JPH0718958B2 - Radiation image conversion panel - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a radiation image conversion panel using a stimulable phosphor, and more particularly to a radiation image conversion panel that gives a radiation image with high sharpness.

2. Description of the Related Art Radiation images such as X-ray images are often used for disease diagnosis. In order to obtain this X-ray image, X-rays that have passed through the subject are irradiated onto the phosphor layer (fluorescent screen), thereby generating visible light, and this visible light is used in the same way as when taking a normal photograph. A so-called radiograph in which a film containing salt is irradiated and developed is used. However, in recent years, a method for directly taking out an image from the phosphor layer has been devised without using a film coated with silver salt. As this method, the radiation that has passed through the subject is absorbed by the phosphor, and then the phosphor is excited by, for example, light or thermal energy so that the radiation energy accumulated by the absorption by the phosphor is emitted as fluorescence. , There is a method of detecting this fluorescence and imaging. Specifically, for example, U.S. Pat. No. 3,859,527 and JP-A-55-12144.
Japanese Patent No. 3187242 discloses a radiation image conversion method using a stimulable phosphor and using visible light or infrared light as stimulated excitation light. This method uses a radiation image conversion panel in which a stimulable phosphor layer is formed on a support, and the radiation that has passed through the subject is applied to the stimulable phosphor layer of this radiation image conversion panel to apply the radiation to each part of the subject. A latent image is formed by accumulating the radiation energy corresponding to the radiation transmittance, and thereafter, the stimulable phosphor layer is scanned with stimulable excitation light to radiate the accumulated radiation energy of each part to generate a latent image. The light is converted into light and an image is obtained by an optical signal depending on the intensity of the light.
This final image may be played back as a hard copy or on a CRT. Now, the radiation image conversion panel having the stimulable phosphor layer used in this radiation image conversion method has the same radiation absorption rate and light conversion rate (including both) as in the case of the radiographic method using the above-mentioned fluorescent screen. It is required that the image has good graininess and high sharpness, not to mention high radiation sensitivity. However, in general, a radiation image conversion panel having a stimulable phosphor layer coats a support or a protective layer with a dispersion containing a particle-shaped stimulable phosphor having a particle size of about 1 to 30 μm and an organic binder. Since it is produced by drying, the packing density of the stimulable phosphor is low (filling rate 50%), and the stimulable phosphor layer is used as shown in FIG. It was necessary to increase the layer thickness of. As is clear from the figure, the layer thickness of the stimulable phosphor layer is 200 μm.
In this case, the deposition amount of the stimulable phosphor is 50 mg / cm ² , and the radiation sensitivity increases linearly up to 450 μm until the layer thickness reaches 350 μm.
It saturates above. Incidentally, the radiation sensitivity is saturated, because when the stimulable phosphor layer becomes too thick, the scattering of the stimulable phosphor layer among the stimulable phosphor particles results in This is because the stimulated emission does not come out to the outside. On the other hand, as shown in FIG. 5 (b), the sharpness of the image obtained by the radiation image conversion method tends to be higher as the layer thickness of the stimulable phosphor layer of the radiation image conversion panel is smaller. In order to improve the property, it was necessary to reduce the thickness of the stimulable phosphor layer. Further, since the graininess of the image in the radiation image conversion method is determined by the spatial fluctuation of the radiation quantum number (quantum mottle) or the structural disorder of the stimulable phosphor layer of the radiation image conversion panel (structure mottle), etc. , When the thickness of the stimulable phosphor layer becomes thin, the number of radiation quantum absorbed in the stimulable phosphor layer decreases and the quantum mottle increases, or structural disorder becomes apparent and the structural mottle increases. As a result, the image quality is degraded. Therefore, in order to improve the graininess of the image, the stimulable phosphor layer needs to be thick. That is, as described above, in the conventional radiation image conversion panel, the sensitivity to radiation and the graininess of the image, and the sharpness of the image show the opposite tendency to the layer thickness of the stimulable phosphor layer. The radiation image conversion panel has been made at the expense of some sensitivity to radiation, graininess and sharpness. By the way, it is well known that the sharpness of the image in the conventional radiographic method is determined by the spread of the instantaneous light emission (light emission at the time of radiation irradiation) of the phosphor in the phosphor