JPH0784589B2 - Radiation image conversion method and radiation image conversion panel used in the method - Google Patents

Description

The present invention relates to a radiation image conversion method and a radiation image conversion panel used in the method, and more particularly to a radiation image conversion method using a stimulable phosphor and the method. The present invention relates to a radiation image conversion panel used in.

(Prior Art) Conventionally, a so-called radiographic method using a silver salt to obtain a radiographic image has been used, but a method of imaging a radiographic image without using a silver salt has been desired.

As an alternative to the radiographic method, the radiation that has passed through the subject is absorbed by the phosphor, and then this phosphor is excited with a certain energy to radiate the radiation energy accumulated by this phosphor as fluorescence. In fact, a method of detecting this fluorescence and imaging it has been considered. As a specific method, a method of converting a radiation image by using a thermoluminescent phosphor as a phosphor and heat energy as excitation energy has been proposed (UK Patent No. 1,462,769 and JP-A No. 51-29889). This conversion method uses a panel in which a thermoluminescent phosphor layer is formed on a support, and the thermoluminescent phosphor layer of this panel absorbs the radiation that has passed through the subject and accumulates radiation energy corresponding to the intensity of the radiation. Then, the radiation energy accumulated by heating the thermoluminescent phosphor layer is taken out as a light signal,
An image is obtained by the intensity of this light. However, since this method heats the accumulated radiation energy when converting it into a signal of light, it is absolutely necessary that the panel has heat resistance and is not deformed or deteriorated by heat. There are great restrictions on the materials for the fluorescent phosphor layer and the support. In this way, the radiation image conversion method using the thermoluminescent fluorescent substance as the fluorescent substance and the thermal energy as the excitation energy has a great difficulty in application. On the other hand, a radiation image conversion method using a panel having a stimulable phosphor layer formed on a support and using one or both of visible rays and infrared rays as excitation energy is also known (US Pat. No. 3,895,527). This method does not require heating when converting the stored radiation energy into a light signal as in the above method, and therefore, the panel does not need to have heat resistance. I can say.

Conventionally, LiF: Mg, BaSo ₄ : Mn, CaF ₂ : Dy, etc. are known as thermoluminescent phosphors among the phosphors used in the radiation image conversion method, and visible light or infrared light is used as excitation energy. As the stimulable phosphor used, Kcl: Tl,
BaFX: Eu system (X: Cl, Br, I) described in JP-A-59-75200
Phosphors and the like are known.

By the way, when the radiation image conversion method is used for X-ray image conversion for the purpose of medical diagnosis, it is desirable that the method be as sensitive as possible in order to reduce the exposure dose to the patient. It is desirable for the stimulable phosphor to have a luminescent brightness as high as possible.

Further, in the above method, in order to improve the operating efficiency of the system, it is necessary to increase the reading speed of the radiation image, and therefore the stimulable phosphor used in the method has a response speed of stimulated emission to excitation light. It is desirable to be fast.

Further, in the above method, the radiation image conversion panel is generally used repeatedly after erasing the afterimage caused by the previous use, but the remaining erasure time of the radiation image conversion panel may be short in order to improve the operation efficiency of the system. It is desirable that the stimulable phosphor used in the method has a high afterimage erasing speed.

However, the stimulable phosphor is not sufficiently satisfactory in all of the stimulated emission brightness, the response speed of stimulated emission and the afterimage erasing speed, and improvements thereof are desired.

Further, in the above method, it is desirable that the reader for reading the radiation image is small, low-priced, and simple.
For that reason, it is inevitable to use a semiconductor laser as an excitation light source rather than a gas laser such as Ar ⁺ laser or He-Ne laser.Therefore, the stimulable phosphor used in the method has an oscillation wavelength of the semiconductor laser. It is desirable to have a stimulated excitation spectrum adapted to (750 nm or more).

However, the stimulable phosphor hardly exhibits stimulated emission at the oscillation wavelength of the semiconductor laser, and there is a demand for a longer wavelength of the stimulated excitation spectrum.

(Object of the Invention) The present invention allows a stimulable phosphor to absorb radiation transmitted through an object, and then the stimulable phosphor is used to emit visible light and / or
Or, by exciting with an electromagnetic wave in the infrared range to release the radiation energy accumulated in this stimulable phosphor as fluorescence, and in the radiation image conversion method of detecting this fluorescence, it shows more stimulated luminescence. It is an object of the present invention to provide a highly sensitive radiation image conversion method using a stimulable phosphor.

Another object of the present invention is to provide a high-speed readable radiographic image conversion method using a stimulable phosphor that has a fast response speed of stimulated emission to excitation light.

It is another object of the present invention to provide a radiation image conversion method using a stimulable phosphor having a high afterimage erasing speed during repeated use and having a short afterimage erasing time.

A further object of the present invention is to provide a radiation image conversion method in which a semiconductor laser can be used as an excitation light source using a stimulable phosphor whose stimulable excitation spectrum is expanded to the near infrared region.

