JPS58216041A - Apparatus and method of displaying x- ray image - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an X-ray image display device and an image display method. By controlling the electron beam that impinges on the phosphor crystal, a clear and bright X-ray still image can be instantly recorded and observed on the phosphor surface, and the recording can be erased at any time to create new The present invention provides a novel X-ray image display device and image display method that can record X-ray images on a fluorescent surface.

The principle and apparatus of the X-ray image display device of the present invention will be explained below.

By irradiating a human body or object with X-rays and projecting and detecting the spatial intensity distribution of the transmitted X-rays onto a two-dimensional surface, it is possible to non-destructively diagnose the inside of the human body or object, which cannot be observed with the naked eye. For this reason, X-ray diagnosis has been widely used as a powerful technique for clinical diagnosis in hospitals and still for non-destructive testing in industry. Among the X-rays mentioned here, γ
Of course, lines are also included. In these X-ray diagnostics, the d-space intensity distribution of the beam transmitted through the object is projected onto an X-ray photographic film coated with silver halide, and after exposing the silver halide, a developing operation is added. The method used was to fix the X-ray image onto X-ray photographic film. The sensitivity of silver oxide to X-rays is low, and in order to obtain an X-ray image necessary for diagnosis, a large amount of X-ray irradiation is required. Irradiation of a large amount of X-rays causes radiation damage to the human body, especially when the subject is a human body, and is therefore a health problem.

As a method for obtaining clear X-ray images on X-ray photographic film even when the amount of X-ray irradiation is reduced, the method of inserting an intensifying screen between the subject and the X-ray film has been somewhat effective, and currently, This method is used. An intensifying screen is a phosphor film coated on a special mount with a phosphor that can absorb X-rays well and convert the energy into light in the wavelength range to which X-ray photographic film is sensitive. . Since no other method of obtaining clear, large X-ray images could be found, the above-mentioned method of using a combination of X-ray film and intensifying screen was used as an important means for X-ray diagnosis. It's here. The disadvantages of this method are that it takes time to develop the film in a dark room from the time of X-ray irradiation to the time when the X-ray image can be diagnosed. Because the slope of the photosensitivity to dose, the so-called 1 degree photosensitive curve, is gentle, special image processing is required to emphasize the necessary information and obtain a clear X-ray image on photographic film. In addition, economic reasons have been added to this in recent years. In other words, silver resources, which are the main material for X-ray photographic films, have been depleted, making silver expensive and silver in short supply inevitable. It is possible to avoid instability in supply due to depletion of silver resources, not rely on silver, and further shorten the time required for diagnosis.If possible, clear X-ray images can be obtained immediately without image processing. The development of a recording device was awaited.

An X-ray image intensifier is one of the devices that meet the above requirements. This device uses a special cathode ray tube, which includes a photocathode that emits photoelectrons by absorbing X-rays at one end, an accelerating electrode that accelerates the emitted photoelectrons, an electron lens system that expands the spatial intensity distribution of photoelectrons, and an accelerator. Using a component made of a fluorescent film that emits light when struck by photoelectrons has the advantage that an immediate X-ray image can be observed. However, as a limitation due to the structure of this cathode ray tube,
Inconveniently, the X-ray image that can be obtained is limited to a narrow area of the subject, and the X-ray image of the fluorescent film appears only when X-rays are being irradiated.

Furthermore, when making a diagnosis using an X-ray image intensifier, the image intensifier itself does not have the ability to store records, so the subject is inevitably exposed to polyacid X-rays, which poses health concerns. There is a big problem that comes from this.

As an alternative to this, a new X-ray image recording method uses a fluorescent film coated with a phosphor that emits so-called thermoluminescence, which occurs when X-rays are irradiated at room temperature and then heated to a high temperature above room temperature. A method is being considered in which the object is made, irradiated with X-rays that have passed through the object, and then irradiated with a scanning laser beam to detect the luminescence that appears due to local heating. Fluorescent films using so-called bright phosphors, which emit visible light when irradiated with X-rays and then infrared light, are also being considered. In addition to the inconvenience of not being able to obtain visible light immediately, these fluorescent films also have sufficient
It has no line sensitivity and has not reached the level of practical use. Another method is to apply a high electric field to a sheet coated with a certain type of dielectric material to charge it, and then irradiate it with X-rays, which causes the charge to disappear.This method is used to create an electrostatic image using dry development. Xerographs have also been considered, but have not reached the point of widespread practical use.

The present invention provides an X-ray image display device and an image display method based on a novel principle. By using this device and method, all of the above-mentioned conventional drawbacks can be solved, and a small amount of X-rays can be displayed. Not only can a sharp and bright X-ray image be projected on the fluorescent film of a cathode ray tube at any time depending on the amount of irradiation, but the X-ray image can also be continuously projected on the fluorescent surface for any desired period of time. Furthermore, the X-ray image on the fluorescent film can be erased and another X-ray image can be newly projected on the fluorescent film.

The device according to the invention takes advantage of the following properties of phosphor crystals. A phosphor film is created by applying powdered phosphor crystals, which emit bright visible light when irradiated with electron beams, to a thickness of about 20 micrometers on a conductive plate. After applying a suitable voltage to the conductive plate and removing the voltage, a certain amount of polarization remains on the phosphor film. This polarization remains inside the phosphor crystal and is called internal sustained polarization. When the phosphor film with the internally sustained polarization is irradiated with X-rays of a moderate amount, and electron-hole pairs exceeding a critical value are created in the phosphor crystal, the internally sustained polarization is immediately eliminated. . This phenomenon is well known and has been applied to xerography, in which charged toner is attached to a charged area to create an image.

