JPH043059B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a new radiation image conversion apparatus for performing medical diagnosis and the like using radiation. More specifically, a first stimulable phosphor screen is provided inside the electron tube to accumulate a radiation image, and a second reading phosphor screen is scanned with an electron beam to emit a second fluorescent light to generate the radiation image. is read out as the first fluorescence, the photocathode is excited with the light, it emits photoelectrons, the photoelectrons are converted into electrical signals, and the electrical signals are directly or electrically processed into images to be displayed on television monitors or films. This is a device that reproduces images and performs diagnosis, etc. Technical Background and Problems of the Invention Conventionally, to obtain radiographic images, there has been a direct imaging method using an intensifying screen and a silver halide film, and an X-ray image intensifier (II) has been used to capture the output surface optical image.
II indirect photography, which takes pictures on 100mm or 35mm silver halide film, was used. Recently, a radiation latent image is formed on a stimulable phosphor screen, and then a laser beam is scanned onto this phosphor screen and converted into an electrical signal using a condensing device and a photomultiplier. A method has been proposed in which the image is played back on a television monitor or film for diagnosis. This is USP 3859527 and JP-A-55-
It is disclosed in Publication No. 15025, "Eizo Information" magazine, April 1982 issue (P409), etc. However, with the above-mentioned direct imaging method, problems such as the depletion of silver resources on a global scale have been raised, and in the II indirect imaging method, the shape of the X-ray entrance surface of X-ray II is a curved surface, and There was a problem that it was difficult to create square or rectangular surfaces. On the other hand, the above-mentioned method in which a latent radiation image is formed on a storage type (also called stimulable) fluorescent surface and is read by emitting light by irradiating a laser beam, the patient's exposure dose is small and the X-ray incident Although the surface is flat and the effective surface can be arbitrarily square or rectangular, there are disadvantages as described below. That is, first of all, the principle of this system is as shown in FIGS. 1 to 3, quoting from the above-mentioned "Eizo Information" magazine. In FIG. 1, X-rays 2 emitted from an X-ray tube 1 pass through a human body 3, reach an imaging plate 4, that is, a stimulable phosphor plate, and form an X-ray latent image. This imaging plate is the third
As shown in the figure, halide crystals of a stimulable phosphor are coated in a highly packed manner on a support 31, and the whole is placed in a dark box for photographing. The imaging plate on which the latent X-ray image has been recorded is placed on an ultra-precision feed table 21 in a dark room, as shown in FIG. is scanned. Blue fluorescent light is then emitted from the imaging plate 4 , and this light is collected at one point by an optical fiber 25, converted into an electrical signal 27 by a photomultiplier 26, and extracted in time series. Here, to explain the principle of blue fluorescence emitted from the imaging plate 4, the stimulable phosphor is
Even if the crystal is excited by an excitation source such as X-rays, the energy state within the crystal changes and almost no light is emitted.
630 nm), this is due to the phenomenon that light is emitted at a shorter wavelength (peak wavelength 370 nm) than this second excitation spectrum. The other scanning of the imaging plate 4 is performed by rotating the roller 22 of the ultra-precision feed table 21 at a constant speed. The electrical signals read in this way are sent to a high-speed image processor 6, a computer 7, and a magnetic memory 8.
The image is then processed, recorded on a suitable film 10 by a high-precision image recorder 9, and processed by an automatic processor 11 to obtain a diagnostic X-ray photograph 12. The process of recording, reading and erasing the imaging plate 4 is illustrated in FIGS. 3a-e. Figure 3a
1 is an unused imaging plate 4, and FIG. 1b shows a state in which an X-ray image has been recorded. When the X-ray quantum 34 is incident on the stimulable fluorescent surface 32, its energy is stored in the crystal. 33
35 schematically shows an unaccumulated state and an accumulated state.
