Scintillator panel and radiation imaging device

Abstract

To provide a technology advantageous for improving MTF while suppressing reduction in DQE.SOLUTION: A scintillator panel comprises: a support; a scintillator that generates light in response to incident radiation; a light reflection layer that is arranged between the support and the scintillator, and reflects the light; a semi-transmissive layer that is arranged between the light reflection layer and the scintillator, and reflects part of the light and transmits the other part; and an optical adjustment layer that is arranged between the light reflection layer and the semi-transmissive layer, and adjusts an optical distance between the reflection layer and the semi-transmissive layer to a length at which the light resonates.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a scintillator panel and a radiation imaging device. [Background technology]

[0002] Flat panel detectors (FPDs) used in radiography for medical image diagnosis and non-destructive testing include indirect conversion type FPDs, which convert radiation passing through a subject into light using a scintillator and detect the light emitted by the scintillator using a light receiving element. FPDs are required to be able to clearly depict smaller objects for the purpose of early detection of lesions and miniaturization of medical devices such as stents implanted in the body. In other words, FPDs are required to have a high modulation transfer function (MTF) and high detective quantum efficiency (DQE). Patent Document 1 shows that when forming a scintillator layer, the crystallinity of the columnar crystals at the initial stage of formation is improved to improve the sharpness (MTF), and the luminance (DQE) is improved by arranging a reflective layer on the opposite side of the scintillator layer from the sensor panel. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-061637 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the scintillator layer, it is difficult to completely prevent the generated light from diffusing between the columnar crystals. Furthermore, when a reflective layer is provided as shown in Patent Document 1, the DQE increases, but the amount of scattered light increases relatively, resulting in a decrease in the MTF.

[0005] An object of the present invention is to provide a technique that is advantageous for improving MTF while suppressing a decrease in DQE. [Means for solving the problem]

[0006] In view of the above problems, a scintillator panel according to an embodiment of the present invention is characterized in that it includes a support, a scintillator that generates light in response to incident radiation, a light reflecting layer arranged between the support and the scintillator and that reflects the light, a semi-transmitting layer arranged between the light reflecting layer and the scintillator and that reflects part of the light and transmits the other part, and an optical adjustment layer arranged between the light reflecting layer and the semi-transmitting layer for adjusting the optical distance between the reflecting layer and the semi-transmitting layer to a length at which the light resonates. Effect of the Invention

[0007] The above-mentioned means provides a technique that is advantageous for improving MTF while suppressing a decrease in DQE. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of a radiation imaging device using a scintillator panel according to an embodiment of the present invention. [Diagram 2] 2 is a graph showing an example of the emission spectrum of a scintillator used in the scintillator panel of FIG. 1. [Diagram 3] 2 is a graph showing the reflectance of the light-reflecting member of the scintillator panel of FIG. 1 and a scintillator panel of a comparative example at an incident angle of 5°. [Figure 4] 2 is a graph showing the reflectance of the light-reflecting member of the scintillator panel of FIG. 1 and a scintillator panel of a comparative example at an incident angle of 45°. [Diagram 5] 2 is a graph showing the angle dependency of reflected light from a light reflecting member of the scintillator panel of FIG. 1. [Figure 6] 13 is a graph showing the angle dependency of reflected light from a light reflecting member of a scintillator panel of a comparative example. [Figure 7] FIG. 2 is a diagram showing a modification of the radiation imaging apparatus in FIG. [Figure 8]FIG. 2 is a diagram showing a scintillator used in the scintillator panel of FIG. [Figure 9] FIG. 2 is a diagram showing a scintillator used in the scintillator panel of FIG. [Figure 10] 2 is a graph showing the characteristics of the scintillator panel of FIG. 1 and a scintillator panel of a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the embodiments will be described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims. Although the embodiments describe a number of features, not all of these features are essential to the invention, and the features may be combined in any manner. Furthermore, in the attached drawings, the same reference numbers are used for the same or similar configurations, and duplicated descriptions are omitted.

[0010] Furthermore, radiation in the present invention may include α-rays, β-rays, γ-rays, and the like, which are beams produced by particles (including photons) emitted by radioactive decay, as well as beams having the same or greater energy, such as X-rays, particle beams, and cosmic rays.

[0011] A scintillator panel according to this embodiment and a radiation imaging device using the scintillator panel will be described with reference to Figs. 1 to 10. Fig. 1 shows an example of the configuration of a radiation imaging device 200 using a scintillator panel 100 according to this embodiment. The radiation imaging device 200 includes the scintillator panel 100 and a sensor panel 201 for receiving light emitted from a scintillator 101 included in the scintillator panel 100. The sensor panel 201 includes a plurality of imaging elements and converts an optical image output from the scintillator 101 into an electrical signal. Radiation 202 may be irradiated from the side of the scintillator panel 100 as shown in Fig. 1, or may be irradiated from the side of the sensor panel 201.

