JPS58201883A - Radiation image conversion - Google Patents

Abstract

PURPOSE:After radiation rays passing through the object are absorbed in a specific accelerable fluorescent substance, the flurescence is emitted by making the substance with electromagnetic waves and the fluorescence is detected, thus effecting conversion of radiation image with very high sensitivity. CONSTITUTION:Radiation rays that have passed through the object are absorbed in at least one selected from fluorescent bustances of formula I and II (Re is La, Gd, Y, Lu; A is alkaline earth metal such as Ba, Sr, Ca; x is F, Cl, Br; x is 1X10<-4>-3X10<-1>; y is 1X10<-4>-1X10<-1>; n/m is 1X10<-3>-7X10<-1>. Then, the fluorescent substance is made to excite with electromagnetic rays of visible or infrared rays of longer than 500nm, preferably shorter than 1,100nm to make the radiation energy stored in the substance emit as fluorescence and the emission is detected to effect image conversion. As the above electromagnetic waves, are cited preferably laser beam.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radiation image conversion method, and more particularly to a radiation image conversion method using a stimulable phosphor.

Conventionally, so-called radiography using silver salts has been used to obtain radiographic images, but in recent years, due to problems such as depletion of silver resources on a global scale, methods of imaging radiographic images without using silver salts have been developed. It became desired.

As an alternative to the above-mentioned radiographic method, the radiation transmitted through the subject is absorbed by a phosphor, and then this phosphor is excited with a certain kind of energy, and the phosphor emits the accumulated radiation energy as fluorescence. Therefore, methods of detecting this fluorescence and creating images are being considered. A specific method has been proposed in which a thermofluorescent phosphor is used as the phosphor and thermal energy is used as the excitation energy to convert a radiation image (British Patent No. 1,462,769).
No. and Japanese Patent Publication No. 51-29889). This conversion method uses a panel with a thermoluminescent phosphor layer formed on a support.
The thermofluorescent 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, and then heats this thermofluorescent phosphor layer to accumulate radiation energy. It extracts the light as a light signal and obtains an image based on 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 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 a major drawback in terms of processing. On the other hand, radiation image conversion methods using one or both of visible light and infrared rays as excitation energy are also known (US Pat. No. 3,859,5
No. 27).

Unlike the above method, this method does not require heating when converting the accumulated radiation energy into a light signal, and therefore the panel does not need to be heat resistant, which makes it a more preferred radiation image conversion method. I can say it. However, the only phosphors used in this method are cerium and samarium activated strontium sulfide phosphors (SrS:
Ce18m), europium and samarium activated strontium sulfide phosphor (SrS: Eu, Sm),
Europium and samarium activated acid/lanthanum sulfide phosphor (La202S: Eu, Sm), manganese and halogen activated zinc sulfide/cadmium phosphor ((ZnXCd)
) S: Mn, Improvements are desired. In the present invention, radiation transmitted through an object is absorbed by a phosphor, and then this phosphor is excited with electromagnetic waves that are visible light and/or infrared rays, and the radiation energy accumulated in the phosphor is emitted as fluorescence. Therefore, it is an object of the present invention to provide a practical radiation image conversion method that has extremely high sensitivity in a radiation image conversion method that detects this fluorescence. In order to achieve the above object, the present inventors have been searching for phosphors that can be used in the above method. As a result, the radiation that has passed through the subject is absorbed by at least one of the phosphors represented by the general formula 〇) or wholesale, and then this phosphor is
The above object is achieved by a radiation image conversion method characterized in that the phosphor is excited with electromagnetic waves selected from visible light and infrared rays with a wavelength of 0 nm or more to emit radiation and energy accumulated in the phosphor as fluorescence, and the fluorescence is detected. It turns out that it can be achieved.

General formula (T) nReFs ・mAX2/EL1x General formula ([D nReF, -mAX2 /Bux・Sm
In the formula y, Re is at least one type of La1Gd, Y, Lutr), A is an alkaline earth metal, Ba, Sr, C
At least one of a, X is F, CI, at least one of B'', X is 1 x 10'' to 1, n7m is I Xl0-3
~7 represents XIO'.

In the radiation image conversion method of the present invention, the radiation transmitted through the object is absorbed by one or more of the phosphors contained in the phosphor, and then this phosphor is The phosphor is characterized in that it is excited by electromagnetic waves that are one or both of long-wavelength visible light and infrared rays to cause the phosphor to emit accumulated radiation energy as fluorescence, and this fluorescence 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 plate having a visible to infrared stimulable phosphor layer containing a phosphor represented by the general formula (1) σ1);
4 is a light source as an excitation source for emitting the radiation latent image of the radiation image conversion plate as fluorescence; 5 is a photoelectric conversion device that detects the fluorescence emitted from the radiation image conversion plate; 6 is a photoelectric conversion device W5 that detects the fluorescence emitted from the radiation image conversion plate; 7 is a device for displaying the reproduced image; 8 is a light source 4;
This is a filter for cutting reflected light from the radiation image conversion plate 3 and transmitting only the light emitted from the radiation image conversion plate 3.

