JP2677823B2 - Radiation image conversion panel - Google Patents

Description

The present invention relates to a radiation image conversion panel having a stimulable phosphor layer, and more specifically to a radiation image with high sharpness. The present invention also relates to a radiation image conversion panel having a stimulable phosphor layer that is less deformed by warpage or the like and has less uneven sensitivity.

(Prior Art) Radiation images such as X-ray images are widely used for diagnosis of diseases and the like.

In order to obtain this X-ray image, an X-ray image conversion method for directly extracting an image from a phosphor layer instead of a silver halide photosensitive material has been devised.

This method uses radiation transmitted through the subject (generally X-rays)
Is absorbed by the phosphor, and then the phosphor is excited by, for example, light or heat energy, so that the phosphor emits the radiation energy accumulated by the radiation absorption, and the fluorescence is detected. This is a method for imaging.

Specifically, for example, U.S. Pat.No. 3,859,527 and JP-A-55-12144 show a radiation image conversion method using stimulable phosphor and using visible light or infrared light as stimulating excitation light. .

This method uses a radiation image conversion panel (hereinafter abbreviated as a conversion panel) having a stimulable phosphor layer (hereinafter abbreviated as a stimulable layer).
The latent image is formed by applying radiation transmitted through the subject to the stimulating layer of the conversion panel, accumulating radiation energy corresponding to the radiation transmittance of each part of the subject, and then forming the stimulating layer. By scanning with stimulating excitation light, the radiation energy stored in each section is emitted and converted into light, and an image is obtained by an optical signal based on the intensity of the light.

This final image may be reproduced as a hard copy or reproduced on a CRT.

The conversion panel used in this radiation image conversion method releases the stored energy by scanning the stimulated excitation light after storing the radiation image information, so that the radiation image can be stored again after the scanning and repeated use is possible. It is possible.

Such a conversion panel usually comprises a photostimulable layer (1), a support (2) and a protective layer (3) as shown in FIG. 1, and the photostimulable layer (1). In order to protect the panel from external physical or chemical irritation, the periphery of the conversion panel is often further sealed with a sealing member (4).

(Problems to be Solved by the Invention) However, in the conversion panel as described above,
Since the support and the protective layer are fixed by the sealing member, if the environmental temperature of the conversion panel changes greatly during transportation etc., the conversion panel may be warped due to the difference in thermal expansion coefficient between the support and the protective layer. Deformation may occur, the sealing part may peel off,
Problems such as cracking of the protective layer and / or the support have occurred.

Deformation such as warpage causes uneven sensitivity. This unevenness in sensitivity occurs because the distance between the condensing system of the radiation image converter and the conversion panel is not constant due to the deformation of the conversion panel.

Peeling of the sealed portion, cracking of the protective layer and / or the support, and the like are unfavorable because they lead to a decrease in the moisture resistance of the conversion panel.

Therefore, an object of the present invention is to provide a conversion panel having a photostimulable layer which gives a radiation image with high sharpness, has less deformation such as warpage, has less sensitivity unevenness, and has excellent durability.

[Structure of the Invention] (Means for Solving the Problems) The present invention has a support, a stimulable phosphor layer, and at least one protective layer, and the stimulable fluorescent layer is provided between the support and the protective layer. In the radiation image conversion panel in which the layer body is enclosed and hermetically sealed, the difference in the coefficient of linear thermal expansion between the support and the protective layer is 60 × 10
^It relates to a radiation image conversion panel characterized by being ^-7 / ℃ or less.

The stimulable phosphor used in the present invention means that after being irradiated with the first light or high-energy radiation, it is stimulated by light, thermal, mechanical, chemical or electrical (stimulation excitation). Although it is a phosphor that shows stimulated emission corresponding to the dose of the first light or high-energy radiation, from the practical point of view, it is preferably a phosphor that shows stimulated emission by stimulated excitation light of 500 nm or more. Such stimulable phosphor, for example BaSO are described in JP 48-80487 discloses _4: AX, it is described in JP-A-48-80489 SrS0 _4: AX, JP Li ₂ B ₄ O ₇ : Cu, Ag of Japanese Patent Publication No. 53-39277
Etc., Japanese Patent Laid-Open No. 54-47883, Li ₂ O. (B ₂ O ₂ ) x: Cu and L
i ₂ O ・ (B ₂ O ₂ ) x: Cu, Ag, etc., SrS: C of US Pat. No. 3,859,527
Examples thereof include phosphors represented by e, Sm, SrS: Eu, Sm, La ₂ O ₂ S: Eu, Sm and (Zn, Cd) S: Mn.