The X-ray image display device according to the present invention installs the fluorescent film inside a cathode ray tube, and utilizes the internal sustained polarization appearing in the fluorescent film and the cancellation of the internal sustained polarization due to X-ray irradiation. This is a new cathode ray tube that controls the electron beam that enters the photonic crystal, irradiates a small amount of X-rays, and projects a bright X-ray image onto the phosphor film using the electron flow from the cathode.

More specifically, a fluorescent film that emits bright light when exposed to electron beams,
It is formed on a transparent conductive film formed on the substrate of the face plate, and a negative voltage is applied to the transparent conductive film so that the side irradiated with the electron beam becomes the negative electrode to create internal sustained polarization in the fluorescent film. Made into fluorescent particles. In this state, the electron flow accelerated at a specified voltage is repelled by the negative electric field created by the internal sustained polarization appearing in the phosphor, so it cannot reach the phosphor crystal and instead hits the inner wall of the cathode ray tube. It is collected by an attached first collection electrode. Therefore, the fluorescent film does not emit light. When a part or the entire surface of the fluorescent film is irradiated with X-rays, x? The internal sustained polarization of the phosphor in the illuminated part of s is canceled.

The electron beam from the cathode can enter the phosphor crystal only in the part of the phosphor film where this internal sustained polarization has been eliminated, so the phosphor film emits light only in that part. Light emission can be continued by momentarily applying a negative voltage to the transparent conductive film until internal sustained polarization is created in the phosphor crystal again. In this way, the internal sustained polarization that appears in the phosphor crystal and the
By irradiating the phosphor film with a beam and effectively utilizing the partial cancellation of the internal sustained polarization in the phosphor film, it is possible to control the electron beam that enters each phosphor crystal that forms the phosphor film. and an X-ray image can be obtained. Since the amount of X-rays required to control the electron beam is small, an X-ray image can be constantly projected on the phosphor film for any desired period with a very small amount of X-ray exposure. The X-ray image is erased when a negative potential is applied to the transparent conductive film to form sustained internal polarization in the phosphor crystal. The time required for the internal sustained polarization of the phosphor to resolve is very short. Normally, when a fluorescent film is irradiated with X-rays within a period of 1 to 10 microseconds to create electron-hole pairs in the crystal in excess of a critical value, internal sustained polarization disappears within a period of 10 to 1000 microseconds. do.

In this way, when using the X-ray image display device of the present invention, the amount of X-ray irradiation to the subject can be extremely reduced, and
A quick, bright and clear X-ray image can be projected on the fluorescent surface for any desired period of time.

The phosphor film of the cathode ray tube, which can display and erase X-ray images, is made using a special method; fluoresce films made by the conventional method using a binder cannot display X-ray images. I can't do that.

The phosphor film of the cathode ray tube according to the present invention is such that the surface of each phosphor crystal forming the phosphor film is free from impurities other than the phosphor crystals, such as the binder used in the preparation of the phosphor film or the like. It must not be contaminated by decomposition residues or by the formation of an impurity layer on the crystal surface, even if it is one atomic layer deep. Preferably, the phosphor film is made only of phosphor crystals with clean surfaces. If impurities are present on the surface, the incident secondary electrons will plunge into these impurities before they enter the phosphor crystal, thereby acting to prevent subsequent incident secondary electrons from accessing the phosphor crystal. Have a lucky day. It happens as follows. -When the next incident electron enters an impurity, it emits an intrinsic secondary electron. At this time, an electrostatic attraction is exerted between the holes left in the impurity crystal and the intrinsic secondary electrons emitted outside the impurity crystal, and the two are brought together at a very close distance through the surface of the impurity crystal. They combine and become motionless.

In this way, surface-bound electrons are formed on the surface of the impurity. When looking at the phosphor film from the electron gun side of a cathode ray tube, the phosphor crystal is effectively shielded by the negative electric field caused by the surface-bound electrons formed on the surface of the impurity. - In order for the secondary incident electron to penetrate this shield, it must have an energy of approximately 2 keV, and the primary incident electron with energy below 2 keV is repelled by surface-bound electrons and approaches the phosphor crystal. do not have. The energy of the primary incident electrons required to penetrate the negative electric field due to the internal sustained polarization of the phosphor crystal is approximately 200 eV, so the electric field due to the surface-bound electrons on the impurity surface is approximately 10 times that of the internal sustained polarization.
It is twice the size. Therefore, when impurities are attached to the surface of the phosphor crystal, the control effect of the electron flow entering the phosphor crystal using the electric field caused by the internal sustained polarization of the phosphor crystal described above is It is completely hidden and rendered powerless by surface-bound electrons on the impurity surface formed just before.

For this reason, the surface of the phosphor crystal that forms the phosphor film of the cathode ray tube of the present invention must not be contaminated with impurities or be covered with impurities, and must always be clean. .

Fluorescent materials that emit bright light are generally good dielectrics and insulators. Therefore, when a phosphor crystal is irradiated with X-rays and electron beams, 7 surface-bonded electrons are also formed on the phosphor crystal surface. When irradiating X-rays, since X-rays are electromagnetic waves with strong penetrating power, they can penetrate the electric field caused by surface-bound electrons and enter the phosphor crystal without being hindered. Therefore, when X-rays are used to eliminate internal persistent polarization in a phosphor crystal or cause a phosphor crystal to emit light, the formation of surface bound electrons is not a problem and is generally ignored. However, for the reasons mentioned above, 2ke
When a phosphor crystal is irradiated with an electron stream having the energy below, the formation of surface-bound electrons becomes a major problem.

