EP1906432B1 - Correction of the distortion of an image intensifier electron tube - Google Patents

Correction of the distortion of an image intensifier electron tube Download PDF

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Publication number
EP1906432B1
EP1906432B1 EP07116775A EP07116775A EP1906432B1 EP 1906432 B1 EP1906432 B1 EP 1906432B1 EP 07116775 A EP07116775 A EP 07116775A EP 07116775 A EP07116775 A EP 07116775A EP 1906432 B1 EP1906432 B1 EP 1906432B1
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EP
European Patent Office
Prior art keywords
radiation
input screen
photocathode
tube according
primary
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Not-in-force
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EP07116775A
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German (de)
French (fr)
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EP1906432A1 (en
Inventor
Andréas Koch
Daniel Gally
Clément Vallois
Eric Marche
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Thales SA
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Thales SA
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J31/00—Cathode ray tubes; Electron beam tubes
    • H01J31/08—Cathode ray tubes; Electron beam tubes having a screen on or from which an image or pattern is formed, picked up, converted, or stored
    • H01J31/50—Image-conversion or image-amplification tubes, i.e. having optical, X-ray, or analogous input, and optical output
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2231/00—Cathode ray tubes or electron beam tubes
    • H01J2231/50—Imaging and conversion tubes
    • H01J2231/50057—Imaging and conversion tubes characterised by form of output stage

