JP2006113046A - Radiographic image photographing apparatus and radiation image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiographic image photographing apparatus and radiation image forming method in which the radiation image obtained by photographing the phase contrast satisfy all of the image quality granularity, sharpness and image defects. <P>SOLUTION: The radiographic image photographic apparatus has a small-focus radiation source 1 for irradiating a subject 3 with radiation, a holding member 2 for holding the subject and a radiographic image detector 4 reading radiographic image information based on radiographic having transmitted the subject, and performs phase contrast photographing the subject held by the subject-holding member. The radiation detector has a phosphor plate, containing stimulable phosphor particle having a polyhedral crystal structure. The charged fraction of stimulable phosphor in the stimulable phosphor layer of the phosphor plate is 60 to 80%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a radiographic image capturing apparatus and a radiographic image forming method.

  X-ray images using the action of X-rays, which are one type of radiation, passing through a substance are widely used for medical image diagnosis, non-destructive inspection and the like. The X-ray image is a shadow image that is generated when the X-ray transmission amount varies depending on the atomic amount of the substance constituting the subject when the X-ray passes through the subject. That is, X-rays are radiated from the X-ray source, a two-dimensional distribution of the X-ray dose after passing through the subject is detected by an X-ray detector, and an X-ray image based on the X-ray absorption contrast of the subject is formed.

  Recently, an image called a phase contrast image has been proposed for an X-ray image. The phase contrast image is also called a refraction contrast image, and is obtained by imaging with a monochromatic parallel X-ray obtained from a synchrotron radiation X-ray source such as SPring-8 or by a micro-focus X-ray source having a focal size of about 10 μm. It is what Compared to a normal image with only absorption contrast, the contrast at the boundary of the subject can be drawn higher, and a high-definition X-ray image can be obtained.

  The phase contrast image is refracted when the X-ray passes through the subject by taking an image at a distance between the subject and the radiological image detector that detects the X-rays that have passed through the subject, so that As the X-ray density becomes sparse, the outside of the subject overlaps with the X-rays that do not pass through the subject, the X-ray density increases, and the edge that is the boundary portion of the subject is emphasized.

  By the way, when the distance between the subject and the radiographic image detector is increased, the size of the radiographic image is enlarged with respect to the size of the subject. For example, when a doctor uses the image for medical diagnosis, the actual size is used. It is convenient to diagnose with a large image. Therefore, the subject is magnified, a phase contrast image is taken, and then output at a reduction ratio 1 / M corresponding to the magnified magnification M, so that an actual image can be recorded on a recording medium using a recording device. preferable.

As described above, as a radiation image forming system for forming a phase contrast image as an actual size image, it has been conventionally photographed by a radiation image photographing apparatus in which the distance between the subject table and the radiation image detector can be freely changed. There is a radiation image forming system that calculates an enlargement ratio from the distance between the subject table and the radiation image detector, reduces an image based on the enlargement ratio, and outputs the image to an image output apparatus (see, for example, Patent Document 1).
2001-238871

  However, in the above-described radiographic image forming system, the distance between the radiation source and the detector is larger than the imaging method in which the normal subject and the radiographic image detection are adjacent to each other. Radiation images satisfying all of the properties, sharpness, and image defects could not be obtained.

  Therefore, an object of the present invention is to provide a radiographic imaging apparatus and a radiographic image forming method in which a radiographic image obtained by phase contrast imaging has image quality satisfying all of graininess, sharpness and image defects. .

  The above object of the present invention is achieved by the following configurations.

(Claim 1)
A small-focus radiation source that irradiates a subject with radiation, a holding member that holds the subject, and a radiation image detector that reads radiation image information based on the radiation that has passed through the subject, and is held by the subject holding member In a radiographic imaging device for performing phase contrast imaging of a subject, the radiation detector has a phosphor plate containing stimulable phosphor particles having a polyhedral crystal structure, and the stimulable phosphor of the phosphor plate A radiographic imaging device, wherein the filling rate of the stimulable phosphor in the layer is 60 to 80%.

(Claim 2)
The radiographic image capturing apparatus according to claim 1, wherein the photostimulable phosphor particles are a mixture of two or more photostimulable phosphor particles having different average particle diameters.

(Claim 3)
Among the two or more different photostimulable phosphor particles, the average particle size of the large photostimulable phosphor particles is 6.0 to 10.0 μm, and the average particle size of the small photostimulable phosphor particles is 3 The radiographic image capturing apparatus according to claim 2, wherein the radiographic image capturing apparatus is 0.0 to 5.0 μm.

(Claim 4)
Among the two or more different photostimulable phosphor particles, the mixing ratio of the large photostimulable phosphor particles and the small photostimulable phosphor particles is 95: 5 to 50:50 in mass ratio. The radiographic imaging device according to claim 2.

(Claim 5)
The radiation image capturing apparatus according to claim 1, wherein the photostimulable phosphor is represented by the following general formula (1).

General formula (1)
Ba1-xM2xFBryI1-y: aM1, bLn, cO
[Wherein, M1: at least one alkali metal atom selected from Li, Na, K, Rb and Cs, M2: at least one alkaline earth metal atom selected from Be, Mg, Sr and Ca, Ln: Ce, At least one rare earth element selected from Pr, Sm, Eu, Gd, Tb, Tm, Dy, Ho, Nd, Er, and Yb, x, y, a, b, and c are 0 ≦ x ≦ 0.3, 0 ≦ y ≦ 1.0, 0 ≦ a ≦ 0.05, 0 <b ≦ 0.2, 0 <c ≦ 0.1. ]
(Claim 6)
A radiographic image forming method, wherein the radiographic image capturing apparatus according to claim 1 captures and outputs a magnified image recorded in a reduced size to a subject area.

  The radiographic image capturing apparatus and radiographic image forming method according to the present invention have excellent effects on all of the granularity, sharpness, and image defects of the radiographic image obtained by phase contrast imaging.

  Hereinafter, the present invention will be described in more detail.

  The present invention has a small-focus radiation source that irradiates a subject with radiation (X-rays), a holding member that holds the subject, and a radiation image detector that reads radiation image information based on the radiation that has passed through the subject. In the radiation (X-ray) imaging device that performs phase contrast imaging of the subject held by the subject holding member, the radiation (X-ray) detector includes fluorescence containing stimulable phosphor particles having a polyhedral crystal structure. A radiographic imaging device, wherein the stimulable phosphor filling rate in the photostimulable phosphor layer of the phosphor plate is 60 to 80%. For the first time, the radiographic image obtained by phase contrast imaging, which is the object of the present invention, has graininess. Both sharpness and image defects were satisfied.

