JP2583417B2 - Radiation image forming method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a radiation image forming method using a radiographic intensifying screen / film photographing system.

[Technical Background and Prior Art of the Invention] In radiographic photography in various fields such as medical radiography such as X-ray photography for medical diagnosis and industrial radiography for non-destructive inspection of substances. A radiographic intensifying screen (intensifying screen) is used so as to be in close contact with one side or both sides of a radiographic film (for example, an X-ray film).

The radiographic film has a basic structure comprising a support and a photographic emulsion layer provided on one or both sides thereof and comprising a binder containing and supporting silver halide in a dispersed state.

The radiographic intensifying screen has a basic structure including a support and a phosphor layer provided on one surface thereof. The phosphor layer is made of a binder that contains and supports the phosphor particles in a dispersed state, and the phosphor particles have a property of emitting high-luminance light when excited by radiation such as X-rays. is there. Therefore, the phosphor emits light of high brightness in accordance with the amount of radiation that has passed through the subject, and the radiographic film, which is placed in contact with the surface of the phosphor layer of the radiographic intensifying screen, is superposed on this phosphor. Since the body is also sensitized by light emission from the body, sufficient exposure of the radiation film can be achieved with a relatively small radiation dose.

Conventionally, a radiographic film having a structure in which a photographic emulsion layer is provided on one side of a support (single-sided film) and a radiographic intensifying screen is arranged on the photographic emulsion layer side of this film. -A film photography system (single-sided system) is known.

Generally, the image quality (sharpness, graininess, etc.) of an image obtained by an imaging system largely depends on the characteristics of a radiographic intensifying screen incorporated in the system, and an image having an excellent image quality as an intensifying screen. It is desired to provide

For example, to increase the sharpness of an image,
A radiation intensifying screen has been proposed in which phosphor particles are arranged so that the particle diameter of the phosphor constituting the phosphor layer is large on the screen surface side (the side from which fluorescence is extracted) and small on the support side. No. 55-33560, JP-A-58-71500
No.). Also, Japanese Patent Application Laid-Open No. Sho 58-160952 discloses a single-sided system that gives an image with improved sharpness without loss of sensitivity, by arranging particles of a rare-earth phosphor having a large particle diameter on the side close to the film, from the film. There is described an intensifying screen system using a radiographic intensifying screen that is arranged so that the particle diameter of the phosphor becomes smaller as the distance increases. In a single-sided system using such an intensifying screen, it is possible to achieve high sensitivity because the particle size of the phosphor on the side close to the film is relatively large, in other words, the particle size distribution of the phosphor is determined by its thickness. When the sensitivity is the same as that of a conventional intensifying screen that is uniform in the direction, sharpness can be increased. In addition, since the phosphor particles having a small particle diameter on the support side play a role as a reflective layer, they can be extracted from the screen surface by shortening the reflection and scattered light paths of the fluorescent light, thereby also providing sharpness (low frequency region). Is enhanced.

[Summary of the Invention] It is an object of the present invention to provide a radiographic image forming method using a radiographic intensifying screen that provides an image with improved image quality, particularly sharpness and granularity.

It is another object of the present invention to provide a radiation image forming method which provides an image with high sensitivity and improved sharpness.

The above object is to provide a radiographic image forming method using a screen / film photographing system in which a radiographic intensifying screen is disposed on a rear surface of a radiographic film when viewed from a radiation incident direction, wherein the radiographic intensifying screen comprises a support and And a phosphor layer provided thereon, and the phosphor particles constituting the phosphor layer are arranged such that the particle size increases from the screen surface side close to the radiographic film toward the support side. It can be achieved by the radiation image forming method of the present invention, which is characterized in that:

In the present invention, the screen surface means the surface of the intensifying screen on the side opposite to the support, and means the surface of the phosphor layer or, if a protective film is provided thereon, the surface of the protective film.

As a result of repeated studies to obtain an image with improved image quality, the present inventors have found that the phosphor particles constituting the phosphor layer of the radiographic intensifying screen are completely opposite to those known in the art, and the screen surface side (extraction of fluorescence) On the other hand, by arranging the particles so that the particle diameter is small on the side and the particle diameter is large on the support side, an image with improved sharpness and granularity can be obtained.

That is, the radiographic intensifying screen having the above-described configuration is placed on one side of the radiographic film so that the screen surface faces the film (the rear side of the film in the radiation incident direction)
According to the radiation image forming method of the present invention using a photographing system arranged at a high sensitivity, an image having high sharpness and excellent graininess can be obtained without significantly lowering the sensitivity.

In particular, when a single-sided film in which the photographic emulsion layer is composed of tabular silver halide grains is used as the radiographic film, a high-sensitivity and high-sensitivity imaging system can be realized at the same time.