screen. The sharpness of the image in the radiation image conversion method using the stimulable phosphor is not determined by the spread of the stimulated emission of the stimulable phosphor in the radiation image conversion panel, that is, as in radiography. It is not determined by the spread of the emission of the phosphor, but depends on the spread of the stimulated excitation light in the panel. In this radiation image conversion method, since the radiation image information accumulated in the radiation image conversion panel is taken out in time series, it is desirable that the stimulated emission due to the stimulated excitation light irradiated at a certain time (ti). Is described as the output from a certain pixel (xi, yi) on the panel that was all illuminated and was irradiated with stimulated excitation light at that time, but if the stimulated excitation light spreads in the panel due to scattering, etc. , If the stimulable phosphor existing outside the irradiation pixel (xi, yi) is also excited, the output from the pixel (xi, yi) above is recorded as the output from a wider area than that pixel. This is because it will end up. Therefore, the stimulated emission by the stimulated excitation light irradiated at a certain time (ti) is emitted from the pixel (xi, yi) on the panel that was actually irradiated with the stimulated excitation light at that time (ti). If only the luminescence is emitted, the sharpness of the obtained image will not be affected regardless of the extent of the luminescence. Under such circumstances, some methods for improving the sharpness of radiographic images have been devised. For example, JP-A-55-146447
Method of mixing white powder in the stimulable phosphor layer of the radiation image conversion panel described in JP-A-55-163500, the radiation image conversion panel described in JP-A-55-163500 in the stimulable excitation wavelength region of the stimulable phosphor. For example, there is a method of coloring so that the average reflectance is smaller than the average reflectance in the stimulated emission wavelength region of the stimulable phosphor. However, these methods are not preferable methods because the sensitivity inevitably decreases remarkably when the sharpness is improved. On the other hand, the applicant of the present invention has already proposed in Japanese Patent Application No. 59-196365 a new radiation image conversion panel which is a novel radiation image conversion panel that improves on the conventional defects in the radiation image conversion panel using the stimulable phosphor as described above. A radiation image conversion panel in which the luminescent phosphor layer does not contain a binder is proposed. According to this, since the stimulable phosphor layer of the radiation image conversion panel does not contain a binder, the filling rate of the stimulable phosphor is significantly improved and the transparency of the stimulable phosphor layer is improved. The sensitivity of the radiation image conversion panel to radiation and the graininess of the image are improved, and at the same time, the sharpness of the image is improved. However, in the radiation image conversion method, the sensitivity,
The demand for image quality with excellent sharpness without impairing graininess is becoming more severe.

[Object of the Invention]

The present invention relates to the above proposed radiation image conversion panel using a stimulable phosphor, which is to further improve it.
It is an object of the present invention to provide a radiation image conversion panel which has improved sensitivity to radiation and provides an image with high sharpness. It is another object of the present invention to provide a radiation image conversion panel which improves the graininess and gives an image with high sharpness.

[Structure and operation of the invention]

The above-mentioned object of the present invention is a radiation image conversion panel having at least one binder-free photostimulable phosphor layer on a support, wherein the photostimulable phosphor layer has a substantially layer thickness inside. The present invention is achieved by a radiation image conversion panel, characterized in that it has a large number of minute voids extending in the direction, and the porosity of the voids in the stimulable phosphor layer is 3 to 30%. . Next, the present invention will be specifically described. FIG. 1 is a cross-sectional view in the thickness direction of a radiation image conversion panel of the present invention (hereinafter sometimes simply referred to as a panel when the meaning is clear). In the figure, reference numeral 10 shows the form of the panel of the present invention. Reference numeral 11 represents a support, and 12 represents a stimulable phosphor layer formed on the support by a vapor deposition method. Support 11 and stimulable phosphor layer 12
If necessary, an adhesive layer for improving the adhesive between the layers may be provided, or a reflective layer or an absorption layer for stimulated excitation light and / or stimulated emission may be provided. . A large number of fine voids 13 are provided in the stimulable phosphor layer 12. The voids 13 preferably have an elongated shape extending in a direction substantially perpendicular to the surface of the support in order to prevent light from being scattered laterally. The spacing between the voids 13 is preferably 100 μm or less, more preferably 40 μm or less. It is good to say Further, the voids 13 are provided so that the porosity of the stimulable phosphor layer 12 is 3 to 30%. More preferably the porosity is 10
