JPS60141782A - Conversion of radiation image - Google Patents

Abstract

PURPOSE:To obtain radiation image for medical diagnosis with a small exposed dose, by absorbing radiation transmitted through a subject in a specific fluorescent substance of alkaline earth metal phosphate activated with Eu<2+>, irradiating the fluorescent substance with electromagnetic wave, releasing accumulated radiation energy as stimulation light, detecting it. CONSTITUTION:Radiation transmitted through a subject or emitted from a test specimen is absorbed in a fluorescent substance (e.g., compound shown by the formula II, etc.) of alkaline earth metal phosphate activated with bivalent europium shown by the formula I [MII is Ca, Sr, or Ba; 0<x<=0.2 (x is preferably number value of 10<-5>-10<-2>)]. The fluorescent substance is irradiated with electromagnetic wave at 450-900nm (preferably laser beam of Ar ion), and radiation energy accumulated in the fluorescent substance is released as stimulation light. The stimulation light is detected.

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 an alkaline earth metal phosphate phosphor activated with divalent europium. It is something.

Traditionally, the so-called radiographic method, which uses a combination of a radiographic film having an emulsion layer made of a silver salt photosensitive material and an intensifying screen, has been used to obtain a radiographic image as an image. There is.

On the other hand, in recent years, as an alternative to the radiographic method described above, a radiation image conversion method using a stimulable phosphor, as described in Japanese Patent Application Laid-open No. 55-12145, has been developed. developed and receiving attention. This method involves absorbing radiation transmitted through the subject or radiation emitted from the subject into a stimulable phosphor, and then exciting this phosphor with electromagnetic waves (excitation light) such as visible light or infrared light. This causes the radiation energy stored in the phosphor to be emitted as fluorescence (stimulated luminescence), and this fluorescence is read photoelectrically to produce an electrical signal fU, which is then visualized.

The above radiographic image conversion method has the advantage that a radiographic image rich in information can be obtained with a much lower exposure dose than when conventional radiography is used. Therefore, this radiation image conversion method has a very high utility value especially in direct medical radiography such as X-ray photography for the purpose of medical diagnosis.

In the radiation image conversion method described above, a stimulable phosphor is used which emits light (stimulated luminescence) upon excitation of electromagnetic waves in the visible to infrared region after being irradiated with radiation such as X-rays. Conventionally, such stimulable phosphors include divalent europium-activated alkaline earth metal fluoride halide phosphors (
M"FX: Eu2+; However, Mll is at least one kind of alkaline earth metal selected from the group consisting of Mg, Ca and Ba, and X is at least one kind of halogen selected from the group consisting of O, Br and I. -1-Ropium and samarium activated lanthanum oxysulfide phosphor (La202S:
Eu, Sm); -L-ropium activated barium aluminum oxide phosphor (B a O・A fL203: Eu
); europium-activated alkaline earth metal silicate phosphor (M'0.5i02:Eu; however, M2+ is Mg
, at least one alkaline earth metal selected from the group consisting of Ca and Ba); cerium-activated rare earth oxyhalide phosphor (LnOX:Ce;
n is at least one kind of rare earth element selected from the group consisting of La, Y, Gd and Lu, and X is at least one kind of halogen selected from the group consisting of C1, Br and I).

An object of the present invention is to provide a radiation image conversion method using a novel stimulable phosphor.

The present inventor has been searching for a stimulable phosphor, and as a result, discovered that an alkaline earth metal phosphate phosphor newly activated with divalent europium exhibits stimulable luminescence. This invention has been achieved.

That is, the radiation image conversion method of the present invention absorbs radiation transmitted through a subject or emitted from the subject into a divalent europium-activated alkaline earth metal phosphate phosphor represented by the following compositional formula CI). After that, by irradiating the phosphor with electromagnetic waves in the wavelength range of 450 to 900 nm, the radiation energy stored in the phosphor is released as photostimulated light, and this photostimulated light is detected. Features.

