JPS62137596A - Radiation intensifying screen - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Field of origin] The present invention relates to radiation intensifying screens.

[Technical background of the invention] A radiation intensifying screen is used for medical radiation i! such as X-ray photography for the purpose of medical diagnosis. l Industrial radiation for the purpose of photography and non-destructive testing of materials! ! ! In radiography in various fields such as shadows, to improve the sensitivity of the imaging system, radiographic films (e.g.
′ on one or both sides of ? r: These are used by overlapping them so that they can be viewed easily.

This radiation intensifying screen basically consists of a support and a phosphor layer provided on one side of the support. Note that the surface of this phosphor layer opposite to the support (the surface not facing the support) is generally provided with a transparent protective film made of plastic film, etc. It protects the layer from chemical alteration or physical impact.

The phosphor layer is made of a binder that contains and supports phosphor particles in a dispersed state, and these phosphor particles have the property of emitting high-intensity light when excited by radiation such as X-rays. be. Therefore, depending on the amount of radiation that passes through the subject, the phosphor emits high-intensity light and emits! ! The radiographic film stacked and stirred in contact with the surface of the phosphor layer of the intensifying screen is also sensitized by this emission, so it is possible to achieve sufficient sensitization of the radiographic film with a relatively small dose of radiation. can. Then, a radiation image of the subject is formed on the radiation film ball.

It is generally desired that the radiation intensifying screen used in radiography has as high a sensitivity as possible in order to reduce the exposure dose of the subject as much as possible. Also,
It is desired that the resulting image has high image quality (sharpness, graininess, etc.).

In medical radiography where the human body is the subject,
Because the absorption rate (transmittance) of radiation such as X-rays differs depending on the part of the human body, when a normal radiation intensifying screen with uniform sensitivity is used, the density on the radiation film differs markedly in some areas. Images tend to be obtained.

For example, in the case of the chest 1111 shadow, since the radiation absorption rate in the peripheral area is higher than that in the lung field, an image is obtained in which the density is high in the center and low in the peripheral area.

In order to reduce or eliminate such a significant difference in image density that occurs between radiation films, radiation intensifying screens (sensitivity compensation intensifying screens) in which the thickness of the phosphor layer is varied in one direction are known. There is. That is, since the sensitivity differs at both ends of the intensifying screen, an image with substantially uniform density can be obtained even if the amount of radiation irradiated to the screen differs due to differences in the thickness of the subject.

However, when this sensitivity compensation type intensifying screen is used, although the density of one image is uniform, the thickness of the phosphor layer is different, resulting in images with significantly different image quality, especially sharpness, at both ends. This is causing problems.

[Summary of the Invention] An object of the present invention is to provide a radiation-sensitizing screen in which phosphor layers have different thicknesses and provide images with uniform image quality, particularly sharpness.

Another object of the present invention is to provide a radiation intensifying screen that provides images with uniform image density and sharpness.

The above object is to provide a radiation intensifying screen having a support, a phosphor layer made of a supporting binder containing a phosphor in a dispersed state, and a protective film in this order, in which the layer thickness of the phosphor layer is partially different. The present invention is characterized in that the film thickness of the a-retaining film is locally different such that it is larger in areas where the phosphor layer is thinner and smaller in areas where the phosphor layer is thicker. This can be achieved with a radiosensitizing screen.

That is, the present invention provides uniform sharpness (sharpness compensation type) and The present invention provides a sensitivity compensation type intensifying screen.

According to the radiation intensifying screen of the present invention, the insulation layer is provided on the phosphor layer so as to correspond to the change in the layer thickness of the phosphor layer. ! Since the thickness of the film is also varied, images with uniform sharpness can be obtained.

Specifically, the phosphor layer and The thickness of the protective film is preferably 2g1m.

Therefore, even if the radiation absorption rate of the subject differs markedly locally, such as in lower extremity angiography or imaging of a patient with scoliosis, the sensitivity of the intensifying screen will change the radiation absorption accordingly. Not only does the density of the obtained image become uniform because the difference is compensated for, but also the sharpness is improved because the difference in the layer thickness of the phosphor layer is compensated for by the difference in the thickness of the protective film. A uniform image can be obtained.

[Configuration of the Invention] The configuration of the radiation intensifying screen of the present invention will be explained with reference to the accompanying drawings. Note that FIGS. 1 to 3 are sectional views schematically showing the structure of the radiation intensifying screen of the present invention.

