JPH0271200A - Radiation image conversion panel - Google Patents

Abstract

PURPOSE:To enable keeping of a high quality sharpness by reducing spreading of stimulating rays by scattering of beam in a protection layer. CONSTITUTION:A conversion panel is constituted of a stimulation layer 3, a low refraction index layer 2 and a protection layer 1 provided on a carrier body 1. Then, a haze ratio of the protection layer 1 is set to be lower than 3% and a wide spreading of stimulating rays by scattering of the beam is suppressed and a downgrading of a sharpness is prevented and also a high transmissivity is obtained at a very wide range of wave length, as well. Also, the low refraction index layer 2 is made of a material having lower refraction index than the protection layer 1, and is contacted closely with the stimulation layer 3. A conversion panel 43 is formed in this way and when a radiation from a radiation generator 41 is irradiated to the panel 43 through a photo- object, the incident radiation is absorbed by the stimulation layer 3 and an accumulated image of a transmissive image is formed. Then, this transmissive image is excited by a stimulating rays source 44 and stimulated luminous signals are displayed on an image display device 47 as an image through a photo-electro converter 45 and an image refreshing device 46, and therewith a radiation penetrating image can be observed.

Description

Detailed Description of the Invention [Objective 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 having a stimulable phosphor layer. The present invention relates to a radiation image conversion panel that has excellent image sharpness because the spread of stimulated excitation light due to scattering is small.

(Prior Art) Radiographic images such as X-ray images are widely used and popular 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 by light or thermal energy, so that the phosphor accumulates due to the absorption of the radiation. This is a method in which radiation energy is emitted as fluorescence, and this fluorescence is detected and imaged.

Specifically, for example, U.S. Pat. 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 stimulable phosphor layer (hereinafter referred to as a ``stimulable layer'') on a support.
A radiographic image conversion panel (hereinafter referred to as “
This method uses a conversion panel (abbreviated as "conversion panel"), and the radiation that has passed through the object is applied to the photostimulable layer of this conversion panel, and radiation energy corresponding to the radiation transparency of each part of the object is accumulated to form a latent image. Thereafter, by scanning this photostimulation layer with photostimulation excitation light, the radiation energy accumulated in each part is emitted and converted into light, and an image is obtained by an optical signal depending 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 photostimulated excitation light, so it can store the radiation image again after scanning, and 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 that purpose,
The stimulable layer of the conversion panel needs to be sufficiently protected from external physical or chemical stimuli.

In conventional conversion panels, in order to solve the above problems, a method has been adopted in which a protection 11 is provided to cover the stimulable 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 disclosed 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.

A thin protective layer made of an organic polymer is generally used as the protective layer. Such a thin protective layer is used to prevent deterioration of 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 M at spatial frequencies of 1+2 p/mm and 2 ffp/mm.
It is shown in Table 1 using TF (modulation transfer function). In Table 1, PET is polyethylene terephthalate film.

As shown in Table 1, the thicker the protective layer, the lower the sharpness.

The reason for this is that reflected and scattered light of the incident photostimulative 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 is, the farther the reflected and scattered light will travel and mix in information from pixels other than the target pixel, resulting in a decrease in sharpness.

In a general type intensifying screen-film system used for X-ray photography, the MTF is approximately 65% in the case of 1 Qp/mm, and 2Qp/mm.
In the case of mm, the value is about 35%, so it is not desirable for the conversion panel to be inferior to the value of the intensifying screen-film system. Therefore, considering only the sharpness, the thickness of the protective layer is preferably 10 μm or less. .

However, the commonly used thin protective layers made of organic polymers are permeable to a certain degree of moisture and/or moisture, so that the photostimulation layer absorbs moisture, resulting in a reduction in the radiation sensitivity of the conversion panel or photostimulation. The attenuation of the accumulated energy until receiving light irradiation is large, resulting in variation and/or deterioration of the image quality of the obtained radiation images.

For example, the moisture permeability of PET with a thickness of 10 μm is approximately 60 (g/
m2・24hr) and 60g per unit area per day
Permeates moisture. For stretched polypropylene (hereinafter referred to as rOPPJ) with a film thickness of 10 μm, the
”・24hr).

By increasing the thickness of the protective layer in this way, the defects caused by the thinness can be eliminated, but the sharpness decreases as described above. Beyond these contradictory phenomena, we have improved moisture resistance, strength, and sharpness without compromising sharpness.
Improvements in impact resistance are desired.