Try to be ~ 25%. When the porosity is 3% or less, a dense photostimulable phosphor layer is gradually formed, and sufficient sharpness cannot be obtained. On the other hand, when it is 30% or more, the layer thickness of the stimulable phosphor layer necessary for obtaining sufficient radiation sensitivity becomes large, and conversely the sharpness is lowered. A protective layer 14 is preferably provided on the stimulable phosphor layer 12. FIG. 2 shows another example of the panel of the present invention as a sectional view in the thickness direction. Reference numeral 21 is a support, 22 is a stimulable phosphor layer composed of a parallel structure of fine columnar blocks extending in a direction substantially perpendicular to the support surface, 22ij represents each fine columnar block, and (22ij) is (22ij) It represents a gap in the form of a crack, groove, or depression between 22ij. Further, a large number of fine voids 23 are provided in the fine columnar block so that the stimulable phosphor layer 22 has a porosity of 3% to 30%. The preferable shape of the void 23 is the same as that described in the description of FIG. Further, 24 is a protective layer which is preferably provided. In the panel of the present invention having the structure as shown in FIG. 2, the support 21 is a support having a large number of fine concavo-convex patterns on its surface as described in, for example, Japanese Patent Application No. 59-266913. Alternatively, it may be a support having a surface structure such as a large number of minute tile-like plates, which are separated from each other by minute gaps and spread as described in Japanese Patent Application No. 59-266914. It may be a support having a fine wire net which surrounds each of the minute tile-shaped plates and divides each of the minute tile-shaped plates on the surface as described in Japanese Patent Application No. 59-266915. The average diameter of the fine columnar blocks 22ij is preferably 1 to 400 μm, and the gap between the fine columnar blocks (22ij)
May be any interval as long as the fine columnar blocks 22ij are optically independent of each other, but 0 to 20 μm on average.
m is preferred. When the stimulable excitation light is incident on the stimulable phosphor layer having fine voids, the excitation light reaches the bottom surface of the stimulable phosphor layer while being repeatedly reflected inside by the void surface. Therefore, the sharpness of the image due to stimulated emission can be significantly increased. In addition to the voids, a stimulable phosphor layer having a fine columnar block juxtaposed structure as shown in FIG. 2 can similarly obtain the above-mentioned effects, but is more effective. The thickness of the stimulable phosphor layer of the panel of the present invention varies depending on the sensitivity of the panel to radiation, the type of the stimulable phosphor, etc., but is preferably in the range of 10 to 800 μm, and 50 to 500 μm.
The range of m is more preferable. In the radiation image conversion panel of the present invention, the stimulable phosphor means a stimulus such as an optical, thermal, mechanical, optical, or electrical (stimulant excitation) after being irradiated with the first light or high-energy radiation. ), A phosphor that exhibits stimulated emission corresponding to the dose of the first light or high-energy radiation is mentioned, but from a practical point of view, a phosphor that exhibits stimulated emission by stimulated excitation light of 500 nm or more is preferable. is there. Examples of the stimulable phosphor used in the radiation image conversion panel of the present invention include BaSO ₄ : Ax (where A is at least one of Dy, Tb and Tm) described in JP-A-48-80487. Yes, x is
0.001 ≦ x <1 mol%. ), MgSO ₄ : Ax described in JP-A-48-80488 (where A is Ho or Dy
And 0.001 ≦ x ≦ 1 mol%)
A phosphor represented by SrSO ₄ : Ax described in JP-A-48-80489 (wherein A is at least 1 of Dy, Tb and Tm)
It is a seed and x is 0.001 ≦ x <1 mol%. ), Na ₂ described in JP-A-51-29889
A phosphor obtained by adding at least one of Mn, Dy and Tb to SO ₄ , CaSO ₄ and BaSO _4, etc., fluorescence of BeO, LiF, MgSO ₄ and CaF ₂ described in JP-A-52-30487. Body, JP-A-53-3
9277 Li ₂ B ₄ O ₇ : Cu, phosphor such as Ag, Li ₂ O. (B ₂ O ₂ ) x: Cu described in JP-A-54-47883
(However, x is 2 <x ≦ 3), and Li ₂ O · (B ₂ O ₂ ) x: Cu, Ag
(Where x is 2 <x ≦ 3) or the like, US Pat. No. 3,859,52
SrS: Ce, Sm, SrS; Eu, Sm, La ₂ O ₂ S: E described in No. 7
Examples include phosphors represented by u, Sm and (Zn, Cd) S: Mn, X (where X is a halogen). Further, a ZnS: Cu, Pb phosphor described in JP-A-55-12142, whose general formula is BaO.xAl ₂
O ₃ : Eu (provided that 0.8 ≦ x ≦ 10) barium aluminate phosphor, and the general formula is M ^II O · xSiO ₂ : A (provided that M ^II
Is Mg, Ca, Sr, Zn, Cd or Ba, and A is Ce, Tb, Eu, Tm, Pb, Tl,
At least one of Bi and Mn, and x is 0.5 ≦ x ≦
2.5. ) Alkaline earth metal silicate-based phosphors represented by Further, the general formula is (Ba _1- x _- yMgxCay) FX: eEu ²⁺ (where X is at least one of Br and Cl, and x, y
And e are 0 <x + y ≦ 0.6, xy ≠ 0 and 10 ⁻⁶ ≦, respectively.