Definitions

  • the invention relates to the distortion correction of an image intensifier electron tube.
  • An image intensifier electron tube includes an input screen for receiving said primary electromagnetic radiation and an output screen emitting radiation depending on the primary radiation.
  • Intensifiers are for example used in medical radiology.
  • the intensifier receives X-radiation that has passed through the body of a patient.
  • the intensifier transmits on its second screen a visible image according to the X-radiation received by the input screen.
  • the intensifier amplifies the intensity of the received image.
  • this amplification makes it possible to reduce the dose of X-radiation received by the patient.
  • the amplification is carried out in a conventional manner by converting the radiation received by the input screen into emitted electrons in a cavity where the vacuum prevails.
  • the electrons are then accelerated by means of electrodes and then converted by the output screen into a visible image.
  • the invention is not limited to medical radiology, it can be implemented in all types of intensifiers whatever the radiation received or emitted by the screens.
  • the invention is for example applicable to light image intensifiers as for example described in the document FR 2 866 714 A1 .
  • the use of electrons accelerated by electrodes makes the intensifier sensitive to electromagnetic disturbances occurring in the environment of the intensifier. These disturbances create a spatial distortion of the image emitted by the output screen relative to the image received by the input screen.
  • Another solution is to project on the input screen a luminous pattern which we just analyze the distribution on the output screen as for example described in the documents WO 02/095457 - A2 and EP 0 949 651 A1 .
  • This solution avoids the displacement of mechanical parts such as the grid but is nevertheless cumbersome to implement and requires to interrupt the projection of the pattern to achieve a so-called useful image.
  • it is difficult to ensure sufficient dimensional stability of this pattern. In a common case, it would be necessary to ensure a stability of the order of 10 microns so that the accuracy of the test pattern is better than the dimension of a pixel in case of digitization of the image obtained on the output screen.
  • the invention aims to overcome the problems mentioned above by providing an intensifier tube in which the pattern can be permanently present without disturbing the primary radiation.
  • the subject of the invention is an image intensifier electronic tube according to claim 1.
  • the spectrum change of the primary radiation is common in medical imaging. For example, when using an X-ray source having a tube in which an electron beam is bombarding a target, a voltage change applied to electrodes accelerating the electron beam causes a change in the X-ray spectrum. Another reason for modifying the X-ray spectrum is related to the object whose image is to be obtained. Specifically, the thickness of an object (a patient in medical imaging) influences the spectrum of primary radiation received by the input screen.
  • An alteration of the primary radiation is generally not independent of the primary radiation spectrum and requires recalibration of the tube. The fact of not altering the primary radiation therefore avoids any recalibration between two successive images.
  • the figure 1 represents a tube 1 substantially elongated along an axis 2.
  • the tube 1 comprises a casing 3 inside which there is a sufficient vacuum so that electrons can move there.
  • An input screen 4 forms a first end of the envelope 3 and an exit screen 5 forms a second end of the envelope 3.
  • An input window 6 makes it possible to seal the envelope 3 at level of its first end. It is possible to dispense with the input window 6 and, in this case, the first screen 4 seals the envelope at its first end.
  • the output screen 5 can seal the envelope 3 at its second end.
  • X-radiation enters the tube 1 substantially along the axis 2 in a direction shown by an arrow 8.
  • This radiation through an object 9 which is to obtain a radiographic image.
  • the primary radiation for example X
  • the input screen 4 comprises a scintillator 10 on the face of the input screen 4 receiving X-radiation and a photocathode 11 on the opposite side of the input screen 4.
  • the scintillator 10 converts the primary radiation received by the input screen 4 into a secondary radiation such as for example visible light.
  • This secondary radiation is then absorbed by the photocathode 11 which converts it into electrons.
  • the electrons are then emitted inside the envelope 3 in the direction of the output screen 5.
  • the schematic path of the electrons inside the envelope 3 is materialized on the figure 1 by arrows 12.
  • the tube 1 also comprises several electrodes 13, 14, as well as an anode 15 located inside the envelope 3 making it possible to accelerate the electrons emitted by the photocathode 11 and guide them towards the output screen 5.
  • the acceleration of the electrons brings them energy allowing the intensification of the image.
  • the output screen 5 receives the electrons emitted by the photocathode 11 and converts them into radiation, for example visible, emitted towards the outside of the envelope 3 in the direction of the arrow 16.
  • This visible radiation may, for example , to be analyzed by a camera, represented on the figure 1 by its entrance pupil 17.
  • the optical axis of the entrance pupil 17 is substantially coincident with an axis of the output screen, in this case the axis 2.
  • the figure 2 is a pattern 20 belonging to the input screen 4.
  • the pattern 20 is formed of a plurality of points 21 distributed on the input screen 4.
  • the points 21 form for example a network uniformly distributed on the surface of the input screen 4.
  • the points 21 are for example round as shown on the figure 2 .
  • Other forms of points are of course possible, for example a square shape.
  • the target 20 comprises means for locally altering the secondary radiation which, for example, linearly modifies the transfer function between the primary radiation and the secondary radiation. In other words, at each point 21 of the target 20, the gain between the secondary radiation and the primary radiation is increased or decreased. The modification of the gain is determined so that the points 21 appear with sufficient contrast on the image obtained on the secondary screen 5 in the presence of an object 9 and at different doses of X-radiation.
  • figure 2 an example of evolution of the gain along an x axis crossing a point 21 in the form of a curve is shown. Outside point 21, the gain is maximum and inside the gain is reduced. Tests have shown that a reduction in gain of between 30 and 50% allows a certain recognition of the points 21 in the middle of an image of an object 9.
  • the tube comprises means making it possible to produce a light offset of the photocathode 11.
  • the corpuscular noise of this radiation can be important and make the recognition of the points difficult if the noise ratio on a signal is in the same order as the reduction of the gain by the points 21.
  • a remedy is the application of a luminous offset ie of a uniform illuminance of the photocathode 11.