Further, ZnS: C described in JP-A-55-12142
u, Pb phosphors, barium aluminate phosphors represented by the general formula BaO.xAl ₂ O ₃ : Eu, and alkaline earth metal silicate phosphors represented by the general formula M ^II O.xSiO ₂ : A To be Further, an alkaline earth fluorohalide phosphor represented by the general formula (Ba _1-xy Mg _x Ca _y ) FX: eEu ²⁺ described in JP-A-55-12143, JP _-A- 55- Phosphor represented by the general formula LnOX: xA described in Japanese Patent No. 12144, and fluorescence represented by the general formula (Ba _1-x M ^II _x ) FX: yA described in Japanese Patent Laid-Open No. 55-12145. , A phosphor represented by the general formula BaFX: xCe, yA described in JP-A-55-84389, and a general formula M ^II FX.xA: yLn described in JP-A-55-160078. A divalent metal fluorohalide phosphor activated by a rare earth element represented by the general formula ZnS: A, CdS: A, (Zn, Cd) S: A, S: A, ZnS: A,
Phosphors represented by X and CdS: A, X, one of the general formulas xM ₃ (PO ₄ ) ₂ · NX ₂ : yA M ₃ (PO ₄ ) described in JP-A-59-38278. ₂ : Phosphor represented by yA, any of the following general formula nReX ₃ · mAX ′ ₂ : xEu nReX ₃ · mAX ′ ₂ : xEu, ySm described in JP-A-59-155487 , and JP 61-72087 following general formula is described in ^{JP-M I X · aM II X '} 2 · bM III X "3:. indicates Charles alkali halide phosphor, and the like in cA especially alkali halide Phosphors are preferable because they can easily form a stimulable layer by a method such as vapor deposition and sputtering.

However, the stimulable phosphor used in the conversion panel of the present invention is not limited to the above-described phosphor, and is a phosphor that shows stimulable luminescence when irradiated with stimulating excitation light after being irradiated with radiation. Any fluorescent material may be used.

The conversion panel of the present invention may be a stimulable layer group comprising one or more stimulable layers containing at least one of the stimulable phosphors. Further, the stimulable phosphor contained in each stimulable layer may be the same or different.

The layer thickness of the stimulable layer of the conversion panel varies depending on the sensitivity of the intended conversion panel to radiation, the type of stimulable phosphor, etc., but in the case of containing no binder, it is in the range of 10 μm to 1000 μm, more preferably 20 μm To 800 μm, and when the binder is contained, it is selected from the range of 20 μm to 1000 μm, preferably 50 μm to 500 μm.

Such a photostimulable layer is formed on a support by a coating method, a vapor deposition method, or the like. Alternatively, the photostimulable layer may be formed on a protective layer and then laminated on the support.

Examples of the vapor deposition method include a vapor deposition method, a sputtering method, and a CVD method.
And the like.

When the photostimulated layer formed by the vapor deposition method is subjected to heat treatment, the sensitivity to X-rays is improved. In addition, after forming a stimulable phosphor base layer (hereinafter abbreviated as “phosphor base layer”) containing no activator on the support or the protective layer, the phosphor base layer is formed by a method such as a thermal diffusion method. It is also possible to dope an activator to form a predetermined stimulable layer.

The support and protective layer used in the present invention have a difference in linear thermal expansion coefficient of 60 × 10 ⁷ / ° C. or less, preferably 40 × 10 ⁻⁷ / ° C. or less, more preferably 25 × 10 ^{−. It is 7} / ° C. or less, and particularly preferably 0.

When the difference in the coefficient of linear thermal expansion exceeds the above range, the conversion panel may be deformed such as warped or the airtightness may be deteriorated.

Examples of such a combination of the support and the protective layer include the following. When crystallized glass is used as the support and borosilicate glass, barium borosilicate glass, transparent crystallized glass, or quartz is used as the protective layer, an alumina sintered plate is used as the support, and borosilicate glass or barium is used as the protective layer. When using borosilicate glass or soda glass, transparent crystallized glass is used as the support, and when transparent crystallized glass, quartz, borosilicate glass or barium borosilicate glass is used as the protective layer, an alumina-silica sintered plate is used as the support. And using borosilicate glass, barium borosilicate glass, or the like as the protective layer.