[0012] As shown in FIG. 1, the scintillator panel 100 includes a support 102, a light reflecting layer 103, an optical adjustment layer 104, a semi-transmitting layer 105, and a scintillator 101. The scintillator 101 generates light in response to incident radiation. The light reflecting layer 103 is disposed between the support 102 and the scintillator 101, and reflects light emitted by the scintillator 101. The semi-transmitting layer 105 is disposed between the light reflecting layer 103 and the scintillator 101, and reflects a portion of the light emitted by the scintillator 101 and transmits the other portion. The optical adjustment layer 104 is disposed between the light reflecting layer 103 and the semi-transmitting layer 105, and sets the optical distance between the light reflecting layer 103 and the semi-transmitting layer 105 to a length at which the light emitted by the scintillator 101 resonates. Here, the combination of the support 102, the light reflecting layer 103, the optical adjustment layer 104, and the semi-transmitting layer 105 may be referred to as a light reflecting member 107. In addition, as shown in Fig. 1, a protective layer 106 may be further included between the scintillator 101 and the semi-transmitting layer 105. Here, the light reflecting member 107 may include the protective layer 106. The protective layer 106 will be described later.

[0013] The scintillator panel 100 (scintillator 101) is sealed with a protective film (not shown), thereby preventing the infiltration of moisture and preventing deterioration of the characteristics of the scintillator 101. The protective film is not particularly limited as long as it has moisture resistance, and various materials can be used. From the viewpoints of moisture resistance and covering properties, parylene (paraxylylene-based polymer) or the like may be used as the protective film.

[0014] The support 102 is a member for holding the light reflecting layer 103, the optical adjustment layer 104, the semi-transmitting layer 105, and the protective layer 106, which are components of the light reflecting member 107. In addition, in the configuration shown in FIG. 1, the support 102 transmits radiation 202. As the support 102, various materials can be used without particular limitation as long as it can hold each component of the light reflecting member 107 and transmit radiation 202. For example, glass, amorphous carbon, plastic, metal, or a composite material combining these materials may be used as the support 102. When a metal is used as the support 102, the support 102 can also function as the light reflecting layer 103 described later.

[0015] A light reflecting layer 103 is disposed on the support 102. By providing the light reflecting layer 103, light traveling from the scintillator 101 in the opposite direction to the sensor panel 201 is reflected toward the sensor panel 201, making it possible to efficiently utilize the light generated by the scintillator 101. In other words, it is possible to improve the detective quantum efficiency (DQE).

[0016] The light reflecting layer 103 may be made of a metal material such as silver (Ag), aluminum (Al), platinum (Pt), or gold (Au). The light reflecting layer 103 may be made of one material or a plurality of types of materials. That is, the light reflecting layer 103 may contain at least one of silver, aluminum, platinum, and gold. For example, when a material having high reflectance and containing silver as a main component is used as the light reflecting layer 103, the effect of the present embodiment described below may be significantly exhibited. Here, the main component of the light reflecting layer 103 refers to a material that contains the most component in weight ratio or molar ratio among the materials that constitute the light reflecting layer 103.

[0017] The light reflecting layer 103 can be formed by depositing the above-mentioned metal material on the support 102 using a deposition method, a sputtering method, or the like. From the viewpoints of reflectance, flatness, uniformity, and the like, the light reflecting layer 103 may be formed using a sputtering method. Also, as described above, a metal material such as aluminum may be used for the support 102 and function as the light reflecting layer 103.

[0018] The optical adjustment layer 104 is disposed between the light reflecting layer 103 and the semi-transmitting layer 105, and sets the optical distance between the light reflecting layer 103 and the semi-transmitting layer 105 to a length at which the light emitted by the scintillator 101 resonates. More specifically, the optical adjustment layer 104 is a layer used to act as an optical resonator that maintains the reflectance of a specific wavelength (in this embodiment, the peak wavelength of the light emitted by the scintillator 101) by the optical resonance effect, while reducing the reflectance of light of other wavelengths. The optical adjustment layer 104 is not particularly limited as long as it is a layer that satisfies the following optical distance, and various materials can be used.

[0019] The optical path length L [nm] of the optical adjustment layer 104 is required to satisfy the following formula (1). (λ / 4)×(-1-(φ / π)) <L<(λ / 4)×(1-(φ / π))···(1) Here, λ [nm] is the peak wavelength of light emitted by the scintillator 101. φ [rad] is the sum of the phase shifts of light with wavelength λ [nm] in the light reflecting layer 103 and the semi-transmitting layer 105. φ is a negative value.