  • this illumination is applied by a face of the input screen opposite to that which receives the primary radiation called the rear face of the input screen 4.
  • This light offset makes it possible to better detect the points 21.
  • the offset is then subtracted from the images obtained 5.
  • the offset also has an inherent corpuscular noise but is significantly lower than the corpuscular noise of the primary radiation. Of course, the offset noise must not exceed the primary radiation signal.
  • the offset is for example applied by means of a beam emitted by a light-emitting diode illuminating uniformly the rear face of the input screen 4.
  • the array of points 21 is moved under the influence of the magnetic fields in a non-homogeneous manner.
  • an example of a pattern 20 is shown on the figure 1 above the input screen 4.
  • An image 22 of this pattern 20, obtained on the output screen 5, is represented in continuous lines above the output screen 5.
  • an undistorted image of the pattern 20 on the output screen 5 has been shown in broken lines in superposition of the image 22.
  • the tube 1 comprises means for analyzing the distribution of the plurality of points 21 received by the output screen 5. More precisely, the measurement of this distortion is carried out by analyzing the distribution of the points in the image 22 of the target 20. For the points of the image located between the points of the target 20, the determination of the distortion can be done by interpolation from the measured distortion for the points of the target 20 closest to the considered point of the image 22.
  • the measurement can be absolute and the analysis consists in comparing the distribution of the points in the image 22 relative to to a theoretical distribution.
  • the measurement can be relative, and in this case, the comparison is made with respect to an image 22 made during a calibration phase during which the distortion of the image is controlled.
  • the means for locally altering the secondary radiation linearly modifies the transfer function between the primary radiation and the secondary radiation.
  • the transfer function is determined so as not to completely mask the primary radiation at the points 21 to be able to reconstruct the information contained in the primary radiation with the aid of a suitable treatment. More precisely, it has been realized that, in the absence of a pattern 20, the input screen 4 and more precisely the conversion between primary and secondary radiation has essentially multiplicative gain faults.
  • the defects already linearly alter the transfer function between the primary radiation and the secondary radiation. It is known to correct such defects for example by dividing a so-called useful image, obtained when X radiation passes through an object 9, by a reference image obtained when the same X radiation passes through no object.
  • the set of means for realizing the pattern belongs to the input screen 4 and more precisely, for each point 21 of the target 20, the means for locally altering the secondary radiation include a layer deposited on a surface of the input screen 4. This layer can be absorbent or reflective secondary radiation. It is indeed possible to increase the gain at point 21 instead of reducing it as explained in the box insert. figure 2 .
  • the figure 3 illustrates the operation of the points 21 of the target 20.
  • the input screen 4 formed by the scintillator 10 and the photocathode 11 and the input window 6.
  • the path of the primary radiation is materialized the arrows 8.
  • the primary radiation passes through the input screen 6 and is converted into secondary radiation whose path is represented by the arrows 30 which end on the photocathode 11 which transforms the secondary radiation into a beam of electrons 31.
  • the points 21 of the test pattern 20 are deposited and absorb a portion of the secondary radiation.
  • the absorption is indicated by arrows 30 in fine lines after passing through the point 21 by the secondary radiation.
  • the Figures 4a, 4b and 4c represents several examples of arrangement of the points 21 of the test pattern 20 on an input screen 4.
  • the scintillator 10 comprises a substrate 35 and a scintillator substance 36 for example made of cesium iodide.
  • the layer forming each point 21 is deposited on the substrate 35 and more precisely on one side of the substrate 35 carrying the scintillating substance 36.
  • the emission of the secondary radiation in the scintillating substance 36 is partly towards the rear, that is to say in a direction opposite to that of the arrow 8.
  • the layer forming each point 21 can either reflect the part of the secondary radiation emitted by the rear and in this case, the gain in the conversion between primary and secondary radiation is increased or absorb this part of the secondary radiation and in this case reduce the reflection of the secondary radiation on the substrate 35 and thus reduce the gain of the conversion.
  • the layer forming each point 21 is deposited on the intermediate layer 32 separating the scintillator 10 and the photocathode 11 is on the side of the scintillator 10, the case of the figure 4b , from side of the photocathode 11, case of the figure 4c .
  • the pattern can be made between the scintillator 10 and the intermediate layer 32 or between the intermediate layer 32 and the photocathode 11.
  • the intermediate layer 32 may comprise a conductive layer supplying the photocathode 11.
  • the pattern 20 may be made inside this conductive layer. In this case, it is advantageous to provide one or more additional layers to avoid degradation of the photocathode 11 and / or the conductive layer by the material of the pattern 20.
  • the layer may be made by vacuum evaporation of aluminum particles tending to reflect the second radiation, or carbon particles tending to absorb the second radiation.
  • the points 21 of the test pattern 20 are possible such as a local change of physical property of the surface of the scintillator 10 in contact with the intermediate layer 32.
  • a scintillating substance 36 such as cesium iodide is deposited on its substrate 35 in the form of needle growth.
  • the needle tips may be locally smoothed to locally alter the secondary radiation.
  • Another embodiment consists in making a physical or chemical modification of one of the components of the input screen 4. By way of example, it is possible to deviate from a stoichiometric composition or to modify crystalline properties.
  • the points 21 of the pattern 20 are made between the intermediate layer 32 and the photocathode 11, the points can alter the secondary radiation.
  • the points 21 then modify the gain of the photocathode 11 in the transformation of the energy carried by the secondary radiation into electron emission.
  • the photocathode 11 comprises for example a semiconductor material whose composition is stoichiometric. To achieve the points 21, one can for example deviate locally from the stoichiometric composition.
  • the modification of the gain of the photocathode 11 can also be implemented in a light image intensifier whose input screen is represented schematically on the figure 4e which is not part of the present invention.
  • This input screen has no scintillator and directly transforms the primary radiation into electrons. By acting on the gain of the photocathode 11, without altering the primary radiation, it is independent of the spectrum of the primary radiation.