  In the present invention, the photostimulable phosphor particles in the phosphor plate (radiation (X-ray) detector) are a mixture of two or more photostimulable phosphor particles having different average particle diameters. It is preferable in that the effect of the present invention is further exerted, and the average particle size of the large stimulable phosphor particles among the two or more different photostimulable phosphor particles is 6.0 to 10.0 μm, The average particle size of the small photostimulable phosphor particles is 3.0 to 5.0 μm, and among the two or more different photostimulable phosphor particles, large photostimulable phosphor particles and small photostimulability It is particularly preferable that the mixing ratio with the phosphor particles is 95: 5 to 50:50 in terms of mass ratio, in view of the effects of the present invention.

  According to a fifth aspect of the present invention, there is provided a radiographic image forming method for performing phase contrast imaging on a subject using the radiographic image capturing apparatus according to any one of the first to fourth aspects of the present invention.

  Next, the radiographic imaging device will be described with reference to FIG.

  Normally, the components of the radiographic image capturing apparatus include a subject holding member 2 and an X-ray detector 4 that determine the positions of the X-ray source 1 and the subject 3 and fix them, and are fixed to the X-ray source 1. The distance between the subject 3 and the subject 3 is represented by R1, and the distance between the subject 3 and the X-ray detector 4 is represented by R2.

  In the present invention, the X-ray detector 4 has a phosphor plate containing stimulable phosphor particles having a polyhedral crystal structure, and the photostimulable phosphor in the photostimulable phosphor layer of the phosphor plate is used. The filling rate is 60 to 80%, and the object of the present invention can be achieved.

  The radiographic image forming method of the present invention is an image forming method for performing phase contrast imaging of a subject using the radiographic imaging device as described above.

  The stimulable phosphor particles having a polyhedral crystal structure of the present invention (hereinafter also referred to as polyhedral particles) are three-dimensional particles surrounded by four or more planes, such as hexahedron, octahedron, and tetrahedron. It means a body, a quadrangular pyramid, etc., and is not particularly limited.

  Polyhedral particles are obtained, for example, under the following production conditions. That is, a method for producing an oxygen-introduced rare earth-activated alkaline earth metal fluoride halide photostimulable phosphor in the liquid phase by adding an inorganic fluoride aqueous solution to a barium halide aqueous solution, and thereby adding a rare earth activated alkaline earth metal fluoride. It can be obtained by simultaneously performing a step of obtaining a precipitate of a halide halide photostimulable phosphor precursor crystal and a step of removing the solvent from a solution having a barium concentration of 3.3 mol / L or more in the reaction mother liquor.

  The stimulable phosphor filling factor is a value calculated as follows.

The protective layer of the screen is peeled off, the phosphor layer is eluted with methyl ethyl ketone, filtered, dried, and baked in an electric furnace at 600 ° C. for 1 hour to remove the resin on the surface, and the mass of the phosphor is O ₁ g. When the phosphor layer thickness is P ₁ cm, the screen area Q ₁ cm ² used for elution, and the phosphor specific gravity is R ₁ g / cm ³ ,
Phosphor filling factor (V ₁ %) = [O ₁ ÷ (P ₁ × Q ₁ × R ₁ )] × 100
The filling rate of the present invention can be adjusted, for example, as follows. After the stimulable phosphor layer is coated on the support or the support provided with the undercoat layer and dried under desired conditions, the stimulable phosphor layer is formed into a phosphor sheet. In general, a temperature and pressure are applied between a highly smooth nip roller having a diameter of 1 to 100 cm and a heatable roller facing the nip roller. By applying this compression treatment, the filling rate of the photostimulable phosphor in the photostimulable phosphor layer can be improved.

  The compression method using a calender roll is not particularly limited. For example, it is described in “Resin Processing Technology Handbook (Edition of Polymer Society): Nikkan Kogyo Shimbun, June 12, 1965”. Can be applied with reference to the method. Moreover, the method of compressing with a press machine may be used.

  FIG. 2 is a schematic diagram showing an example of compression processing preferably used in the present invention.

  In FIG. 2, first, the stimulable phosphor layer coating solution is applied by the coater 4 to the support 7 that has been fed from the supply roll 6 in the transport direction D, and then introduced into the drying zone 8 and arranged vertically. Dry by blowing hot air from the nozzle. Next, the dried support 7 (also referred to as phosphor sheet) coated with the stimulable phosphor layer is subjected to a compression treatment using a combination of calendar rolls 9-1 to 9-3, and the winding roll 10 Take up around. As a structure of a calendar roll, it is preferable that the calendar rolls 9-1 and 9-3 are heat rolls, and the calendar roll 9-2 is a resin compliant roll.

  The calender roll is not particularly limited in its structure or type of resin, but, for example, a high-rigidity base using iron as an inner core and its outer peripheral surface are covered with, for example, a hard resin outer cylinder. A roller can be mentioned, and specifically, elagrass (manufactured by Kinyo Metal Co., Ltd.), mirror tex roll (manufactured by Yamauchi Rubber Co., Ltd.) and the like can be mentioned.

  In this invention, it is preferable to perform the compression process by a calender roll on the conditions of 1.96MPa-49.0MPa, Especially preferably, it is the conditions of 3.92MPa-24.5MPa. By performing the compression conditions within the range specified above, the filling rate and smoothness of the photostimulable phosphor layer are improved, and as a result, image unevenness of the photostimulable phosphor is reduced and good sharpness is achieved. Can be obtained. In particular, under the above conditions, the phosphor layer compressibility near the support is increased.

  In the above conditions, a sufficient compressibility and smoothness cannot be obtained at a temperature of less than 1.96 MPa and less than the Tg of the polymer resin, and the temperature exceeds 49.0 MPa and is equal to or higher than the softening point of the support. This is not preferable because the photostimulable phosphor particles may be destroyed and the support may be deformed, and the brightness may not be restored by refiring.

  A high-contrast image can be obtained using an X-ray tube usually used in a medical facility or the like without using a synchrotron in a huge facility or a microfocus X-ray source having a weak X-ray dose. The X-ray tube used here is preferably a rotary anode X-ray tube. In this rotary anode X-ray tube, X-rays are generated when an electron beam emitted from the cathode collides with the anode.

  This is incoherent (incoherent) like natural light, and is not divergent X-rays but divergent light. If the electron beam continues to hit the place where the anode is fixed, the anode is damaged by the generation of heat. Therefore, in an X-ray tube that is usually used, the anode is rotated to prevent the anode from being shortened. An electron beam is made to collide with the surface of a certain size of the anode, and the generated X-rays are emitted from the plane of the certain size anode toward the subject. A portion of this plane viewed from the X-ray irradiation direction is called a focus. This focal spot size is assumed to be D. The focal spot size of the present invention can be measured from the half width of the intensity distribution of the radiation source. The focal point has various shapes, but in the case of a square, the length of one side thereof, in the case of a rectangle or a polygon, the length of a short side, and in the case of a circle, the diameter thereof is defined as a focal point size D.

  The X-ray detector converts X-ray energy into other energy and takes it out as image information. Examples include a screen (intensifying screen) / film, a photostimulable phosphor described later. There are a system used, a system combining an X-ray phosphor and a CCD or CMOS, a system combining an X-ray phosphor and an X-ray photoconductor and a TFT. In the present invention, it is preferable to use an X-ray tube having a focal spot size of 30 μm or more.