[Problem that the invention seeks to solve]

As mentioned above, in conversion panels using conventional photostimulable phosphors, when a thin protective layer is used to improve image sharpness, chemical stimulation from the outside, especially the intrusion of moisture or There are problems in that the radiographic images obtained by this method may vary and deteriorate, and the photostimulable layer may be damaged due to external physical stimulation.

On the other hand, when a thick protective layer is used for the purpose of protection from such chemical and physical stimulation, image quality may deteriorate depending on the optical properties of the protective layer.

That is, the thicker the protective layer, the greater the extent to which the spread due to scattering of the excitation light inside the protective layer is amplified, resulting in a decrease in the sharpness of the image.

Therefore, the present invention is capable of sufficiently protecting the photostimulable layer from external physical and chemical stimuli, especially moisture, without impairing the sharpness of images, and which provides high sensitivity and high sensitivity of the photostimulable layer. It is an object of the present invention to provide a highly durable and durable conversion panel that maintains sharpness and high graininess for a long period of time and can be used in good condition.

[Structure of the invention]

(Means for Solving the Problems) The conversion panel of the present invention includes a stimulable phosphor layer, a low refractive index layer, and a protective layer provided on a support in this order, and the low refractive index layer located in the middle. The refractive index of the protective layer is set lower than the refractive index of the protective layer, and the haze rate of the protective layer is 3% or less.

The configuration of the conversion panel of the present invention will be explained based on the accompanying drawings. FIGS. 1 and 2 are schematic sectional views showing an example of the conversion panel of the present invention. In the figures, 1 represents a protective layer, 2 represents a low refractive index layer, 3 represents a photostimulable layer, 4 represents a support, and 5 represents a protective layer holding member.

The conversion panel of the present invention has a support 4 as shown in FIG.
A photostimulable layer 3, a low refractive index layer 2, and a protective layer 1 are provided thereon in this order. Further, the conversion panel of the present invention may have a protective layer holding member 5 as shown in FIG. One end of this protective layer holding member 5 is in close contact with the support body 4, and the other end is in close contact with the protective layer 1. Further, the peripheral edge of the stimulable layer 3 and the protective layer holding member 5 may be in contact with each other or may be apart from each other. Therefore, in the case of a conversion panel having the protective N@holding member 5 as a component, the low refractive index layer 2 includes the protective layer 11, the photostimulable layer 3 (or the photostimulable layer 3 and the support 4), and the protective layer holding member 5. It is constructed in a state where it is isolated from the external atmosphere by the member 5.

The protective layer in the conversion panel of the present invention is based on JISK671
The haze rate (!! value) defined by No. 4 is 3% or less, preferably 1% or less.

When this haze rate exceeds 3%, the spread of stimulated excitation light becomes large due to the spread of light scattering inside the protective layer, and the sharpness of the image deteriorates.

In addition, it is preferable that the protective layer has good translucency and can be formed into a sheet. Further, in order to efficiently transmit stimulated excitation light and stimulated luminescence, the protective layer preferably exhibits high transmittance over a wide wavelength range, and more preferably has a transmittance of 80% or more.

The moisture permeability of the protective layer is measured by the cup method (JIS 20208) to be lo, og/m''·24 hr or less, preferably 5.0 g/m''·24 hr or less.

The thickness of the protective layer is determined in relation to the haze rate and moisture resistance of its constituent materials, but in practice it is 10 μm to 10 μm.
4 mm, preferably 100 μm or more in order to have a predetermined haze rate and obtain good moisture resistance. When the thickness of this protective layer is 200 μm or more, it is preferable because a conversion panel with excellent durability and durability can be obtained.

Examples of materials forming such a protective layer include plate glass such as quartz, borosilicate glass, and chemically strengthened glass, and organic polymer compounds such as PET, OPP, and polyvinyl chloride.

Here, for example, an example of borosilicate glass with a thickness of 500 μm has a haze rate of 0.6%, and a thickness of 330 nm to 2.6 μm
It exhibits a transmittance of 80% or more in the wavelength range of . Thickness 500μ
An example of quartz glass having a haze ratio of 0.0% shows higher transmittance than borosilicate glass even at shorter wavelengths.

The haze rate also changes depending on the thickness and surface treatment of the protective layer. If the protective layer is plate glass, those with higher abrasive grades generally have lower haze rates. Furthermore, in the case of plastic films, those that are laminated or have matte or embossed surfaces generally have a high haze rate.

