JPH0523420B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a radiation image imaging system that records a radiation image on a radiation image recording medium having a layer containing a photostimulable phosphor and converts this radiation image into an image. , relates to an effective means for eliminating noise in a radiation image recording medium (hereinafter abbreviated as stimulable medium or sheet) having a layer containing a stimulable phosphor that is repeatedly used in the imaging system. The above-mentioned photostimulable phosphor refers to radiation (X-rays, α-rays,
After being irradiated with beta rays, gamma rays, ultraviolet rays, etc., and then excited with a certain type of energy such as light or heat, the phosphor exhibits stimulated luminescence depending on the radiation energy accumulated in the phosphor. A fluorescent material. Traditionally, radiography has been used to obtain radiographic images. This method can easily obtain a fluoroscopic image of the inside of a subject, and has been widely used as an extremely effective method, particularly in the field of medical diagnosis. However, with this method, there are small differences in the X-ray transmittance of each tissue in the human body, the contrast of the image obtained is low because the X-rays are scattered within the subject, and the X-rays are harmful to the human body. However, there were drawbacks such as a narrow latitude and difficult shooting conditions. In order to compensate for these shortcomings, we use an X-ray detector with high sensitivity and wide latitude to convert X-ray images into electrical signals and perform image processing, thereby creating high-quality images that have less impact on the human body. A method to obtain this has been explored. An example of such radiography is that the radiation transmitted through the object is absorbed and stored in some kind of phosphor, and then this phosphor is excited with some kind of energy so that the phosphor is A method has been considered in which the accumulated radiation energy is emitted as fluorescent light, and this fluorescent light is detected and imaged. As a specific method, for example, US Patent No. 3,859,527
No. 55-12144 proposes a radiation image conversion method using a photostimulable phosphor as a phosphor and electromagnetic radiation selected from visible light and infrared rays as excitation energy. This conversion method uses a stimulable medium with a stimulable phosphor layer formed on a support, and allows the stimulable phosphor layer to absorb the radiation that has passed through the subject, thereby responding to the intensity of the radiation. By accumulating radiation energy and then scanning this photostimulable phosphor layer with photostimulable excitation light, the accumulated radiation energy is extracted as a light signal, and an image can be created depending on the intensity of this light. It's something you get. This final image may be reproduced as a hard copy or on a picture tube such as a CRT. Here, the stimulable medium is a general term for various forms such as a plate-like (panel-like), drum-like, or flexible film-like medium having a stimulable phosphor layer on its surface. In such a radiation image conversion method, all of the radiation energy once stored in the stimulable medium is not released by normal excitation light. Therefore, when the stimulable medium is used repeatedly, the radiation energy accumulated last time remains as an afterimage and causes a problem. This is called afterimage noise. Furthermore, if the stimulable medium is left undisturbed, some kind of radiation energy may accumulate in the stimulable medium over time. This is called accumulated noise. Afterimage noise and accumulated noise caused by each of the above causes are collectively referred to as "noise." When using this stimulable medium repeatedly, it is necessary to release all of the accumulated radiation energy to such an extent that these noises do not become a nuisance, that is, it is necessary to eliminate the noises. US patent
