Patent Application
20140091209
1. Field of the Invention
The present invention generally relates to a radiation detecting apparatus, and more particularly, it relates to a laminate structure of a sensor panel and a light source unit in a radiation detecting apparatus which may be useful in, for example, a medical imaging apparatus used for diagnostic purposes, or a nondestructive inspection apparatus.
2. Description of Related Art
In a commercially available radiation detecting apparatus, a sensor panel having a light detecting sensor that detects light, and a scintillator layer that converts radiation into light are arranged one above the other. Such a radiation detecting apparatus is generally referred to as an indirect-type radiation detecting apparatus. In a known sensor panel, pixels formed of planarly-arranged or stacked photoelectric conversion elements and elements such as thin film transistors (TFT) are provided as light detecting sensors.
In the indirect-type radiation detecting apparatus described above, dark current sometimes occurs in still-image capturing. Dark current is caused by, for example, irradiation history of radiation, bias application history, a residual charge remaining within a photoelectric conversion element, or a trapped charge trapped in a lattice defect within the photoelectric conversion elements. In moving-image capturing in which images are acquired multiple times, the properties of the aforementioned elements sometimes change. A change in the properties of the photoelectric conversion elements generally results in an adverse effect on the characteristics of an obtained image. In particular, if photoelectric conversion elements each having a non-monocrystalline semiconductor layer composed of, for example, amorphous silicon are used, the photoelectric conversion elements would have many defects. Thus, the effect of a trapped charge trapped in a lattice defect is significant.
As a countermeasure, there is a known technology for improving the properties of the photoelectric conversion elements by disposing a light irradiation source at the rear side of the radiation detecting apparatus and making the light irradiation source radiate light toward the photoelectric conversion elements. This technology is also referred to as, for example, light resetting, bias light irradiation, or light calibration. In this technology, with the irradiation of light, an electric charge is forcedly generated by the photoelectric conversion elements and can be read out without being used as image information, or an electric charge equivalent to an amount to be taken into a lattice defect is generated so as to compensate for a crystal lattice defect level.
For the light irradiation source mentioned above, the use of a light source unit having a structure similar to that of a light source for a liquid crystal display device has been studied. Specifically, such a light source unit has light-emitting sources along an edge thereof and spreads light planarly by using a light guide plate, a diffusing plate, and a reflective plate. Generally, the structure of a light source unit having light-emitting sources along an edge thereof is as follows. Several light-emitting sources to several hundreds of light-emitting sources are arranged in contact with the light guide plate along one edge or two opposite edges of a rectangular unit. A reflective plate is disposed below the light guide plate in close contact therewith; and a diffusing plate is disposed above the light guide plate. Generally, the light guide plate, the reflective plate, and the diffusing plate are not adhered to one another by an adhesive or the like, but are simply disposed with air layers interposed therebetween so that the optical characteristics thereof can be maintained. Furthermore, in order to supply electric power to the light-emitting sources, flexible leading wiring is disposed below the light-emitting sources and is connected to an external power supply. Because the light source unit has the above-described structure, the components included in the light source unit are generally secured by using, for example, metal or plastic fasteners or a frame.
In order to reduce the overall thickness and weight of the radiation detecting apparatus, it is desirable that the light source unit be reduced in thickness and weight. Therefore, unlike in the configuration of a light source for a liquid crystal display device, which is fixed at a position distant from the sensor panel, the light source unit in a radiation detecting apparatus needs to be disposed in close contact with the rear face of the sensor panel. In this case, there are problems in terms of a method for bonding the sensor panel and the light source unit to each other as well as the flatness of the light source unit.
For example, Japanese Patent Laid-Open Nos. 2006-322746 and 2007-163216 each propose a method for bonding a light source unit to a sensor panel while maintaining the surface flatness of the entire light source unit by disposing a support member below a region excluding the region of the diffusing plate. However, in the configuration discussed in Japanese Patent Laid-Open No. 2006-322746, the periphery of the light source unit is supported by multiple components, including the support member, an electromagnetic shield, and the light sources, so that the surface flatness may be achieved. With this configuration, it is difficult to achieve complete flatness due to, for example, dimensional errors of the components. In addition, since the light source unit is bonded along the periphery thereof alone, there is a problem in terms of the strength thereof. In order to increase the strength, the sensor panel and the light source unit need to be fully adhered to each other by using, for example, an adhesive. Such full adhesion may lead to a loss of light diffusing effect of the diffusing plate of the light source unit. On the other hand, in the configuration discussed in Japanese Patent Laid-Open No. 2007-163216, the diffusing plate has the same size as the sensor panel. Therefore, in order to bond the sensor panel and the light source unit to each other without any differences in level therebetween, the sensor panel and the light source unit need to be fully adhered to each other by using, for example, an adhesive. As mentioned above, such full adhesion may lead to a loss of light diffusing effect of the diffusing plate.