Compositional formula (I): M"3 (PO4)2 : xEu2+ (I) (where MI[ is at least one alkaline earth metal selected from the group consisting of Ca, Sr and Ba; X is O
<x≦0.2)” Bivalent europium-activated alkaline earth metal phosphate phosphors, which are represented by the bipedal composition formula (I), have conventionally been shown to exhibit visible light when excited with radiation such as ultraviolet rays. Fluorescence in the area (instantaneous luminescence)
is known to show.

According to the studies of the present inventors, it was newly discovered that the foot-light body exhibits fluorescence when excited with electromagnetic waves in the wavelength range of 450 to 900 nm after being irradiated with radiation such as X-rays. That is, this phosphor is a stimulable phosphor and exhibits stimulated luminescence under the above conditions, so it can be used in a radiation image conversion method.

Next, the present invention will be explained in detail.

The schematic diagram shown in FIG. This will be explained in detail.

In FIG. 1, 11 is a radiation generating device such as an X-ray;
2 is a subject, 13 is a radiation image conversion panel containing divalent europium-activated alkaline earth metal phosphate phosphor, 1
Reference numeral 4 denotes a light source as an excitation source for emitting the image of accumulated radiation energy on the radiation image conversion panel 13 as fluorescence; 15 a photoelectric conversion device for detecting the fluorescence emitted from the radiation image conversion panel 13; and 16 a photoelectric conversion device. 17 is a device for displaying the reproduced image; and 18 is a radiation image conversion panel 1 that does not transmit the reflected light from the light source 14.
This is a filter that allows only the fluorescence emitted from No. 3 to pass through.

Although FIG. 1 shows an example of obtaining a radiographic image of a subject, the subject 12 itself may emit radiation (
In this specification, this is referred to as a subject), there is no particular need to install the radiation generating device 11 described above. Furthermore, the series of devices including the photoelectric conversion device 15, the image reproducing device 16, and the image display device 17 may be replaced with other suitable devices that can visualize and reproduce the image information emitted as fluorescence from the radiation image conversion panel 13 in some form. You can also change it.

As shown in FIG. 1, when a radiation generator 11 irradiates a subject 12 with radiation such as X-rays, the radiation passes through the subject 12 in proportion to the radiation transmittance of each part of the subject 12. The radiation transmitted through the subject 12 enters the radiation image conversion panel 13 and is absorbed by the phosphor layer of the radiation image conversion panel 13 in proportion to the intensity of the radiation. That is, an S-product image (a kind of latent image) of radiation energy corresponding to a radiation transmission image is formed on the radiation image conversion panel 13J2.

Next, using the light source 14 on the radiation image conversion panel 13,
When irradiated with electromagnetic waves in a wavelength range of 0 to 900 nm, the accumulated radiation energy image formed on the radiation image conversion panel 13 is emitted as fluorescence. The emitted fluorescence is proportional to the intensity of the radiation energy absorbed by the phosphor layer of the radiation image conversion panel 13. Image information composed of the intensity of this fluorescence is converted into an electrical signal by a photoelectric conversion device 15 such as a photomultiplier tube, reproduced as an image by an image reproduction device 16, and this image is displayed by an image display device 17. do.

The operation of reading out the image information accumulated in a radiation image conversion panel as fluorescence is generally performed by scanning the panel in time series with a laser beam, and by photoelectron amplification of the fluorescence emitted from the panel through an appropriate light condenser. This is done by detecting with a photodetector such as a multiplier tube and obtaining time-series electrical signals.

In order to obtain an image with better observation and interpretation performance, this readout may consist of a pre-reading operation by irradiating low-energy excitation light and a main-reading operation by irradiating high-energy excitation light (JP-A-58 (Refer to Publication No.-67240). By performing this pre-read operation, there is an advantage that the read conditions for the main read operation can be suitably set.

Furthermore, solid photoelectric conversion elements such as photoconductors and photodiodes can also be used as photoelectric conversion devices (Japanese Patent Application No. 58-86226, Japanese Patent Application No. 58-862).
No. 27, Japanese Patent Application No. 1983 [filed on November 21, 1982 (3)] and Japanese Patent Application No. 1983 [November 2, 1982]
1-day application (4)] and JP-A-58-12
(See Publication No. 1874). In this case, a large number of solid-state photoelectric conversion elements may be configured to cover the entire surface of the panel, and may be integrated with the panel, or may be arranged in close proximity to the panel. Further, the photoelectric conversion device may be a line sensor in which a plurality of photoelectric conversion elements are connected in a linear manner, or may be composed of one solid-state photoelectric conversion element corresponding to one pixel.