Furthermore, it aims at resisting the radiation image conversion panel which satisfies the said objective.

(Structure of the invention) The present inventors show various stimulated luminescence of high brightness in accordance with the object of the present invention, as a result of various studies on the stimulable phosphor having a stimulated excitation spectrum expanded to the near infrared region, A photostimulable phosphor containing an alkali halide phosphor represented by the following general formula (I) absorbs radiation transmitted through or emitted from a subject, and then the phosphor is used for visible light and / or infrared light. The radiation energy accumulated in the phosphor is excited by an electromagnetic wave selected from the above to release it as fluorescence, and the radiation image conversion method is characterized by detecting this fluorescence. The object of the invention is achieved.

General formula ^{(I) M I X · aM} II X 2 '· bM III X 3 ": cA However, M ^I is at least one alkali metal selected Li, Na, K, from Rb and Cs.

M ^II is at least one divalent metal selected from Be, Mg, Ca, Sr, Ba, Zn, Cd and Ni. When A is Tl,
Zn, Cd and Ni are not included. M ^III is Sc, Y, La, Pm, L
It is at least one trivalent metal selected from u, 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, T
It is at least one metal selected from m, Dy, Pr, Ho, Nd, Yb, Er, Gd, Sm, Tl, Na, Ag and Cu. However, when M ^I includes Rb and Cs and A is Na, Ag, and Cu, two or more kinds are included, and M ^I and A are always different metals. Also, a is a numerical value in the range of 0 <a <0.5, but is 0 when A is Eu.
<A <0.25, a value of 0 ≦ b <0.5, and a value of 0 <c ≦ 0.2.

That is, the stimulable phosphor of the composition according to the present invention exhibits stimulated emission of higher brightness than conventionally known stimulable phosphors when excited by electromagnetic waves in the visible to infrared region, and particularly in the near infrared region. It is possible to obtain a radiation image conversion method having a high sensitivity for practical use.

The radiation image conversion method of the present invention is carried out in a form using a radiation image conversion panel containing the stimulable phosphor of the general formula (I).

The radiation image conversion panel basically comprises a support and at least one stimulable phosphor layer provided on one side or both sides of the support. In general, a protective layer for chemically or physically protecting the stimulable phosphor layer is provided on the surface of the stimulable phosphor layer opposite to the support. That is, the radiographic image conversion method of the present invention is a radiographic image conversion panel consisting essentially of a support and at least one stimulable phosphor layer containing a stimulable phosphor provided on the support. In, the radiation image conversion panel is characterized in that at least one of the stimulable phosphor layers contains the stimulable phosphor represented by the general formula (I).

The photostimulable phosphor of the general formula (I) absorbs radiation such as X-rays and then emits light in the visible or infrared region, preferably 50
When it is irradiated with light (excitation light) in the wavelength range of 0 to 900 nm, it exhibits stimulated emission. Therefore, the radiation transmitted through the subject or emitted from the subject is absorbed by the stimulable phosphor contained in the stimulable phosphor layer of the radiation image conversion panel in proportion to the radiation dose, and the radiation image conversion is performed. A subject or a radiation image of the subject is formed on the panel as a latent image in which radiation energy is accumulated. This latent image is 500nm
Excitation with excitation light in the above wavelength region causes stimulated emission proportional to the accumulated radiation energy, and by photoelectrically reading this stimulated emission, a latent image with accumulated radiation energy is visualized. It becomes possible.

The present invention will be described in detail below.

FIG. 1 shows the response characteristics of the stimulable phosphor represented by the general formula (I) used in the radiation image conversion method of the present invention to excitation light in comparison with the stimulable phosphor used in the conventional method. Show.

In FIG. 1, (a) shows the response characteristics of the stimulable phosphor used in the radiation image conversion method of the present invention to excitation light, and (b) and (c) show the stimulable fluorescence used in the conventional method. It is the response characteristics of the bodies BaFBr: Eu and BaFCl: Eu. The broken line shows the state of the excitation light whose intensity changes in a rectangular shape.

As is clear from FIG. 1, the stimulable phosphor used in the radiation image conversion method of the present invention has remarkably excellent response characteristics to excitation light, and the reading speed of the radiation image is higher than that of the conventional method. It is possible to speed up.

FIG. 2 shows the afterimage erasing characteristics of the stimulable phosphor represented by the general formula (I) used in the radiation image conversion method of the present invention in comparison with the stimulable phosphor used in the conventional method.

In FIG. 2, (d) is a decay characteristic of accumulated energy when the stimulable phosphor used in the radiation image conversion method of the present invention is irradiated with a certain amount of radiation and then the accumulated energy is erased by tungsten lamp light, (E) and (f) are stimulable phosphors BaFBr: Eu and Ba used in the conventional method.
It is the decay characteristic of the stored energy when FCl: Eu is measured in the same manner as above.

