JPH01316698A - Radiograph transformation panel - Google Patents

Abstract

PURPOSE:To form a radiograph transformation panel provided with a stimulable phosphor panel which gives clear radiographs, is less in sensitivity unevenness, and has an excellent durability by setting the difference in coefficient of thermal linear expansion between a supporting body and protective body to <=60X10<-7>/ deg.C. CONSTITUTION:This transformation panel is constituted of a stimulable phosphor layer 1, supporting body 2, and protective layer 3. The peripheral margin of the panel is sealed with a sealing member 4 so as to prevent the layer 1 from an external physical or chemical stimulus. The difference in coefficient of thermal linear expansion between the supporting body 2 and protective layer 3 is set to <=60X10<-7>/ deg.C. Since the difference is coefficient of thermal linear expansion between the supporting body 2 and protective layer 3 is small, deformation, such as a bend, etc., does not occur while the panel is used. Therefore, unevenness in sensitivity can be made smaller and the panel has a sufficient durability even when the panel is exposed to a severe temperature condition.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a radiation image conversion panel having a stimulable phosphor layer, and more specifically to a radiation image conversion panel that provides 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 due to warping or the like and has small sensitivity unevenness.

(Prior Art) Radiographic images such as x11 images are often used for disease diagnosis.

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

In this method, radiation (generally X-rays) transmitted through the object is absorbed by a phosphor, and then this phosphor is excited with light or thermal energy, so that the phosphor accumulates due to the absorption of the radiation. This method emits the radiation energy in the form of fluorescence and detects this fluorescence to create an image.

Specifically, for example, U.S. Patent No. 3,859,527 and Japanese Unexamined Patent Publication No. 55-12144 disclose a radiation image conversion method using a stimulable phosphor and using visible light or infrared rays as stimulable excitation light. It is shown.

This method uses a radiation image conversion panel (hereinafter referred to as conversion panel) that has a photostimulable phosphor layer (hereinafter referred to as photostimulable layer). to accumulate radiation energy corresponding to the radiation transmittance of each part of the subject to form a latent image, and then scan this photostimulation layer with photostimulation excitation light to emit the accumulated radiation energy of each part. This is converted into light, and an image is obtained using an optical signal based on the intensity of this light.

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

The conversion panel used in this radiation image conversion method stores radiation image information and then releases the stored energy by scanning the stimulated excitation light, so it is possible to store radiation images again within the scanning diameter, and it can be used repeatedly. It is possible.

Such a conversion panel is usually composed of a photostimulable layer (1), a support (2) and a protective layer (3), as shown in FIG. In order to protect the conversion panel from external physical or chemical stimulation, 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 significantly during transportation, etc.
The difference in thermal expansion coefficients between the support and the protective layer has caused problems such as warpage and other deformation of the conversion panel, peeling of the sealed portion, and cracking of the protective layer and/or the support.

Further, deformation such as one-point warpage causes sensitivity unevenness. This sensitivity unevenness occurs because the distance between the light collection system of the radiation image conversion device and the conversion panel is not constant due to deformation of the conversion panel.

Peeling of the sealed portion, cracking of the protective layer and/or support, etc. are undesirable because they result in a decrease in moisture resistance of the conversion panel.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a conversion panel having a stimulable layer that provides a highly sharp radiographic image, has less deformation such as warping, has less unevenness in sensitivity, and has excellent durability.

[Structure of the Invention] (Means for Solving the Problems) The present invention comprises a support, a photostimulable phosphor layer, and at least one protective layer, and a stimulable phosphor layer between the support and the protective layer. In a radiation image conversion panel in which the body layer is encapsulated and sealed, the difference in linear thermal expansion coefficient between the support and the protective layer is 60X1.
0'/''0 or less.

What is the stimulable phosphor used in the present invention?

After the initial light or high-energy radiation has been applied, a stimulus (such as a priori, thermal, mechanical, chemical or electrical) (
It is a phosphor that exhibits stimulated luminescence depending on the amount of initial light or high-energy radiation irradiation due to H exhaustion excitation).
From a practical standpoint, it is preferably a phosphor that exhibits stimulated luminescence by stimulated excitation light of 50 C) nm or more. Examples of such stimulable phosphors include BaSO4:Ax described in JP-A-48-80487;
SrSO4:Ax described in Publication No. 80489,
JP-A-53-39277 (7) L i 2 B
aO7: Cu, Ag, etc., JP-A-54-47
Li2O.(B202)X:Cu and Li20h(B202)x:Cu of Publication No. 883.

SrS:Ce of Ag et al., U.S. Pat. No. 3,859,527.
, Sm, SrS:Eu, Sm, La2O2S:Eu
, Sm, and (Zn, Cd)S:Mn.