It is a number that satisfies the condition of e ≦ 5 × 10 ^-2 . ) The fluorescent substance represented by this is mentioned. The general formula is LnOX: xA (where Ln is at least one of La, Y, Gd and Lu, and X is Cl.
And / or Br, A is Ce and / or Tb, and x is 0 <x ≦
Represents a number that satisfies 0.1. ), A phosphor represented by
The general formula described in No. 5-12145 is (Ba _1- xM ^II x) FX: yA (where M ^II is at least one of Mg, Ca, Sr, Zn and Cd, and X is Cl, At least one of Br and I is A
Is at least one of Eu, Tb, Ce, Tm, Dy, Pr, Ho, Nd, Yb and Er, and x and y are numbers satisfying conditions 0 ≦ x ≦ 0.6 and 0 ≦ y ≦ 0.2. . ), A phosphor represented by
The general formula described in -84389 is BaFX: xCe, yA (where X is at least one of Cl, Br and I, A is In,
It is at least one of Tl, Gd, Sm, and Zr, and x and y are 0 <x ≦ 2 × 10 ⁻¹ and 0 <y ≦ 5 × 10 ⁻² , respectively. ), A phosphor represented by the formula: M ^II FX, xA: yLn (where M ^II is at least Mg, Ca, Ba, Sr, Zn and Cd) Type 1, A is BeO, MgO, CaO, SrO, BaO, ZnO, Al ₂ O ₃ , Y ₂ O ₃ , La
₂ O ₃ , In ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , GeO ₂ , SnO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ and
At least one of ThO ₂ and Ln is Eu, Tb, Ce, Tm, Dy, Pr,
At least one of Ho, Nd, Yb, Er, Sm and Gd,
X is at least one of Cl, Br and I, and x and y are numbers satisfying the conditions of 5 × 10 ⁻⁵ ≦ x ≦ 0.5 and 0 <y ≦ 0.2, respectively. ) Rare earth element activation 2
Valuate metal fluorohalide phosphor, with general formula ZnS: A, (Zn,
Cd) S: A, CdS: A, ZnS: A, X and CdS: A, X (where A is Cu, Ag,
Au or Mn, and X is halogen. ), The general formula [I] or [II] described in JP-A-57-148285, and the general formula [I] xM ₃ (PO ₄ ) ₂ · NX ₂ : yA general formula [ II] M ₃ (PO ₄ ) ₂ · yA (wherein M and N are at least one of Mg, Ca, Sr, Ba, Zn and Cd, and X is at least one of F, Cl, Br, and I) One, A represents at least one of Eu, Tb, Ce, Tm, Dy, Pr, Ho, Nd, Er, Sb, Tl, Mn and Sn, and x and y are 0.