In accordance with at least one embodiment of the present invention, the above-noted shortcomings of the related art are addressed by a radiation detecting apparatus having high surface flatness for a light source unit, a high light diffusing function, and high impact resistance while maintaining the light diffusing effect of the light source unit.
In one aspect of present invention, a radiation detecting apparatus includes a sensor panel that has a plurality of photoelectric conversion elements on one surface thereof; a light source unit that has a light guide plate, a light-emitting source disposed at a side surface of the light guide plate, a diffusing plate having a plurality of protrusions on a surface thereof and disposed at one surface of the light guide plate, and a reflective plate disposed at an opposite surface of the light guide plate from the one surface thereof; and a support substrate that supports the light source unit. The light source unit is provided between the sensor panel and the support substrate. The plurality of protrusions of the diffusing plate are in contact with an opposite surface of the sensor panel from the one surface thereof. The light source unit is adhered to the sensor panel via an adhesive member in a region excluding a region where the diffusing plate is disposed, and the adhesive member extends to the support substrate.
According to the present invention, the surface flatness of the light source unit can be maintained while the light diffusing effect is maintained. In addition, the impact resistance of the radiation detecting apparatus can be enhanced since the light source unit and the sensor panel are tightly adhered to each other by using the adhesive member.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Embodiments of the present invention will be described below with reference to the drawings. For the sake of convenience, with regard to each of radiation detecting apparatuses 100a to 100g according to embodiments, the side that receives radiation will be referred to as “upper side”, whereas the opposite side thereof will be referred to as “lower side”. Furthermore, a direction orthogonal to an incident direction of radiation will be referred to as “planar direction”. In each of the drawings, the direction in which radiation enters the radiation detecting apparatuses 100a to 100g is indicated by an arrow X. In each of the embodiments of the present invention, the term “radiation” refers to electromagnetic radiation including, for example, a γ ray, a β ray, in addition to X ray radiation.
The adhesive 6 is applied along the periphery of the light source unit 4. Specifically, in plan view from the incident direction of the radiation X, the diffusing plate 43, the light guide plate 44, and the reflective plate 45 have outside dimensions that are smaller than the outside dimensions of the sensor panel 1 and the support substrate 5. The adhesive 6 is applied so as to extend from the side surfaces of the diffusing plate 43, the light guide plate 44, and the reflective plate 45 to a surface of a peripheral region of the sensor panel 1. The adhesive 6 is also applied to a region where the light-emitting sources 41 and the flexible leading-wiring section 42 exist. This peripheral region has a freely-chosen width that ranges between several micrometers and several tens of millimeters from each side surface of the light source unit 4. In order to ensure the adhesivity from the side surfaces of the light source unit 4, it is desirable that the width be 5 mm or larger. However, the light-emitting region of the light source unit 4 (i.e., a region from which light is radiated toward the sensor panel 1) needs to be wider than the effective pixel region 32 of the sensor panel 1. Therefore, the peripheral region (i.e., an adhesive application region) needs to be narrower than the width measured from each edge of the sensor panel 1 to the effective pixel region 32.
The light-emitting sources 41 serve as light sources of the light source unit 4. For example, multiple small-size light-emitting sources 41 are arranged (as shown in
The flexible leading-wiring section 42 functions as power-supply wiring for driving the light-emitting sources 41. The light-emitting sources 41 are mounted on the flexible leading-wiring section 42. The flexible leading-wiring section 42 having the light-emitting sources 41 mounted thereon serves as a light-emitting-source unit. The flexible leading-wiring section 42 extends along an edge of the light guide plate 44 along which the light-emitting sources 41 are mounted. The flexible leading-wiring section 42 is fixed to a surface of the reflective plate 45 by using, for example, adhesive tape. Furthermore, the flexible leading-wiring section 42 is provided with a connection section to be connected to the outside.
