JPH03135798A - Radiograph conversion panel - Google Patents

Abstract

PURPOSE:To protect a stimulation layer from an external chemical stimulus without impairing the sharpness of images and to use the above panel while maintaining the high sensitivity, high sharpness and high graininess thereof over a long period of time by constituting the protective layer on a base of an org. high-polymer layer and a glassy layer. CONSTITUTION:This panel is used to obtain the images for diagnosis of diseases. The panel is constituted of the stimmulable phosphor layer 3 which accumulates images, the low-refractive index layer 5 which does not degrade the sharpness by thicknesses and the protective layer. The protective layer consists of the org. high-polymer layer 1 and the glassy layer 2. The high-polymer layer 1 has resilience, absorbs the distortion by the coefft. of thermal expansion and has excellent strength and impact resistance if not only PET and OPP but also cellulose acetate and nitricellulose, etc., are used as the org. high polymer for forming this high-polymer layer. A thin glass sheet which has excellent moisture absorptivity, has a high transmissivity for its high sensitivity and is small in layer thickness in order to decrease distortions is used for the glassy layer 2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a radiation image conversion panel using a stimulable phosphor layer, and more particularly to a radiation image conversion panel with excellent durability.

[Background of the invention]

Radiographic 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 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) that has passed 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. This method involves emitting radiation energy as fluorescence, detecting this fluorescence, and creating an image.

Specifically, for example, U.S. Patent No. 3,859.527 and Japanese Patent Application Laid-open No. 12144/1987 disclose a radiation image conversion method using a stimulable phosphor and using visible light or infrared rays as stimulable excitation light. ing.

This method uses a radiation image conversion panel (hereinafter referred to as conversion panel) in which a photostimulable phosphor layer (hereinafter referred to as photostimulable layer) is formed on a support. A latent image is formed by applying radiation that has passed through the object to accumulate radiation energy corresponding to the radiation transmittance of each part of the object, and then by scanning this photostimulable layer with photostimulation excitation light, the accumulated radiation energy of each part is The system radiates radiation energy, converts it into light, and obtains an image 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.

Therefore, it is desirable that the conversion panel has the ability to withstand repeated use for a long period of time or many times without deteriorating the quality of the obtained radiographic image. For this purpose, the stimulable layer in the conversion panel needs to be sufficiently protected from external physical or chemical stimulation.

In order to solve the above problems in conventional conversion panels, a method has been adopted in which a protective layer is provided to cover the photostimulable layer surface on the support of the conversion panel.

This protective layer can be formed by directly applying a protective layer coating solution onto the stimulable layer, as described in JP-A No. 59-42500, or by applying a separately formed protective layer in advance. It is formed by a method of adhering on the final layer.

Generally, a thin protective layer made of an organic polymer is used. A thin protective layer has the advantage that it hardly reduces 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 expressed by the spatial frequency I Cp/mm and M of 212p/m+o.
It is shown in Table 1 using TF (modulation transfer function).

As shown in the table, the thicker the protective layer, the lower the sharpness. The reason for this is that reflected and scattered light of the incident stimulated excitation light on the surface of the stimulated layer is reflected at the protective layer-air interface and re-enters the stimulated layer.

The thicker the protective layer, the further the reflected and scattered light reaches, and the information of pixels other than the target pixel is mixed in.

In the general intensifying screen-film system used for X-ray photography, the MTF at 1ffp/■■ is approximately 65%, and 2Qp/
In the case of l11m, the value is about 35%, so it is not preferable that the value is inferior to that of the intensifying screen-film system in the conversion panel. Therefore, the thickness of the protective layer is desirably 10III+ or less.

However, the thin protective layers of commonly used organic polymers are to some extent permeable to water and/or humidity;
The photostimulable layer absorbs moisture, and as a result, the radiation sensitivity of the conversion panel decreases or the accumulated energy until it is irradiated with photostimulating excitation light is greatly attenuated, resulting in variation and/or deterioration of the image quality of the obtained radiation image. was.