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  • Image-Pickup Tubes, Image-Amplification Tubes, And Storage Tubes (AREA)

Abstract

The tube has an input screen (4) for receiving primary rays e.g. X-rays and an output screen (5) emitting rays, based on the function of the primary rays. The input screen includes a photocathode (11) on its surface for emitting electron beams in a direction of the output screen based on the function of primary rays. The input screen has a test chart (20) formed of a set of points distributed on the input screen. The test chart includes secondary rays e.g. visible light, absorbing/reflecting layer for locally altering the electron beams.

Description

L'invention se rapporte à la correction de distorsion d'un tube électronique intensificateur d'image.The invention relates to the distortion correction of an image intensifier electron tube.

Un tube électronique intensificateur d'image comprend un écran d'entrée destiné à recevoir un rayonnement électromagnétique dit primaire et un écran de sortie émettant un rayonnement fonction du rayonnement primaire. Les intensificateurs sont par exemple utilisés en radiologie médicale. Dans ce cas, l'intensificateur reçoit un rayonnement X qui a traversé le corps d'un patient. L'intensificateur émet sur son second écran une image visible fonction du rayonnement X reçu par l'écran d'entrée. En plus de la conversion des rayonnements X en rayonnements visibles formant l'image visible, l'intensificateur amplifie l'intensité de l'image reçue. En radiologie médicale, cette amplification permet de réduire la dose de rayonnement X reçue par le patient. L'amplification est réalisée de façon classique en convertissant le rayonnement reçu par l'écran d'entrée en électrons émis dans une cavité où règne le vide. Les électrons sont ensuite accélérés au moyen d'électrodes puis convertis par l'écran de sortie en image visible.An image intensifier electron tube includes an input screen for receiving said primary electromagnetic radiation and an output screen emitting radiation depending on the primary radiation. Intensifiers are for example used in medical radiology. In this case, the intensifier receives X-radiation that has passed through the body of a patient. The intensifier transmits on its second screen a visible image according to the X-radiation received by the input screen. In addition to converting X-radiation into visible radiation forming the visible image, the intensifier amplifies the intensity of the received image. In medical radiology, this amplification makes it possible to reduce the dose of X-radiation received by the patient. The amplification is carried out in a conventional manner by converting the radiation received by the input screen into emitted electrons in a cavity where the vacuum prevails. The electrons are then accelerated by means of electrodes and then converted by the output screen into a visible image.

II est bien entendu que l'invention n'est pas limitée à la radiologie médicale, elle peut être mise en oeuvre dans tous types d'intensificateurs quels que soient les rayonnements reçus ou émis par les écrans. L'invention est par exemple applicable aux intensificateurs d'images lumineuses comme par exemple décrit dans le document FR 2 866 714 A1 .It is understood that the invention is not limited to medical radiology, it can be implemented in all types of intensifiers whatever the radiation received or emitted by the screens. The invention is for example applicable to light image intensifiers as for example described in the document FR 2 866 714 A1 .

L'utilisation d'électrons accélérés par des électrodes rend l'intensificateur sensible à des perturbations électromagnétiques survenant dans l'environnement de l'intensificateur. Ces perturbations créent une distorsion spatiale de l'image émise par l'écran de sortie par rapport à l'image reçue par l'écran d'entrée.The use of electrons accelerated by electrodes makes the intensifier sensitive to electromagnetic disturbances occurring in the environment of the intensifier. These disturbances create a spatial distortion of the image emitted by the output screen relative to the image received by the input screen.

Cette distorsion est nuisible par exemple lorsque l'on doit effectuer des opérations entre plusieurs images successives comme par exemple l'angiographie numérique par soustraction, bien connue dans la littérature anglo-saxonne sous le nom de DSA pour Digital Substraction Angiographie, qui réclame une bonne superposition des images à soustraire, malgré d'éventuels changements du champ magnétique ambiant. La correction de distorsion est également importante pour la reconstitution des images tomographiques au moyen d'images prises sous différentes vues. Dans cette dernière utilisation, l'orientation du tube est modifiée entre deux images successives, ce qui risque de perturber le trajet des électrons sensibles notamment au champ magnétique terrestre qui reste fixe.This distortion is detrimental for example when operations are to be carried out between successive images, for example digital subtraction angiography, well known in the American literature under the name DSA for Digital Substraction Angiography, which calls for good superposition of the images to be subtracted, despite possible changes in the ambient magnetic field. Distortion correction is also important for image reconstruction Tomography using images taken in different views. In this last use, the orientation of the tube is changed between two successive images, which may disturb the path of the sensitive electrons in particular the terrestrial magnetic field which remains fixed.

De nombreuses applications non médicales sont aussi exigeantes en matière de réduction de la distorsion. On peut citer la diffraction des rayons X, et tous les contrôles au cours desquels on soustrait des images pour repérer des écarts par rapport à un modèle.Many non-medical applications are also demanding in reducing distortion. We can mention X-ray diffraction, and all the controls in which images are subtracted to identify deviations from a model.

