DE2245696A1 - IMAGE AMPLIFIER TUBE - Google Patents

Description

Image intensifier tube

The invention relates to image intensifier tubes having a shell containing an input screen and an output screen spaced therefrom. between which an electron-optical system is arranged, by means of which the output screen can be irradiated in an imagewise distribution with electrons / which are emitted from the input screen as a function of an imagewise irradiation of the same with electromagnetic radiation. _:

It is known to convert an incident radiation pattern / from X-rays into a corresponding radiation pattern Electron beam / transfer by taking the x-rays on an input screen with a fluorescent phosphor layer, the photons of which have a Adjacent photoemissive, i.e. layer that emits electrons stimulate. The electrons emitted by the photoemissive layer are then transmitted through an electron-optical System accelerates and on one at an exit screen located fluorescent phosphor layer thrown, which is arranged in the focal plane of the electron optical system. A reduced photograph, · that of the incident X-ray pattern is generated on the phosphor layer of the output screen. the Exceeds the brightness of the light image on the output screen the brightness produced on the phosphor layer of the input screen. This gain is due to the acceleration of the electrons and the reduction in size »One-such Image reduction, although not required to / I, is commonly applied to in the film cameras or television cameras, which normally record the optical output signal of the image intensifier tube, optical elements of suitable physical dimensions

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(small expansions) to be able to use.

The operational characteristics and disadvantages associated with this type of amplifier tube are known. Particularly Significant disadvantages are the low resolution, the low contrast and the poor Signal-to-Noise Ratio SNR. Usually, such X-ray image intensifier tubes have resolving power from approximately 1 to 2 line pairs per millimeter compared to 6 to 16 line pairs per millimeter, as is the case with conventional film-screen systems. Because of the low resolution and the low contrast, these intensifier tubes are not suitable for Generate X-ray images of the quality required for most of the usual medical X-ray technology is. The use of such tubes is therefore mainly limited to the following areas of application:

1. Investigations in the fluorescence method, because with such fluoroscopic examinations the disadvantages of the low Resolving power can be canceled out by the advantages of the lower radiation exposure of the patient and '

2. Dynamic X-ray technology (e.g. fluoroscopic Cinematography), where the poor SNR is partly due to the integration time of the sneaking eye when viewing of the finished film or the television picture is compensated. '

The image-generating properties of image intensifier tubes are usually determined by the modulation transfer

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bearing function MTF described. Bad MTF and bad / SNR of known X-ray image intensifier tubes can to a large extent be traced back to the phosphors , which are present in particle form, as are used in input dishes.

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and at the output screen of the known amplifier tubes be used. If assumed the noise in the amplifier tube is primarily due to the statistical changes caused by the incident X-ray beam, then the SNR can be used with the known ^ on the input screen Phosphors only enlarged by this

! are achieved by increasing the proportion that is absorbed by the incident X-ray beam. Normal travel the phosphors in the commercially available intensifier tubes absorb about 15% of the incident ones X-rays. The absorption of X-rays can be increased by increasing the thickness of the phosphor layer enlarged. An increase in SNR achieved in this way would, however, be reduced by a decrease in the MTF accompanied. This fact is a consequence of the internal light-scattering property a phosphor layer consisting of particles. The MTF more common, made up of particles Phosphor layers for the input screen, as used for known X-ray image intensifier tubes, is approximately 4 line pairs per millimeter at a modulation level of 4%. Therefore ask, as already mentions the phosphors present in particle form on the input screen and on the output screen in known image intensifier tubes the outstanding factors - by which the total MTF and the SNR in the currently known. Image intensifier tubes grounded in an unfavorable way.

Known fluorescent entrance screens for X-rays we.isen in the known image intensifier tubes on a carrier material on which -fine coating of a Fluorescent compound, for example from calcium tungstate, Zinc Sulphide or Zinc Cadmium Sulphiil in a suitable Carrier or binder is dispersed, is and are

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known in the art as "powder screens" or "salt ^{screens 11.} Screens of this type have found widespread use in X-ray technology, but have not proven to be entirely satisfactory when fine details are to be recorded. This is primarily due to the granular type Structure of the phosphor layers, because this granular or grainy structure causes a not inconsiderable light scattering and thus a reduction in contrast in small image details This means that, especially when using "hard" or more penetrating X-rays, the image information with which the subject has modulated the X-rays is only partially used and the majority of the X-rays penetrate the screen without being evaluated.

