radiation is an energy component that is not used for radiography, and is an energy component that is ½ or less of the energy distribution of the radiation emitted from the radiation generator. 14. The radiation imaging apparatus according to any one of 14.

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