As is clear from FIG. 2, the stimulable phosphor used in the radiation image conversion method of the present invention has accumulated energy (afterimage).
Since the decay speed is high, it is possible to shorten the afterimage erasing time as compared with the conventional method.

FIG. 3 schematically shows an embodiment example in which the stimulable phosphor represented by the general formula (I) is used in the form of a radiation image conversion panel in the radiation image conversion method of the present invention.

In FIG. 3, 11 is a radiation generator, 12 is a subject, and 13 is a radiation image conversion panel having a visible or infrared stimulable phosphor layer containing the stimulable phosphor represented by the general formula (I). , 14 is an excitation light source for emitting the radiation latent image of the radiation image conversion panel 13 as fluorescence, 15 is a photoelectric conversion device for detecting the fluorescence emitted from the radiation image conversion panel 13, 16 is detected by the photoelectric conversion device 15. A device for reproducing the photoelectrically converted signal as an image, a device 17 for displaying the reproduced image, and a device 18 for cutting the reflected light from the light source 14 and transmitting only the light emitted from the radiation image conversion panel 13. It is a filter. Although FIG. 3 shows an example of obtaining a radiation transmission image of a subject, the radiation generator 11 is not particularly necessary when the subject 12 itself emits radiation (subject). Further, the photoelectric conversion device 15 and thereafter may be any device capable of reproducing the optical information from the panel 13 as an image in some form, and is not limited to the above. As shown in FIG. 3, when the subject 12 is arranged between the radiation generator 11 and the radiation image conversion panel 13 and is irradiated with the radiation, the radiation is transmitted according to the change in the radiation transmittance of each part of the subject 12, and the transmission thereof is performed. An image (that is, an image of the intensity of radiation) is incident on the radiation image conversion panel 13. The incident transmission image is absorbed by the stimulable phosphor layer of the radiation image conversion panel 13, whereby a number of electrons and / or holes proportional to the amount of radiation absorbed in the stimulable phosphor layer is generated. However, this is accumulated in the trap level of the photostimulable phosphor. That is, a latent image is formed by accumulating the energy of the radiation transmission image.
Next, this latent image is excited by light energy to become visible. That is, the photostimulable phosphor layer is irradiated with a light source 14 that emits light in the visible or infrared region to drive out the electrons and / or holes accumulated at the trap level and release the accumulated energy as fluorescence. . The intensity of the emitted fluorescence is proportional to the number of accumulated electrons and / or holes, that is, the intensity of the radiation energy absorbed in the stimulable phosphor layer of the radiation image conversion panel 13, and this optical signal Is converted into an electric signal by a photoelectric conversion device 15 such as a photomultiplier tube, reproduced as an image by the image processing device 16, and this image is displayed by the image display device 17. It is more effective if the image processing device 16 uses not only an electric signal to be reproduced as an image signal but also a so-called image processing, image calculation, image storage and storage.

When excited by light energy in the method of the present invention,
It is necessary to separate the reflected light of the excitation light and the fluorescence emitted from the stimulable phosphor layer, and the photoelectric converter that receives the fluorescence emitted from the stimulable phosphor layer generally has a short wavelength of 600 nm or less. The fluorescence emitted from the stimulable phosphor layer preferably has a spectral distribution in the shortest wavelength region because it has high sensitivity to the light energy.
The emission wavelength range of the stimulable phosphor used in the method according to the present invention is 300 to 500 nm, while the excitation wavelength range is 500 to 900 nm, so that the above conditions are satisfied at the same time.

That is, all of the stimulable phosphors used in the present invention show light emission having a main peak at 500 nm or less, which is easy to separate from the excitation light and matches well with the spectral sensitivity of the light receiver, so that light can be efficiently received. As a result, the sensitivity of the image receiving system can be increased.

As the excitation light source 14 used in the method of the present invention, a light source containing the stimulable excitation wavelength of the stimulable phosphor used in the radiation image conversion panel 13 is used. In particular, the use of laser light simplifies the optical system, and since the intensity of the excitation light can be increased, the stimulated emission efficiency can be increased, and more preferable results can be obtained. As the laser, He-Ne laser, He-Cd laser, Ar ion laser, Kr ion laser,
There are N ₂ laser, YAG laser and its second harmonic, ruby laser, semiconductor laser, various dye lasers, metal vapor lasers such as copper vapor laser, and the like. Usually, a continuous wave laser such as a He-Ne laser or an Ar ion laser is desirable, but a pulsed laser can also be used if the scanning time of one pixel on the panel is synchronized with the pulse. Further, in the case of the method of separating by utilizing the delay of light emission shown in JP-A-59-22046 without using the filter 18, it is preferable to use a pulse oscillation laser rather than modulation using a continuous oscillation laser. preferable.

Among the various laser light sources described above, the semiconductor laser is particularly preferable because it is small and inexpensive, and a modulator is unnecessary.