Since tabular silver halide grains have high covering power, high sensitivity is obtained even if the amount of silver per unit area of the radiation film is reduced, and characteristic curves (graphs showing the relationship between exposure and photographic density) , Which indicates the photosensitive characteristic of the film) can be maintained at a high value. Since the amount of the binder can be reduced along with the reduction in the amount of silver, the same sensitivity can be obtained with the same layer thickness as the emulsion layer on one side of the conventional double-sided film.

A radiographic film is usually subjected to processing including development, fixing, washing with water and drying in a short time (for example, 90 seconds in Dry to Dry). Since the amount is small, there are no problems such as incomplete fixation (poor printing), poor washing, poor drying, and residual color contamination.

Until now, with regard to the sensitivity of the single-sided system, it was difficult to emit fluorescence from the screen surface even if the phosphor layer of the radiographic intensifying screen was thickened, making it difficult to increase the sensitivity of the screen. By using a possible high-sensitivity single-sided film, it is possible to achieve a high-sensitivity single-sided system. Therefore, by using the radiation film in the imaging system (single-sided system) according to the present invention, it is possible to enhance the imaging system in addition to improving the image quality such as sharpness and granularity.

In addition, the single-sided system using the radiation film,
Compared with a known double-sided system using an intensifying screen in which phosphor particles are arranged so that the particle size increases from the support side toward the screen surface side, the sensitivity is the same, and very high sharpness Degree images can be given.

[Configuration of the Invention] A typical configuration example of the radiation intensifying screen of the present invention is as follows.
As shown in FIG.

FIG. 1 is a sectional view showing an example of a photographing system according to the present invention. In FIG. 1, the radiation intensifying screen 1 is composed of a support 1a, a phosphor layer 1b and a protective film 1c in this order, and the phosphor particles in the phosphor layer 1b are on the screen surface side (protective film side).
Are arranged such that the particle size increases from the surface toward the support.

Note that the radiation intensifying screen of the present invention is not limited to the above-described embodiment, and the phosphor particles constituting the phosphor layer are arranged such that the particle diameter increases from the screen surface side toward the support side. Various configurations can be adopted as long as they are provided. For example, various known layers such as a light reflection layer and an undercoat layer may be provided between the respective layers.

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

The support used in the present invention can be arbitrarily selected from various materials known as materials for producing a radiographic intensifying screen. Examples of such materials include films of plastic substances such as cellulose acetate, polyester, polyethylene terephthalate, polyamide, polyimide, triacetate, polycarbonate, aluminum foil, metal sheets such as aluminum alloy foil, ordinary paper, baryta paper, range Coated paper,
Pigment paper containing a pigment such as titanium dioxide, paper sized with polyvinyl alcohol, and the like can be given. However, in consideration of various characteristics as the radiation intensifying screen, a particularly preferred support material in the present invention is a plastic film. A light-absorbing substance such as carbon black may be kneaded in the plastic film, or a light-reflecting substance such as titanium dioxide may be kneaded in the plastic film. The former is a support suitable for a high-sensitivity type radiographic intensifying screen, and the latter is a support suitable for a high-sensitivity type radiographic intensifying screen.

On the surface of the support, a polymer substance such as gelatin is applied to form an adhesion-imparting layer for the purpose of strengthening the bond with the phosphor layer provided thereon, or titanium dioxide or the like is used for the purpose of enhancing sensitivity or image quality. A light-reflective layer made of a light-reflective substance, or a light-absorbent layer made of a light-absorbing substance such as carbon black, or a metal foil such as a lead foil, a lead alloy foil, or a tin foil for the purpose of removing scattered radiation. May be provided.

Further, as described in JP-A-58-182599, the surface of a support (an adhesion-providing layer, a light-reflective layer, a light-reflecting layer, If an absorbing layer or a metal foil is provided, it means the surface thereof).

 Next, a phosphor layer is formed on the support.

The phosphor layer, which is a characteristic feature of the present invention, is a layer made of a binder that contains and supports phosphor particles in a dispersed state.