Fortunately, if the surface of each individual phosphor crystal that forms the phosphor film of a cathode ray tube is clean, surface-bound electrons on the phosphor crystal surface can be transferred to the phosphor with the help of a collection electrode. It was found that it could be easily removed from the surface of the crystal. The physical reason why surface-bound electrons are easily removed in the case of phosphor crystals is currently unclear, but it appears to be closely related to the recombination of electrons and holes created within the crystal. A first collection electrode 18 installed as a collection electrode on the entire inner wall surface of the cathode ray tube excluding the face plate, or on a part thereof.
There is a second collecting electrode consisting of a transparent conductive film formed on the substrate of the fluorescent film and a net-like structure disposed immediately in front of the fluorescent film when viewed from the cathode side. This net-like electrode functions as a second collection electrode even if the iJE potential, which is several volts higher than the voltage applied to the transparent conductive film, is applied to it, or even if the same potential is applied to it. If the net-like electrode is to have the same potential as the transparent conductive film, the material for the net-like electrode can be vapor-deposited onto the transparent conductive film through a mask, or the fine powder of the electrode material can be coated with a photosensitive binder. After mixing with the solution and coating the slurry on a transparent conductive film, the photosensitive resin is irradiated with light that has passed through a mask from the side of the glass substrate that will become the substrate, or from the opposite side. When exposed to light and subjected to development processing, the electrode material adheres only to the exposed areas. When this is heated and the binder resin is removed by thermal decomposition, a net-like electrode is created on the transparent conductive film. When using a photosensitive method, the mesh electrode does not need to be mesh-like, and may be made by depositing an electrode group consisting of a set of discontinuous points on the transparent conductive film. The thickness of the net-like or fish-shaped electrode formed on the transparent conductive film is preferably equal to or greater than the thickness of the fluorescent film formed on the transparent conductive film. When a phosphor is applied between the reticular or fish school electrodes to form a phosphor film, the electrodes cooperate with the transparent conductive film to form a second collection electrode, and the surface bonding of the phosphor surface Works effectively to collect electrons. Although using the first or second collecting electrode described above alone is effective and removes many of the surface-bound electrons from the phosphor crystal surface, using the first and second collecting electrodes in combination , the trapping effect of surface-bound electrons on the surface of the phosphor crystal is emphasized. A collection electrode consisting of the above combination works effectively to remove surface-bound electrons formed on the surface of a phosphor crystal with a clean surface, but it is effective for removing surface-bound electrons formed on the surface of a phosphor crystal with a clean surface. Even if the crystal surface is clean, it has no effect on removing surface-bound electrons formed in the crystal. For the same reason, it does not work effectively to remove surface-bound electrons formed on the surface of impurity crystals that have contaminated the phosphor crystal surface.

The phosphor used in the fluorescent surface of the cathode ray tube according to the present invention is a phosphor that emits bright light in the visible light range when exposed to electron beams, and any phosphor having internal sustained polarization can be used.

Generally, a light-emitting substance that emits bright light when exposed to electron beams also emits bright light when exposed to X-rays. It is also caused by X-rays,
This is because electron and hole pairs are also created in the phosphor crystal by the electron beam, and recombination of these electron and hole pairs is the main cause of light emission from the phosphor. Also, the internal sustained polarization in the phosphor crystal is
Eliminated by X-rays and electron beams entering the phosphor crystal. However, the reason for this is not clearly understood at present.

Presumably, the important factors for the cancellation of internal sustained polarization are the creation of many electron-hole pairs and the recombination of electron-hole pairs via recombination centers. As the phosphor used in the X-ray image display device of the present invention, it is desirable to use a phosphor that emits bright light when exposed to electron beams and at the same time quickly eliminates internal sustained polarization when irradiated with X-rays.

In particular, it is desirable from a health standpoint to use a phosphor that has a small critical value for the X-ray irradiation dose that eliminates internal sustained polarization, since this reduces the amount of X-ray radiation.

Such a phosphor is one in which more electron and hole pairs are created in the crystal depending on the amount of X-ray irradiation. Same-
In order to create a large number of electron and hole pairs in the crystal depending on the amount of X-ray irradiation, the phosphor crystal should be able to absorb as many X-rays as possible. It is better if the material is composed of an element with a large X-ray absorption coefficient. The absorption coefficient of X-rays is proportional to the size of the atomic number, so it is better if the phosphor crystal is made of an element with a large atomic number.
It is desirable as a phosphor for use in the X-ray image display device of the present invention.

The above-mentioned phosphors include terbium, praseodymium,
Cerium, europium, gadolinium containing at least one element of dysprosium or samarium as an activator, sulfide containing at least one element of lanthanum, yttrium, or lutetium as a main constituent of the base crystal; Phosphors of compounds, oxides, aluminates, silicates, and halides, or copper or silver are used as activators, and elements from the ■-Mu group or ■-human group of the periodic table are used as co-activators. Zinc sulfide and lead cadmium sulfide phosphors, zinc oxide phosphors, and lead silicate phosphors containing manganese as an activating agent.

and calcium tungstate phosphors.

