JPH058237B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a radiation image conversion method, and more particularly to a radiation image conversion method using a photostimulable phosphor. (Prior art) Conventionally, silver salt was used to obtain radiographic images.
Although so-called radiography has been used, in recent years, there has been a desire for a method of imaging radiographic images without using silver salts, particularly due to problems such as depletion of silver resources on a global scale. As an alternative to the above-mentioned radiographic method, the radiation transmitted through the object is absorbed by a phosphor, and the phosphor is then excited with a certain type of energy to release the radiation energy stored in the phosphor. A method has been considered in which the fluorescent light is emitted and the fluorescent light is detected and imaged. A specific method has been proposed in which a thermally fluorescent phosphor is used as the phosphor and thermal energy is used as the excitation energy to convert the radiation image (UK Patent No. 1462769 and Japanese Patent Application Laid-Open No. 1983-1993). No. 29889). This conversion method uses a panel with a thermally fluorescent phosphor layer formed on a support.
The thermofluorescent phosphor layer of this panel absorbs the radiation that has passed through the subject, accumulates radiation energy corresponding to the intensity of the radiation, and then heats the thermofluorescent phosphor layer. The accumulated radiation energy is extracted as a light signal, and an image is obtained by varying the intensity of this light. However, since this method heats the accumulated radiation energy when converting it into a light signal, it is absolutely necessary that the panel be heat resistant and not deformed or altered by heat. There are major restrictions on the materials of the thermally fluorescent phosphor layer and the support. As described above, the radiation image conversion method using a thermofluorescent phosphor as the phosphor and thermal energy as the excitation energy has major drawbacks in terms of application. On the other hand, radiation image conversion methods using one or both of visible light and infrared rays as excitation energy are also known (U.S. Pat.
No. 3859527). Unlike the above method, this method does not require heating when converting the accumulated radiation energy into optical signals, and therefore the panel does not need to be heat resistant.From this point of view, it is a more preferred radiation image conversion method. I can say that. However, the phosphors used in this method are only cerium- and samarium-activated strontium sulfide phosphors (SrS: Ce・Sm), eurobium- and samarium-activated strontium sulfide phosphors (SrS: Eu・Sm),
Sm), eurobium and samarium activated acid/lanthanum sulfide phosphor (La ₂ O ₂ S: Eu/Sm), manganese and halogen activated zinc sulfide/cadmium phosphor [(Zn/Cd)S: Mn/X , where X is a halogen], etc., and the sensitivity of methods using these fluorophores is extremely low, and it is desired to improve the sensitivity from a practical point of view. ing. (Objective of the Invention) The present invention allows radiation transmitted through an object to be absorbed by a phosphor, and then this phosphor is excited with electromagnetic waves, which are visible light and/or infrared rays, so that the phosphor accumulates. It is an object of the present invention to provide a practical radiation image conversion method with extremely high sensitivity in a radiation image conversion method in which radiation energy emitted as fluorescent light is emitted and this fluorescent light is detected. (Structure of the Invention) In order to achieve the above object, the present inventors have searched for a phosphor that can be used in the above method. As a result, the phosphor represented by the following general formula () or (), which exhibits a relative luminescence intensity several thousand times higher than that of conventional photostimulable phosphors, is particularly suitable for radiation image conversion methods. I found out. The present invention absorbs the radiation that has passed through the object into at least one of the phosphors represented by the following general formula () or (), and then absorbs the phosphor into an electromagnetic wave that is one or both of visible light and infrared rays. This constitutes a practical radiation image conversion method with extremely high sensitivity, which is characterized by exciting the phosphor to emit the accumulated radiation energy as fluorescence, and detecting this fluorescence. General formula ()nReX ₃・mAX′ ₂ : Eu _x General formula ()nReX ₃・mAX′ ₂ : Eu _x・Smy In the formula, Re is at least one trivalent metal selected from La, Gd, Y, and Lu. Yes, A is Ba, Sr
and Ca, and X and X' are at least one halogen selected from F, Cl, and Br. x
is 1×10 ^-4 ~3×10 ^-1 , y is 1×10 ^-4 ~1×10 ¹
+, m, and n represent numerical values defined by m>0, n>0, m+n=1, and n/m=1×10 ⁻¹ to 7×10 ⁻¹ . Re and A may be composed of two or more kinds, and for example, the total sum is expressed as Re (or A), such as Y _0.4 Gd _0.6 . Similarly, X and
X' may also be two or more types, for example F _1.2 Br _1.8 or F _0.9 Br _1.1 , which is expressed as X ₃ or X' ₂ in total. An example of such a compound is 0.1LaF ₃ .