As a material forming the protective layer, the above-mentioned plate glass is preferable because it has excellent haze rate, transmittance, and moisture resistance.

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

The refractive index of the protective layer is not particularly limited, but in practice it is 1.4.
A range of ~2.0 is typical.

Two or more protective layers can be provided as necessary.

The low refractive index layer of the conversion panel of the present invention is a layer made of a material having a lower refractive index than the protective layer. The material constituting the low refractive index layer is not particularly limited as long as it has a refractive index lower than that of the protective layer, but it is necessary to appropriately select a material that is preferable depending on the configuration of the conversion panel.

In a conversion panel that does not include a protective layer holding member, a low refractive index layer is provided between the protective layer and the photostimulable layer in a state as shown in FIG. 1, for example.

This low refractive index layer is made of, for example, CaF, (refractive index 1.2
3-1.26), Na5A (2F6 (refractive index 1, 35
), MgFi (refractive index 1.38), and 5iOz (refractive index 1.46).

The low refractive index layer can be formed on the surface of the photostimulable layer or protective layer by vapor deposition such as vapor deposition, or by laminating a thin film previously formed by a similar method on the surface of the photostimulable layer or protective layer. method can be applied.

In a conversion panel including a protective R holding member, the low refractive index layer exists in a state where it is shielded from the external atmosphere by the protective layer holding member. By using the protective layer holding member in this manner, the thickness of the protective layer can be substantially increased, so that the moisture resistance and durability of the conversion panel can be further improved.

The low refractive index layer can be the same as described above, but when it includes a protective layer holding member, for example, ethanol (refractive index 1.36), methanol (refractive index 1.36), etc.
33) and a layer consisting of a liquid such as diethyl ether (refractive index 1.35); or a layer consisting of a gas such as air, nitrogen, argon, etc. and a layer having a refractive index of substantially 1, such as a vacuum layer; is preferable because of its configuration.

As the low refractive index layer of the conversion panel including the protective layer holding member, a gas layer or a vacuum layer is preferable because it is highly effective in preventing deterioration of sharpness.

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

In order to sufficiently impart to the low refractive index layer of the present invention the effect of reducing a decrease in sharpness, it is preferable that the low refractive index layer is in close contact with the photostimulable layer.

Therefore, if the low refractive index layer is a liquid layer, a gas layer, or a vacuum layer, it may be left as is;
, Na5A12F6. MgF2. S! When the photostimulating layer and the low refractive index layer are formed on the surface of the protective layer using 02 or the like, the photostimulable layer and the low refractive index layer are brought into close contact with each other using, for example, an adhesive. In this case, the refractive index of the adhesive is preferably close to the refractive index of the stimulable layer.

The protective layer holding member used in the conversion panel of the present invention is not particularly limited as long as it can be formed while shielding the low refractive index layer from the external atmosphere, and may be made of glass, ceramics, metal, plastic, etc. Can be used.

Also, Ho W! The layer holding member has a moisture permeability of log/m2
- It is preferable that it is 24 hours or less. If this moisture permeability is too large, the stimulable phosphor will deteriorate due to moisture entering from the outside, which is not preferable.

The thickness of the protective layer holding member (a in FIG. 2) may be greater than the thickness of the photostimulable layer.

That is, the thickness of the protective layer holding member is the same as the thickness of the photostimulable layer, or is greater than that thickness.

When the thickness of the protective layer holding member and the photostimulable layer are the same, for example, the low refractive index layer is a vacuum layer. In this case, the existence of a vacuum layer between the photostimulable layer and the protective layer so as to be optically discontinuous is sufficient as a low refractive index layer, and therefore the two layers are in contact with each other. You can leave.

If the thickness of the protective layer holding member exceeds the thickness of the stimulable layer,
The thickness of the protective layer holding member can be determined in relation to the thickness of the low refractive index layer to be formed.

The width of the protective layer holding member (b in Figure 2) mainly determines the moisture resistance (
1 to 3.
0 mm is preferred. If the width of the protective layer holding member is too small, this is not preferred from the viewpoint of stability, strength, and moisture resistance of the protective layer holding member. Moreover, if it is too large, the conversion panel becomes larger than necessary, which is not preferable.

Note that the moisture permeability of the portion in close contact between the protective layer holding member, the support body, and the protective layer is preferably 1Og/m2·24hr or less.