Among the above-mentioned phosphors, phosphors containing sulfur or halogen are used in the normal manufacturing process of cathode ray tubes, especially in the phosphor coating process, even if the surface of the phosphor powder is clean. During the heating process in the air, the surface may undergo chemical changes and become contaminated, so when using these phosphors, it is necessary to take great care to avoid contamination when manufacturing cathode ray tubes. . In particular, the use of binders containing metal elements must be avoided in the process of forming the fluorescent film. In addition, when making a fluorescent film using an organic binder, it is necessary to select conditions that do not chemically change the crystal surface of the phosphor during the process of oxidizing the binder and removing it by thermal decomposition. A membrane must be created.

By using a cathode ray tube consisting of the components shown schematically in FIG. 1, it is possible to measure the emitted intensity of the phosphor film depending on the accelerating voltage of the electron flow irradiating the phosphor.

In this case, the transparent conductive film 6 provided with the dotted second collection electrode
When the thickness of the phosphor film 5 coated on top is 2 to 5 layers in terms of average particle number, the surface-bonded electrons of the phosphor crystal are easily removed, and the phosphor's original properties are reduced. Emission intensity characteristics that depend on the accelerating voltage can be obtained. When the thickness of the phosphor film is greater than 6 layers, the removal effect of surface-bound electrons decreases with increasing thickness. A mesh electrode at the same electrical potential as the torn transparent conductive film 6, or at a positive potential several volts higher than it, is used as a second collection electrode, and is placed immediately before the fluorescent film or in the fluorescent film. If the mesh electrode is buried so that its surface appears above the phosphor film when viewed from the cathode, surface-bound electrons on the surface of the phosphor crystal can be removed regardless of the thickness of the phosphor film. The observed intensity of light emitted from the fluorescent film decreases as the thickness of the fluorescent film increases, as a result of the emitted light undergoing optical scattering within the fluorescent film in the process of exiting to the observation side. The optimum thickness of the fluorescent film for extracting the emitted light is between 2 and 6 layers in terms of average particle diameter.

When the luminescence intensity from the fluorescent film 6 is determined as a function of the voltage applied to the transparent conductive film 6 using the apparatus shown in FIG. 1, the hysteresis phenomenon shown in FIG. 2 is obtained.

For this measurement, the electron flow from the cathode 2 is kept constant. The cathode 2 is grounded, and a voltage equal to or slightly lower than the voltage vT shown in FIG. 2 is applied to the first collection electrode 3. In this state, a negative voltage, for example -300 volts, is applied to the transparent conductive film 6 with respect to the cathode 2 for a moment, and then the transparent conductive film 6 is brought to zero potential, and then the positive potential is gradually increased. go. At this time, even if the potential of the transparent conductive film 6 exceeds the critical voltage shown in FIG. 2, the fluorescent film does not emit light for several tens of volts, or only very weak light is still observed. As the applied voltage approaches the vH point in the figure,
The intensity of the weak light is slightly strengthened, but the intensity is so weak that it can only be slightly observed with the naked eye. When the applied voltage approaches the vH point in FIG. 2, the emission intensity suddenly increases.

In the applied voltage range above the vH point, the emission intensity is expressed by a first-order linear increasing function with the applied voltage. Once a voltage higher than vH is applied to the transparent conductive film electrode, even if the voltage is lowered below the vH point, the relationship of a first-order linear increasing function is maintained up to the critical voltage vT, as shown in Figure 2. As shown in
A hysteresis phenomenon appears between the applied voltage and the emission intensity. Once a voltage of vH or more is applied to the transparent conductive film 6, or once an electron flow accelerated with a voltage of vH or more is irradiated, a critical voltage of vH or more is generated between the applied pressure of the transparent conductive film and the emission intensity. In the voltage range of , the relationship of -order linear increasing function is always maintained, and no hysteresis phenomenon is observed. The linear increasing function relationship observed between Vr(!:VH) disappears when a negative potential is momentarily applied to the transparent conductive film 6. The above linear-order increasing function relationship holds true even if the phosphor crystal is momentarily irradiated with an electromagnetic wave with energy other than an electron beam, and no hysteresis phenomenon is observed.In other words, the fundamental absorption of the phosphor crystal If the phosphor film is irradiated with electromagnetic waves with higher energy than the edge, such as X-rays, γ-rays, and ultraviolet rays from the face plate side, and more than a specified amount of electron and hole pairs are created in the phosphor crystal, the hysteresis phenomenon will occur. In order to repeatedly reproduce the hysteresis phenomenon shown in FIG. If you create sustained polarization, it will work.

The history phenomenon can be used as follows. After applying a negative voltage to the transparent conductive film 6, the voltage changes from vT to v as shown in FIG.
An arbitrary voltage va between H is applied.

In this state, the fluorescent film 6 does not emit light, or even if emitted light is detected, its intensity is extremely weak when observed with the naked eye. When this fluorescent film 6 is irradiated with X-rays over the entire surface of the fluorescent film through the face plates 1 and 7, the fluorescent film 5 is exposed to the electron flow from the cathode 2 due to the hysteresis phenomenon shown in FIG. By,
It emits light steadily at the intensity indicated by the arrow in the figure.

