JP2705943B2 - Radiation image conversion panel - Google Patents

Description

The present invention relates to a radiation image conversion panel having a stimulable phosphor layer, and more particularly, to a radiation image conversion panel which is not deteriorated by invasion of moisture. The present invention relates to a radiation image conversion panel having a stimulable phosphor layer having excellent initial performance.

(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 thereafter, the phosphor is excited by, for example, light or heat energy to cause the phosphor to emit radiation energy accumulated by the radiation absorption as fluorescence, and the fluorescence is detected. This is a method of imaging.

Specifically, for example, US Pat. No. 3,859,527 and JP-A-55-12144 disclose a radiation image conversion method using a 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).
A radiation image transmitted through the subject is applied to the stimulating phase of the conversion panel to accumulate radiation energy corresponding to the radiation transmittance of each part of the subject to form a latent image, and then the stimulating layer is formed. 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 emits the stored energy by scanning the stimulating excitation light after accumulating the radiation image information, so that the radiation image can be accumulated again after the scanning, and can be used repeatedly. It is possible.

Therefore, it is desirable that the conversion panel has a performance that can withstand long-term use or repeated use many times without deteriorating the image quality of the obtained radiation image. For this purpose, the photostimulable layer of the conversion panel needs to be sufficiently protected from external physical or chemical stimuli.

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

This protective layer is formed, for example, by directly applying a coating liquid for a protective layer on the photostimulable layer, as disclosed in JP-A-59-42500, or a protective layer formed separately in advance. It is formed by a method of bonding on the photostimulable layer.

As the protective layer, a thin protective layer (about several tens μm in thickness) made of an organic polymer is generally used. The reason why such a thin protective layer is used is to prevent a reduction in sharpness of the conversion panel.

For example, the relationship between the sharpness of a conversion panel having a photostimulable layer and the thickness of a protective layer is determined by using a spatial frequency of 1 p / mm and a 2 lp / mm MTF.
(Modulation transfer function) is shown in the table below.

As shown in the table, the sharpness decreases as the protective layer becomes thicker. This is because the reflected scattered light of the stimulating excitation light on the surface of the stimulating layer is reflected at the protective layer-air interface and reenters the stimulating layer. The thicker the protective layer, the farther the reflected scattered light reaches, and mixes information of pixels outside the target pixel, so that the sharpness is reduced.

In a general intensifying screen-film system used for X-ray photography, the MTF at 1 p / mm is about 65%, and the MTF at 2 lp / mm is about 3%.
Since it shows 5%, it is not preferable for the conversion panel to be inferior to the value of the intensifying screen-film system.
The thickness of the protective layer is desirably 10 μm or less.

(Problems to be solved) However, a thin protective layer made of a commonly used organic polymer is permeable to a certain amount of moisture, moisture, and the like,
The stimulable layer absorbs moisture, resulting in a decrease in radiation sensitivity of the conversion panel or a large attenuation of stored energy until irradiated with stimulating excitation light, resulting in unevenness and deterioration in the image quality of the obtained radiation image. .

When a conversion panel having such a thin protective layer is used under severe temperature and humidity conditions, or when a conversion panel using a stimulable phosphor that does not have sufficient resistance to moisture is used, the protective layer Deterioration of the photostimulable layer due to a small amount of moisture that penetrates and penetrates the film has become a problem. For example, in the case of a polyethylene terephthalate film having a thickness of 20 μm (hereinafter abbreviated as PET film) which is a commonly used protective layer, its moisture permeability is 25 g / m ² · 24 hr, and 25 g per unit area per day.
It is permeable to moisture.

Such a conversion panel, in order to improve the moisture resistance,
It is manufactured by sealing a peripheral portion of a laminate comprising a support, a stimulable phosphor and a protective layer. As a sealing method,
For example, a method of sealing the peripheral portion with a sealant and fixing the sealant from the outside with a fixing agent (Japanese Patent Laid-Open No. 61-237099), or sealing with the peripheral portion covered with an extension of the protective layer The method (JP-A-61-237100) and the like are used.

However, the effect of moisture permeating the protective layer on the photostimulable layer cannot be sufficiently prevented only by sealing in this manner.

Accordingly, an object of the present invention is to provide a radiation image conversion panel which prevents deterioration of a stimulable phosphor due to intrusion of moisture, improves initial performance, and has good sharpness.

