JPS6144988A - Radiation image conversion method - Google Patents

Abstract

PURPOSE:To provide the titled method which is highly sensitive as compared with prior arts, by allowing a radiation passed through a material to be absorbed by a storing phosphor, exciting the phosphor with electromagnetive waves to release the stored radiation energy as fluorescence and detecting the fluorescece. CONSTITUTION:A radiation passed through a material is allowed to be absorbed by a storing phosphor contg. a rare earth element-activated composite halide phosphor of the formula (where X, X' are the different groups and each is Cl, Br, I; MI is an alkali metal; MII is an alkaline earth metal; MIII is Al, Ga, Y, La, Lu; Ln is Eu, Ce, Tb; 0.6<=a<=1.4, 0<=b<=4, 0<=c<=4, 0<=d<=0.5, 0<=e<=0.2). The phosphor is irradiated with electromagnetic waves in the wavelength region of visible light and/or infrared rays (450-1,100nm) of release radiation energy stored in the phosphor as excited fluorescense which is then detected. A radiation image conversion method which is highly sensitive as compared with methods using conventional light-stimulable phosphor, can be provided.

Description

[Detailed description of the invention]

(Industrial Application Field) This invention relates to a radiation image conversion method, and more specifically to a radiation@image conversion method using a phosphor that accumulates. (Prior Art) Conventionally, a so-called radiographic method using tin salt has been used to obtain a radiographic image, but a method of imaging a radiographic image without using a tin salt has become desirable. 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 radiation image is converted using a thermofluorescent phosphor as the phosphor and thermal energy as the excitation energy (British Patent No. 1,462,76.9).
No. and Japanese Patent Publication No. 51-29889). 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 and accumulates radiation energy corresponding to the intensity of the radiation, and then The accumulated radiation energy is extracted as a light signal, and an image is obtained 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 has heat resistance and will not be deformed or deteriorated by heat. There are major restrictions on the materials of the photofluorescent layer and the support. The radiation image conversion method using a thermofluorescent phosphor as the phosphor and using thermal energy as the excitation energy has major drawbacks in terms of application. On the other hand, a method of converting a radiation image using a panel having a stimulable phosphor layer formed on a support and using one or both of visible light and infrared rays as excitation energy is also known. (U.S. Pat. No. 3,895,52
No. 7). 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 No. 58-109897, there is at least one of the compositional formula %I, and X and y are each 0 (a number satisfying the conditions x≦lO and 0<y≦0.2). ) The divalent europium-activated complex shown in
The radiation transmitted through the object is absorbed by a storage phosphor including a fluoride phosphor, and then this phosphor is excited with electromagnetic waves in the wavelength range of 450 to 1100 nm to cause the phosphor to accumulate. A radiation-to-image conversion method is described which is characterized in that the radiation energy contained in the image is emitted as fluorescence and the fluorescence is detected. By the way, when the radiation image conversion method is used for X# image conversion for the purpose of medical diagnosis, it is desirable that the method be as sensitive as possible in order to reduce the radiation dose to the patient, and therefore It is desirable that the luminance of light emitted by the stimulable phosphor #'i is as high as possible. From this point of view, the above BaFX-xNaX'
: It is desired that the radiation image conversion method using a photoluminescent phosphor such as yEu''10 has the same sensitivity as the same due to the same emission brightness due to the stimulation of the phosphor. (Objective of the Invention) This book The invention involves absorbing the radiation transmitted through the object into a storable phosphor, and then exciting the phosphor with electromagnetic waves in the range of tunable light and/or infrared (450 to 11l100n) to emit this fluorescent light. In a radiation image conversion method in which radiation energy accumulated in the body is emitted as fluorescence and this fluorescence is detected, the conventional BaFX-xNaX'
: ) The object of the present invention is to provide a highly sensitive radiation-image conversion method using a phosphor that exhibits stimulated luminescence with higher brightness than a photoluminescent phosphor such as FE11'2+ as a storage phosphor. shall be. (Structure of the Invention) The object of the present invention described above 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 an object, After that, the phosphor is scanned and irradiated with electromagnetic waves in a wavelength range of 450 to 1]00 nm, the radiation energy accumulated in the phosphor is emitted as excitation fluorescence, and the excitation fluorescence is detected. This is accomplished by a radiographic image conversion method. General formula [I] BaX2 ・aBaX'2 ・bMIF-cMIIFl
・dMmFl: In the eLn formula, X and X' are chlorine,
At least one of bromine and iodine, and X and X
