JPS60217287A - Conversion of radiographic image - Google Patents

Abstract

PURPOSE:Radiation is transmitted through a copying original and absorbed in an accumulating fluorescent material containing an Eu<2+>-doped composite halide fluorescent material, the fluorescent material is excited with a specific electromagetic radiation, and the radiation energy released as fluorescent light is detected. CONSTITUTION:Radiation passed through a copying original is absorbed in an accumulating fluorescent material containing an Eu<2+>-doped composite halide fluorescent material of formula (X is Cl, Br or I; 0.9<=a<1; 0<x<=10<-1>; 0<y<= 2X10<-1>). The fluorescent material is excited by electromagentic radiation of 550-700nm wavelength, and the accumulated radiation energy released as a fluorescent light is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) 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 has been used to obtain a radiographic image, but a method of imaging a radiographic image without using a silver salt has become desirable.

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 and Japanese Patent Application Laid-open No. 1983-1992). No. 29889). This conversion method uses a panel with a thermofluorescent phosphor layer formed on a support, and the thermofluorescent phosphor layer of this panel absorbs the radiation that has passed through the subject, accumulating radiation energy corresponding to the intensity of the radiation. Then, by heating this 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 fluorescent phosphor layer and the support. 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, a radiation image conversion method is also known that uses a panel in which a stimulable phosphor layer is formed on a support and uses visible light and/or infrared rays as excitation energy. (U.S. Patent 3.895
, No. 527). Unlike the above-mentioned method, this method does not require heating when converting the accumulated radiation energy into optical signals, so the panel does not need to be heat resistant, and from this point of view it is a more preferred radiation image conversion method. I can say it.

For example, in JP-A-58-109897, the composition formula is B.
aFX-xNaX': yEu2+ (however, X and
′ is at least one of CQ, Br, and ■, and X and y are each O<x≦10−1
and o<y≦0.2. ) The radiation transmitted through the object is absorbed by a stimulable phosphor containing a divalent europium-activated composite halide phosphor represented by
A radiation image conversion method is described in which a phosphor is excited by electromagnetic waves in the +m wavelength range to cause the phosphor to emit accumulated radiation energy as fluorescence, and to detect this fluorescence.

3- 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 patient's exposure dose, and therefore, the method It is desirable that the stimulable phosphor used in this invention has as high an emission brightness as possible due to photostimulation. From this point of view, the above BaFX-xNaX':
Regarding the radiation image conversion method using the yEu2+ phosphor, it is also desired to improve the sensitivity by increasing the luminance of light emitted by the phosphor being stimulated.

(Objective of the Invention) The present invention allows radiation transmitted through an object to be absorbed by a stimulable phosphor, and then this phosphor is excited with electromagnetic waves in the visible light and/or infrared range to cause the phosphor to accumulate. 11aFX4x'NaX' :yE m 2 is accumulated as a phosphor that exhibits stimulated luminescence with higher brightness than the phosphor. The purpose of the present invention is to provide a highly sensitive radiation image conversion method using a fluorescent phosphor.

4- (Structure of the invention) The present invention, etc.
・xNaX': yEu2+ As a result of various studies on improving the luminescence brightness by photostimulation of the phosphor, the following general formula (1
) A stimulable phosphor containing a divalent europium-activated composite halide phosphor is made to absorb the radiation transmitted through the subject, and the phosphor is excited with electromagnetic waves in the range of 550 to 700 nm to produce the fluorescence. The object of the present invention is achieved by a radiation image conversion method characterized in that radiation energy stored in the body is emitted as fluorescence and the fluorescence is detected.

General formula CI) Ba24 Bra* xNaX :yEu2+ In the formula, X
is a hasidene atom and represents at least one kind of atom of chlorine, bromine and iodine, alx and y are 0.9≦a1,
Represents a numerical value that satisfies 0≦10−1 and o<y≦2X10−′.

That is, the phosphor having the composition according to the present invention has a temperature of 550 to 700 r+m.
When excited with electromagnetic waves in the range of
It exhibits stimulated luminescence in the near-ultraviolet region with higher brightness than the phosphor having X-xNaX':yEu2+, and this can change the method of converting radiation images with high sensitivity in practice.

