US3334229A - Recording method and member of x-ray images and means for displaying said images - Google Patents

Description

Aug. 1, 1967 KATSUO MAKINO 3,334,229 RECORDING METHOD AND MEMBER OF X-RAY IMAGES AND MEANS FOR DISPLAYING SAID IMAGES Filed June 11, 1964 u PHOTOCONDUCTIVE LAYER SEMICONDUCTIVE LAYER 4 ELECTROLUMINESCENT LAYER -|3 INVENTOR KATSUO MAKINO ORNE'YS United States Patent 3,334,229 RECORDING METHOD AND MEMBER OF X-RAY IMAGES AND MEANS FOR DISPLAYING SAID IMAGES Katsuo Makino, Odawara-shi, Japan, assignor to Fuji Shashin Film Kabushiki Kaisha, Kanagawa-ken, Japan, a corporation of Japan Filed June 11, 1964, Ser. No. 374,245 Claims priority, application Japan, June 15, 1963, 38/ 31,858 4 Claims. (Cl. 250-65) This invention relates to a method of recording radiation images and in particular to storage and display of X-ray images and a new radiation sensitive recording element therefor. In this recording method, an X-ray image or other radiation image is memorized after the radiation sensitive recording element is exposed to a pattern radiation, and the memorized image is displayed at any time during an optional duration as a visible image.

Further to be concrete, in a method of recording radiation images or X-ray images of this invention there is used an X-ray sensitive memory member comprising at least two layers, the first being a layer of photoconductive material whose electrical resistivity is lowered by X-ray irradiation and remains lowered over a long period of time after X-ray irradiation is discontinued, and the sec- 0nd being a layer of phosphors which emits light on applying A.C. or/and DC. voltage across the layer, the

above two layers being sandwiched between two electrodes, one of which is at least transparent for visible light and another is at least transparent to X-rays. The X-ray sensitive memory member is exposed to an X-ray image, then the X-ray image is stored in the sensitive member as a latent pattern of lowered electrical resistivity which is maintained after X-ray irradiation is stopped, this phenomenon being called after effec in photoconductivity, and at any time and during an optional duration of time the stored latent image is displayed as the visible image.

It is accordingly a major object of this invention to provide a novel method in which an X-ray image is memorized for a long period of time as an electrical resistivity pattern in photoconductors and then is displayed at the desirable time and during an optional duration as a visible image.

It is another object of this invention to provide a simple method of recording X-ray images in which the latent X-ray image stored in the X-ray sensitive recording member is displayed as the visible image only by electrical operation without any process such as development and fixing or other chemical treatments.

It is still another object of this invention to provide a method of recording X-ray images in which the X-ray sensitive recording element can be used repeatedly.

It is a further object of this invention to provide a simple method of recording an X-ray image in which memorizing is carried out only by X-ray image irradiation without any voltage supply such as is used in usual storage devices such as a light or X-ray image storage panel.

X-ray radiography using silver halide emulsions, which has been known for a long time, requires, after X-ray image irradiation, many troublesome chemical procedures such as chemical development, fixing, washing and drying, which cancel the value of its good image quality.

Another type of X-ray radiography called X-ray clairvoyance is known in which an X-ray image is converted into a visible light image by using a fluorescent screen. Since image conversion occurs and the visible light image can be observed only when the X-ray image is projected upon the fluorescent screen, an X-ray lesion becomes seri- Patented Aug. 1, 1967 ice ous in the case of a long observation period of time required. The X-ray image intensity, therefore, must be decreased, which causes a fault of darkening the fluores cent image. Further an X-ray image intensifier has been developed as an X-ray radiography in order to remove the fault of the X-ray fluorescent screen but the apparatus is very extensive as well as too bulky and heavy to be carried. In this method, also, a visible image can be displayed only when an X-ray image is projected, and can not remain after the X-ray irradiation is discontinued. An X-ray television method, which has been developed instead of the X-ray image intensifier, has the same faults. Improved methods are an X-ray television storage tube method and an X-ray image storage panel which have been devised to store or memorize an X-ray image. The former, in which an X-ray image is converted to television signals and displayed for a long period of time as a visible light image by using a storage tube, requires an expensive equipment and complicated operations. In the latter the image storage is carried out by using a solid state image intensifier comprising a photoconductive layer whose electrical conductivity is changeable by X-ray irradiation and an electroluminescent layer, and by feeding back the light energy from the electroluminescent layer to the photoconductive layer in some methods. This storage panel is a little complicated and has a fault that if visible image displaying is interrupted, the same image can not be displayed again.