  Next, the photostimulable phosphor of the present invention will be described.

  The stimulable phosphor of the present invention is preferably a stimulable phosphor represented by the following general formula (1).

General formula (1)
Ba1-xM2xFBryI1-y: aM1, bLn, cO
[Wherein, M1: at least one alkali metal atom selected from Li, Na, K, Rb and Cs, M2: at least one alkaline earth metal atom selected from Be, Mg, Sr and Ca, Ln: Ce, At least one rare earth element selected from Pr, Sm, Eu, Gd, Tb, Tm, Dy, Ho, Nd, Er, and Yb, x, y, a, b, and c are 0 ≦ x ≦ 0.3, 0 ≦ y ≦ 1.0, 0 ≦ a ≦ 0.05, 0 <b ≦ 0.2, 0 <c ≦ 0.1. ]
For the production of stimulable phosphor precursors by the liquid phase method, the precursor production method described in JP-A-10-140148 and the precursor production apparatus described in JP-A-10-147778 can be preferably used. Here, the photostimulable phosphor precursor indicates a state in which the substance represented by the general formula (1) does not pass a high temperature of 600 ° C. or higher. Little luminescence is shown. In the present invention, the precursor is preferably obtained by the following liquid phase synthesis method.

  The production of the oxygen-introduced rare earth-activated alkaline earth metal fluoride halide photostimulable phosphor having the general formula (1) is not a solid phase method in which the particle shape is difficult to control, but a liquid in which the particle size is easily controlled. It is preferable to carry out by the phase method. In particular, it is preferable to obtain a photostimulable phosphor by the following liquid phase synthesis method.

Production method: including halides of BaI ₂ and Ln, when x in general formula (1) is not 0, further M2 halide, if y is not 0, BaBr ₂ and M1 halide. And a step of preparing a solution having a BaI ₂ concentration of 3.3 mol / L or more, preferably 3.5 mol / L or more after the dissolution; the solution is heated to a temperature of 50 ° C. or more, preferably 80 ° C. or more. While maintaining the solution, a solution of an inorganic fluoride (ammonium fluoride or alkali metal fluoride) having a concentration of 5 mol / L or more, preferably 8 mol / L or more is added to the rare earth activated alkaline earth metal fluoride iodide system. A step of obtaining a precipitate of the stimulable phosphor precursor crystal; a step of removing the solvent from the reaction solution while adding the inorganic fluoride; a step of separating the precursor crystal precipitate from the reaction solution; A production method including a step of firing while avoiding sintering was separated precursor crystals precipitate.

  The particles (crystals) according to the present invention preferably have an average particle size of 1 to 10 μm and are monodisperse, have an average particle size of 1 to 5 μm and an average particle size distribution (%) of 20% or less. The average particle size is preferably 1 to 3 μm, and the average particle size distribution is preferably 15% or less.

  The average particle diameter in the present invention is obtained by randomly selecting 200 particles from an electron micrograph of particles (crystals) and obtaining an average by volume particle diameter in terms of sphere.

  Details of the method for producing the photostimulable phosphor will be described below.

(Preparation of precursor crystal precipitate, stimulable phosphor)
First, raw material compounds other than fluorine compounds are dissolved in an aqueous medium. That is, a halide of BaI ₂ and Ln, and if necessary, further a halide of M2, and further a halide of M1 are placed in an aqueous medium and mixed well and dissolved to prepare an aqueous solution in which they are dissolved. However, the quantitative ratio between the BaI ₂ concentration and the aqueous solvent is adjusted so that the BaI ₂ concentration is 3.3 mol / L or more, preferably 3.5 mol / L or more.

  At this time, if the barium concentration is low, a precursor having a desired composition cannot be obtained, or even if obtained, the particles are enlarged. Therefore, it is necessary to select the barium concentration appropriately, and as a result of the study by the present inventors, it was found that fine precursor particles can be formed at 3.3 mol / L or more.

At this time, if desired, a small amount of acid, ammonia, alcohol, water-soluble polymer, water-insoluble metal oxide fine particle powder or the like may be added. It is also a preferred embodiment that an appropriate amount of lower alcohol (methanol, ethanol) is added within a range in which the solubility of BaI ₂ is not significantly reduced. This aqueous solution (reaction mother liquor) is maintained at 80 ° C.

  Next, an aqueous solution of inorganic fluoride (ammonium fluoride, alkali metal fluoride, etc.) is injected into the aqueous solution maintained at 80 ° C. and stirred. This injection is preferably carried out in the region where the stirring is particularly intense. By injecting the inorganic fluoride aqueous solution into the reaction mother liquor, an oxygen-introduced rare earth-activated alkaline earth metal fluoride halide phosphor precursor crystal corresponding to the general formula (1) is precipitated.

  In the present invention, the solvent is removed from the reaction solution when adding the inorganic fluoride aqueous solution. The timing for removing the solvent is not particularly limited as long as it is being added. The ratio of the total mass after removal of the solvent to the mass before removal (the sum of the mass of the reaction mother liquor and the mass of the added aqueous solution) (hereinafter referred to as the removal ratio) is preferably 0.97 or less. If it exceeds 0.97, the crystal may not be fully BaFI. Therefore, the removal ratio is preferably 0.97 or less, and more preferably 0.95 or less. Moreover, even if it removes too much, inconvenience may arise in terms of handling, such as an excessive increase in the viscosity of the reaction solution.

  Therefore, the solvent removal ratio is preferably up to 0.5. The time required for removing the solvent not only greatly affects the productivity, but also the shape and particle size distribution of the particles are affected by the method of removing the solvent, so the removal method needs to be appropriately selected. Generally, when removing the solvent, a method of heating the solution and evaporating the solvent is selected. This method is also useful in the present invention. By removing the solvent, a precursor having the intended composition can be obtained. Furthermore, in order to increase productivity and to keep the particle shape appropriately, it is preferable to use other solvent removal methods in combination. The method for removing the solvent used in combination is not particularly limited. It is also possible to select a method using a separation membrane such as a reverse osmosis membrane. In the present invention, it is preferable to select the following removal method from the viewpoint of productivity.

  1. The reaction vessel for ventilating the dry gas is sealed, and at least two holes through which gas can pass are provided, and the dry gas is vented therefrom. The kind of gas can be selected arbitrarily. Air and nitrogen are preferable from the viewpoint of safety. Depending on the amount of saturated water vapor in the gas to be vented, the solvent is entrained in the gas and removed. In addition to the method of venting the void portion of the reaction vessel, a method of jetting gas as bubbles in the liquid phase and absorbing the solvent in the bubbles is also effective.

  2. Depressurization As is well known, by reducing the pressure, the vapor pressure of the solvent decreases. The solvent can be efficiently removed by the vapor pressure drop. The degree of reduced pressure can be appropriately selected depending on the type of solvent. When the solvent is water, 86 kPa or less is preferable.