[0020] The optical distance L is determined by the refractive index n and film thickness l [nm] of the optical adjustment layer 104 at a wavelength λ [nm], as shown in the following formula (2): L = n × l (2) Therefore, by adjusting the film thickness l [nm] according to the refractive index n of the material of the optical adjustment layer 104, it is possible to adjust the resonance wavelength.

[0021] A transparent inorganic material or a transparent resin may be used as the optical adjustment layer 104. For example, the optical adjustment layer 104 may include at least one of silicon oxide (SiO2), aluminum oxide (Al2O3), titanium (IV) oxide (TiO2), tantalum oxide (Ta2O5), indium tin oxide (ITO), zinc oxide (ZnO, ZnO:Al, ZnO:Ga), acrylic resin (PMMA), polyethylene terephthalate (PET), polycarbonate (PC), and the like. As shown in FIG. 1, the optical adjustment layer 104 may have a single-layer structure using the above-mentioned materials. In addition, the optical adjustment layer 104 may have a multi-layer structure using the above-mentioned materials, but since consideration must be given to reflection at the interface, a single-layer structure may be easier to design than a laminated structure.

[0022] Depending on the material used, the optical adjustment layer 104 can be formed by a deposition method, a sputtering method, a spin coating method, a slit coating method, a spraying method, etc. From the viewpoint of flatness, uniformity, etc., the optical adjustment layer 104 may be formed by a sputtering method in the case of a transparent inorganic material, and may be formed by a spin coating method in the case of a transparent resin.

[0023] The semi-transmitting layer 105 is an extremely thin metal film, and is a layer that has both a function of transmitting light and a function of reflecting light. A part of the light incident on the semi-transmitting layer 105 from the scintillator 101 passes through the semi-transmitting layer 105 and the optical adjustment layer 104, and is reflected by the light reflecting layer 103, and further, a part of the reflected light is reflected again by the semi-transmitting layer 105. This action generates an optical resonance effect, and depending on the film thickness of the optical adjustment layer 104, it acts as an optical resonator that maintains the reflectance of light of a specific wavelength while reducing the reflectance of light of the other wavelengths.

[0024] The semi-transmitting layer 105 may contain at least one of silver, aluminum, platinum, and gold, as in the case of the light reflecting layer 103. The semi-transmitting layer 105 may be made of one material, or may be made of a plurality of types of materials. For example, the semi-transmitting layer 105 may be made of silver as a main component and have a thickness of 5 nm or more and 20 nm or less. Here, the reason why the semi-transmitting layer 105 is 5 nm or more is that a metal thin film mainly made of silver or the like tends to become island-shaped and not form a layer if the film thickness is too thin. On the other hand, the reason why the semi-transmitting layer 105 is 20 nm or less is that the light transmittance becomes too low. In other words, the proportion of light that enters the optical resonator 108 composed of the light reflecting layer 103, the optical adjustment layer 104, and the semi-transmitting layer 105 out of the light emitted by the scintillator 101 is reduced, and the effect of the optical resonator 108 is weakened.

[0025] The semi-transmitting layer 105 can be formed by using the above-mentioned metal material on the optical adjustment layer 104 using a deposition method, a sputtering method, or the like. When a metal thin film of about 5 nm is formed using a deposition method, the grown metal tends to become island-shaped and not form a layer. Therefore, from the viewpoint of flatness, uniformity, and the like, the semi-transmitting layer 105 may be formed using a sputtering method. In addition, since the semi-transmitting layer 105 is a thin film, the metal may be formed using, for example, an atomic layer deposition (ALD) method.

[0026] The scintillator 101 converts radiation into light. In order to efficiently transmit the emitted light to the sensor panel 201, a material in which a small amount of an activator is added to columnar crystals whose main component is an alkali metal halide compound is widely used as the scintillator 101. In the scintillator 101, gaps are formed between each columnar crystal, and due to the difference in refractive index between the crystal and air, part of the light is repeatedly totally reflected within the crystal, effectively guiding the emitted light to the sensor panel 201.

[0027] For example, an alkali metal halide compound such as sodium iodide (NaI), cesium iodide (CsI), or cesium bromide (CsBr) may be used as the scintillator 101. Of these materials, cesium iodide may be used because it has a relatively high conversion rate from radiation (X-rays) to visible light and a relatively low deliquescence.

[0028] Since cesium iodide alone has low luminous efficiency, various activators may be added to the scintillator 101 in addition to cesium iodide, which is the phosphor base. As the activator, halides such as thallium (Tl), europium (Eu), indium (In), lithium (Li), potassium (K), rubidium (Rb), and sodium (Na) may be used. The scintillator 101 can be formed by evaporating the activator together with cesium iodide. For example, thallium iodide (TlI) may be used as the activator. When forming the scintillator 101 by the evaporation method, the crystallinity of the formed columnar crystals can be improved by placing a substrate vertically above the evaporation source of the scintillator material and obliquely with respect to the vertical axis, and the MTF can be improved.