The light guide plate 44 is a plate-shaped optical member having a function of uniformly guiding the light emitted by the light-emitting sources 41 toward the diffusing plate 43 while spreading the light in the planar direction. A reflective dot pattern is formed over the surface of the light guide plate 44 facing away from the diffusing plate 43 by, for example, printing. Light entering the light guide plate 44 spreads over a wide range in the planar direction by repeatedly undergoing surface reflection. When the light becomes incident on the reflective dot pattern, the light is diffused so that light having a strong rectilinear advance property toward the diffusing plate 43 is produced. Thus, the light is radiated toward the diffusing plate 43 while being guided over a wide range in the planar direction. By changing the pitch or the diameter of the reflective dot pattern, the degree of light diffusion can be adjusted. Thus, the intensity of light emitted from a freely-chosen area can be increased. Alternatively, a configuration in which adjustment is performed to make the entire light guide plate 44 emit light uniformly is also permissible. The light guide plate 44 is an organic/inorganic resin material, such as PET. The light guide plate 44 has a thickness of, for example, about several hundreds of micrometers to several millimeters, and is generally the thickest layer in the light source unit 4.
The diffusing plate 43 has a function of radiating the light emitted by the light-emitting sources 41 and propagated through the light guide plate 44 toward the sensor panel 1 while diffusing the light in the planar direction. The surface of the diffusing plate 43 is provided with a plurality of protrusions. The protrusions of the diffusing plate 43 come into contact with the surface of the sensor panel 1 that is opposite the surface thereof provided with the photoelectric conversion elements 13. When the light travels through the plurality of protrusions and is radiated to the outside (i.e., atmosphere), the light is diffused by being refracted in various directions. Accordingly, the diffusing plate 43 diffuses the light by utilizing light refraction, which is caused by a difference between the refractive index of the material and the refractive index of an air layer that is in contact with the surface from which the light is output, and a change in the light output direction caused by the irregular shape of the surface. Therefore, if the surface of the diffusing plate 43 provided with the protrusions is embedded with, for example, an adhesive having the same refractive index as the material of the diffusing plate 43 (i.e., if the surface is not in contact with an air layer), the light diffusing effect of the diffusing plate 43 may possibly deteriorate. The diffusing plate 43 is desirably composed of, for example, PET. The diffusing plate 43 has a thickness of, for example, several micrometers to several millimeters. The protrusions on the surface desirably have a size (i.e., average roughness Ra along the center line) of, for example, 0.1 μm to 100 μm, and more desirably, 0.5 μm to 10 μm. The average roughness Ra along the center line is measured at a suitable length within a measurement length range of 0.08 mm to 25 mm.
The reflective plate 45 has a function of enhancing the light guiding performance of the light guide plate 44 as well as increasing the amount of light output toward the diffusing plate 43. The light emitted by the light-emitting sources 41 and the light output toward the opposite side of the diffusing plate 43 by the light guide plate 44 are reflected toward the light guide plate 44 by the reflective plate 45. The reflective plate 45 is desirably composed of, for example, PET or metal. The reflective plate 45 has a thickness of several micrometers to several millimeters. The surface of the reflective plate 45 that faces away from the light guide plate 44 is the outermost section of the light source unit 4. Therefore, this surface is given a scratch-proof or dent-proof treatment or is configured not to be affected by the surface texture pixels at the light guide plate 44 side of the reflective plate 45 even if the surface becomes, for example, scratched or dent.
The support substrate 5 is disposed below the reflective plate 45 of the light source unit 4 (i.e., at the side of the reflective plate 45 facing away from the light guide plate 44) and is adhered to the sensor panel 1 via the adhesive 6. The support substrate 5 is formed of a thin sheet member or a rigid plate member. In particular, the support substrate 5 is desirably a rigid plate member since it supports the light source unit 4. Furthermore, the support substrate 5 has high flatness. The support substrate 5 is desirably composed of, for example, a resin material, such as PET, or a metallic material, such as Al, Au, SUS, or Pb. The support substrate 5 may have a thickness selected from a wide thickness range. For example, the thickness may range between several micrometers and several centimeters. The support substrate 5 and the light source unit 4 are bonded to each other by using the adhesive 6. Alternatively, the two may be bonded to each other by using a material other than the adhesive 6. In addition, the reflective plate 45 and the support substrate 5 may be bonded to each other by using an adhesive. However, in that case, the reflective plate 45 is bonded to the support substrate 5 in a state where the flatness of the support substrate 5 is maintained. In plan view from the incident direction of the radiation X, the support substrate 5 has the same size as the sensor panel 1 or is larger than the sensor panel 1.