  3. The solvent can be efficiently removed by enlarging the liquid film evaporation area. As in the present invention, when the reaction is performed by heating and stirring using a reaction container having a constant volume, the heating method is either immersed in the liquid or the heating means is mounted outside the container. The method is common. According to this method, the heat transfer area is limited to the portion where the liquid and the heating means are in contact with each other, and the heat transfer area decreases with the removal of the solvent, and thus the time required for the solvent removal increases. In order to prevent this, a method of increasing the heat transfer area by spraying on the wall surface of the reaction vessel using a pump or a stirrer is effective. Such a method of spraying a liquid on the reaction vessel wall surface to form a liquid film is known as a “wetting wall”. Examples of the method for forming the wet wall include a method using a stirrer described in JP-A-6-335627 and JP-A-11-235522, in addition to a method using a pump.

  These methods may be used not only alone but also in combination. A combination of a method of forming a liquid film and a method of reducing the pressure in the container, a combination of a method of forming a liquid film and a method of ventilating dry gas, and the like are effective. The former is particularly preferable, and the methods described in JP-A-6-335627 and Japanese Patent Application No. 2002-35202 are preferably used.

  Next, the above phosphor precursor crystals are separated from the solution by filtration, centrifugation, etc., sufficiently washed with methanol or the like, and dried. A sintering inhibitor such as alumina fine powder or silica fine powder is added to and mixed with the dried phosphor precursor crystal, and the fine powder of sintering inhibitor is uniformly attached to the crystal surface. It should be noted that the addition of the sintering inhibitor can be omitted by selecting the firing conditions.

  Next, the phosphor precursor crystals are filled in a heat-resistant container such as a quartz port, an alumina crucible, or a quartz crucible, and placed in the core of an electric furnace to be fired while avoiding sintering. The range of 400-1300 degreeC is suitable for a calcination temperature, and the range of 500-1000 degreeC is preferable. The firing time varies depending on the filling amount of the phosphor raw material mixture, the firing temperature, the removal temperature from the furnace, etc., but generally 0.5 to 12 hours is appropriate.

  As the firing atmosphere, a neutral atmosphere such as a nitrogen gas atmosphere or an argon gas atmosphere, a weakly reducing atmosphere such as a nitrogen gas atmosphere containing a small amount of hydrogen gas, a carbon dioxide atmosphere containing carbon monoxide, or a small amount of oxygen introduced The atmosphere is used. As the firing method, the method described in JP-A No. 2000-8034 is preferably used. The target oxygen-introduced rare earth activated alkaline earth metal fluoride halide photostimulable phosphor is obtained by the above firing, and a radiation image conversion panel having a phosphor layer formed using the phosphor is produced.

  Various polymer materials are used as the support used in the radiation image conversion panel of the present invention. In particular, a material that can be processed into a flexible sheet or web as an information recording material is suitable. In this respect, cellulose acetate film, polyester film, polyethylene terephthalate film, polyethylene naphthalate film, polyamide film, polyimide A plastic film such as a film, a triacetate film or a polycarbonate film is preferred.

  The layer thickness of these supports varies depending on the material of the support used, but is generally 80 μm to 1000 μm, and more preferably 80 μm to 500 μm from the viewpoint of handling. The surface of these supports may be a smooth surface, or may be a mat surface for the purpose of improving the adhesion to the photostimulable phosphor layer.

  Further, these supports may be provided with an undercoat layer on the surface on which the photostimulable phosphor layer is provided for the purpose of improving the adhesion to the photostimulable phosphor layer.

  The undercoat layer according to the present invention preferably contains a polymer resin that can be crosslinked by a crosslinking agent and a crosslinking agent.

  The polymer resin that can be used in the undercoat layer is not particularly limited. For example, polyurethane, polyester, vinyl chloride copolymer, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, Vinyl chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (nitrocellulose, etc.), styrene-butadiene copolymer, various synthetic rubber resins, phenol resin, epoxy resin, urea Examples thereof include resins, melamine resins, phenoxy resins, silicon resins, acrylic resins, urea formamide resins, and the like. Among them, polyurethane, polyester, vinyl chloride copolymer, polyvinyl butyral, nitrocellulose and the like can be mentioned. In the invention according to claim 2, the average glass transition temperature (Tg) of the polymer resin used in the undercoat layer can be mentioned. ) Is preferably 25 ° C. or higher, more preferably a polymer resin having a Tg of 25 to 200 ° C. is used.

  The crosslinking agent that can be used in the undercoat layer according to the present invention is not particularly limited, and examples thereof include polyfunctional isocyanates and derivatives thereof, melamine and derivatives thereof, amino resins and derivatives thereof, and the like. It is preferable to use a polyfunctional isocyanate compound as the agent, and examples thereof include Coronate HX and Coronate 3041 manufactured by Nippon Polyurethane.

  The undercoat layer used in the present invention can be formed on a support by, for example, the following method.

  First, the polymer resin and the crosslinking agent described above are added to an appropriate solvent, for example, a solvent used in the preparation of a stimulable phosphor layer coating liquid described later, and mixed sufficiently to prepare an undercoat layer coating liquid. .

  The amount of crosslinking agent used varies depending on the characteristics of the intended radiation image conversion panel, the type of materials used for the stimulable phosphor layer and the support, the type of polymer resin used in the undercoat layer, etc. Considering the maintenance of the adhesive strength of the phosphor layer to the support, it is preferably added at a ratio of 50% by mass or less, particularly preferably 15 to 50% by mass with respect to the polymer resin.

  The thickness of the undercoat layer varies depending on the characteristics of the intended radiation image conversion panel, the type of materials used for the stimulable phosphor layer and the support, the type of polymer resin and crosslinking agent used in the undercoat layer, etc. In general, the thickness is preferably 3 to 50 μm, and particularly preferably 5 to 40 μm.

  Examples of the binder used in the phosphor layer in the present invention include proteins such as gelatin, polysaccharides such as dextran, or natural high molecular substances such as gum arabic; and polyvinyl butyral, polyvinyl acetate, and nitrocellulose. , Represented by synthetic polymer materials such as ethyl cellulose, vinylidene chloride / vinyl chloride copolymer, polyalkyl (meth) acrylate, vinyl chloride / vinyl acetate copolymer, polyurethane, cellulose acetate butyrate, polyvinyl alcohol, linear polyester, etc. Examples of the binder include a resin mainly composed of a thermoplastic elastomer. Examples of the thermoplastic elastomer include polystyrene-based thermoplastic elastomers and polyolefins described above. Thermoplastic elastomers, polyurethane thermoplastic elastomers, polyester thermoplastic elastomers, polyamide thermoplastic elastomers, polybutadiene thermoplastic elastomers, ethylene vinyl acetate thermoplastic elastomers, polyvinyl chloride thermoplastic elastomers, natural rubber heat Examples thereof include thermoplastic elastomers, fluororubber-based thermoplastic elastomers, polyisoprene-based thermoplastic elastomers, chlorinated polyethylene-based thermoplastic elastomers, styrene-butadiene rubber, and silicon rubber-based thermoplastic elastomers. Among these, polyurethane-based thermoplastic elastomers and polyester-based thermoplastic elastomers have good dispersibility due to their strong bonding strength with phosphors, and are also excellent in ductility, and have excellent flexibility against radiation intensifying screens. This is preferable. These binders may be crosslinked by a crosslinking agent.

