Radiant ray image intensifier tube

Abstract

 A radiant ray image intensifier tube has a radiant ray image intensifier tube assembly and an image pick up tube assembly. The image intensifier tube is capable of producing an electrical signal corresponding to an input radiant ray image. The radiant ray image intensifier tube assembly and the image pick up tube assembly are optically coupled through an optical fibre assembly. The envelopes of the two tube assemblies are separated from each other in an airtight manner by the optical fibre assembly.

Description

[0001] The present invention relates to radiant ray image intensifier tubes having both a radiant ray image intensifier tube assembly and an image pick up tube assembly and being capable of generating an electrical signal corresponding to an incident radiant ray image.

[0002] Apparatus for converting radiant ray images, for example X-ray and 1-ray images, into electrical signals are known. A conventional apparatus includes a radiant ray image intensifier tube assembly, an image pick up tube assembly and an optical lens system therebetween. The intensifier tube converts an incident radiant ray image into an amplitude modulated optical image. The optical lens system focuses the optical image on a target surface of the image pick up tube assembly and the latter converts the optical image into an electrical signal. This apparatus inevitably becomes large because of the optical lens system. Further, the optical lens system has a relatively large optical loss.

[0003] Some approaches have been proposed for eliminating such drawbacks. Figure 1 shows one of such approaches. This apparatus has a radiant image intensifier tube assembly 102 having an output plate 104 in the form of an optical fibre plate, and an image pick up tube assembly 106 having a face plate 108 in the form of an optical fibre plate. An output phosphor screen 110 and a photoconductive target 112 are formed on output plate 104 and face plate 108, respectively. Output plate 104 of the intensifier tube assembly and face plate 108 of the pick up tube assembly are positioned close to each other and their optical fibre plates are optically coupled. An optical image produced by phosphor screen 110 is transmitted to photoconductive target 112 by the optical fibre plates 104 and 108, instead of by an optical lens system. This apparatus can be made compact. However, output plate 104 and face plate 108 each form part of the wall of the vacuum envelopes of the intensifier tube assembly and the image pick up tube assembly, respectively. Therefore, the fibre plates constituting output 104 and face plate 108 must be sufficiently thick to withstand the mechanical forces exerted thereon and also be airtight. Generally, the thickness of each fibre plate must be more than 4 mm, so that the total thickness becomes mpre than 8 mm. A problem arises in that manufacturing faults in fibre plates increase as their thickness increases. The fault produces a black spot in the picture represented by the electrical signals generated by the devices so as to degrade the quality of the image.

[0004] The present invention overcomes these problems.

[0005] The present invention includes three major integers - an airtight optical fibre assembly, a radiant ray image intensifier tube assembly and an image pick up tube assembly. The image pick up tube assembly and the image intensifier tube assembly are connected through the airtight optical fibre assembly. Vacuum regions in the two tube assemblies are separated from each other by the optical fibre assembly. The optical fibre assembly has first and second surfaces and is airtight between these surfaces.

[0006] The radiant ray image intensifier tube assembly includes a first vacuum container in cooperation with the optical fibre assembly, an input screen for converting an incident radiant image into a photoelectric image, an output screen for converting the photoelectronic image into an optical image, a focusing electrode and an anode_.electrode. The first surface of the optical fibre assembly constitutes a part of the inner wall of the first vacuum container, and the output screen is provided on said first surface. The input screen is provided in the first vacuum container and is opposite to the output screen. The anode electrode is provided near the output screen and the focusing electrode is provided between the input screen and the anode electrode.

[0007] The image pick up tube assembly includes a second vacuum container co-operating with the optical fibre assembly, a photoconductive target for converting the optical image into an electron charged image, an electron gun for emitting a read out electron beam and an output electrode for leading out an electrical signal. The second surface of the optical fibre assembly constitutes a part of the inner wall of the second vacuum container, and the photoconductive target is provided on the second surface of the optical fibre assembly.

[0008] The optical fibre assembly constitutes parts of the inner walls of both the first and second vacuum containers. Therefore, only one airtight optical fibre assembly is required by the present invention. A total thickness of the optical fibre assembly can thereby be reduced compared to the prior art apparatus and any deterioration of image quality can be reduced.

[0009] In order that the invention may be more readily understood, it will now be described, by way of example only, with reference to the accompanying drawings, in which:-

Figure 1 is a cross-section of a prior art radiant ray image intensifier tube;

Figure 2 is a cross-section of an image intensifier tube of the present invention;

Figure 3 is an enlarged cross-section of a main portion of the image intensifier tube of Figure 2;

Figure 4 is a sectional elevation of an image intensifier tube assembly;

Figure 5 is a sectional side elevation of a target portion of an image pick up tube assembly;

Figure 6 is a sectional view of a body portion of the image pick up tube assembly;

Figures 7 and 8 show an optical fibre plate and a supporting ring at different stages of construction;

Figures 9 and 10 show a second optical fibre plate and an auxiliary metal ring at different stages of construction;

Figure 11 is a cross-section of another embodiment of the present invention;

Figures 12, 13 and 14 show cross-sections of the embodiment shown in Figure 11 at different stages of assembly; and

Figure 15 is an enlarged cross-section of a main part of a further embodiment of the present invention.