−6=5 Any device that can reproduce the optical information from digit 3 as an image in some form is sufficient, and is not limited to the above. As shown in FIG. 1, when the subject 2 is placed between the radiation generating bag N1 and the radiation image converting plate 3 and irradiated with radiation, the radiation passes through each part of the subject 2 according to changes in the radiation transmittance. A transmitted image (that is, an image of the intensity of radiation) enters the radiation image conversion plate 3. This incident transmitted image is absorbed by the phosphor layer of the radiation image conversion plate 3, and a number of electrons or holes are generated in proportion to the amount of radiation absorbed in the phosphor layer, which reaches the trap level of the phosphor. Accumulated. 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 that are long-wavelength visible light of 500 nm or more and/or infrared rays to expel the electrons or holes accumulated at the trap level and emit the accumulated image as fluorescence. The intensity of this emitted fluorescence is proportional to the number of accumulated electrons or holes, that is, the intensity of the radiation energy absorbed by the phosphor layer of the radiation image conversion plate 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 reproduction device 6, and this image is displayed by an image display bag w7. Next, the radiation image conversion plate used in the radiation image conversion method of the present invention and the excitation light source for emitting the accumulated image as fluorescence will be explained in detail.

The structure of the radiation image conversion plate consists of a support 21 and a phosphor layer 22 formed on one side of the support 21, as shown in FIG. 2(a). It goes without saying that this phosphor layer ρ is made of one or more of the phosphors contained in the above-mentioned phosphors. The phosphor used here exhibits strong stimulated luminescence when excited by electromagnetic waves, which are long-wavelength visible light of 500 nm or more and/or infrared rays, after being irradiated with radiation. When the concentration is about 0-4 to 1 gram atom, the photostimulation intensity becomes extremely strong, and by using these as the phosphor layer of the radiation image conversion plate, particularly efficient radiation image conversion can be achieved.

Exemplary compounds of the phosphor used in the present invention represented by the general formula (■) include 0.1 LaF, + 0
．． 9 There is a composition BaFCI/EuO, 0g4, and the measured Xll1! The excitation emission spectrum is shown in Figure 3.

The spectrum shown in FIG. 3 shows strong light emission with a peak at 385 nm, and the light emission brightness is five times that of conventional CaWO4. Furthermore, this phosphor emits light with a peak at 185 nm when excited by 2537X ultraviolet light.
Its emission brightness is (S r, Mg ) t Pt 07
Cag reaches three times that of /Eu, and even with cathode ray excitation
The luminance is three times that of o, .

In the phosphor used in the present invention, even the matrix excluding the activator is, for example, Xll1! CaWO upon excitation
, and this luminance can be further increased by activation with Eu2+.

Next, an example of a method for manufacturing a radiation image conversion plate 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 (a mixture of acetone, ethyl acetate, and butyl acetate) to prepare a coating solution having a viscosity of approximately centistokes. Next, this coating solution is uniformly applied onto a horizontally placed polyethylene terephthalate film (support), and allowed to stand day and night to air dry to form a phosphor layer with a thickness of about 300 .mu.m, thereby forming a radiation image converting plate.

For example, a transparent glass plate or a thin metal plate made of aluminum or the like may be used as the support.

In addition, the radiation image conversion plate is a transparent substrate such as two glass plates as shown in FIG. It may be of a structure in which the surrounding area is sealed.

In the radiation image conversion method of the present invention, the light source for the light energy that excites the phosphor layer of the radiation image conversion plate is as follows:
In addition to a light source that emits light with a band spectral distribution in one or both of the long wavelength visible region of 500 nm or more and the infrared region, He-Ne laser light (633 nm) is used.
, YAG laser light (1064 nm), ruby laser light (694 nm), argon laser, semiconductor laser, etc., are used. Particularly when using laser light, high excitation energy can be obtained. Among laser beams, it is particularly preferable to use He-pJe laser beam.

In the method of the present invention, as an excitation light source for emitting the radiation energy accumulated in the phosphor layer as fluorescence, one or both of long-wavelength visible light with a wavelength of 500 nm or more and infrared rays can be used. The area trap is shallow, the regression (7-eding) phenomenon is significant, and therefore the information retention period is short, which is not very desirable in practice.

For example, when obtaining an image, the phosphor layer of the exposed radiation image conversion plate is often scanned and excited with infrared rays, and the emitted light is electrically processed. Since scanning the entire surface takes a certain amount of time, there is a risk that there will be a difference between the first read value and the last read value even if the same radiation dose is irradiated.

For this reason, the phosphors shown in general formula (T) and (2) used in the radiation image conversion method of the present invention have deep traps and can be excited efficiently with higher energy light, that is, light with a wavelength as short as possible. It is more desirable that the phosphor used in the present invention has an optimum excitation wavelength range of 500 to 900 nm, which is the visible and near-infrared light region. It has a high ability to store and store radiation latent images.

