JPS59155487A - Method of radiation image conversion - Google Patents

Abstract

PURPOSE:To highly sensitively accomplish the titled conversion by absorbing radiation which has passed through an object by a specified highly sensitive fluorescent body, discharging the accumulated radiation energy as fluorescent light by exciting the fluorescent body with an electromagnetic wave, and detecting and converting the fluorescent light into an image. CONSTITUTION:After radiation which has passed through an object is absorbed by at least one of a fluorescent body of formula I or II (wherein Re is La, Gd, Y or Lu; A is alkali metal, Ba, Sr or Ca; X and X' are each F, Cl or Br; x is 1X10<-4>-3X10<-1>; y is 1X10<-4>-1X10<-1>; n/m is 1X10<3>-7X10<-1>), the radiation energy accumulated in the fluorescent body is discharged as fluorescent light by exciting the fluorescent body with an electromagnetic wave selected from visible and infrared light, and the fluorescent light is detected and converted into an image. It is possible to effect remarkably high sensitive radiation image conversion.

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 photostimulable phosphor.

(Conventional technology) Conventional radiological images? So-called radiography, which uses silver salts, is used to obtain radiographic images, but in recent years, due to problems such as the depletion of silver resources on a global scale, there has been an increase in the demand for methods of imaging radiographic images without using silver salts. became.

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. 1,462,769).
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 accumulates it by heating this thermofluorescent phosphor layer. The radiation energy is extracted as the original signal, and an image is obtained based on the intensity of this original signal. 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 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 (US Pat. No. 3.85
No. 9,527). 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. However, the phosphors used in this method are only cerium and samarium activated strontium sulfide phosphor (SrS:Ce-8m), europium and samarium activated strontium sulfide phosphor (SrS:
Eu-8m), Ni0bium and samarium activated acid/lanthanum sulfide phosphor (Lat02S: Eu”
Sm), manganese and nitrogen-activated myelinated zinc-cadmium phosphor [(Zn-Cd) S: Mn
-X, where X is /.logen], and the sensitivity of the methods using these fluorophores is extremely low, making it difficult to improve sensitivity from a practical point of view. Improvement is desired.

(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 of visible light and/or infrared rays, so that the phosphor accumulates. The object of the present invention is to provide a practical radiation image conversion method that has extremely high sensitivity in a radiation image conversion method that detects the fluorescent light, which is not emitted as radiation energy.

(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 (I) or revised) has a relative luminescence intensity several thousand times higher than that of conventional photostimulable phosphors in the visible light and infrared regions. It is particularly suitable for radiographic image conversion methods. The radiation transmitted through the subject of the present invention is adsorbed to at least one of the phosphors represented by the following general formula (I) f or...), and then this phosphor is exposed to electromagnetic waves selected from visible light and infrared rays. The radiation energy accumulated by the phosphor is excited by the fluorophore and emitted as fluorescence, and this fluorescence is detected. It is something.

General formula (I) nReX5 @mAXt: Euz
General formula onReXs ・mAX; : Eux・Smy
In the formula, Re is at least one of La + Gd + Y + Lu, A is an alkaline earth metal, Ba, Sr
, at least one of Ca, X and X' are F + C
At least one of I + Br, X is 1 xlO-'
~3 mowing 0-11y is I Xl0-' ~I XIO,V
m represents 1 xlO-" to 7 xlO-1. Re
and A may be composed of two or more types, for example, Yo
, 4Gd0.6, which is expressed as Re (or A) as a sum. Similarly, KX and X' may also be of two or more types, for example, Fl, 2Br1. B or Fo, 9
B r 1.1 indicates something that can be expressed as a sum of X or a stone.