For example, the moisture permeability of a polyethylene terephthalate film (hereinafter simply referred to as rPETJ) with a thickness of 10 μm is approximately 60 (g/m”・24 hr), and 60 g of water per unit area permeates per day. Film thickness 10 μm 0PP (
IL about 15 (g/a”・24
hr) There is. The moisture permeability of the protective layer is 1 (g/+
2.24 hr) or less, and in order to achieve this, a thickness of about 600 μm or more for PET and about 150 μm or more for OPP is required.

In view of the above-mentioned drawbacks and mutuality between characteristics, the present applicant provided a layer with a lower refractive index than the protective layer between the photostimulable layer and the protective layer in Japanese Patent Application No. 63-6474. We are proposing a conversion panel. According to this, even if a thick protective layer is used, sharpness does not deteriorate, so high sensitivity and
It is possible to maintain high sharpness and high graininess.

However, in order to achieve the above purpose,
There are major restrictions on the materials of the protective layer and support. Using an inflexible material (for example, plate glass) for the protective layer has a great effect on moisture resistance, but on the other hand, if the difference in the coefficient of thermal expansion on the support is not small enough, the panel will warp significantly. The distortion caused by this reduces moisture resistance and long-term durability. Furthermore, since it lacks flexibility, it is insufficient in terms of strength and impact resistance. On the other hand, when an organic polymer layer is used, it is flexible, so distortion can be absorbed even if the thermal expansion coefficients are different, and it is also preferable from the viewpoint of strength and impact resistance, but on the other hand, it can last for a longer period of time. It is not sufficient if moisture resistance and durability are required.

Beyond these contradictory phenomena, there has been a desire for a conversion panel that has excellent strength and impact resistance, as well as moisture resistance and durability over a longer period of time.

[Purpose of the invention]

In accordance with the above requirements for conversion panels using stimulable phosphors, an object of the present invention is to sufficiently protect the stimulable layer from external chemical stimuli, especially moisture, without impairing image sharpness. To provide a highly durable and long-lasting conversion panel that can maintain high sensitivity, high sharpness, and high graininess of the stimulable layer for a long period of time, and can be used in good condition. be.

Another object of the present invention is to sufficiently protect the photostimulable layer from external physical stimuli without impairing the sharpness of the image, thereby improving durability and durability for long-term and repeated use. The goal is to provide a conversion panel that allows

[Structure of the invention]

The object of the present invention is to provide a radiation image conversion panel having a stimulable phosphor layer, a low refractive index layer, and a protective layer on a support, in which the protective layer is composed of an organic polymer layer and a vitreous layer. Achieved by panels.

The present invention will be explained in detail below.

FIG. 1 shows a structural cross section of the conversion panel of the present invention, where l is an organic polymer layer, 2 is a glassy layer, 3 is a photostimulable layer, 4 is a support, and 5 is a low refractive index. It is a layer. 1.2 may be reversed.

Figure 2 shows a configuration in which a glassy layer is sandwiched between two organic polymer layers, and Figure 3 shows a configuration in which an organic polymer layer is sandwiched between two glassy layers. It's a meal.

These vitreous layers and organic polymer layers may be laminated in more layers than shown in FIGS. 1 to 3; they may have a multilayer structure. that time,
It is preferable that the glassy layers and the organic polymer layers are alternately laminated.

The vitreous layer used in the protective layer according to the present invention includes:
In order to prevent deterioration of properties due to moisture absorption of the stimulable layer, a material with excellent moisture resistance is preferable.

Further, it is preferable that the material has high transmittance for both stimulated excitation light and stimulated luminescence. This is to use the energy of the stimulated excitation light as effectively as possible to generate stimulated luminescence of the stimulable phosphor, and to detect the stimulated luminescence with as high sensitivity as possible.

Further, the glassy layer of the present invention preferably has a thin layer thickness in order to absorb distortion caused by warpage of the conversion panel.

A glass sheet can be mentioned as a glassy layer that can meet the above-mentioned requirements for a protective layer. Here, the glass sheet refers to a flat sheet with a thickness of 1000 μm or less. Typical examples of specific glass sheets include Microsheet (0211) manufactured by Corning and D263 manufactured by Desark, but the glass sheet is not limited to these and may be of any composition as long as it meets the requirements for the protective layer. But it doesn't matter.