Since the filter 18 transmits the stimulated emission emitted from the radiation image conversion panel 13 and cuts the excitation light, this is the stimulated emission wavelength of the stimulable phosphor contained in the radiation image conversion panel 13. And the wavelength of the excitation light source 14 in combination. For example, the stimulated excitation wavelength is 500-900 nm
In the case of a practically preferable combination in which the stimulated emission wavelength is 300 to 500 nm, the filter is, for example, C manufactured by Toshiba Corporation.
-39, C-40, V-40, V-42, V-44, Corning 7-5
4,7-59, Spectrofilm BG-1, BG-3, BG-25, B
A purple to blue colored glass filter such as G-37 or BG-38 can be used. Further, if an interference filter is used, a filter having arbitrary characteristics can be selected and used to some extent.

The photoelectric conversion device 15 may be a photoelectric tube, a photomultiplier tube, a photodiode, a phototransistor, a solar cell, a photoconductive element, or any other device that can convert a change in the amount of light into a change in an electronic signal.

Next, the radiation image conversion panel used in the radiation image conversion method of the present invention will be described.

As described above, the radiation image conversion panel comprises a support and at least one stimulable phosphor layer containing the stimulable phosphor represented by the general formula (I) provided on the support. Composed.

The stimulable phosphor represented by the general formula (I) has Na, K, R as M ^I in the general formula (I) in terms of stimulated emission luminance.
At least one alkali metal selected from b and Cs is preferable, and at least one alkali metal selected from Rb and Cs is particularly preferable. For M ^II , Be, Wg, C
At least one alkaline earth metal selected from a, Sr and Ba is preferable, and as M ^III , at least one trivalent metal selected from Y, La, Lu, Al, Ga and In is preferable. X ″ is preferably at least one halogen selected from F, Cl and Br. The value a representing the content of M ^II X ₂ ′ and the value b representing the content of M ^III X ₃ ″ are 0 ≦ a <0.4 (However, 0 <a <0.2 when A is Eu)
5) and 0 ≦ b ≦ 10 ⁻² are preferred. When the value of a is a> 0.5, the stimulated emission luminance drops sharply, which is not particularly preferable.

In the general formula (I), the activator A is Eu, Tb, C.
At least one metal selected from e, Tm, Dy, Ho, Gd, Sm, Tl and Na is preferable, and at least one metal selected from Eu, Ce, Sm, Tl and Na is particularly preferable. However, M ¹
Include Rb and Cs, and when A is Na, Ag, and Cu, two or more kinds are included, and M ^I and A are always different. Further, the C value representing the amount of the activator is preferably selected from the range of 10 ⁻⁶ <C <0.1 from the viewpoint of stimulated emission luminance.

Stimulable phosphor M ^I X · aM ^II X ₂ according to the present invention 'bM ^III X ₃ ": cA
Is manufactured, for example, by the manufacturing method described below.

First, as stimulable phosphor materials, I) LiF, LiCl, LiBr, LiI, NaF, NaCl, NaBr, NaI, KF, KCl, KB
1 of r, KI, RbF, RbCl, RbBr, RbI, CsF, CsCl, CsBr, CsI
II) BeF ₂ , BeCl, BeBr ₂ , BeI ₂ , MgF ₂ , MgCl ₂ , MgBr ₂ , MgI ₂ , CaF
_{2, CaCl 2, CaBr 2,} CaI 2, SrF 2, SrCl 2, SrBr 2, SrI 2, BaF 2, BaCl
₂ , BaBr ₂ , BaBr ₂・ 2H ₂ O, BaI ₂ , ZnF ₂ , ZnCl ₂ , ZnBr ₂ , ZnI ₂ , CdF
_{1 of 2} , CdCl ₂ , CdBr ₂ , CdI ₂ , NiF ₂ , NiCl ₂ , NiBr ₂ , NiI ₂
Species or two or more _{III) ScF 3, ScCl 3,} SeBr 3, ScI 3, YF 3, YCl 3, YBr 3, YI 3, LaF 3,
LaCl ₃ , LaBr ₃ , LaI ₃ , PmF ₃ , PmCl ₃ , PmBr ₃ , PmI ₃ , LuF ₃ , LuCl ₃ ,
LuBr ₃ , LuI ₃ , AlF ₃ , AlCl ₃ , AlBr ₃ , AlI ₃ , GaF ₃ , GaCl ₃ , GaBr ₃ ,
One or more of GaI ₃ , InF ₃ , InCl ₃ , InBr ₃ , InI ₃ , and IV) Eu compound group, Tb compound group, Ce compound group, Tm compound group, Dy compound group, Pr compound group , Ho compound group, Nd compound group, Yb compound group, Er compound group, Gd compound group, Sm compound group, Tl compound group, Na compound group, Ag compound group, Cu compound group Activator raw material is used.