No. 3859527 states that if there is no noise left on the stimulable medium after reading, it can be used repeatedly, and if noise remains, the noise can be erased by irradiation with light or heating, and the stimulable medium can be used repeatedly. It has been shown that it can be returned to its initial state and reused. However, it has the disadvantage that it requires large-scale equipment and a long time to eliminate noise by either light irradiation or heating to an extent that does not interfere with repeated use. FIG. 1 shows how noise is eliminated by light irradiation. Initially, the amount of noise is rapidly attenuated by light irradiation, but the speed of attenuation gradually slows down and reaches an attenuation saturation level that is difficult to eliminate. In order to eliminate noise at this attenuation saturation level, an extremely large amount of light is required, so a large-scale device must be used or a long period of time must be spent. FIG. 2 shows how noise is eliminated by heating. When the amount of noise is removed by heating to a certain attenuation saturation level, the noise reaches an attenuation saturation level from which it does not decrease any further. The time it takes to reach a certain level and the amount of noise at that time vary depending on the heating temperature. A higher heating temperature is preferable because the time required to reach the final noise attenuation saturation level is shorter and the amount of noise is smaller. however,
The heating temperature is determined by the support, protective film, and
Limited by the heat resistance of the binder, etc. For this reason, when the stimulable medium is heated within the allowable temperature range, it takes a long time to eliminate noise, as in the case of light irradiation. The ability to repeatedly use a photostimulable medium is one of the major features of a radiation image conversion method using a photostimulable phosphor, and the difficulty in eliminating noise is a major obstacle in putting this method into practical use. The present inventors have already proposed a technology for eliminating noise to a completely practical level by using light irradiation and heating in combination as a noise eliminating means in such a system (Patent Application No. 1983-
No. 23175). In other words, when erased by either light irradiation or heating, in the case of light irradiation, electrons and/or holes trapped in trap levels that are difficult to be released by light irradiation remain without being released, or in the case of heating. In this case, electrons and/or holes trapped in the trap level, which are difficult to be released by heating, remain unreleased and become noise. However, by using both means together as proposed by the present inventors, noise can be eliminated to a practically satisfactory degree in a short time. Furthermore, Japanese Patent Application Laid-open No. 83839/1983 states that erasing noise from a stimulable medium can be carried out most efficiently by using an erasing light source that mainly emits light with a wavelength of 400 to 600 nm. However, since no heating effect can be expected with light in this wavelength range, electrons and/or holes that are not emitted unless heated as described above are not erased and remain as noise, making it impossible to remove noise to a practical level. Furthermore, although it is considered to be a small amount compared to the overall amount of noise, there is some noise that remains and cannot be erased unless it is irradiated with light with a long wavelength of 600 nm or more, and this method is also insufficient as a practical means of erasing it. be. As mentioned above, it is desirable to use both light irradiation and heating to eliminate noise, but this method requires two devices, one for the light irradiation means and the other for the heating means, and the equipment is There are problems such as increased size, time consuming, and increased power consumption, and improvements have been desired. SUMMARY OF THE INVENTION An object of the present invention is to provide a means for eliminating noise in a stimulable medium that can eliminate the noise that becomes a problem during repeated use in a radiation image conversion method using a stimulable medium to a practically satisfactory level. Another object of the present invention is to provide a means for eliminating noise in a stimulable medium, which takes a short time to eliminate the noise to a practically satisfactory level and can be eliminated using a simple device. . In order to achieve this objective, the present inventors have conducted extensive research into an effective means for eliminating noise in stimulable media, and have found that by simultaneously performing light irradiation and heating at the same location, the method can be effectively used in a shorter time. We have discovered that it is possible to eliminate noise without waste. That is, the object of the present invention is to stimulate the energy of the irradiated radiation imagewise accumulated in the recording medium by irradiating a radiation image recording medium having a layer containing a stimulable phosphor with radiation. In the radiation conversion method of stimulating luminescence with excitation light and creating an image,