Various kinds of phosphors are already known. Examples of the phosphor that emits light in the near ultraviolet to visible region (blue region, green region and red region) preferably used in the present invention include the following compounds: tungstate-based fluorescence Body (CaWO ₄ , MgWO ₄ , CaWO ₄ : Pb
Terbium-activated rare earth oxysulfide phosphor [Y ₂ O ₂ S:
Tb, Gd ₂ O ₂ S: Tb, La ₂ O ₂ S: Tb, (Y, Gd) ₂ O ₂ S: Tb, (Y, G
d) ₂ O ₂ S: Tb, Tm, etc.], terbium-activated rare earth phosphate-based phosphors (YPO ₄ : Tb, GdPO ₄ : Tb, LaPO ₄ : Tb, etc.), terbium-activated rare earth oxyhalide phosphors (LaOBr : Tb 、 La
OBr: Tb, Tm, LaOCl: Tb, LaOCl: Tb, Tm, GdOBr: Tb, GdOCl:
Tb etc.), thulium-activated rare earth oxyhalide-based phosphors (LaOBr: Tm, LaOCl: Tm, etc.), barium sulfate-based phosphors [BaSO ₄ : Pb, BaSO ₄ : Eu ²⁺ , (Ba, Sr) SO ₄ : Eu ²⁺ etc.], divalent europium activated alkaline earth metal phosphate phosphors [Ba ₃ (PO ₄ ) ₂ : Eu ²⁺ , (Ba, Sr) ₃ (PO ₄ ) ₂ : Eu ²⁺ etc.],
Divalent europium activated alkaline earth metal fluoride halide-based phosphor [BaFCl: Eu ²⁺ , BaFBr: Eu ²⁺ , BaFCl: Eu ²⁺ , T
b 、 BaFBr: Eu ²⁺ , Tb 、 BaF ₂・ BaCl ₂・ KCl: Eu ₂ ⁺ 、 BaF ₂・ BaC
l ₂ xBaSO ₄ KCl: Eu ²⁺ , (Ba, Mg) F ₂ BaCl ₂ KCl: Eu ²⁺
Etc.], iodide-based phosphors (CsI: Na, CsI: Tl, NaI, KI: Tl
Etc.), sulfide-based phosphors [ZnS: Ag, (Zn, Cd) S: Ag, (Zn,
Cd) S: Cu, (Zn, Cd) S: Cu, Al, etc.), hafnium phosphate-based phosphor (HfP ₂ O ₇ : Cu, etc.), europium-activated rare earth oxysulfide-based phosphor [Y ₂ O ₂ S : Eu, Gd ₂ O ₂ S: Eu, La ₂ O ₂ S: Eu,
(Y, Gd) ₂ O ₂ S: Eu, etc.], europium-activated rare earth oxide-based phosphor [Y ₂ O ₃ : Eu, Gd ₂ O ₃ : Eu, La ₂ O ₃ : Eu, (Y, Gd)
₂ O ₃ : Eu], europium activated rare earth phosphate phosphor (YP
O ₄ : Eu, GdPO ₄ : Eu, LaPO ₄ : Eu, etc.), europium-activated rare earth vanadate phosphor [YVO ₄ : Eu, GdVO ₄ : Eu, LaV
O ₄ : Eu, (Y, Gd) VO ₄ : Eu].

The phosphor used in the present invention is not limited to these, and any phosphor may be used as long as it emits light in the near ultraviolet region or visible region upon irradiation with radiation.

However, it is necessary to prepare phosphor particles having different particle diameters. Specifically, two or more kinds of phosphors having different average particle diameters are prepared. For example, a phosphor having an average particle diameter in a range of 8 to 15 μm is prepared as a phosphor having a large particle diameter, and a phosphor having an average particle diameter in a range of 2 to 5 μm is prepared as a phosphor having a small particle diameter. I do. Preferably, three types of phosphors having an average particle diameter in the range of 8 to 15 μm, 5 to 8 μm, and 2 to 5 μm, respectively, are prepared.

Examples of the binder for the phosphor layer include proteins such as gelatin, polysaccharides such as dextran, and natural high molecular substances such as gum arabic; and polyvinyl butyral, polyvinyl acetate, nitrocellulose, ethylcellulose, vinylidene chloride, and the like. Vinyl chloride copolymer,
Examples thereof include binders represented by rigid polymer substances such as polyalkyl (meth) acrylate, vinyl chloride / vinyl acetate copolymer, polyurethane, cellulose acetate butyrate, polyvinyl alcohol, and linear polyester. Particularly preferred among such binders are nitrocellulose, linear polyesters, polyalkyl (meth) acrylates, mixtures of nitrocellulose and linear polyester, and mixtures of nitrocellulose and polyalkyl (meth) acrylate. It is.

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

In the formation of the phosphor layer, first, for each type of the phosphor having a different average particle size, the phosphor particles and the binder are added to an appropriate solvent, and the resulting mixture is mixed well to obtain a fluorescent solution in the binder solution. A coating liquid in which body particles are uniformly dispersed is prepared.

Examples of the solvent for preparing the coating liquid include lower alcohols such as methanol, ethanol, n-propanol and n-butanol; hydrocarbons containing chlorine atoms 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 such as methyl acetate, ethyl acetate and butyl acetate with lower alcohols; ethers such as dioxane, ethylene glycol monoethyl ether and ethylene glycol monomethyl ether; Mixtures can be mentioned.

