JPH077119B2 - Radiation image conversion panel having an intermediate layer with restricted physical properties - Google Patents

Description

TECHNICAL FIELD The present invention relates to a radiation image conversion panel using a stimulable phosphor, and more particularly to a radiation image conversion panel that can withstand long-term use. Is.

[Background of the Invention]

Radiation images such as X-ray images are often used for disease diagnosis.

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

According to this method, the radiation (generally X-rays) transmitted through the subject is absorbed by the phosphor, and thereafter, the phosphor is excited by, for example, light or thermal energy, and the radiation accumulated by the phosphor is absorbed. In this method, energy is emitted as fluorescence, and this fluorescence is detected and imaged.

Specifically, for example, U.S. Pat.
No. 5-12144 discloses a radiation image conversion method using a stimulable phosphor and using visible light or infrared light as stimulated excitation light.

This method uses a radiation image conversion panel (hereinafter abbreviated as a conversion panel) having a stimulable phosphor layer (hereinafter abbreviated as abbreviated layer) formed on a support. The radiation energy corresponding to the radiation transmittance of the subject part is accumulated by applying the radiation that has passed through the subject to form a latent image, and then the photostimulable layer is scanned with the photostimulable excitation light to accumulate the respective parts. Radiation energy is emitted and converted into light, and an image is obtained by an optical signal depending on the intensity of the light.

This final image may be played back as a hard copy or 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.

Therefore, it is desirable that the conversion panel has a performance capable of withstanding long-term use or repeated use many times without deteriorating the image quality of the obtained radiation image. For that purpose, the photostimulable layer in the conversion panel must be sufficiently protected from external physical or chemical irritation.

In the conventional conversion panel, in order to solve the above problems, a method of providing a protective layer for covering the photostimulable layer surface on the support of the conversion panel has been adopted.

This protective layer is formed, for example, as described in JP-A-59-42500, by directly coating a protective layer coating solution on the photostimulable layer, or by forming a protective layer separately formed in advance. It is formed by a method of adhering on the exhaust layer.

Generally, a thin protective layer made of an organic polymer is used. The thin protective layer has the advantage of hardly reducing the sharpness of the conversion panel.

The relationship between the sharpness of a conversion panel having a photostimulable layer and the thickness of the protective layer is shown by MTF (modulation transfer function) at spatial frequencies of 1 lp / mm and 2 lp / mm.
Are shown in Table 1.

As shown in the table, the thicker the protective layer, the lower the sharpness. The cause is that reflected scattered light of incident photostimulable excitation light on the surface of the photostimulable layer is reflected at the protective layer-air interface and re-enters the photostimulable layer. The thicker the protective layer, the farther the reflected and scattered light reaches, and the information of pixels outside the target pixel is mixed.

In a general type intensifying screen-film system used for X-ray photography, the MTF at 1lp / mm is about 65%, and at 2lp / mm is about 35%.
%, It is not preferable that the conversion panel is inferior to the numerical value of the intensifying screen-film system, so that the thickness of the protective layer is preferably 10 μm or less.

However, a thin protective layer made of a commonly used organic polymer is permeable to a certain amount of moisture and / or humidity, and the stimulating layer absorbs moisture, and as a result, the radiation sensitivity of the conversion panel is reduced or the stimulating layer is stimulated. Accumulation of accumulated energy until receiving the irradiation of excitation light is large, resulting in variation and / or deterioration of image quality of the obtained radiation image.

For example, a polyethylene terephthalate film having a thickness of 10 μm (hereinafter simply referred to as “PET”) has a water vapor transmission rate of about 60 (g
/ m ² · 24hr), and permeates up to 60g of water per unit area per day. It is about 15 (g / m ² · 24 hr) for OPP (stretched polypropylene) with a film thickness of 10 μm. The moisture permeability of the protective layer is preferably 1 (g / m ² · 24hr) or less. To achieve this, PET is about 600 μm or more and OPP is about 150 μm.
The above thickness is required.