0.9BaFCl: Eu _0.001 , 0.1LaF ₃・0.9BaFCl:
Eu _0.01 , 0.1LaF ₃・0.9BaBr：Eu _0.03 , 0.1YF ₃・
0.9BaFCl: Eu _0.01 , 0.1GdF ₃・0.9BaFCl: Eu _0.01 ,
0.3LaF ₃・0.7BaFCl: Eu _0.03 , 0.1LaF ₃・
0.9BaFBr: Eu _0.01 , 0.1LaFBr ₂・0.9BaF _0.9
Br _1.1 : Eu _0.01 , 0.1LaF ₃・0.9Sr _0.5 Ba _0.5 FBr:
Eu _0.03 , 0.2LaF ₃・0.8 (Ca _0.1 Ba _0.8 , Sr _0.1 ) FBr:
Eu _0.03 , 0.2GdF ₂・0.8 (Ca _0.1 , Sr _0.1 Ba _0.8 ) FBr:
Eu _0.03 , 0.4La _0.5 Lu _{0.5 F3}・0.6BaFBr: Eu _0.01 ,
0.1YF ₃・0.9BaFBr: Eu _0.01 , 0.2 (Y _0.4 Gd _0.6 ) F _1.2
Br _1.8・0.8BaFBr: Eu _0.05 , 0.3 (La _0.3 Gd _0.3 Y _0.4 )・
0.7BaFBr: Eu _0.03 , 0.1LaF ₃・0.9BaFBr:
En _0.01・Sm _0.003 , 0.1GdF ₃・0.9BaFBr：Eu _0.03・
Sm _0.005 , 0.1LaF ₃・0.9BaFBr：Eu _0.001・
Sm _0.0003 , _0.3LaF3・0.7BaFBr：Eu _0.03・Sm _0.005 ,
0.3LaF ₃・0.7 (Sr _0.5 Ba _0.5 ) FBr: Eu _0.03・Sm _0.001 ,
0.2GdF ₂・0.8 (Ca _0.1 Sr _0.1 Ba _0.8 ) FBr: Eu _0.03・
Sm _0.0005 , 0.2LaF ₃・0.8 (Ca _0.1 , Sr _0.1 Ba _0.8 )
FBr: Eu _0.03・Sm _0.001 , 0.1LuF ₃・BaFBr:
Eu _0.01・Sm _0.0003 , 0.4(La _0.5 Lu _0.5 )F ₃・
0.8BaFBr: Eu _0.01・Sm _0.003 , 0.3 (La _0.3 Gd _0.3 Y _0.4 )
_F3・0.7BaFBr：Eu _0.03・Sm _0.01 , 0.2(Y _0.4 ,
Gd _0.6 ), 0.8BaFBr: Eu _0.05 , Sm _0.01 , etc. In the radiation image conversion method of the present invention, radiation transmitted through a subject is absorbed by one or more of the above-mentioned phosphors, and then this phosphor is converted into one or both of visible light and infrared rays. The fluorescent material is excited by an electromagnetic wave to cause the accumulated radiation energy to be emitted as fluorescent light, and this fluorescent light is detected. The radiation image conversion method of the present invention will be specifically explained using schematic diagrams. In FIG. 1, 1 is a radiation generating device, 2 is a subject, and 3 is a radiation image conversion having a visible and/or infrared stimulable phosphor layer containing a phosphor represented by the above general formula ()(). 4 is a light source as an excitation source for emitting the radiation latent image of the radiation image conversion panel 3 as fluorescence; 5 is a photoelectric conversion device for detecting the fluorescence emitted from the radiation image conversion panel 3; 6 is a photoelectric conversion device; A device for reproducing the photoelectric conversion signal detected by the conversion device 5 as an image; 7 a device for displaying the reproduced image; 8 a device for cutting reflected light from the light source 4 and light emitted from the radiation image conversion panel 3; It is a filter that only allows the light to pass through. The photoelectric conversion device 5 and subsequent devices may be any device that can reproduce optical information from the panel 3 as an image in some form, and are not limited to the above. As shown in FIG. 1, the subject 2 is
When placed between the radiation image conversion panel 3 and the radiation image conversion panel 3 and irradiated with radiation, the radiation passes through the subject 2 as the radiation transmittance changes in each part, and the transmitted image (that is, the image of the intensity of the radiation) is displayed on the radiation image conversion panel. 3
incident on . This incident transmitted image is absorbed by the phosphor layer of the radiation image conversion panel 3, thereby generating a number of electrons and/or holes proportional to the absorbed radiation dose in the phosphor layer. It accumulates at the trap level of the fluorophore. That is, an accumulated radiographic image (a kind of latent image) is formed. This latent image is then excited with light energy to become visible.