In the present invention, the phosphor BaF2-a according to the present invention
l1ra -xNaX :yEu'' is characterized by the a value and X, symbolically expressed as P C (a)
Br:10-'Eu'' is P C (0,998) [Jr
). In addition, the conventionally known phosphor BaFX-xNa
X':yEu2÷ is characterized by X and X' and symbolically expressed as P' ((X)
r ・10-'NaBr :10-'Eu''l;t P
'C(Br)Br).

In an embodiment of the present invention, the phosphor P C according to the present invention
In (a)X), it is preferable that the a value is 0.95≦a<1.0.

Also, excitation light for the phosphor PC(a)X), 550
Preferably, laser light is used for electromagnetic waves in the range of ~700 nm, providing advantageous embodiments in terms of excitation efficiency and practical operation.

The present invention will be explained in detail below.

The phosphor P ((a)X) according to the present invention is manufactured, for example, by the manufacturing method described below.

First, as a phosphor raw material, at least one of (1) barium fluoride (BaF2), (2) barium bromide (BaBr2), and barium bromide dihydrate (BaBr2.2H20) is used.
Seeds, ■) Sodium chloride (NaCQ), sodium bromide (
(1) At least one of NaBr) and sodium iodide (NaI); and (2) a compound of trivalent europium such as a halide or oxide.

Using the above phosphor raw materials, BaF24Br.
xNaX:yEu”°
Select from at least one of QlBr and ■, a,
x and y each indicate 0.9≦a<1, O<x
The ingredients are weighed so as to satisfy the following conditions: ≦1o°1 and o<y≦0.2, and thoroughly mixed using a mortar, ball mill, mixer mill, etc. Next, the obtained phosphor raw material mixture was poured into stone 7.
- It is filled into a heat-resistant container such as an English crucible or an aluminum crucible and fired in an electric furnace. Firing temperature is 600 to 1000
℃ is suitable, more preferably Fuji 0 to 900℃
It is. The firing time varies depending on the filling amount of the raw material mixture, the firing temperature, etc., but in general, 1 to 6 hours is appropriate. The firing atmosphere is preferably a weakly reducing atmosphere such as a nitrogen gas atmosphere containing a small amount of hydrogen gas, 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, left to cool, and pulverized.The fired product powder is then filled into a heat-resistant container again, placed in the electric furnace, and fired under the same firing conditions as above. Re-baking can further increase the luminance of the phosphor.

The phosphor obtained after firing is pulverized and then processed by various operations commonly employed in the production of phosphors, such as washing, drying, sieving, etc., to obtain the phosphor of the present invention.

After being irradiated with radiation such as X-rays, the phosphor PC(a) Shows ultraviolet light emission. The luminance due to the photostimization is stronger than that of the conventional phosphor P'[(x)X'] described in JP-A-58-109897.
Therefore, the radiation image conversion method of the present invention using the phosphor P' ((a)
)X'] is more sensitive than the radiographic image conversion method using

FIG. 1 illustrates the emission spectrum due to stimulation of the phosphor P C(a)X) according to the present invention, and shows P ((
0,'95)Br) phosphor (x= 10-3.y=
After irradiating 10-3) with X-rays with a tube voltage of 80 KV,
This is an emission spectrum measured by exciting the phosphor with tie-Ne laser light (633 nm). Although it differs slightly depending on the composition of the phosphor, the phosphor P according to the present invention used in the radiation image conversion method of the present invention [(a)
) exhibits near-ultraviolet emission as shown in FIG. 1 due to photostimulation.

FIG. 2 illustrates the excitation spectrum of the phosphor PC(a)X-) according to the present invention.
P C (
0,95)Br) Phosphor (x=10-3, y=10
-') excitation spectrum. As is clear from FIG.
50 to 700 n tn is the optimal excitation wavelength range.

The wavelength range that can be excited by the phosphor PC(a)
and the optimum excitation wavelength is 550 to 700 nm.