The method of recording X-ray images of this invention has been developed to remove the above mentioned faults. Distinctive features of this method are inexpensiveness and simplicity in operation and construction. Moreover the X-ray sensitive recording element of this invention is usable repeatedly. Since an X-ray image projected on the sensitive recording member is stored as a latent electric conductive image for a long period of time, this stored X-ray image can be displayed as a visible light image at any time even after the X-ray image projection is interrupted. When the stored image is converted into the visible light image, the stored image is scarcely spoiled, so the same stored image can be displayed many times. Further, as the stored image can easily be erased by infrared radiation and/or heat, the sensitive "recording member can be used repeatedly by erasing the first stored image and storing the next image. The procedure of this method does not require chemical treating, such as, development, fixing, washing and drying, etc., but it requires only an electric operation. As no equipment except the sensitive recording member is required when an X-ray image is projected on and stored in the member, it is very simple in operation and construction.

The means for accomplishing the foregoing objects and other advantages, which will be apparent to those skilled in the art, are set forth in the following specification and claims, and are illustrated in the accompanying drawing dealing with a basic embodiment of the present invention. Reference is made now to the single figure in which the invention has been schematically illustrated in section.

The sensitive recording member used in the method of this invention comprises substantially at least two layers and two electrodes, i.e. the photoconductive layer and the electroluminescent layer, and one electrode which is transparent for X-rays or other radiation to be stored and one electrode which is transparent for visible light to emit out from the member. The above-mentioned photoconductive layer is one which reduces its electrical resistance during irradiation when irradiated with X-rays as well as shows the after effect in photoconductivity, i.e. such 'a' property that the electric resistivity is in the reduced state for a long period of time after the X-ray irradiation is removed. The abovementioned electroluminescent layer is one which shows such a property that it emits visible light when a DC. and/or A.C. voltage is applied across it.

The sandwich construction of a photoconductive layer and an electroluminescent layer is known as a solid state image amplifier, and it is also known that this amplifier is effective for X-ray as well as visible light. The photoconductive layer used in the known solid state image amplifiers, however, shows only such a property that it decreases its electrical resistivity only when irradiated by a light or radiation and does not show any after effect in photoconductivity. Its electrical resistivity is restored rapidly after irradiation is moved. This is an essentially distinguishable point between the photoconductive layers in this invention and in the known solid state image amplifiers. In the known solid state image amplifiers, the after-image is abhorrent. The most difficult point in the solid state image amplifier is a time lag of an image, i.e., an after-image. The after-image is mainly caused by the after effect of the photoconductive layer. A duration of the after-image in the solid state image amplifier is, however, at most the order of 100 msec. It is about msec. for instance, in the reported image amplifier using cadmium sulfide, which is said to be too long in the case of amplifying a TV image on a cathode ray tube face. On the other hand, in this invention, the afterimage effect is utilized constructively and effectively. The period of life of the after-image is more than 1 hour. The radiation sensitive recording member used in this invention is essentially distinguishable from the aforementioned solid state image amplifier in its objects, methods, the construction of the member, and its materials, and it has been developed as the results of our investigations. The above great disparity of periods of afterimage life between the afore-mentioned process and this invention points out the above fact. Further, in order to store an image in the solid state image amplifier, such a method has been employed that the light emitted from an electroluminescent layer is fed back to the photoconductive layer, but in this method there is a fault in that the stored image becomes fuzzy gradually. This fault is removed in this invention. The image storing method using the solid state image amplifier exhibits the fact that this invention differs from the known image amplifiers, and the method in this invention is an original one.