In FIG. 1, a radiation intensifying screen is shown on support 1.
It is composed of a phosphor layer 2 and a protective film 3. The thickness of the phosphor layer 2 gradually decreases in one direction such that it is large at one end and becomes small at the opposite end, and conversely, the thickness of the protective film 3 is It gradually becomes smaller in the opposite direction, being larger at the thinner end of the layer and smaller at the thicker end of the phosphor layer.

- In Fig. 2, the radiation intensifying screen is composed of a support 1', a phosphor layer 2' and a protective film 3',
The thickness of the phosphor layer 2' gradually increases radially from the center, being smaller at the center and larger at the periphery, and conversely, the thickness of the protective film 3' increases at the center. They gradually become smaller in a radial manner, becoming smaller at the periphery.

In FIG. 3, the radiation intensifying screen has a support 1"
, a phosphor layer 2'' and a protective layer g13''. The thickness of the phosphor layer 2'' gradually decreases radially such that it is largest at the center and smallest at the periphery, and the thickness of the protective film is smallest at the center and smallest at the periphery. However, these three embodiments are examples of the structure of the radiation intensifying screen of the present invention, and wood 9. light is limited to the above embodiments. Instead, it is sufficient that the thickness of the protective film changes at least in response to changes in the layer thickness of the phosphor layer to compensate for the difference in the layer thickness of the phosphor layer. Various intermediate layers or undercoat layers may be provided between or on the surface of the body layer and the protective film.

The radiation intensifying screen of the present invention can be manufactured, for example, by the method described below.

The support used in the present invention can be arbitrarily selected from various materials known as materials for producing radiation intensifying screens. Examples of such materials are cellulose acetate, polyester, polyethylene terephthalate, polyamide, polyimide, triacetate.

Films of plastic materials such as polycarbonate,
Examples include metal sheets such as aluminum foil and aluminum alloy foil, ordinary paper, baryta paper, resin coated paper, pigment paper containing pigments such as titanium dioxide, and paper sized with polyvinyl alcohol. However, in consideration of various properties as a radiation intensifying screen, a particularly preferred material for the support in the present invention is a plastic film. This plastic film may be kneaded with a light-absorbing substance such as carbon black, or may be kneaded with a light-reflecting substance such as titanium dioxide. It is a support suitable for screens, the latter being a support suitable for radiation intensifying screens of the high-sensitivity type.

In known radiation-sensitizing screens, gelatin is added to the surface of the support on the side where the phosphor layer is provided, in order to strengthen the bond between the support and the phosphor layer, or to improve the sensitivity or image quality of the radiation-sensitized screen. It is also possible to form a four-layer adhesive layer by coating a polymeric substance such as , or to provide a light-reflecting layer made of a light-reflecting substance such as titanium dioxide, or a light-absorbing layer made of a light-absorbing substance such as carbon black. It is being done. In addition, in radiation-sensitizing screens used in industrial radiography for the purpose of non-destructive testing of substances, lead foil or lead alloy is used on the surface of the support on the side where the phosphor layer is provided for the purpose of removing scattered radiation. The support used in the present invention can also be provided with a metal foil such as foil or tin foil.These various layers can also be provided on the support used in the present invention.

Furthermore, as described in JP-A-58-182599, in order to improve the sharpness, the surface of the support on which the phosphor layer is provided (adhesive properties are applied to the surface of the support on that side) When a layer, a light reflection layer, a light absorption layer, a metal foil, etc. are provided, minute irregularities may be provided on the surface thereof.

A phosphor layer is formed on this support.

The phosphor layer is a layer made of a binder containing and supporting phosphor particles in a dispersed state.

Various types of phosphors are already known. Examples of phosphors that emit light in the near ultraviolet to visible range that are preferably used in the present invention include the following compounds. Tungstate-based phosphor (Ca WO
a, MgWO4, CaWO4:Tb, etc.), terbium-activated rare earth #sulfide phosphor [Y2O2S:Tb, Gd2
O2S:Tb, La2O2S:Tb, (Y, Gd
) 202S:Tb, (Y, Gd) 202
S: Tb, Tm, etc.], terbium-activated rare earth phosphate phosphor (YPO,:Tb, GdPO4:T
b, LaPO4:Tb, etc.), terbium-activated rare earth oxyhalide phosphor (LaOBr: Tb, L
a0B r near r b , Tm, La0C1: Tb
, La0Cu : Tb , Tm, Gd0B r : T
b, Gd0C1:Tb3), thulium-activated rare earth oxyhalide phosphor (LaOB r : Tm, La
0C1:Tm, etc.), fE barium acetate phosphor [Ba5O
, :Pb, Ba5O, : Eu2°, (Ba,5r)S
Oa: Eu” etc.], divalent europium activated alkaline earth metal phosphate phosphor [Ba= (POa)2:
Eu'', (Ba, Sr)3 (PO4)2:
Single-layer divalent europium-activated alkaline earth metal fluorohalide phosphor [BaFCl: Eu'', etc.
BaFBr:Eu”, BaFCJl:Eu”°, Tb,
BaFBr:Eu”, Tb, BaF2aBaC sentence, -K
CI: Eu2°, BaF, *BaCJ1 No. 2 x
BaSO4*KCJl:Eu”, (Ba, Mg)F
2 life BaC12IIKC1:Eu''+ etc.], iodide-based phosphor (CsI:Na.