That is, the light source 4 irradiates the phosphor layer with electromagnetic waves in the form of visible light and/or infrared rays to drive out the electrons and/or holes accumulated at the trap level, causing the accumulated image to be emitted as fluorescent light. The strength of this emitted fluorescent light is proportional to the number of accumulated electrons and/or holes, that is, the strength of the radiation energy absorbed by the phosphor layer of the radiation image conversion panel 3, and this optical signal is For example, it is converted into an electrical signal by a photoelectric conversion device 5 such as a photomultiplier tube, reproduced as an image by an image processing device 6, and this image is displayed by an image display device 7. It is more effective to use an image processing device 6 that is capable of not only reproducing electrical signals as image signals, but also capable of so-called image processing, image calculation, image storage, storage, etc. Next, the radiation image conversion panel used in the radiation image conversion method of the present invention and the excitation light source for emitting the accumulated image as fluorescent light will be explained in detail. The structure of the radiation image conversion panel 3 consists of a support 21 and a phosphor layer 22 formed on one side of the support 21, as shown in FIG. 2a. Needless to say, this phosphor layer 22 is made of one or more of the above-mentioned phosphors. The phosphor used here exhibits strong stimulated luminescence when excited with electromagnetic waves of visible light and/or infrared rays after being irradiated with radiation. When the amount is about 10 ^-4 to 1 gram atom, the photostimulation intensity becomes extremely strong, and by using the phosphor layer of these radiation image conversion panels, particularly efficient radiation image conversion can be achieved. As an exemplary compound of the phosphor used in the present invention represented by the general formula (), 0.1LaF ₃ .
There is a composition called 0.9BaFBr:Eu _0.03 , and the stimulated emission spectrum measured for this phosphor is
In addition, the photostimulated excitation spectrum is shown in FIG.
The spectrum in Figure 3 shows strong light emission with a peak at 390 nm, and the light emission brightness is that of conventional SrS:
It is 2000 times higher than Eu _0.0001 and Sm _0.0001 . In the method of the present invention, one or both of visible light and infrared rays can be used as an excitation light source for emitting the radiation energy accumulated in the phosphor layer as fluorescent light. It is shallow, the degeneration (fading) phenomenon is remarkable, and therefore the information storage period is short, so it is not very desirable in practice. For example, when obtaining an image, the phosphor layer of the exposed radiation image conversion panel is often scanned and excited with infrared rays, and the emitted light is electrically processed. Since it takes a certain amount of time to scan the entire area, there is a risk that there will be a difference between the initial read value and the final read value even if the same radiation dose is emitted. For these reasons, the phosphors shown in the general formulas () and () used in the radiation conversion method of the present invention have a deep trap, higher energy light,
In other words, it is more desirable that excitation can be efficiently performed with light of as short a wavelength as possible. As shown in FIG. 4, the phosphor used in the present invention has an optimal excitation wavelength range in the visible and near-infrared light regions, and therefore has little fading, resulting in the accumulation of latent radiation images accumulated in the phosphor layer. It has high preservation ability. In the radiation image conversion method of the present invention, as a light source for exciting the phosphor layer of the radiation image conversion panel, the latent image excited with a wavelength that is too long is not suitable for practical use because it causes large fading as described above. It is preferable to excite and emit light with a wavelength of 1100 nm or less as the excitation light. In addition, from the point of view of ease of separating the reflected light of the excitation light and the stimulated luminescence, it is preferable that the wavelength of the excitation light is 500 nm or more. However, if separation is possible, it is not limited to this. Preferred light sources include He-Ne as well as light sources that emit light with a band spectral distribution in one or both of the visible and near-infrared regions.