  The mixing ratio of the binder and the stimulable phosphor in the coating solution varies depending on the set value of the haze ratio of the intended radiation image conversion panel, but is preferably 1 to 20 parts by mass with respect to the phosphor, and more preferably 2 to 2. 10 parts by mass is more preferable.

  As a protective layer provided in a radiation image conversion panel having a coating-type phosphor layer, a polyester film provided with an excitation light absorption layer having a haze ratio measured by the method described in ASTM D-1003 of 5% or more and less than 60%, Polymethacrylate film, nitrocellulose film, cellulose acetate film and the like can be used, but stretched films such as polyethylene terephthalate film and polyethylene naphthalate film are preferable as a protective layer in terms of transparency and strength. A vapor deposition film obtained by depositing a thin film such as a metal oxide or silicon nitride on the polyethylene terephthalate film or the polyethylene terephthalate film is more preferable from the viewpoint of moisture resistance.

  The haze ratio of the film used in the protective layer can be easily adjusted by selecting the haze ratio of the resin film to be used, and a resin film having an arbitrary haze ratio can be easily obtained industrially. As a protective film for a radiation image conversion panel, an optically highly transparent film is assumed. As such a highly transparent protective film material, various plastic films having a haze value in the range of 2 to 3% are commercially available. In order to obtain the effect of the present invention, the preferred haze ratio is 5% or more and less than 60%, and more preferably 10% or more and less than 50%. If the haze ratio is less than 5%, the effect of eliminating image unevenness and linear noise is low, and if it is 60% or more, the effect of improving sharpness is impaired.

The film used in the protective layer used in the present invention has optimum moisture resistance by laminating a plurality of vapor deposited films obtained by depositing a metal oxide or the like on a resin film or resin film in accordance with the required moisture resistance. In consideration of moisture absorption deterioration prevention of the photostimulable phosphor, the moisture permeability is preferably at least 5.0 g / m ² · day or less. There is no restriction | limiting in particular as a lamination method of a resin film, You may use any well-known method.

  In addition, it is preferable to provide an excitation light absorption layer between the laminated resin films so that the excitation light absorption layer is protected from physical impact and chemical alteration and stable plate performance can be maintained for a long period of time. Further, the excitation light absorption layer may be provided at a plurality of locations, or a color material may be contained in the adhesive layer for stacking to form the excitation light absorption layer.

  The protective film may be in close contact with the photostimulable phosphor layer via an adhesive layer, but has a structure (hereinafter also referred to as a sealing or sealing structure) provided to cover the phosphor surface. Is more preferable. In sealing the phosphor plate, any known method may be used, but the outermost resin layer on the side in contact with the phosphor sheet of the moisture-proof protective film may be a moisture-proof resin film. This is one of the preferred forms in that the protective film can be fused and the phosphor sheet can be efficiently sealed.

  Furthermore, a moisture-proof protective film is disposed above and below the phosphor sheet, and the upper and lower moisture-proof protective films are heated and fused with an impulse sealer or the like in a region where the periphery is outside the periphery of the phosphor sheet. The sealing structure is preferable because it can prevent moisture from entering from the outer peripheral portion of the phosphor sheet. In addition, the moisture-proof protective film on the support surface side is a laminated moisture-proof film formed by laminating one or more aluminum films, so that moisture entry can be reduced more reliably. It is easy and preferable. In the method of heat-sealing with the impulse sealer, heat-sealing under a reduced pressure environment is more preferable in terms of preventing displacement of the phosphor sheet in the moisture-proof protective film and eliminating moisture in the atmosphere.

  The outermost resin layer and the phosphor surface having the heat-sealing property on the side where the phosphor surface of the moisture-proof protective film is in contact may or may not be adhered. Here, the state of non-adhesion means that the phosphor surface and the moisture-proof protective film are optically and mechanically discontinuous even if the phosphor surface and the moisture-proof protective film are in point contact. It is a state that can be treated as a body. The resin film having the above-mentioned heat-fusibility is a resin film that can be fused with a commonly used impulse sealer. For example, ethylene vinyl acetate copolymer (EVA), polypropylene (PP) film, polyethylene ( PE) film and the like can be mentioned, but the present invention is not limited to this.

  Examples of the organic solvent used for the preparation of the stimulable phosphor layer coating solution include lower alcohols such as methanol, ethanol, isopropanol and n-butanol, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, methyl acetate, Esters of lower fatty acids and lower alcohols such as ethyl acetate and n-butyl acetate, ethers such as dioxane, ethylene glycol monoethyl ether, ethylene glycol monomethyl ether, aromatic compounds such as triol and xylol, methylene chloride, ethylene chloride, etc. Examples thereof include halogenated hydrocarbons and mixtures thereof.

  In the coating solution, a dispersing agent for improving the dispersibility of the phosphor in the coating solution, and the binding force between the binder and the phosphor in the photostimulable phosphor layer after formation are improved. Various additives such as a plasticizer may be mixed.

  Examples of the dispersant used for such purpose include phthalic acid, stearic acid, caproic acid, lipophilic surfactant and the like. Examples of plasticizers include phosphoric acid esters such as triphenyl phosphate, tricresyl phosphate and diphenyl phosphate; phthalic acid esters such as diethyl phthalate and dimethoxyethyl phthalate; ethyl phthalyl ethyl glycolate and butyl phthalyl butyl glycolate And a polyester of triethylene glycol and adipic acid, a polyester of polyethylene glycol and an aliphatic dibasic acid such as a polyester of diethylene glycol and succinic acid, and the like.

  In addition, a dispersing agent such as stearic acid, phthalic acid, caproic acid or a lipophilic surfactant is mixed in the stimulable phosphor layer coating solution for the purpose of improving the dispersibility of the stimulable phosphor particles. Also good.

  The coating solution for the photostimulable phosphor layer is prepared using a dispersing device such as a ball mill, a bead mill, a sand mill, an attritor, a three-roll mill, a high-speed impeller disperser, a Kady mill, or an ultrasonic disperser. .

  A coating film is formed by uniformly coating the coating solution prepared as described above on the surface of a support described later. As a coating method that can be used, usual coating means such as a doctor blade, a roll coater, a knife coater, a comma coater, a lip coater and the like can be used.

  The coating film formed by the above means is then heated and dried to complete the formation of the photostimulable phosphor layer on the support. The thickness of the photostimulable phosphor layer varies depending on the characteristics of the intended radiation image conversion panel, the type of stimulable phosphor, the mixing ratio of the binder and the phosphor, and is usually 10 to 1000 μm. More preferably, it is 10-500 micrometers.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, the embodiment of this invention is not limited to these.