The layer thickness of the support varies depending on the material of the support used and the like, but is generally 80 μm to 5000 μm, and more preferably 200 μm to 2000 μm from the viewpoint of handling.

The moisture permeability of the support is preferably low, and the moisture permeability is preferably 10 (g / m ² · 24 hr) or less and 1 (g / m ²
m ² · 24 hr) or less. Glass, ceramics, etc. that have excellent airtightness and substantially zero moisture permeability
Metals and the like are particularly preferred.

In the case of performing the heat treatment of the photostimulable layer as described above, the support is required to have heat resistance, and it is preferable that the support does not crack or deform even when continuously used at 500 ° C. or higher. Furthermore, during the heat treatment, it reacts with the stimulable phosphor and X
It is preferable that performance such as line sensitivity is not affected. Examples of the support having excellent heat resistance and poor reactivity with the stimulating layer include crystallized glass, quartz, and a sintered plate of alumina or alumina-silica.

Crystallized glass is also called glass-ceramics.After melt-molding a glass with the following special composition, it is reheated under well-controlled conditions, and while maintaining its original shape, the coagulation of uniform fine crystals from the amorphous state It has changed into a collective. The main constituents of the crystallized glass currently in practical use include, for example, Li ₂ O-- as a silicate glass.
_{SiO 2, Na 2 O-CaO} -MgO-SiO 2, Li 2 as aluminosilicate _{O-Al 2 O 3 -SiO 2} , Na 2 O-Al 2 O 3 -SiO 2, MgO-Al 2 O 3 -
_{SiO 2, PbO-ZnO-B} 2 O 3 as borate _{glasses, ZnO-B 2 O 3 -SiO} 2 and the like as Houkeu glasses.

Among the crystallized glass composition systems, Li ₂ O—SiO ₂ , Na ₂ O—CaO
Silicate glass such as -MgO-SiO ₂ or Li ₂ O-Al _2,
Aluminosilicate glasses such as O ₃ —SiO ₂ , Na ₂ O—Al ₂ O ₃ —SiO ₂ , and MgO—Al ₂ O ₃ —SiO ₂ are preferred.

Further, Li ₂ O—Al ₂ O ₃ —SiO ₂ glass is preferable, and the composition ratio of each component is more preferably stoichiometric ratio of Li ₂ O: Al ₂ O ₃ : SiO ₂ = 1: 1: 4.

However, the crystallized glass used for the support of the conversion panel of the present invention is not limited to the above-mentioned crystallized glass, and is excellent in heat resistance, and is also crystallized glass excellent in planarity when heated, It may be any crystallized glass.

The surface of the support may be a smooth surface or a mat surface for the purpose of improving the adhesion to the stimulable phosphor layer. Also, the surface of the support may be an uneven surface,
A surface structure in which minute tile plates independent of each other are densely arranged may be used.

Further, on these supports, an undercoat layer may be provided on the surface on which the stimulable layer is provided for the purpose of improving the adhesiveness with the stimulable layer, and if necessary, a light reflecting layer and a light absorbing layer may be provided. May be provided.

As the protective layer used in the conversion panel of the present invention, a protective layer having good translucency and capable of being formed into a sheet is used. In order to efficiently transmit stimulating excitation light and stimulating light, the protective layer preferably has a high transmittance in a wide wavelength range, and the transmittance is preferably 80% or more in a wavelength range of 400 nm to 800 nm, and 90% or more. The above is more preferable. Also, 360nm ~ 4
In the range of 00 nm, 60% or more is preferable, and 80% or more is more preferable.

Further, it is preferable to provide an anti-reflection layer such as MgF _{2 on} the surface of the protective layer, because it has an effect of efficiently transmitting the stimulating excitation light and the stimulating light emission, and has the effect of reducing the decrease in sharpness.

The thickness of the protective layer is 25 μm to 5 mm, and 100 μm to 3 mm is preferable in order to obtain good moisture resistance and impact resistance.

The moisture permeability of the protective layer is preferably low from the viewpoint of the moisture resistance of the panel, and the moisture permeability is preferably 10 (g / m ² · 24 hr) or less, more preferably 1 (g / m ² · 24 hr) or less. Glass that is excellent in airtightness, has a water vapor transmission rate of substantially 0, and has good light transmissivity is particularly preferable.