In addition to a point light source such as a laser, the light source in the above case may be a line light source such as an array of light emitting diodes (LEDs), semiconductor lasers, etc. By performing readout using a suitable device, it is possible to prevent loss of fluorescence emitted from the panel, and at the same time, increase the solid angle of light reception and increase the S/N ratio. Further, since the obtained electrical signal is converted into a time series by electrical processing of a photodetector rather than by time-series irradiation of excitation light, it is possible to increase the readout speed.

The radiation image conversion panel from which the image information has been read is erased by irradiating it with light in the wavelength range of the excitation light of the phosphor or by heating it to erase the remaining radiation energy. It doesn't matter, and it's preferable to do so (Japanese Patent Laid-Open No. 56-1
1392 and JP-A-56-12599)
. By performing this erasing operation, it is possible to prevent noise from occurring due to afterimages when the panel is used next time. Furthermore, by performing the erasing operation twice, once after reading and immediately before the next use, it is possible to prevent the generation of noise due to natural radioactivity and perform the erasing more efficiently (Japanese Patent Laid-Open No. 116300/1983). (see official bulletin).

In the radiation image conversion method of the present invention, the radiation used to obtain a radiation transmission image of the subject is such that the phosphor exhibits stimulated luminescence when excited by the electromagnetic waves after being irradiated with the radiation. Any type of radiation may be used as long as it is transparent, and for example, commonly known radiation such as X-rays, electron beams, and ultraviolet rays can be used. Further, when obtaining a radiation image of the subject, the radiation directly emitted from the subject may be any radiation that is similarly absorbed by the phosphor and serves as an energy source for stimulated luminescence. Example 2 Examples include radiation such as gamma rays, alpha rays, and beta rays.

As a light source of excitation light for exciting the phosphor that has absorbed radiation from the subject or the subject, 450 to 900
In addition to light sources that emit light with a band spectral distribution in the nm wavelength region, for example, Ar ion laser-1He
-Ne laser, Luhi laser, semiconductor laser,
Lasers such as glass lasers, YAG lasers, Kr ion lasers, 1 dye lasers, and light sources such as light emitting diodes can also be used. Among these, various lasers are preferable as the excitation light source used in the present invention, since lasers can irradiate a radiation image conversion panel with a laser beam having a high energy density per unit area. Among these, preferred lasers are Ar ion lasers and Kr ion lasers from the viewpoint of matching with the stimulated excitation spectrum of divalent europium-activated alkaline earth metal phosphate phosphors. In addition, semiconductor lasers are small, require low driving power,
It is preferable as an excitation light source because direct modulation is possible and the laser output can be easily stabilized.

Further, the light source used for erasing may be any light source that emits light in the excitation wavelength range of the stimulable phosphor, and examples thereof include a tungsten lamp, a fluorescent lamp, and a halogen lamp.

The radiation image conversion method of the present invention includes: a storage section that absorbs and stores radiation energy in a stimulable phosphor; a photodetection (readout) section that irradiates the phosphor with excitation light and emits the radiation energy as fluorescence; It can also be applied to a built-in type radiation image conversion device in which an erasing section for emitting energy remaining in the phosphor is built into one device (Japanese Patent Application No. 57-84436 and Japanese Patent Application No. 58-6
6730 specification). By using such a built-in device, the radiation image conversion panel (or the recording material containing the stimulable phosphor) can be reused and a stable and homogeneous image can be obtained. can.

Further, by using a built-in type, the device can be made smaller and lighter, and its installation and movement become easier. Furthermore, by mounting this device on a mobile vehicle, it becomes possible to carry out circular radiography.

Next, a stimulable phosphor having the following compositional formula (I) used in the radiation image conversion method of the present invention will be described.

