EP0173851B1 - Electronic vacuum image intensifier for x-ray diagnosis devices - Google Patents

Description

Electronic vacuum image intensifier for diagnostic X-ray equipment

The invention relates to electronic vacuum image intensifiers for devices for diagnosis with X-rays according to the preamble of claim 1. Such a device is described in EP-A-0 087 674.

X-ray diagnostic devices known, for example, from US Pat. No. 3,622,786, which comprise an x-ray image intensifier, to which a lens, for example an x-ray television chain, is connected, are a series of separately constructed sub-devices, i. H. an image intensifier to which a separate lens is assigned. In the optical transmission path, distances remain between the areas over which the output image is transmitted. This leads to reflections at the optical interfaces and especially in the support of the exit light screen of the image intensifier. Such reflections and the resulting scattered light on the one hand worsen the contrast, on the other hand undesirably increase the background of the image and thus reduce the image quality.

In order to avoid interfaces in known X-ray television chains, such as are described, for example, in US Pat. No. 3,055,021, fiber optic connections are made between the output of the image intensifier and the input of a television recording camera. However, this has the disadvantage that in addition to the loss of light through self-absorption of the fiber optics, there are also loss of resolution. It is also not possible to split the light between several receivers. On the other hand, attempts were also made to largely remove the background by means of absorption and to improve the contrast. However, the gray glass or absorption layers used to manufacture the fluorescent screen support result in a loss of light and have the disadvantage that they cause additional costs.

In order to improve the output images of a picture tube, attempts have already been made according to the above-mentioned EP-A-0 087 674 to make the glass support of the exit fluorescent screen so much thicker that total reflections on the inside of its exit surface no longer reach the viewing surface. In order to be able to use a fluorescent screen with a conventional support, its exit surface has been glued to the inside surface of the exit window pane of the tubular bulb to form a stack of suitable thickness. If necessary, a transparent plate should also be glued to the outside of the window pane to achieve sufficient thickness. Such a stack requires at least one cement that lies in the tube bulb. However, because there are currently no putties available that are optically perfect and vacuum-resistant, no picture tube according to EP-A-0 087 674 has yet appeared on the market.

From US-A-2 346 810 a picture tube for television display is known, in which a part of the vacuum bulb acts as a carrier of the output luminescent layer. In the area of this support, the vacuum piston has a thickness such that total reflections are directed to areas that lie outside the field of view. In order to achieve the same effect, a thick plate can also be cemented on the carrier, which has the same thickness as the rest of the piston, according to this patent specification. With this arrangement, interference from total reflections is almost completely avoided. However, it has the disadvantage that it is not possible or can only be implemented with difficulty in a known image intensifier, since, owing to the high rejection of the phosphor layers, these can expediently only be applied to an exchangeable carrier.

DE-A-2 423935 describes an X-ray image intensifier in which the output window carrying the fluorescent screen is inserted into a metallic frame connected to the anode. However, such a structure does not enable the subsequent component of the X-ray diagnostic device to be coupled as tightly as possible, since the full high voltage is applied to the frame and thus sufficient high-voltage insulation is not ensured.

A flat-screen amplifier is known from FR-A-2 333 035, in which the output window carrying the fluorescent screen is placed on a spacer ring. The exit window has the same diameter as the entrance window and the sensing ring. Since the sensing ring is supported directly on the entrance and exit windows, it is made of insulating material. It has a Z-shaped profile so that the potential fields are deformed and voltage flashovers are avoided. The special design of the spacer ring, however, makes the manufacture of such a flat-screen amplifier difficult. The problem of high voltage resistance to subsequent components does not arise here either, since flat-panel amplifiers are only used for direct observation.

The invention has for its object to provide a vacuum image intensifier for a device for diagnosis with X-rays according to the preamble of claim 1, which is easy and inexpensive to produce with the means available today with good quality, in which no kit layers within the Vacuum and which has sufficient high voltage strength even against directly coupled system components.

According to the invention, this object is achieved by the features specified in patent claim 1. Appropriate refinements and developments are the subject of the dependent claims.

By applying the luminescent layer directly to a carrier, which is the exit window of the vacuum bulb, ge compared to the solution known from EP-A-0 087674 avoided a putty surface which must be in the high vacuum of the picture tube.

The fact that the exit window projects beyond the opening of the wall of the vacuum piston means that larger creepage distances are created. The high-voltage insulation is further increased by designing the groove formed by the wall of the vacuum piston and the larger exit window in diameter by the casting compound.

The thickness of the exit window can also be obtained without difficulty by means of a corresponding plate made of optical glass, which is cemented onto the outer surface of a carrier plate. On the one hand, the putty used does not have to be permanently vacuum-resistant and, on the other hand, the plate, which must have optical quality, can be attached at a point in time at which the production of the actual picture tube is completed, so that neither the putty surface nor the optical glass plate of the case the bake required for the manufacture of the picture tube needs to be exposed. The production of the picture tube itself can be carried out in the usual way.