II est possible de corriger cette distorsion en plaçant devant l'écran d'entrée une grille laissant passer ou arrêtant, dans des zones précises, le rayonnement reçu par l'écran d'entrée comme par exemple décrit dans le document FR 2 803 394 A1 . On peut analyser l'image émise par l'écran de sortie pour retrouver, dans l'image émise, les zones définies par la grille et ainsi déterminer pour chacune des zones la distorsion de l'image émise par l'écran de sortie par rapport à l'image reçue par l'écran d'entrée. Pour chaque point de l'image reçue, on peut ensuite déterminer la distorsion par interpolation entre les zones. Lors de l'utilisation de l'intensificateur pour recevoir une image utile, il faudra bien entendu déplacer la grille hors de la scène observée par l'écran d'entrée de l'intensificateur. On pourra ainsi corriger l'image utile émise par l'écran de sortie en utilisant les valeurs de distorsion déterminées pour chaque point de l'image.It is possible to correct this distortion by placing in front of the input screen a grid passing or stopping, in specific areas, the radiation received by the input screen as for example described in the document FR 2 803 394 A1 . The image emitted by the output screen can be analyzed to find, in the transmitted image, the zones defined by the grid and thus to determine for each of the zones the distortion of the image emitted by the output screen relative to to the image received by the input screen. For each point of the received image, it is then possible to determine the distortion by interpolation between the zones. When using the intensifier to receive a useful image, it will of course move the grid out of the scene observed by the input screen of the intensifier. It will thus be possible to correct the useful image emitted by the output screen by using the distortion values determined for each point of the image.

En procédant ainsi, il est nécessaire de recommencer la détermination de la distorsion dès que l'environnement de l'intensificateur est modifié, par exemple lorsqu'on déplace une machine électrique à proximité de l'intensificateur ou lorsqu'on déplace l'intensificateur lui-même. Le déplacement de l'intensificateur est fréquent en radiologie médicale car il est souvent plus facile de déplacer la source de rayonnement X et l'intensificateur que le patient lui-même. L'utilisation d'une grille que l'on positionne devant l'écran d'entrée pour déterminer la distorsion puis que l'on enlève constituerait une procédure lourde et délicate à mettre en oeuvre. La procédure serait lourde car elle nécessite un temps non négligeable pour la manipulation de la grille. La procédure serait délicate car il serait nécessaire de maîtriser avec une grande précision le positionnement de la grille par rapport à l'écran d'entrée.In doing so, it is necessary to restart the determination of the distortion as soon as the environment of the intensifier is modified, for example when moving an electric machine near the intensifier or when the intensifier is moved. -even. Movement of the intensifier is common in medical radiology because it is often easier to move the X-ray source and the intensifier than the patient himself. The use of a grid that is positioned in front of the input screen to determine the distortion and then removed is a cumbersome and difficult procedure to implement. The procedure would be heavy because it requires a significant amount of time for handling the grid. The procedure would be tricky because it would be necessary to control with great precision the positioning of the grid relative to the input screen.

Une autre solution consiste à projeter sur l'écran d'entrée une mire lumineuse dont on vient analyser la répartition sur l'écran de sortie comme par exemple décrit dans les documents WO 02/095457 - A2 et EP 0 949 651 A1 . Cette solution permet d'éviter le déplacement de pièces mécaniques telles que la grille mais reste néanmoins lourde à mettre en oeuvre et nécessite d'interrompre la projection de la mire pour réaliser une image dite utile. De plus, il est difficile d'assurer une stabilité dimensionnelle suffisante de cette mire. Dans un cas courant, il faudrait assurer une stabilité de l'ordre de 10 µm pour que la précision de la mire soit meilleure que la dimension d'un pixel en cas de numérisation de l'image obtenue sur l'écran de sortie.Another solution is to project on the input screen a luminous pattern which we just analyze the distribution on the output screen as for example described in the documents WO 02/095457 - A2 and EP 0 949 651 A1 . This solution avoids the displacement of mechanical parts such as the grid but is nevertheless cumbersome to implement and requires to interrupt the projection of the pattern to achieve a so-called useful image. In addition, it is difficult to ensure sufficient dimensional stability of this pattern. In a common case, it would be necessary to ensure a stability of the order of 10 microns so that the accuracy of the test pattern is better than the dimension of a pixel in case of digitization of the image obtained on the output screen.

L'invention vise à pallier les problèmes cités plus haut en proposant un tube intensificateur dans lequel la mire peut être présente en permanence sans perturber le rayonnement primaire.The invention aims to overcome the problems mentioned above by providing an intensifier tube in which the pattern can be permanently present without disturbing the primary radiation.

A cet effet, l'invention a pour objet un Tube électronique intensificateur d'image selon la revendication 1.For this purpose, the subject of the invention is an image intensifier electronic tube according to claim 1.