[Constitution of the Invention] (Means for Solving the Problems) The present invention relates to a radiation image conversion panel having a stimulable phosphor layer (hereinafter referred to as a stimulable layer) between a support and a protective layer. A sealing member provided around the stimulable phosphor layer; and a low refractive index layer having a lower refractive index than the protective layer between the stimulable phosphor layer and the protective layer. The stimulable phosphor layer and the desiccant are sealed in a space formed by the support, the protective layer, and the sealing member.

FIG. 3 schematically shows an example of the conversion panel of the present invention, wherein 1 is a photostimulable layer, 2 is a protective layer, 3 is a support,
Reference numeral 4 denotes a moisture absorbing agent, 5 denotes a sealing member, 6 denotes a spacer, and 7 denotes a low refractive index layer.

The stimulable phosphor used in the present invention refers to a stimulable phosphor (stimulated stimulus) such as optical, thermal, mechanical, chemical or electrical after irradiation with the first light or high energy radiation. It is a phosphor that exhibits stimulated emission corresponding to the dose of the first light or high-energy radiation. However, from a practical viewpoint, it is preferably a phosphor that exhibits stimulated emission by excitation light of 500 nm or more. Such stimulable phosphors include, for example, Ba described in JP-A-48-80487.
SO _4: AX, are described in JP-A-48-80489 SrSO _4:
AX, Li ₂ B ₄ O _{7 of} JP-A-53-39277: Cu, Ag, etc.
4-47883, Li ₂ O. (B ₂ O ₂ ) _x : Cu and Li ₂ O. (B ₂ O ₂ ) _x : C
SrS: Ce, Sm, SrS: Eu, S of U.S. Patent 3,859,527
m, La ₂ O ₂ S: Eu, Sm and (Zn, Cd) S: Mn.

Also, ZnS: C described in JP-A-55-12142
u, Pb phosphor general formula BaO · xAl ₂ O _3: barium aluminate phosphor represented by Eu, and the general formula M ^II O · xSiO _2: alkaline earth metal silicate phosphor represented by A is exemplified Can 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, formula is described in 12144 JP LnOX: phosphor represented by xA, the general formulas described in ^{_{JP-a-55-12145 (Ba 1-x M II}} x) FX: fluorescent represented by yA Body, a phosphor represented by the general formula BaFX: xCe, yA described in JP-A-55-84389, and a general formula M ^II FXxA: yLn described in JP-A-55-160078. A rare-earth activated bivalent metal fluorohalide phosphor represented by the general formula ZnS: A, CdS: A, (Zn, Cd) S: A, S: A, ZnS: A,
X and CdS: A, phosphor represented by X, the following which are described in JP-A-59-38278 one of the general formula _{xM 3 (PO 4) 2 ·} NX 2: yA M 3 (PO 4) _2: phosphor represented by yA, following which are described in JP-a-59-155487 any of formulas _{nReX 3 · mAX '2: xEu} nReX 3 · mAX' 2: xEu, fluorescent represented by ySm body, below and are described in JP-a-61-72087 formula ^{M I X · aM II X '} 2 · bM III X "3:. alkali halide phosphor, etc. represented by cA can be mentioned in particular alkali Halide phosphors are preferred because they can easily form a photostimulable layer by methods 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 stimulable layer in the conversion panel of the present invention may be a stimulable layer group including one or two or more stimulable layers containing at least one kind of the stimulable phosphor described above. Further, the stimulable phosphor 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 when no binder is contained, a range of 10 μm to 1000 μm, preferably 20 μm to Selected from the range of 800 μm,
When it contains a binder, it is selected from the range of 20 μm to 1000 μm, preferably the range of 50 μm to 500 μm.

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

Examples of the support used in the present invention include various polymer materials, glass, ceramics, and metals.

Examples of the polymer material include films of cellulose acetate film, polyester film, polyethylene terephthalate, polyamide, polyimide, triacetate, polycarbonate and the like. Examples of the metal 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 the ceramic include a sintered plate of alumina or zirconia.

The support used in the present invention desirably has a low moisture permeability. The moisture permeability is preferably 10 (g / m ² · 24 hr) or less,
(G / m ² · 24 hr) or less is more preferable. A metal sheet or a metal plate having excellent airtightness and substantially zero moisture permeability, glass, ceramics, and the like are particularly preferable.