Numerous proposals have been made to overcome the above-mentioned and other problems associated with powder umbrellas. For example, US Pat. No. '2 292 914 proposes melting the phosphor materials into glass-like plates or sheets. Such cast plates, however, have too little intrinsic strength, especially if they are "larger plates." Many suitable X-ray phosphors, for example Gd ₃ O ₃ , calcium tungstate and barium lead sulfate, cannot be melted without In addition, meticulous polishing is required, followed by chemical and physical treatment in order to activate the phosphors contained.

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The cast sheets or plates usually have has an undesirably thin thickness and the percentage of high energy radiation converted has been found to be less than that for most x-ray applications is desirable. C. Albrecht and others

suggest in the publication "Medica Mundi", Vol. 5 _f

No. 2/3, pages 80 to 84, (1959), X-ray screens made of K; aluminum iodide and cesium iodide in the form of single crystals the size 6 cm 6 cm, the thickness of which is 3 mm and the thallium as an activating and doping agent for the Contain phosphors. A larger screen of this type, made up of a series of potassium iodide crystals doped with Tnellium (ΚΙ: ΤΪ) is produced in such a way that that 16 of the aforementioned monocrystalline pieces in silicone oil embedded and attached to an aluminum sheet to achieve greater strength. Comparison tests with a commercially available powder screen with ZnCdS show that the monocrystalline patterns give higher absorption and better image sharpness. Here it still shows, however, that the border areas between the crystalline pieces in the assembled large screen represent sources of strong light scattering, and that the inhomogeneity of the embedding material gives rise to severe loss of contrast. In addition, the production of Monocrystals and the division of the same into suitable pieces for the construction of a screen are extremely complex and time-consuming and very expensive. The size of the single crystals that can be achieved is also extremely limited due to technical problems related to the growth of the single crystals.

It can therefore be seen that there is a need in the art for an image intensifier tube with an improved phosphor screen.

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22A5696

The invention is therefore based on the object of creating an image intensifier tube of the type in question, whose fluorescent screen accounts for a large part of the incident

so far only uses radiation energy, like this / with a thick screen is the case, but at the same time has a high image sharpness, as is the case with a thin screen, wherein Furthermore, a high inherent strength should be given, especially in the case of large-area screens, without such scattering effects occur, as is the case when single crystals are joined together to form a large-area, composite screen.

In an image intensifier tube of the type mentioned at the outset, this object is achieved according to the invention in that at least one of the two screens contains a hot-pressed "phosphor." . ·· ',

As used herein, "hot-pressed" refers to the production of polycrystalline phosphor elements. At the A microcrystalline powder is hot pressed into a press mold entered, the mold is heated to a temperature below the melting point of the crystalline material lies, and it becomes a. Pressing force applied for a period of time sufficient to an optical element to form whose density is at least 99% of the theoretical single crystal density of this material. The pressure force is then removed again and heating is stopped. The mold and the new element formed in it are then allowed to cool and the element is then removed the mold out. Hot-pressed elements obtained in this way clearly differ from glass-like materials, as they are obtained in the known melting process. Such vitreous materials are of very low inherent strength, have a lower temperature

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and require careful polishing before use. In contrast, the hot-pressed elements are from high intrinsic strength and can be produced in any desired dimension, thickness and shape, for example for the commercial sizes of image intensifier tubes, the diameter of which is usually 12.7 cm (5 "), 15.2 6 "and 9" respectively. The hot-pressed elements can also be made in other sizes or formats getting produced. These elements are still essential free from optical defects and can, if so desired, be used immediately after hot pressing taken without further treatment. A more detailed description of the "hot pressing" technique can be found in British Patent 1,077,725.

As far as the terms "fluorescent material" or "fluorescent material compound" Find use, these relate to compounds that have such a crystal structure that they can be hot-pressed to polycrystalline materials, which in turn when exposed to high-energy radiation emit radiation that is in the electromagnetic spectrum in the range between that of the ultraviolet Light neighboring spectral range and "the infrared range lies. The term "ilochen energy radiation" here includes X-rays (10 to 1.0 nm), gamma rays (10 to 10 nm) and ultraviolet radiation (1 to 400 nm). . -. . '

The absorption of energy from the incident imagewise radiation pattern creates excited electrons in the hot-pressed material. These electrons can go through transitions that result from emitting a certain amount of energy can be accompanied to return to a lower energy level. The term "luminescence" which means the The appearance of phosphorescence includes describes the

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Appearance of energy absorption by the phosphor and the re-emission of part of this energy in Form of visible light. When the incident radiation is in the range of the X-ray spectrum, i.e. has wavelengths of 10 to 1.0 nm, then rial called X-ray phosphor.