Before radiation irradiation, the radiation energy remaining in the radiation image recording medium is removed by a light irradiation means and a
This is achieved by a radiation image conversion method characterized in that heating means are simultaneously used at the same location at a predetermined temperature within the range of .degree. C., and each of the means is configured to be controllable and erased. (Effect of the invention) As mentioned above, the inventors of the present invention have already proposed the use of light irradiation and heating in combination, but as a result of further research, it was surprisingly possible to perform light irradiation and heating at the same place. We have found that noise can be eliminated particularly effectively. This is very advantageous because the time required for erasing can be shortened and the device can also be made smaller. Figure 3 shows the case where light irradiation and heating are performed simultaneously at the same place with the same erasing light intensity, the same heating temperature, and the same time (a)
The noise cancellation characteristics of (b) are shown when both are performed separately. It can be seen that although the same energy is applied, noise is canceled much more effectively when light irradiation and heating are performed at the same location at the same time than when they are performed separately. Note that the simultaneous heating and light irradiation at the same place includes light irradiation or heat treatment that continues while the effect of heating or light irradiation remains. To use this light irradiation and heating at the same time, it is recommended to use a lamp that functions as both a light source and a heat source, such as a halogen lamp or xenon lamp, which has a spectral distribution ranging from the visible light region to the infrared region. preferable. In other words, if a lamp with the functions of both a light source and a heat source is used as a means for eliminating noise, the device can be made more compact, there is no need to provide a separate heating means, and the time required for noise elimination can be shortened. This makes it possible to reduce costs. Here, the photostimulable phosphor used in the present invention will be described in detail. In the radiation image conversion method described above, this photostimulable phosphor efficiently separates the excitation light during reading and the stimulated luminescence from the photostimulable phosphor, and suppresses weak stimulated luminescence. Because accurate detection is required, it is desirable to detect stimulated luminescence in the range of 300 to 500 nm using excitation light in a wavelength range longer than 500 nm, and a photostimulable phosphor having such properties is preferred. Examples of such photostimulable fluorophores include BaSO ₄ :Ax (where A is at least one of Dy, Tb and Tm, and x is 0.001≦ x<1 mol%), a phosphor described in JP-A-48-80488
MgSO ₄ : A phosphor represented by Ax (where A is either Ho or Dy, and 0.001≦x≦1 mol%), SrSO ₄ described in JP-A-48-80489: Ax (where A is Dy, Tb and
At least one type of Tm, x is 0.001≦x
<1 mol%. ), Na ₂ SO ₄ described in JP-A-51-29889,
Fluorescent substance made by adding at least one of Mn, Dy and Tb to CaSO ₄ and BaSO ₄ , etc., JP-A-1987-
30487, phosphors such as BeO, LiF, MgSO ₄ and CaF ₂ ; phosphors such as Li ₂ B ₄ O ₇ :Cu, Ag, etc. described in JP-A-53-39277; Li ₂ O・(B ₂ O ₂ ) described in JP-A-54-47883
x: Cu (where x is 2<x≦3), and Li ₂ O・
(B ₂ O ₂ )x: Fluorescent material such as Cu, Ag (where x is 2<x≦3), as described in U.S. Patent No. 3,859,527
SrS: Ce, Sm, SrS: Eu, Sm, La ₂ O ₂ S: Eu,
Examples include phosphors represented by Sm and (Zn, Cd)S:Mn, X (where X is a halogen). Also,
ZnS:Cu, which is described in JP-A-55-12142,
Pb phosphor, the general formula is BaO・xAl ₂ O ₃ :Eu (however, 0.8
≦x≦10), and the general formula is M〓O・xSiO ₂ :A (however, M〓
is Mg, Ca, Sr, Zn, Cd or Ba, and A is
At least one of Ce, Tb, Eu, Tm, Pb, Tl, Bi, and Mn, and x satisfies 0.5≦x≦2.5. ) are alkaline earth metal silicate-based phosphors. Also, the general formula is (Ba ₁ −x− _y Mg _x Ca _y )FX: _e Eu ²⁺ (However, X is at least one of Br and Cl, and x, y, and e are each 0<x+y≦
0.6, xy≠0 and a number that satisfies the following conditions: 10 ^-6 ≦е≦5×10 ^-2 . ) The general formula of the alkaline earth fluorohalide phosphor described in JP-A-55-12142 is LnOX: _x A (However, Ln represents at least one of La, Y, Gd, and Lu. , X represents Cl and/or Br, A represents Ce and/or Tb, and x represents a number satisfying 0<x<0.1.