As the organic polymer forming the organic polymer layer, the above-mentioned P
ET, OPP, cellulose acetate, nitrocellulose, polymethyl methacrylate, polyvinyl chloride, polyvinyl butyral, polycarbonate, polyethylene, polyvinylidene chloride, nylon, polytetrafluoroethylene, polyethylene trifluorochloride, vinylidene chloride-vinyl chloride Examples include copolymers, vinylidene chloride-acrylonitrile copolymers, and the like.

The thickness of the single vitreous layer according to the present invention is preferably 1 to 600 μm, more preferably 2 to 300 μm.

The thickness of the single organic polymer layer is preferably 10 μm to 3-1 μm.

Further, in order to obtain better durability, it is preferable that the thickness of a single glass layer and/or the entire thickness is smaller than the thickness of a single layer and/or the entire organic polymer layer. More preferably,
The thickness of a single vitreous layer and/or the whole is 1/2 or less of the thickness of a single organic polymer layer and/or the whole.

Next, a method for forming a protective layer according to the present invention will be described.

The first method is to apply a solution prepared by dissolving a highly transparent polymer substance in an appropriate solvent to the surface of the glass sheet on which the protective layer is to be installed, as disclosed in JP-A No. 59-42500. There is a method in which a protective layer is formed by applying the protective layer to the surface and drying it.

A second method is to bond a glass sheet and an organic polymer layer via a suitable adhesive to form a protective layer.

As a third method, as disclosed in Japanese Patent Application No. 61-220492, there is a method in which a glass sheet is placed in an organic polymer sheet bag and then vacuum-sealed to form a protective layer.

An antireflection layer such as MgF may be provided on the surface of these protective layers. By doing so, the photostimulable excitation light and the photostimulable luminescence are efficiently transmitted, and the reduction in sharpness is also reduced, which is preferable. Although the refractive index of the protective layer is not particularly limited, most materials that can be practically used have a refractive index between 1.4 and 2.0.

Examples of the low refractive index layer according to the present invention include air, inert gases such as nitrogen and argon, liquids such as methyl alcohol and ethyl alcohol, CaF2. Na5AQF,, MgF!
.

Examples include thin films of substances such as Sin.

A practical thickness of the low refractive index layer is 0.05 μI11 to 3+am.

In the case of providing a gas layer or a vacuum layer as a low refractive index layer in the present invention, there is a method of maintaining a constant thickness by providing spacers 6 at the side edges of the conversion panel, as shown in FIG. 4, for example.

Further, as shown in FIG. 5, a gas layer or a vacuum layer may be provided by dispersing a spacer material 7 between the protective layer and the photostimulable layer. As the spacer material, for example, a fine glass fiber piece with a diameter of several μm, which is used as a spacer material for liquid crystal panels, can be used.

The stimulable phosphor used in the present invention is irradiated with the first light or high-energy radiation, and then the stimulable phosphor is
A phosphor that exhibits stimulated luminescence corresponding to the amount of initial light or high-energy radiation irradiation due to mechanical, chemical, or electrical stimulation (stimulated excitation), but from a practical standpoint, preferably 500 nm. This is a phosphor that exhibits stimulated luminescence by the above-mentioned stimulated excitation light. Examples of the stimulable phosphor include Ba5O, which is described in JP-A No. 48-40487:
AX, 5rSO described in JP-A-4880489
a: AX-LixB40 of JP-A-53-9277
y: Cu, Ag, etc., LlxO” (BtO*) of JP-A No. 54-47883 x: Cu and LixO・
(B*0z)x: Cu, Ag, etc., US Patent 3,8
SrS of No. 59.527: Ce, SrS, SrS
: Eu.