It is a number that satisfies the condition of <x ≦ 6, 0 ≦ y ≦ 1. ), A phosphor represented by the general formula [III] or [IV] general formula [III] nReX ₃ · mAX ′ ₂ : xEu general formula [IV] nReX ₃ · mAX ′ ₂ : xEu, ySm (where Re Represents at least one of La, Gd, Y and Lu, A represents an alkaline earth metal, at least one of Ba, Sr and Ca, and X and X ′ represent at least one of F, Cl and Br. Further, x and ^{y, 1 × 10 -4 <x <} 3 × 10 -1, 1 × 10 - 1 4
<Y <1 × 10 ^-1 is a number satisfying the condition, and n / m is 1 × 1
The condition of 0 ^-3 <n / m <7 × 10 ^{-1 is} satisfied. Phosphor represented by), and the general formula ^{M I X · aM II X '} · bM II X ": cA ( provided that at least one alkali metal M ^I Li, Na, K, selected from Rb, and Cs And M ^II is Be, Mg, Ca, Sr, B
It is at least one divalent metal selected from a, Zn, Cd, Cu and Ni. M ^II is Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, D
It is at least one trivalent metal selected from y, Ho, Er, Tm, Yb, Lu, Al, Ga, and In. X, X'and X "are at least one halogen selected from F, Cl, Br and I. A is Eu, Tb, Ce, Tm, Dy, Pr, Ho, Nd,
It is at least one metal selected from Yb, Er, Gd, Lu, Sm, Y, Tl, Na, Ag, Cu and Mg. Also, a is a numerical value in the range of 0 ≦ a <0.5, and b is 0 ≦ b <
It is a numerical value in the range of 0.5, and c is a numerical value in the range of 0 <c ≦ 0.2. ) Alkali halide phosphors represented by). In particular, the alkali halide phosphor is preferable because it facilitates the formation of a stimulable phosphor layer by a method such as vacuum deposition and sputtering. However, the stimulable phosphor used in the radiation image conversion panel of the present invention is not limited to the above-mentioned phosphor,
Any phosphor may be used as long as it exhibits stimulated emission when it is irradiated with radiation and then stimulated by excitation light. The radiation image conversion panel of the present invention may have a stimulable phosphor layer group composed of one or two or more stimulable phosphor layers containing at least one kind of the stimulable phosphor described above. The stimulable phosphor contained in each stimulable phosphor layer may be the same or different. In the radiation image conversion panel of the present invention, various polymeric materials, glass metals and the like are used as the support. In particular, a material that can be processed into a flexible sheet or web for handling as an information recording material is preferable,
From this point of view, for example, cellulose acetate film, polyester film, polyethylene terephthalate film, polyamide film, polyimide film, triacetate film, polycarbonate film and other plastic films, metal sheet of aluminum, iron, steel, chromium or the like, or coating of the metal oxide Metal sheets with layers are preferred. The layer thickness of these supports varies depending on the material of the support used, etc., but is generally 80 μm to 1000 μm, and more preferably 80 μm to 500 μm from the viewpoint of handling. In the radiation image conversion panel of the present invention, a protective layer for physically or chemically protecting the stimulable phosphor layer group is generally provided on the surface on which the stimulable phosphor layer is exposed. It is preferable. This protective layer may be formed by directly coating the protective layer coating solution on the stimulable phosphor layer, or by forming a protective layer separately formed in advance on the stimulable phosphor layer. Good. Materials for the protective layer include cellulose acetate, nitrocellulose, polymethylmethacrylate, polyvinyl butyral, polyvinyl formal, polycarbonate, polyester, polyethylene terephthalate, polyethylene, polypropylene, polyvinylidene chloride, nylon, polytetrafluoroethylene, polytrifluoride. Materials for the protective layer such as ethylene chloride monochloride, ethylene tetrafluoride-hexafluoropropylene copolymer, vinylidene chloride-vinyl chloride copolymer, vinylidene chloride-acrylonitrile copolymer and the like are used. In addition, this protective layer is formed by vacuum deposition, sputtering, etc.
It may be formed by stacking inorganic materials such as SiC, SiO ₂ , SiN, and Al ₂ O ₃ . Next, the vapor phase deposition method of the stimulable phosphor layer will be described. The first method is a vapor deposition method in an inert gas atmosphere. In this method, first, the support is placed in the vapor deposition apparatus, and then the apparatus is evacuated to a vacuum degree of about 10 ^-7 Torr. Then, after heating the support surface by a heater for heating the support to 300 to 500 ° C, the temperature of the support is set to 100 to 2
The temperature is set to 00 ° C., preferably about 150 ° C., and an inert gas is introduced to obtain a low vacuum degree of about 1 × 10 ⁻³ Torr. Examples of the inert gas include helium gas, nitrogen gas and argon gas, with argon gas being particularly preferred. Next, the port or crucible is energized, and the stimulable phosphor in the boat or crucible, for example, the rubidium bromide phosphor with thallium as the activator, is evaporated by the resistance heating method. Then, the stimulable phosphor is crystallized at the same time as being deposited on the support, and columnar crystals are formed in the vertical direction from the surface of the support. At this time, due to the adsorption of the atmospheric gas, a crystal plane that promotes crystal growth and a plane that suppresses crystal growth occur during the vapor deposition process. Therefore, this phenomenon becomes more remarkable as the gas pressure of the atmosphere gas increases. The surface on which crystal growth is promoted grows in the direction in which vaporized molecules or atoms attach. In this way, the stimulable phosphor layer is formed by vapor deposition on the support. At this time, a large number of fine voids extending in a direction substantially perpendicular to the support surface are formed in the stimulable phosphor layer. To be done. In the vapor deposition step, co-evaporation can be performed using a plurality of resistance heaters or electron beams. After completion of vapor deposition, a protective layer is preferably provided on the side of the stimulable phosphor layer opposite to the side of the support, if necessary, to produce the radiation image conversion panel of the present invention. Incidentally, after forming the stimulable phosphor layer on the protective layer, a procedure of providing a support may be adopted. Further, in the vapor deposition method in the inert gas atmosphere, co-evaporation of the stimulable phosphor raw material using a plurality of resistance heaters or electron beams, to synthesize the target stimulable phosphor on the support At the same time, it is possible to form a stimulable phosphor layer. Further, in the vacuum vapor deposition method, the stimulable phosphor layer may be heat-treated after the vapor deposition. The second method is a sputtering method. In this method, as in the vapor deposition method, after the support is placed in the sputtering apparatus, the inside of the apparatus is once evacuated to a vacuum degree of about 10 ^-6 Torr, and then an inert gas such as Ar or He is used as a gas for sputtering. The gas is introduced into the sputtering apparatus to a gas pressure of about 10 ^-3 Torr.