The protective layer of the present invention may be a single layer, or may be a multilayer as long as the effects of the present invention are not impaired, and may be composed of two or more layers of different materials. For example, a case where glass is used as the first protective layer and an organic polymer layer is used as the second protective layer. If the thickness of the second protective layer is sufficiently smaller than the thickness of the first protective layer, the linear thermal expansion coefficient of the protective layer is substantially equal to the linear thermal expansion coefficient of the first protective layer, and The peeling between the first and second protective layers and the warp of the protective layer itself do not pose a problem. When a highly hygroscopic organic polymer layer such as polyvinyl alcohol or ethylene-vinyl alcohol copolymer is provided as the second protective layer on the stimulating layer side of the first protective layer, the stimulating layer is adsorbed during sealing. Since the second moisture is adsorbed and removed by the second protective layer, deterioration of the photostimulation layer due to moisture is prevented and the initial performance of the conversion panel is improved, which is preferable.

The protective layer may or may not adhere to the photostimulable layer,
The presence of a layer having a lower refractive index than the protective layer between the two layers is preferable because the sharpness is small even when the protective layer is thickened.
Examples of such a low refractive index layer include an inert gas such as air, nitrogen, and argon, a liquid such as methyl alcohol and ethyl alcohol, and a thin film of a substance such as CaF ₂ , Na ₃ AlF ₆ , MgF ₂ , and SiO _2. Is mentioned.

The thickness of the low refractive index layer is practically 0.05 μm to 3 mm.

In order to form the low refractive index layer, a protective layer holding member (spacer) may be provided between the support and the protective layer so as to surround the photostimulable layer. Examples of such a spacer include glass, ceramics, metal, and plastic.

Furthermore, in order to seal the photostimulable layer between the support and the protective layer, and to seal it, the peripheral edge of the photostimulable layer is sealed with a sealing member, or
Alternatively, the adhesive member for the spacer and the support and the protective layer is sealed.

Further, by further sealing the periphery of the spacer by using a sealing member, by sealing glass by using sealing glass such as low melting point glass, or by sealing with an extension portion of the protective layer. Good.

As the sealing member to be used, one having high airtightness and low moisture permeability is suitable, and specifically, epoxy resin, phenol resin, cyanoacrylate resin, vinyl acetate resin, vinyl chloride resin are used. Examples include organic polymer adhesives such as resins, polyurethane resins, acrylic resins, ethylene vinyl acetate resins, polyolefin resins, chloroprene rubber and nitrile rubber, and silicone adhesives. Epoxy-based resins and silicone-based resins used for encapsulating semiconductors and electronic components are preferred because of their excellent moisture resistance, and epoxy-based adhesives are particularly preferred because of their low moisture permeability.

The conversion panel produced according to the invention is used in the radiation image conversion direction shown schematically in FIG.

That is, the radiation R from the radiation generator 41 enters the conversion panel 43 through the subject.

This incident radiation is absorbed by the photostimulable layer of panel 43,
The energy is accumulated, and an accumulation image of the radiation transmission image is formed.

Next, this accumulated image is excited by stimulating light from the stimulating light source 44 and emitted as stimulating light. Since the intensity of the emitted stimulating luminescence is proportional to the amount of the accumulated radiation energy, this optical signal is photoelectrically converted by a photoelectric conversion device 45 such as a photomultiplier tube, and reproduced as an image by an image reproduction device 46. By displaying the image on the display device 47, a radiographic image of the subject can be observed.

(Example) Next, the present invention will be described with reference to examples.

Example 1 A crystallized glass support (400 mm × 500 mm) having a linear thermal expansion coefficient of 10 × 10 ⁻⁷ / ° C. having a thickness of 1.1 mm was subjected to an electron beam method (EB method).
It was installed in the vapor deposition device according to. Next, a press-molded alkali halide (RbBr) as an evaporation source was placed in a water-cooled crucible.

Subsequently, the evaporator was evacuated to a vacuum degree of 5 × 10 ⁻⁶ Torr. The BE gun was then powered to RbBr vaporize while maintaining the support at 40-45 ° C.

In order to obtain a target RbBr layer, the deposition rate was detected by a film thickness monitor, and the deposition rate was controlled so as to be 10 ⁵ Å / min. The electron beam was used to scan the surface of the crucible vapor deposition source in a raster pattern.