Examples of such compounds include 0.1LaF, 1.0
．． 9BaFIJ': EuO, oOi, 0.1LaF
3*0.9BaF(J: guO,ol,0,I
LaF3m 0.9BaBr: Eu□, oa, 0.
lYF3” 0.9BaF (J: EuO,01,0
, IGdFllIo, 9BaFCl: Eu0.01.
0.3LaFs” 0.7BaFCji! :Euo,
oa, 0. ILaF, 0.9BaFBr: Euo
, ol, 0.1LaFBr, ・0.9BaF□, gB
rl, 1: ELlo, 01, 0.1LaF,,
Fist 0.9SrO, 5BaO, 5FBr: Eu6,
63.0.2LaFII* 0.8(Cao, IBao
, s-Sro, 1) FBr: Euo, oa.

0.2GdF3・0.8(Ca□, 1, Sro, 1
Bao, 5) FBr: EuO, oa, 0.4La (
1.5Luo, 5F, 0.6BaFBr: Euo
, 01.0. IYFs' 0.9BaFBr :EuO
,01,0,2(Yo,4GdO,6)Fl,2Br1
．． 8°0.8BaFBr: Euo, os.

0.3 (Lao, 3. Gdo3Yo, +) 0.7.
BaFBr: Euo, oa, 0.1LaF, 0.
9BaFBr: EuO, oI Smo, oa3.0
゜lGdF3 @0.9BaFBr: EuO, o3
'Smo, oos, 0.1LaF3°0.9BaFB
r: Euo, oox ″Smo, ooo3.0.3
LaFe0.7BaFBr: Euo, oa*S
mo, oos, 0.3LaF3 ”0.7(Sr+),
5Bao, 5) FBr: Euo, o3°Sm0.0
01% Gdo, 2Fm.

0.8(Cao, xSroIBao, a)FBr:
Euo, os lISm(+, ooos, 0.2La
F, @0.8 (CaO11, SrO, IBao, 5)F
Br: Euo, o3@Smo, oot, 0. IL
uF8*BaFBr: Euo, ollSmo, o
oa3.0.4 (La0.5Luo,s)Fg l
IO,8BaFBr:Eu6. ox”Smo,o
oa, 0.3'(Lao, 5Gdo, 3Yo, 4)Fg
・0.7BaFBr: Euo, o318mo, otS
O-2 (YO, 4v Gdo, s) 80.8BaFB
r: EuO, (+5118m0.01, etc.)

In the radiation image conversion method of the present invention, the radiation transmitted through the subject is absorbed by one or more types of phosphors included in the phosphor, and then this phosphor is exposed to visible light. It is characterized in that it is excited by electromagnetic waves such as one or both of infrared and infrared rays to cause the fluorescent material to emit the accumulated radiation energy 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 phosphor containing a phosphor represented by the general formula (I) σJ).
A radiation image conversion panel having a visible or infrared stimulable phosphor layer, 4 is a radiation latent image of the radiation image conversion panel 3?
A light source as an excitation source for emitting fluorescence; 5 is a photoelectric conversion device that detects the fluorescence emitted from the radiation image conversion panel 3; 6 is a photoelectric conversion signal detected by the photoelectric conversion device 5 that is reproduced as an image. 7 is a device for displaying the reproduced image, and 8 is a filter for cutting the reflected light from the light source 4 and transmitting only the source emitted from the radiation image conversion panel 3. The source m conversion device 5 and subsequent devices may be any device that can reproduce the source information from the panel 3 as an image in some form, and are not limited to the above. As shown in FIG. 1, when a subject 2 is placed between the radiation generator 1 and the radiation image conversion panel 3 and irradiated with radiation, the radiation passes through each part of the subject 2 according to changes in radiation transmittance. The image (that is, the image of the intensity of radiation) enters the radiation image conversion pile 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. It accumulates at the trap level of the body. 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, a photoelectric conversion device 5 such as a photomultiplier tube converts it into an electrical signal, an image processing device 6 reproduces it as an image, and an image display device 7 displays this image. 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 stored image as fluorescent light will be explained in detail.