At this time, Ar gas is particularly preferable. Next, the support is heated to 100 to 200 ° C., preferably around 150 ° C., and a stimulable phosphor, for example, rubidium bromide with thallium as an inactivating agent is sputtered as a target, so that it is almost perpendicular to the support surface. It is possible to form a stimulable phosphor layer having a large number of fine voids extending to the inside. In the sputtering step, it is possible to form the stimulable phosphor layer in a plurality of times in the same manner as in the vapor deposition method in an inert gas atmosphere, and a plurality of targets made of different stimulable phosphors may be used. Using, simultaneously or sequentially,
It is also possible to form a stimulable phosphor layer by sputtering the target. After the sputtering is completed, the radiation image conversion panel of the present invention is manufactured by providing a protective layer preferably on the side opposite to the support side of the stimulable phosphor layer, if necessary, as in the vapor deposition method in an inert gas atmosphere. It Incidentally, after forming the stimulable phosphor layer on the protective layer, a procedure of providing a support may be adopted. In the sputtering method, a plurality of stimulable phosphor raw materials are used as targets and simultaneously or sequentially sputtered to synthesize a target stimulable phosphor on a support and simultaneously form a stimulable phosphor layer. It is also possible to form.
Further, in the sputtering method, if necessary, O ₂ , H ₂
Reactive sputtering may be performed by introducing a gas such as the above. Further, in the sputtering method, the stimulable phosphor layer may be heat-treated after the completion of sputtering, if necessary. Another method is the CVD method. In this method, a target stimulable phosphor or an organometallic compound containing a raw material for a stimulable phosphor is decomposed by energy such as heat or high-frequency power to give a binder containing no binder on the support. A fluorescent phosphor layer is obtained. Further, when the columnar block structure forming method described in Japanese Patent Application No. 59-266912 to 266916 is used together, as shown in FIG. 2, the photostimulability having both the fine columnar block parallel structure and the fine voids. A phosphor layer can be formed. FIG. 3 (a) shows an example of the relationship between the stimulable phosphor layer of the radiation image conversion panel of the present invention obtained by the vapor deposition method and the amount of the stimulable phosphor attached corresponding to the layer thickness and the radiation sensitivity. Is represented. Since the stimulable phosphor layer by the vapor deposition method according to the present invention does not contain a binder, the amount of the stimulable phosphor attached (filling rate) is the same as that obtained by coating a conventional stimulable phosphor. It is about twice as thick as the stimulable phosphor layer, and the radiation absorptivity per unit thickness of the stimulable phosphor layer is improved and the sensitivity to radiation is high, and the graininess of the image is improved. Furthermore, the stimulable phosphor layer by the vapor deposition method is excellent in transparency, has high transparency to stimulated excitation light and stimulated emission, and has a layer thickness larger than that of the stimulable phosphor layer by a conventional coating method. It is possible to make it thicker and to be more sensitive to radiation. An example of the sharpness of the panel of the present invention having the stimulable phosphor layer having fine voids obtained as described above is shown by 31 in FIG. 3 (b). The panel of the present invention has a finer structure than the fine columnar block structure described in Japanese Patent Application No. 59-266912 to 266916, and stimulated excitation light is internally reflected by the void surface due to the light induction effect. Since this is repeated, it becomes clear that the sharpness of the image is improved and the brilliance is improved as compared with 32 of FIG. It is possible to further improve the sharpness as the layer thickness of the exhaustive phosphor increases. The characteristics of a conventional panel obtained by dispersing and coating stimulable phosphor particles on a binder are shown in 33 of FIG. This clearly shows that the sharpness of the image is excellent. The radiation image conversion panel of the present invention provides excellent sharpness and graininess when used in the radiation image conversion method shown schematically in FIG. That is, in FIG. 4, 41 is a radiation generator, 42 is a subject, 43 is a radiation image conversion panel of the present invention, 44 is a stimulated excitation light source, and 45 is stimulated emission emitted from the radiation image conversion panel. Photoelectric conversion device, 46 is a device for reproducing the signal detected by 45 as an image, 47 is a device for displaying the reproduced image, 48 is a separation of stimulated excitation light and stimulated emission, only