Stoichiometric formula _{^{M I X · aM II X 2}} '· bM III X 3 represented by (I) ": In cA, 0 <a <0.5, preferably 0 <a <0.4 (where, When A is Eu, 0 <a <0.25), 0 ≦ b <0.5, preferably 0 ≦
The stimulable phosphor raw materials of I) to IV) above are weighed so that a mixed composition of b ≦ 10 ⁻² , 0 <c ≦ 0.2, preferably 10 ⁻⁶ <c <0.1, and a milk needle or a ball mill. Mix well using a mixer mill.

Next, the obtained stimulable phosphor raw material mixture is filled in a heat-resistant container such as a quartz crucible or an alumina crucible and fired in an electric furnace. A firing temperature of 500 to 1000 ° C is suitable. The firing time varies depending on the filling amount of the raw material mixture, the firing temperature, etc., but is generally 0.5 to 6 hours. The firing atmosphere is preferably a nitrogen gas atmosphere containing a small amount of hydrogen gas, a weak reducing atmosphere such as a carbon gas atmosphere containing a small amount of carbon monoxide, or a neutral atmosphere such as a nitrogen gas atmosphere or an argon gas atmosphere. After firing once under the above firing conditions, the fired product is taken out of the electric furnace and crushed,
After that, the fired product powder is filled again in a heat-resistant container, placed in an electric furnace, and re-fired under the same firing conditions as described above, whereby the emission brightness of the phosphor can be further increased. Further, when cooling the calcined product to room temperature from the calcining temperature, the desired stimulable phosphor can be obtained by taking the calcined product out of the electric furnace and allowing it to cool in the air. By cooling in a weak reducing atmosphere or a neutral atmosphere, the emission luminance of the obtained stimulable phosphor can be further enhanced. Further, by moving the fired product from the heating unit to the cooling unit in the electric furnace and quenching it in a weak reducing atmosphere or a neutral atmosphere, the luminescent brightness due to the stimulation of the obtained stimulable phosphor is further enhanced. Can be increased.

The stimulable phosphor according to the present invention is obtained by pulverizing the stimulable phosphor obtained after firing and then treating it by various operations that are generally adopted in phosphor production such as washing, drying and sieving. obtain.

The average particle size of the stimulable phosphor used in the radiation image conversion panel 13 of the present invention is usually in the range of 0.1 to 100 μm in consideration of the sensitivity and granularity of the radiation image conversion panel 13. To be selected. More preferably, those having an average particle size of 1 to 30 μm are used.

In the radiation image exchange panel 13 of the present invention, generally, the stimulable phosphor of the present invention is dispersed in a suitable binder and applied to a support. Examples of the binder include proteins such as gelatin, polysaccharides such as dextran or gum arabic, polyvinyl butyral, polyvinyl acetate, nitrocellulose, ethyl cellulose,
Binders usually used for layer formation such as vinylidene chloride-vinyl chloride copolymer, polymethylmethacrylate, vinyl chloride-vinyl acetate polymer, polyurethane, cellulose acetate butyrate, polyvinyl alcohol and the like are used.

Generally, the binder is 0.01 per part by weight of the stimulable phosphor.
Used in the range of up to 1 part by weight. However, in terms of the sensitivity and sharpness of the obtained radiation image conversion panel 13, it is preferable that the amount of the binder is small, and the range of 0.03 to 0.2 parts by weight is more preferable in consideration of the ease of application.

Furthermore, in the radiation image conversion panel 13 of the present invention, generally, a surface that is exposed to the outside of the stimulable phosphor layer (a surface that is not hidden by the bottom of the phosphor layer substrate) has a stimulable phosphor layer physically or A protective layer is provided for chemical protection. This protective layer may be formed by directly applying a protective coating solution onto the stimulable phosphor layer, or a separately formed protective layer may be adhered onto the stimulable phosphor layer. Good.

As a material for the protective layer, a usual protective layer material such as nitrocellulose, ethyl cellulose, cellulose acetate, polyester, polyethylene terephthalate, etc. is used.

It should be noted that this protective layer is selected so as to transmit the stimulated emission light and also transmit the excitation light when the excitation light is irradiated from the protective layer side. Also, the preferable film thickness is about 2 to 40
μm.

Next, an example of a method of manufacturing the radiation image conversion panel 13 will be described below.

First, the pulverized photostimulable phosphor powder, the binder and the solvent are mixed and sufficiently kneaded to prepare a coating solution in which the photostimulable phosphor is uniformly dispersed.

Examples of the solvent include lower alcohols such as methanol, ethanol, n-propanol and n-butanol, chlorine-containing hydrocarbons such as methylene chloride and ethylene chloride, ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, methyl acetate, Examples thereof include lower esters such as ethyl acetate and butyl acetate, and ethers such as dioxane, ethylene glycol monomethyl ether and ethylene glycol monoethyl ether. These solvents may be mixed and used.