The structure of the radiation image conversion panel 3 is composed of a support 21 and a phosphor layer 22 formed on one side of the support 210, as shown in FIG. 2(a). Needless to say, this phosphor layer n may be composed of one or more types of phosphors included in the above-mentioned phosphors. The phosphor 1 used here
After irradiation with radiation, when excited with electromagnetic waves in the form of visible light and/or infrared rays, strong stimulated luminescence is exhibited, especially when the content of the activating agent is approximately 10-
When it is 4 to 1 gram atom, the photostimulation intensity becomes extremely strong, making it suitable for use as a phosphor layer in these radiation image conversion panels.
Therefore, particularly efficient radiation image conversion can be performed.

As an exemplary compound of the phosphor used in the present invention represented by the general formula CI), 0.1LaF3''0.9B
There is a composition called aFBr:EuO,03, and the stimulated emission spectrum measured for this phosphor is shown in Figure 3.
Figure 4 shows the photostimulated excitation spectrum. The spectrum in Figure 3 shows strong light emission with a peak at 390 nm, and the light emission brightness is comparable to that of conventional SrS:Eu(10-').
It reaches 2000 times that of Sm(10-').

In the method of the present invention, one or both of visible light and infrared light can be used as an excitation light source for emitting the radiation energy accumulated in the phosphor layer as fluorescence, but traps in the region emitted by infrared light It is shallow, and the regression (7-edding) phenomenon is remarkable, so the information storage period is short, and it is not very desirable in practice. For example, when obtaining an image, the phosphor layer of the exposed radiation image conversion channel 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 body layer, 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 as well, the phosphor represented by the general formula (Il, ([1)] used in the radiation conversion method of the present invention has a deep chitrap, and it is preferable to use light with a higher energy source, that is, with a wavelength as short as possible. It is more desirable that the excitation can be carried out efficiently.As shown in Fig. 4, the optimal excitation wavelength range of the phosphor used in the present invention is in the visible and near-infrared light region, and therefore there is little fading and the fluorophore is It has a high ability to accumulate and preserve radiation latent images accumulated in body layers.

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 described above, if the wavelength is too long, the 7-edition is too long, so it is not practical. Instead, the wavelength of excitation t is 1l10
It is preferably 0n or less. In addition, from the viewpoint 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.
If separation is possible by the method shown in No. 744, the method is not limited to this. Specifically, a He Ne laser (632
, 8 nm), YAG laser light (1064 nm), ruby laser (694.3 nm), argon laser, semiconductor laser, and other light sources that emit a single wavelength source are used.

Particularly when a laser source is used, high excitation efficiency can be obtained.

Among the laser sources, 514.5n of Ks Ar ion laser is shown in Japanese Patent Application No. 185086/1986.
Better results are obtained using m oscillation lines.

Or, if prioritizing the miniaturization of the device, a small Ke −
No laser (632.8 nm) is preferred.

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 IX converter that receives the fluorescent light emitted from the phosphor layer generally has a short wavelength of 600 nm or less. For the reason that the sensitivity to the light energy of It emits light with a main peak, is easily separated from the excitation light, and matches well with the spectral sensitivity of the photoreceiver, allowing efficient light reception and increasing the sophistication of the image receiving system.

In the phosphor represented by the general formula (I) used in the present invention, the EuO temperature affects the photostimulable intensity. 0
．． FIG. 5 shows the change in stimulated luminescence intensity when the Eu concentration is changed in a luminescent series having 1 Lap, 0.98aFBr as the base material. From Figure 5, it can be seen that the Eu concentration is preferably in the range of 1X10"-' mol to 3X10' mol per 1 mol of the base. Also, the Eu concentration of the activator is fixed at 1X10-2 mol per 1 mol of the base. and the mother body is L
When considering a compound series of aF3 and BaFBr, LaF
FIG. 6 shows the change in stimulated luminescence intensity with respect to the change in the number n of moles in the matrix of BaFBr and the number m of moles in the matrix of BaFBr.

From FIG. 6, it can be seen that the stimulated luminescence efficiency is good when the total matrix composition is set in the range of X10-3 to 7X10-'. The phosphor is expressed by the general formula (I), and the activator is lXl0-'mol-lXl0- This is because the addition 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. Sm
The addition of phosphor (I) exhibits the same characteristics as phosphor (I) except for a decrease in afterglow.