of 10 to 1.0 nm, then such a material is

In the present invention, an evacuated tube having an input member or screen and a Output element or output screen applied, at least one of which is fluorescent, hot-pressed, optically homogeneous and is translucent and emits photons when excited by X-rays. A pictorial Radiation patterns from X-rays incident on the input screen cause the fluorescent phosphor layer of the input screen, preferably a fluorescent, hot-pressed, optically homogeneous phosphor input layer, Emits photons that excite an adjacent electron-emitting layer in the input screen. The electrons emitted by the electron-donating layer are accelerated by the electron-optical system and focused on the output screen, which is a fluorescent, hot-pressed, optically homogeneous phosphor layer may contain, which is arranged in the focal plane of the electron optical system. In the case of the phosphor layer the output screen can also be a conventional powder Act binder or a vapor-deposited phosphor layer. In addition to other known facilities, in Connection with the output screen, for example, also optically homogeneous phosphors, electron-sensitive photographic ones Emulsions, still cameras, executions for cinematographic fluoroscopy, television cameras, etc. application Find.

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The invention is illustrated below with reference to the drawing in FIG individually explained.

Show it:

1 shows a schematic and partially broken away perspective illustration an image intensifier tube;

Fig. 2 and 3 schematically drawn longitudinal sections of the input screen or the output screen of known image intensifier tubes;

4 shows a longitudinal section of an image intensifier tube according to an embodiment the invention;

5 and 6 are longitudinal sections through the input screen and output screen of the image intensifier, tubes according to further execution examples games of the invention;

7 and 8 schematically drawn side views of image intensifier tubes according to further embodiments of the invention and

Fig. 9 and IO diagrams in which properties of embodiments of image intensifier tubes according to the invention with the corresponding Properties of well-known BiZd amplifier tubes are compared.

1 shows an image intensifier tube 10 with an evacuated envelope 11 made of glass, at one end of which an input screen 12 and at the other end an output screen 13 are provided and which contains a focusing electron-optical system 14. The electron optical system 14 is preferably of the type described on page 7 of the publication "Dual Field X-Ray Image Intensifier Image Quality and Dose Characteristics for Television and Cineflubrography" * by LF Guyot., Edited by Thomson-Houston, Nov. 8th 1963, 6 Rue Mario Nikis, Paris 15 °. However, the electron-optical system can also be of another conventional type, as described in patents 2,523,132, 2,698,912, 2,700,116 or 3,235,737. The electron optical system 14 is arranged between the screens 12 and 13. The input screen 12 has a fluorescent phosphor input layer and an electron emitting layer. The output screen 13 has a fluorescent phosphor output layer. The tube 10 is arranged so that the input screen 12 is oriented to receive an image-wise x-ray pattern 15, and a television or movie camera 16 can be oriented to the output screen 13 to display the output visual images that are received X-ray patterns correspond and appear on the output screen 13, picks up and records. ■ '■>

FIG. 2 shows a longitudinal section through the input screen 12 of a known image intensifier tube. This input screen 12 has a plurality of layers, namely a permeable Röntenstrahlen Röhrenstlmwand 17 _f an intermediate space 19, a carrier layer 21, a input phosphor layer 23, a release layer 25 trnct a © electron emitting or photoemisslve Schicht.27. Forehead-

wall 17 of the tube is made of glass and usually has a Thickness on the order of about 2.5 mm. The carrier layer 21, which is a light reflective, for X-rays permeable layer is, for example, made of aluminum and about 0.1 ram thick. The carrier layer 21 serves as a mirror for what is emitted by the phosphor layer 23 Light and ensures that all of the light emitted by the layer 23 against the photoemissive Layer 27 is thrown. The size of the space 19 varies depending on the manufacturer and structure of the relevant Image intensifier tube and, of course, the smaller the tube in question, the smaller it is. As shown below is, the gap 19, which is usually about 6.3 mm, in the invention described here, further, can be reduced in size or completely eliminated.

The input phosphor layer 23 is usually at least 200 nm thick and usually consists of an inorganic substance in an organic binder, e.g. silver- doped zinc cadmium sulfide, SnCdSsAg / embedded in a Plastic binder layer. Suitable scintillating substances include polycyclic compounds such as. Stilbene, Anthracene, naphthalene and phenanthrene in connection with Calcium-titanium-silicates, calcium-titanium-stannates, cocrystallization products based on lanthanum silicate, cerium oxide, calcium orthophosphate / stannate and calcium orthophosphate /

Cerium oxide. Sometimes found calcium volframate. mixed with lead tungstate and a halogen use. Further known compounds are zinc silicate, zinc selenide, zinc sulfide, barium lead sulfate, zinc cadmium sulfide, magnesium wolf Ramate and zinc beryllium silicate combined with one Halogen and / or another activating agent. The composition the input phosphor layer 23 is normal

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wisely chosen so that the radiation that is emitted from the phosphor layer 23, in substantially the band or spectral range of greatest sensitivity the photoemissive layer 27 corresponds.