Further, various useful agents such as a dispersant for complementing the dispersibility of the stimulable phosphor in the coating liquid or a plasticizer for ensuring the bondability between the binder particles after coating and drying and the phosphor particles are used. Additives may be added.

Examples of the dispersant include phthalic acid, stearic acid, caproic acid, and lipophilic surfactants.

Examples of the plasticizer include phosphoric acid esters such as triphenyl phosphate, tricresyl phosphate, diphenyl phosphate, diethyl phthalate, phthalic acid esters such as dimethoxyethyl phthalate, glycols ethylphthalylethyl glycol, butylphthalacrylbutyl glycolate and the like. Examples thereof include polyethylene glycol-aliphatic dibasic acid polyesters such as triethylene glycol-adipic acid polyester and diethylene glycol-succinic acid polyester.

The coating liquid prepared as described above is uniformly applied to the support by a commonly used coating method such as a roll coater method or a blade doctor method to form a stimulable phosphor layer.

As the support used in the present invention, various synthetic resin sheets (for example, sheets of cellulose acetate, polyester, polyethylene terephthalate, polyamide, polyimide, triacetate, polycarbonate, etc.), various metal sheets (for example, sheets of aluminum, aluminum alloys, etc.), various Examples thereof include paper sheets (for example, sheets such as baryta paper, resin-coated paper and pigment paper).

The dry thickness of the stimulable phosphor layer varies depending on the purpose of use of the radiation image conversion panel, the kind of the stimulable phosphor, the mixing ratio of the binder and the stimulable phosphor, etc. 10 μm to 1000 μm is suitable, preferably 80 μm
m to 600 μm.

Furthermore, in order to increase the sharpness of the image formed on the radiation image conversion panel 13, white powder is dispersed in the stimulable phosphor layer as described in JP-A-55-146447, for example. May be. Further, as described in JP-A-55-163500, the sharpness of the image of the stimulable phosphor layer is improved by dispersing a coloring agent that absorbs excitation light in the stimulable phosphor layer. It may be colored appropriately to increase or absorb the excitation light. Further, for the purpose of improving the sharpness and sensitivity of the radiation image conversion panel 13, a light reflecting layer is provided between the support and the stimulable phosphor layer as disclosed in JP-A-56-11393. You may

Further, in the radiation image conversion panel of the present invention, in addition to the coating method described above, a phosphor layer can be formed on the support by a vacuum deposition method, a sputtering method, or the like. In this case, no binder is required, the packing density of the stimulable phosphor can be increased, and a radiation image conversion panel that is preferable in terms of sensitivity and resolution can be obtained.

Phosphor M ^I X · aM according to the present invention obtained as described above
^An emission spectrum of ^II X ₂ ′ · bM ^III X ₃ ″: cA by photostimulation is shown in FIG. 4. The specific composition is as follows.

(A) RbBr / 0.05BaFBr / 0.01AlF ₃ : 0.001Eu (b) 0.99RbBr / 0.01CsF / 0.05BaFCl / 0.01LaF ₃ : 0.001
Tl (c) CsBr · 0.05BaFCl · 0.01YF ₃ : 0.002Tl These photostimulable phosphors were irradiated with X-rays of 80 kVp and then measured by exciting the phosphors with a semiconductor laser having an oscillation wavelength of 780 nm. It is an emission spectrum.

The phosphor according to the present invention in FIG. 5 _{^{M I X · aM II X 2}} '· bM III
The excitation spectrum of X ₃ ″: cA is illustrated. X at 80 kVp
It is an excitation spectrum of the photostimulable phosphors (a), (b) and (c) irradiated with rays.

(Example) Next, the present invention will be described with reference to an example.

Example 1 Each stimulable phosphor raw material was weighed as shown in (1) to (21) below, and then thoroughly mixed using a ball mill.
Various types of phosphor raw material mixtures were prepared.

Next, each of the 21 kinds of stimulable phosphor raw material mixture was packed in a quartz board, placed in an electric furnace and fired. Firing is 2
Nitrogen gas containing hydrogen gas of volume% was flown at a flow rate of 2500 cc / min for 2 hours at 650 ° C., and then cooled to room temperature.

After crushing the obtained fired product using a ball mill, 150
After sieving through a mesh to make the particle diameter uniform, each stimulable phosphor was obtained.

Next, a radiation image conversion panel of the present invention was manufactured using the 21 types of stimulable phosphors. Each radiation image conversion panel was manufactured as follows.

First, 8 parts by weight of the stimulable phosphor was dispersed in a solvent prepared by mixing 1 part by weight of polyvinyl butyral (binder) with an equal amount of acetone and ethyl acetate, and this was placed horizontally on a polyethylene terephthalate film (support). A radiation image conversion panel of the present invention having a film thickness of about 300 μm was prepared by uniformly applying the composition on the above using a wire bar and naturally drying.