[0029] Since the scintillator 101, in which a small amount of an activator is added to columnar crystals of an alkali metal halide compound, exhibits deliquescent properties, contact between the semi-transparent layer 105, which uses a metal, and the scintillator 101 may cause problems such as corrosion of the semi-transparent layer 105. For this reason, a protective layer 106 may be disposed between the semi-transparent layer 105 and the scintillator 101.

[0030] The protective layer 106 may be made of a transparent inorganic material or a transparent resin. The transparent inorganic material may be made of one or more materials selected from silicon oxide (SiO2), aluminum oxide (Al2O3), titanium (IV) oxide (TiO2), tantalum oxide (Ta2O5), etc. The transparent resin may be made of one or more materials selected from polyurethane resin, polyamide resin, polyimide resin, epoxy resin, acrylic resin, parylene, etc. Parylene also has a moisture-proof effect, and is suitable for use in the protective layer 106 when corrosion and other factors are taken into consideration. The protective layer 106 may have a single-layer structure or a multi-layer structure in which the above-mentioned materials are laminated. For example, a transparent inorganic material and a transparent resin may be laminated, or different types of transparent inorganic materials or different types of transparent resins may be laminated.

[0031] The protective layer 106 can be formed by a deposition method, a sputtering method, a spin coating method, a slit coating method, a spray method, or the like, depending on the material used. For example, a composite film in which a transparent inorganic material is formed by a sputtering method and then parylene is formed by a deposition method may be used as the protective layer 106. In this case, the film using a transparent inorganic material in the protective layer 106 is a film for suppressing oxidation and clouding of the semi-transmitting layer 105, which is an extremely thin metal film. Therefore, the light reflecting layer 103, the optical adjustment layer 104, the semi-transmitting layer 105, and the transparent inorganic material film in the protective layer 106 may be formed consistently by a sputtering method. For example, from the formation of the light reflecting layer 103 to the formation of the transparent inorganic material film in the protective layer 106, the support 102 may be repeatedly formed in succession so as not to be exposed to the atmosphere in the sputtering device.

[0032] The sensor panel 201 converts light converted from radiation by the scintillator panel 100 and light selectively resonated by an optical resonator 108 including a light reflecting layer 103, an optical adjustment layer 104, and a semi-transmitting layer 105 into an electric signal. The sensor panel 201 may be configured to include, for example, a PIN-type imaging element or an MIS-type imaging element using amorphous silicon. The sensor panel 201 may include a plurality of pixels including photodiodes constituting photoelectric conversion elements such as a PIN-type imaging element or an MIS-type imaging element, arranged in a two-dimensional array. The sensor panel 201 may also be configured to include a CMOS circuit such as an amplifier that processes electric signals output from the plurality of pixels. The electric signal obtained by the sensor panel 201 is sent to an external electric board by a wiring structure such as an FPC (not shown), and a radiological image can be obtained by performing image processing or the like.

[0033] Next, the principle of improving MTF while suppressing the decrease in DQE by the scintillator panel 100 of this embodiment will be described in detail with reference to Fig. 2 to Fig. 6. Fig. 2 is a diagram showing an example of the spectrum of light emitted by the scintillator 101. Here, the scintillator 101 will be described as a scintillator (CsI:Tl) composed of needle-shaped crystals using cesium iodide as a base material and thallium iodide as an activator. As shown in Fig. 2, CsI:Tl used as the scintillator 101 has an emission peak wavelength in the vicinity of 550 nm, and has a broad emission spectrum from about 300 nm on the shorter wavelength side of the peak wavelength to about 900 nm on the longer wavelength side.

[0034] 3 is a diagram showing the reflectance at an incident angle of 5° of the light reflecting member 107 of the present embodiment and the light reflecting member of the comparative example. Here, the light reflecting member 107 of the present embodiment is a substrate in which silver as the light reflecting layer 103, silicon oxide as the optical adjustment layer 104, a silver thin film as the semi-transmitting layer 105, and silicon oxide as the protective layer 106 are laminated by a sputtering method on the glass as the support 102. On the other hand, the light reflecting member of the comparative example is a substrate in which aluminum (indicated as Al in FIG. 3) or silver (indicated as Ag in FIG. 3) as the light reflecting layer 103 and silicon oxide as the protective layer 106 are formed by a sputtering method on the glass as the support 102. In other words, the light reflecting member of the comparative example does not include an optical resonator 108 constituted by the light reflecting layer 103, the optical adjustment layer 104, and the semi-transmitting layer 105.

[0035] 3, the light reflecting member 107 of this embodiment has a reflection peak near 550 nm, which is the peak wavelength of light emitted by the scintillator 101, due to the optical resonator 108. On the other hand, the light reflecting member of the comparative example not equipped with an optical resonator has a broad reflectance with little change due to wavelength, whether it is made of aluminum or silver.