While conventional device glass with a thickness of 0.5 to 10 mm, in particular 1 mm, can be used for the actual support of the luminescent layer, optical glass is used for the thick plate. With this plate, the large areas of which should have optical accuracy so that no image defects occur, a total thickness of at least half the diameter of the image should be obtained together with the support and the cement layer, i.e. with conventional X-ray image converters are in the order of 8 to 20 mm. The dimensions result from the fact that, depending on the refractive index of the glass used, a pixel from the outermost edge of the image is no longer reflected back to the phosphor within the image circle by total reflection at the glass air surface.

In itself, it is sufficient to make the support of the exit fluorescent screen of the image intensifier correspondingly thick. However, it is necessary to make the plate made of optical glass, which is delimited with parallel planes. This is expensive and in many cases is not technologically feasible and manageable. Optical glasses generally have too high an electrical conductivity.

In a simple and safe manner, a thick support is achieved by producing the exit fluorescent screen in the usual way on a thin support plate, placing it on the output window of the image intensifier and, after checking the image intensifier, cementing on a correspondingly thick plate made of optical glass. The expensive optical element does not need to be used until all parts of the image intensifier have been checked for full functionality. For the glass of the carrier and as optical glass, only materials are to be selected which together provide the insulating ability required for the exit window.

A window of sufficient mechanical and electrical stability as well as optical quality can also be obtained by inserting a plate made of technical glass which is thick in accordance with the required electrical resistance between the support plate and the plate made of optical glass. This glass can be produced with sufficient electrical resistance, which cannot be achieved with many optical glasses because of the other important optical glass parameters there. It has proven to be expedient to make the diameter of the intermediate pane made of technical glass larger in comparison with that of the other panes in the stack of panes. Thus, in the sense of the construction of conventional insulators, a large insulating distance between the fluorescent screen support and the plate made of optical glass is effective due to the laterally protruding surfaces of the intermediate pane.

• Fig. 1 ein Blockschaltbild einer Röntgenbildverstärker-Fernsehkette,
• Fig. einen Querschnitt durch das Ausgangsfenster des in der Fernsehkette verwendeten Bildverstärkers,
• Fig. und 4 Querschnitte durch abgewandelte Ausführungsformen des Ausgangsfensters.

The outer surface of the plate made of optical glass can be additionally improved by covering it with an anti-reflective layer, because then the back reflections on the phosphor layer are reduced. The background still contained in the original image due to a certain residual reflection can be reduced by using an absorption layer or gray glass in one of the glass panes. Compared to the known arrangements, the strength of the absorption effect can be kept low, because the main thing of the substrate is already eliminated by the use of the thick plate. Further details and advantages of the invention are explained in more detail below with reference to the exemplary embodiments shown in the drawing. Show it:

• 1 is a block diagram of an X-ray image intensifier television chain,
• 1 shows a cross section through the output window of the image intensifier used in the television chain,
• Fig. And 4 cross-sections through modified embodiments of the output window.

An X-ray image intensifier television chain of a device for diagnosis with X-rays is shown in the FIG. It has an image intensifier 1, to the output of which an image recording tube 3 is connected via an objective 2. The image recorded by the image recording tube 3 can be displayed in a viewing device 4, which receives the signals from the target of the image recording tube 3 via an amplifier 5. The X-ray image of a patient 8 falling on the image intensifier 1 is applied to the output fluorescent screen 6 of the image intensifier 1 and by means of the usual parts of the image intensifier 1, ie a fluorescent screen 9, a photo cathode 10, control electrodes 11, 12 and 13 and a high voltage source 14 transfer window 7 in the lens 2. The required voltages are applied to the photocathode 10 and the control electrodes 11, 12 and 13 via lines 10.1, 11.1, 12.1 and 13.1. The voltage is divided by means of a potentiometer 15.

The actual image is created by means of the rays 17 emerging from an X-ray tube 16, which produce a light image in the screen 9 which triggers electrons in the photocathode 10. These electrons are then imaged on the output fluorescent screen 6 via the electrodes 11 to 13. In this way, an image is obtained via the lens 2 in the recording tube 3 and is then reproduced in the viewing device 4.

In the exemplary embodiment according to FIG. 2, the output window 7 attached to the output flange 20 of the image intensifier 1 consists of a plate 21 made of optical glass, which has a thickness of 16 mm and a diameter of 60 mm. On its side facing the interior of the image intensifier 1, the plate 21 carries the fluorescent screen 6. On its outside it is coated with an anti-reflective layer 22. It reduces back reflections on the phosphor. For connection to the image intensifier 1, the diameter of the plate 21 made of optical glass is chosen to be larger than that of the opening of the output flange 20 of the image intensifier 1, so that a groove remains, which is designed with a casting compound 23. This ensures that larger creepage distances are created for the high-voltage insulation. The layer 24 of black lacquer attached to the side of the plate 21 should absorb light that is not used for imaging as far as possible. It consists of high-voltage-resistant optical matt lacquer.