When a constant voltage is applied to the transparent conductive film 6 and the relationship between the X-ray beam irradiated to the fluorescent film and the luminescence intensity of the fluorescent film is determined, FIG. 3 is obtained. That is, when the fluorescent film is irradiated with an X-ray dose above a critical value, the fluorescent film emits light by electron beams. When irradiated with an X-ray dose below a critical value, the phosphor film does not emit light from the electron beam. The value of the critical value depends on the type of 4-fluorophore. Therefore, if the amount of X-rays irradiated through the subject and onto the fluorescent surface of the cathode ray tube is selected to be around the critical value shown in Figure 3,
The X-ray image of the object is subjected to image processing according to the relationship shown in FIG. 3, and a clear X-ray image with no intermediate tones is projected onto the fluorescent film. This relationship can also be used as follows. When the amount of X-rays irradiated to the subject is sequentially changed and the fluorescent film is irradiated with the X-rays that have passed through the subject, tomographic X-ray images depending on the depth of the subject can be sequentially displayed on the fluorescent surface. in this case,
During each X-ray irradiation, a negative voltage is applied to the transparent conductive film,
Of course, it is necessary to add an operation to erase the X-ray image.

The brightness of the fluorescent surface emitted by the electron beam after being irradiated with X-rays depends on the voltage Va applied to the transparent conductive film 6. If va is brought closer to vH in Figure 2, the brightness of the fluorescent surface will increase, but the intensity of weak luminescence when no X-rays are irradiated will also increase, and the contrast of the X-ray image on the fluorescent surface will deteriorate. Because of this, I can't get too close to vH. It is best to determine and set the optimum applied voltage V for each device.

It has been found that the voltage of the first collection electrode 3 plays an important role in improving the brightness and contrast of the XFS gap projected on the fluorescent surface. vH shown in FIG. 2 on the first collection electrode 3
When applying a slightly lower voltage V, and using the same method used to obtain Fig. 2, the dependence characteristics of the emission intensity depending on the voltage applied to the transparent conductive film 6 were measured, as shown in Fig. 4. An upwardly convex hysteresis phenomenon is obtained. That is, after applying a negative potential to the transparent conductive film 6, when the voltage is increased positively, the second
As shown in the figure, the luminescence increases rapidly near vH, and vH
In the above, a linear-order increasing function is established between the emission intensity and the voltage applied to the transparent conductive film. Once a voltage higher than vH is applied and then lowered to a voltage lower than vH, the luminescence intensity does not have a linear-order increasing function relationship with the applied voltage, and the brightness is almost constant at a voltage of several tens of volts. After holding for a while, it rapidly decreases near Vτ. It does not emit light at voltages below vT. Once the voltage of the first collection electrode is increased to a voltage higher than vH, no hysteresis phenomenon is observed and only an upwardly convex curve is obtained.

When the hysteresis shown in FIG. 4 is used, the brightness of the fluorescent surface is significantly improved compared to when the hysteresis shown in FIG. 2 is used. This is clear from FIG.

The enhancement of the hysteresis phenomenon shown in FIG. 4 can be explained as follows. The electron flow emerging from the cathode 2 is caused by the voltage of the transparent conductive film 6 being V,
If it is lower, each electron will have an energy of eVy, accelerated by the constant voltage v2 applied to the first collection electrode. An electron with an energy of eVy has the required θV to penetrate the negative electric field caused by the internal sustained polarization of the phosphor.
Smaller than H. Therefore, while the phosphor has internal sustained polarization, the electron flow from the cathode, even though accelerated by the voltage at the first collection electrode, is electrostatically repelled at the phosphor crystal. , cannot enter the phosphor crystal and cause the phosphor to emit light, and is collected by the first collection electrode.

Once the phosphor crystal is irradiated with an electron flow accelerated at a potential higher than vH or with X-rays, the internal sustained polarization disappears and
An electron stream with energy y rushes into the phosphor crystal, causing the phosphor to emit light. The emission intensity of that fold is eVy
Therefore, approximately constant emission intensity is ensured in the voltage range applied to the transparent conductive film between vT and v)l. The same result can be obtained by using another electrode in place of the first collection electrode and accelerating the electron flow from the cathode with a voltage V to irradiate the phosphor. For example, when a first anode is attached in front of the cathode and a voltage lower than vH is applied to it to accelerate the electron flow, the effect is the same as applying the same voltage to the first collection electrode.

FIG. 5 is a schematic diagram of the X-ray image display device according to the present invention for explaining the operation thereof. The operation of the device will be explained based on the figure. First, after applying a moderate negative voltage to the transparent conductive film 16, an arbitrary voltage V that is within the voltage range that indicates the hysteresis phenomenon and is greater than or equal to Vτ but less than or equal to vH is applied. In this state, the entire surface of the fluorescent film 16 is constantly irradiated with a stream of electrons emitted from the plurality of cathodes 11 at a uniform density.

In this case, an arbitrary voltage V lower than vH is applied to the plurality of tubes of anodes 12 each attached in front of the plurality of tubes of cathodes.

When applied, this anode has two effects on the electron flow from the cathode. One of them is that the electron flow from the cathode is accelerated by the electric field V of the anode and has energy evF. The other one is the field electron lens effect created by vy. The electron lens action is caused by the first collection electrode 13
It also depends on the electric field applied to the By appropriately combining the electric fields from both the first collection electrode and the anode, the electron flow from the multiple tube cathodes can be brought into overfocus and adjusted so that the electron flow is irradiated onto the fluorescent surface with uniform density. can.