The thickness of the support varies depending on the material of the support to be used and the like, but is generally 80 μm to 5 mm, and is preferably 200 μm to 3 mm from the viewpoint of easy handling.
mm.

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 photostimulable layer is provided for the purpose of improving the adhesiveness with the photostimulable layer, and if necessary, a light reflecting layer, a light absorbing layer 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 wavelength range of 00 nm, it is preferably at least 60%, more preferably at least 80%.

Examples of such a material include plate glass such as quartz, borosilicate glass, and chemically strengthened glass, and organic polymer compounds such as PET, drawn polypropylene, and polyvinyl chloride. Borosilicate glass has a wavelength range of 330 nm to 2.6 μm
It shows a transmittance of 80% or more, and quartz glass shows a high transmittance even at a shorter wavelength.

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 protective layer used in the present invention desirably has a low moisture permeability, and the moisture permeability is preferably 10 (g / m ² · 24 hr) or less.
(G / m ² · 24 hr) or less is more preferable. Glass having excellent airtightness and having substantially zero moisture permeability is particularly preferred.

Further, the thickness of the protective layer is 100 μm to 5 mm, and preferably 300 μm to 3 mm in order to obtain good moistureproofness and impact resistance.

The protective layer of the present invention may be a single layer, a multilayer, or may be composed of two or more types of layers having different materials. For example, a film in which two or more organic polymer films are combined can be used. Examples of a method for producing such a composite polymer film include methods such as dry lamination, extrusion lamination, and coextrusion coating lamination.

Combinations of two or more protective films are not limited to organic polymer layers, and include plate glass layers and a sheet glass and organic polymer layer. For example, as a method of combining a sheet glass and a polymer layer, there is a method in which a protective layer coating liquid is directly applied to the sheet glass to form or a separately formed polymer protective layer is adhered to the sheet glass. . Note that two or more protective layers may be in close contact with each other or may be separated from each other.

This protective layer may be formed by directly applying a protective layer coating solution on the photostimulable layer, or by bonding or placing a separately formed protective layer on the photostimulable layer, A stimulable layer may be formed on the substrate.

The protective layer may or may not adhere to the photostimulable layer,
When a layer having a lower refractive index than the protective layer (hereinafter referred to as a low refractive index layer) is provided between the two layers, even if the protective layer is thickened, the sharpness decreases little and a conversion panel excellent in both moisture resistance and sharpness can be obtained. Obtained and preferred.

As the low refractive index layer, a gas layer having a refractive index of substantially 1 is particularly preferable, and examples thereof include air, nitrogen, and argon.

When a low-refractive-index layer made of a gas layer is provided, a spacer 6 may be provided between the protective layer and the support in order to maintain the interval between the photostimulable layer and the protective layer, as shown in FIG. . As the spacer, plastic, metal, glass, ceramics, or the like can be used.

Examples of the hygroscopic agent used in the present invention include silica gel, CaCl ₂ , for LiCl, polyvinyl alcohol, highly hygroscopic organic polymer compounds such as ethylene-vinyl alcohol copolymer, and the like, and these may be used as they are. Alternatively, it may be used after being molded, or may be used as a form in which these hygroscopic agents are contained in a resin.

The moisture absorbent has a water adsorption amount per gram of stimulable phosphor.
Use an amount that will be between 0.1 and 50 mg.

The hygroscopic agent may be anywhere between the layer between the support and the protective layer, but excludes the layer between the photostimulable layer and the protective layer in the area where the stored X-ray energy is converted and used as an image. The hygroscopic agent may be continuous or intermittent. Preferably, the hygroscopic agent is filled without gaps between the support and the protective layer and between the outer portion of the photostimulable layer and the sealing member.

Examples of the sealing member used in the present invention include an epoxy resin, a phenol resin, a cyanoacrylate resin, a vinyl acetate resin, a vinyl chloride resin, a polyurethane resin, an acrylic resin, an ethylene vinyl acetate resin, and a polyolefin. Organic resin-based adhesives such as resin-based resins, chloroprene-based rubber, and nitrile-based rubber, and silicone-based 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. Further, in addition to the above-described adhesive, sealing may be performed by glass fusion using sealing glass such as low melting point glass, or sealing may be performed at an extension of the protective layer.

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

That is, the radiation from the radiation generator 41
The light enters the conversion panel 43 through 42.