S+a, La2O2S: Eu, Ss and (Zn,
Cd) S: Phosphor represented by Mn, JP-A-55-1
ZnS described in No. 2142: Cu.

pb phosphor, general formula BaO-xAQgos: Barium aluminate phosphor, general formula BaO-xAQgos: Eu
sio, : Alkaline earth metal silicate phosphor represented by A, general formula (Ba, x-yMgxCay) described in JP-A-55-12143 FX: eEu2+
Alkaline earth fluorohalide phosphor represented by the general formula LnOX described in JP-A-55-12144:
Phosphor represented by xA, general formula (Ba, xMIx) described in JP-A-55-12145 FX: Phosphor represented by yA, general formula BaFX described in JP-A-55-84389 : Phosphor represented by xCe, yA, general formula M described in JP-A-55-160078
]IFX-xA: Rare earth element activated divalent metal fluorohalide phosphor represented by yLn, general formula ZnS: A
, CdS: A, (Zn,Cd)S: A, S:
A, ZnS: A, X and CdS: A, a phosphor represented by :
xEu and nReX1 ・mAX'= : xEu,
ysm, and the following general formula M-X-aM
Examples include an alkali halide phosphor represented by IIx'2.bMIx"3:cA. In particular, an alkali halide phosphor is preferred because it facilitates formation of a stimulable layer by methods such as vapor deposition and sputtering.

However, the stimulable phosphor used in the panel according to the present invention is not limited to the above-mentioned phosphor, 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 kind of the above-mentioned stimulable phosphors. Furthermore, the stimulable phosphors contained in each stimulable layer may be the same or different.

The stimulable layer of the present invention may be formed by either a coating method or a vapor deposition method.

The layer thickness of the photostimulable layer in the panel of the present invention varies depending on the radiation sensitivity of the intended conversion panel, the type of photostimulable phosphor, etc., but in the case of not containing a binder, it is lOμlll-1.
000 μm, more preferably 20 μm to 800 μm
It is preferably selected from the range of m, and when it contains a binder, it is preferably selected from the range of 20 μm to 1000 μm, more preferably from the range of 50 μm to 500 μm.

Supports for the conversion panel of the present invention include various polymeric materials,
Glass, ceramics, metal, etc. can be used.

Examples of the polymeric material include films such as cellulose acetate film, polyester film, polyethylene terephthalate, polyamide, polyimide, triacetate, and polycarbonate. As a metal,
Examples include metal sheets or metal plates of aluminum, iron, copper, chromium, etc., or metal sheets or metal plates having a coating layer of the metal oxide. Examples of the glass include chemically strengthened glass and crystallized glass. Furthermore, 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, but is generally 80 μm to 2000 μm, more preferably 80 μm to 10 μm from the viewpoint of handling.
00μ pus.

The surfaces of these supports may be smooth or matte for the purpose of improving adhesion to the phosphor layer.

Further, the surface of the support may be an uneven surface, or may have a surface structure in which individual micro tile-like plates are closely arranged.

Further, on these supports, a subbing layer may be provided on the surface on which the phosphor layer is provided for the purpose of improving the adhesion with the phosphor layer.

In the conversion panel of the present invention, the protective layer can also serve as a support. In that case, the support referred to in the present invention does not need to have substantially the ability to support the stimulable layer.

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

That is, in FIG. 6, 11 is a radiation generating device;
2 is a subject, 13 is a conversion panel according to the present invention, 14 is a photostimulated excitation light source, 15 is a photoelectric conversion device that detects stimulated fluorescence emitted from the conversion panel, and 16 is a signal detected by 15 as an image. A reproduction device, 17 a device for displaying the reproduced image, and 18 a filter that separates stimulated excitation light and stimulated fluorescence and transmits only stimulated fluorescence. It should be noted that the elements after 15 are not limited to the above, as long as they can reproduce the optical information from 13 as an image in some form.

As shown in FIG. 6, radiation from the radiation generating device 11 enters the conversion panel 13 through the subject 12.

This incident radiation is absorbed by the stimulable layer of the panel 13,
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 I4 to emit stimulated luminescence.

Since the strength of the emitted stimulated luminescence is proportional to the amount of accumulated radiation energy, this optical signal is photoelectrically converted by, for example, a photoelectric conversion device 15 serving as a photoelectron multiplier, and then transmitted to an image reproduction device 16.
By reproducing the image as an image and displaying it on the image display device 17, a radiographic image of the subject can be observed.

〔Example〕

Next, the present invention will be explained by examples.

Example 1 Alkali halide phosphor (RbBr; 0.0006T2) was deposited on a 500μ thick crystallized glass support using a vapor deposition device.
) was deposited to a thickness of 300 μm.