Next, as shown in figure c, a laser beam 36 of approximately 6330 Å
When irradiated with , the X-ray energy accumulated on the storage fluorescent surface 32 is extracted as blue fluorescent light 37 . The imaging plate 4 that has been read is
The X-ray latent image is completely erased by irradiating the entire surface with the light 38 again as shown in FIG. Such conventional methods have the following disadvantages. ○B Immediate reading after shooting is not possible. ○B Since a mechanical method is used as the reading means, it takes a long time of several tens of seconds to read one sheet, which is inefficient. ○C Accuracy control of the reading device becomes extremely complicated and expensive. Purpose of the Invention The present invention solves the above-mentioned inconveniences, enables immediate reading, enables high-speed imaging, allows the radiation image converting section to be formed into a flat, rectangular effective surface, and converts everything electrically. An object of the present invention is to provide a radiation image conversion device whose accuracy can be easily controlled. Summary of the Invention The present invention is an electron tube similar to a television cathode ray tube, in which the vacuum container has a large-diameter portion having a radiation entrance window, and a portion opposite thereto has a small-diameter portion. ) A radiation image conversion panel having a fluorescent surface and a reading fluorescent surface for reading out radiation accumulated images from the stimulable fluorescent surface as fluorescent light is built into the large diameter portion, and is located near the stimulable fluorescent surface. It has a photocathode that converts the fluorescence of the radiation accumulation image read out into photoelectrons using a readout fluorescent surface, and collects the photoelectrons emitted from the photocathode to multiply secondary electrons and generate electrical signals. A secondary electron multiplier that takes out the electrons outside the tube is arranged near the photocathode, and an electron gun and deflection means that generate electron beams for sequentially emitting light from the readout fluorescent surface are connected to the small diameter section. This radiation image intensifier tube device is characterized by converting a radiation image incident on its large-diameter surface into an electrical signal in preparation for the Incidentally, to accumulate the radiation image, a stimulable fluorescent surface having the characteristics as shown in FIGS. 1 to 3 is used and placed in a vacuum container. However, in the conventional method, the radiation latent image recorded on the stimulable fluorescent surface is read out over several tens of seconds, whereas in the device of the present invention, the radiation latent image recorded on the stimulable fluorescent surface is read out at high speed, for example within 1 second, so It is better for the afterglow of the fluorescent surface to be as short as possible. The same can be said of the reading fluorescent surface. Furthermore, in the conventional method, the stimulable phosphor screen was mechanically read out using a laser beam in a dark room, whereas in the present invention, the electron beam is scanned at high speed using an electrical deflection device to excite the read phosphor screen. It emits long-wavelength fluorescence, this light excites a stimulable phosphor screen to emit relatively short-wavelength fluorescence corresponding to a radiation image, and the emitted light is further converted into photoelectrons by a photocathode.
It is characterized by extracting these photoelectrons outside the tube as time-series electrical signals. Embodiment of the Invention FIG. 4 shows an embodiment of the invention. Identical parts are represented by the same symbols. The vacuum container 101 is made of a thin metal plate made of aluminum, titanium, stainless steel, or an alloy thereof that has good radiation transparency, or
A large-diameter radiation entrance window 102 made of borosilicate glass with good radiation transmission, a small-diameter neck portion 105 made of glass, and a body portion 103 and a conical portion that connect the radiation entrance window 102 and the neck portion 105. 10
Consists of 4. The body portion 103 and the conical portion 104 are made of metal such as stainless steel, KOV, aluminum, etc., which have sufficient mechanical strength, or glass. Inside the radiation entrance window 102, a metal support frame 125 is provided.
A radiation image conversion panel 110 fixed to
15. There is a photoelectron detection element such as one or more secondary electron multipliers 122 located outside the effective diameter of the radiation image conversion panel 110 at a location where the photocathode 115 is viewed. The electron gun 1 is installed in the network section 105.
20 is built in, and a deflection yoke 121, which is one of the deflection means, is disposed outside of the deflection yoke 121. FIG. 5 is an explanatory diagram of the radiation image conversion panel 110 and the photocathode 115. Made of borosilicate glass, for example, thickness 2
An electron gun 120 is mounted on a rectangular glass substrate 111 of mm.