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, the accumulated image is excited by the stimulating light from the stimulating light source 44, and the intensity of the stimulating light is proportional to the amount of accumulated radiation energy. By performing the photoelectric conversion by the conversion device 45, reproducing the image by the image reproduction device 46, and displaying the image by the image display device 47, the radiation transmission image of the subject can be observed.

Since the moisture absorbing agent is sealed in the conversion panel of the present invention, it is possible to effectively adsorb and remove moisture entering from the sealing portion of the periphery of the conversion panel with the moisture absorbing agent. In addition, during the production of the conversion panel, the moisture that has been gradually adsorbed by the photostimulable layer is reliably adsorbed and removed by the hygroscopic agent, so that the photostimulable layer is prevented from deteriorating due to moisture, and the initial performance of the conversion panel is improved. be able to.

In particular, regarding a conversion panel with a thick protective layer and low moisture permeability, the penetration of moisture from the protective layer is slight, and the penetration of moisture from the sealing part is dominant. When the agent is provided, the moisture is adsorbed and removed by the hygroscopic agent effectively, and the effect of improving the moisture resistance and the initial performance is remarkable.

In the case where a low refractive index layer made of a gas layer is provided, moisture is taken into the gas layer during the production of the conversion panel, and this moisture can also be adsorbed and removed by the moisture absorbent. Furthermore, since the moisture adsorbed by the photostimulable layer diffuses in the gas layer and reaches the hygroscopic agent, even if the hygroscopic agent is provided at the peripheral portion of the photostimulable layer, the water is removed over the entire photostimulable layer. Therefore, it is particularly effective when a low refractive index layer composed of a gas layer is provided.

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

Reference Example 1 A 1.0 mm thick crystallized glass support (400 mm x 500 mm)
It was set in a vapor deposition device by the electron beam method (EB method). Next, an alkali halide phosphor (RbBr; 0.0006T1) was placed in a water-cooled crucible, and pressed to form a crucible.

Subsequently, the inside of the vapor deposition apparatus was evacuated to a vacuum degree of 5 × 10 ⁻⁶ Torr. Next, while maintaining the support at 40 to 45 ° C., power was supplied to the EB gun to evaporate the stimulable phosphor.

In order to obtain a desired photostimulable layer, the deposition rate was controlled by a film thickness monitor to be 10 ⁵ Å / min. The electron beam scanned the stimulable phosphor surface of the crucible in a raster pattern.

The vapor deposition was terminated when the thickness of the photostimulable layer reached 300 μm. The deposition area of the photostimulable layer was 370 mm × 470 mm using a stainless steel plate mask.

Next, in a portion of the support where the photostimulable layer is not deposited (outside of the photostimulable layer), polyethylene (Hisheet Dry, manufactured by Marutani Koki Co., Ltd., 25 ° C., 1.8g of equilibrium moisture absorption rate 3.3% at 80% RH)
(Layer thickness: 300 μm) It was arranged as shown in FIG. Further, a protective layer of polyvinylidene chloride having a thickness of 20 μm was adhered on the photostimulated layer (the surface opposite to the support) with a polyurethane adhesive (T-600, manufactured by Nippon Soda Co., Ltd.). This is heated at 80 ° C. for 1 hour and dried, and the periphery is epoxy resin-based adhesive (AV
138 + HV998, manufactured by Nippon Ciba Geigy Co., Ltd.) to produce a conversion panel as shown in FIG.

The radiation image conversion panel thus obtained was examined for the following characteristics, and the results are shown in Table 1.

Relative sensitivity Two hours after the sealing, the relative sensitivity of the conversion panel was examined as follows.

X-rays with a tube voltage of 80 KVp are irradiated for 10 mR, and after t seconds, stimulated by semiconductor laser light (780 nm), and stimulated emission emitted from the stimulable phosphor layer is detected by a photodetector (photomultiplier). The photoelectric conversion was performed, and a voltage value V _(t) of the signal was obtained. The voltage value of the signal obtained in the same manner for the conversion panel of the comparative example described later was defined as V0 _(t), and V ₍₅₎ / V0 ₍₅₎ was defined as the relative sensitivity.

Residual sensitivity After sealing for 2 hours at 40 ° C and 40% relative humidity, 1
After two weeks, one week, and one month Determined by

Sharpness MTF (modulation transfer function) at spatial frequency 1p / mm
%), And the sharpness of the conversion panel was evaluated.