The photoemissive layer 27 generates an emitted electron beam raster corresponding to the light radiation emitted by the input phosphor layer 23. the Photoemissive layer 20 usually consists of substances which are also sensitive to the incident X-rays, for example bismuth, as described in US Pat. No. 2,897,388. This creates the strength the electron emission is additionally increased.

The separating layer 25, which is normally formed from glass or another chemically inert transparent material , is usually about 100 nm thick and separates the input phosphor layer 23 and the photoemissive layer 27 in order to prevent any chemical reaction between these layers. 'ν

Fig. 3 shows a simplified schematic representation of the longitudinal section through the output screen 13 of a conventional image intensifier tube. The output screen 13 has a plurality of layers, namely an optical barrier layer 29, an output phosphor layer 31 and a support-forming window 33 made of glass ". The barrier layer 29 is normally made of a material, for example aluminum alum, with a Thickness of about 0.1 mm, which acts as a reflector in order to intensify the light output of the tube and which also serves to prevent the light from the output phosphor layer 31 from affecting the photoemissive layer 27.

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The starting phosphor layer 31 is made of the same materials like the input phosphor layer 23 and is usually a few microns thick.

If an X-ray pattern 15 falls on the input phosphor layer 23, then this layer emits photons which pass through the separating layer 25 to the photoemissive layer 27. The photoemissive layer 27 releases electrons as a function of this, which are accelerated by the electron optical system 14 and focused on the output screen 13, the output phosphor layer 31 of which is arranged in the focal plane of the electron optical system.

The electrons striking the output phosphor layer 31 "cause this phosphor layer 31 to generate photons which produce a light image in the phosphor layer 31 which corresponds to the incident X-ray pattern 15. A television or film camera 16 (see FIG. 1) is sometimes used for this used this photograph to record ^v. Alternatively, this photo can also be directly ~ "be viewed through a lens ^system? which is not shown and through which the image is enlarged to the desired extent. In the case of an input phosphor layer 23 and an output phosphor layer 31, if these phosphor layers are designed in the usual way, their components are in particle form, which, as already mentioned above, results in poor values with regard to the MTF and the SNR. "

4 'shows an image intensifier tube according to an embodiment of the invention utilizing an improved input screen 12 'and an improved output screen 13' Find. The input screen 12 'has several layers,

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namely an end wall 17 * of the envelope of the tube, which is made of glass and is permeable to X-rays, an intermediate space 19 ', a hot-pressed input phosphor layer 23', a separating layer 25 'and a photoemissive layer 27'. The hot-pressed input phosphor layer has an extremely high optical homogeneity and transparency with regard to its own luminescent radiation and is an effective absorber for radiation in the usual medical X-ray spectrum. Therefore, there is no light scattering or, if one so wishes, which is the case with some systems, no absorption of the light emitted by the phosphor. Inlet phosphor layers made from hot-pressed gadolinium oxide, thorium oxide and zinc sulfide have been found to have excellent optical homogeneity and transparency. One or more substances can be added as doping agents to the phosphor before the hot pressing is carried out in order to increase the efficiency of the fluorescence and / or to change the spectral emission properties of the input phosphor layer. As has been found, europium is particularly suitable as a doping agent for some of these phosphors. Gd ₃ O ₃ and ThO ₂ are effective X-ray phosphors "and absorb at least 80% of a common medical X-ray spectrum within a phosphor layer 0.5 mm thick, hot-pressed layers of Gd ₃ O ₃ and ThO ₂ , whose thickness is 0.5 mm, If they are used as a material for a hot-pressed input phosphor layer 23 *, the image intensifier has a resolution of between 15 and 20 lines per millimeter. This is the case with both doped and undoped layers, since doping is only low This is why hot-pressed homogeneous phosphors, such as Gd ₃ O ₃ ThO ₂ and, to a lesser extent, ZnS, result in an image intensifier,

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whose SNR is better by at least a factor of 2 compared to conventional phosphors in particle form, such as ZnCdS. At the same time, the MTF is from 1 to 4 lines per millimeter to at least 6 lines increased per millimeter if an output screen of conventional design is used. Other benefits are additional given if a hot-pressed, optically homogeneous and optically transparent entrance screen is used ο Since the hot-pressed entrance phosphor layer 23 * 'is self-supporting, the carrier layer 21 of the usual image intensifier tube (see FIG. 2) is not required. Although it is common

SiQ 'or is unnecessary, a separating layer 25', which consists of / SiO ₂ ,

Providing between the hot-pressed phosphor ^{layer 23 s} and the photoemissive layer 27 ″ in order to prevent mutual chemical reaction enables the optical quality of the hot-pressed homogeneous “materials. · Targetable surface that is smaller in thickness of a separating layer 'can be realized if such an application is, this gauge or thickness of the separation layer 25' 25 maybe in the order of 0, ^N l nm or · similar values at the Eingangeschirm 12 ⁹ whereas the image intensifier tube shown in FIG. 2 requires a much thicker separating layer 25 "The thinner the separating layer, however, the sharper the image, since there is less light scattering between the phosphor and the photoemissive layer."