The protective layer holding member is required to be in close contact with the support and the protective layer in order to impart moisture resistance to the conversion panel and to maintain a constant layer thickness of the low refractive index layer. Here, in order to bring the protective layer holding member into close contact with the support and the protective layer, for example,
An adhesive or the like is used, but it is preferable that the adhesive has moisture-proof properties. Specifically, epoxy resins, phenol resins, cyanoacrylate resins, vinyl acetate resins, vinyl chloride resins, polyurethane resins, acrylic resins, ethylene vinyl acetate resins, and 1. Organic polymer adhesives such as J-olefin resins, chloroprene rubbers, and nitrile rubbers, silicone adhesives, and the like can be used. Among these, epoxy resins and silicone resins used for sealing semiconductors and electronic parts are preferred because they have excellent m resistance and properties, and epoxy resin adhesives are particularly suitable because of their low moisture permeability.

In order to improve the adhesion between the protective layer holding member and the support, or between the protective layer holding member and the protective layer, the contact surface between the protective layer holding member, the support, and the protective layer and other layers is It is also possible to provide an undercoat layer or to perform surface roughening treatment.

The stimulable phosphor constituting the stimulable layer in the conversion panel of the present invention refers to the stimulable phosphor that is irradiated with the first light or high-energy radiation, and is then irradiated with the stimulable phosphor, which is irradiated with the first light or high-energy radiation. It is a phosphor that exhibits stimulated luminescence when stimulated (stimulated excitation) by irradiation with initial light or high-energy radiation, but from a practical standpoint, it is a phosphor that exhibits stimulated luminescence when stimulated with excitation light of 500 nm or more. The body is desirable.

As such a photostimulable phosphor, for example, Japanese Patent Application Laid-open No. 1986-
Ba5O, described in No. 80487: Ax,
5rSO described in JP-A-48-80489,
: Ax, Li2B4O7Cu, Ag, etc. described in JP-A-53-39277J+, JP-A-54-478
Li2O・(B, O,) x described in No. 83:
Cu and Li2O・(B202)X: Cu, Ag
et al., U.S. Pat. No. 3,859.527, SrS: Ce
, Sm, SrS: Eu, Sm, La2O2
S: Eu.

Examples include phosphors represented by Sm and (Zn, Cd)S:Mn, X.

In addition, ZnS described in JP-A-55-12142
:Cn, Pb phosphor, general formula % formula %: barium aluminate phosphor and general formula, M■
An example is an alkaline earth metal silicate phosphor represented by C1xSiO,:A. Also, an alkaline earth fluorohalide phosphor having the general formula % described in JP-A No. 55-12143, LnO
X: phosphor represented by xA, general formula described in JP-A-55-12145, (B a l-, Mx) A phosphor with the general formula described in No. 84389, BaFX: xCe, yA, a rare earth element-activated divalent phosphor with the general formula described in JP-A-55-160078, MIIFX-xA: yLn Metal fluorohalide phosphor, general formula, ZnS:A, CdS:A, (Zn,Cd)S:A.

A phosphor represented by ZnS: A, X and Cds: A, : )' AM
, (POυ2:yA phosphor, any of the following general formulas described in JP-A-59-155487, nReX3mAX2: xEu nReX, ・mAX,: xEu, ySm phosphor) , and the following general formula described in JP-A No. 61-72087: M-X-aM"X'2 ・bMIX": c is preferable since it is easy to form a stimulable 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-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 stimulable layer in the conversion panel of the present invention may be a stimulable layer group consisting of one or more stimulable layers containing at least one type of the above-mentioned stimulable phosphor. 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 conversion panel to radiation, the type of stimulable phosphor, etc., but it is in the range of 10 to 1000 μm, more preferably 20 to 1000 μm when no binder is included. It is preferably selected from the range of 800 μm, and when a binder is included, the diameter is from 20 to 10 μm.
The thickness is preferably selected from the range of 00 μm, more preferably from 50 to 500 μm.

Supports used in the present invention include various polymeric materials, glass, ceramics, metals, and the like. The moisture permeability of the support is less than Log/m" 24hr, preferably 5
．． 0g/m”・24hr or less.

Examples of polymeric materials include films of cellulose acetate, polyester, polyethylene terephthalate, polyamide, polyimide, triacetate, polycarbonate, and the like.