Furthermore, when exciting with 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 is generally sensitive to light energy with a short wavelength of 600 nm or less. Because of the higher sensitivity,
It is desirable that the fluorescence emitted from the phosphor layer has a spectral distribution in the short wavelength region as much as possible, and the phosphor used in the method of the present invention also satisfies this condition.

That is, all of the phosphors used in the present invention have 5
It emits light with a main peak at 00 nm or less, is easily separated from excitation light, and matches well with the spectral sensitivity of the photoreceiver, allowing efficient light reception and increasing the sensitivity of the image receiving system.

Table 1 shows the sensitivity of the radiation image conversion method of the present invention as SrS:
This figure shows a comparison with the sensitivity of a conventional radiation image conversion method using Eu and Sm phosphors. In Table 1, the sensitivity is determined by irradiating the radiation image converting plate with X-rays at a tube voltage of 80 KVp, exciting it with He-Ne laser light, and collecting the fluorescence emitted from the phosphor layer using a receiver (spectral sensitivity S- SrS: Eu.

The sensitivity is expressed as a relative value with the sensitivity of a conventionally known method using Sm phosphor being set to 1.

(Table 1) 13- As is clear from Table 1 above, the radiation image conversion methods (A2 to A5) of the present invention are different from the conventionally known radiation image conversion methods (
It is significantly more sensitive than AI).

As described in detail above, the present invention provides a radiation image conversion method with extremely high sensitivity, and has great industrial utility value as a method that replaces conventional radiography.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram of the radiation image conversion method of the present invention, and FIGS. 2(a) and (b) are sectional views of a radiation image conversion plate used in the radiation image conversion method of the present invention. The figure shows LaF used in the radiation image conversion method of the present invention, ・0
．． 9 is an emission spectrum of 9BaFCI/Eu O,03 phosphor. 1... Radiation generator 2... Subject 3... Radiation image conversion plate 4... Light source 5... Photoelectric conversion device
6... Image playback device 7... Image display device
8...Filter 21...Support n.
...Phosphor layer 14-n and U...Transparent support agent Yoshimi Kuwahara Figure 1 Figure 2 Figure 5 (α) (b) 15- Procedural amendment (voluntary) February 1982 21st 1 Display of the case Patent Application No. 85585 filed in 1982 2 Title of the invention Radiographic image conversion method 3 Relationship with the amendment person case Patent applicant address 1-26-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Name Name (+27) Representative Director of Konishiroku Photo Industry Co., Ltd. Nobuhiko Kawamoto 4, Agent Address: 191 Sakura-cho, Hino-shi, Tokyo Konishiroku Photo Industry Co., Ltd. Voluntary office 6; "Claims" column and "Detailed Description of the Invention" column 7, Contents of amendment (1) The "Claims" of the specification will be corrected as shown in the attached sheet. (2) The "Detailed Description of the Invention" in the specification is corrected as follows. (a) Lines 18 to 19 on page 5 of the specification say, "X represents 1x10-19' m represents 1x10-7x10.""I represents lX10-' ~ 3X10. 7 is 1
×10 to 1×10, and now represents 1×10 to 7×10. ” and (b) “composition resulting in rEuO,03” on page 9, line 4.
゜0.1 LaFg" 0.8BaFBr/Eu
0,03, etc., = 2- Attached Claim (1) The radiation transmitted through the subject is expressed by the following general formula (I
) 'i! The radiation energy accumulated in the phosphor is absorbed by at least one of the phosphors indicated by 0 or 0, and then this phosphor is excited with electromagnetic waves selected from visible light of 500 mm or more and infrared rays. A radiation image conversion method characterized in that the fluorescent light is emitted as fluorescent light and the fluorescent light is detected. General formula (■) nR*F1 @ mAX, / Eu
1 General formula (1) nR@F3 m mAXz / E
uz IISmy (wherein, Re is Las Gds Y
At least one type of XLu, A is an alkaline earth metal, Bus
At least one type of Srs Ca, X represents at least one type of F, CI, Br, and I represents 1 cut O-43 10 to 7X10. )i. (2) The radiation image conversion method according to claim 1, wherein the wavelength of the electromagnetic wave is below 11,0 On-. (3) The radiation conversion method according to claim 2, wherein the electromagnetic wave is a laser beam.

Claims (3)

[Claims] (1) The radiation transmitted through the object is absorbed by at least one of the phosphors represented by the following general formula (I) or (■), and then this phosphor is exposed to electromagnetic waves selected from visible light and infrared rays of 500 nm or more. A radiation image conversion method characterized in that the radiation energy accumulated in the phosphor is excited by the phosphor and emitted as fluorescence, and the fluorescence is detected. General formula (I) nReF, mAX2/EuX general formula ([
D nReFs ・mAx! 1Eux・Smy (where Re is at least one of La5Gd, SY, Lu, A is an alkaline earth metal, at least one of Ba, Sr, Ca, X is at least one of F, CI, 13r, lX10'~1, n7 stone is lXl0''~7x1
(represents 0″) (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 electromagnetic wave is a laser beam.