(Preparation of phosphor particle 1; according to the method described in JP-A-2003-246980)
Put a) BaBr ₂ aqueous solution (1.5 mol / L) 1200 ml to the reaction vessel made of SUS316 volume of 4000 ml, this EuBr ₃ aqueous solution (0.2 mol / L) 37.5 ml, a KBr ₃ 0. 9 g, the CaBr ₂ · 2H ₂ O was added 3.54g and water 1762.5Ml. The reaction mother liquor (BaBr ₂ concentration: 1.00 mol / L) in the reaction vessel was kept at 60 ° C., and a screw-type stirring blade having a diameter of 60 mm was rotated at 500 rpm to stir the reaction mother liquor. 300 ml of NH ₄ F aqueous solution (5 mol / L) was injected into the above reaction mother liquor kept warm with stirring at a liquid feed rate of 5.0 ml / min using a roller pump to generate a precipitate. After completion of the injection, the precipitate was aged by maintaining the temperature and stirring for 2 hours. The precipitate was then filtered off and washed with 2 L of methanol. Next, the washed precipitate was taken out and vacuum dried at 120 ° C. for 4 hours to obtain about 350 g of europium-activated barium fluorobromide phosphor precursor crystal (BaFBr crystal).

  In order to prevent changes in particle shape due to sintering during firing and particle size distribution due to fusion between particles, 0.2% by mass of ultrafine powder of alumina was added thereto, and the mixture was sufficiently stirred with a mixer. Thus, an ultrafine particle powder of alumina was uniformly attached to the crystal surface. This is filled in a quartz boat, baked at 850 ° C. for 2 hours in a hydrogen gas atmosphere using a tube furnace, and further, the above phosphor particles are classified to obtain a europium-activated barium fluorobromide phosphor crystal (BaFBr crystal). ) When the obtained crystals were observed with a scanning electron microscope, most of them were tetrahedral crystals. Next, this crystal was measured with a light diffraction type particle size distribution measuring instrument (Horiba, Ltd .: LA-500), and it was confirmed that the average crystal size was 8.0 μm.

(Preparation of phosphor particles 2; according to the method described in JP-A 2003-246980)
b) 2850 ml of BaI ₂ aqueous solution (4.0 mol / L) was placed in a 4000 ml volume SUS316 reaction vessel, and 90 ml of EuI ₃ aqueous solution (0.2 mol / L) and 60 ml of water were added thereto. The reaction mother liquor (BaI ₂ concentration: 3.80 mol / L) in the reaction vessel was kept at 50 ° C., and a screw-type stirring blade having a diameter of 60 mm was rotated at 500 rpm to stir the reaction mother liquor. 720 ml of an HF aqueous solution (5 mol / L) was injected into the above reaction mother liquor kept warm with stirring at a liquid feed rate of 12 ml / min using a roller pump, thereby generating a precipitate. After completion of the injection, the precipitate was aged by continuing the incubation and stirring for 2 hours. The precipitate was then filtered off and washed with 2 L of isopropanol. Next, the washed precipitate was taken out and vacuum-dried at 120 ° C. for 4 hours to obtain about 1000 g of europium-activated barium iodide phosphor precursor crystals (BaFI crystals).

  In order to prevent changes in particle shape due to sintering during firing and particle size distribution due to fusion between particles, 0.2% by mass of ultrafine powder of alumina was added thereto, and the mixture was sufficiently stirred with a mixer. Thus, an ultrafine particle powder of alumina was uniformly attached to the crystal surface. This is filled in a quartz boat, baked at 850 ° C. for 2 hours in a hydrogen gas atmosphere using a tube furnace, and further, the above-mentioned phosphor particles are classified to obtain a europium-activated barium iodide phosphor crystal (BaFI crystal). Obtained. When the obtained crystals were observed with a scanning electron microscope, most of them were tetrahedral crystals. Next, this crystal was measured with a light diffraction type particle size distribution measuring device, and it was confirmed that the average crystal size was 4.5 μm.

(Preparation of phosphor particles 3; hexahedral small particles according to the method described in JP-A No. 2003-268369)
In order to synthesize a stimulable phosphor precursor of europium-activated barium fluoroiodide, 2500 ml of BaI ₂ aqueous solution (4 mol / L) and 26 EuI ₃ aqueous solution (0.2 mol / L) 26 were placed in a pressure-resistant container having _two holes. .5 ml was placed in the reactor. Furthermore, 992 g of potassium iodide was added to the aqueous solution. The reaction mother liquor in this reactor was kept at 85 ° C. with stirring. While ventilating dry air at a rate of 10 l / min, 600 ml of an aqueous ammonium fluoride solution (10 mol / L) was used in the reaction mother liquor while concentrating the solvent while maintaining the pressure in the reaction vessel at 36.3 kPa using a circulating aspirator. The mixture was poured over 1 hour using a roller pump to form a precipitate. After completion of the reaction, the mass ratio of the solution before and after aeration was 0.92. The mixture was stirred for 60 minutes at the same temperature. The mixture was stirred for 60 minutes, filtered, washed with 2000 ml of ethanol, and dried at 80 ° C. to obtain about 1000 g of europium-activated barium iodide phosphor precursor crystals (BaFI crystals).

  In order to prevent changes in particle shape due to sintering during firing and particle size distribution due to fusion between particles, 0.2% by mass of ultrafine powder of alumina was added thereto, and the mixture was sufficiently stirred with a mixer. Thus, an ultrafine particle powder of alumina was uniformly attached to the crystal surface. This was filled in a quartz boat and baked at 850 ° C. for 2 hours in a hydrogen gas atmosphere using a tube furnace to obtain europium-activated barium fluoroiodide phosphor particles.

  When the obtained crystals were observed with a scanning electron microscope, most of them were hexahedral crystals. Next, this crystal was measured with a light diffraction type particle size distribution measuring device, and it was confirmed that the average crystal size was 4.5 μm.

(Preparation of phosphor particles 4; hexahedral large particles according to the method described in JP-A No. 2003-268369)
In order to synthesize a stimulable phosphor precursor of europium-activated barium fluoroiodide, 2500 ml of BaI ₂ aqueous solution (4 mol / L) and 26 EuI ₃ aqueous solution (0.2 mol / L) 26 were placed in a pressure-resistant container having _two holes. .5 ml was placed in the reactor. Furthermore, 992 g of potassium iodide was added to the aqueous solution. The reaction mother liquor in the reactor was kept warm at 92 ° C. with stirring. While ventilating dry air at a rate of 10 l / min, 600 ml of an aqueous ammonium fluoride solution (10 mol / L) was used in the reaction mother liquor while concentrating the solvent while maintaining the pressure in the reaction vessel at 42.3 kPa using a circulating aspirator. Was poured over 3 hours using a roller pump to form a precipitate. After completion of the reaction, the mass ratio of the solution before and after aeration was 0.92. The mixture was stirred for 60 minutes at the same temperature. The mixture was stirred for 60 minutes, filtered, washed with 2000 ml of ethanol, and dried at 80 ° C. to obtain about 1000 g of europium-activated barium iodide phosphor precursor crystals (BaFI crystals).