The mixing ratio of the binder and the phosphor in each coating solution differs depending on the characteristics of the intended radiographic intensifying screen, the type of the phosphor, and the like, but generally, the mixing ratio of the binder and the phosphor is 1: 1 or more. It is selected from the range of 1: 100 (weight ratio), and particularly preferably from the range of 1: 8 to 1:40 (weight ratio).

In each coating solution, a dispersant for improving the dispersibility of the phosphor particles in the coating solution, and the binding force between the binder and the phosphor particles in the formed phosphor layer are improved. Various additives such as a plasticizer may be mixed. Examples of dispersants used for such purposes include phthalic acid, stearic acid, caproic acid, and lipophilic surfactants. Examples of the plasticizer include phosphoric esters such as triphenyl phosphate, tricresyl phosphate and diphenyl phosphate; phthalic esters such as diethyl phthalate and dimethoxyethyl phthalate; ethylphthalylethyl glycolate, butylphthalylbutyl glycolate and the like. And polyesters of polyethylene glycol and aliphatic dibasic acid, such as polyesters of triethylene glycol and adipic acid, and polyesters of diethylene glycol and succinic acid.

A plurality of coating liquids prepared as described above are uniformly and simultaneously layer-coated on the surface of the support to form a coating film of the coating liquid. At this time, the coating liquid containing the phosphor particles having the largest average particle diameter is arranged on the support side, and the coating liquid containing the phosphor particles having the smaller average particle diameter is arranged farther from the support to perform simultaneous multilayer coating. Do. This coating operation can be performed by using ordinary coating means, for example, a doctor blade, a roll coater, a knife coater, or the like. Next, the formed coating film is dried by gradually heating to complete the formation of the phosphor layer on the support.

Alternatively, a multilayer phosphor layer may be formed on the support by repeating the operation of coating and drying each coating solution one by one.

The thickness of the phosphor layer (total thickness) varies depending on the characteristics of the intended radiographic intensifying screen, the type of the phosphor, the mixing ratio of the binder and the phosphor, and is usually in the range of 200 μm to 1 mm. And preferably in the range of 50 to 500 μm.

In the present invention, the particle diameter of the phosphor in the phosphor layer is large near the support, and may be smaller near the opposite screen surface, and preferably gradually increases from the screen surface side toward the support side. Preferably, they are arranged such that The particle size of the phosphor varies depending on the intended characteristics of the radiation intensifying screen, but preferably the average particle size in the vicinity of the screen surface is 2 to 5
μm, and the average particle diameter near the support is 8
〜15 μm. When the phosphor layer is formed using a plurality of kinds of coating solutions having different average particle diameters of the phosphor as described above, the ratio between the binder and the phosphor in each coating solution and the amount of each coating are determined by the It is suitably adjusted according to the type of body, average particle size and the like.

Note that the phosphor layer does not necessarily need to be formed by directly applying a coating solution on the support as described above.
Separately, after forming a phosphor layer by applying a coating solution and drying on a sheet such as a glass plate, a metal plate, and a plastic sheet in the same manner as above, press this on a support, or apply an adhesive. The support and the phosphor layer may be bonded together by using.

On the surface of the phosphor layer opposite to the side in contact with the support,
A protective film may be provided for the purpose of physically and chemically protecting the phosphor layer.

The transparent protective film is, for example, a cellulose derivative such as cellulose acetate or nitrocellulose; or a transparent polymer material such as polymethyl methacrylate, polyvinyl butyral, polyvinyl formal, polycarbonate, polyvinyl acetate, or a synthetic polymer such as vinyl chloride / vinyl acetate copolymer. It can be formed by a method in which a solution prepared by dissolving a high-molecular substance in an appropriate solvent is applied to the surface of the phosphor layer. Alternatively, it can be formed by a method such as bonding a transparent thin film formed in advance of polyethylene terephthalate, polyethylene, vinylidene chloride, polyamide or the like to the phosphor layer and the surface using an appropriate adhesive. The thickness of the transparent protective film is desirably about 3 to 20 μm.

The radiation film used in the radiation image forming method of the present invention has, as a basic structure, a support and a photographic emulsion layer provided on one side of the support.

Examples of the material of the support include a plastic film such as polyethylene terephthalate. The plastic film may be colored with a suitable coloring agent such as a blue dye or a red dye in order to block the crossover light and further improve the image quality of the image.

The photographic emulsion layer is composed of a binder such as gelatin which contains and supports silver halide in a dispersed state.

Examples of silver halide include AgCl, AgBr, AgI, and mixed crystals thereof. The silver halide may be regular grains (cubic, octahedral, tetradecahedral, epitaxial grains) or non-regular grains (tabular, potato-like).

