JPH0644080B2 - Radiation image conversion method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a radiation image conversion method, and more particularly to a radiation image conversion method using a stimulable phosphor.

(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 above radiographic method, the phosphor that absorbs the radiation that has passed through the subject is absorbed, and then this phosphor is excited with a certain amount of energy to fluoresce the radiation energy accumulated in the phosphor. A method of detecting the fluorescence and forming an image is considered. As a specific method, a method of converting a radiation image by using a thermofluorescent fluorescent substance as a fluorescent substance and heat energy as excitation energy has been proposed (British Patent No. 1,462,769 and Japanese Patent Laid-Open Publication No. Sho. 51-29889). This conversion method uses a panel in which a thermoluminescent fluorescent layer is formed on a support, and the thermoluminescent fluorescent layer of this panel absorbs the radiation that has passed through the subject and the radiation energy corresponding to the intensity of the radiation. And then the thermoluminescent fluorescent material layer is heated to take out the accumulated radiation energy as a light signal, and 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 major restrictions on the materials of the fluorescent layer and the support. In this way, the radiation image conversion method using the thermofluorescent fluorescent substance as the fluorescent substance and the thermal energy as the excitation energy has a great difficulty in application. On the other hand, there is also known a radiation image conversion method using a panel having a stimulable phosphor layer formed on a support and using one or both of visible light and infrared light as excitation energy. (US Patent 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.

For example, in JP-A-58-109897, the composition formula is BaFX.xNaX ': yEu ²⁺ (wherein X and X'are at least one of Cl, Br and I, and x and y are respectively 0 <x ≦
It is a number satisfying the conditions of 10 ⁻¹ and 0 <y ≦ 0.2. ) A stimulable phosphor containing a divalent europium-activated composite halide phosphor represented by is allowed to absorb the radiation transmitted through the subject, and then the phosphor is excited by an electromagnetic wave in the wavelength range of 450 to 1100 nm. Then, a radiation image conversion method is described in which the radiation energy accumulated in the fluorescent material is emitted as fluorescence and the fluorescence is detected.

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 has high sensitivity as much as possible in order to reduce a patient's exposure dose. It is desirable that the stimulable phosphor has a high emission luminance due to photostimulation. From such a point, a radiation image conversion method using a photostimulable phosphor such as BaFX · xNaX ′: yEu ²⁺ can also improve its sensitivity by improving the emission brightness by stimulating the phosphor. Is desired.

(Object of the Invention) The present invention makes a stimulable phosphor absorb the radiation transmitted through an object, and then the phosphor is excited by an electromagnetic wave in the visible light and / or infrared range (450 to 1100 nm). This phosphor emits radiation energy accumulated as fluorescence, and in a radiation image conversion method for detecting this fluorescence, it has higher brightness than the photostimulable phosphor such as the conventional BaFX / xNaX ′: yEu _2+. It is an object of the present invention to provide a highly sensitive radiation image conversion method using a phosphor exhibiting stimulated emission as a stimulable phosphor.

(Structure of the Invention) The above-described object of the present invention is to allow a stimulable phosphor containing a rare earth element-activated composite halide phosphor represented by the following general formula [I] to absorb radiation transmitted through a subject: Thereafter, the phosphor is scanned and irradiated with an electromagnetic wave in a wavelength region of 450 to 1100 nm, and the radiation energy accumulated in the phosphor is emitted as an excitation fluorescence, and the excitation fluorescence is detected. This is achieved by a radiation image conversion method.

Formula (I) ^{_{BaX 2 · aBaX '2 · bM}} I F · dM III F 3: eLn wherein, X and X' is at least one among chlorine, bromine and iodine, and X and X 'are Different from each other.

M ^I is at least one alkali metal selected from the group consisting of Li, Na, K, Rb and Cs. M ^III is A
It is at least one selected from the group consisting of 1, Ga, Y, La and Lu. Ln represents at least one of Eu, Ce and Tb. Also, a, b, d and e are
0.6 ≦ a ≦ 1.4, 0 ≦ b ≦ 3, 0 ≦ d ≦ 0.5 and 0 <, respectively
It is a numerical value that satisfies the condition of e ≦ 0.2.