According to FIG. 1, the exit window 7 contains a carrier plate 30 as the carrier of the luminous layer 6. On this carrier plate 30, the plate 21 made of optical glass is attached by means of a layer 31 made of an optical cement, which carries the anti-reflective layer 22 on its outside. Here, too, the plate 21 is laterally provided with a layer 24 consisting of black lacquer.

In the embodiment of the exit window 7 according to FIG. 4, the plate 21 made of optical glass is cemented onto the carrier plate 30 of the exit fluorescent screen 6 with the interposition of an approx. 3 mm thick plate 40 made of technical glass, which protrudes laterally about 10 mm beyond the stack. In order to increase the absorption of the side wall of the plate 21, in addition to the layer 24, this is also provided with grooves 41 of 2 cm in width and 2 cm in depth which are made in the circumference of the plate 21. These grooves 41 act like diaphragms or light traps, so that reflections are additionally prevented from emerging from the plate 21 and from being reflected back onto the exit fluorescent screen 6. The anti-reflective layer 22 is attached to the outside of the plate 21 in order to avoid back reflections on the phosphor layer as far as possible.

The plate 21 can, as shown in DE-A-1 514832, Fig. 4, be curved. While in the known arrangement the curved phosphor support makes sense to enable a simpler electron optics and thus a better distribution of sharpness on the fluorescent screen, according to the invention it is achieved that back and forth reflections in this plate are avoided and thus the image contrast is improved.

In addition, the plate 21 can be provided with a certain absorption, so that there is an improvement in the contrast due to suppression of back and forth reflections (gray glass). The absorption is limited to about 30% of the transmitted light so that not too much useful signal is lost.

Claims (9)

1. Electronic vacuum image intensifier (1) for X-ray diagnostic devices, with which the image to be intensified, on an input screen (9, 10), is converted into an electron image which is then accelerated electron-optically (11 to 13) towards a fluorescent output screen (6) and is displayed there, this screen lying on the inner wall of the output window (7) of the vacuum bulb whose thickness is dimensioned so that total reflexions occurring on the image output surface of the output window (7) of the vacuum image intensifier (1) reach back at the most to areas of the fluorescent screen lying outside the observation area, characterised in that the output window (7) is placed onto an aperture in the wall (20) of the vacuum bulb of the vacuum image intensifier (1) to form a tight seal in such a way that it projects laterally over the vacuum bulb in the area of the aperture, in that the wall of the vacuum bulb is so shaped that between it and the output window (7) a circumferential groove is formed and in that this groove is filled with a sealing compound (23).

2. Electronic vacuum image intensifier according to claim 1, characterised in that the output window (7) has a plate (21) of optical glass on whose inner wall the fluorescent output screen (6) is applied.

3. Electronic vacuum image intensifier according to claim 1, characterised in that the output window (7) has a layer structure which comprises glass discs transparently stuck together, of which a carrier plate (30) placed onto the aperture of the vacuum bulb carries the fluorescent layer (6) of the fluorescent output screen (6) and has dimensions which are adequate for tightly sealing the bulb and carrying the fluorescent layer, and in that stuck to the outer surface of this carrier plate (30) there is a plate (21) made of optical glass providing the remaining thickness of the structure.

4. Electronic vacuum image intensifier according to claim 3, characterised in that between the carrier plate (30) and the plate (21) of optical glass there is stuck a plate (40) of electrically insulating apparatus glass whose dimensions are selected with regard to the electrical insulation.

5. Electronic vacuum image intensifier according to one of claims 1 to 4, characterised in that the lateral edge of the plate (21) of optical glass has a light-absorbing coating (24), in particular blacking.

6. Electronic vacuum image intensifier according to claim 5, characterised in that the lateral edge of the optical platte (21) is additionally provided with circumferential grooves (41) acting as light traps or stops.

7. Electronic vacuum image intensifier according to one of claims 1 to 6, characterised in that the carrier (21, 30) includes a layer absorbing at the most 50% of the light passing through or is dyed throughout.

8. Electronic vacuum image intensifier according to one of claims 1 to 7, characterised in that the plate (21) is of inked optical glass which absorbs up to 40% of the light coming from the fluorescent screen (6).

9. Use of an electronic vacuum image intensifier according to one of claims 1 to 8 in an X-ray diagnostic device in which the lens (2) of an image-receiving and processing device (3 to 5) is connected on the output side of the output window (7).

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