Among them, tabular silver halide grains are particularly preferable because they can form an image with a small amount of silver since the silver image has a large covering power when developed. Further, since the tabular grains have a large specific surface area, a large amount of a sensitizing dye can be adsorbed on the grain surface without the inherent desensitization of silver halide. Since the light absorption coefficient of the sensitizing dye is larger than the light absorption coefficient of the indirect transition of silver halide, most of the light emitted from the phosphor is absorbed by the dye, so that the crossover light should be greatly reduced. Can be. Furthermore, since the tabular grains are arranged parallel to the support surface when coated and dried, they do not scatter the incident light much in the lateral direction, and the spread of the light in the lateral direction in the photographic emulsion layer can be reduced. .

The tabular grains used in the present invention generally have an average diameter.
It is in the range of 0.4 to 10 μm, preferably in the range of 0.5 to 5 μm. The ratio of the average thickness to the average diameter (diameter / thickness) is in the range of 4 to 20, preferably in the range of 6 to 15.

The photographic emulsion layer can be formed, for example, by coating a gelatin solution in which silver halide grains are dispersed on a support and drying. A sensitizing dye, a coupler and the like may be appropriately added to the gelatin solution. The silver halide are generally contained in an amount per unit area from 1 to 20 g / m ² of the emulsion layer, preferably in the range of 2 to 10 g / m ^2. Also,
The photographic emulsion layer is usually provided on a support with a layer thickness in the range of 1 to 50 µm.

Further, a protective layer made of gelatin or the like may be provided to physically and chemically protect the photographic emulsion layer.

Next, the radiation image forming method of the present invention using an imaging system in which a radiographic film and a radiographic film in which the particle diameter of the phosphor differs in the thickness direction of the phosphor layer will be described with reference to the accompanying drawings. .

FIG. 1 is a cross-sectional view showing an example of an imaging system (single-sided system) according to the present invention, and FIG. 2 is an example of a radiation image forming method of the present invention using the imaging system shown in FIG. It is a figure which shows schematically.

In FIG. 1, as described above, the radiation intensifying screen 1 is composed of a support 1a, a phosphor layer 1b and a protective film 1c in this order, and the phosphor particles in the phosphor layer 1b are directed from the screen surface side to the support side. (In the direction of incidence of the radiation) so that the particle size is gradually increased. The radiographic film 2 comprises a photographic emulsion layer 2b and a protective layer 2c provided on one side of a support 2a. The screen 1 and the film 2 face each other such that the surfaces of the protective film 1c and the protective layer 2c face each other.

In FIG. 2, a screen / film photographing system 3 includes a radiographic film 2 located on the radiation incident side and a radiographic intensifying screen 1 disposed behind the radiographic film 2. The imaging system 3 is disposed so as to face the radiation generator 5 with the subject 4 interposed therebetween.

After the radiation emitted from the radiation generator 5 has passed through the subject 4, a portion of the radiation directly exposes the radiation film 2. On the other hand, the remaining radiation is transmitted through the film 2 and then absorbed by the phosphor particles of the intensifying screen 1 and converted into fluorescence, and this light further exposes the adjacent film 2.

In this manner, a radiation image of the subject is formed on the radiation film 2, and after photographing, the film is developed to obtain a visible image on the film.

Next, examples and comparative examples of the present invention will be described. However, these examples do not limit the present invention.

Example 1 (1) Production of Radiation Intensifying Screen Terbium-activated gadolinium oxysulfide phosphor particles (Gd ₂ O ₂ S: Tb, average particle diameter: 4.4 μm), and linear polyester (Vylon # 500, Toyobo ( Co., Ltd.) and nitrification degree 11.
Mixture with 5% nitrocellulose (weight mixing ratio, 8: 2)
Was added to methyl ethyl ketone to prepare a dispersion containing the phosphor particles in a dispersed state. Further, tricresyl phosphate, n-butanol and methyl ethyl ketone were added to the dispersion, and the mixture was sufficiently stirred and mixed using a propeller mixer to uniformly disperse the phosphor particles, and the mixing ratio between the phosphor and the binder was 10%. : 1 (weight ratio) and viscosity 25-35PS
(25 ° C.) coating solution A was prepared.

A coating solution B was prepared by performing the same operation as described above except that terbium-activated gadolinium oxysulfide phosphor particles (average particle diameter: 6.0 μm) were used. Further, a coating solution C was prepared by performing the same operation as described above except that terbium-activated gadolinium oxysulfide phosphor particles (average particle diameter: 9.6 μm) were used.