However, when Ln is Eu, M ^I is Li, Na, Rb
And at least one alkali metal selected from the group consisting of Cs, and b is a numerical value satisfying the condition of 0 <b ≦ 3.

The phosphor according to the present invention is manufactured, for example, by the manufacturing method described below.

First, as a fluorescent material, for example, at least one of I) barium chloride (BaCl ₂ ), II) barium bromide (BaBr ₂ ) and dihydrate barium bromide (BaBr ₂ · 2H ₂ O), III) Lithium fluoride (LiF), Strontium fluoride (Sr
F ₂ ), aluminum fluoride (AlF ₃ ) and IV) compounds such as trivalent europium compounds such as halides and oxides, etc., and stoichiometrically BaX ・ aBaX ′ ・ bM
_{^{I F · CM II F 2 ·}} dM III F 3: eLn become mixed so that the composition X and X 'Cl, select it Chigae one another from at least one of Br and I, a, b, c, d 0.6 ≦ a ≦ 1.4, 0 ≦ b ≦ 3, 0 ≦ c ≦ 4, 0 respectively
Weigh so that the conditions <d ≦ 0.5 and 0 ≦ e ≦ 0.2 are met, and mix well using a mortar, ball mill, mixer mill, and the like. Next, the obtained phosphor raw material mixture is filled in a heat-resistant container such as a quartz crucible or an alumina crucible and baked in an electric furnace. The firing temperature is suitably 600 to 1000 ° C, more preferably 750 to 900 ° C. The firing time varies depending on the filling amount of the raw material mixture, the firing temperature, etc.
Generally, 1 to 6 hours is suitable. The firing atmosphere is preferably a nitrogen gas atmosphere containing a small amount of hydrogen gas, a weak reducing atmosphere such as a carbon dioxide 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, allowed to cool, and then crushed, and then the fired product powder is charged again into the heat-resistant container and placed in the electric furnace.
Re-firing under the same firing conditions as described above can further increase the emission brightness of the phosphor.

The phosphor obtained after calcination is crushed and then treated by various operations generally employed in phosphor production such as washing, drying and sieving to obtain the phosphor of the present invention.

The phosphor according to the present invention obtained by the above-described manufacturing method or the like is irradiated with radiation such as X-rays, and then 450 to 1
It emits near-ultraviolet emission when excited by electromagnetic waves in the range of 100 nm. The emission luminance due to the stimulation is disclosed in JP-A-58-10.
9897, which is stronger than the conventional photostimulable phosphor described above, and thus the radiation image conversion method of the present invention using the phosphor according to the present invention is a radiation image using the conventional phosphor. It is more sensitive than the conversion method.

FIG. 1 is an illustration of the emission spectrum of the phosphor according to the present invention due to photostimulation. After irradiation with X-rays at a tube voltage of 80 KVp, the phosphor was excited by He-Ne laser light (633 nm). It is the emission spectrum measured by doing. Although slightly different depending on the composition of the phosphor, the phosphor according to the present invention used in the radiation image conversion method of the present invention exhibits near-ultraviolet emission as shown in FIG.

FIG. 2 exemplifies the excitation spectrum of photostimulation of the phosphor according to the present invention, which is the excitation spectrum of the phosphor of the present invention measured using a sample irradiated with X-rays at a tube voltage of 80 KVp. is there. As is apparent from FIG. 2, the wavelength range in which the phosphor according to the present invention can be excited is slightly different depending on the composition of the phosphor, but in general, it is 450 to 900 nm which is almost the same as the result shown in FIG. The optimum excitation wavelength is 550 to 850 nm.

In the method of the present invention, a light source in the wavelength region of 450 to 900 nm can be used as the excitation light source for emitting the radiation energy accumulated in the phosphor layer as fluorescence.
As shown in the figure, the phosphor of the present invention has an optimum excitation wavelength of 550.
Since it is in the range of 850 nm to 850 nm, a light source that emits light of 550 nm to 850 nm is more preferable.

Higher excitation energy can be obtained by using laser light as the excitation light source. He-Ne laser (633 nm), YAG laser (second harmonic 532 nm), ruby laser (694 nm), Ar ⁺
A light source that emits light of a single wavelength such as a laser (514.5 nm) or a semiconductor laser is used. The phosphor of the present invention has a wavelength of 800 nm.
Efficiently emits excitation light in the vicinity, so downsizing of the device,
It is preferable to use a semiconductor laser in order to reduce the cost.