The general formula described in No. 12145 is (Ba ₁ − _x M〓 _x )FX: _y A (where M〓 represents at least one of Mg, Ca, Sr, Zn and Cd, and and at least one of I, A is Eu, Tb, Ce, Tm,
At least one of Dy, Pr, Ho, Nd, Yb and Er, x and y are 0≦x≦0.6 and 0
Represents a number that satisfies the condition ≦y≦0.2. ), the general formula described in JP-A-55-84389 is BaFX: _x Ce, _y A (where X is at least one of Cl, Br and I, A is In, Tl,
at least one of Gd, Sm and Zr, and x and y are 0<x≦2×10 ⁻¹ and 0<y≦5×10 ⁻² , respectively. ), the general formula described in JP-A-55-160078 is M〓FX・_x A: _y Ln (where M〓 is at least one of Mg, Ca, Ba, Zn, and Cd). Type 1, A is BeO, MgO, CaO,
SrO, BaO, _ZnO , _{Al2O3 , Y2O3} , _{La2O3 ,}
In ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , GeO ₂ , SnO ₂ ,
At least one of Nb ₂ O ₅ , Ta ₂ O ₅ and ThO ₂ , Ln is Eu, Tb, Ce, Tm, Dy, Pr, Ho,
At least one of Nd, Yb, Er, Sm and Gd, and x and y are each 5×10 ^-5 ≦x
This is a number that satisfies the conditions of ≦0.5 and 0<y≦0.2. ) Rare earth element-activated divalent metal fluorohalide phosphor, whose general formula is ZnS:A, CdS:
A, (Zn, Cd)S: A, ZnS: A, X and
CdS: A phosphor represented by A, [], General formula [] _x M ₃ (PO ₄ ) ₂・NX ₂ : _y A General formula [] M ₃ (PO ₄ ) ₂ : _y A (In the formula, M and N are Mg, Ca, Sr, respectively
At least one of Ba, Zn and Cd, X is at least one of F, Cl, Br and I, A
are Eu, Tb, Ce, Tm, Dy, Pr, Ho, Nd, Yb,
At least one of Er, Sb, Tl, Mn and Sn
Represents a species. Also, x and y are 0<x≦6, 0
This is a number that satisfies the condition ≦y≦1. ) and the general formula [ ] or [ ] General formula [ ] _o ReX ₃・_n AX ₂ ′: _x Eu General formula [] _o ReX ₃・_n AX ₂ ′: _x Eu, _y Sm (formula Among them, Re is at least one of La, Gd, Y, and Lu; A is an alkaline earth metal; and at least one of Ba, Sr, and Ca; X and X' are F, Cl, and Br;
represents at least one of the following. Moreover, x and y are 1×10 ^-4 <x<3 10 ^-1 , 1×10 ^-4 <y<
It is a number that satisfies the condition of 1×10 ^-1 , and n/m is 1
The condition ×10 ^-3 <n/m<7×10 ^-1 is satisfied. )
Examples include, but are not limited to, fluorescent substances represented by the following. Hereinafter, the noise canceling means of the present invention will be explained using a block diagram of an apparatus used to implement the means. FIG. 4 schematically shows a radiation image conversion method using the present invention. In the figure, 11 is a radiation generating device, 12 is a subject, 13 is a stimulable medium having a visible or infrared stimulable phosphor layer, and 14 is for emitting a radiation latent image of the stimulable medium as stimulated luminescence. 15 is a photoelectric conversion device that detects stimulated luminescence emitted from the stimulable medium; 16 is an image processing device that reproduces the photoelectric conversion signal detected by the photoelectric conversion device 15 as an image; and 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 allows only the light emitted from the stimulable medium 13 to pass through. 13 after 15
It may be any device that can reproduce optical information from the source as an image in some form, and is not limited to the above. Alternatively, to cut off the reflected light from the light source 14, the filter 18 may not be used, but a separation method using delay in light emission as shown in Japanese Patent Application Laid-Open No. 59-22046 may be used. Further, FIG. 5 is a schematic diagram of an apparatus including noise canceling means in the present invention. The erasing light source section 19 is
The light emitted by a suitable light source 20 is uniformly irradiated onto the stimulable medium 13, and a filter 21 is inserted to remove the light that becomes an obstacle, if necessary. This filter 21 is, for example, a filter that cuts out light having a shorter wavelength than the excitation light wavelength region. This is because light with a shorter wavelength than the excitation light wavelength region accumulates energy as noise rather than erasing noise. This filter 21 may be omitted, and the type,
The number of sheets is also not limited to this. Heating section 2
2 is, for example, a plate-shaped electric heater 23 that is in close contact with the stimulable medium 13, or a hot air blowing device 2.