Reference Example 2 Ethylene vinyl alcohol copolymer (20
2.7 g at 300 ° C, equilibrium moisture absorption at 65% RH (layer thickness 300 μm)
A conversion panel was manufactured in the same manner as in Reference Example 1 except that was used, and its characteristics were evaluated. The results are shown in Table 1.

Example 1 A 1.0 mm thick crystallized glass support (400 mm × 500 mm)
In the same manner as in Reference Example 1, the alkali halide phosphor (RbB
r; 0.0006T1) was deposited until the layer thickness became 300 μm.

Next, polyethylene (silica gel) is sealed as a hygroscopic agent in a portion of the support on which the photostimulable layer is not deposited (outside of the photostimulable layer) (equilibrium moisture absorption at 25 ° C., 80% RH: 14%).
7 g (layer thickness 1 mm) was arranged as shown in FIG.

A glass spacer having a thickness of 1 mm and a width of 5 mm was arranged as shown in FIG. 3 so that an air layer having a thickness of 700 μm was provided on the stimulable layer.

A glass protective layer having a thickness of 1.0 mm is further placed thereon, and then heated and dried at 80 ° C. for 1 hour, and the periphery is epoxy resin adhesive (AV138 + HV998, manufactured by Nippon Ciba Geigy Co., Ltd.). Then, a conversion panel as shown in FIG. 3 was manufactured.

The conversion panel thus manufactured was evaluated for characteristics in the same manner as in Reference Example 1, and the results are shown in Table 1.

Example 2 Ethylene vinyl alcohol copolymer (20
A conversion panel was manufactured in the same manner as in Example 1 except that 9.0 g (layer thickness: 1 mm) of equilibrium moisture absorption of 3.9% at 65 ° C. and 65% RH was used, and its characteristics were evaluated. The results are shown in Table 1.

Comparative Example 1 Reference Example 1 except that 1.0 mm plate glass was used as the protective layer.
A conversion panel was manufactured in the same manner as described above, and its characteristics were evaluated. The results are shown in Table 1.

Comparative Example 2 A conversion panel as shown in FIG. 4 was manufactured in the same manner as in Reference Example 1 except that no hygroscopic agent was used. The characteristics were evaluated and the results are shown in Table 1.

Comparative Example 3 A conversion panel as shown in FIG. 3 was manufactured in the same manner as in Example 1 except that no hygroscopic agent was used. The characteristics were evaluated and the results are shown in Table 1.

[Effect of the Invention] The radiation image conversion panel of the present invention has a low refractive index layer having a lower refractive index than the protective layer between the support and the protective layer, and further includes a photostimulable layer and a moisture absorbent. The moisture absorbent adsorbs and removes moisture that enters from a sealing portion around the conversion panel, and also absorbs and removes moisture contained in the stimulable layer at the time of manufacturing the conversion panel. The initial performance can be improved and the sharpness can be prevented from lowering without being deteriorated by moisture.

Therefore, according to the present invention, it is possible to provide a conversion panel that exhibits excellent characteristics even when used under severe temperature and humidity conditions or when a stimulable phosphor having poor moisture resistance is used.

[Brief description of the drawings]

FIG. 3 is a cross-sectional view of an embodiment of the radiation image conversion panel of the present invention, FIG. 1 is a cross-sectional view of a reference example, FIG. 2 is a cross-sectional view taken along line AA ′ of FIG. FIG. 4 is a sectional view of a radiation image conversion panel of a comparative example, and FIG. 5 is an explanatory diagram of a radiation image conversion method using the radiation image conversion panel. DESCRIPTION OF SYMBOLS 1 ... Photostimulation layer 2 ... Protective layer 3 ... Support 4 ... Adsorbent 5 ... Sealing member 6 ... Spacer 7 ... Low refraction layer 41 ... Radiation generator 42 ... Subject 43 ... Radiation image conversion panel 44 Photostimulation excitation light source 45 Photoelectric conversion device 46 Radiation image reproducing device 47 Radiation image display device 48 Filter

Claims (1)

(57) [Claims] 1. A radiation image conversion panel having a stimulable phosphor layer between a support and a protective layer, wherein: a sealing member provided around the stimulable phosphor layer; A low-refractive-index layer having a lower refractive index than the protective layer between the luminescent phosphor layer and the protective layer; and in a space formed by the support, the protective layer, and the sealing member. A radiation image conversion panel, wherein the stimulable phosphor layer and a moisture absorbent are enclosed.