The adhesive 6 is used for adhering (joining) the sensor panel 1 and the support substrate 5 to each other. Moreover, the adhesive 6 is also in contact with the layers (i.e., the diffusing plate 43, the light guide plate 44, and the reflective plate 45) of the light source unit 4, the light-emitting sources 41, and the flexible leading-wiring section 42, and has a function of fixing these components in position. Therefore, the adhesive 6 is applied so as to extend to (or reach) both the sensor panel 1 and the support substrate 5 from the side surfaces of the light source unit 4. In plan view from the incident direction of the radiation X, the light source unit 4 has outside dimensions that are smaller than the outside dimensions of the sensor panel 1 and the outside dimensions of the support substrate 5. Therefore, when the sensor panel 1, the light source unit 4, and the support substrate 5 are stacked, a groove-like region is formed around the outer periphery thereof. The adhesive 6 is applied to this groove-like region. Consequently, the sensor panel 1, the light source unit 4, and the support substrate 5 become adhered to each other. As shown in
The scintillator layer 7 converts radiation radiated from an external radiation source into light with a wavelength that can be detected by the photoelectric conversion elements 13. For example, a scintillator having a columnar crystal structure is known. The scintillator layer 7 having a columnar crystal structure is composed of a material containing alkali halide as a main component. Specific examples of the material of the scintillator layer 7 include CsI:Tl, CsI:Na, CsBr:Tl, NaI:Tl, LiI:Eu, and KI:Tl. If CsI is used, for example, the scintillator layer 7 can be fabricated by simultaneously depositing CsI and TlI over the sensor panel 1. Alternatively, for example, a scintillator in the form of particles or a scintillator in the form of a paste may be used as the scintillator layer 7. The scintillator layer 7 desirably has a thickness of several tens of micrometers to 1000 micrometers.
Of the light converted from radiation by and emitted from the scintillator layer 7, the reflective layer 9 reflects the light traveling away from the sensor panel 1 so as to guide the light toward the sensor panel 1. The reflective layer 9 enhances the light utilization efficiency in this manner. The reflective layer 9 may desirably be formed of a highly-reflective metal thin film composed of, for example, Al or Au, or metallic foil. Alternatively, the reflective layer 9 may be composed of, for example, a highly-reflective plastic material. The reflective layer 9 desirably has a thickness of 1 μm to 100 μm. If the reflective layer 9 is thinner than 1 μm, pin hole defects may easily occur during the formation process of the reflective layer 9. On the other hand, a reflective layer 9 thicker than 100 μm absorbs a large amount of radiation, possibly leading to a lower image quality of an acquired image or to an increased radiation dosage in a subject when capturing an image thereof.
The reflective-layer adhesive layer 8 is used for bonding the surface of the scintillator layer 7 (i.e., a scintillator protection layer (not shown) provided on the surface of the scintillator layer 7) and the reflective layer 9 to each other. The reflective-layer adhesive layer 8 may be, for example, a double-faced adhesive sheet or a liquid-curing-type adhesive. The reflective-layer adhesive layer 8 desirably has a thickness of 10 μm to 200 μm. With a reflective-layer adhesive layer 8 thinner than 10 μm, sufficient adhesive strength cannot be obtained, possibly causing the scintillator layer 7 and the reflective layer 9 to separate from each other. A reflective-layer adhesive layer 8 with a thickness larger than or equal to 200 μm may cause the light generated at the scintillator layer 7 or the light reflected by the reflective layer 9 to scatter readily at the reflective-layer adhesive layer 8. This may possibly lead to lower resolution of an image acquired by the radiation detecting apparatus 100a. The reflective-layer adhesive layer 8 may be composed of an organic material or an inorganic material. For example, the reflective-layer adhesive layer 8 may be composed of an acrylic-based, epoxy-based, silicon-based, natural-rubber-based, silica-based, urethane-based, ethylene-based, polyolefin-based, polyester-based, polyurethane-based, polyamide-based, or cellulose-based material. Any one of the above materials may be used alone, or a mixture of the above materials may be used. Alternatively, the reflective-layer adhesive layer 8 may be composed of hot-melt resin. Hot-melt resin is in its solid state at room temperature, does not contain a polarized solvent, water, or a solvent, and is defined as adhesive resin composed of a 100% nonvolatile thermoplastic material. Hot-melt resin melts as the temperature thereof increases, and solidifies as the temperature thereof decreases. Furthermore, hot-melt resin in a thermally molten state has adhesivity to other organic materials and inorganic materials, but has no adhesivity in its solid state at room temperature. Hot-melt resin is different from adhesive resin of a solvent volatile curable type, which is formed by a solvent coating method after melting thermoplastic resin in a solvent. Hot-melt resin is also different from adhesive resin of a chemical reaction type, such as epoxy resin as a representative example, which is formed by chemical reaction. The reflective-layer adhesive layer 8 may be formed independently of other components. In that case, the reflective layer 9 and the reflective-layer protection layer 10 are bonded to the scintillator layer 7 by using the reflective-layer adhesive layer 8 that is independent of the two layers. Alternatively, the reflective-layer adhesive layer 8 may be provided on the reflective layer 9 and the reflective-layer protection layer 10 in advance such that these layers are integrated into a sheet. In that case, the reflective layer 9 and the reflective-layer protection layer 10 are bonded to the scintillator layer 7 by using the reflective-layer adhesive layer 8 integrated with the reflective layer 9 and the reflective-layer protection layer 10.