CsI: Tl, NaI, KI: Tl'9), sulfide phosphor [ZnS:Ag, (Zn, Cd)S: Ag, (Zn, Cd)S: Cu, (Zn, Cd)
S: Cu, A pattern, etc.], hafnium phosphate phosphor (Hf
P207: Cu, etc.), europium-activated rare earth oxysulfide phosphor [Y2O2S:Eu, Gd2O2S:E
u, La2O2S:Eu, (Y,Gd)2025:Eu
etc.], Ni-O pium activated rare earth oxide phosphor [Y2O
3: Eu, Gd2O,: Eu, La 20
．． :Eu, (Y, Gd) 203
:Eu], europium-activated rare earth phosphate phosphor (Y
PO4: Eu, GdPOa:Eu, LaPO4:E
u, etc.), europium-activated rare earth vanadate-based phosphors [YVO4: Eu, GdVO, :Eu, LaVO, :
Eu, (Y, Gd)VO2:Eu].

However, the phosphor used in the present invention is not limited to these, and may be any phosphor that emits light in the near-ultraviolet region or visible region when irradiated with radiation.

Examples of binders for the phosphor layer include proteins such as gelatin,
Polysaccharides such as dextran, or natural polymeric substances such as gum arabic; and polyvinyl butyral, polyvinyl acetate, nitrocellulose, ethylcellulose, vinylidene chloride/vinyl chloride copolymer, polyalkyl (meth)acrylate, donyl chloride/acetic acid Binders typified by synthetic polymeric materials such as vinyl copolymers, polyurethanes, cellulose acetate butyrate, polyvinyl alcohol, linear polyesters, etc. may be mentioned. Particularly preferred among such binders are nitrocellulose, linear polyester,
These are polyalkyl (meth)acrylates, mixtures of nitrocellulose and linear polyester, and mixtures of nitrocellulose and polyalkyl (meth)acrylates.

The phosphor layer can be formed on the support, for example, by the following method.

First, the above-mentioned phosphor and binder are added to a suitable solvent and thoroughly mixed to prepare a coating solution in which phosphor particles are uniformly dispersed in the binder solution.

Examples of solvents for preparing coating solutions include lower alcohols such as methanol, ethanol, n-propanol, and n-butanol; chlorine-containing hydrocarbons such as methylene chloride and ethylene chloride; aromatic hydrocarbons such as benzene and toluene. Ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; Esters of lower fatty acids and lower alcohols such as methyl acetate, ethyl acetate, and butyl acetate; Ethers such as dioxane, ethylene glycol monoethyl ether, and ethylene glycol monomethyl ether; Mention may be made of mixtures of.

What is the mixing ratio of binder and phosphor in the coating solution?

The mixing ratio of the binder and the phosphor is generally selected from the range of 1:1 to 1:100 (weight ratio), although it varies depending on the characteristics of the intended radiation-sensitizing screen, the type of phosphor, etc. In particular, it is preferable to select from the range of 1:8 to 1:40 (weight ratio).

The coating liquid contains a dispersant to improve the dispersibility of the phosphor particles in the coating liquid, and a dispersant to improve the bonding force between the binder and the phosphor particles in the phosphor layer after formation. Examples of dispersants used for such purposes include phthalic acid, stearic acid, caproic acid, and lipophilic surfactants. be able to. Examples of plasticizers include phosphate esters such as triphenyl phosphate, tricresyl phosphate, and diphenyl phosphate; phthalate esters such as diethyl phthalate and dimethoxyethyl phthalate; ethyl phthalyl ethyl glycolate, butyl phthalyl butyl glycolate, etc. glycolic acid ester; and polyester of triethylene glycol and adipic acid,
Examples include polyesters of polyethylene glycol and aliphatic dibasic acids, such as polyesters of diethylene glycol and succinic acid.