Next, a titanium dioxide kneaded polyethylene terephthalate sheet (support, thickness: 2) placed horizontally on a glass plate
Coating solutions A, B, and C are arranged in this order on the surface of the support in the order of distance from the support, and the layers are uniformly and simultaneously coated using a doctor blade. The coating was dried by gradually increasing the temperature in the vessel from 25 ° C. to 100 ° C. In this manner, a phosphor layer composed of coating films C, B, and A was formed on the support in order, and each dried coating film had a thickness of about 60 μm and a total thickness of about 180 μm.

Then, a transparent film of polyethylene terephthalate (thickness: 12 μm, to which a polyester-based adhesive is applied) is placed on the phosphor layer with the adhesive layer side facing down, and adhered to the transparent protective film. To manufacture a radiographic intensifying screen I comprising a support, a phosphor layer having a phosphor particle diameter increasing from the screen surface side toward the support side, and a transparent protective film [FIG. (I), a: support, b: phosphor layer, c: protective film].

(2) Radiographic photography (formation of radiographic image) Obtained radiographic intensifying screen and single-sided radiographic film (trade name: Fuji MI-NH, Fuji Photo Film Co., Ltd.)
Was pressed in a cassette to form a screen / film photographing system as shown in FIG. 1, and X-ray photography was performed in the arrangement shown in FIG.

After the photographing, the radiation film was developed to obtain an X-ray photograph.

[Comparative Example 1] In Example 1, the coating liquids A and B were arranged in the order of distance from the support.
By performing the same operation as in the method of Example 1 except that the phosphor layers are arranged so as to be C and C, the phosphor layer in which the particle diameter of the phosphor decreases from the support surface side to the support side is reduced. And a radiographic intensifying screen II composed of a transparent protective film [FIG. 3 (I
I)].

An X-ray was taken to obtain an X-ray image on a radiographic film by performing the same operation as in Example 1 except that the obtained radiographic intensifying screen was used.

Comparative Example 2 The coating liquids A, B and C of Example 1 were mixed in equal amounts to prepare coating liquids containing phosphor particles having various particle diameters dispersed therein.

In Example 1, by performing the same operation as in the method of Example 1 except that this coating solution was used alone,
A radiographic intensifying screen III comprising a support, a phosphor layer having a uniform phosphor particle size distribution from the screen surface side to the support side, and a transparent protective film was manufactured [FIG. 3 (III)].

An X-ray was taken to obtain an X-ray image on a radiographic film by performing the same operation as in Example 1 except that the obtained radiographic intensifying screen was used.

Each of the above-described radiographic intensifying screens and radiographic photographs was evaluated by the image sharpness test, image granularity test and sensitivity test described below.

(1) Image sharpness test A screen / film photographing system is irradiated with X-rays at a tube voltage of 80 KVp through a resolving power chart to perform X-ray photography, and a contrast transfer function (CTF) of the obtained X-ray photograph is obtained.
Was measured and expressed as a value of a spatial frequency of 2 cycles / mm.

(2) Image graininess test X-rays with a tube voltage of 80 KVp are applied to a screen / film photographing system through a water phantom (thickness: 10 cm) and an aluminum plate (thickness: 10 mm) at a density of 1.2. X-ray photography was performed. The X-ray photographic film was processed for 90 seconds at a temperature of 35 ° C. using a developing solution (RD III, manufactured by Fuji Photo Film Co., Ltd.) using an automatic developing machine (New RN, manufactured by Fuji Photo Film Co., Ltd.). The obtained film was measured with a microphotometer (aperture: 300 μm × 300 μm), and the RMS
The value was determined.

(3) Sensitivity test An X-ray photograph was taken by irradiating a screen / film photographing system with X-rays having a tube voltage of 80 KVp. The sensitivity was measured from the image density of the obtained X-ray photograph.

 The results obtained are summarized in Table 1.

As is clear from the results shown in Table 1, the radiation image forming method (Example 1) of the present invention using the screen / film photographing system shown in FIG. Compared with the conventional method (Comparative Example 2) using the conventional radiographic intensifying screen (III) having a uniform particle size distribution of the body, the sharpness and the graininess of the image were remarkably improved although the sensitivity was slightly lower. .

Further, the method of the present invention (Example 1) is compared with a known method (Comparative Example 1) using a known radiographic intensifying screen (II) in which phosphor particles having a large particle diameter are arranged on the film side. Also, both the sharpness and the graininess were remarkably improved.

[Example 2] (1) Potassium bromide 6g during manufacture water 1 radiographic film, gelatin 25g and thioether _{[OH (CH 2) 2 S-} (CH 2) 2 S (SH 2) 2 OH] 0.5
After adding 20 cc of the weight% solution, the vessel is kept at 60 ° C., and further stirred vigorously in this vessel while 30 cc of a 0.88 M silver nitrate aqueous solution and a mixture of potassium bromide and potassium iodide in a molar ratio of 96: 4 of 0.88 30 cc of an aqueous M halogen solution was added simultaneously over 30 seconds.