stimulated emission Is a filter that transmits the light. It should be noted that after 45, it is not limited to the above as long as the optical information from 43 can be reproduced as an image in some form. As shown in FIG. 4, the radiation from the radiation generator 41 enters the radiation image conversion panel 43 of the present invention through the subject 42. The incident radiation is absorbed by the photostimulable phosphor layer of the panel 43, the energy is accumulated, and an accumulated image of a radiation transmission image is formed. Next, this accumulated image is excited by stimulated excitation light from the stimulated excitation light source 44 and emitted as stimulated emission. In the radiation image conversion panel 43 of the present invention, since the stimulable phosphor layer has fine voids, during scanning with the stimulable excitation light, the stimulable excitation light is in the stimulable phosphor layer. It suppresses the diffusion. Since the intensity of the stimulated emission emitted is proportional to the amount of accumulated radiation energy, this optical signal is photoelectrically converted by the photoelectric conversion device 45 such as a photomultiplier tube, and reproduced as an image by the image reproduction device 46 to form an image. By displaying with the display device 47, a radiation transmission image of the subject can be observed.

【Example】

Next, the present invention will be described with reference to examples. Example 1. An aluminum plate having a thickness of 0.5 mm was used as a support, and the support was placed in an evaporator. Next, in the molybdenum crucible for resistance heating
RbBr: 0.004 Tl was added and set on the resistance heating electrode, and then the vaporizer was evacuated to a vacuum degree of 1 × 10 ⁻⁷ Torr. Then, the surface of the support was cleaned by heating it to 300 to 500 ° C. with a heater for heating the support, the support was placed at 150 ° C., and argon gas was introduced to make the degree of vacuum about 1 × 10 ⁻³ Torr. . Next, the stimulable phosphor RbBr: 0.004Tl was evaporated by a resistance heating method to form a stimulable phosphor layer having a layer thickness of about 250 μm and a porosity of about 20.
A radiation image conversion panel A of the present invention having% fine voids was obtained. A tube voltage of 80 KV was applied to the panel A of the present invention thus obtained.
After irradiating 10 mR of X-ray of p, it is stimulated by exciting with a semiconductor laser beam (780 nm), and the stimulated emission emitted from the stimulable phosphor layer is photoelectrically converted by a photodetector (photomultiplier tube). This signal was reproduced as an image by an image reproducing device and recorded on a silver salt film. From the magnitude of the signal, the sensitivity of the radiation image conversion panel A to X-rays was examined, and from the obtained image,
The modulation transfer function (MTF) and graininess of the image were investigated and are shown in Table 1. In Table 1, the sensitivity to X-rays is shown as a relative value with the radiation image conversion panel A of the present invention as 100. The modulation transfer function (MTF) has a spatial frequency of 2 cycles /
It is the value when mm. Example 2 An aluminum plate having a thickness of 0.5 mm was used as a support, and an electric current of 1 A / dm ² was applied in an 8% oxalic acid solution for about 2 hours to form an anodic oxide film layer on one surface of the aluminum plate, and then, in boiling water. A sealing treatment was performed for about 1 hour at 400 ° C., and a heat treatment at 400 ° C. was further performed to prepare a support having a surface structure such that the tile-shaped plates were separated by fine gaps and spread. Next, the support is placed during vapor deposition, and RbBr: 0.004Tl is vapor-deposited by the same vapor deposition method as in Example 1 to obtain a stimulable phosphor layer having a layer thickness of about 250 μm and a porosity of about 20%. A panel B of the present invention having a stimulable phosphor layer having a structure in which fine columnar blocks having fine voids are arranged side by side was obtained. This panel B of the present invention was evaluated in the same manner as in Example 1, and the results are also shown in Table 1. Comparative Example 1. 8 parts by weight of stimulable phosphor RbBr: 0.004Tl, 1 part by weight of polyvinyl butyral resin and 5 parts by weight of solvent (cyclohexanone) were mixed and dispersed to prepare a coating liquid for the stimulable phosphor layer. did. Next, this coating solution was uniformly applied on a black polyethylene terephthalate film as a support having a thickness of 300 μm placed horizontally, and naturally dried to form a stimulable phosphor layer having a thickness of 250 μm. The comparative panel P thus obtained was evaluated in the same manner as in Example 1, and the results are also shown in Table 1. As is clear from Table 1, the radiation image conversion panels A and B of the present invention have X compared to the comparative radiation image conversion panel P.