  In order to prevent changes in particle shape due to sintering during firing and particle size distribution due to fusion between particles, 0.2% by mass of ultrafine powder of alumina was added thereto, and the mixture was sufficiently stirred with a mixer. Thus, an ultrafine particle powder of alumina was uniformly attached to the crystal surface. This was filled in a quartz boat and baked at 850 ° C. for 2 hours in a hydrogen gas atmosphere using a tube furnace to obtain europium-activated barium fluoroiodide phosphor particles.

  When the obtained crystals were observed with a scanning electron microscope, most of them were hexahedral crystals. Next, when this crystal was measured with a light diffraction type particle size distribution measuring device, it was confirmed that the average crystal size was 8 μm.

(Preparation of phosphor particles 5; in accordance with the method described in JP-A-2004-138440)
To synthesize a stimulable phosphor precursor of europium-activated barium fluoroiodide, 2780 ml of 3.6 mol / L BaI ₂ aqueous solution and 27 ml of 0.2 mol / L EuI ₃ aqueous solution were placed in a reactor, The reaction mother liquor in this reactor was kept at 83 ° C. with stirring. Subsequently, 322 ml of an 8 mol / L aqueous ammonium fluoride solution was injected into the reaction mother liquor using a roller pump to form a precipitate. After completion of the injection, the mixture was kept warm and stirred for 2 hours to age the precipitate.

  Next, the precipitate was separated by filtration, washed with ethanol, and vacuum-dried to obtain europium-activated barium fluoroiodide crystals. In order to prevent changes in particle shape due to sintering during firing and particle size distribution due to fusion between particles, 0.2% by mass of ultrafine powder of alumina was added thereto, and the mixture was sufficiently stirred with a mixer. Thus, an ultrafine particle powder of alumina was uniformly attached to the crystal surface. This was filled in a quartz boat and baked at 850 ° C. for 2 hours in a hydrogen gas atmosphere using a tube furnace to obtain europium-activated barium fluoroiodide phosphor particles. Next, the phosphor particles were classified to obtain particles having an average particle diameter of 7 μm.

(Production of phosphor 6; according to the method described in JP-A-2004-125398)
In order to synthesize a stimulable phosphor precursor of europium-activated barium fluoroiodide, 2780 ml of BaI2 aqueous solution (3.6 mol / L) and 27 ml of EuI3 aqueous solution (0.15 mol / L) were placed in a reactor. The reaction mother liquor in this reactor was kept at 83 ° C. with stirring. Next, 322 ml of an aqueous ammonium fluoride solution (8 mol / L) was injected into the reaction mother liquor using a roller pump to form a precipitate. After completion of the injection, the mixture was kept warm and stirred for 2 hours to age the precipitate. Next, the precipitate was filtered off, washed with ethanol, and then vacuum dried to obtain europium activated barium fluoroiodide crystals. In order to prevent changes in particle shape due to sintering during sintering and particle size distribution change due to inter-particle fusion, 0.2% by mass of ultrafine powder of alumina is added, and the crystal surface is stirred thoroughly with a mixer. An ultrafine powder of alumina was uniformly adhered to the surface. This was filled in a quartz boat and baked at 850 ° C. for 2 hours in a hydrogen gas atmosphere using a tube furnace to obtain europium-activated barium fluoroiodide phosphor particles. Next, the phosphor particles were classified to prepare a phosphor having an average particle diameter of 4 μm.

(Preparation of phosphor layer coating solution)
The phosphors prepared above were mixed at a ratio shown in Table 1 so that the total amount was 480 g, and 57.0 g of a polyurethane resin (Nipporan 2304 (solid content 35%), manufactured by Nippon Polyurethane Co., Ltd.) having a Tg of 30 ° C. and methyl ethyl ketone: toluene Was added to a 1: 1 mixed solvent and dispersed by a propeller mixer to prepare a phosphor layer coating solution having a viscosity of 25 to 30 mPa · s.

  (Preparation of undercoat layer coating solution) 100 parts by mass of a polyester resin (Byron 300, manufactured by Toyobo Co., Ltd.) and 5% by mass of a silane coupling agent (γ-mercaptopropyltrimethoxysilane) are mixed and further crosslinked. 10 parts by mass of Coronate HX (manufactured by Nippon Polyurethane Co., Ltd.), which is a polyfunctional isocyanate compound, is mixed as an agent, added to this mixture in a 1: 1 mixed solvent of methyl ethyl ketone: toluene, dispersed by a propeller mixer, and a viscosity of 500 mPa · s undercoat layer coating solution was prepared.

<Application of undercoat layer>
On the black polyethylene terephthalate support that has been kneaded with carbon having a thickness of 250 μm, the prepared undercoat layer coating solution is applied using a knife coater so that the dry film thickness is 15 μm, and then dried and subtracted. A layer-coated sample was prepared.

<Heat treatment of the sample coated with the undercoat layer>
The prepared undercoat layer-coated sample was subjected to heat treatment (aging treatment) at 60 ° C. for 100 hours.

<Application of phosphor layer>
The prepared phosphor layer coating solution is applied on the undercoat layer of each heat-treated sample and untreated sample so that the dry film thickness is 380 μm, and then dried for 30 minutes at 100 ° C. A phosphor sheet was formed.

  A part of the coated and dried photostimulable phosphor sheet was subjected to a compression treatment with a roll group having the structure shown in FIG.

  The compression part has a three-roll configuration in series and forms two nips with two heat rolls 9-1 and 9-3 and one compliant roll 9-2 on the surface where the stimulable phosphor layer is formed. It adjusted so that a compliant roll might touch. Reference numeral 6 denotes a supply roll, reference numeral 10 denotes a winding roll, reference numeral 8 denotes a drying zone, reference numeral 7 denotes a support, and reference numeral 4 denotes a coater. Moreover, the code | symbol D shows a conveyance direction. The heat rolls 9-1 and 9-3 have a diameter of 300 mmφ and a surface of 0.2 S, the compliant roll 9-2 has a diameter of 250 mmφ, the hardness is Shore D75 °, the crown amount is 0 μm, JIS- A polyester mirrortex roll (manufactured by Yamauchi Rubber) having a center line average surface roughness Ra defined by B-0601 of 0.4 μm was used. The compression treatment was performed by setting the heat roll temperature to 70 ° C. and adjusting the linear pressure to 1 kN / cm.

About each obtained fluorescent substance sheet, according to said formula, the fluorescent substance filling factor was measured and computed. The thickness of the phosphor layer was measured, and the specific gravity of the phosphor was calculated as 5.4 g / cm ³ from the phosphor mass per 100 cm ² area of the phosphor sheet.