A color selection filter film 116, a stimulable fluorescent surface 112, a reading fluorescent surface 113, and an aluminum thin film 114 are formed in this order from the side. And on the X-ray entrance window side of the glass substrate 111
A photocathode 115 made of a material such as Sb-Cs, Sb-Cs-K, or Sb-Cs-K-Na is formed. The stimulable fluorescent surface 112 is made of halide crystals coated with a binder to a thickness of about 100 to 500 μm, and the halide includes BaFCl:
Eu( ^10-3 ), BaFCl:Ce( ^10-8 ), BaFBr:Eu(8
×10 ^-4 ), (Ba _0.9 , Mg _0.1 ) FBr: Eu (10 ^-3 ),
( _Ba0.7 , _Ca0.3 ) FBr: Eu (3×10 ^-3 ), BaFBr:
Ce (10 ^-4 ), Tb (10 ^-4 ), etc., such as BaFCl:
Eu(10 ^-3 ) has a peak wavelength of 3800 Å and an afterglow of several 100 μsec, as shown by reference numeral 140 in FIG. The reading phosphor surface 113 is suitably a short afterglow phosphor for flying spots, with an emission spectrum that leans toward long wavelengths, and is coated with a binder to a thickness of approximately 5 to 20 μm. 112. Suitable phosphors for this include ZnO:Zn, (Zn, Cd)
S: Ag, Ni, Gd ₂ O ₂ S: (Tb, La) ₂ O ₂ S: Tb,
(Y, Gd) ₂ O ₂ S: Tb, Y ₃ Al ₅ O ₁₂ : Ce, etc.
For example, the emission spectrum of Y ₂ Al ₅ O ₁₂ :Ce phosphor has a peak wavelength of 5300, as shown by reference numeral 141 in FIG.
The afterglow is also several 100 nanoseconds. As another example
ZnO: The emission spectrum of Zn is shown at 143 in the same figure.
As shown, the peak wavelength is 5100 Å and the afterglow is several μsec. The aluminum thin film 114 is the same as the metal back used in ordinary cathode ray tubes, and has a thickness of about 500 to 5000 Å, and serves to stabilize the surface potential of the reading phosphor screen 113 and protect the phosphor surface from ion bombardment. Motsu. The color selection filter 116 includes a blue inorganic coloring agent such as cobalt blue, cerulean blue, chromium oxide, _TiO2 -ZnO-CoO-NiO pigment, and the like.
The color selection filter 1 is also mounted on the glass substrate 111.
16, the glass substrate 111 itself may be made of a blue glass filter material. An example of this is "B-370" manufactured by Hoya Glass Co., Ltd., whose transmission spectrum is shown at 144 in FIG. Indicated by Next, the secondary electron multiplier 122 may be the same as the dynode of a normal photomultiplier, and is made by forming an Sb-Cs film on a plurality of Ni plates. Apply. Next, regarding the operating principle of the device of the present invention, FIG.
This will be explained using FIGS. 5 and 7. () X-ray latent image recording: The radiation flux 34 that has passed through the human body (not shown) passes through the entrance window 102 and the glass substrate 111 and enters the stimulable fluorescent surface 112, as shown in FIG. 3b. Similarly, radiation energy is stored in a stimulable phosphor crystal. () Reading: The electron beam 131 emitted from the electron gun 120 whose cathode voltage is set to about -20 KV and focused is deflected by a magnetic field by the deflection yoke 121, and is read by the radiation image conversion panel 110 . A point on the light surface 113 is excited to emit bright yellow or red light.
This light enters the stimulable fluorescent surface 112, acts on the crystal that has previously accumulated energy due to the radiation, and blue fluorescent light is emitted from this area.
This blue light passes through the glass substrate 111 and acts on the photocathode 115, and photoelectrons 132 are emitted from the photocathode 115. The photoelectrons 132 are attracted to the secondary electron multiplier 122, which has a higher potential than the photocathode, and are multiplied by the signal output terminal 1.
24 as an electrical signal. In the above process, the emission spectrum of the reading fluorescent surface 113 is as shown in FIG. 7 141 or 142,
The emission spectrum of the stimulable fluorescent surface 112 is 14
0, when the sensitivity characteristic of the photocathode 115 is 142,
A part of the light from the reading fluorescent surface 113 is transmitted to the stimulable fluorescent surface 1.