[0036] 4 is a diagram showing the reflectance of the light reflecting member 107 of this embodiment and a light reflecting member of a comparative example at an incident angle of 45°, which differs from FIG. 3 only in the incident angle of light.

[0037] As is clear from Fig. 4, the light reflecting member 107 of this embodiment has a reflection peak near 480 nm when the incident angle is 45°. Therefore, the peak wavelength of the light emitted by the scintillator 101 and the peak wavelength of the reflection of the light reflecting member 107 are shifted, and the intensity of the reflected light is reduced compared to when the incident angle of light is 5°. On the other hand, the light reflecting member of the comparative example has a broad reflectance even when the incident angle of light changes.

[0038] Fig. 5 shows the angle dependency of reflected light when light is incident from the scintillator 101 on the light reflecting member 107 of this embodiment. Due to the characteristics of the optical resonator 108 constituted by the light reflecting layer 103, the optical adjustment layer 104, and the semi-transmitting layer 105 as described above, when the angle of incidence of light deviates from the normal direction of the light reflecting member 107, the resonance (interference) wavelength shifts, and the intensity of the reflected light decreases. Therefore, as shown in Fig. 5, the light reflecting member 107 of this embodiment has directional reflection characteristics in which the intensity of light reflected in the normal direction of the light reflecting member 107 is high.

[0039] Fig. 6 shows the angle dependency of reflected light when light is incident on the light reflecting member of the comparative example from the scintillator 101. The light reflecting member of the comparative example has almost no angle dependency in reflectance as shown in Figs. 3 and 4, and therefore has isotropic reflection characteristics as shown in Fig. 6.

[0040] As described above, of the light emitted by the scintillator 101, light emitted toward the light reflecting member 107 has a low reflected intensity when it is incident obliquely with respect to the normal direction of the light reflecting member 107 (i.e., scattered light). On the other hand, light close to the normal direction of the light reflecting member 107 is reflected with a high reflectance. As a result, the scintillator panel 100 including the light reflecting member 107 of this embodiment not only achieves a high DQE by providing the light reflecting layer 103, but also reduces the scattered light components and realizes a high MTF.

[0041] The radiation imaging device 200 shown in Fig. 1 has a configuration in which the scintillator panel 100 is bonded to the sensor panel 201 via a bonding member such as an adhesive (not shown). The main component of the bonding member needs to have adhesiveness when bonding the scintillator panel 100 and the sensor panel 201, and for example, an acrylic, epoxy, olefin, silicone, or other resin may be used. An acrylic resin with high optical transmittance may be used as the bonding member. Furthermore, a thermoplastic resin, a thermosetting resin, or a hot melt resin that is heated and solidified (for example, a resin mainly composed of a polyolefin, polyester, polyamide, or the like) may be used as the bonding member.

[0042] Furthermore, after the scintillator panel 100 and the sensor panel 201 are bonded together, a resin material or the like (not shown) may be filled into the gap on the side where the scintillator panel 100 and the sensor panel 201 are bonded together. This prevents moisture from penetrating from the side where the scintillator panel 100 and the sensor panel 201 are bonded together, thereby preventing deterioration of the characteristics of the scintillator 101. There are no particular limitations on the resin material as long as it is moisture-proof, and various materials can be used. For example, epoxy resin can be used.

[0043] In this manner, the scintillator panel 100 including the light reflecting member 107 equipped with the optical resonator 108 constituted by the light reflecting layer 103, the optical adjustment layer 104, and the semi-transmitting layer 105 is bonded to the sensor panel 201. With this configuration, it is possible to realize a radiation imaging device 200 capable of improving the MTF while suppressing a decrease in DQE.

[0044] The radiation imaging device 200 is not limited to the above-mentioned configuration in which the scintillator panel 100 and the sensor panel 201 are bonded together. In the radiation imaging device 200' shown in Fig. 7, the scintillator 101 is formed directly on the sensor panel 201 by a deposition method or the like, and then a light reflecting member 107 having an optical resonator 108 is bonded to the scintillator 101. In either configuration, the sensor panel 201 is disposed on the side of the scintillator 101 opposite to the side of the optical resonator 108 formed by the light reflecting layer 103, the optical adjustment layer 104, and the semi-transmitting layer 105.

[0045] 1, in the configuration in which scintillator panel 100 and sensor panel 201 are bonded together, the scintillator 101 may be thinner on the side of light reflecting member 107 than on the side of sensor panel 201. On the other hand, in the configuration shown in Fig. 7, the scintillator 101 may be thinner on the side of sensor panel 201 than on the side of light reflecting member 107. That is, in the configuration shown in Fig. 7, because the scintillator 101 is formed directly on the sensor panel 201, the structure of the scintillator 101 may be upside down compared to the scintillator 101 shown in Fig. 1.