Photoconductive material used in this invention must have a remarkable photoconductive after effect. Generally, resistivity of a photoconductor is decreased under X-ray irradiation less than that in the dark or under a no radiation condition. When X-rays are prevented from striking the photoconductor, the latter rapidly recovers its initial resistivity. A recovery time constant, for example, of well known zinc sulfide photoconductor is as fast as less tha n100 msec. It is preferable in this invention, however, to use a photoconductor in which the resistivity is kept in the decreased state for more than 100 sec. after removing X-ray radiation.

The photoconductive layer of this invention is com-- posed of a selenium material containing a heavy metal halide, such as tin bromide, lead iodide, antimony iodide and lead bromide. For example, the photoconductive layer prepared by vacuum deposition of selenium containing 1 mol percent of tin bromide shows a marked decrease in the electric resistivity during irradiation by a light beam or X-ray and its lower resistivity is maintained more than ten minutes, even after the irradiation is removed.

For the electroluminescent layers, many known materials are available, for instance, zinc sulfide powders doped with silver and a halogen, and a better result can be obtained by the addition of copper as the activators. Those powders may be used by dispersing them in a silicone resin, etc.

A radiation sensitive recording member comprising a photoconductive layer showing the after effect and are electroluminescent layer sandwiched by electrodes may be used in this invention. In more detail, it comprises basically a photoconductive layer 11 on an electrode 10 which is transparent to X-ray or other radiations, a semiconducting thin layer 12 formed on the photoconductive layer 13, which interrupts visible light to penetrate to the photoconductive layer, an electroluminescent layer on the semiconducting thin layer and an electrode 14 which permits visible light to emit from the electroluminescent layer to outside of the member and sandwiches the member with the counter electrode, from both electrodes electric leads 15 being drawn.

When an X-ray radiation image strikes the aforementioned member, the electrical resistivity of the photoconductive layer is lowered and remains low after the X-ray radiation is removed. On applying an A.C. and/ or DC. voltage to the both electrodes of this member in the selectively low resistivity state after irradiation by the radiation, light emission from the electroluminescent layer occurs with the light intensity corresponding to the selective resistivity change, so that a visible image can be observed corresponding to the X-ray image. When the voltage is not applied to the member with the stored image, the visible image can not be observed because of the absence of light emission from the electroluminescent layer. The visible image can be observed repeatedly, however, by applying the voltage as long as the low resistivity of the photoconductive layer is maintained accordingly as the resistivity recovers, the visible image of light emission from the electroluminescent layer becomes dim and fades away. The selectively low resistivity state or the stored image can be diminished and the dark adapted state or initial state can be restored rapidly by an infrared radiation and/ or thermal heating. After the stored image is removed, the member is in the prepared state for the next X-ray to be stored.

The above embodiments of this invention refer the case where the photoconductive layer is formed on the electroluminescent layer with or without having a thin intermediate semiconductor layer. However, a layer consisting of a mixture of the photoconductive material and the electroluminescent material may be used instead of the above composite layer.

Though the above-mentioned are the explanations about the storage and display of an X-ray image mainly, it should be understood that the invention is not limited to the case of X-ray, and the method and the sensitive recording member of this invention can be used for other radiations, such as, a light.