4. Any device that can uniformly heat the sheet 13 may be used, such as an infrared lamp. As the erasing light source 20, a tungsten lamp, a halogen lamp,
Mercury lamps, xenon lamps, sodium lamps, etc. can be used, but as mentioned above, if you use a lamp such as a halogen lamp that has a spectral distribution from the visible light range to the infrared wavelength range and is effective as a heat source, the above A separate device as such heating section is not required and is preferred. Further, in the erasing light source 20, a mirror may be disposed on the back side of the erasing light source as a reflecting mirror for intensifying the light from the light source. A mirror that selectively reflects only light in a certain wavelength range, such as a dichroic mirror, may be used as this mirror. In this case filter 2
1 may be unnecessary and is effective. In addition, in FIG. 5, a stimulable medium feeding device may be provided in order to improve the efficiency of noise cancellation. The effective temperature range for noise cancellation is 50 to 500.
℃, and the upper limit temperature is naturally limited by the material that makes up the sheet, but if light irradiation and heating are used simultaneously at the same place, noise cancellation is more effective even at lower temperatures than when they are done separately. It will be done.
In this respect as well, the load on the performance of the stimulable medium depending on its heat resistance is reduced, and the range of material selection can be expanded. The stimulation medium and the excitation light source for emitting the radiation image as stimulated luminescence in the radiation image conversion method using the noise canceling means of the present invention will be described below. The structure of the stimulable medium consists of a support 25 and a stimulable phosphor layer 26 formed on one side of the support 25, as shown in FIG. 6a. Next, an example of a method for producing a stimulable medium will be shown below. First, the stimulable phosphor is mixed with a binder solvent solution such as polyvinyl butyral or nitrified cotton (solvents such as cyclohexane, acetone, acetic acid, ethyl, and acetic acid/butyl mixture), and a coating solution with a viscosity of approximately 50 centistokes is applied. Prepare. Next, this coating solution is uniformly applied onto a horizontally placed polyethylene terephthalate film (support) and allowed to stand overnight to dry naturally, thereby forming a stimulable phosphor layer with a thickness of preferably about 300 μm. and make it a shining medium. As the support, for example, a transparent glass plate or a thin metal plate made of aluminum or the like may be used. The stimulable medium is 2 as shown in Figure 6b.
It may also have a structure in which a photostimulable phosphor is sandwiched between a transparent substrate 27 such as a glass plate and a support 25 to form a photostimulable phosphor layer 26 of an arbitrary thickness, and the periphery of the stimulable phosphor layer 26 is sealed. good. In the radiation image conversion method of the present invention, the light source for the light energy that excites the stimulable phosphor layer of the sheet is a light source that emits light with a band spectrum distribution in the visible and/or infrared region. In addition, He-Ne laser light (633nm), YAG laser light (1064nm), 8th harmonic of YAG laser (532nm), ruby laser light (694nm), Ar ⁺
A light source emitting light of a single wavelength, such as a laser or a semiconductor laser, is used. Particularly when using laser light, high excitation energy can be obtained. (Example) Next, the present invention will be explained using an example. Example 1 The stimulable medium was prepared by dispersing 8 parts by weight of a stimulable phosphor made of BaFBr:Eu and 1 part by weight of polyvinyl butyral using a solvent (cyclohexanone), and uniformly coating this on a polyethylene terephthalate substrate. A stimulable phosphor layer of about 300 .mu.m was formed by leaving it for a day and night and drying it naturally.