The reflective-layer protection layer 10 is composed of a material that prevents the reflective layer 9 from breaking due to an impact or from corroding due to, for example, moisture. For example, the reflective-layer protection layer 10 may be composed of a film material, such as polyethylene terephthalate, polycarbonate, vinyl chloride, polyethylene naphthalate, or polyimide. The reflective-layer protection layer 10 desirably has a thickness of 10 μm to 100 μm.
The wiring readout section 2 electrically connects the electrical connection section 14 and the wiring connection section 3. The wiring readout section 2 is electrically connected to the wiring connection section 3 by, for example, an anisotropic electro-conductive adhesive. The wiring connection section 3 has, for example, an IC component mounted thereon for reading out an electric signal converted by each photoelectric conversion element 13. For example, a tape carrier package (TCP) is desirably used as the wiring connection section 3.
According to the first embodiment of the present invention, the light source unit 4 and the sensor panel 1 can be tightly joined to each other with the adhesive 6. Therefore, the flatness of the light source unit 4 can be maintained. In addition, the impact resistance of the radiation detecting apparatus 100a can be enhanced. Moreover, the light diffusing effect of the diffusing plate 43 can be maintained.
The frame substrate 20 supports the sensor panel 1 and the light source unit 4. The frame substrate 20 is bonded to the support substrate 5 by using the substrate adhesive 19. The frame substrate 20 desirably has a thickness of several millimeters to several tens of millimeters. Since the frame substrate 20 needs enough strength to support the sensor panel 1 and the light source unit 4, the thickness thereof is desirably 10 mm or larger. The frame substrate 20 may be composed of metal, such as Al or SUS, or a resin material, such as PET. The frame substrate 20 is fixed to the lower cover frame 27 via the sensor fixation member 29 by using the screw 28. The frame substrate 20 may alternatively be configured to function as the support substrate 5. In that case, the substrate adhesive 19 is not necessary.
The front plate 25 is disposed at the outermost side of the radiation detecting apparatus 100b that receives the radiation X. Therefore, the front plate 25 is composed of a selected material that is harmless to humans and that has high radiation transmittance. Furthermore, the front plate 25 is desirably composed of a material that is highly resistant to, for example, impact and moisture. Specifically, the front plate 25 may be composed of carbon or CFRP. The front plate 25 has a thickness of several millimeters to several tens of millimeters.
The cover frame 201 includes the upper cover frame 26 and the lower cover frame 27. The upper cover frame 26 and the lower cover frame 27 constitute the housing 200 of the radiation detecting apparatus 100b together with the front plate 25. The housing 200 functions as a reinforcement member that ensures the strength of the radiation detecting apparatus 100b. The upper cover frame 26 and the lower cover frame 27 are composed of a lightweight material that is resistant to, for example, impact and vibration. For example, the cover frame 201 may be composed of a common resin material (plastic), an organic/inorganic resin material, or metal.
According to each of the above embodiments of the present invention, the surface flatness of the light source unit 4 can be maintained while the light diffusing effect of the diffusing plate 43 is maintained. Furthermore, since the light source unit 4 and the sensor panel 1 are tightly adhered to each other by the adhesive 6, the impact resistance of each of the radiation detecting apparatuses 100a to 100g can be enhanced.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. Furthermore, the embodiments described above are merely examples of the invention and may be combined, where appropriate.
This application claims the benefit of Japanese Patent Application No. 2012-219633 filed Oct. 1, 2012, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-219633 | Oct 2012 | JP | national |