Ne pas altérer le rayonnement primaire permet de conserver un contraste constant de la mire sur l'écran secondaire même en cas de changement de spectre du rayonnement primaire. On a constaté qu'en agissant sur le rayonnement primaire, le contraste de la mire est modifié ce qui rend plus difficile la suppression de la mire d'image observée sur l'écran de sortie du tube Le changement de spectre du rayonnement primaire est courant en imagerie médicale. Par exemple, lorsqu'on utilise une source de rayonnement X comportant un tube dans lequel un faisceau d'électrons bombarde une cible, une modification de tension appliquée à des électrodes accélérant le faisceau d'électrons entraîne une modification du spectre du rayonnement X. Une autre cause de modification du spectre du rayonnement X est lié à l'objet dont on veut obtenir une image. Plus précisément, l'épaisseur d'un objet (un patient en imagerie médicale) influe sur le spectre du rayonnement primaire reçu par l'écran d'entrée.Not altering the primary radiation makes it possible to maintain a constant contrast of the pattern on the secondary screen even in the event of a change in the spectrum of the primary radiation. It has been found that by acting on the primary radiation, the contrast of the pattern is changed which makes it more difficult to remove the image pattern observed on the output screen of the tube. The spectrum change of the primary radiation is common in medical imaging. For example, when using an X-ray source having a tube in which an electron beam is bombarding a target, a voltage change applied to electrodes accelerating the electron beam causes a change in the X-ray spectrum. Another reason for modifying the X-ray spectrum is related to the object whose image is to be obtained. Specifically, the thickness of an object (a patient in medical imaging) influences the spectrum of primary radiation received by the input screen.

Une altération du rayonnement primaire n'est généralement pas indépendante du spectre du rayonnement primaire et impose une recalibration du tube. Le fait de ne pas altérer le rayonnement primaire permet donc d'éviter toute recalibration entre deux images successives.An alteration of the primary radiation is generally not independent of the primary radiation spectrum and requires recalibration of the tube. The fact of not altering the primary radiation therefore avoids any recalibration between two successive images.

L'invention sera mieux comprise et d'autres avantages apparaîtront à la lecture de la description détaillée d'un mode de réalisation donné à titre d'exemple, description illustrée par le dessin joint dans lequel :

  • La figure 1 représente schématiquement les principaux éléments d'un tube électronique intensificateur d'image ;
  • la figure 2 représente un exemple de mire réalisée sur un écran d'entrée du tube ;
  • la figure 3 illustre le fonctionnement de points de la mire;
  • les figures 4a, à 4e représente plusieurs exemples de disposition des points de la mire sur un écran d'entrée du tube.
The invention will be better understood and other advantages will appear on reading the detailed description of an embodiment given by way of example, a description illustrated by the attached drawing in which:
  • The figure 1 schematically represents the main elements of an image intensifier electronic tube;
  • the figure 2 represents an example of a pattern made on an input screen of the tube;
  • the figure 3 illustrates the operation of points of the test pattern;
  • the Figures 4a, 4th represents several examples of the arrangement of the points of the test pattern on an input screen of the tube.

Par souci de clarté, les mêmes éléments porteront les mêmes repères dans les différentes figures.For the sake of clarity, the same elements will bear the same references in the different figures.

La figure 1 représente un tube 1 sensiblement allongé selon un axe 2. Le tube 1 comporte une enveloppe 3 à l'intérieur de laquelle règne un vide suffisant pour que des électrons puissent s'y déplacer. Un écran d'entrée 4 forme une première extrémité de l'enveloppe 3 et un écran de sortie 5 forme une seconde extrémité de l'enveloppe 3. Une fenêtre d'entrée 6 permet d'assurer l'étanchéité de l'enveloppe 3 au niveau de sa première extrémité. II est possible de se passer de la fenêtre d'entrée 6 et, dans ce cas, le premier écran 4 assure l'étanchéité de l'enveloppe au niveau de sa première extrémité. De même, l'écran de sortie 5 peut assurer l'étanchéité de l'enveloppe 3 au niveau de sa seconde extrémité.The figure 1 represents a tube 1 substantially elongated along an axis 2. The tube 1 comprises a casing 3 inside which there is a sufficient vacuum so that electrons can move there. An input screen 4 forms a first end of the envelope 3 and an exit screen 5 forms a second end of the envelope 3. An input window 6 makes it possible to seal the envelope 3 at level of its first end. It is possible to dispense with the input window 6 and, in this case, the first screen 4 seals the envelope at its first end. Similarly, the output screen 5 can seal the envelope 3 at its second end.