Further, in the conventional conversion panel having the thin protective layer as described above, the surface hardness of the protective layer is small, so that the protective layer surface may be scratched or thin due to contact with a mechanical part such as a transport roller during transport. Since the protective layer has insufficient impact resistance, it tends to be cracked or bent in the photostimulable layer, and the image quality of the obtained radiation image is deteriorated as the number of times of repeated use increases. On the other hand, if the protective layer is thickened, the defects due to the thinness can be erased, but the sharpness is lowered as described above. Beyond these contradictory events, improvements in moisture resistance, strength and impact resistance have been desired without impairing sharpness.

[Object of the Invention]

In line with the above requirements in a conversion panel using a stimulable phosphor, the object of the present invention is to sufficiently protect the stimulable layer against external chemical stimuli, particularly moisture, without impairing the sharpness of the image. A high-sensitivity, high-sharpness and high-graininess of the photostimulable layer can be maintained for a long period of time, and a conversion panel with high durability and durability that can be used in good condition can be provided. .

Another object of the present invention is to improve the durability and durability for long-term and repeated use by sufficiently protecting the photostimulation layer against external physical stimulus without impairing the sharpness of the image. To provide a conversion panel.

[Structure of Invention]

The object of the present invention is a radiation image conversion panel having a stimulable phosphor layer and a protective layer on a support, and at least two intermediate layers between the stimulable phosphor layer and the protective layer. A first intermediate layer having a lower refractive index than the protective layer, a second intermediate layer having a higher refractive index than the first intermediate layer between the intermediate layer in Table 1 and the stimulable phosphor layer, and The second intermediate layer is achieved by a radiation image conversion panel characterized by high hygroscopicity.

Hereinafter, the present invention will be described in detail.

FIG. 1 schematically shows a cross section of a conversion panel of the present invention, where 1 is a protective layer, 2 is a first intermediate layer, 3 is a second intermediate layer, 4 is a photostimulating layer, and 5 is a support. Is.

Hereinafter, the first intermediate layer may be referred to as a low refractive index layer and the second intermediate layer may be referred to as a high refractive index layer. In the present invention, by providing the medium interposed between the protective layer and the photostimulable layer with the relationship between the magnitude of the refractive index and the optical path as described above, the effect of reducing the sharpness reduction can be provided even if the protective layer is thick. it can.

Japanese Patent Application Laid-Open No. 62-63929 discloses an image recording / reading device in which a filter means is provided in front of the image storage layer to increase the excitation light absorbed in the image storage layer to increase the reading sensitivity. There is. In the present invention, the technical idea is different from the above invention,
It is an object of the present invention to provide a conversion panel having excellent durability and durability without impairing the sharpness of images.

Each constituent element will be described in more detail below.

As the protective layer of the present invention, a material that has good translucency and can be formed into a sheet can be used. For example, quartz, borosilicate glass, plate glass such as chemically strengthened glass, PET, OP
Examples include organic polymers such as P and polyvinyl chloride.

The protective layer of the present invention may be a single layer or a multilayer, and may be composed of two or more types of layers made of different materials. For example, a film in which two or more layers of organic polymer films are combined can be used. Examples of the method for producing such a composite polymer film include methods such as dry lamination, extrusion lamination and coextrusion coating lamination. The combination of two or more protective layers is not limited to those of organic polymers, but includes glass sheets of glass, glass sheets and organic polymer layers, and the like. For example, as a method of combining the plate glass and the polymer layer, there is a method of directly applying the protective layer coating solution onto the plate glass or forming a polymer protective layer separately formed in advance and adhering the same onto the plate glass. To be The two or more protective layers may be in close contact with each other or separated from each other.

The thickness of the protective layer of the present invention is practically 10 μm to 3 mm. In order to obtain good moisture resistance and impact resistance, the thickness of the protective layer is preferably 100 μm or more, and particularly when a protective layer of 500 μm or more is provided, a conversion panel excellent in durability and durability can be obtained, Even more preferable.

Further, when plate glass is used as the protective layer, it is particularly preferable because it has excellent moisture resistance.