12, Photocathode 11 transmitted through glass substrate 111
If 5 is reached, 1 appears in Figure 7.
Since the photocathode has a wide sensitivity range as shown by 42, the photoelectrons 32 are included as noise components. In order to eliminate this drawback, for example, a color selective optical filter film 116 having transmission characteristics as shown at 144 in FIG.
By forming the filter between the glass substrate 111 and the glass substrate 111, the above-mentioned noise component can be removed. Further, as mentioned above, the color selection filter film 1 is placed on the glass substrate 111.
16, the glass substrate 111 itself may be a blue selective filter glass as shown at 144 in FIG. Furthermore, in order to collect as much photoelectron flow 132 as possible, it is better to provide a plurality of secondary electron multipliers 122, and if the signal extraction terminals of each of them are connected in parallel, a high-level signal with less noise can be obtained. A signal is obtained and the S/N ratio is improved.
The electron beam 131 scans the radiation image conversion panel two-dimensionally by the deflection yoke 121, and the scanning speed is selected depending on the afterglow characteristics of the reading fluorescent surface 113 and the stimulable fluorescent surface 112.
That is, for example, when the electron beam moves from point A to the adjacent point B, if the fluorescence from the stimulable fluorescent surface at point A is not extinguished, the resolution characteristics will deteriorate. The afterglow is now 10μsec (temporarily assuming 1% afterglow)
Considering the case of , assuming that the number of pixels on the entire effective surface is 500 x 500, the readout time for one screen is:
It is 2.5 seconds. () Erasing: Increase the electron beam 131 as much as possible, put it in a defocus state, and then move the deflection yoke 121
The data is erased by scanning the entire reading fluorescent surface of the radiation image conversion panel once or several times. Note that the energy of the electron beam may be increased only during this erasing, or the amount of the electron beam may be increased. FIG. 6 shows another embodiment of the radiation image conversion panel 110 , which is provided with a protective film 117 to prevent chemical interaction between the fluorescent materials of the readout fluorescent surface 113 and the stimulable fluorescent surface 112. The protective film 117 must prevent chemical interaction between the two phosphor materials and must be transparent to the light from the reading phosphor surface. As such a material, Al ₂ O ₃ , In ₂ O ₃ , water glass, or the like can be used. FIG. 8 shows another embodiment of the invention. In this embodiment, the radiation image conversion panel 1
As shown in FIG. 9, 10 is a flat plate 151 of a substrate with good radiation transmission, such as aluminum (thickness: 1 mm).
A stimulable fluorescent surface 112 and a reading fluorescent surface 113 are laminated in this order, and a photocathode 115 is provided on the side surface of the electron gun.
is covered. and secondary electron image magnification device 12
2 is a body portion 103 facing the photocathode 115 and a conical portion 1;
It is located near 04. The radiation latent image recorded by the radiation 34 stimulates the reading fluorescent surface 113 of the radiation image conversion panel 110 with an electron beam (reading beam) 131 to emit yellow or red fluorescent light, and this fluorescent light is accumulated. The light enters the fluorescent surface 112 to excite it, and blue fluorescent light is read out. This blue fluorescent light is transmitted through the reading fluorescent surface 113 and the photocathode 1
15 and generates photoelectrons 132. The other operations are as explained using the fourth example. 10 and 11 show modified examples of the radiation image conversion panel 110 used in the embodiment of FIG. 8.
In FIG. 10, a color selection filter layer 116 is provided between the reading fluorescent surface 113 and the photocathode 115, and in FIG. 11, a transparent conductive layer is further provided between the color selection optical filter layer 116 and the photocathode 115. A sexual coating 152 is provided. As mentioned above, the eighth
In the illustrated embodiment, the photocathode 115 and the secondary electron multiplier 122 can be manufactured extremely easily. In this case, since the photocathode 115 is directly impacted by the electron beam 131, it is necessary to use a photocathode that is resistant to electron beam impact. FIGS. 12 and 13 show still another embodiment of the present invention. As shown in FIG. 13, a radiation image conversion panel 110 is arranged on the radiation incident window side of a thin transparent glass substrate 161 with a thickness of about 100 to 500 μm. A stimulable fluorescent surface 112 is placed on one side, and a reading fluorescent surface 11 is placed on the opposite side.