FIG. 3 is an excitation spectrum of the P [(1,05)Br ] phosphor in which a is outside the range of the phosphor according to the present invention and a>1. As is clear from FIG. 3, the optimum excitation wavelength range of this phosphor is 450 to 600 nm, and P ((0,9≦a<1)X
) is different from the phosphor. When the a value is 1<a<2, the photostimulation excitation spectrum of the phosphor P C(a) and the optimal excitation wavelength range is 450
600r+n+.

Also, when the a value is O<a<0.9, the phosphor P C(a)
Although the photostimulation excitation spectrum of X) differs slightly depending on the composition of the phosphor, it is generally almost the same as the result shown in FIG. 2, and the optimum excitation wavelength range is 550 to 700 nm. However, if the X and y values are the same, the luminance due to stimulation is lower than that of the phosphor of the present invention.

Figure 4 shows the tube voltage of 80K for the phosphor P ((a)Br).
This is a graph showing the relationship between the a value (horizontal axis) and the emission luminance due to photostimulation when the phosphor is excited with l1e-Ne laser light (633 nm) after being irradiated with X-rays of Vp. Fourth
As is clear from the figure, the phosphor p [(a) Dr ] according to the present invention whose a value is in the range of 0.9≦a<1 has an a value of 0.
Phosphor P when <a<0.9 or 1≦a<2
((a)Br) Shows stimulated luminescence with higher brightness than Br. Furthermore, when the a value is 0.95≦a<1, the phosphor P [:
(a) Br) exhibits particularly high-intensity n-exhaustive light emission.

Note that FIG. 4 shows the relationship between the a value and the luminescence luminance due to photostimulation for the phosphor PC(a)Br); a) I) and phosphor P ((a
) For C1 as well, the relationship between the a value and the emission brightness due to photostimulation was almost the same as the results shown in FIG. 4. In addition, Figure 4 shows that the y value, which is the amount of sodium halide, is 10
This shows the relationship between the a-value and the luminance due to photostimulation for a phosphor with -3, but it also shows that phosphors with changed y-values are photostimulated in the range of a-value 0.9≦a<1. The relationship is shown in which the luminance increases due to Furthermore, Figure 4 shows that
This shows the relationship between the a value and the luminance due to photostimulation for a phosphor whose y value, which is the amount of Eu'', is 10-3, but it also shows the relationship between the a value and the luminance due to photostimulation for a phosphor whose y value has changed. It was found that the relationship with luminance has the same tendency as shown in Figure 4. In the method of the present invention, the wavelength of 450 to 900 nm is used as an excitation light source for emitting the radiation energy accumulated in the phosphor layer as fluorescence. Although a light source in the wavelength range can be used, a light source that emits light in the wavelength range of 550 to 700 nm is more preferable because the optimum excitation wavelength of the phosphor of the present invention is 550 to 700 nm as shown in FIG. Higher excitation energies can be obtained using laser light, and He--Ne lasers are particularly preferred in the method of the invention.

A phosphor P ((0,9≦a<1)X) having an a value in the range of 0.9≦a<1, such as the phosphor according to the present invention, is
By using a light source that emits light in the range of 550 to 700 nm as an excitation light source, there are the following advantages in addition to obtaining high-intensity light emission due to stimulation.

After irradiating excitation light and reading a radiation image, a radiation image conversion panel is generally subjected to light irradiation or heat treatment to erase any remaining afterimage. When the phosphor of the present invention is used in comparison with the phosphor P [(1≦a×2) By performing erasing, the time required to erase afterimages to a practical level can be shortened to ~h. Therefore, it is possible to simplify the afterimage erasing device and shorten the afterimage erasing time.

The radiation image conversion method of the present invention will be specifically explained using schematic diagrams.