Furthermore, Zns described in JP-A No. 55-12142: Cu, Pb phosphor, - formula Baoa
xAi203': A barium aluminate phosphor represented by Eu, and an alkaline earth metal silicate phosphor represented by the formula M"O.xsio2:A.

In addition, alkaline earth fluorohalide phosphors having the general formula % described in JP-A-55-12143, general formula % described in JP-A-55-12144, %: A phosphor represented by the general formula % formula described in JP-A No. 55-12145. A phosphor represented by %: A phosphor represented by the general formula % formula described in JP-A-55-84389. % phosphor, general formula % formula described in JP-A No. 55-160078 Rare earth element activated divalent metal fluorohalide phosphor, - formula ZnS: A, CdS: A .

(Zn, Cd) SEA, S: A, ZnS: A, X and C
dS: Phosphor shown by A, X, JP-A-59-3827
Any of the following general formula % formula % described in Publication No. 8: A phosphor represented by near, any of the following general formula % formula % described in JP-A-59-155487: and an alkali halide phosphor represented by the following formula % described in JP-A No. 61-72087. In particular, alkali halide phosphors are preferable because they facilitate the formation of a stimulable layer using methods such as vapor deposition and φ sputtering.

However, the stimulable phosphor used in the conversion panel of the present invention is not limited to the above-mentioned phosphors, but is a phosphor that exhibits stimulated luminescence when irradiated with radiation and then irradiated with stimulable excitation light. Any phosphor may be used.

The conversion panel of the present invention may be a stimulable layer group consisting of one or more stimulable layers containing at least one of the above-mentioned stimulable phosphors. Furthermore, the stimulable phosphors contained in each stimulable layer may be the same or different.

The 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 no binder, it is 10-1000 μm.
, more preferably from the range of 20Q to 800-, and when containing a binder, the range is 20μ to too-
, preferably from 50μ to 500μ.

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

Examples of vapor deposition methods include evaporation, sputtering, and CVD.
Examples include laws.

Heat treatment of the photostimulated layer formed by vapor deposition improves the sensitivity to X-rays. In addition, after forming a stimulable phosphor matrix layer (hereinafter referred to as "phosphor matrix layer") that does not contain an activator on the support or protective layer, it is attached to the phosphor matrix layer by a method such as a thermal diffusion method. A predetermined stimulable layer can also be formed by doping with an active agent.

The support and the protective layer used in the present invention have a linear thermal expansion coefficient difference of 60XIO-7/'0 or less, preferably 40X10-'/'C! It is more preferably 25X10-'/'Q or less, particularly preferably 0.

If the difference in linear thermal expansion coefficient exceeds the above range, the conversion panel may be deformed such as warping or its airtightness may be reduced.

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

Further, the layer thickness of the support varies depending on the material of the support used, etc., but in terms of number, it is 80JIJ1 to 5000.

From the viewpoint of handling, it is preferably 200
-~200ou.

From the viewpoint of moisture resistance, it is desirable that the support has low moisture permeability.
The moisture permeability is preferably 10 (g/rn" @ 24 hr) or less, more preferably 10 (g/rn" @ 24 hr) or less, and the glass, ceramic, metal has excellent airtightness and moisture permeability is substantially O. etc. are particularly preferred.

In addition, when heat-treating the stimulable layer as described above,
The support is required to have heat resistance, and it is preferable that it does not crack or deform even when used continuously at 500°C or higher.
Furthermore, as a support that has excellent heat resistance and has poor reactivity with the stimulable layer, it is preferable that it does not react with the stimulable phosphor during heat treatment and affect performance such as X-ray sensitivity. Examples include crystallized glass, quartz, alumina, and alumina-silica sintered plates.

Crystallized glass, also known as glass ceramics, is made by melting and forming glass with the special composition shown below, and then reheating it under well-controlled conditions to solidify it from an amorphous state into uniform microcrystals while maintaining its original shape. It has turned into a collective. The main composition systems of crystallized glass currently in practical use are 1, for example, Li2O as silicate glass.
-3i02, Na20-CaO-MgO-5i02
, as aluminosilicate-based L I20-A 1203
-S I02, Na20-A I203-5 I
02.

Mg0-A 1203-5 I02, PbO-Zn0-B203 as borate glass, Zn0-B203-3 I02 as borosilicate glass, and the like.

Among the crystallized glass composition systems, Li20-S i 02
, N A20-Cao-MgO-S + 02, or Li20-A 1203-
3 I02, Na20-A 1203-S I02
, Mg0-A 1203-S +02 are preferred.

Furthermore, Li20-Al203-5i02 glass is preferable, and the composition ratio of each component is Li20:A120 in stoichiometric ratio.
More preferably, 3:5i02=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,
Any crystallized glass may be used as long as it has excellent heat resistance and flatness when heated.