The electron flow has energy any. When there is an effect of internal sustained polarization formed in the phosphor film 16, this energy electron flow is electrostatically repelled by the negative electric field caused by the internal sustained polarization, and cannot enter the phosphor crystal. , are collected by the first collection electrode 13, forming a closed circuit. Therefore, the fluorescent film 16 does not emit light, or even if it does emit light, it is extremely weak. This fluorescent film 16 is coated with an X on a part or the entire surface of the fluorescent film from the face plate side.
When irradiated with X-rays, the area irradiated with X-rays becomes a fluorescent film 16.
Due to the hysteresis characteristics of the cathode 11, it emits light constantly due to the electron flow from the cathode 11. If a subject is placed between the X-ray source and the X-ray image display device of the present invention, the projected image of the spatial intensity distribution of the X-rays after passing through the subject onto a two-dimensional fluorescent surface will be bright and clear. The image is projected onto a fluorescent surface as an X-ray image. This X-ray image can be maintained on the fluorescent film until a negative erase voltage is applied to the transparent conductive film 16. After applying the erasing operation, the method described above can be repeated to project a new X-ray still image onto the phosphor film, which has no history of the previous X-ray image. Erasing and recording operations can be repeated any number of times using the same device.

As described above, in the X-ray image display device of the present invention, by utilizing the hysteresis phenomenon that appears between the applied voltage and the emission intensity of the phosphor and the elimination of the hysteresis phenomenon due to X-ray irradiation, , it is possible to instantaneously project a clear, bright X-ray still image onto a phosphor film using image processing.

Further, the use of the X-ray image display device of the present invention has the advantage that the time required for X-ray diagnosis can be extremely shortened compared to the case where conventional X-ray photographic film is used. Further, the X-ray image display device of the present invention has a simple structure, and not only can a fluorescent surface of any size on which an X-ray image is projected and hung, but also can display a displayed X-ray image. can be projected onto the fluorescent film for any period of time without damaging the
Many of the inconveniences encountered when using X-ray image intensifiers are eliminated. Still, the image on the X-ray image display device according to the present invention has the advantage that it is bright and clear, does not require a dark room to observe the image, and can be sufficiently observed even under normal indoor lighting. Furthermore, the X-ray image display device of the present invention not only does not use silver, which is a depleted resource, as the main material, but also allows new X-ray images to be displayed with the same fluorescence any number of times using the same device by adding an erasing operation. Since it can be projected onto a film, it greatly contributes to resource conservation. As described above, the X-ray image display device according to the present invention brings great improvements in terms of technology, X-ray diagnosis, and resource saving, and makes a great contribution when applied industrially.

The present invention will be explained below using Examples.

(Example 1) A transparent conductive film made of indium tin oxide is formed on the inner surface of a glass substrate that becomes the face plate of a cathode ray tube. A slurry made by mixing conductive carbon powder and a photosensitized water-soluble polyvinyl alcohol solution is coated onto the transparent conductive film so as to have a uniform thickness. After this is dried, the coating film is irradiated with ultraviolet rays from the face plate side through a mask having dot-shaped holes with an opening diameter of 100 micrometers, thereby curing the coating film in the areas irradiated with the light. When this is developed using hot water, conductive carbon sticks to the transparent conductive film in the form of dots, which will become the second collection electrode. On this surface, a slurry made by mixing a yttrium oxide phosphor (Y2O3: Eu) containing 0.001 mole of europium, which emits red and white light, and an aqueous solution of water-soluble polyvinyl alcohol, which is endowed with photosensitivity, was placed. Apply.

After drying this coating film with hot air at 70°C, when the entire coated surface is exposed to ultraviolet rays from the face plate side, only the fluorescent film on the surface that is not coated with conductive carbon is exposed and hardened. do. When this is developed using warm water,
Fluorescent particles are applied, filling the gaps where there are no dots of conductive carbon. During the exposure, if the exposure is not completely completed in the thickness direction of the fluorescent film,
After development, a phosphor film is obtained in which clean phosphor crystal surfaces to which no photosensitive substance is attached are arranged on top. A cathode, an anode, and a first collection electrode were attached to the cathode ray tube with a built-in fluorescent film thus produced, and the tube was evacuated, and the usual manufacturing process for cathode ray tubes was added.

As a result, a cathode ray tube consisting of the components shown schematically in FIG. 6 is obtained. In this cathode ray tube, the transparent conductive film 16 is
After applying a negative voltage of 0000 volts for a moment, for example, 1 millisecond, a positive voltage is gradually applied to the transparent conductive film.
The hysteresis phenomenon shown in the figure is observed. Furthermore, constant voltages of 180 volts and 140 volts are applied to the anode 12 and the first collection electrode 13, respectively, and after the potential applied to the transparent conductive film 16 is once made negative, the potential is gradually increased to a positive voltage. As the voltage is applied, an upwardly convex hysteresis phenomenon is observed between 110 volts and 210 volts as shown in FIG. In order to display an X-ray image on this cathode ray tube, the following procedure may be performed. The cathode 11 is grounded, the anode is 180 volts, the first collection electrode 13 is 150 volts, and the transparent conductive film 16 is once -3
After applying 00 volts, a constant voltage of 16 o volts is applied. In this state, the fluorescent film does not emit light, or even if it does emit light, the intensity is extremely low. When the fluorescent film is momentarily irradiated with moderate X-rays through the face plate 17, the portion of the fluorescent film irradiated with the X-rays is exposed to the cathode 1.
It constantly emits red and white light due to the electron beam from 1.