What is claimed is:

1. A process for recording a radiation image which comprises exposing to a radiation of the image to be stored and displayed a radiation sensitive recording member consisting of at least two layers one of which is a photoconductive layer composed of a selenium photoconductive material containing a heavy metal halide and which will show the after elfect when irradiated by the radiation, and another layer which is an electroluminescent layer emitting visible rays when an electric potential is applied thereacross, said layers further being sandwiched between two electrodes, one of said electrodes being transparent to visible rays and another being transparent to said radiation, the radiation image being stored in the photoconductive layer through the radiation-transparent electrode and applying an electric potential between the two electrodes to display the stored radiation image through the visible ray-transparent electrode as a visible image. 2:

2. A process for recording a radiation image which comprises exposing to a radiation of the image to be stored and displayed a radiation sensitive recording member consisting of at least two major layers having interlayered therein a thin intermediate semiconductor layer, one of said major layers being a photoconductive layer composed of a selenium photoconductive material containing a heavy metal halide and a showing the after effect when irradiated by radiation, and another major layer being an electroluminescent layer emitting visible rays when an electric potential is applied across said electroluminescent layer, said layers further being sandwiched between two electrodes, one of said electrodes being transparent to visible rays and another being transparent to said radiation, the radiation image being stored in the photoconductive layer through the radiation-transparent electrode, and applying an electric potential between the two electrodes whereby the stored radiation image is displayed through the visible ray-transparent electrode as a visible image.

3. A radiation sensitive recording member comprising at least two layers sandwiched between two electrodes, one of said layers being a photoconductive layer composed of a selenium photoconductive material containing a heavy metal halide, said layer showing the after eifect when irradiated by a radiation, and another layer being an electroluminescent layer emitting visible rays when an electric potential is applied thereacross, and the one of said electrodes lying adjacent said electroluminescent layer being transparent to visible rays and the electrode lying adjacent said photoconductive layer being transparent to said radiation.

4. A radiation sensitive recording member comprising at least two layers sandwiched between two electrodes,

6 said two layers having interlayered therebetween a thin intermediate semiconductor layer, one of said layers being a photoconductive layer composed of a selenium material containing a heavy metal halide and showing the after etfect when irradiated by radiation, another layer being an electroluminescent layer emitting visible rays when an electric potential is applied across said electroluminescent layer, said electrodes adjacent said electroluminescent layer being transparent to visible rays and said electrode adjacent said photoconductive layer being transparent to said radiation.

References Cited UNITED STATES PATENTS 2,334,554 11/1943 Hewlett 117-200 3,041,166 6/1962 Bardeen 96--1 3,052,540 9/1962 Greig 1l7-201 3,121,006 2/1964 Middleton et a1. 96l 3,160,503 12/1964 Cady 117201 OTHER REFERENCES Solid State Panel by Kazan; Electronics, September 12, 1958; 250-65.

RALPH G. NILSON, Primary Examiner.

A. L. BIRCH, Assistant Examiner.

Claims (1)

1. A PROCESS FOR RECORDING A RADIATION IMAGE WHICH COMPRISES EXPOSING TO A RADIATION OF THE IMAGE TO BE STORED AND DISPLAYED A RADIATION SENSITIVE RECORDING MEMBER CONSISTING OF AT LEAST TWO LAYERS ONE OF WHICH IS A PHOTOCONDUCTIVE LAYER COMPOSED OF A SELENIUM PHOTOCONDUCTIVE MATERIAL CONTAINING A HEAVY METAL HALIDE AND WHICH WILL SHOW THE AFTER EFFECT WHEN IRRADIATED BY THE RADIATION, AND ANOTHER LAYER WHICH IS AN ELECTROLUMINESCENT LAYER EMITTING VISIBLE RAYS WHEN AN ELECTRIC POTENTIAL IS APPLIED THEREACROSS, SAID LAYERS FURTHER BEING SANDWICHED BETWEEN TWO ELECTRODES, ONE OF SAID ELECTRODES BEING TRANSPARENT TO VISIBLE RAYS AND ANOTHER BEING TRANSPARENT TO SAID RADIATION, THE RADIATION IMAGE BEING STORED IN THE PHOTOCONDUCTIVE LAYER THROUGH THE RADIATION-TRANSPARENT ELECTRODE AND APPLYING AN ELECTRIC POTENTIAL BETWEEN THE TWO ELECTRODES TO DISPLAY THE STORED RADIATION IMAGE THROUGH THE VISIBLE RAY-TRANSPARENT ELECTRODE AS A VISIBLE IMAGE.

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