The surface of these supports may be a smooth surface, or may be a matte surface for the purpose of improving adhesion with the stimulable phosphor layer, or the surface of the support may be an uneven surface. It may also be a surface structure in which individual micro tile-like plates are closely arranged.

Furthermore, on these supports, a subbing layer may be provided on the surface on which the stimulable layer is provided for the purpose of improving adhesion with the m alternating layers, and if necessary, a light reflecting layer, a light absorbing layer, etc. may be provided.

As the protective layer used in the conversion panel of the present invention, one that has good translucency and can be formed into a sheet shape is used. In order to efficiently transmit stimulated excitation light and stimulated luminescence, the protective layer desirably exhibits high transmittance in a wide wavelength range, and preferably has a transmittance of 80% or more in the wavelength range of 400 nm to 800 nm, and % or more is more preferable,
Moreover, in the range of 360ns+ to 400n■, 60% or more is preferable, and 80% or more is more preferable.

Further, it is preferable to provide an anti-reflection layer such as MgF2 on the surface of the protective layer, since it allows stimulated excitation light and stimulated luminescence to pass through efficiently and reduces the decrease in sharpness.

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

It is desirable that the moisture permeability of the protective layer is low in terms of the temperature resistance of the panel, and the moisture permeability is 10 Cg/rrI'-24hr).
The following is preferable, 1 (g/rn' -24hr
) The following are more preferable: glass having excellent airtightness, substantially zero water vapor permeability, and good translucency is particularly preferable.

The protective layer of the present invention may be a single layer, or may be multilayered as long as it does not impair the effects of the present invention, and may be composed of two or more layers made of different materials. For example, the first protective layer may be made of glass. This is a case where the organic polymer layer is used as the second protective layer.

If the thickness of the second protective layer is sufficiently thin compared to the thickness of the first protective layer, the coefficient of linear thermal expansion of the protective layer is substantially equal to the coefficient of linear thermal expansion of the first protective layer; Also.

Peeling between the first and second protective layers and warpage of the protective layer itself are not a problem.The second protective layer is a highly hygroscopic organic polymer layer, such as polyvinyl alcohol or ethylene-vinyl alcohol co-ffi combination. When provided on the photostimulable layer side of the first protective layer, the moisture adsorbed by the photostimulable layer during sealing is adsorbed and removed by the second protective layer, thereby preventing deterioration of the photostimulable layer due to moisture. This is preferable because the initial performance of the conversion panel is improved.

The protective layer may or may not be adhered to the photostimulable layer, but if there is a layer with a lower refractive index than the protective layer between the two layers, the sharpness will decrease less even if the protective layer is thickened. Preferably, such a low refractive index layer includes air, an inert gas such as nitrogen or argon, a liquid such as methyl alcohol or ethyl alcohol, CaF2. Na5AIFs, MgF2,5t
Examples include a thin film of a substance such as O2.

The practical thickness of the low refractive index layer is 0.05-3 m+w.

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

Furthermore, in order to encapsulate and seal the stimulable layer between the support and the protective layer, the periphery of the stimulable layer is sealed with a sealing member, or the adhesive portion between the spacer, the support and the protective layer is sealed. Seal.

Furthermore, the periphery of the spacer may be sealed using a sealing member, sealed by glass fusion using sealing glass such as low melting point glass, or sealed with an extension of the protective layer. Good too.

As the sealing member used, one with high airtightness and low moisture permeability is suitable. Specifically, epoxy resin,
Phenolic resin, cyanoacrylate resin, vinyl acetate resin, vinyl chloride resin, polyurethane resin,
Examples include organic polymer adhesives such as acrylic resins, ethylene vinyl acetate resins, polyolefin resins, chloroprene rubbers, and nitrile rubbers, and silicone adhesives. Epoxy resins and silicone resins used for sealing semiconductors and electronic parts are preferred because they have excellent moisture resistance, and epoxy adhesives are particularly preferred because they have low moisture permeability.

The conversion panel manufactured according to the present invention is used in the radiation image conversion method shown schematically in FIG.

That is, the radiation R from the radiation generator 41 enters the conversion panel 43 through the subject 42 .

This incident radiation is absorbed by the stimulable layer of the panel 43,
The energy is stored and a cumulative radiographic image is formed.

Next, this accumulated image is excited with stimulated excitation light from the stimulated excitation light source 44 to emit stimulated luminescence.

Since the intensity of the emitted stimulated luminescence is proportional to the amount of accumulated radiation energy, this optical signal is photoelectrically converted by a photoelectric conversion device 45 such as a photomultiplier tube, and one image reproduction device W14 is used.
6 and displayed as an image on the image display device 47, a radiographic image of the subject can be observed.

(Example) Next, the present invention will be explained by examples.