Thereafter, further 1.600M of a silver nitrate aqueous solution of 1.70M and a mixture molar ratio of 96: 4 1.75M consisting of potassium bromide and potassium iodide
And a halogen aqueous solution (600 cc) were simultaneously added over 70 minutes. The temperature of the container was lowered, and salts in the emulsion were removed by washing with water by a sedimentation method. 10 at 55 ° C using both gold sensitization and sulfur sensitization
Aged for 0 minutes.

In this way, the average thickness is 0.160 μm and the average diameter is
An emulsion composed of tabular silver iodobromide grains having a diameter / thickness ratio of 7.8 .mu.m was obtained. The content of silver iodide was 4 mol%.

Next, a green sensitizing dye [anhydro-5,5'-dichloro-9-ethyl-3,3'-di (3
-Sulfopropyl) oxacarbocyanine hydroxide sodium salt] 500 mg and potassium iodide 500 mg
At a rate of Further, 4-hydroxy-6-methyl-1,3,3a, 7-tetrazaindene and an average molecular weight of 4
An emulsion solution was prepared by adding 7,000 polyacrylamide. The weight ratio of gelatin to silver (gelatin / silver) in the emulsion solution was 0.86.

Separately, a gelatin solution containing a matting agent (polymethylmethacrylate fine particles), a coating aid (sodium t-octylphenoxyethoxyethaneethanesulfonate), an antistatic agent (polyethylene oxide) and a hardening agent was prepared.

The above emulsion solution and gelatin solution were coated on a polyethylene terephthalate film (support, thickness: 180 μm) by a coextrusion coating method and dried to obtain a single-sided film comprising a support, a photographic emulsion layer and a protective layer in this order. . The coated silver amount of the film was 3.5 g / m ² , the gelatin amount of the emulsion layer was 3 g / m ² , and the gelatin coated amount of the protective layer was 1.2 g / m ² .

(2) Radiographic imaging (formation of radiographic image) The radiographic intensifying screen obtained in Example 1 and the radiographic film are pressure-bonded in a cassette to constitute a screen / film imaging system as shown in FIG. Then, X-ray photography was performed with the arrangement shown in FIG. After the photographing, the radiation film was developed to obtain an X-ray photograph.

Example 3 The procedure of Example 2 was repeated, except that an emulsion composed of potato-like grains (average diameter of spheres: 1.0 μm) was used instead of the tabular grains. A single-sided film comprising a support, a photographic emulsion layer and a protective layer was obtained in this order. The amount of silver applied on the film is 7.0 g
/ m ² , the amount of gelatin in the emulsion layer was 6 g / m ² , and the gelatin / silver ratio (weight ratio) was 0.86.

Example 2 except that this radiographic film was used.
By performing the same operation as in the above method, X-ray photography was performed to obtain an X-ray image on a radiation film.

Example 4 The procedure of Example 2 was repeated, except that an emulsion composed of potato-like grains (average diameter of spheres: 1.0 μm) was used instead of the tabular grains. A single-sided film comprising a support, a photographic emulsion layer and a surface protective layer was obtained in this order. The amount of silver applied on the film is
It was 7.0 g / m ^2, the amount of gelatin of the emulsion layer is 3 g / m ^2, the ratio of gelatin / silver weight ratio was 0.43.

Example 2 except that this radiographic film was used.
By performing the same operation as in the above method, X-ray photography was performed to obtain an X-ray image on a radiation film.

Example 5 The procedure of Example 2 was repeated, except that an emulsion composed of potato-like grains (average diameter of spheres: 0.6 μm) was used instead of the tabular grains. A single-sided film comprising a support, a photographic emulsion layer and a surface protective layer was obtained in this order. The amount of silver applied on the film is
It was 3.5 g / m ^2, the amount of gelatin of the emulsion layer is 3 g / m ^2, the ratio of gelatin / silver weight ratio was 0.86.

Example 2 except that this radiographic film was used.
By performing the same operation as in the above method, X-ray photography was performed to obtain an X-ray image on a radiation film.

Each radiographic photographing of Examples 2 to 5 was evaluated by the above-described image graininess test and sensitivity test, and further by a drying treatment test and a residual color test described below. Fog and Dmax were determined from the characteristic curves.

(4) Drying treatment test After X-ray photography, the degree of drying of the film when the radiation film was processed using an automatic processor from development to drying (Dry to Dry) for 90 seconds was determined by visual inspection and hand feeling. It was judged. The degree of drying was evaluated on the following four scales.

A: The film was sufficiently dry.

B: Moisture remained in the film.

C: Drying of the film was insufficient.

D: The film was not dried at all.