Separately, a 500 μm thick glass sheet (manufactured by Desark Co., Ltd., D 263; refractive index 1-52) was bonded to a 500 μm thick transparent PET (refractive index 1.54) using epoxy adhesive for protection. formed a layer.

Next, a protective layer was provided on the photostimulable layer with a low refractive index layer (air layer: 200 μm, refractive index 1.0) interposed therebetween. In this way, a conversion panel A according to the present invention was obtained.

Example 2 Example 1 except that the thickness of the glass sheet was 200 μm
In the same manner as above, a conversion panel B according to the present invention is obtained.

Example 3 Example I except that the thickness of the glass sheet was 100 μm
In the same manner as above, a conversion panel C according to the present invention is obtained.
.

Example 4 Glass sheet thickness: 50μW% PET thickness: 25%
A conversion panel D according to the present invention was obtained in the same manner as in Example 1 except that the thickness was 0 μm.

Example 5 As a protective layer, a 50 μm-thick glass sheet was used as the center, and 100 μm PET and 50 μl glass sheets were laminated on both sides of the glass sheet, and PUT, glass sheet, and PET were laminated in this order using an epoxy adhesive. A conversion panel E according to the present invention was obtained in the same manner as in Example 1 except for the formation. .

Example 6 A glass sheet with a thickness of about 100 μm was replaced with a glass sheet with a thickness of 100 μm
Example 1 except that a protective layer was formed by placing it in an ET bag and sealing the opening r:Im while vacuuming the inside of the bag.
In the same manner as above, a conversion panel F according to the present invention was obtained.

Comparative Example Comparative panels P and Q were obtained in the same manner as in Example 1, except that 1000 μm thick plate glass or 1000 μm thick PET was used alone as the protective layer.

The conversion panels A to F according to the present invention and comparative panels P and Q thus obtained are shown in Table 2.

These radiation image conversion panels were repeatedly evaluated for durability.

Repeated durability is -40℃~50℃ in 12 hour cycle.
The temperature change from C to -40°C was repeated, and the time until abnormality occurred in the conversion panel was measured. From the result table,
Comparative panel P had excellent moisture resistance, but due to the difference in thermal expansion coefficient from the support, peeling occurred at the sealed portion. In addition, although panel Q does not cause peeling of the sealed part,
Since the inherent moisture permeability of the protective layer was inferior to that of Panel P, the sensitivity decreased significantly due to the moisture that entered.

On the other hand, since the panel of the present invention combines a flexible organic polymer sheet with a glass sheet having excellent moisture resistance, the repeated durability of the panel is superior to that of the comparative panel. A decrease in sensitivity did not occur until an abnormality was observed in the panel.

In particular, panels B, C, D, E, and F have glass sheets that are thinner than the organic polymer sheet, so that the panels receive less distortion, and their repeated durability is significantly improved compared to panel A.

In addition, in the present invention, as in Panels D and F, the overall thickness of the protective layer can be made thinner without reducing the repeated durability, so the absorption of stimulated luminescence light and X-rays in the protective layer can be reduced. This is also effective in terms of improving sensitivity.

〔Effect of the invention〕

The present invention provides a radiation image panel having a stimulable phosphor layer, a low refractive index layer, and a protective layer on a support, in which sharpness is impaired by providing a protective layer consisting of a vitreous layer and an organic polymer layer. It was possible to provide a conversion panel that sufficiently protects the stimulable layer from external chemical and physical stimulation without any problems, and has excellent durability and durability.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the basic configuration of the present invention, and FIGS. 2 to 5 are diagrams showing other configuration examples of the present invention. FIG. 6 is an explanatory diagram of a radiation image conversion method using a conversion panel. ■...Organic polymer layer 2...Vitreous layer 3...Stimulable phosphor layer 4...Support 5
...Low refractive index layer (air layer) 6 ... Spacer 7
・・・ Spacer material

Claims (1)

[Claims] 1. A radiation image conversion panel comprising a stimulable phosphor layer, a low refractive index layer, and a protective layer on a support, wherein the protective layer comprises an organic polymer layer and a vitreous layer.