In order for the protective layer to efficiently transmit stimulated excitation light and stimulated emission, it is desirable that the protective layer exhibit high transmittance in a wide wavelength range, and the transmittance is preferably 80% or more. For example quartz glass,
Examples include borosilicate glass. 330 nm for borosilicate glass
It exhibits a transmittance of 80% or more in the wavelength range of up to 2.6 μm, and quartz glass exhibits a high transmittance even at a shorter wavelength.

Further, it is preferable to provide an antireflection layer such as MgF _{2 on} the surface of the protective layer, because it has the effect of efficiently transmitting stimulated excitation light and stimulated emission and reducing the decrease in sharpness. The refractive index of the protective layer is not particularly specified, but most practically usable materials have a refractive index between 1.4 and 2.0.

The low refractive index layer of the present invention is made of a material having a lower refractive index than the protective layer. For example, the substances shown in Table 2 can be used, and they are preferably used in the state of a thin film formed by a vapor deposition method. Alternatively, the liquid layer shown in Table 3 can be used. Further, as the low refractive index layer of the present invention, it is particularly preferable to use a layer having a refractive index of substantially 1 such as a gas layer of air, nitrogen, argon or the like, or a vacuum layer because the effect of preventing sharpness reduction is high. .

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

The high refractive index layer in the present invention is made of a substance having a higher refractive index than the low refractive index layer. For example, an organic polymer film such as PET may be used, or a vapor deposition material used for an antireflection film or the like may be used. As the vapor deposition material, for example, those shown in Table 4 can be used.

Table 4 Material Refractive index Al ₂ O ₃ 1.62 Sb ₂ O ₃ 2.04 CeO ₂ 2.42 CeF ₃ 1.63 La ₂ O ₃ 1.95 LaF ₃ 1.59 PbF ₃ 1.75 NdF ₃ 1.60 Pr ₆ O ₁₁ 1.92 SiO 2.0 SIO ₂ 1.46 TiO ₂ 2.2 ˜2.7 ThO ₂ 1.8 ThF ₄ 1.52 ZnS 2.35 ZrO ₂ 2.1 Furthermore, if a substance having high hygroscopicity is used as the high refractive index layer, even higher moisture resistance can be imparted. Here, the hygroscopicity means the equilibrium moisture absorption rate.

When a high hygroscopic substance is used for the high refractive index layer 3 in FIG. 1, the high refractive index layer adsorbs and retains the moisture that has permeated the protective layer 1 and the low refractive layer 2 and / or the moisture that has permeated from the side edge of the conversion panel. And functions to prevent moisture from reaching the stimulating layer. Alternatively, the highly hygroscopic second intermediate layer takes away the water adsorbed to the stimulating layer during the production of the conversion panel, and further functions to dry the stimulating layer. Therefore, as described above, a conversion panel having excellent moisture resistance is manufactured by using a relatively thick protective layer having low moisture permeability and using a highly hygroscopic substance for the high refractive index layer (second intermediate layer). You can Second
The higher the equilibrium moisture absorption of the intermediate layer, the more preferable. The equilibrium moisture absorption of the second intermediate layer at a temperature of 25 ° C. and a relative humidity of 65% is practically 1% or more, preferably 2% or more, and particularly preferably 5% or more. The material for the second intermediate layer having high hygroscopicity can be selected from organic polymer materials, for example. As the organic polymer having a relatively high hygroscopicity, for example,
Polyvinyl alcohol, polyacrylamide, polyglycine, polymethacrylic acid, polyacrylic acid, polyvinylpyrrolidone, polyvinylamine, cellulose diacetate, cellulose triacetate, nylon 4, nylon 6, nylon 12, nylon 66, polyvinyl acetate, polymethylallyl alcohol Are preferred. The material of the second intermediate layer having high hygroscopicity is not limited to the organic polymer,
Any material having high equilibrium hygroscopicity may be used.