Next, an example of a method of assembling 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 (a mixture of acetone, ethyl acetate, and butyl oxide) to prepare a coating solution having a viscosity of approximately centistokes. Next, this coating solution was uniformly applied onto a horizontally placed polyethylene terephthalate film (support), and -
A phosphor layer of about 300 μm is formed by leaving the panel to dry naturally day and night, thereby forming a radiation image conversion panel.

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

The radiation image conversion panel consists of two transparent substrates such as glass plates as shown in FIG. It may also have a structure in which the surrounding area is sealed.

Table 1 shows the sensitivity of the radiation image conversion method of the present invention with SrS
This figure shows a comparison with the sensitivity of a conventionally known radiation image conversion method using Eu vs. Sm phosphors. In Table 1, the sensitivity is determined at a tube voltage of 80 KVP for the radiation image conversion panel.
After irradiating with X1m of
514.5 nm), and the fluorescence emitted from the phosphor 1e is received by a photoreceiver (photomultiplier tube with spectral sensitivity S-5), and is expressed as the emission intensity. The sensitivity of the conventionally known method using SrS:Eu''Sm phosphor is assumed to be 1, and is expressed as a relative value.

(Table 1) As is clear from Table 1 above, the radiation image conversion methods (A62 to A7) of the present invention have significantly higher sensitivity than the conventionally known radiation image conversion methods (/161).

Further, Table 2 shows the results when the method of /163 in Table 1 of the above Example was carried out in the same manner except that a Ha-Ne laser was used as the excitation light source.

('Table 2) As shown in Table 2, the sensitivity decreases slightly (e
- It can be seen that sufficient excitation can be achieved even with a Ne laser.

(Effects of the Invention) According to the present invention, a practical radiation image conversion method has been developed that has sensitivity increased up to several thousand times K compared to the conventional method, and a significant reduction in radiation dose is achieved when generating a radiation image on a panel. In addition, image conversion unevenness caused by fading has been eliminated, and image reproduction has been speeded up, 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, and FIGS. 2(a) and 2(b) are sectional views of a radiation image conversion panel used in the radiation image conversion method of the present invention. The figure shows L used in the radiation image conversion method of the present invention.
aF, ・0.9BaFC'l: Euo, the stimulated emission spectrum of the o3 fluorophore, FIG. 4 shows the stimulated excitation spectrum of the fluorophore, and FIG.
Figure 6 shows the stimulated luminescence intensity with respect to changes in Eu doping concentration for a phosphor series of 8aFBr.
FIG. 3 is a diagram showing the stimulated luminescence intensity with respect to changes in parent composition when a compound series with aFBr is used. 1...Radiation generator 2...Subject 3...Radiation image conversion panel 4...Light source 5...-5'
e-military conversion device 6... Image processing device 7...
...Image display device 8...Filter 2
1... Support n... Fluorescent layer
24... Transparent support also has section 1 and line 2 (a) (l:)) 2122 2522 2 domo 55o 4oo 4507 skin surface (υsu

Claims (6)

[Claims] (1) The radiation transmitted through the subject is calculated using the following general formula (1
) or sub)), and then excites this phosphor with an electromagnetic wave selected from visible light and infrared rays to generate radiation stored in the phosphor. A radiation image conversion method characterized by detecting fluorescent light without emitting energy as fluorescent light. General formula (I) nReXs-mAX't: EuX
General formula ([1) nReX3 ・mAX; : Eu
x-8my (wherein, Re is La, Gd, Y +
At least one type of Lu, A is an alkaline earth metal, B
at least one of a, Sr, Ca, X and X
' is at least one of F, ICI, Br, X is 1xlO-' to 3X10-', y is lX10-' to 1x
1o7', 1m represents 1 cutting 0-3 to 7X10-'. ) (2) The radiation image conversion method according to claim 1, wherein the wavelength of the electromagnetic wave is 1l100n 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-No laser beam.