[0046] 7, the light reflecting member 107 is attached to the scintillator 101 via a bonding member such as an adhesive (not shown). The bonding member that bonds the light reflecting member 107 to the scintillator 101 can be made of the same material as the bonding member used to bond the scintillator panel 100 and the sensor panel 201 described above.

[0047] 7, after the light reflecting member 107 and the scintillator 101 are bonded together, a resin material or the like (not shown) may be filled into the gap on the side where the light reflecting member 107 and the scintillator 101 are bonded together. This prevents moisture from penetrating from the side where the light reflecting member 107 and the scintillator 101 are bonded together, thereby preventing deterioration of the characteristics of the scintillator 101. There are no particular limitations on the resin material as long as it is moisture-proof, and various materials can be used. For example, epoxy resin or the like can be used.

[0048] 7 also includes a light reflecting member 107 having an optical resonator 108, similar to the radiation imaging device 200 shown in Fig. 1. Therefore, it is possible to provide a radiation imaging device 200' capable of improving the MTF while suppressing a decrease in DQE, similar to the radiation imaging device 200 described above.

[0049] The scintillator panel 100 of the embodiment and a scintillator panel of a comparative example will be described below. First, the comparative example will be described.

[0050] Comparative Example 1 A glass substrate was prepared as the support 102. Next, a light reflecting layer 103 using aluminum and (a part of) a protective layer 106 using silicon oxide were successively formed on the support 102 to a thickness of 120 nm and 20 nm, respectively, using a sputtering method. Next, a protective layer 106 using parylene was formed to a thickness of 12 μm, respectively, using a vapor deposition method. A scintillator 101 having a columnar crystal structure using cesium iodide as a base material and thallium iodide as an activator was formed on the light reflecting member of Comparative Example 1 obtained by the above steps, using a vapor deposition method, to obtain a scintillator panel of Comparative Example 1.

[0051] After forming the scintillator 101, the tip side of the scintillator 101 was attached to a CMOS photodetector via a Fiber Optic Plate (FOP), and X-rays conforming to the radiation quality RQA5 of the international standard were irradiated from the side of the support 102. At this time, as the DQE value, which is an index representing the noise of the scintillator 101 (scintillator panel), the DQE(0) value corresponding to a spatial frequency of 0 line pairs (0Lp / mm) per mm was set to 100, and was compared relatively with the DQE(0) values ​​of Examples 1 to 4 and Comparative Example 2 described later. In addition, as the MTF value, which is an index of the resolution of the scintillator 101 (scintillator panel), the value corresponding to a spatial frequency of 2 line pairs (2Lp / mm) per mm was obtained by an edge method using a tungsten knife edge. The MTF(2) value at this time was set to 100, and was compared relatively with the MTF(2) values ​​of Examples 1 to 4 and Comparative Example 2 described later.

[0052] Comparative Example 2 A glass substrate was prepared as the support 102. Next, on the support 102, a light reflecting layer 103 using silver and (a part of) a protective layer 106 using silicon oxide were successively formed to a thickness of 120 nm and 20 nm, respectively, using a sputtering method. Next, a protective layer 106 using parylene and (a part of) was formed to a thickness of 12 μm using a deposition method. On the light reflecting member of Comparative Example 2 obtained by the above steps, a scintillator 101 having a columnar crystal structure was formed using a deposition method with cesium iodide as a base material and thallium iodide as an activator. That is, except for the use of silver in the light reflecting layer 103, the scintillator panel of Comparative Example 2 has the same structure as the scintillator panel of Comparative Example 1 described above. The prepared scintillator panel of Comparative Example 2 was evaluated using the same evaluation method as Comparative Example 1.

[0053] Example 1 First, the film thickness of the optical adjustment layer 104 was estimated. Here, the design was carried out assuming that silver was used for the light reflecting layer 103, silicon oxide with high light transmittance was used for the optical adjustment layer 104, silver was used for the semi-transmitting layer 105, and silicon oxide was used for the portion of the protective layer 106 that contacted the semi-transmitting layer 105. The refractive index n of silicon oxide is 1.46, the peak wavelength λ of the light emitted by the scintillator 101 is 550 nm, and the sum φ [rad] of the phase shifts when light of wavelength λ (550 nm) is reflected by the light reflecting layer 103 and the semi-transmitting layer 105 is approximately -π. Therefore, using the above formula (1), the optical distance L of the optical adjustment layer 104 is given by 0nm <L<275nm Therefore, the thickness of the silicon oxide of the optical adjustment layer 104 is calculated by using the formula (2): 0nm <L<188nm It is estimated that.