In FIG. 5, 11 is a radiation generating device, 12 is a subject,
13 is a radiation image conversion panel having a visible or infrared stimulable phosphor layer containing a phosphor represented by the general formula (1), and 14 is for emitting the radiation latent image of the radiation image conversion panel 13 as fluorescence. 15 is a photoelectric conversion device that detects fluorescence emitted from the radiation image conversion panel 13, 16 is a device that reproduces the photoelectric conversion signal detected by the photoelectric conversion device 15 as an image, and 17 is a device that reproduces the reproduced image. The display device 18 is a filter for cutting off the reflected light from the light source 14 and transmitting only the light emitted from the radiation image conversion panel 13. Photoelectric conversion device 15
Thereafter, any device that can reproduce the optical information from the panel 13 as an image in some form is sufficient, and is not limited to the above. As shown in FIG. 15, when the subject 12 is placed between the radiation generator 11 and the radiation image conversion panel 13 and irradiated with radiation, the radiation passes through each part of the subject 12 as the radiation transmittance changes, and the transmitted image is (that is, an image of the intensity of radiation) enters the radiation image conversion panel 13. This incident transmitted image is transmitted to the radiation image conversion panel 3
is absorbed into the phosphor layer, thereby generating a number of electrons and/or tags proportional to the amount of radiation absorbed in the phosphor layer, which are accumulated at the trap level of the phosphor.

That is, an accumulated radiographic image (a kind of latent image) is formed. Next, this latent image is excited with light energy to become visible. That is, the phosphor layer is irradiated with a light source 14 that emits light of 550 to 700 r+n+ to drive out the electrons and/or genuine tag accumulated at the trap level, and the accumulated image is emitted as fluorescence. The intensity of this emitted fluorescence is proportional to the number of electrons and/or holes accumulated in M, that is, the intensity of radiation energy absorbed by the phosphor layer of the radiation image conversion panel 13, and this optical signal is Convert it into an electrical signal with a photoelectric conversion device 15 such as a photomultiplier tube,
The image processing device 16 reproduces the image as an image, and the image display device 17 displays this image. Image processing device 1
It is more effective to use a device that not only reproduces electrical signals as image signals but also can perform so-called image processing, image calculations, image storage, and preservation.

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. In order to increase sensitivity, it is desirable that the fluorescence emitted from the phosphor layer has a spectral distribution in a short wavelength region. The emission wave range of the phosphor PC(a)X) used in the method according to the present invention is 3
50-450 nm, while the excitation wavelength range is 550-7
Since 0Or+I++, the above conditions are satisfied at the same time.

That is, all of the phosphors used in the present invention have 4
It emits light with a main peak below 50r+n+, is easy to separate from the excitation light, and matches well with the spectral sensitivity of the photoreceiver, so it can efficiently receive light and increase the sensitivity of the image receiving system.

(Example) Next, the present invention will be explained by examples.

As shown in (1) to (11) below, each phosphor raw material was
6- After weighing, mix thoroughly using a ball mill and add to 11.
Different kinds of phosphor raw material mixtures were prepared, and the phosphor P [''(a)X) according to the present invention was prepared as follows.

In addition, 11 types of comparative sample phosphors P' [(X)

(1) BaF2175.7g (1,002 mol)Ba
Br2・2L0332.5g (0,998 mol) NaB
r 0.206 g (2X 10-'mol) Eu2030
．． 352g (IXIO-'mol) (2) BaF217
6.2g (1,005 mol) I3aBr2.2H203
31,5g (0,995mol) NaBrO, 206g
(2X 10-3 mol) Eu20s 0.352g (I
X 10-3 mol) (3) BaF2175, Ig (1
, 01 mol) 11aBr2294, 2g (0,99 mol) NaBr O, 208g (2X 10-3 mol) Eu
2(1+ 0.352 g (IX 10-3 mol) (4)
BaF2 177, Ig (1,01 mol)' BaB
r2・21120329.8g (0.99 mol) NaC
Q 00116g (2X 10-3 mol) Eu20s
O, 352 g (LX 10-3 mol) (5) l1aF
2177.1g (1,01 mol) BaBr2.2H20
329.8 g (0.99 mol) Nal O, 300 g (
2X 10-3 mol) EuF30,418g (2X 1
0-3 mol) (6) BaF2177, ig(1,01
mole) BaBr2294.2g (0.99 mole) NaB
r 000206 g (2X 10-'mol) Eu2(1
+ 0.352g (IX 10-3 mol) (7) Ba
F2 177.1g (1,01 mol) BaBr2・2t
120329.8g (0.99 mol) NaBr O,2
06g (2X 10-3 mol) Eu2(1+ 0.03
52g (IX 10-'mol) (8) BaF2177
．． 1g (1,01 mol) BaBr2294.4g (0,
99 mol) NaBr 000206g (2X 10-'
mole) EuF30.0418 (2X 10-' mole) (
9) BaF2 1fufu, 1g (1.0f mol) Ba
Br2.2H20329.8g (0.99mol) NaB
rO,0206g (2X 10-1 mole)Eu203
0,0352g (LX 10-4 mol) (10) BaF
2184. Ig (1,05 mol) BaBr2.2H20
316.5 g (0.95 mol) NaBr O, 206 g
(2X 10-'mol) Eu20, 0.352g (IX
10-3 mol) (11) BaF2192.9g (1,
1 mole) BaBr2267.4g (0.9 mo)Iy)
NaBr 0.206g (2X 10-3 mol) EuF
+ 0.418 g (2X 10-'mol) then 11 above
Each type of phosphor raw material mixture was packed into a quartz boat and fired in an electric furnace.