The fluorescent substance of the present invention has the following advantages in addition to the fact that light emission due to high-intensity photostimulation is obtained using the above-mentioned light source.

The radiation image conversion panel after irradiating the excitation light and reading the radiation image is generally subjected to light irradiation or heat treatment in order to erase the residual image, but in the method of the present invention, it is used as a light source. Since halogen lamps and tungsten lamps can be preferably used in addition to the light lamp, the afterimage erasing time can be shortened.

The radiation image conversion method of the present invention will be specifically described with reference to schematic diagrams.

In FIG. 3, 11 is a radiation generator, 12 is a subject, 13 is a radiation image conversion panel having a visible or infrared stimulable phosphor layer containing the 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, and 15 is a radiation image conversion panel
A photoelectric conversion device that detects the fluorescence emitted from 13, 16 is a device that reproduces the photoelectric conversion signal detected by the photoelectric conversion device 15 as an image, 17 is a device that displays the reproduced image, and 18 is a light source 14 Radiation image conversion panel that cuts off reflected light
It is a filter for transmitting only the light emitted from 13. The photoelectric conversion device 15 and later may be any device that can reproduce the optical information from the panel 13 as an image in some form,
It 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 becomes the subject.
The transmitted image (that is, an image of the intensity of the radiation) is transmitted according to the change in the radiation transmittance of each part of 12 and enters the radiation image conversion panel 13. This incident transmission image is absorbed by the phosphor layer of the radiation image conversion panel 13, whereby a number of electrons and / or holes proportional to the amount of absorbed radiation is generated in the phosphor layer, and this is the fluorescence. Accumulated at the trap level of the body. That is, an accumulated image (a kind of latent image) of the radiation transmission image is formed. Next, this latent image is excited by light energy to make it noticeable. That is, the light source 14 that emits light of 450 to 1100 nm irradiates the fluorescent substance layer to expel the electrons and / or holes accumulated at the trap level and emit the accumulated image as fluorescent light. 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 phosphor layer of the radiation image conversion panel 13. The photoelectric conversion device 15 such as a photomultiplier tube converts the electric signal into an electric signal, the image processing device 16 reproduces it as an image, and the image processing device 17 displays this image. 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 phosphor layer, and the photoelectric converter that receives the fluorescence emitted from the phosphor layer generally emits light with a short wavelength of 600 nm or less. It is desirable that the fluorescence emitted from the phosphor layer has a spectral distribution in the short wavelength region as much as possible, because the sensitivity to energy becomes high. The emission wavelength range of the phosphor used in the method according to the present invention is 350 to 450 nm, while the excitation wavelength range is 450 to 1100 nm, so that the above conditions are satisfied at the same time.

That is, each of the phosphors used in the present invention is 45
It exhibits emission having a main peak at 0 nm or less, is easy to separate from excitation light, and is in good agreement with the spectral sensitivity of the photoreceiver. As a result, light can be received efficiently, and the sensitivity of the image receiving system can be increased.

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

Each phosphor raw material was weighed as shown in the following (1) to (5), and then thoroughly mixed using a ball mill to prepare five types of phosphor raw material mixtures, and the phosphor according to the present invention was prepared as follows. Adjusted as per.

(1) BaCl ₂ 208.3 g (1 mol) BaBr ₂ 297.2 g (1 mol) LiF 25.9 g (1 mol) EuCl ₃ 0.517 g (2 × 10 ⁻³ mol) (2) BaCl ₂ 208.3 g (1 mol) BaBr ₂ · 2H ₂ O 333.2 g (1 mol) NaF 42.0 g (1 mol) Eu ₂ O ₃ 0.352 g (1 × 10 ⁻³ mol) (3) BaBr ₂ · 2H ₂ O 333.2 g (1 mol) BaI ₂ 391.2 g (1 mol) RbF 104.5 g (1 mol) Eu ₂ O ₃ 0.352 g (1 × 10 ⁻³ mol) (4) BaCl ₂ 208.3 g (1 mol) BaBr ₂ · 2H ₂ O 333.2 g (1 mol) CsF 151.9 g (1 mol) Eu ₂ O ₃ 0.352 g (1 × 10 ^-3 mol) (5) BaCl ₂ 208.3 g (1 mol) BaBr ₂ · 2H ₂ O 333.2 g (1 mol) Ce ₂ O ₃ 0.328 g (1 × 10 ^-3 mol) Next, the above five types of fluorescence Each body material mixture was packed in a quartz boat and placed in an electric furnace for firing. The firing was performed at 850 ° C. for 2 hours while flowing a nitrogen gas containing 2% by volume of hydrogen gas at a flow rate of 2500 cc / min, and then allowed to cool at room temperature.