′ are different from each other. MI is at least one alkali metal selected from the group consisting of Lt, Na, K, Rb and CB. MII is at least one alkaline earth metal selected from the group consisting of Mg, Ca, Sr and Be. MlnHLll, Ga, Y, Lll and Lu
There is at least one keyaki selected from Seishingun Yori. Ln represents at least one of Eu, Ce and Tb. Also, a, b, c, d and e, each 0.6≦a≦1.4.
0≦b≦4.0≦C≦4, O≦d≦0,5, and 0≦e
This is a numerical value that satisfies the condition of ≦0.2. The phosphor according to the present invention is manufactured, for example, by the manufacturing method described below. First, as the phosphor raw material, for example, at least one of I) barium chloride (B, c7!2), II)-Its barium (BaBr2) and dihydrate barium bromide (BaBr2.2H20); ) Lithium fluoride (LiF), strontium fluoride (S
rF2) and aluminum fluoride (An), and
aX'bMIF-CMnF, ・dMmF, : eL
X and X' are changed to CA', Br so as to have a mixed composition n.
and a.
, b, c, d and e each indicate 0.6≦a≦1.
4.0≦b≦4.0≦C≦4.0≦d≦0.5 and 0
The ingredients are weighed so as to satisfy the condition ≦e≦0.2, and thoroughly mixed using a mortar, ball mill, mixer mill, etc. Next, the obtained phosphor raw material mixture is filled into a heat-resistant container such as a quartz crucible or an aluminum crucible, and fired in an electric furnace. The firing temperature is preferably 600 to 100°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., 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 neutral nitrogen gas atmosphere or an argon gas atmosphere. In addition, after firing a batch under the above firing conditions, the fired product was taken out of the electric furnace, left to cool, and then pulverized.The fired product powder was then filled into a heat-resistant container again, placed in the electric furnace, and fired in the same manner as above. The luminance of the phosphor can be further increased by re-firing it under certain conditions. The phosphor of the present invention is obtained by processing by various commonly employed operations.The phosphor of the present invention obtained by the manufacturing method described above is irradiated with radiation such as Tri
When excited by electromagnetic waves in the range of 0 to 1]00 nm, it emits near-ultraviolet light. The emission brightness due to its stimulation is stronger than that of the conventional bright phosphor described in JP-A No. 58-109897, and therefore, the radiation image conversion of the present invention using the phosphor of the present invention The method is more sensitive than conventional radiographic image conversion methods using fluorophores. FIG. 1 illustrates the emission spectrum due to stimulation of the phosphor according to the present invention. After irradiating tube 1 with X-rays at a pressure of 80 KVp, the phosphor is exposed to He-Ne laser light (633 KVp).
This is the emission spectrum measured by excitation at 1 nm). Although it varies slightly depending on the composition of the phosphor, 211:
The phosphor according to the present invention used in the radiation image conversion method of the present invention exhibits near-ultraviolet light emission as shown in FIG. 1 upon stimulation. Figure 2 illustrates the excitation spectrum of the phosphor according to the present invention, and the excitation spectrum of the phosphor according to the invention measured using a sample irradiated with X-rays with a tube voltage of 80 KVp. It is a spectrum. As is clear from FIG. 2, the wavelength range in which the phosphor according to the present invention can be excited varies slightly depending on the composition of the phosphor, but generally it is from 450 to 450, which is approximately the same as the result shown in FIG. 2. 900 nm, and the optimal excitation wavelength is 5
The wavelength is 50 to 850 nm. In the method of the present invention, a light source in the wavelength range of 450 to 900 nm can be used as an excitation light source for emitting the radiation energy accumulated in the phosphor layer as fluorescent light. Since the optimal excitation wavelength of the fluorophore is between 550 and 850 nm,
More preferred is a light source that emits light at 50 nm. Higher excitation energy can be obtained by using laser light as the excitation light source, such as He-No laser (633 nm),
YAG laser (second harmonic 532nm), ruby laser (694nm), Ar+ laser (514.5nm)
, a light source emitting light of a single wavelength, such as a semiconductor laser, is used. Since the phosphor of the present invention efficiently emits even excitation light of around 800 Hm, it is preferable to use it as a semiconductor laser in order to make the device smaller and lower in price. The phosphor of the present invention has the following advantages in addition to being able to emit high-intensity stimulated light using the above-mentioned light source. After irradiating a radiation image with excitation light and reading a radiation image, the radiation image conversion panel is generally subjected to light irradiation or heat treatment to erase any remaining afterimages, but in the method of the present invention, fluorescent light is used as the light source. Since a halogen lamp or a tungsten lamp can be preferably used in addition to a light lamp, it is possible to shorten the afterimage erasing time. The radiation image conversion method of the present invention will be specifically explained using schematic diagrams. In Figure 3