These 21 kinds of radiation image conversion panels of the present invention X-ray tube tube voltage 80 kVp, tube current 100 mA at a distance of 100 cm from the focal point
After irradiating X-rays for 0.1 seconds, it is irradiated with semiconductor laser light (7
The fluorescence due to photostimulation emitted from the photostimulable phosphor layer was measured with a photodetector. First result
Shown in the table.

Comparative BaF ₂ 175.4g (1 mole) of stimulable phosphor material in Example 1 Example _{1, BaBr 2 · 2H 2 O333.3g} (1 mol) and Eu ₂ O ₃ 0.352 g
A stimulable phosphor BaFBr: 0.001Eu was obtained in the same manner as in Example 1 except that the amount was (0.001 mol). Using this stimulable phosphor, a comparative radiation image conversion panel was prepared in the same manner as in Example 1, and the stimulated emission luminance was measured using a semiconductor laser (780 nm, 10 mW). The results are also shown in Table 1.

Comparative Example 2 Instead of using the semiconductor laser in Comparative Example 1, He-Ne
The stimulated emission luminance was measured in the same manner as in Comparative Example 1 except that a laser (633 nm, 10 mW) was used. The results are also shown in Table 1.

From Table 1, the emission luminance due to stimulus of the radiation image conversion panel of the present invention produced by using the stimulable phosphors of the samples (1) to (21) according to the present invention is shown in Comparative Example 1. Higher than the emission brightness due to the stimulus measured under the same conditions of the comparative radiation image conversion panel manufactured using the conventional stimulable phosphor BaFBr: Eu, and therefore the radiation image conversion panel of the invention using the radiation image conversion panel of the invention. The radiation image conversion method was more sensitive than the conventional radiation image conversion method using a comparative radiation image conversion panel.

By the way, the conventional stimulable phosphor Ba taken up in Comparative Example 1 was used.
FBr: Eu has a peak wavelength of stimulated excitation spectrum near 600 nm, and the excitation light source is He-Ne laser light (633 nm).
Are said to be particularly preferable (JP-A-55-15025, etc.).
Therefore, for the comparative radiation image conversion panel manufactured using BaFBr: Eu, in the method for measuring the stimulated emission luminance, the semiconductor laser (780 nm) was changed to He-Ne laser (633 nm)
The results are shown in Table 1 above as Comparative Example 2 measured under the same conditions, except that the comparative radiation image conversion panel had lower stimulated emission luminance than any of the radiation image conversion panels of the present invention. . Therefore, the radiation image conversion method of the present invention using the radiation image conversion panel of the present invention, since the semiconductor laser can be used as an excitation light source, it can be miniaturized than the conventional radiation image conversion method using the He-Ne laser. At the same time, it was highly sensitive.

Example 2 Excitation light whose intensity changes into a rectangular shape after the radiation image conversion panel of the present invention using the stimulable phosphor (9) prepared in Example 1 was irradiated with X-rays in the same manner as in Example 1. He-Ne as
The laser was irradiated for 10 μsec, and the change in brightness of the stimulated emission emitted from the stimulable phosphor layer was measured with a photodetector. The time required for the luminance change of stimulated emission to change from 10% to 90% was determined as the response speed of the stimulable phosphor to the excitation light, and is shown in Table 2.

Comparative Example 3 The radiation image conversion panel (9) of the present invention in Example 2
The response speed was determined in the same manner as in Example 2 except that the comparative radiation image conversion panel prepared in Comparative Example 1 was used instead of.

The results are shown in Table 2.

From Table 2, the photostimulable phosphor according to the present invention has a response speed about 3 times slower than that of the comparative photostimulable phosphor, and the radiation image in the radiation image conversion method using the photostimulable phosphor according to the present invention. It is possible to make the reading speed of 3 times faster than when using the comparative stimulable phosphor.

Example 3 The radiation image conversion panel of the present invention used in Example 2 was irradiated with X-rays in the same manner as in Example 1, and then the stored energy was erased with a halogen lamp of 10,000 lux for 10 seconds. Next, this was excited by a He-Ne laser (10 mW) and the stimulated emission luminance emitted from the stimulable phosphor layer was measured by a photodetector. The measurement results are shown in Table 3 with the stimulated emission luminance before erasing by the halogen lamp as 1.

Comparative Example 4 The stimulated emission luminance was measured in the same manner as in Example 3 except that the comparative radiation image conversion panel prepared in Comparative Example 1 was used instead of the radiation image conversion panel of the present invention. . As in Example 3, the measurement results are shown in Table 3 with the stimulated emission luminance before erasing by the halogen lamp being 1.

From Table 3, the stimulable phosphor according to the present invention has an erase speed of accumulated energy (afterimage) of about 4 as compared with the comparative stimulable phosphor.
The afterimage erasing time in the radiation image conversion method using the stimulable phosphor according to the present invention can be shortened to 1/4 of that of the comparative stimulable phosphor.