Examples of the metal 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 5 mm, and is preferably 200 μm for ease of handling.
~3mm.

The surface of these supports may be smooth or matte for the purpose of improving adhesion to the stimulable 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.

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

In order to impart further moisture resistance to the conversion panel of the present invention, it is preferable to seal the side edges of the protective layer and the support or the peripheral edge of the protective layer holding member. As this sealing method, for example, a sealing method using glass fusion bonding or a sealing method using an epoxy resin adhesive can be applied.

Further, 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 have to substantially exhibit the function of supporting the photostimulable layer.

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

That is, the radiation from the radiation generating device 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, and since the intensity of stimulated luminescence is proportional to the amount of accumulated radiation energy, this signal is converted into a photoelectric converter using, for example, a photomultiplier tube. By performing photoelectric conversion in the device 45, reproducing it as an image by the image reproducing device 46, and displaying it on the image display device 47, a radiation transmitted image of the subject can be observed.

〔Example〕

Next, the present invention will be explained by examples.

Examples 1 to 4 and Comparative Example 1.2 3 Alkali halide phosphors (RbBr; 0.0006TQ) were applied to a 1 mm thick crystallized glass support using a vapor deposition device.
A stimulable layer was formed by vapor deposition to a thickness of 00 μm. Next, CaF (refractive index 1.25) was vapor-deposited to a thickness of 0.1 μm on the surface of each protective layer having the thickness and haze ratio shown in Table 2 to form a low refractive index layer. Thereafter, the support and the protective layer were adhered with an epoxy resin adhesive so that the respective photostimulable layers and low refractive index layers were aligned to obtain a converted pile.

Further, a conversion panel of a comparative example was obtained in the same manner as in the example except that the protective layer was different.

Note that the soda glasses (A) and (B) have the same composition but different degrees of hardening. For PET, (a) is the transparent type, (b)
(c) is the reprint popular type and (c) is the hazy type.

Table 2 Image conversion panels obtained in these Examples and Comparative Examples
Vacuum drying was performed for 1 hour under the condition of °Os 1O-3 torr. Afterwards, the side edges of the support and the glass protective layer or the peripheral edge of the protective layer holding member were sealed with an epoxy adhesive. It was used as a sample. This sample was evaluated for sharpness using MTF.

Table 3 shows the spatial frequency I Qp/mm and 2Qp/mm of each sample.
Each protective layer having a haze ratio of mm Table 3 was adhered in the same manner as described above. By performing this series of steps in a normal atmosphere, the low refractive index layer was made into an air layer, and a conversion panel of the present invention was obtained.

Moreover, conversion panels of comparative examples were obtained in the same manner as in Examples 5 to 8 except that the protective layer was different.

Table 4 As is clear from the table, the conversion panel of the present invention has excellent sharpness, but the conversion panel of the comparative example whose protective layer has a high haze ratio has low sharpness.

Examples 5 to 8 and Comparative Example 3.4 Alkali halide phosphor (RbBr; O,0O06T1) was applied to a 1 mm thick crystallized glass support using a vapor deposition device.
was deposited to a thickness of 300 μm to form a stimulable layer. Next, a glass sheet having a width of 5 mm and a thickness of 1 mm was adhered onto the support using an epoxy resin adhesive so as to surround the stimulable layer. After that, 80℃, 10""
Vacuum drying was performed under torr conditions for 1 hour.

Next, the other side of the glass sheet and the obtained I obtained in these Examples and Comparative Examples shown in Table 4;
The MTF at Qp/cam was measured.

The results are shown in Table 5.

As is clear from the table, the conversion panel of the present invention has excellent sharpness, but the conversion panel of the comparative example in which the haze ratio of the protective layer is high has low sharpness.

〔Effect of the invention〕

The image conversion panel of the present invention has excellent sharpness because the spread of stimulated excitation light due to light scattering within the protective layer is small.

[Brief explanation of the drawing]

1 and 2 are schematic sectional views of an image conversion panel of the present invention, and FIG. 3 is an explanatory diagram of a radiation image conversion method using the conversion panel.

Claims (1)

[Claims] A radiation image conversion method in which a stimulable phosphor layer, a low refractive index layer, and a protective layer are provided in this order on a support, and the refractive index of the intermediate low refractive index layer is set to be lower than the refractive index of the protective layer. A radiation image conversion panel, wherein the protective layer has a haze rate of 3% or less.