During their production, the hot-pressed Le'üchtstof fschicht 23 "be formed so that it" has a strength in the case of a particularly effective "illustration of the striking diverging X-rays takes place, or are shaped so that in the vicinity of the photoemissive layer 23 ', curved equipotential surfaces are formed, which may be required when high-resolution electron-optical

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Systems find application.

In the image intensifier tube according to the invention, the improved output screen 13 has a plurality of layers, namely a barrier layer 29 *, a hot-pressed output phosphor layer 31 'and a window 33 * made of glass. The thickness and composition of the layer 29 'is similar to the barrier layer 29 of the tube according to FIG. 3 and does not need to serve as a support for the output phosphor layer 31', but is preferred for other reasons, which will be explained below provided as part of the exit screen 13 '. The hot-pressed output phosphor layer 31 ', which is preferably made sufficiently thick to adapt to the accelerated and focused photoelectron radiation, is produced in the same manner as the input phosphor layer 23' and has similar properties. Hot-pressed Gd ₃ O ₃ , ThO-ZnS, potassium iodide (KI) and cesium iodide (CsI) are examples of hot-pressed phosphors for the starting phosphor layer 31 '. As mentioned above, the output phosphor layer 31 ′ is arranged in the focal plane of the electron optical system 14.

A reflective element can be attached to the front surface of the input screen to reflect light emitted from the back of the photons Layer is emitted in order to increase the efficiency of the usable photon emission. Alternatively could also.ein absorbent element be provided in order to internal, due to, reflections To prevent light conduction, as such reflected light could cause a reduction in contrast. The application the reflective surface results in increased fluorescent light output with a slight decrease the contrast and the MTF. The application of the

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absorbing surface results in a lower light output power with improved MTF and better contrast at the same time.

Two types of coatings can be provided for the entrance screen be that cover the entire surface of the input phosphor layer, with the exception of the photoemissive Area assigned to layer. The first type of such cover, the one here. Type I is called is reflective and is the type of coating currently used in home screens, the phosphor have layers in particulate form. A coating of type I brings back luminescent light to the photoemissive layer, which in the absence of the reflector the system would get lost. The advantage here is ... that an increase in sensitivity occurs because a larger part of the luminescence generated by the X-ray radiation in the photoemissive Layer is absorbed. There is some loss in terms of contrast and .MTF.

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Type II is absorbent (in terms of, the wavelengths the emission of the input fluorescent tube) and is the preferred type.

Type II prevents internal light propagation due to internal reflections on the surface of the phosphor layer, which is adjacent to the vacuum, with such * reflections arise at this media transition due to the different refractive indices of these two media. The use of an absorber gives advantages in terms of increased contrast and improved MTF, whereby some sensitivity is lost. ·

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Fig. 5 shows another structure of an input screen for an image intensifier tube according to the invention. As shown, the input screen 12 has a plurality of for X-ray transparent layers, namely an end wall 17 "of the shell of the tube made of glass, a hot-pressed phosphor layer 23 "," a release layer 25 "and a photoemissive layer 27". The hot-pressed phosphor layer 23 "is, preferably by cementing, attached to the end wall 17 ". Due to the inherent strength of the hot-pressed phosphor layer 23" .die End wall 17 ″ in comparison to the end wall 17, in known image intensifier tubes by the strength of the phosphor Layer, which is preferably about 0.5 mm, can be reduced. The strength of the tube end wall is normally about 2.5 mm, but this value changes with the respective tube diameters. the The end wall of the tube envelope can be omitted entirely if the self-supporting, hot-pressed phosphor layer has a sufficient thickness. As has already been mentioned in connection with FIG. 4, the separating layer be necessary or superfluous, depending on whether there is chemical compatibility between the hot-pressed phosphor layer and the photoemissive layer is given or not. In any case, however, the separating layer 25 ″ can be approximately 1000 times thinner, that is to say in one Thickness of about 0.1 nm can be carried out than is the case with the separating layer 25 - as is the case with known image intensifier tubes with usual entry screens is required and as shown in Fig. 2 where the strength the separation layer is approximately 1000 nm. Due to the thinner separating layer, as can be used in the invention, there is the advantage of a smaller one Light absorption and light scattering in the separating layer.