The thickness of the high refractive index layer according to the present invention is practically from 30 nm to 500 μm, but is preferably 50 μm or less, and more preferably 10 μm or less in order to enhance the effect of reducing the deterioration of sharpness.

The high refractive index layer may be in close contact with or separated from the photostimulating layer. One method is to use an adhesive to bring the high refractive index layer and the photostimulable layer into close contact, but in that case,
The refractive index of the adhesive is preferably close to the refractive index of the stimulating layer or the high refractive index layer.

When a gas layer or a vacuum layer is provided as the low refractive index layer in the present invention, there is a method of providing a spacer 6 at the side edge portion of the conversion panel to maintain a constant thickness, for example, as shown in FIG. Further, as shown in FIG. 3, a gas layer or a vacuum layer may be provided by dispersing a spacer material 7 between the protective layer and the high refractive index layer. As the spacer material, for example, a fine glass fiber piece having a diameter of several μm, which is used as a spacer material for a liquid crystal panel, can be used.

The stimulable phosphor used in the present invention is, after being irradiated with the first light or high-energy radiation, optical, thermal,
It is a phosphor that shows stimulated emission corresponding to the dose of initial light or high-energy radiation by mechanical, chemical, or electrical stimulation (stimulated excitation), but it is preferably 500 nm from a practical viewpoint. It is a phosphor that exhibits stimulated emission by the above stimulated excitation light. The stimulable phosphor, for example, described in JP-A-48-80487 BaSO _4: AX, JP 48
SrSO ₄ : AX described in JP-80489, JP-A-53-39277
No. of _{Li 2 B 4 O 7: Cu} , Ag , etc., Li ₂ O · of JP 54-47883 (B ₂
O ₂ ) x: Cu and Li ₂ O. (B ₂ O ₂ ) x: Cu, Ag, etc., U.S. Pat.
No. 9,527 SrS: Ce, Sm, SrS: Eu, Sm, La ₂ O ₂ S: Eu, Sm and (Z
n, Cd) S: Mn, X.

Further, the ZnS: Cu, Pb phosphor described in JP-A-55-12142, the barium aluminate phosphor represented by the general formula BaO.xAl ₂ O ₃ : Eu, and the general formula M ^II O.xSiO Examples thereof include alkaline earth metal silicate-based phosphors represented by ₂ : A. Further, the general formulas described in _{JP-A-55-12143 (Ba 1 -x-yMgxCay)} FX: eEu alkaline earth fluoride halide phosphor represented by ^2+, JP 55-12144 The phosphor represented by the general formula LnOX: xA described in JP-A-55-12145, and the phosphor represented by the general formula (Ba ₁ -xM ^II x) FX: yA described in JP-A-55-12145. 55-84389, a phosphor represented by the general formula BaFX: xCe, yA, and a rare earth element represented by the general formula M ^II FX.xA: yLn described in JP-A-55-160078. Activated divalent metal fluorohalide phosphors, phosphors represented by the general formulas ZnS: A, CdS: A, (Zn, Cd) S: A, ZnS: A, X and CdS: A, X A phosphor represented by any one of the following general formulas described in 59-38278, xM ₃ (PO ₄ ) ₂・ NX ₂ : yA M ₃ (PO ₄ ) ₂ : yA, one of the following general formulas nReX ₃・ _{mAX '2: xEu nReX 3 ·} mAX' 2: xEu, phosphor represented by YSM, and the following general formula ^{I X · aM II X '2} · bM III X "3:. Alkali halide phosphor, etc. represented by cA can be mentioned in particular alkali halide phosphor is deposited, easy to form a luminescent尽層by a method such as sputtering preferable.

However, the stimulable phosphor used in the conversion panel according to the present invention is not limited to the above-mentioned phosphor, and a phosphor that exhibits stimulated emission when irradiated with stimulated excitation light after being irradiated with radiation. Any phosphor may be used as long as it is a phosphor.

The conversion panel of the present invention may be a stimulating layer group composed of one or two or more stimulating layers containing at least one kind of the stimulable phosphor described above. The stimulable phosphors contained in the respective stimulable layers may be the same or different.