[1 is the radiation generator, 12 is the subject,
I3 is a radiation image conversion panel having a visible to infrared stimulable phosphor layer containing a phosphor represented by the general formula CI), and 14 is a radiation image conversion panel that emits the latent radiation image of the radiation image conversion panel 13 as fluorescent light. 15 is a photoelectric conversion device that detects the fluorescence emitted from the radiation image conversion panel 13; 6 is a device that reproduces the photoelectric conversion signal detected by the photoelectric conversion device 15 as an image; 17 is a reproduction device; A device 18 for displaying the image is a filter that cuts out the reflected light from the light source 14 and transmits only the light emitted from the radiation image conversion panel 13. Photoelectric conversion device 15
Thereafter, any device may be used as long as it can reproduce the optical information from the panel 13 as an image in some form, and is not limited to the above. 5 to 7 as shown in Figure 3. When the subject 12 is placed between the radiation generator 11 and the radiation image conversion panel [3] and irradiated with radiation, radiation? fs is transmitted according to changes in the radiation transmittance of each part of the subject 12, and the transmitted image (
In other words, the image of the intensity of radiation) is the radiation image conversion panel 1
3. This incident transmitted image is absorbed by the phosphor layer of the radiation image conversion panel 3, and a number of electrons and/or holes are generated in proportion to the amount of radiation absorbed in the phosphor layer. An accumulated image of radiographic images (a kind of latent image) that is placed at the trap level of the body
is formed. This latent image is then excited with light energy to make it noticeable. That is, the phosphor layer is irradiated with light tri 14 emitting light of 450 to 400 nm to drive out electrons and/or holes accumulated at the trap level, and the accumulated image is emitted as fluorescent light. The intensity of this emitted fluorescent light is proportional to the number of accumulated electrons and/or holes, that is, the intensity of radiation energy absorbed by the phosphor layer of the radiation image conversion panel 13, and this optical signal is For example, it is converted into an electrical signal by a photoelectric conversion device 15 such as a photomultiplier tube, reproduced as an image by an image processing device 16, and this image is displayed by an image display device 17. It is more effective to use an image processing device 16 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. 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 from the fluorescent light emitted from the phosphor layer, and the photoelectric converter that receives the fluorescent light emitted from the phosphor layer generally uses light with a short wavelength of 600 nm or less. It is desirable that the fluorescent light emitted from the phosphor layer has a spectral distribution in as short a wavelength region as possible because of the high sensitivity to energy. The emission wave range of the phosphor used in the method according to the present invention is 350 to 450 nm.
On the other hand, since the excitation wavelength range is from 450 nm to 00 nm, the above conditions are satisfied at the same time. That is, all of the phosphors used in the present invention are 4
It emits light with a main peak at 50 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. (Example) Next, the present invention will be explained with reference to an example. After weighing each of the phosphor raw materials as shown in hl to (14) below, they were thoroughly mixed using a ball mill to prepare 11 types of phosphor raw material mixtures. (1) BaCd2・208.3,9 (1 mol
)BaBr2297.2g (1mol)Eu2030
0.35'2g (I XtOmol) (2) Ba
C1t208.25g (1mol) BaI, 391
．． 2. ji' (1 mol) -EuC130,51
711 (2XIOmol) (3) BaBr2・2
H20333, 2g (1 mol) BaI2391.2p
(1 mol) Eu403 0.352 g (IXIO
mol) (4) Ba(J, 208.3p(1m
'ol)BaBr2297.29 (1mol)Li
Br 86.8,9 (1 mol) EuC110
,5179(2XIOmol)(5) BaC1t
208.3Ji' (1 mol) BaBr2・2H203
33,2Ji' (1 mol) NaF 42. O
fj (1 mol) Eu203 0.3529 (1x
to mol ) (6) Ba(Jt 208.
3g (1mol) BaI, 391.2.9 (1m
ol ) KF 58.1.9 (1 mol ) E
u203 0. :(52,9(IXIOmol)(7
) BaBr2・2H20333, 2g (1mol
)HaI, 391.2. ) i' (1 mol)
RbF 104.5g (1mol) Eu20g
0.352.9 (IXIOmol) (8) Ba
C71t208.3. ! il (1 mol) BaBrt・
2H10333, 2g (1 mol) CsF 15
1.9. +9 (1mol)Euto3 0.352
, ji' (I XIQ mol) (9)
BaC7+2 208.3.9 (Lmol)BaI
2 391.2. ! ii' (1 mol) CaF2
78.089 (1 mol) BuvOs 0.3
52g (I XIOmol) (10) BaBr
t2Ht0333.2Ii (1 mol) B=I,
391.21! (1 mol) MgFz 62.3
Ji' (1 mol) Eu203 0.3529
(I Xl0-3"') (11) BaCAt
208.3'jj (1mol)BaBr2・2
H20333,2J$ (1mol)SrF2 1
25.6. li' (1 mol) Eu2030.35
2! j (I XIOmol) (12) BaBr
2・2H20333,2,li' (1 mol) Bal
, 391.2g (1mol) YF, 14
．． 6 g (0.1 mol) Euz03 0.3529
(I XLOmol) (13) BaCl2
208.3 g (1 mol) BaBrl H2H20
333.2g (1mol) Ce203 0.3289(
IXlOmol ) (14) BaC7+2 20
8.3 g (1 mol) BaBr2・2H1033
3.2 g (1 mol) LiF 25.9. +7
(1 mol) SrF2 125.6.9 (1 mol)
klFs 8.40 i (I XIOmol)
Eu203 0.352Ji'(IXIQ mol
) Next, each of the above 14 kinds of phosphor raw material mixtures was packed into a quartz boat and fired in an electric furnace. Firing is performed using an electronic gas containing 2% by volume of water 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 the following 14 types of phosphors were obtained. Next, radiation image storage panels were manufactured using the 14 types of phosphors described above. Both radiographic image conversion/cinels were manufactured as follows. (1) BaCl2・BaBr2 H2XlOBu (
2) BaC7+2・BaI2・2X10 Eu(
3) BaBr2・BaI2・2Xl, OEu(
4) BaCl2・BaBr, -LiBr2XIQ
Eu(5) BaCl2-BaBr, ・NaF・2
XlOEu(6) BaClt-Ba12・kF・
2XIOEu(7) BaBr2・Ba11・RbF
・2XlOEu(8) BaCl2・BaBr2・
CsF・2XIOEu(9) BaCl2・BaI,
・CaF2・2XIOEu(10) BaBr2-B
aI2・MgF2・2X10 Eu(11) Ba
Cl2・BaBr2・SrF2・2XLOEu(12)
BaBr2・BaI2・0. lYF32X10
Eu(13) BaC/, HBaBr212
XIOCA' (14) BaCA! 2.BaBr,・
LiP”-8rF,・0.IA7!F3・2XlO-'
A part of the mass phosphor 8-layer noodles was dispersed in a polyvinyl butyral (binder) lit part using a solvent mixed with equal amounts of acetate and ethyl acetate, and this was placed horizontally and the white pigment titanium oxide was kneaded. A radiographic image conversion panel having a film thickness of about 300 μm was prepared by uniformly coating the polyethylene terephthalate film (support) using a wire bar and drying it naturally. These 14 types of radiation image conversion panels were irradiated with X-rays at a tube voltage of 5 oicvp and a y-current of 100 mA for 0.1 seconds at a distance of +oocm from the X-ray tube focal point, and then excited with semiconductor laser light (800 nm). Fluorescence due to photostimulation emitted from the phosphor layer was measured with a photodetector. As a result, the emission brightness due to exhaustion of these radiation image conversion panels is as shown in Table 1 below. The radiation brightness is higher than that of the panel due to starvation, and therefore the radiation image conversion method of the present invention using the radiation image conversion panel has higher sensitivity than conventional radiation image conversion methods. Table-1