[0054] Therefore, the reflectance of light reflecting member 107 was evaluated by changing the film thickness of silicon oxide in optical adjustment layer 104. By setting the film thickness of silicon oxide in optical adjustment layer 104 to 160 nm, light reflecting member 107 having a peak reflection wavelength in the vicinity of 550 nm, as shown in FIG.

[0055] Specifically, on a support 102 using a glass substrate, a light reflecting layer 103 using silver with a thickness of 120 nm, an optical adjustment layer 104 using silicon oxide with a thickness of 160 nm, a semi-transmitting layer 105 using silver with a thickness of 8 nm, and a protective layer 106 (part of) using silicon oxide with a thickness of 20 nm were successively formed using a sputtering method. Next, a protective layer 106 (part of) using parylene with a thickness of 12 μm was formed using a deposition method. On the light reflecting member 107 of Example 1 obtained by the above steps, a scintillator 101 having a columnar crystal structure using cesium iodide as a base material and thallium iodide as an activator was formed using a deposition method, thereby obtaining a scintillator panel 100 of Example 1. The formation of the scintillator 101 is the same as that of Comparative Examples 1 and 2 described above, including Examples 2 to 4 described later.

[0056] Observation of the formed scintillator 101 using a SEM (scanning electron microscope) confirmed the formation of columnar crystals. The film thickness of the obtained scintillator 101 was 860 μm. Analysis using an EDS (energy dispersive X-ray spectrometer) revealed that the thallium concentration relative to the cesium iodide on the support 102 side of the scintillator 101 was 0.29 mol%, and the thallium concentration relative to the cesium iodide on the sensor panel 201 side of the scintillator 101 was 1.40 mol%.

[0057] FIG. 8 is an SEM observation image of the initial deposition side (support 102 side) of scintillator 101 of this embodiment. FIG. 9 is an SEM observation image of the tip side (sensor panel 201 side) of scintillator 101 of this embodiment. From FIG. 8 and FIG. 9, the thickness of the columnar crystals of scintillator 101 on the initial deposition side in the direction intersecting with the crystal growth direction (the direction of the arrow shown in FIG. 8 and FIG. 9) was approximately 1.0 μm to 2.2 μm. On the other hand, the thickness of the columnar crystals of scintillator 101 on the tip side in the direction intersecting with the crystal growth direction was approximately 4.9 μm to 7.8 μm. As is clear from FIG. 8 and FIG. 9, it was found that the crystal size of scintillator 101 at the initial deposition stage was finer than the crystal size at the tip side.

[0058] The scintillator panels 100 provided with the light reflecting members 107 of this embodiment produced in Example 1 and Examples 2 to 4 described below were evaluated using the same evaluation method as in Comparative Examples 1 and 2.

[0059] Example 2 The device was produced in the same manner as in Example 1, except that the thickness of the silver used in the semi-transmitting layer 105 was 6 nm.

[0060] Example 3 The device was produced in the same manner as in Example 1, except that the thickness of the silver used for the semi-transmitting layer 105 was 10 nm.

[0061] Example 4 The device was produced in the same manner as in Example 1, except that the thickness of the silver used in the semi-transmitting layer 105 was 12 nm.

[0062] Next, the characteristics of the scintillator panels 100 of Examples 1 to 4 and the scintillator panels of Comparative Examples 1 and 2 will be described with reference to Fig. 10. First, comparing the scintillator panels of Comparative Example 1 and Comparative Example 2, Comparative Example 2, which uses silver having high reflectivity in the light reflecting layer 103, obtained a higher DQE(0) value than Comparative Example 1. However, the MTF(2) value is significantly lower. This is because, in the scintillator panel of Comparative Example 2, although more light is reflected by the light reflecting layer 103, as shown in the problem, the amount of scattered light components becomes relatively large.

[0063] On the other hand, the scintillator panels 100 of Examples 1 to 4 all had improved MTF(2) values ​​compared to the scintillator panel of Comparative Example 1. The MTF(2) value also depended on the thickness of the silver used in the semi-transmitting layer 105, and showed a maximum value in Example 1 with a thickness of 8 nm, resulting in an MTF(2) value 1.3 times higher than that of Comparative Example 1. It was also found that the scintillator panel 100 of Example 1 also suppressed the decrease in the DQE(0) value (-3%) compared to the scintillator panel of Comparative Example 1.

[0064] In the scintillator panel 100 of Example 2, in which the film thickness of the silver in the semi-transmitting layer 105 was 6 nm, which was thinner than the scintillator panel 100 of Example 1, the MTF(2) value was lower than that of Example 1. A possible reason for the decrease in the MTF(2) value is that, of the light reflected by the light reflecting layer 103, the component that transmits through the semi-transmitting layer 105 increased, weakening the resonance in the optical resonator 108 formed by the light reflecting layer 103, the optical adjustment layer 104, and the semi-transmitting layer 105. Another possible reason for the decrease in the MTF(2) value in Example 2 is that, because the film thickness of the silver in the semi-transmitting layer 105 was as thin as 6 nm, the silver was formed in an island shape, which deteriorated the uniformity of the film of the semi-transmitting layer 105.