When the thickness of the RbBr layer reached 300 μm, the vapor deposition was terminated, and a vapor-deposited panel was obtained. The vapor deposition panel RbBr was doped with Tl by placing the vapor deposition panel in a quartz crucible containing activated dopant powder (RbBr: 10 ^-4 Tl), covering the lid, and heating at 600 ° C. for 1 hr. Next, 1.1mm on the photostimulation layer
A thick borosilicate glass having a linear thermal expansion coefficient of 65 × 10 ^-7 / ℃ was placed. Then, the periphery of the photostimulation layer was coated with an epoxy resin adhesive (AV138 + HV998, manufactured by Ciba-Geigy Co., Ltd.)
After curing at 00 ° C. and sealing, a radiation image conversion panel as shown in FIG. 1 was obtained.

A tube voltage of 80 was applied to the radiation image conversion panel thus obtained.
After irradiating 10mR of V line of KVp, semiconductor laser light (780nm)
The photostimulated luminescence emitted from the stimulable phosphor layer is photoelectrically converted by a photodetector (photomultiplier tube), and this signal is reproduced as an image by an image reproducing device, Recorded in. The operating temperature of the radiation image conversion panel at this time was 40 ° C. ± 1 ° C.

The unevenness of the relative sensitivity was examined from the obtained images and shown in Table 1. Here, the unevenness of the relative sensitivity refers to a value obtained by dividing the standard deviation of the relative sensitivity of 2048 × 2048 pixels by the average value of the relative sensitivity as a percentage.

In addition, the obtained conversion panel was examined for warpage at a use temperature of 40 ° C., and the results are shown in Table 1. The warpage in Table 1 is indicated by the average value of the four corners rising when the conversion panel is placed on a flat plate with the concave side of the warp facing up.

Repeated durability is -40 ° C to 50 ° C to 12 hours.
By repeating the temperature change of 40 ° C., the time until the conversion panel became abnormal was measured. The results are shown in Table 1.

Examples 2 to 13 Conversion panels were produced in the same manner as in Example 1 except that the support and the protective layer had the combinations shown in Table 1 (thicknesses were all 1.1 mm). However, in Example 10, the surface of the glass protective layer on the side of the photostimulating layer had a thickness of 50% as the second protective layer.
The ethylene-vinyl alcohol copolymer layer having a thickness of μm was adhered with a urethane adhesive (T-600, manufactured by Nippon Soda Co., Ltd.). These were evaluated in the same manner as in Example 1 and are also shown in Table 1.

Comparative Examples 1-2 A conversion panel was produced in the same manner as in Example 1 except that the combination of the support and the protective layer was as shown in Table 1. This was evaluated in the same manner as in Example 1 and is also shown in Table 1.

As shown in Table 1, in Comparative Examples 1 and 2, the sensitivity unevenness is very large because of the large warpage of the conversion panel. Further, an abnormality occurred in a short time with respect to the repeated temperature change.

On the other hand, in the conversion panels of Examples 1 to 13, since the warpage was small, the sensitivity unevenness was small and good images were obtained. In addition, the durability against repeated temperature changes is significantly improved.

[Advantages of the Invention] The radiation image conversion panel of the present invention has a small difference in linear thermal expansion coefficient between the support and the protective layer, and therefore does not cause deformation such as warping of the panel at the time of use, resulting in small sensitivity unevenness. Moreover, it has sufficient durability even if the conversion panel is exposed to severe temperature conditions. Therefore, the conversion panel of the present invention is highly useful.

[Brief description of the drawings]

1 and 3 are sectional views of the radiation image conversion panel of the present invention, FIG. 2 is a sectional view taken along the line AA ′ of FIG. 1, and FIG. 4 is a radiation image using the radiation image conversion panel. It is explanatory drawing of a conversion method. 1 ... Photostimulation layer 2 ... Support 3 ... Protective layer 4 ... Sealing member 5 ... Protective layer holding member (spacer) 41 ... Radiation generator 42 ... Subject 43 ... Radiation image conversion panel 44 ...... Photostimulated excitation light source 45 …… Photoelectric conversion device 46 …… Radiation image reproduction device 47 …… Radiation image display device 48 …… Filter

Claims (1)

(57) [Claims] 1. A radiation image conversion panel comprising a support, a stimulable phosphor layer and a protective layer, wherein the stimulable phosphor layer is enclosed and sealed between the support and the protective layer. A radiation image conversion panel characterized in that the difference in linear thermal expansion coefficient between the body and the protective layer is 60 × 10 ^-7 / ℃ or less.