[Brief explanation of the drawing]

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 excitation wavelength and 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 surface image conversion panel 14... Stimulation excitation light source 15... Photoelectric conversion device 18... Filter agent Patent attorney Field 1) Parent-in-law Figure 1 Tortoise liquid length (h…)

Claims (1)

[Scope of Claims] A stimulable phosphor containing a rare earth element-activated composite halide phosphor represented by the following general formula [I] is made to absorb radiation transmitted through a copying material, and then the phosphor is 450 to
A radiation image conversion method comprising scanning and irradiating electromagnetic waves in a wavelength range of 1100 nm to 1100 nm, causing the phosphor to emit the accumulated radiation energy as excitation fluorescence, and detecting the excitation fluorescence. General formula [I] BaX_2・aBaX′_2・bMIF・cMIIF_
2.dMIIIF_3:eLn [wherein x and X' are at least one kind of chlorine, bromine, and iodine, and X and X' are different from each other. MI is at least one alkali metal selected from the group consisting of Li, Na, K, Rb and cs. MII is at least one alkaline earth metal selected from the group consisting of Mg, Ca, Sr, and Be. MIII is at least one selected from the group consisting of AL, Ga, Y, La, and Lu. Ln represents at least one of Eu, Ce and Tb. Also a, b, c
, d and e are 0.6≦a≦1.4, 0≦b≦4, respectively.
These are numerical values that satisfy the following conditions: 0≦c≦4, 0≦d≦0.5, and 0≦e≦0.2. ]