[0010] A radiant ray image intensifier tube assembly 120 and an image pick up tube assembly 122 are connected through an optical fibre assembly 124. Tube assemblies 120 and 122 have airtight envelopes separated from each other by the optical fibre assembly 124. Image intensifier tube assembly 120 has a glass envelope 126 with one open end 128 connected to a metal frame 130. An input screen 132 is positioned within the envelope opposite to open end 128. Input screen 132 has a substrate, a phosphor screen and a photoemissive layer (not shown), as do conventional image intensifier tubes. A focusing electrode 134 is provided along an inner wall of envelope 126 and an anode 136 is provided near open end 128.

[0011] Image pick up tube assembly 122 includes a glass envelope 138, a metal frame 140 connected to the glass envelope, and electrodes 142, 144 and 146 forming an electron gun within the envelope. A deflection coil 148 and a focusing coil 150 are provided around glass envelope 138.

[0012] Referring now to Figure 3, where an enlarged view of the optical fibre assembly 124 is shown, a first optical fibre plate 152 is attached in an airtight manner to a supporting ring 154 by a glass frit. Supporting ring 154 is air.tightly welded to metal frame 130 at their peripheries 156. An output screen 158 of the image intensifier tube assembly, having a phosphor layer, is formed on the surface of the optical fibre plate 152 which is within the envelope 126. Optical fibre plate 152 and supporting ring 154 constitute a part of the airtight container of the image intensifier tube assembly. Optical fibre a plate 152 is preferably as thin as possible, however, airtightness is required between opposite surfaces. Generally, its thickness is less than 4 mm, preferably 2 to 3 mm. On the other surface of the optical fibre plate 152, a photoconductive target 160 is provided. This target has a second optical fibre plate 162 in contact with optical fibre plate 152. Second optical fibre plate 162 is thinner than optical fibre plate 152 and is less than 1.5 mm in thickness, preferably 0.5 mm. Second plate 162 need not be airtight between its opposite faces and is preferably as thin as possible. However, its thickness is limited by mechanical strength. On a surface of the second optical fibre plate 162, a photoconductive layer 164 for the image pick up tube assembly is provided. An auxiliary metal ring 166 is attached to the second plate 162. A plurality of springs 168 fixed to the metal frame 140 push the auxiliary metal ring 166 towards the optical fibre plate 152, and the second optical fibre plate 162 is thereby urged into contact with optical fibre plate 152. The open end of metal frame 140 is airtightly connected to connecting ring 170 which, in turn, is airtightly connected to supporting ring 154.

[0013] The connections between metal frame 140 and connecting ring 170 and between supporting ring 154 and connecting ring 170 are performed by welding. An output terminal 172 for conducting an electrical signal is welded through glass envelope 138, and a conductive spring member 174 contacting photoconductive layer 164 is attached to the output terminal 172.

[0014] A method of making the image intensifier tube described above will be explained below. As shown in Figures 4, 5 and 6, image intensifier tube assembly 120, target portion 160 of the image pick up assembly and main body portion 122 of the image pick up assembly are assembled separately from each other and then they are interconnected. Referring to Figure 7, an optical fibre plate 176 of thickness T is airtightly bonded around the periphery of one of its surfaces to supporting ring 154 by a glass frit 178. Supporting. ring 154 has adequate mechanical strength to support optical fibre plate 176 and withstand the vacuum within glass envelope 126. The other surface of optical fibre plate 176 is then polished until the thickness is reduced to t, as shown in Figure 8. The thickness t is preferably 2 to 3 mm after polishing, while the initial thickness T is 4 to 6 mm. The thickness t should be less than 4 mm. Then, an output phosphor screen and an aluminium layer forming output screen 158 are provided on the optical fibre plate. Connecting ring 170 is then attached to the supporting ring by welding.

[0015] Input screen 132, focusing electrode 134 and any other electrodes are built into the image intensifier tube envelope 126. Supporting ring 154 is then connected to the metal frame 130 of the image intensifier tube assembly by welding. Tube envelope 126 is then heated to a temperature of more than 200°_C and is exhausted to a high vacuum, then a photoelectric layer is formed on an input screen 132 and the image intensifier tube assembly is completed.