The linear sensitivity was about twice as high and the image graininess was excellent.
This is because the radiation image conversion panel of the present invention does not contain a binder in the stimulable phosphor layer and has a higher filling rate of the stimulable phosphor and a higher X-ray absorption rate than the comparative panel. Is. Further, the radiation image conversion panels A and B of the present invention were superior to the comparative radiation image conversion panel P in terms of sharpness in spite of higher X-ray sensitivity. This is because the stimulable phosphor layer of the radiation image conversion panel of the present invention has a large number of fine voids, and therefore the scattering in the stimulable phosphor layer of the semiconductor laser, which is the stimulated excitation light, is reduced. This is because

【The invention's effect】

As described above, according to the present invention, since the stimulable phosphor layer has a large number of fine voids, the scattering of the stimulable excitation light in the stimulable phosphor layer is significantly reduced, and as a result, It is possible to improve the sharpness of the image. Further, according to the present invention, since the deterioration of the sharpness of the image due to the increase of the stimulable phosphor layer thickness is small, by increasing the thickness of the stimulable phosphor layer, the image sharpness is not deteriorated without decreasing the image sharpness. It is possible to improve the graininess of the. Further, according to the present invention, the radiation image conversion panel of the present invention can be manufactured inexpensively and stably. The present invention is extremely effective and industrially useful.

[Brief description of drawings]

FIG. 1 is a sectional view showing a part of a radiation image conversion panel according to an example of the present invention. FIG. 2 is a sectional view showing a part of a radiation image conversion panel of another example of the present invention. FIG. 3 (a) is a diagram showing the photostimulable phosphor layer thickness and deposition amount and radiation sensitivity in the radiation image conversion panel of the present invention, and FIG. 3 (b) is a spatial frequency and a modulation transfer function (MTF). It is a figure which shows the relationship of. FIG. 4 is a schematic diagram of a radiation image conversion device in which the panel of the present invention is used. FIG. 5 (a) is a diagram showing the stimulable phosphor layer thickness and the amount of adhesion and the sensitivity to radiation in the conventional radiation image conversion panel, and FIG. 5 (b) is the stimulability in the conventional radiation image conversion panel. It is a figure which shows a phosphor layer thickness and a modulation transfer function (MTF) in case spatial frequency is 2 cycles / mm. 11 …… Support 12 …… Photostimulable phosphor layer 13 …… Voids 14 …… Protective layer 21 …… Support 22 …… Fine columnar blocks Photostimulable phosphor layer with a parallel structure 23 …… Voids 24 …… Protective layer 31 …… Characteristics of radiation image conversion panel of the present invention 32 …… Characteristics of radiation image conversion panel having fine columnar block structure 33 …… Characteristics of conventional radiation image conversion panel 41 …… Radiation generator 42 …… Subject 43 …… radiation image conversion panel 44 …… stimulated excitation light source 45 …… photoelectric conversion device 46 …… image reproduction device 47 …… image display device 48 …… filter

Continuation of front page (56) References JP-A-59-126299 (JP, A) JP-A-59-60300 (JP, A)

Claims (1)

[Claims] 1. A radiation image conversion panel having at least one binder-free photostimulable phosphor layer on a support, wherein the photostimulable phosphor layer extends inside the photostimulable phosphor layer in a substantially layer thickness direction. A radiation image conversion panel having a large number of fine voids and having a porosity of 3 to 30% in the stimulable phosphor layer.