Ml3 (PO4)2 : xEu'' (I) (where M'' is at least one alkaline earth metal selected from the group consisting of Ca, Sr and Ba; X is O<x
≦0.2) The divalent europium-activated alkaline earth metal phosphate phosphor represented by the above composition formula (I) is, for example,
It can be manufactured as follows according to the manufacturing method disclosed in Japanese Patent Publication No. -22411.

As raw materials for the phosphor, 1) alkaline earth metal hydrogen phosphate, 2) alkaline earth metal carbonate, and 3) europium compounds such as halides, oxides, nitric salts, and sulfates are used. After weighing and mixing in an amount that stoichiometrically corresponds to the composition formula (n) Ml3 (POa) z : xE u (I[) (however, the definitions of Ml and X are the same as above), a small amount In a weakly reducing atmosphere such as a nitrogen gas atmosphere containing hydrogen gas, or a carbon dioxide atmosphere containing -carbon oxide, 500
Bake at a temperature of -1300°C for 0°5-6 hours. Above 3
) When a trivalent europium compound is used as a phosphor raw material, the trivalent europium is reduced to divalent europium in the firing process.

A powdered phosphor is obtained by the above baking process, but the obtained powdered phosphor is further subjected to various general operations in the production of phosphors, such as washing, drying, and sieving, as necessary. It's okay, though.

The divalent europium-activated alkaline earth metal phosphate phosphor represented by the above compositional formula (I) fluoresces (fluoresces) when excited with electromagnetic waves in the wavelength range of 450 to 900 nm after being irradiated with radiation such as X-rays. The peak wavelength is approximately 420 nm.

FIG. 2 shows a divalent europium-activated barium phosphate phosphor [
B a 3 (POa) z: E u2+] d,
The stimulated emission spectrum obtained when the tube was irradiated with X-rays at a tube voltage of 80 KVp and then excited with Ar ion laser light (514.5 nm) is shown.

FIG. 3 shows the photostimulation excitation spectrum at the peak wavelength of one emission when the divalent europium-activated barium phosphate phosphor is irradiated with X-rays at a tube voltage of 80 KVp and then excited with excitation light of different wavelengths.

According to experiments conducted by the present inventor, the stimulated emission spectrum and stimulated excitation spectrum of the phosphors of the present invention other than the divalent europium-activated barium phosphate phosphor described above are as follows: It has been confirmed that they are similar.

In the divalent europium-activated alkaline earth metal phosphate phosphor, from the viewpoint of stimulated luminescence brightness, Ml in the composition formula (I) is preferably Ba, and X is 10''≦X≦
Preferably, the value is in the range 10'''2.

The divalent europium-activated alkaline earth metal phosphate phosphor used in the radiation image conversion method of the present invention is generally used in the form of being contained in a radiation image conversion panel. This radiation image storage panel is essentially composed of a support and a phosphor layer provided on the support and comprising a binder containing and supporting a stimulable phosphor in a dispersed state.

The radiation image conversion panel having the above configuration is, for example,
It can be manufactured by the method described below.

First, the above-mentioned stimulable phosphor particles and binder are mixed in a suitable solvent (
For example, a lower alcohol, a chlorine-containing hydrocarbon, a ketone, an ester, an ether) are added thereto and thoroughly mixed to prepare a coating solution in which the stimulable phosphor is uniformly dispersed in the binder solution.

Examples of binders include binders typified by proteins such as gelatin, synthetic polymeric substances such as polyvinyl acetate, nitrocellulose, polyurethane, polyvinyl alcohol, polyalkyl (meth)acrylate, and linear polyester. be able to.

The mixing ratio of the binder and the stimulable phosphor in the coating solution is usually selected from the range of 1:8 to 1:40 (weight ratio).

Next, this coating liquid is uniformly applied to the surface of the support to form a coating film of the coating liquid, and then this coating film is dried to complete the formation of the phosphor layer on the support. The thickness of the phosphor layer is generally between 50 and 500 gm.