- A light source emitting light of a single wavelength is used, such as a laser (632.8 nm), YAG laser light (1064 nm), ruby laser (694.3 nm), argon laser, or semiconductor laser. Particularly when using laser light, high excitation energy can be obtained. Among laser beams, as shown in Japanese Patent Application No. 185086/1986, Ar ion laser at 514.5 nm
Better results are obtained using the oscillation line of Alternatively, if miniaturization of the device is a priority, a small He-Ne laser (632.8 nm) is preferable. In addition, when exciting with light energy in the method of the present invention, it is necessary to separate the reflected light of the excitation light from the fluorescent light emitted from the phosphor layer, and the need to receive the fluorescent light emitted from the phosphor layer. Photoelectric converters are generally
It is desirable for the fluorescent light emitted from the phosphor layer to have a spectral distribution in the short wavelength region as much as possible because it is sensitive to light energy with a short wavelength of 600 nm or less. The phosphor used also satisfies this condition. That is, all of the phosphors used in the present invention emit light with a main peak at 500 nm or less, are easy to separate from excitation light, and match well with the spectral sensitivity of the photoreceiver, resulting in efficient light reception. , the sensitivity of the image receiving system can be increased. In the phosphor represented by the general formula () used in the present invention, the concentration of Eu affects the stimulated luminescence intensity. Figure 5 shows the changes in stimulated luminescence intensity when the Eu concentration is changed in the luminescent series with 0.1LaF ₃ 0.9BaFBr as the host. From Figure 5
It can be seen that the Eu concentration is preferably in the range of 1×10 ⁻⁴ mol to 3×10 ⁻¹ mol per mol of the base material. In addition, the Eu concentration of the activator was adjusted to 1 × 1 mole of the base material.
When the number of moles of LaF 3 in the matrix is fixed as 10 ^-2 mol and the matrix is a compound series of LaF ₃ and BaFBr, the number n of moles of LaF ₃ in the matrix is
FIG. 6 shows the change in stimulated luminescence intensity with respect to the change in the ratio n/m of the number of moles of BaFBr in the matrix. From FIG. 6, it can be seen that when the matrix composition is set in the range of n/m from 1×10 ⁻³ to 7×10 ⁻¹ , the stimulated luminescence efficiency is good. However, when viewed universally including other matrix compositions, n/m is given as 1×10 ⁻¹ to 7×10 ⁻¹ . Further, the phosphor represented by the general formula () used in the present invention is added to the phosphor represented by the general formula () and an activator of 1×10 ^-4 mol to 1× 10 ⁻¹ mol of Sm was additionally added because the addition of a small amount of Sm significantly reduces the afterglow of stimulated luminescence. When the radiation image reading speed is high, the addition of Sm is effective because afterglow deteriorates the image quality. The addition of Sm exhibits the same characteristics as the phosphor (2008), except for a reduction in afterglow. Next, an example of a method for manufacturing a radiation image conversion panel will be shown below. First, 8 parts by weight of the phosphor and 1 part by weight of nitrified cotton are mixed using a solvent (acetone, a mixture of acetate/ethyl and acetate/butyl) to prepare a coating solution having a viscosity of approximately 50 centistokes. Next, this coating solution was uniformly applied onto a horizontally placed polyethylene terephthalate film (support), and left to dry naturally overnight to form a phosphor layer of approximately 300 μm, which was then used as a radiation image conversion panel. do. For example, a transparent glass plate or a thin metal plate made of aluminum or the like may be used as the support. The radiation image conversion panel consists of two transparent substrates 23, such as glass plates, as shown in FIG. 2b.