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The intensity of the X-ray radiation to be used can therefore be lower and the result is a sharper picture.

6 shows an output screen 13 ″ of a further exemplary embodiment, which has a holdout layer 29 "and a hot-pressed starting phosphor layer 31". the The barrier layer 29 ″ is similar in its thickness and composition to the barrier layer 29 (see FIG. 3) and needs it not to serve as a carrier for the phosphor layer 31 ", but is provided in the exit screen 13 ″ for other reasons, which will be discussed below. A window made of glass, as 'shown in Fig. 4 in the form of a window 33', is here due to the self-supporting Properties of the hot-pressed phosphor layer 31 "are not provided.

As mentioned above, the starting phosphor layer 31 has (see Fig. 3) in conventional image intensifier tubes has a particle shape and has an MTF of approximately 6 to 8 lines per · Millimeter. This is likely to be the uppermost limit of the resolution that can be achieved with conventional phosphor layers. An improvement in the total MTF of the image intensifier tube results when a phosphor layer 31 of particle shape is replaced by an optically homogeneous phosphor layer described here, for example by a hot-pressed Output fluorescent layer 31 or 31 ". Will Such an exchange is then carried out by the image intensifier tube 10 zv / ar emitted a smaller amount of light, which for the television or film camera 16 (see Fig. 1) to Is available than would be the case if a luminous material layer 31 (see FIG. 3) were to be used. This decrease the amount of light emitted is a consequence of the media transfer at the interface between the phosphor layer and air, v / o

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optical phenomena due to the sudden change in the refractive index occur (reflection phenomena, "light piping "). The decrease in the amount of light emitted, the results when using hot-pressed homogeneous starting phosphor layers 31 'or 31 ", but becomes more as offset by the increase in X-ray absorption such as is achieved when homogeneous hot-pressed Input phosphor layers 23 'or 23 "can be used. ·, · - · -

When the phosphor layer 23 "or 23" in connection If a conventional exit screen 13 is used, the result is an increase in the light output of the order of magnitude the factor 4. An improvement in the SNR by a factor of 2 and the resolution by at least a factor 2 also results. Therefore, it results in an image intensifier tube according to the invention having a homogeneous input phosphor layer 23 'and a homogeneous hot-pressed starting phosphor layer 31' on v / ei st ,, as in Fig. 4 shows an output light intensity which is comparable to that of a conventional image intensifier tube, however the SNR is improved by a factor between approximately 2 and 4 and the resolving power is improved by at least the factor

gate 4 has risen. It can be clearly seen that an image intensifier tube as described here either shields one of the novel input screens? ¹ or 12 "and / or one of the new output screens 13 'or 13" is a remarkable technical improvement.

Whether a conductive light blocking layer 29 'or 29 "application 4 and 6, when a hot-pressed starting phosphor layer 31 'or 31 "is used, depends on several considerations.

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electron optical system 14, as in an image intensifier tube Application requires that the electron potential be applied to the starting homogeneous hot-pressed phosphor layer remains constant, or that the charge created by the incident photoelectrons on the hot-pressed starting phosphor layer is caused ", is neutralized by the fact that it is brought about by a place with a fixed potential is derived. When the homogeneous hot-pressed starting phosphor layer 31. ' or "31" corresponding electrical Has resistance properties, for example

on the order of 10 ohm-cm, then there is a barrier layer 29 'or 29 ", which-represents an electrical conductor, not required for charge dissipation. In addition, if the emitted wavelengths of the homogeneri hot-pressed starting phosphor layer does not match the "absorption wavelength range of the photoemisslven layer coincides or overlaps them in one area, none Retention layer 29 'or 29 "required for optical decoupling. The reflective ability of the barrier layer 29 ' or 29 ", although it reduces the amount of light emitted by the homogeneous hot-pressed starting phosphor layer increases the effective MTF. Therefore, the decision whether or not depends a barrier layer 29 'or 29 "may or may not be provided as part of the output screen 13' or 13" from the loss from the MTF and the amount of light emitted for the intended use of a specific

fenden image intensifier tube is ready. .