Un rayonnement X pénètre dans le tube 1 sensiblement suivant l'axe 2 dans une direction matérialisée par une flèche 8. Ce rayonnement traverse un objet 9 dont on veut obtenir une image radiographique. En aval de l'objet 9, le rayonnement primaire, par exemple X, atteint l'écran d'entrée 4 en traversant la fenêtre d'entrée 6. L'écran d'entrée 4 comporte un scintillateur 10 sur la face de l'écran d'entrée 4 recevant le rayonnement X et une photocathode 11 sur la face opposée de l'écran d'entrée 4. Le scintillateur 10 convertit le rayonnement primaire reçu par l'écran d'entrée 4 en un rayonnement secondaire comme par exemple de la lumière visible. Ce rayonnement secondaire est ensuite absorbé par la photocathode 11 qui le convertit en électrons. Les électrons sont alors émis à l'intérieur de l'enveloppe 3 en direction de l'écran de sortie 5. Le trajet schématique des électrons à l'intérieur de l'enveloppe 3 est matérialisé sur la figure 1 par des flèches 12.X-radiation enters the tube 1 substantially along the axis 2 in a direction shown by an arrow 8. This radiation through an object 9 which is to obtain a radiographic image. Downstream of the object 9, the primary radiation, for example X, reaches the input screen 4 by passing through the input window 6. The input screen 4 comprises a scintillator 10 on the face of the input screen 4 receiving X-radiation and a photocathode 11 on the opposite side of the input screen 4. The scintillator 10 converts the primary radiation received by the input screen 4 into a secondary radiation such as for example visible light. This secondary radiation is then absorbed by the photocathode 11 which converts it into electrons. The electrons are then emitted inside the envelope 3 in the direction of the output screen 5. The schematic path of the electrons inside the envelope 3 is materialized on the figure 1 by arrows 12.

Le tube 1 comporte également plusieurs électrodes 13, 14, ainsi qu'une anode 15 situées à l'intérieur de l'enveloppe 3 permettant d'accélérer les électrons émis par la photocathode 11 et de les guider vers l'écran de sortie 5. L'accélération des électrons leur apporte de l'énergie permettant l'intensification de l'image. L'écran de sortie 5 reçoit les électrons émis par la photocathode 11 et les convertit en un rayonnement, par exemple visible, émis vers l'extérieur de l'enveloppe 3 dans la direction de la flèche 16. Ce rayonnement visible peut, par exemple, être analysé par une caméra, représentée sur la figure 1 par sa pupille d'entrée 17. L'axe optique de la pupille d'entrée 17 est sensiblement confondu avec un axe de l'écran de sortie, en l'occurrence l'axe 2.The tube 1 also comprises several electrodes 13, 14, as well as an anode 15 located inside the envelope 3 making it possible to accelerate the electrons emitted by the photocathode 11 and guide them towards the output screen 5. The acceleration of the electrons brings them energy allowing the intensification of the image. The output screen 5 receives the electrons emitted by the photocathode 11 and converts them into radiation, for example visible, emitted towards the outside of the envelope 3 in the direction of the arrow 16. This visible radiation may, for example , to be analyzed by a camera, represented on the figure 1 by its entrance pupil 17. The optical axis of the entrance pupil 17 is substantially coincident with an axis of the output screen, in this case the axis 2.

La figure 2 représente une mire 20 appartenant à l'écran d'entrée 4. La mire 20 est formée d'une pluralité de points 21 répartis sur l'écran d'entrée 4. Les points 21 forment par exemple un réseau uniformément réparti sur la surface de l'écran d'entrée 4. Les points 21 sont par exemple ronds comme représenté sur la figure 2. D'autres formes de points sont bien entendues possibles comme par exemple une forme carrée. La mire 20 comporte des moyens pour altérer localement le rayonnement secondaire qui par exemple modifient de façon linéaire la fonction de transfert entre le rayonnement primaire et le rayonnement secondaire. Autrement dit, en chaque point 21 de la mire 20, le gain entre le rayonnement secondaire et le rayonnement primaire est augmenté ou diminué. La modification du gain est déterminée pour que les points 21 apparaissent avec un contraste suffisant sur l'image obtenue sur l'écran secondaire 5 en présence d'un objet 9 et à différentes doses de rayonnement X. En encart de la figure 2, on a représenté un exemple d'évolution du gain le long d'un axe x traversant un point 21 sous forme d'une courbe. A l'extérieur du point 21, le gain est maximum et à l'intérieur le gain est réduit. Des essais ont montré qu'une réduction de gain comprise entre 30 et 50% permettait une reconnaissance certaine des points 21 au milieu d'une image d'un objet 9.The figure 2 is a pattern 20 belonging to the input screen 4. The pattern 20 is formed of a plurality of points 21 distributed on the input screen 4. The points 21 form for example a network uniformly distributed on the surface of the input screen 4. The points 21 are for example round as shown on the figure 2 . Other forms of points are of course possible, for example a square shape. The target 20 comprises means for locally altering the secondary radiation which, for example, linearly modifies the transfer function between the primary radiation and the secondary radiation. In other words, at each point 21 of the target 20, the gain between the secondary radiation and the primary radiation is increased or decreased. The modification of the gain is determined so that the points 21 appear with sufficient contrast on the image obtained on the secondary screen 5 in the presence of an object 9 and at different doses of X-radiation. figure 2 an example of evolution of the gain along an x axis crossing a point 21 in the form of a curve is shown. Outside point 21, the gain is maximum and inside the gain is reduced. Tests have shown that a reduction in gain of between 30 and 50% allows a certain recognition of the points 21 in the middle of an image of an object 9.