(Production of moisture-proof protective film)
The thing of the following structure (A) was used as a protective film of the fluorescent substance layer coating surface side of the produced fluorescent substance sheets 1-8.

Configuration (A)
NY15 /// VMPET12 /// VMPET12 /// PET12 /// CPP20
NY: Nylon PET: Polyethylene terephthalate CPP: Casting polypropylene VMPET: Alumina-deposited PET (commercial product: manufactured by Toyo Metallizing Co., Ltd.)
The numbers described behind each resin film indicate the film thickness (μm) of the resin layer.

  The above “///” means a dry lamination adhesive layer, and means that the thickness of the adhesive layer is 3.0 μm. As the adhesive used for dry lamination, a two-component reaction type urethane adhesive was used.

  The protective film on the back side of the support of the phosphor sheet was a dry laminate film having a structure of CPP 30 μm / aluminum film 9 μm / polyethylene terephthalate (PET) 188 μm. In this case, the thickness of the adhesive layer was 1.5 μm, and a two-component reaction type urethane adhesive was used.

(Preparation of phosphor plate)
After cutting the prepared phosphor sheets into squares each having a side of 20 cm, the peripheral portion is fused and sealed using an impulse sealer under reduced pressure using the prepared moisture-proof protective film. Body plates 1-8 were prepared. In addition, it fused so that the distance from a fusion | melting part to a fluorescent substance sheet peripheral part might be set to 1 mm. The impulse sealer heater used for fusion was a 3 mm wide heater.

(Evaluation of sharpness)
In FIG. 1, a lead MTF chart is mounted at a position 1 m from the X-ray source, and a phosphor plate is placed in the X-ray image detector 4 so that a projected image of the MTF chart enters a position 1.7 m from the X-ray source. After irradiation with X-rays with a tube voltage of 80 kVp in a mounted state, the plate is excited by operating with a He—Ne laser beam, and the stimulated luminescence emitted from the phosphor layer is received by a photoreceiver (with a spectral sensitivity of S-5). Received by a photoelectron image tube) and converted into an electrical signal, analog / digital converted and recorded on a magnetic tape, and the magnetic tape was analyzed by a computer and one cycle of an X-ray image recorded on the magnetic tape The modulation transfer function (MTF) at / mm was examined, this was defined as the sharpness, and the relative value with the sharpness of the phosphor plate 1 as 100 was displayed.

(Granularity: Evaluation of screen roughness)
In FIG. 1, a chest phantom is mounted at a position 1 m from the X-ray source, and a phosphor plate is placed in the X-ray image detector 4 so that a projected image of the chest phantom enters at a position 1.7 m from the X-ray source. After irradiating X-rays with a tube voltage of 80 kVp in the mounted state, the plate is excited by operating with a He-Ne laser beam, and the stimulated luminescence emitted from the phosphor layer is received by the same light receiver as above. It is converted into an electrical signal, this is reproduced as an image by an image reproducing device, and is reduced to 1 / 1.7 from the output device and printed out. In general, the roughness of the image was evaluated.

A: No graininess of the image is observed at all. B: A feeling of graininess of the image is slightly recognized, but the level of roughness of the image is confirmed but practically acceptable. Table 1 shows the results obtained from the level above which the occurrence of roughness of the image is recognized over the entire surface, causing problems in practical use.

(Evaluation of image defects)
In FIG. 1, an aluminum plate having a thickness of 5 mm is mounted at a position 1 m from the X-ray source, and fluorescence is emitted into the X-ray image detector 4 so that a projected image of the aluminum plate enters a position 1.7 m from the X-ray source. After irradiating the tube plate with X-rays with a tube voltage of 80 kVp, the phosphor plate is excited by operating with a He-Ne laser beam, and the stimulated emission emitted from the phosphor layer is the same as the above Is received and converted into an electrical signal, and the stimulated emission emitted from the phosphor layer is received by the above-described receiver and converted into an electrical signal, which is reproduced as an image by an image reproducing device, and output from an output device. The printout was reduced to 1 / 1.7 so that the optical density was 1.0, and the obtained print image was visually evaluated for image defects according to the following criteria.

A: Image defect is not recognized at all. O: Image defect is slightly recognized, but is almost unnoticeable. Δ: Image defect is confirmed, but practically acceptable level. X: Image defect over the entire surface. Table 1 shows the results obtained from the above levels where the occurrence of the above is recognized and the problem occurs in practice.

  As is apparent from the above results, it can be seen that the phosphor plate of the present invention is superior in characteristics as compared with the comparative phosphor plate.

It is the schematic which shows an example of a part of radiographic imaging apparatus of this invention. It is the schematic which shows an example of the compression process preferably used for this invention.

Explanation of symbols

  2 Subject holding member

Claims (6)

A small-focus radiation source that irradiates a subject with radiation, a holding member that holds the subject, and a radiation image detector that reads radiation image information based on the radiation that has passed through the subject, and is held by the subject holding member In a radiographic imaging apparatus for performing phase contrast imaging of a subject, the radiation detector has a phosphor plate containing stimulable phosphor particles having a polyhedral crystal structure, and the stimulable phosphor of the phosphor plate A radiographic imaging apparatus, wherein the filling rate of the photostimulable phosphor in the layer is 60 to 80%. The radiographic image capturing apparatus according to claim 1, wherein the photostimulable phosphor particles are a mixture of two or more photostimulable phosphor particles having different average particle diameters. Among the two or more different photostimulable phosphor particles, the average particle size of the large photostimulable phosphor particles is 6.0 to 10.0 μm, and the average particle size of the small photostimulable phosphor particles is 3 The radiographic image capturing apparatus according to claim 2, wherein the radiographic image capturing apparatus has a thickness of 0.0 to 5.0 μm. Among the two or more different photostimulable phosphor particles, the mixing ratio of large photostimulable phosphor particles and small photostimulable phosphor particles is 95: 5 to 50:50 in mass ratio. The radiographic image capturing apparatus according to claim 2. The radiation image capturing apparatus according to claim 1, wherein the photostimulable phosphor is represented by the following general formula (1).
General formula (1)
Ba1-xM2xFBryI1-y: aM1, bLn, cO
[Wherein, M1: at least one alkali metal atom selected from Li, Na, K, Rb and Cs, M2: at least one alkaline earth metal atom selected from Be, Mg, Sr and Ca, Ln: Ce, At least one rare earth element selected from Pr, Sm, Eu, Gd, Tb, Tm, Dy, Ho, Nd, Er, and Yb, x, y, a, b, and c are 0 ≦ x ≦ 0.3, 0 ≦ y ≦ 1.0, 0 ≦ a ≦ 0.05, 0 <b ≦ 0.2, 0 <c ≦ 0.1. ] A radiographic image forming method comprising: imaging a radiographic image capturing apparatus according to claim 1; and outputting the enlarged image recorded in a reduced size to a subject area.

Images