In Fig. 7 is one for direct electronic movie recording , provided image intensifier tube with an output phosphor is shown. A mechanism 41 is used for transport an electron sensitive film 43 along the focal plane of an electron optical system 45 which schematizes

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is indicated. Vacuum locks 47 and 49 form passageways / which allow the film 43 to be inserted and removed. Such mechanisms and locks interacting with them are known and readily available. A homogeneous hot-pressed phosphor layer 55 receives an incident x-ray pattern 57 and transmits photons through an adjacent one Separation layer 59. A photoemissive layer 61, which lies on the other side of the separation layer 59, transmits a corresponding pattern of electrons generated by the electron optical system 45 of conventional design onto the film 43 be focused. Such an arrangement enables direct electronic film recording, due to the Use of the improved hot-pressed input phosphor provides both an improvement in the MTF of the recorded Image occurs as well as reducing the X-ray exposure. Suitable footage for such direct recording are commercially available through the Eastman Kodak Company sold under the names "Kodak Electron Image Film" and "Kodak Hig Resolution Film". '. *

With this technique, reduced radiographic recordings can be made can be made directly, the quality of which after the enlargement of the quality libllcher large-format radiographic Recordings is the same as those according to the screen-film system are made. Furthermore, those produced directly by the technique described above have radiographic recordings in such a small format that they were immediately automated into small-format ones Data storage and output systems can be stored. Furthermore, these require radiographic records only an X-ray exposure that is a factor of 4 lower than what is currently used in medical practice

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is common. In addition, the MTF is achieved here both will if a static .playing as well as if a dynamic playback is performed, equal to the MTF achieved in conventional screen-film systems. The SNR is four times better than the known systems. If you summarize these factors, so. shows that with Applying the invention to obtain a diagnostic agent in the form of a dynamic cinematographic fluorography that is approximately equivalent in its quality to the quality which is currently achievable at best with static radiography.

In Fig. 8 is an embodiment for a direct Video output shown. A vidicon or an image orthocön 60 with conventional electron optics 63 is in an evacuated one Sheath 62 housed an image intensifier tube. A vidicon surface 65 is a homogeneous hot-pressed one Phosphor layer 67 arranged adjacent. As from the Drawing can be seen, "are the phosphor layer 67 and the vidicon surface 65 to one another. Electron optics of the usual type focus the electron pattern image-wise corresponds to an incident X-ray pattern and that in a photoemissive layer 71 as a function is generated by photons generated by a homogeneous hot-pressed phosphor layer 73 »Die auf Photons falling on the photoemissive layer 71 are dependent on this layer 71 via a separating layer 75 supplied by the incidence of X-rays 77 corresponding pattern. · __

That through the electron optics 69 on the phosphor layer 67 focused image patterns reproduce the image information. If the phosphor layer 67 is chosen so that the spectral range the 'radiated radiation the spec-

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The beam area of the photosensitivity of the photoemissive layer 79 does not overlap, then no optical feedback takes place between the phosphor layer 67 and the photoemissive layer 71 . An advantage here is that a high resolution and a high amount of light emitted are achieved if the optical feedback is prevented . It is essential that the electron optics 69 of the image intensifier tube do not interfere with the electron optics 63 of the television recording device or are interfered with by them. With this system there is a direct optical coupling at the output of the image intensifier tube, whereby refractive air spaces are eliminated, which would result in a reduction in the light output. A further improvement to this system is possible if the electron image pattern were used directly, without the use of the output phosphor screen, in conjunction with a system which produces an output display similar to a beam-inverted vidicon.

τ ■ ■ ■

■, - V

Figure 9 shows those with a hot-pressed ZnS phosphor screen (0.5 mm, curve Λ; 2 mm curve B) achieved MTF when using a filtered medical 70 kV X-ray spectrum is exposed. It can be seen that the hot-pressed phosphor of 0.5 mm thick is a remarkable one in terms of MTF There is an improvement compared to conventional umbrellas, such as the DuPont high-speed umbrella made with lead doped tem barium sulfate (BaSO. ": -Pb, curve C) and the DuPont-Par-Speed-umbrella from calcium tungstate (Cal.O., curve D). The curve E shows the MTF of a typical ZnCcIS powder input screen.

Reference is now made to FIG. Since hot-pressed phosphor layers on the basis of Cd "O ~ (curve F) around ThO "(curve G) a higher X-ray absorption

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exhibit as ZnS (curve H) or calcium fluoride (CaF ₂ , curve I), it can be seen that an MTF on the order of twenty line pairs per millimeter is obtained using these phosphor layers which absorb at least 80% of the incident X-rays. The phosphor layers in the form of particles, as used in conventional image intensifier tubes, absorb approximately 15% of the incident radiation and have an MTF of the order of magnitude of four line pairs per millimeter. The use of hot-pressed, optically homogeneous phosphor _{layers made of materials such as Gd 3} O ₃ , ThO ₃ , ZnS, CsI and KI results in single-screen screens with much better resolution and increased light output, which is at least / increased by a factor of 4, as well as with an SNR that is at least is better by a factor of two.