A coating film of the coating solution is formed by applying the coating solution containing the phosphor and binder prepared as described in Section L onto the surface of the support. This coating operation.

This is carried out by using conventional coating means, such as a doctor blade, roll coater, knife coater, etc., and by gradually changing the coating speed, thereby forming coating films of different thicknesses. Alternatively, the thickness of the coating may be changed by embossing the coating before it dries.

Then, the formed PliS is gradually heated and dried to complete the formation of the phosphor layer on the support.

The thickness of the phosphor layer varies depending on the intended use of the radiation intensifying screen, the type of phosphor, the mixing ratio of the binder and the phosphor, and is usually 10 #Lm to 1 mm.

However, the thickness of this layer is preferably 20 to 500 ILm. Also.

The maximum difference in the layer thickness of the phosphor layer, which is a characteristic requirement in the present invention, is preferably in the range of 20 to 300 μm. This change in layer thickness may be gradual or stepwise. It may be.

Note that the phosphor layer does not necessarily have to be formed by directly applying a coating liquid onto the support as described above; for example, it is possible to form the phosphor layer by separately applying the coating liquid onto a sheet such as a glass plate, metal plate, or plastic sheet. After forming phosphor layers with different thicknesses by drying, the phosphor layers may be bonded to the support by pressing them against the support or by using an adhesive.

Next, a protective film is provided on the surface of the phosphor layer opposite to the side that contacts the support in order to physically and chemically protect the phosphor layer.

Transparency! The membrane may be made of a transparent material such as a cellulose 7A conductor such as cellulose acetate or nitrocellulose; or a synthetic polymeric material such as polymethyl methacrylate, polyvinyl butyral, polyvinyl formal, polycarbonate, polyvinyl acetate, or vinyl chloride-vinyl acetate copolymer. The film thickness can be varied by coating the surface of the phosphor layer with a solution prepared by dissolving a polymeric substance in an appropriate solvent while gradually changing the coating speed. Alternatively, it can also be formed by a method such as adhering transparent thin films of different thicknesses formed in advance from polyethylene terephthalate, polyethylene, vinylidene chloride, polyamide, etc. to the surface of the phosphor layer using a suitable adhesive.

The thickness of the transparent protective film, which is a characteristic requirement of the present invention, is preferably about 3 to 207 zm, and the maximum difference in film thickness is preferably in the range of 3 to 15 μm. It may be done gradually or in stages.

Furthermore, in order to make the sharpness of the obtained image uniform, the phosphor layer or the MH may be colored with a coloring agent that absorbs light in the emission wavelength range of the phosphor.

Next, Examples and Comparative Examples of the present invention will be described.

However, each of these does not limit the present invention.

[Example 1] A coating solution containing fine particles of titanium dioxide in a dispersed state was uniformly applied onto a polyethylene terephthalate film (support, thickness: 250 ILm) placed horizontally on a glass plate using a doctor blade. After drying, a light reflecting layer having a layer thickness of 30 μm was provided on the support.

Separately, divalent europium-activated barium fluoride bromide phosphor (
Methyl ethyl ketone was added to a mixture of BaFBr:Eu") particles and a linear polyester resin, and nitrocellulose with a degree of nitrification of 11.5% was further added to prepare a dispersion containing phosphor particles in a dispersed state. After adding tricresyl phosphate, n-butanol, and methyl ethyl ketone to this dispersion, the phosphor particles are uniformly dispersed by stirring and mixing thoroughly using a propeller mixer, and the mixing ratio of the binder and the phosphor is 1:20. (weight ratio) and viscosity is 25-3
A 5PS (25°C) coating solution was prepared.

Next, the coating liquid was applied onto the support placed horizontally on the glass plate t with the light-reflecting layer facing up using a doctor blade while gradually increasing the conveyance speed of the doctor blade.

After coating, the support on which the coating film was formed was placed in a dryer, and the temperature inside the dryer was gradually raised from 25° C. to 100° C. to dry the coating film. In this way, a phosphor layer whose layer thickness gradually changed, having a layer thickness of about 50 JLm at one end and about 150 JLm at the other end, was formed on the light reflective layer.

Then, on top of this phosphor layer, a polyethylene terephthalate 9 transparent film (a film with gradually varying thickness, one end having a thickness of 5 μm and the other end having a thickness of 15 JLm, and a polyester adhesive were applied. ), the thicker part of the film overlaps the thinner part of the phosphor layer, and the thinner film overlaps the thicker part of the phosphor layer. A transparent protective film was formed by placing the adhesive layer side down and laminating it as shown in FIG.