Example 1 A 1.111 m thick crystallized glass support (400 mm x 500 m layer) with a linear thermal expansion coefficient of 10XIO-'/'O was placed in an evaporator using an electron beam method (EB method) and then press-molded as a evaporation source. The alkali halide (RbBr) was placed in a water-cooled crucible.

Subsequently, the evaporator was evacuated, and while the zero-order support was maintained at 40°C to 45°C with a vacuum level of 5 x 10' orr,
Power was supplied to the EB gun to vaporize RbBr.

In order to obtain the desired RbBr layer, the deposition rate was detected by a film thickness monitor and controlled so that the base deposition rate was lO5λ/win. In addition, the electron beam scanned the surface of the crucible's deposition source in a raster pattern.

The vapor deposition was terminated when the layer thickness of the RbBr layer reached 300 p1, and a vapor deposited panel was obtained. This vapor-deposited panel was placed in a quartz crucible containing activated doping agent powder (RbBr: 10″4Ti), and after the lid was closed, the vapor-deposited panel was heated at 600°C for 1 hour. The linear thermal expansion coefficient is 65 with a thickness of 1.1 am on the stimulable layer.
Next, the periphery of the photostimulable layer was coated with an epoxy resin adhesive (AV138+
HV998, manufactured by Ciba Geigy Japan) at 100℃
This was cured and sealed to obtain a radiation image conversion panel as shown in FIG.

The radiation image conversion panel thus obtained was subjected to a tube voltage of 80
KVp(7)X! After irradiating L with lomR, it is stimulated with semiconductor laser light (780 nm), and the stimulated luminescence emitted from the stimulable phosphor layer is photoelectrically converted with a photodetector 5 (photomultiplier tube), and this signal is It was reproduced as an image by an image reproduction device and recorded on a silver halide film. The operating temperature of the radiation image conversion panel at this time was 40°C±1°C.

The unevenness of relative sensitivity was investigated from the obtained images and is shown in Table 1. What is the unevenness of relative sensitivity here?

The value obtained by dividing the standard deviation of relative sensitivity of 2048×2048 pixels by the average value of relative sensitivity is expressed as a percentage.

Further, the warpage of the obtained conversion panel at a usage temperature of 40° C. was investigated and is shown in Table 1. The warpage in Table 1 is expressed as the average value of the four times the conversion panel is placed on a flat plate with the concave side facing up.

Repeated durability is -40℃ to 50℃ in a 12 hour cycle.
The temperature change from -40°C was repeated and the time until abnormality occurred in the conversion panel was measured.

The results are shown in Table 1.

Examples 2 to 13 Conversion panels were manufactured in the same manner as in Example 1, except that the support and protective layer were combined as shown in Table 1 (all thicknesses were 1.1 mm). However, in Example 10, a 50-thick ethylene-vinyl alcohol copolymer layer was applied as a second protective layer to the stimulable layer side of the glass protective layer using a urethane adhesive (T-600, Japan). (manufactured by Soda).

These were evaluated in the same manner as in Example 1 and are also listed in Table 1.

Comparative Examples 1-2 Conversion panels were produced in the same manner as in Example 1, except that the support and protective layer were used in the combinations shown in Table 1. This was evaluated in the same manner as in Example 1, and is also listed in Table 1.

As shown in Table 1, in Comparative Examples 1 and 2, the sensitivity unevenness was very large due to the large warpage of the conversion panel, and abnormalities occurred in a short period of time in response to repeated temperature changes.

On the other hand, in the conversion panel of Example 1-13, since the warpage was small, sensitivity unevenness was small and good images were obtained. Furthermore, durability against repeated temperature changes has also been significantly improved.

[Effects of the Invention] Since 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, the panel does not undergo deformation such as warping during use, so sensitivity unevenness is small. Moreover, it has sufficient durability even when the conversion panel is exposed to severe temperature conditions. Therefore, the conversion panel of the present invention is highly useful.

[Brief explanation of the drawing]

1 and 3 are cross-sectional views of the radiation image conversion panel of the present invention, FIG. 2 is a cross-sectional view taken along line A-A' in FIG. 1, and FIG. 4 is a radiation image conversion panel using the radiation image conversion panel. FIG. 3 is an explanatory diagram of a conversion method. 1... Photostimulation layer 2... Support 3... Protective layer 4... Sealing member 5... Protective layer holding member (spacer) 41... Radiation generating device 42... Subject 43 ...Radiation image conversion panel 44...Photostimulation excitation light source 45...Photoelectric conversion device 46...Radiation image reproduction device 47...Radiation image display device 48...Filter FIG. Figure 3 z No.

Claims (1)

[Claims] In a radiation image conversion panel that has a support, a stimulable phosphor layer, and a protective layer, and in which the stimulable phosphor layer is sealed and sealed between the support and the protective layer, A radiation image conversion panel characterized in that the difference in linear thermal expansion coefficients is 60x10^-^7/°C or less.