Due to the improved resolution that results from the image intensifier tube described, one can choose whether one is particularly interested in improved sensitivity or improved SNR, because both of the last-mentioned improvements can be achieved due to the increased absorption. The X-ray exposure of a relevant subject can be reduced, resulting in a lower exposure to radiation for living or other radiation-sensitive subjects, while at the same time maintaining an SNR, as is achieved with conventional fluorescent screens in particle form, without, however, a correspondingly lower exposure to radiation being possible would). Alternatively, the x-ray exposure of the subject to the usual level belassen'werden, as applied in conjunction with image intensifier tubes having -üblichen phosphor layers in particle form, where 'However% n this case would set a better SNR. Therefore eröff-

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net the use of optically homogeneous hot-pressed Phosphor layers on the input screen of X-ray converter tubes the advantageous compared to the use of conventional phosphor layers in particle form Possibility of better radiographic recordings due to the better resolving power at less intense To achieve irradiation.

The improved image intensifier tube described here is also capable of high energy radiations of other types applicable as image-wise X-ray radiation. For example, using a hot-pressed input phosphor tube Incident gamma rays, neutrons, electrons, ultraviolet rays or other high-energy radiation and the image is then enhanced in a manner similar to that described above with respect to FIG X-rays was explained. -

The hot-pressed starting phosphor layer can also be made by means of the use of bundled fiber optics with image evaluation devices be coupled. For example, bundled fiber optics could be used to achieve the Coupling output phosphor layer with a television camera. The advantages of such systems * are that they are light-reflective Surfaces switched off by the optical coupling between the image intensifier tube and the television pickup tube will. Two advantages result in the form of increased light output from the starting phosphor layer as well as in the form of improved contrasts.

Since phosphors with cubic crystalline symmetry give a minimum of internal light scattering, phosphors are with this property preferred. Except

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the preferred phosphors mentioned above, viz. Gadolinium oxide, thorium oxide and zinc sulfide, form the im The following phosphors are further examples of advantage for the production of hot-pressed phosphor layers applicable materials? Sodium iodide, potassium iodide, calcium fluoride, Cesium iodide, barium fluoride, zinc sulfide, zinc cadmium sulfide, Yttrium oxide and other rare earth oxides or oxysulphides. In addition, a variety of doping, agents to be added to these phosphors to increase the fluorescence and / or the spectral properties to change the emission. Examples of applicable doping agents are europium, thallium, silver, copper and the same.

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Claims (8)

Claims 1.JImage intensifier tube with a shell which contains an input screen and an output screen arranged at a distance from this, between which an electron-optical system is arranged, by means of which the output screen can be irradiated with electrons in an image-wise distribution Irradiation of the same with electromagnetic radiation, characterized in that at least one of the two screens (12 ', 12 "and 13', 13") contains a hot-pressed phosphor (23 ^f , 23 ", 31 ', 31", 55, 67 , 73) contains. 2. Image intensifier tube according to claim 1, characterized in that that Gd_O is provided as the luminescent substance ». 3. Image intensifier tube according to claim 1, characterized in that ThO- is provided as the phosphor. ~ * 4. Image intensifier tube according to one of claims 1 to 3, characterized in that the input screen (12 ¹ , 12 ") has a self-supporting, optically homogeneous, hot-pressed phosphor layer (23 ', 23" j 55; 73). -, 5. Image intensifier tube according to one of claims 1 to 3, characterized in that the output screen (13 ¹ , 13 ") has a self-supporting, optically homogeneous, light-pressed fluorescent layer (31 ', 31"; 67). 6. image intensifier tube according to one of claims 1 to 3 ,. through this characterized that both the input screen (12 ·, 12 ") and the output screen (13 *, 13") each have their own 309812/0977 have load-bearing, optically homogeneous, hot-pressed fluorescent layer (23 ^f , 23 ", 73 or 31 ', 31",; 67). 7. Image intensifier tube according to one of claims 1 to 6, characterized / that between the phosphor (23 ¹ , 23 ", 55, 73) and a photoemissive layer (27 ', 27" _f 61, 71) associated therewith a chemical ^{Separation layer (25 1} , 25 ″, 59, 75) preventing reaction between phosphor and photoemissive layer is provided. 8. image intensifier tube according to claim "7, characterized in that that the thickness of the separating layer (25 ', 25 ", J59, 75) is approximately 0.1 nanometer. 9 * image intensifier tube according to claim 8, characterized by one on the surface of the phosphor (23 *, 23 ", 55, 73) that receives the electromagnetic radiation reflective layer. . 3 0 9812 / OQTI