As a support, an intensifying screen (
or an intensifying screen) or a variety of materials used as supports for known radiation image conversion panels. Examples of such materials include films of plastic materials such as cellulose acetate, polyethylene terephthalate, metal sheets such as aluminum foil, ordinary paper, baryta paper, resin-coated paper, and the like. Note that an adhesion-imparting layer, a light-reflecting layer, a light-absorbing layer, etc. may be provided on the surface of the support on which the phosphor layer is provided.
As described in Japanese Patent No. 82431, fine irregularities may be uniformly formed (these irregularities may be formed on the surface of the support on the phosphor layer side by an adhesion imparting layer, a light reflecting layer, a light reflecting layer, etc.). (If an absorbent layer etc. is provided, it is formed on its surface).

Furthermore, a transparent protective film for physically and chemically protecting the phosphor layer may be provided on the surface of the phosphor layer opposite to the side in contact with the support. Examples of materials used for the transparent protective film include cellulose acetate, polymethyl methacrylate, polyethylene terephthalate, and polyethylene. The thickness of the transparent protective film is generally 0.1 to 20 m.

0 ft8, a radiation image conversion panel made of a divalent europium-activated alkaline earth metal phosphate phosphor is disclosed in Japanese Patent Application Laid-open No. 1986-
It may be colored with a coloring agent as described in JP-A-163500, JP-A-57-96300, etc., or it may be colored with a phosphor as described in JP-A-55-146447. White powder may be dispersed in the layer.

Next, examples of the present invention will be described. However, this example does not limit the invention.

[Example] 2 mol of barium hydrogen phosphate (B a HP O4),
One mole of barium carbonate (BaCO3) and 5 x 10-'' moles of europium oxide (Eu203) were thoroughly ground and mixed to prepare a phosphor raw material mixture.

This mixture is mixed under a nitrogen gas atmosphere containing a small amount of hydrogen gas.
After firing at a temperature of 1100°C for 2 hours, the resulting fired product was cooled and pulverized to produce a powdered divalent europium-activated barium phosphate phosphor [B a 3 (POa)
2: 0.0015E u”] was obtained.

Next, the stimulated emission spectrum and stimulated excitation spectrum of the phosphor produced as described above were measured. The results are shown in FIGS. 2 and 3.

FIG. 2 is a graph showing the stimulated emission spectrum when a phosphor is irradiated with X-rays at a tube voltage of 80 KVp and then excited with Ar ion laser light (514.5 nm).

FIG. 3 is a graph showing the photostimulation excitation spectrum at an emission wavelength of 420 nm when the phosphor is irradiated with X-rays at a tube voltage of 80 KVp and then excited with excitation light in the wavelength range of 450 to 900 nm.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram illustrating the radiation image conversion method of the present invention. 11: Radiation generator 12: Subject 13: Radiation image conversion panel 14: Light source 15: Photoelectric conversion device 16: Image reproduction device 17: Image display device 18: Filter FIG. divalent europium activated barium phosphate phosphor [Ba3(PO
a) 2:0.0015Eu”] is a graph showing the stimulated emission spectrum of 1.
a) 2:0.0015Eu2+] (7) It is a graph showing the photostimulation excitation spectrum. Patent applicant Fuji Photo Film Co., Ltd. Agent Patent attorney Yasuo Yanagawa 3

Claims (1)

[Claims] l. After the radiation transmitted through the object or emitted from the object is absorbed into the divalent europium-activated alkaline earth metal phosphate phosphor represented by the composition formula (I) below, the phosphor is A radiation image conversion method comprising: emitting radiation energy stored in the phosphor as photostimulated light by irradiating electromagnetic waves in a wavelength range of 900 nm, and detecting this photostimulated light. Composition formula (1): % formula % () (where Mll is at least one alkaline earth metal selected from the group consisting of Ca, Sr, and Ba;
(X is a numerical value in the range of O<x≦0.2) 2. The radiation image conversion method according to claim 1, wherein Ml in the above compositional formula (I) is Ba. 3゜X in the above compositional formula (I) is 10-5≦X≦10
2. The radiation image conversion method according to claim 1, wherein the numerical value is in the range of -. 4. The radiation image conversion method according to claim 1, 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 Kr ion laser beam. 7. Claims 1 to 7, characterized in that the phosphor is used in the form of being contained in a phosphor layer of a radiation image storage panel that includes a support and a phosphor layer provided thereon. The radiation image conversion method according to any one of item 6.