In this way, a radiation-sensitizing screen consisting of a support, a light-reflecting layer, a phosphor layer, and a transparent protective film was manufactured (the relationship between the thicknesses of the four phosphor layers and the protective film is shown in Figure 1). (as shown).

Next, the obtained radiation intensifying screen was evaluated by the image sharpness test and the image C degree test described below.

(1) Image sharpness test Press the radiation intensifying screen and the
Take an X-ray photograph by irradiating it with X-rays! The contrast transfer function (CTF) of the resulting radiograph was measured and expressed as a spatial frequency of 2 cycles/mm.

(2) Image density test A radiation intensifying screen and an X-ray photographic film were crimped together in a cassette, and the tube voltage was 80K through an aluminum plate (thickness gradually changing in the range of 1 to 50 mm).
A 1M type X-ray photograph was taken by irradiating X-rays of Vp, and the density of the completed X-ray photograph was measured.

The results obtained for the image sharpness test are summarized in Figure 4. For comparison, the results for a known sensitivity compensation type radiation intensifying screen (commercial product, protective film thickness: 10 μm) are also shown. It is shown in Figure 4.

FIG. 4 is a graph in which the thickness of the phosphor layer is plotted on the horizontal axis and the sharpness is plotted on the vertical axis. In FIG. 4, the solid line represents the radiation-sensitizing screen of the present invention (Example 1), and the dotted line represents the known radiation-sensitizing screen for comparison.
The value shown in parentheses in the graph is the thickness of the protective film.

As is clear from the results shown in Fig. 4, in the known sensitivity-compensated radiation intensifying screens that differ only in the thickness of the phosphor layer, the sharpness of the image decreases as the thickness of the phosphor layer increases. became. On the other hand, the radiation intensifying screen of the present invention having different thicknesses of the phosphor layer and the protective film (Example 1)
), images with the same sharpness were obtained regardless of the thickness of the phosphor layer.

It should be noted that the dust level of one image was almost constant regardless of the thickness of the phosphor layer in any intensifying screen.

[Brief explanation of drawings]

1, 2 and 3 are sectional views each showing an embodiment of the radiation intensifying screen of the present invention. FIG. 4 is a graph showing the relationship between the thickness of the phosphor layer and the thickness of the protective film in the radiation intensifying screen and the sharpness. 1.1', l": Support 2.2° 2n: Phosphor layer 3.3°.3": Protective film Patent applicant: Fuji Photo Film Co., Ltd. Attorney Yasushi Yanagawa Figure 1

Claims (1)

[Scope of Claims] 1. A radiation intensifying screen having a support, a phosphor layer made of a supporting binder containing a phosphor in a dispersed state, and a protective film in this order, wherein the layer thickness of the phosphor layer is partially and the thickness of the protective film differs locally such that it is larger in areas where the phosphor layer is thinner and smaller in areas where the phosphor layer is thicker. Radiosensitizing screen. 2. The thickness of the phosphor layer gradually decreases in one direction such that it is largest at one end and smallest at the opposite end, and the thickness of the protective film is The radiation intensifying screen according to claim 1, wherein the radiation intensifying screen gradually increases in size in one direction such that it is smallest at one end and largest at the opposite end. 3. The thickness of the phosphor layer gradually increases in a radial manner such that it is smallest in the center and largest in the periphery, and the thickness of the protective film is largest in the center and largest in the periphery. 2. The radiation intensifying screen according to claim 1, wherein the radiation intensifying screen is gradually reduced in size in a radial manner such that it becomes smallest in the area. 4. The thickness of the phosphor layer gradually decreases in a radial manner such that it is largest at the center and smallest at the periphery, and the thickness of the protective film is smallest at the center and smallest at the periphery. 2. The radiation intensifying screen according to claim 1, wherein the radiation intensifying screen gradually increases in size in a radial manner such that the radiation intensifying screen becomes the largest. 5. The thickness of the phosphor layer is in the range of 20 to 500 μm, the maximum difference in layer thickness is in the range of 20 to 300 μm, and the thickness of the protective film is in the range of 1 to 30 μm, and The radiation intensifying screen according to claim 1, characterized in that the maximum difference in film thickness is in the range of 3 to 15 μm. 6. The radiation intensifying screen according to claim 1, characterized in that a light reflecting layer is provided between the support and the phosphor layer.