Firing is performed using nitrogen gas containing 2% by volume of hydrogen gas at a flow rate of 250.
The reaction was carried out at 850° C. for 2 hours while flowing at 0 cc/min, and then allowed to cool at room temperature.

After pulverizing the obtained baked product using a ball mill,
The particles were passed through a 0 mesh sieve to make the particle size uniform, and each phosphor was obtained.

Next, a radiation image conversion panel was manufactured using the above 11 types of phosphors. Both radiographic image conversion springs 19 were manufactured as follows.

First, add 8 parts by weight of the phosphor to polyvinyl butyral (binder).
A film is formed by dispersing 1 part by weight in a solvent containing equal amounts of acetone and ethyl acetate, applying it uniformly onto a horizontally placed polyethylene terephthalate film (support) using a wire bar, and allowing it to dry naturally. Thickness is about 3
A radiation image conversion panel of 00- was created.

These 11 types of radiation image conversion panels were irradiated with X-rays for 0.1 seconds at a tube voltage of 80 KVp and a tube current of 100 m at a distance of tooC from the X-ray tube focal point, and then
-Ne laser light (633 nm) was used to excite it, and the fluorescence due to stimulation emitted from the phosphor layer was measured with a photodetector.

As a result, as shown in Table 1 below, the emission brightness due to stimulation of these radiation image conversion panels was as follows:
' ((X) '((X)X'
) is more sensitive than the conventional radiation image conversion method that uses only a radiation image conversion panel.

Table-1 p[(a)x]...-BaF2-aB1@・xN
aX:yEu"Pt(X)X']...BaFX
@XNaX′:yEu2+

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the stimulated emission spectrum of the phosphor according to the present invention. FIG. 2 shows the phosphor P ((0,
95) Br) is a diagram showing the relationship between excitation light wavelength and stimulated luminescence brightness. FIG. 3 is a diagram showing the above relationship in a P C (1,05)Br) phosphor that is outside the scope of the phosphor according to the present invention. Figure w54 is P ((a) Br
) It is a figure which shows the relationship between the a value of a fluorescent substance, and luminance. FIG. 5 is a schematic block diagram for explaining the present invention in detail. 11...Radiation generating device 12...Subject 13...
・Radiation image conversion panel 14...excitation light source agent
Patent Attorney Field 1) Legal Parents' Law (PRR) ) 5 Figure 4 Ig IF, +6 1'7

Claims (3)

[Claims] (1) A stimulable phosphor containing a divalent europium-activated composite halide phosphor represented by the following general formula (I) is made to absorb radiation transmitted through a copying material, and the phosphor is
A method for converting a radiation image, which comprises exciting the phosphor with electromagnetic waves in the range of 700 nm to emit radiation energy stored in the phosphor as fluorescence, and detecting the fluorescence. General formula [■] BaF2-aBra-xNaX:yEu'' [wherein, X represents at least one of chlorine, bromine and iodine, a,
x and y represent numerical values that are 04.9≦a<1.0<x≦10”1 and o<y≦2×10°1.] (2) a in the general formula CI) is 0.95≦a<1
．． 0. The radiation image conversion method according to claim #1, characterized in that: 0. (3) The radiation image conversion method according to claim 1 or 2, wherein the electromagnetic wave is a laser beam.