[0016] Referring now to Figure 9, another optical fibre plate 180 of thickness T' is bonded at the periphery of one surface by glass frit 182 to an auxiliary metal ring 166 having considerable mechanical strength. In this case, the bonding need not be airtight. The surface opposite the bonded surface is polished to reduce its thickness and forms an optical fibre plate 162 having a thickness of t', where t' is less then 1.5 mm, and preferably 0.5 to 1.0 mm. Photoconductive layer 164 is then formed on the surface of fibre plate 162 and target portion 160 is completed.

[0017] Electrodes 142, 144 and 146, forming an electron gun, are built into a glass envelope 138 and main body portion 122 is assembled, as shown in Figure 6. Then, the image intensifier tube assembly shown in Figure 4, the target portion shown in Figure 5, and the image pick up tube assembly shown in Figure 6 are assembled, as shown in Figure 3. Optical fibre plate 152 and second optical fibre plate 162 are positioned in contact within each other. The image intensifier tube assembly 120 and the image pick up tube assembly 122 are connected in an airtight manner. That is, connecting ring 170 and metal frame 140 are welded together around their peripheries.

[0018] Next, image intensifier tube assembly 120 and photoconductive layer 164 are held at a temperature of less than 100°C, preferably near to room temperature, while the main body portion of image pick up tube assembly 122 is held at as high a temperature as possible as envelope 138 of image intensifier tube assembly 122 is exhausted to a high vacuum through an exhausting pipe 184 (see Figure 6), completing the image intensifier tube of the present invention.

[0019] The described image intensifier tube operates as follows. An X-ray image is converted into electron density image by input screen 132 and the electron density image is focused and accelerated by focusing electrode 134 and anode 136. It is then reconverted into an optical image at output screen 158. The optical image is transmitted to photoconductive target layer 164 by both optical fibre plates 152 and 162, and then forms an electron charge image on the photoconductive target layer 164. The electron charge image is scanned by an electron beam emitted from the electron gun, and the electric signal is obtained at output terminal 172.

[0020] The second fibre plate need not be airtight so it can be made very thin. Therefore, the total thickness of both optical fibre plates can be thinner than the prior art and defects in the fibre plates can be reduced. Since the optical fibre plates are exposed to atmospheric pressure only temporarily, plate 152 need not be so thick as to reliably maintain airtightness over a long period of time. The thickness of the optical fibre plates can, therefore, be thinner. Further, the radiant ray image intensifier tube assembly and the image pick up tube assembly are exhausted independently. Furthermore, the radiant image intensifier tube assembly can be completed independently from the image pick up tube assembly. The exhausting temperature can be set higher than 200°C and the gas absorbed in the tube is exhausted effectively, so that the radiant image intensifier tube assembly has a long life time as a conventional image intensifier tube.

[0021] In the above described embodiment, the image intensifier tube assembly is completed first, and then image pick up tube assembly is assembled and connected to the image intensifier tube assembly. However, image pick up tube assembly can be completed first; then the image intensifier tube can be assembled and connected to the image pick up tube assembly. Such an embodiment will be explained below, in conjunction with Figure 11. In this embodiment, an image pick up tube assembly 300 is assembled first, then an image intensifier tube assembly 302 is connected to pick up tube assembly 300. The image pick up tube assembly 300 shown in Figure 12 is the same as a conventional image pick up tube, except that face plate 304 is an optical fibre plate and a metal frame 306 is attached to an open end portion 308 of a glass envelope 310. The thickness of optical fibre face plate 304 is 3 to 4 mm. Metal frame 306 is attached to glass envelope 310 through face plate 304 which is connected to glass envelope 310 by indium 312 using the technique of cold press fitting.

[0022] As illustrated in Figure 13, on an outer surface of optical fibre face plate 304, an output screen 314 of the image intensifier tube assembly 300 is formed. Output screen 314 has a phosphor layer 316 and a metal back layer 318. If, during construction, the output screen is formed badly, the output screen is removed and another output screen can be formed again.

[0023] Image intensifier tube assembly 400, as shown in Figure 14, is assembled independently from the image pick up tube assembly. This image intensifier tube assembly is similar to the image intensifier tube shown in Figure 4, except optical fibre plate 152 and supporting ring 154 are not included. Then, image pick up tube assembly 300 shown in Figure 13 and image intensifier tube assembly 400 shown in Figure 14 are connected in an airtight manner. The position of output screen 314 is set at the focal point of the electron lens of image intensifier tube assembly 400. The connection is performed by welding together metal frame 320 and metal frame 306. After that, image intensifier tube assembly 302 is exhausted to a high vacuum and a photoemissive layer, forming an input screen 322, is formed to complete the image intensifier tube of the present invention.

[0024] In this embodiment, only one optical fibre plate is used. Therefore, defects are decreased as compared with the image intensifier tube illustrated in Figures 2 to 10. Further, the image pick up tube assembly, which has a lower manufacturing yield, is assembled and completed first. As a result, only good image pick up tubes are selected for use, so that the total manufacturing yield of the image intensifier tube can be increased.