3. An aluminum thin film 114 is provided, and a photocathode 115 is formed on the inner wall surface of the radiation entrance window 102. The secondary electron multiplier 122 includes the radiation image conversion panel 110 and the radiation entrance window 102.
The photocathode 115 is located outside the effective diameter between the photocathode 115 and the photocathode 115. The reading beam 131 excites the reading phosphor surface 113 to emit yellow or red light. This light passes through the glass substrate 161 and reads out the radiation latent image on the storage phosphor surface on the opposite side. The read blue light stimulates the photocathode 115 formed on the inner surface of the radiation entrance window 102, and photoelectrons 132 are emitted from the photocathode 115 and attracted to the secondary electron multiplier 122, resulting in a multiplied electrical signal. becomes. However, in this embodiment, the reading fluorescent surface 113
A glass substrate 161 is placed between the stimulable fluorescent surface 112 and
is present, it is desirable to make the glass substrate 161 as thin as possible, preferably 300 μm or less. Further, as shown in FIG. 14, a color selection optical filter 116 may be provided on the back side of the storage fluorescent surface 112. Note that the glass substrate may be formed of an optical fiber plate (glass fiber plate), which suppresses undesired diffusion of light and further reduces the noise level. In particular, it is preferable to interpose this optical fiber board in the optical path between the stimulable fluorescent surface and the reading fluorescent surface, thereby increasing the resolution. Effects of the Invention As described above, the following effects can be obtained by the apparatus of the present invention. Can be read immediately after shooting. Reading time can be shortened. Therefore, relatively high-speed imaging is possible. The radiation image converting section can be made into a flat surface or a rectangular effective surface. Since all image conversion is performed electrically, accuracy control is easy and inexpensive. The high sensitivity of the stimulable phosphor surface results in extremely low radiation exposure to the patient. Since almost all the components are installed inside and around a vacuum container with a shape similar to a cathode ray tube, it is compact and easy to handle.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of a conventional radiographic imaging device, and FIGS. 2 and 3 a to e
4 is a schematic configuration diagram showing one embodiment of the present invention, FIG. 5 is an enlarged sectional view of the radiation image converting section, and FIG. 6 is a schematic diagram showing another embodiment of the present invention. 7 is a diagram of its optical characteristics; FIGS. 8 and 9 are schematic configuration diagrams and sectional views of essential parts showing still other embodiments of the present invention; FIGS. 10 to 14
The figures are diagrams showing still other embodiments of the present invention. 101 ...Vacuum container, 102...Radiation entrance window, 110 ...Radiation image conversion panel, 112...
Accumulative fluorescent surface, 113...Reading fluorescent surface, 115...
...Photocathode, 116...Color selection optical filter film,
122... Secondary electron multiplier, 120... Electron gun, 121... Deflection yoke, 34... X-ray quantum,
131...electron beam, 132...photoelectron.