The photostimulable layer of the present invention may be applied by either a coating method or a vapor phase growth method.

The thickness of the stimulable layer of the panel of the present invention varies depending on the sensitivity of the intended conversion panel to radiation, the type of stimulable phosphor, etc., but 10 μm to 1000 μm when a binder is not contained.
The range is more preferably 20 μm to 800 μm, and if the binder is included, the range is 20 μm.
To 1000 μm, more preferably 50 μm to 500 μm
Is preferably selected from the range.

As the support of the conversion panel of the present invention, various polymeric materials,
Glass, ceramics, metal, etc. are used.

Examples of the polymer material include films of cellulose acetate film, polyester film, polyethylene terephthalate, polyamide, polyimide, triacetate, polycarbonate and the like. As a metal,
Examples thereof include a metal sheet or metal plate of aluminum, iron, copper, chromium or the like, or a metal sheet or metal plate having a coating layer of the metal oxide. Examples of the glass include chemically strengthened glass and crystallized glass. Examples of ceramics include sintered plates of alumina and zirconia.

The layer thickness of these supports varies depending on the material of the support used and the like, but is generally 80 μm to 2000 μm, and the handling point is more preferably 80 μm to 1000 μm.

The surface of these supports may be a smooth surface or may be a matte surface for the purpose of improving the adhesiveness with the stimulable phosphor layer. Further, the surface of the support may be an uneven surface, or may have a surface structure in which individual small tile-shaped plates are densely arranged.

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

In the conversion panel of the present invention, it is desirable to seal the side edges of the protective layer and the support in order to obtain further moisture resistance. Examples of the sealing method include glass fusion and a method using an adhesive. Examples of the adhesive include an epoxy resin adhesive and the like. The adhesive preferably has low moisture permeability.

As for the protective layer according to the present invention, as described in Japanese Patent Application No. 61-220492, a conversion panel matrix composed of a support and a photostimulable layer is housed in a protective bag made of a polymer film and the side edges are sealed. It may be in the form. In this case, the low refractive index layer can be formed in advance on the surface of the photostimulable layer or on the surface of the protective bag facing the photostimulable layer. When a gas layer or a vacuum layer is used as the low refractive index layer, the portion of the protective bag facing the photostimulation layer should have rigidity and a spacer should be interposed between the photostimulation layers.

As the sealing method, a heat sealing method, a high frequency sealing method, an ultrasonic sealing method and the like are preferable, but a pressure bonding method using an adhesive or a heat compression method may be used.

In the conversion panel of the present invention, the protective layer may also serve as a support. In that case, the support in the present invention may not have the ability to support the photostimulable layer substantially.

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

That is, in FIG. 4, 41 is a radiation generator, 42 is a subject, 43 is a conversion panel according to the present invention, 44 is a stimulated excitation light source, and 45 is photoelectric conversion for detecting stimulated fluorescence emitted from the conversion panel. A device, 46 is a device for reproducing the signal detected by 45 as an image, 47 is a device for displaying the reproduced image, 48
Is a filter that separates stimulated excitation light and stimulated fluorescence and transmits only stimulated fluorescence. It should be noted that after 45, any light information from 43 can be reproduced as an image in some form,
It is not limited to the above.

As shown in FIG. 4, the radiation from the radiation generator 41 enters the conversion panel 43 through the subject 42. The incident radiation is absorbed by the photostimulable layer of the panel 43, its energy is accumulated, and an accumulated image of a radiation transmission image is formed.

Next, this accumulated image is excited by stimulated excitation light from the stimulated excitation light source 44 and emitted as stimulated emission.

Since the intensity of the stimulated emission emitted is proportional to the amount of accumulated radiation energy, this optical signal is photoelectrically converted by the photoelectric conversion device 45 such as a photomultiplier tube and reproduced as an image by the image reproduction device 46. By displaying with the display device 47, a radiation transmission image of the subject can be observed.