A phosphor layer 22 having an arbitrary thickness may be obtained by sandwiching a phosphor between layers 24, and the periphery of the phosphor layer 22 may be sealed. Table 1 shows the sensitivity of the radiation image conversion method of the present invention.
This figure shows a comparison with the sensitivity of a conventional radiation image conversion method using SrS:Eu/Sm phosphor.
In Table 1, the sensitivity is determined by irradiating the radiation image conversion panel with X-rays at a tube voltage of 80KVp, exciting it with Ar ion laser light (514.5nm), and collecting the fluorescence emitted from the phosphor layer into the receiver. (Spectral sensitivity S-5
It is expressed as the luminous intensity when received by a photomultiplier tube (photomultiplier tube), and is expressed as a relative value with the sensitivity of the conventional method using SrS:Eu Sm phosphor set as 1.

[Table] As is clear from Table 1 above, the radiation image conversion methods (No. 2 to No. 7) of the present invention have significantly higher sensitivity than the conventionally known radiation image conversion method (No. 1). Furthermore, Table 2 shows the results when the method No. 3 in Table 1 of the above-mentioned Example was carried out in the same manner except that a He--Ne laser was used as the excitation light source.

[Table] As can be seen from Table 2, it can be seen that sufficient excitation can be achieved with a He-Ne laser, although the sensitivity is slightly reduced. (Effects of the Invention) According to the present invention, a practical radiation image conversion method has been developed that has sensitivity increased several thousand times compared to the conventional method, and the radiation dose is significant when generating a radiation image on a panel. In addition, image conversion unevenness due to fading has been eliminated, and image reproduction has been accelerated, making it possible to achieve remarkable progress in this field.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram of the radiation image conversion method of the present invention, FIGS. 2 a and b are sectional views of a radiation image conversion panel used in the radiation image conversion method of the present invention, and FIG. Figure ₄ shows the stimulated emission spectrum of the 0.1LaF ₃ 0.9BaFCl:Eu _0.03 phosphor used in the radiation image conversion method of
Figure 6 shows the stimulated luminescence intensity as a function of Eu doping concentration for the 0.9BaFBr phosphor series.
FIG. ₃ is a diagram showing stimulated luminescence intensity with respect to changes in parent composition when using a compound series of LaF 3 and BaFBr. 1...Radiation generating device, 2...Subject, 3...
Radiation image conversion panel, 4... Light source, 5... Photoelectric conversion device, 6... Image processing device, 7... Image display device, 8... Filter, 21... Support, 22
. . . Fluorescent layer, 23, 24 . . . Transparent support.

Claims (1)

[Claims] 1. The radiation transmitted through the subject is absorbed by at least one of the phosphors represented by the following general formula () or (), and then this phosphor is exposed to visible light and/or infrared rays. 1. A radiation image conversion method characterized in that a phosphor is excited with an electromagnetic wave selected from the following to cause a phosphor to emit accumulated radiation energy as fluorescence, and detect this fluorescence. General formula ()nReX ₃・mAX′ ₂ :Eu _x General formula ()nReX ₃・mAX′ ₂ :Eu _x・Sm _y (In the formula, Re is at least one trivalent selected from La, Gd, Y, and Lu. metal, A is Ba, Sr
and Ca, and X and X' are at least one halogen selected from F, Cl, and Br. x
is 1×10 ^-4 ~3×10 ^-1 , y is 1×10 ^-4 ~1×
10 ^-1 , m and n represent numerical values defined by m>0, n>0, m+n=1 and n/m=1×10 ⁻¹ to 7×10 ⁻¹ . 2. The radiation image conversion method according to claim 1, wherein the wavelength of the electromagnetic wave is 1100 nm or less. 3. The radiation image conversion method according to claim 2, wherein the wavelength of the electromagnetic wave is 500 nm or more. 4. The radiation image conversion method according to claims 2 and 3, wherein the electromagnetic wave is a laser beam. 5. The radiation image conversion method according to claim 4, wherein the laser beam is an Ar ion laser beam. 6. The radiation image conversion method according to claim 4, wherein the laser beam is a He-Ne laser beam.