[0025] Figure 15 shows a main portion of another embodiment. In this image intensifier tube, the image pick up tube assembly is assembled and completed first, the same as the image intensifier tube shown in Figures 11 to 14. At first, a transparent conductive layer 502 and a photoconductive layer 504, forming a photoconductive target 506 are formed on an optical fibre face plate 508 of 3 to 4 mm in thickness. Then optical fibre face plate 508 is connected to a glass envelope 510 of an image pick up tube assembly 520, by adhesive material 512, for example, indium. Adhesive material 512 contacts transparent conductive layer 502. Incidentally, an electron gun is built into glass envelope 510, as is conventional in the art.

[0026] A metal ring 514 is also provided around the optical fibre face plate and the glass envelope. Metal ring 514 contacts adhesive material 512 and is electrically connected to transparent conductive layer 502, because indium adhesive material 512 is conductive. Metal ring 514 is used as an output electrode for conducting an electrical signal. Glass envelope 510 is exhausted to complete the image pick up tube assembly. This image pick up assembly is the same as a conventional image pick up tube, except for optical fibre face plate 508.

[0027] On the other surface of optical fibre face plate 508, an output screen 530 of an image intensifier tube assembly is formed. Output screen 530 has a phosphor layer 532 provided on optical fibre face plate 508 and a metal back layer 534 of aluminium. A metal ring 540 is attached to the optical fibre face plate 508 by an adhesive material, for example, indium. This portion of optical fibre face plate 508 at which attachment occurs corresponds to the portion covered by adhesive 512 on the opposite surface. Metal ring 540 is electrically connected to anode electrode 542. The output screen can be formed on the optical fibre face plate after metal ring 540 is attached. In this case, an electrical connection between the metal ring and the metal back layer can be ensured.

[0028] Image intensifier tube assembly 550, like the image intensifier tube shown in Figure 14, is assembled independently from the image pick up tube assembly. Subsequently, image pick up tube assembly 520 and image intensifier tube assembly 540 are connected in an airtight manner. This connection is performed by welding a metal frame 552 and metal frame 540 at their peripheries. Image intensifier tube assembly 550 is then exhausted and a photoemissive layer forming an input screen is formed to complete the image intensifier tube of the present invention.

[0029] A further advantage is obtained in the embodiment of Figure 15 compared with the embodiment of Figures 11 to 14. That is, the image pick up tube assembly and the image intensifier tube assembly are electrically isolated by the optical fibre face plate. The structure of the output electrode for conducting an output signal can be simplified.

Claims

1. A radiant ray image intensifier tube comprising a radiant ray image intensifier tube assembly (120) having an evacuated envelope (126); an image pick up tube assembly (122) having an evacuated envelope (138); and an optical fibre assembly (124) forming an optical link between the intensifier tube assembly (120) and the pick up tube assembly (122), characterised in that said optical fibre assembly (124) is airtight between two surfaces and these surfaces form part of the wall of said respective evacuated envelopes.

2. A radiant ray image intensifier tube as claimed in claim 1, characterised in that said envelopes (126, 128) are each open at one end, the envelopes are arranged with the open ends facing each other and the optical fibre assembly (124) is sealed in the open ends of the envelopes to close off each envelope.

3. A radiant ray image intensifier tube as claimed in claim 2, characterised in that the optical fibre assembly comprises a plate (152) of optical fibres extending between said pair of surfaces, a first metal ring (154) sealed to the plate around the periphery of one of said surfaces and sealed to an open end of one of the envelopes (126) and a second metal ring (140) sealed to said first metal ring and to the open end of the other envelope (138).

4. A radiant ray image intensifier tube as claimed in claim 3, characterised in that said optical fibre plate (152) has a thickness of less than 4 mm.

5. A radiant ray image intensifier tube as claimed in claim 3 or 4, characterised in that said image pick up tube assembly (122) has converting means comprising a second optical fibre plate 162 contacting said optical fibre plate (152) and being thinner than said optical fibre plate (152).

6. A radiant ray image intensifier tube as claimed in claim 2, characterised in that the optical fibre assembly comprises a plate J304) of optical fibres extending between said pair of surfaces, the open end of one envelope (310) is sealed around the periphery of one of said surfaces and a metal frame (306) sealed to the open end of the other envelope (302) is also sealed around the open end of said one envelope (310).

7. A radiant ray image intensifier tube as claimed in claim 6, characterised in that said metal frame (306) is electrically connected to an anode electrode of said image intensifier tube assembly.

8. A radiant ray image intensifier tube as claimed in claim 2, characterised in that the optical fibre assembly comprises a plate (508) of optical fibres extending between said pair of surfaces, and the open ends of said envelopes are sealed to peripheral portions of respective ones of said surfaces.

Drawing