(5) Residual color test After the above-mentioned drying treatment, the radiation film was visually observed, and the degree of residual color contamination (dropping defect) was evaluated on the following four levels.

A: No dropping failure occurred in the film.

B: The film was slightly defective.

C: The film was considerably defective.

D: The film was markedly defective.

 Table 2 summarizes the obtained results.

As is clear from the results shown in Table 2, in the radiographic image forming method according to the present invention, when a radiographic film containing tabular silver iodobromide particles was used (Example 2). As compared with the case of using a radiation film containing conventional potato-like particles (Examples 3 to 5), the sensitivity and the granularity are excellent, and the fog and the maximum density (Dmax) can be sufficiently satisfied. Met. In addition, poor drying and residual color contamination did not occur at all.

On the other hand, in the case of the radiation film containing potato-like particles, when the amounts of silver and gelatin were both large (Example 3), although the sensitivity was relatively high, poor drying and residual color contamination occurred. When only the amount of silver was increased (Example 4), the granularity was poor and residual color contamination occurred. When the particle diameter was reduced (Example 5), the sensitivity was extremely low.

[Example 6] Radiation intensifying screen obtained in Example 1 and Example 2
The radiographic film obtained in the above was crimped in a cassette to form a screen film photographing system as shown in FIG. 1, and X-ray photography was performed in the arrangement shown in FIG. After the photographing, the radiation film was developed to obtain an X-ray photograph.

In Comparative Example 3 Example 6, two radiographic intensifying screens (trade name: Fuji GRENEX G _4, Fuji Photo Film Co., Ltd.) and double-sided radiographic film (trade name: ortho HR-L, Fuji A photographic film (manufactured by Photo Film Co., Ltd.) is operated in the same manner as in Example 6 except that screens are arranged on both sides of the film and pressed in a cassette to form a screen / film photographing system (double-sided system). Thus, X-ray photography was performed to obtain an X-ray image on a radiation film.

Each radiographic photographing of Example 6 and Comparative Example 3 was evaluated by the above sensitivity test, image sharpness test and image granularity test. Table 3 shows the obtained results.

As is clear from the results shown in Table 3, the radiation image forming method of the present invention using the radiographic film containing tabular grains (Example 6) was a single-sided system.
The sensitivity was the same as that of a radiation image forming method using a known double-sided system in which phosphor particles having a large particle diameter were arranged on the film side (Comparative Example 3), and the sharpness was remarkably high.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a screen / film photographing system according to the present invention. FIG. 2 is a schematic diagram illustrating the radiation image forming method of the present invention. FIG. 3 is a sectional view showing an example of a radiographic intensifying screen, wherein (I) is a screen of the present invention, (II) is a known screen, and (III) is a conventional screen. 1: radiographic intensifying screen, 1a, a: support, 1b, b: phosphor layer, 1c, c: protective film 2: radiographic film 2a: support, 2b: photographic emulsion layer, 3c: protective layer 3: Screen / film photography system, 4: subject, 5: radiation generator

Claims (7)

(57) [Claims] 1. A radiographic image forming method using a screen / film photographing system in which a radiographic intensifying screen is disposed on a rear surface of a radiographic film when viewed from a radiation incident direction. A phosphor layer provided thereon, and the phosphor particles constituting the phosphor layer are arranged such that the particle diameter increases from the screen surface side close to the radiographic film toward the support side. A method of forming a radiation image. 2. The phosphor layer of the radiation intensifying screen, wherein the average particle diameter of the phosphor particles near the screen surface is in the range of 2 to 5 μm, and the average particle diameter of the phosphor particles near the support is 8 to 5 μm. Claim 1 in the range of 15 μm
A method for forming a radiation image as described in the above item. 3. The phosphor layer of the radiation intensifying screen, wherein the average particle diameter of the phosphor particles in the vicinity of the screen surface is in the range of 2 to 5 μm, and the average particle diameter of the phosphor particles in the center is 5 to 8 μm. 2. The method according to claim 1, wherein the average particle diameter of the phosphor particles in the vicinity of the support is in the range of 8 to 15 [mu] m. 4. The radiation image forming method according to claim 1, wherein the phosphor particles constituting the phosphor layer of the radiation intensifying screen are terbium-activated rare earth oxysulfide phosphors. 5. The radiographic film is substantially composed of a support and a photographic emulsion layer provided on one side of the support, and the photographic emulsion layer contains tabular silver halide grains. The method for forming a radiation image according to claim 1, which is contained. 6. The method according to claim 5, wherein the ratio of the average diameter to the average thickness of the tabular silver halide grains is in the range of 4 to 20. 7. The method according to claim 5, wherein the ratio of the average diameter to the average thickness of the tabular silver halide grains is in the range of 6 to 15.