If an object is placed between the cathode ray tube and the X-ray source and the X-rays that have passed through the object are momentarily irradiated onto the phosphor film, the spatial intensity distribution of the X-rays that have passed through the object can be projected onto a two-dimensional plane. A projected X-ray image of is stored on the fluorescent surface, and an X-ray image corresponding to the stored image is constantly projected onto the fluorescent surface by an electron beam from the cathode. The X-ray image is stored on the fluorescent film until an erasing operation is performed by applying a negative potential to the transparent conductive film 16. Therefore, the electron beam irradiation from the cathode is temporarily stopped and the electron beam is turned on after a while. When the irradiation is restarted, the same X-ray image can be projected onto the fluorescent surface again. The X-ray image projected on the fluorescent surface is bright and can be observed under normal indoor lighting. When a negative potential of 1,300 volts is applied to the transparent conductive film 16, all information stored in the fluorescent film is erased. On the fluorescent surface that has undergone this erasing operation, other
It is possible to memorize the ray image and project a bright and clear X-ray image on the fluorescent film.

(Example 2) A transparent conductive film made of indium tin oxide is formed on the inner surface of a glass substrate that becomes the face plate of a cathode ray tube. A slurry made from a mixture of a collodion solution and a yttrium sulfate phosphor containing 0,001 moles of terbium, which emits clean white light on the crystal surface, is applied to the entire surface of the transparent conductive film on the face plate, so that the phosphor particles have an average particle size. Apply evenly in three layers. After drying this at a temperature of 100°C or less, the collodion is decomposed by heating to a temperature of 360°C and removed, and a fluorescent film is formed on the transparent conductive film. On this fluorescent film, there are 10 openings that will become the second collection electrode.
A metal mesh electrode made of 0 mesh is placed in close contact with the fluorescent film. In this case, a part of the mesh electrode may be buried in the fluorescent film. Fine gold powder, which will become the first collection electrode, is applied to the inner wall of the cathode ray tube, excluding the face plate.

Further, a cathode and an anode are placed in predetermined positions, and exhaust and other steps necessary for manufacturing a normal cathode ray tube are added to obtain a cathode ray tube having the constituent elements shown schematically in FIG. 6. In this cathode ray tube, the second collection electrode 24 and the transparent conductive film 26 are electrically connected externally and kept at the same potential. Transparent conductive film 26
When a negative potential of 1,400 volts is applied momentarily to the voltage and the positive potential is gradually increased, the hysteresis phenomenon shown in FIG. 2 is obtained in the voltage range from 18 to 330 volts.

A constant voltage of 280 volts is applied to the anode 22 and a constant voltage of 220 volts is applied to the first collection electrode 23.
By once making the potential applied negative and then gradually applying a positive potential, an improved hysteresis curve as shown in FIG. 4 is obtained in the voltage range from 180 volts to 330 volts. To obtain a single X-ray image using this cathode ray tube, proceed as follows.

After the cathode 21 is grounded, a negative voltage of 280 volts is applied to the anode 22, 220 volts is applied to the first collection electrode 23, and a negative voltage of -400 volts is applied to the transparent conductive film 26 and the second collection electrode 24. , a positive voltage of 270 volts is applied. In this state, the fluorescent film does not emit light, or even if it does emit light, the intensity is extremely low. When this fluorescent film is momentarily irradiated with X-rays through the face plate 2, the fluorescent film in the area irradiated with the Emit white light. When a subject is placed between the cathode ray tube and the X-ray source, and the X-rays that have passed through the subject are momentarily irradiated onto the cathode ray's phosphor film, a two-dimensional plane of the spatial intensity distribution of the X-rays after passing through the subject is created. The projected X-ray image is stored on the fluorescent surface, and the X-ray image corresponding to the stored image is constantly projected onto the fluorescent surface 25 by the electron beam from the cathode 21.

The X-ray image is stored on the phosphor film until an erasing operation is performed by applying a negative potential to the transparent conductive film 26, so the irradiation of the electron beam from the cathode is temporarily stopped and the light emitted from the phosphor surface is extinguished. When the electron beam irradiation is restarted after being left in this state for a while, the same X-ray image is reproduced on the fluorescent surface 26. The X-ray image projected on the fluorescent surface is so bright that it can be observed even under normal indoor lighting. When a negative voltage of 1,400 volts is applied to the transparent conductive film 26, all information stored in the fluorescent film is erased, and the fluorescent surface to which this erasing operation has been applied newly displays other X-ray images. can be memorized without having any previous history, and accordingly a bright and clear X-ray image can be projected on the fluorescent film.

If the X-ray image display device and image display method of the present invention are used for diagnosis in hospitals and non-destructive testing in industry,
It is clear from the above examples that diagnosis can be made more quickly than in the conventional method of obtaining an X-ray image and making a diagnosis using a simple device using an Xm photographic film.