After irradiating this stimulable medium with 10 millimeter X-rays with a tube voltage of 80 KV and reading the image with a 25 mW Ar ⁺ laser, the sheet was irradiated with a 500 W tungsten lamp (illuminance of 1000 lux on the sheet surface) and at the same time an electric current was applied. It was erased by heating to 100°C for the same period of time using a heater. 25 to reduce the noise to 1% of the initial signal.
It took seconds. Comparative Example 1 After producing a stimulable medium in the same manner as in Example 1, it was further irradiated with X-rays in the same manner as in Example 1, and the image was read using an Ar ⁺ laser. Table 1 shows the results of measuring the time required for the noise to decrease to 1% of the initial signal by erasing the noise by changing the order and time by irradiating it with light (with an illuminance of 1000 lux) and heating it at 100°C with an electric heater. show. However, the surface temperature of the stimulable medium during light irradiation is 25°C.

【table】

[Table] Example 2 A stimulable medium was prepared in the same manner as in Example 1 except that 0.1YF ₃ 0.9BaFBr:Eu was used as the stimulable phosphor. Using this, measurements were performed in the same manner as in Example 1, and as a result, it took 20 seconds for the noise to decrease to 1% of the initial signal. Comparative Example 2 A photostimulable medium was produced in the same manner as in Example 1, except that 0.1YF ₃ 0.9BaFBr:Eu was used as the photostimulable phosphor.
Table 2 shows several examples of the time required for the noise to decrease to 1% of the initial signal, which was measured using this in the same manner as Comparative Example 1.

[Table] From Examples 1 and 2 and Comparative Examples 1 and 2, it can be seen that by simultaneously using light irradiation and heating, the noise erasing time is shortened and noise is erased more efficiently. As described above, according to the present invention, it is possible to eliminate noise to a practically satisfactory level in a shorter time. Furthermore, since light irradiation and heating are performed in the same space, the entire device can be downsized.

[Brief explanation of the drawing]

FIG. 1 is a graph showing changes in the amount of noise in a conventional erasing method using only light irradiation.
FIG. 2 is a graph showing changes in the amount of noise in the conventional erasing method using only heating. Third
The figure is a graph showing the noise cancellation characteristics in a case where light irradiation and heating are performed simultaneously for the same amount of time, and in a case b when they are performed separately. FIG. 4 schematically shows a radiation image conversion method using the present invention. FIGS. 5a and 5b schematically show an apparatus including noise canceling means according to the present invention. 6th
Figures a and b are schematic diagrams showing the structure of the stimulable medium used in the above means of the present invention. 11...Radiation generating device, 12...Subject, 1
3... Stimulation medium, 14... Stimulation excitation light source, 15...
...Photoelectric conversion device, 16...Image processing device, 17
...Image display device, 18...Filter, 19...
... Erasing light source section, 20 ... Erasing light source, 21 ... Filter, 22 ... Heating section, 23 ... Electric heater, 24 ... Hot air blowing device, 25 ... Support body, 26 ... Stimulable firefly Light layer, 27...transparent support.

Claims (1)

[Claims] 1 By irradiating a radiation image recording medium having a layer containing a stimulable phosphor with radiation, the energy of the irradiated radiation imagewise accumulated in the recording medium is used to stimulate luminescence with stimulable excitation light. In the radiation conversion method for converting radiation into an image, the radiation energy remaining in the radiation image recording medium before radiation irradiation is
A radiation image conversion method characterized in that a light irradiation means and a heating means are simultaneously used at the same place at a predetermined temperature within the range of 50 to 500° C., and each of the means is configured to be controllable and erased.