Claims (1)

[Scope of Claims] 1. A vacuum container having an entrance window made of a material that transmits radiation, in which a large diameter part, a tapered part, and a small diameter part are successively formed; a radiation-transparent substrate arranged as a radiation transmitting substrate; a radiation energy accumulating phosphor screen formed on this substrate; a reading phosphor screen formed on the surface of the stimulable phosphor screen on the side of the small diameter portion; a photocathode provided in close proximity to the stimulable phosphor screen; a photoelectron detection element arranged to capture photoelectrons emitted from the photocathode and converting them into an electrical signal according to the amount of captured photoelectrons; and a small-diameter vacuum container. an electron gun provided in the section and configured to emit an electron beam onto the reading phosphor screen to cause the reading phosphor screen to emit light; and an electron beam deflection device provided outside the tube to scan the electron beam onto the reading phosphor screen. , the electron beam is scanned at high speed by the above-mentioned deflection device, the reading fluorescent screen is excited to emit long-wavelength fluorescence, the emitted light is further converted into photoelectrons by the photocathode, and the photoelectrons are converted into a time series. A radiation image conversion device characterized in that the electrical signal is extracted outside the tube as an electrical signal. 2. The radiation image conversion device according to claim 1, wherein the stimulable phosphor screen is made of a halide crystal, and the maximum value of the fluorescence spectrum is in a wavelength range of 5000 A or less. 3. The radiation image conversion device according to claim 1, wherein the entrance window, the stimulable phosphor screen, the reading phosphor screen, and the photocathode have generally rectangular planar shapes. 4. The radiation image conversion device according to claim 1, wherein the stimulable phosphor screen is formed on one side of a light-transmitting glass substrate, and the photocathode is formed on the other side of the glass substrate. 5. The radiation image conversion device according to claim 1, wherein the entrance window is formed of at least one thin plate selected from aluminum, titanium, stainless steel, or a thin metal plate containing these as main components. 6. The radiation image conversion device according to claim 1, wherein a color selection optical filter is interposed between the stimulable phosphor screen and the photocathode. 7. The radiation image conversion device according to claim 1, wherein the radiation transparent substrate is a glass substrate, and a stimulable phosphor screen is attached to one side of the glass substrate via a color selection optical filter. 8. The radiation image conversion device according to claim 1, wherein a photocathode is formed on the surface of the glass substrate on the side of the entrance window, and a photoelectron detection element is provided at a position facing the photocathode. 9. The radiation image conversion device according to claim 4, wherein the glass substrate is made of an optical fiber board. 10. The radiation image conversion device according to claim 4, wherein a color selection optical filter, a stimulable phosphor screen, a reading phosphor screen, and an aluminum thin film are formed in this order on the electron gun side surface of the glass substrate. 11. The radiation image converting device according to claim 1, wherein a protective layer is interposed between the stimulable phosphor screen and the reading phosphor screen to prevent mutual reaction between the materials of the stimulable phosphor screen and the reading phosphor screen. 12. Claim 1, wherein an aluminum substrate, a stimulable phosphor screen, and a reading phosphor screen are provided in this order from the entrance window side toward the electron gun side, and a photocathode is formed in close contact with the reading phosphor screen. radiation image conversion device. 13. The radiation image conversion device according to claim 12, further comprising a color selection optical filter that cuts the emission spectrum of the reading phosphor screen between the reading phosphor screen and the photocathode. 14. A stimulable phosphor screen, a thin glass plate, a reading phosphor screen, and an aluminum thin film are formed in this order from the entrance window side toward the electron gun side, and a photocathode is formed on the inner wall surface of the entrance window. The radiation image conversion device according to item 1. 15. Claim 4, wherein the glass substrate is made of blue filter glass, and has a light transmission property that allows almost all of the fluorescence from the stimulable phosphor screen to pass therethrough, and almost no fluorescence from the reading phosphor screen to pass through. radiation image conversion device. 16. The radiation image conversion device according to claim 6, wherein the color selection optical filter has a property of cutting off a spectrum having an intensity of 5% or more on the short wavelength side of the emission spectrum of the reading phosphor screen. 17. The radiation image conversion device according to claim 1, wherein the reading phosphor screen has an emission spectrum having a wavelength longer than that of the stimulable phosphor screen, and has a 10% afterglow of 1 msec or less. 18. The radiation image conversion device according to claim 1, wherein the photoelectron detection element includes a secondary electron multiplier. 19. The radiation image conversion apparatus according to claim 1 or 18, wherein a plurality of photoelectron detection elements are provided and their output terminals are connected in parallel to each other. 20. The radiation image conversion device according to claim 1, wherein the photoelectron detection element is operated at a positive potential with respect to the potential of the photocathode. 21. Claim No. 2, wherein an optical fiber board is interposed between the stimulable phosphor screen and the reading phosphor screen so that the light emitted from the reading phosphor screen is irradiated onto the storable phosphor screen through the fibers of the optical fiber board. The radiation image conversion device according to item 1.