〔Example〕

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

Examples 1 to 4 and Comparative Examples A and B Alkali halide phosphor (RbBr; 0.0006Tl) was vapor-deposited in an amount of 300 μm on a 500 μm-thick crystallized glass support by a vapor deposition apparatus.

Next, a protective layer having a thickness of 550 μm, a low refractive index layer and a high refractive index layer were provided on the photostimulable layer in the combination shown in Table 5. However, the value in parentheses in the table indicates the refractive index.

EVAL EFF in Table 5 is a trade name of ethylene-vinyl alcohol copolymer (manufactured by Kuraray Co., Ltd.), and the ethylene copolymerization ratio is 32 mol%. Evar EFF temperature 25 ℃,
The equilibrium moisture absorption at 65% relative humidity is 3.9% and that of PET is 0.2%.

In addition, as Comparative Examples, Comparative Examples A and B in which a protective layer was adhered to the photostimulable layer with an adhesive without using a low refractive index layer and a high refractive index layer using the same support and photostimulable layer It was set up as shown in Table 6.

Comparative example 80% of the photostimulable layer deposited on the support
After vacuum drying at 10 ° C. and 10 ⁻³ torr for 1 hour, a protective layer was provided and the side edges were sealed with an epoxy adhesive.

At this time, in Examples 1, 2, 3, and 4, a glass spacer having a thickness of 400 μm was installed as shown in FIG. 2 to provide an air layer of 75 μm between the high refractive index layer and the protective layer.

The samples were checked for moisture resistance and MTF sharpness.

Samples 1,2,3 and Comparative Example B showed good moisture resistance and
The radiation sensitivity did not decrease at all even when left for 48 hours under the condition of ℃ and humidity of 90%, and the stored energy was attenuated only slightly until it was irradiated with stimulated excitation light. The radiation sensitivity of Sample 1 was about 1.3 times higher than that of the other samples.

In Sample 4, some deterioration was recognized, but there was no problem in practical use. In sample A, the accumulated energy is greatly attenuated until it is irradiated with stimulated excitation light, which is a practical problem.

Table 7 shows MT at spatial frequencies of 1 lp / mm and 2 lp / mm for each sample.
Showed F. In Comparative Example B, the sharpness was remarkably lowered by providing the glass protective layer of 550 μm, while Samples 1, 2, 3, and 4 had the same thick protective layer of 550 μm. However, the sharpness is not significantly reduced.

Samples 1, 2, 3, and 4 had a thin protective layer and were about the same as Sample A, which has high sharpness, and showed clinically durable performance. In addition, Sample 1 had a higher radiation sensitivity than the others, and exhibited particularly excellent performance.

[Advantages of the Invention] The present invention provides a radiation image conversion panel having a stimulable phosphor layer and at least one protective layer on a support, wherein a protective layer is provided between the stimulable phosphor layer and the protective layer. First of low refractive index
The first layer is provided between the first layer and the stimulable phosphor layer.
The second layer, which has a higher refractive index and a higher hygroscopicity than the layer, protects the photostimulable layer from external chemical and physical irritation without sacrificing sharpness, and improves durability and durability. We were able to provide an excellent conversion panel.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic configuration of the present invention, and FIGS. 2 and 3 are diagrams showing a configuration example of the present invention. FIG. 4 is an explanatory diagram of a radiation image conversion method using a conversion panel. 1 ... Protective film 2 ... Low refractive index layer (first intermediate layer) 3 ... High refractive index layer (second intermediate layer) 4 ... Stimulable phosphor layer 5 ... Support

Claims (1)

[Claims] 1. A radiation image conversion panel having a stimulable phosphor layer and a protective layer on a support, wherein at least two intermediate layers are provided between the stimulable phosphor layer and the protective layer. A first intermediate layer having a refractive index lower than that of the protective layer, and a second intermediate layer having a refractive index higher than that of the first intermediate layer is provided between the first intermediate layer and the stimulable phosphor layer. The radiation image conversion panel is characterized in that the intermediate layer has high hygroscopicity.