Furthermore, in the X-ray image display device of the present invention, the phosphor film does not suffer any damage even when erasing and storing are repeated many times, and a bright and clear X-ray image can be displayed on the phosphor film at any time. Therefore, the use of the X-ray image display device of the present invention makes a great contribution to saving resources, and has great industrial effects.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of a cathode ray tube used to measure in detail the relationship between the emission intensity of the phosphor film and the electron accelerating voltage for a phosphor film made using a phosphor crystal with a clean surface. 3 is a diagram showing the skin history phenomenon that appears in the relationship between the electron acceleration voltage and luminescence intensity of the phosphor used in the X-ray image display device according to the present invention, and FIG. FIG. 4 is a characteristic diagram showing the luminescence intensity of the fluorescent film depending on the amount of X-rays irradiated to the fluorescent film, which shows an improvement to significantly increase the brightness of the fluorescent film of the X-ray image display device according to the present invention. The history characteristic diagram obtained with the cathode ray tube, FIG. 6, shows the X
FIG. 6 is a schematic diagram of the X-ray image display apparatus for explaining the operation of the X-ray image display apparatus according to the present invention. 1...Glass tube, 2...Cathode, 3...
...First collection electrode, 4...Second collection electrode, 5.
...Fluorescent film, 6...Transparent conductive film, 7...
...Face plate, 8...Fixed power supply,
9...Variable power supply, 10...Glass tube, 1
1... cathode, 12... anode, 13...
...first collection electrode, 14...second collection electrode,
16... Fluorescent film, 16... Transparent conductive film, 17... Face plate, 18...
・Fixed power supply, 18.19...Variable power supply, 2o.
...Glass, 21...Cathode, 22...
...Anode, 23...First collection electrode, 24...
... Second collection electrode, 25 ... Fluorescent film, 26.
...Transparent conductive film, 27...Face plate), 28, 29...Fixed power supply, 30...
・Variable power supply. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2: Close to the B bar, 4 hours, so pressure Figure 3: υ

Claims (12)

[Claims] (1) The electron beam that enters the phosphor crystal constituting the phosphor film is controlled by utilizing the internal sustained polarization of the phosphor crystal and the phenomenon that the internal sustained polarization is canceled by X-ray irradiation. . An X-ray image display device, characterized in that an X-ray image is projected on the fluorescent film. (2) After applying a negative external electric field to the fluorescent film, when the accelerating voltage of the electron beam irradiated to the fluorescent film is increased from zero, the emission intensity increases rapidly when a predetermined voltage value is reached. However, when the accelerating voltage of the electron beam is further increased in a voltage range equal to or higher than the predetermined voltage value, the emission intensity increases in a first-order linear function with respect to the accelerating voltage of the electron beam, and then the intensity decreases to below the predetermined voltage. As the accelerating voltage of the electron beam is decreased, there is a hysteresis phenomenon in which the emission intensity decreases in a first-order linear function with respect to the accelerating voltage of the electron beam, and after the fluorescent film is irradiated with X-rays, The X-ray image display device according to claim 1, characterized in that the X-ray image display device does not exhibit the hysteresis phenomenon. (3) After applying a negative external electric field to the fluorescent film, it is constantly irradiated with an electron beam accelerated at a voltage lower than a predetermined voltage at a uniform density, but it does not emit light or does not emit light. The phosphor film, which emits extremely weak light even if the 3. The X-ray image display device according to claim 1, further comprising a phosphor film on which a still image of X-rays transmitted through the subject is obtained. (4) The phosphor film emits bright visible light when an electron beam enters the crystal, exhibits internal sustained polarization when an external electric field is applied, and further exhibits the internal sustained polarization when exposed to X-rays. The X-ray image display device according to claim 1, 2, or 3, characterized in that it is made of fine powder of a phosphor crystal that dissolves. (5) The fluorescent film emits bright visible light when an electron beam enters the crystal, exhibits internal sustained polarization when an external electric field is applied, and further exhibits sustained internal polarization when exposed to X-rays. Claims 1, 2, and 3 are characterized in that the device is made of a thin film of phosphor crystal that eliminates polarization.
The X-ray image display device described in 2. (6) The fluorescent crystal is terbium or praseodymium. Cerium, europium, dysprosium. Gadolinium, lanthanum, and i containing at least one rare earth element consisting of zamarium as an activator. Contains at least one element of notrium or lutetium as a main constituent of the base crystal. The X-ray image display device according to claim 4 or 5, characterized in that the X-ray image display device is made of oxides, sulfates, halo oxides, aluminates, silicates, and halides. (7) The phosphor crystal is composed of zinc sulfide and zinc cadmium sulfide containing copper or silver as an activator and an element of group Ill-A or group I-A of the periodic table as a co-activator. Claims 4 and 5 are characterized by
X-ray image display device described in section (8) Claims 4 or 5, characterized in that the phosphor is a zinc silicate phosphor containing manganese as an activator or a calcium tungstate phosphor.
The X-ray image display device described in Section. (9) A conductive material coated on a part or the entire inner wall surface of the cathode ray tube container excluding the face plate and cathode portion is used as the first collection electrode, and a mesh-shaped metal electrode is used as the second collection electrode. A patent claim characterized in that the second collection electrode is installed adjacent to the fluorescent film when viewed from the cathode side, or installed so that a part of the lower surface of the second collecting electrode is buried in the fluorescent film. The X-ray image display device according to the range 1, 2, or 3. (10) A conductive material coated on a part or the entire inner wall surface of the cathode ray tube container excluding the face plate and cathode is used as the first collection electrode, and a second collection electrode is applied on the transparent conductive film on the face plate. Claims 1 and 2 are characterized in that a large number of conductive substances serving as collecting electrodes are deposited in the form of dots, and a fluorescent film is formed in the gaps between the dot-like second collecting electrodes.
3. The X-ray image display device according to item 1 or 3. (11) An anode is installed immediately in front of the cathode, a constant voltage lower than a predetermined voltage is applied to the anode, the electron beam from the cathode is accelerated by the electric field created by the anode, and the accelerated electron beam is transferred to a fluorescent surface. An image display method characterized by projecting an X-ray image on a fluorescent surface by irradiating it with (12) The X-ray image projected on the fluorescent surface is erased by momentarily applying an arbitrary negative external electric field to the fluorescent film, and the X-ray image that has newly passed through the subject is An image display method characterized by irradiating a new X-ray image on the fluorescent surface.