(Effects of the Invention) As described above, since the stimulable phosphor according to the present invention has high sensitivity to radiation, when the radiation image conversion method of the present invention is used for X-ray diagnosis or the like, X-ray exposure of a subject is performed. It is possible to reduce the amount.

Further, the stimulable phosphor according to the present invention has a high response speed to excitation light and a high erase speed of stored energy (afterglow),
It is possible to increase the radiation image reading speed in the radiation image conversion method of the present invention, shorten the afterimage erasing time, and improve the operating efficiency of the system.

Furthermore, since the stimulable excitation spectrum of the stimulable phosphor according to the present invention is extended to the oscillation wavelength region of the semiconductor laser, it can be excited by the semiconductor laser, and the radiation image reading apparatus can be downsized and low. It can be priced and simplified.

[Brief description of drawings]

FIG. 1 is a diagram showing the response characteristics of the stimulable phosphor. FIG. 2 is a diagram showing the afterimage erasing characteristics of the stimulable phosphor. FIG. 3 is an explanatory diagram showing an outline of an example of an embodiment of the method of the present invention. FIG. 4 is a stimulated emission spectrum of an example of the stimulable phosphor according to the present invention, and FIG. 5 is a stimulated excitation spectrum of the example of the phosphor. 11 …… Radiation generator 12 …… Subject 13 …… Radiation image conversion panel 14 …… Excitation light source 15 …… Photoelectric converter 18 …… Filter

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication G21K 4/00 N

Claims (8)

[Claims] 1. Radiation transmitted through or emitted from a subject is absorbed by at least one of the alkali halide stimulable phosphors represented by the following general formula (I):
Thereafter, the photostimulable phosphor is excited by an electromagnetic wave selected from visible light and / or infrared to release the radiation energy accumulated in the photostimulable phosphor as fluorescence, and the fluorescence is detected. Radiation image conversion method. General formula ^{(I) M I X · aM} II X 2 '· bM III X 3 ": cA ( However, M ^I is at least one alkali metal selected Li, Na, K, from Rb and Cs, M ^II Is Be, Mg, C
It is at least one divalent metal selected from a, Sr, Ba, Zn, Cd and Ni. When A is Tl, Zn, Cd and
Ni is not included. M ^III is at least one trivalent metal selected from Sc, Y, La, Pm, 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, T
m, Dy, Pr, Ho, Nd, Yb, Er, Gd, Sm, Tl, Na, at least one metal selected from Cu and Cu, M ^I
Rb and Cs are included, and when A is Na, Ag, and Cu, two or more kinds are included, and M ^I and A are always different metals. Also, a is 0 <a
It is a numerical value in the range of <0.5, but 0 <a <when A is Eu
It is a numerical value in the range of 0.25, b is a numerical value in the range of 0 ≦ b <0.5, and c is a numerical value in the range of 0 <c ≦ 0.2. ) 2. In the general formula (I), b is 0 ≦ b ≦ 10.
The radiation image conversion panel according to claim 1, wherein the radiation image conversion panel is ^-2 . 3. The radiation image conversion according to claim 1 or 2, wherein X ″ in the general formula (I) is at least one halogen selected from F, Cl and Br. Method. 4. The radiation image conversion method according to claim 1, wherein the electromagnetic wave is a laser beam. 5. The radiation image converting method according to claim 1, wherein the laser light is a semiconductor laser. 6. A radiation image conversion panel comprising a support and at least one photostimulable phosphor layer provided on the support, wherein at least one of the phosphor layers has the following general formula (I): A radiation image conversion panel comprising an alkali halide stimulable phosphor represented by: General formula ^{(I) M I X · aM} II X 2 '· bM III X 3 ": cA ( However, M ^I is at least one alkali metal selected Li, Na, K, from Rb and Cs, M ^II Is Be, Mg, C
It is at least one divalent metal selected from a, Sr, Ba, Zn, Cd and Ni. When A is Tl, Zn, Cd and
Cu is not included. M ^III is at least one trivalent metal selected from Sc, Y, La, Pm, 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, T
m, Dy, Pr, Ho, Nd, Yb, Er, Gd, Sm, Tl, Na, at least one metal selected from Ag and Cu, M ^I is
Rb and Cs are included, and when A is Na, Ag, and Cu, two or more kinds are included, and M ^I and A are always different metals. Also, a is 0 <a
It is a numerical value in the range of <0.5, but 0 <a <when A is Eu
It is a numerical value in the range of 0.25, b is a numerical value in the range of 0 ≦ b <0.5, and c is a numerical value in the range of 0 <c ≦ 0.2. ) 7. b in the general formula (I) is 0 ≦ b ≦ 10.
The radiation image conversion panel according to claim 6, wherein the radiation image conversion panel is ^-2 . 8. The radiation image conversion according to claim 6 or 7, wherein X ″ in the general formula (I) is at least one halogen selected from F, Cl and Br. panel.