[0065] The MTF(2) values ​​of the scintillator panels 100 of Examples 3 and 4, in which the thickness of the silver in the semi-transmitting layer 105 was thicker than that of the scintillator panel 100 of Example 1, were also lower than that of Example 1. The reason for the decrease is thought to be that the thickness of the semi-transmitting layer 105 became thicker, resulting in a decrease in the amount of light entering the optical resonator 108 constituted by the light reflecting layer 103, the optical adjustment layer 104, and the semi-transmitting layer 105.

[0066] However, it was found that the scintillator panels 100 of Examples 1 to 4 were able to improve the MTF while suppressing a decrease in DQE, as compared with the scintillator panels of Comparative Examples 1 and 2 that did not include an optical resonator 108. That is, the radiation imaging device 200 using the scintillator panel 100 including the optical resonator 108 constituted by the light reflecting layer 103, the optical adjustment layer 104, and the semi-transmitting layer 105 of this embodiment (this example), and the radiation imaging device 200' including the optical resonator 108 are able to improve the MTF while suppressing a decrease in DQE.

[0067] The invention is not limited to the above-described embodiments, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0068] 100: scintillator panel, 101: scintillator, 102: support, 103: light reflecting layer, 104: optical adjustment layer, 105: semi-transmitting layer

Claims

1. A support; a scintillator that generates light in response to incident radiation; a light reflecting layer disposed between the support and the scintillator and configured to reflect the light; a semi-transmissive layer disposed between the light reflecting layer and the scintillator, the semi-transmissive layer reflecting a part of the light and transmitting the other part of the light; an optical adjustment layer disposed between the light reflecting layer and the semi-transmitting layer for adjusting an optical distance between the light reflecting layer and the semi-transmitting layer to a length at which the light resonates; A scintillator panel comprising:

2. The optical path length L [nm] of the optical adjustment layer is (λ / 4)×(-1-(φ / π))<L<(λ / 4)×(1-(φ / π)) wherein λ [nm] is a peak wavelength of the light, and φ [rad] is a sum of phase shifts of light of wavelength λ [nm] in the light-reflecting layer and the semi-transmitting layer.

3. 3. The scintillator panel according to claim 1, wherein the optical adjustment layer is made of a transparent inorganic material or a transparent resin.

4. 4. The scintillator panel according to claim 3, wherein the optical adjustment layer contains at least one of silicon oxide, aluminum oxide, titanium oxide, tantalum oxide, indium tin oxide, zinc oxide, acrylic resin, polyethylene terephthalate, and polycarbonate.

5. 5. The scintillator panel according to claim 1, wherein the optical adjustment layer has a single layer structure.

6. 6. The scintillator panel according to claim 1, wherein the light reflecting layer contains at least one of silver, aluminum, platinum, and gold.

7. 7. The scintillator panel according to claim 1, wherein the semi-transmissive layer contains at least one of silver, aluminum, platinum, and gold.

8. 8. The scintillator panel according to claim 1, wherein the semi-transmitting layer contains silver and has a thickness of 5 nm or more and 20 nm or less.

9. 9. The scintillator panel according to claim 1, wherein the scintillator comprises columnar crystals containing an alkali metal halide compound as a main component.

10. 10. The scintillator panel according to claim 1, further comprising a protective layer between the scintillator and the semi-transparent layer.

11. 11. The scintillator panel according to claim 10, wherein the protective layer is made of a transparent inorganic material or a transparent resin.

12. 12. The scintillator panel of claim 11, wherein the protective layer contains at least one of silicon oxide, aluminum oxide, titanium oxide, tantalum oxide, indium tin oxide, zinc oxide, polyurethane resin, polyamide resin, polyimide resin, epoxy resin, acrylic resin, and parylene.

13. 13. The scintillator panel according to claim 10, wherein the protective layer has a multi-layer structure.

14. A scintillator panel according to any one of claims 1 to 13; a sensor panel for receiving light emitted from the scintillator; A radiation imaging device comprising:

15. a scintillator that generates light in response to incident radiation; a light reflecting layer that reflects the light; a semi-transmissive layer disposed between the light reflecting layer and the scintillator, the semi-transmissive layer reflecting a part of the light and transmitting the other part of the light; an optical adjustment layer disposed between the light reflecting layer and the semi-transmitting layer for adjusting an optical distance between the light reflecting layer and the semi-transmitting layer to a length at which the light resonates; a sensor panel disposed on a side of the scintillator opposite to a side on which the light reflecting layer is disposed, for receiving light emitted from the scintillator; 13. A radiation imaging apparatus comprising:

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