After crushing the obtained fired product using a ball mill, 150
The particles were sieved with a mesh to make the particle diameter uniform, and the following five types of phosphors were obtained.

Next, a radiation image conversion panel was manufactured using the above-mentioned five kinds of phosphors. Each radiation image conversion panel was manufactured as follows.

(1) BaCl ₂ · BaBr ₂ · LiBr: 2 × 10 ^-3 Eu (2) BaCl ₂ · BaBr ₂ · NaF: 2 × 10 ^-3 Eu (3) BaBr ₂ · BaI ₂ · RbF: 2 × 10 ^-3 Eu (4) BaCl ₂ · BaBr ₂ · CsF: 2 × 10 ⁻³ Eu (5) BaCl ₂ · BaBr ₂ : 2 × 10 ⁻⁴ Cl First, 8 parts by weight of the phosphor is polyvinyl butyral (binder).
Disperse 1 part by weight of a solvent in which acetone and ethyl acetate are mixed in equal amounts, and disperse the solution horizontally on a polyethylene terephthalate film (support) in which white pigment titanium oxide is kneaded and using a wire bar to make it uniform. A radiation image conversion panel having a film thickness of about 300 μm was prepared by applying and naturally drying.

From the X-ray tube focus, these 5 types of radiation image conversion panels
After irradiating X-rays with a tube voltage of 80 KVp and a tube current of 100 mA at a distance of 100 cm for 0.1 seconds, this was irradiated with a semiconductor laser beam (800
nm), and fluorescence due to photostimulation emitted from the phosphor layer was measured with a photodetector.

As a result, the emission luminance of these radiation image conversion panels due to photostimulation is as shown in Table 1 below, and the phosphors according to the present invention are measured under the same conditions. The emission luminance is higher than that of the emission image due to exhaustion, and thus the radiation image conversion method of the present invention using these radiation image conversion panels is more sensitive than the conventional radiation image conversion methods.

[Brief description of drawings]

FIG. 1 is a diagram showing the stimulated emission spectrum of the phosphor according to the present invention, and FIG. 2 is a diagram showing the relationship between the excitation wavelength and the stimulated emission intensity. FIG. 3 is a schematic diagram for explaining the radiation image conversion method of the present invention. 11 ... Radiation generator 12 ... Subject 13 ... Radiation image conversion panel 14 ... Excited excitation light source 15 ... Photoelectric conversion device 18 ... Filter

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Claims (1)

[Claims] 1. A stimulable phosphor containing a rare earth element-activated composite halide phosphor represented by the following general formula [I] absorbs radiation transmitted through an object, and then the phosphor is exposed at 450 to 1100 nm. A method for converting a radiation image, comprising scanning and irradiating an electromagnetic wave in a wavelength region to emit radiation energy accumulated in the phosphor as excitation fluorescence and detecting the excitation fluorescence. Formula (I) ^{_{BaX 2 · aBaX '2 · bM}} I F · dM III F 3: eLn wherein, X and X' is at least one among chlorine, bromine and iodine, and X and X ' Are different from each other. M ^I is at least one alkali metal selected from the group consisting of Li, Na, K, Rb and Cs, and M ^III is A
It is at least one selected from the group consisting of 1, Ga, Y, La and Lu. Ln represents at least one of Eu, Ce and Tb. Further, a, b, d and e are 0.6 ≦ a ≦ 1.4 and 0 ≦ b ≦, respectively.
It is a numerical value satisfying the conditions of 3, 0 ≦ d ≦ 0.5 and 0 <e ≦ 0.2. However, when Ln is Eu, M ^I is at least one alkali metal selected from the group consisting of Li, Na, Rb and Cs, and b is a numerical value satisfying the condition of 0 <b ≦ 3. ]