Avantageusement, le tube comporte des moyens permettant de réaliser un offset lumineux de la photocathode 11. En effet, à très faible intensité du rayonnement primaire, le bruit corpusculaire de ce rayonnement peut être important et rendre la reconnaissance des points 21 difficile si le rapport bruit sur signal est dans le même ordre que la réduction du gain par les points 21. Un remède est l'application d'un offset lumineux c'est à dire d'un éclairement lumineux uniforme de la photocathode 11. Avantageusement, cet éclairement est appliqué par une face de l'écran d'entrée opposée à celle qui reçoit le rayonnement primaire appelée face arrière de l'écran d'entrée 4. Cet offset lumineux permet de mieux détecter les points 21. L'offset est ensuite soustrait des images obtenue sur l'écran secondaire 5. L'offset a également un bruit corpusculaire inhérent mais qui est sensiblement plus faible que le bruit corpusculaire du rayonnement primaire. Bien entendu, le bruit d'offset ne doit pas dépasser le signal du rayonnement primaire. L'offset est par exemple appliqué au moyen d'un faisceau émis par une diode électroluminescente éclairant de façon uniforme la face arrière de l'écran d'entrée 4.Advantageously, the tube comprises means making it possible to produce a light offset of the photocathode 11. In fact, at very low intensity of the primary radiation, the corpuscular noise of this radiation can be important and make the recognition of the points difficult if the noise ratio on a signal is in the same order as the reduction of the gain by the points 21. A remedy is the application of a luminous offset ie of a uniform illuminance of the photocathode 11. Advantageously, this illumination is applied by a face of the input screen opposite to that which receives the primary radiation called the rear face of the input screen 4. This light offset makes it possible to better detect the points 21. The offset is then subtracted from the images obtained 5. The offset also has an inherent corpuscular noise but is significantly lower than the corpuscular noise of the primary radiation. Of course, the offset noise must not exceed the primary radiation signal. The offset is for example applied by means of a beam emitted by a light-emitting diode illuminating uniformly the rear face of the input screen 4.

Pendant le fonctionnement du tube 1, le réseau de points 21 est déplacé sous l'influence des champs magnétiques d'une manière non-homogène. Pour illustrer ce déplacement, un exemple de mire 20 est représenté sur la figure 1 au-dessus de l'écran d'entrée 4. Une image 22 de cette mire 20, obtenue sur l'écran de sortie 5, est représentée en traits continus au-dessus de l'écran de sortie 5. Pour bien visualiser la distorsion entre la mire 20 et son image 22, une image non distordue de la mire 20 sur l'écran de sortie 5 a été représentée en trait interrompu en superposition de l'image 22.During the operation of the tube 1, the array of points 21 is moved under the influence of the magnetic fields in a non-homogeneous manner. To illustrate this displacement, an example of a pattern 20 is shown on the figure 1 above the input screen 4. An image 22 of this pattern 20, obtained on the output screen 5, is represented in continuous lines above the output screen 5. To visualize the distortion between the pattern 20 and its image 22, an undistorted image of the pattern 20 on the output screen 5 has been shown in broken lines in superposition of the image 22.

Avantageusement, le tube 1 comporte des moyens d'analyse de la répartition de la pluralité de points 21 reçus par l'écran de sortie 5. Plus précisément, la mesure de cette distorsion est réalisée par analyse de la répartition des points dans l'image 22 de la mire 20. Pour les points de l'image situés entre les points de la mire 20, la détermination de la distorsion peut se faire par interpolation à partir de la distorsion mesurée pour les points de la mire 20 les plus proches du point considéré de l'image 22. La mesure peut être absolue et l'analyse consiste à comparer la répartition des points dans l'image 22 par rapport à une répartition théorique. La mesure peut être relative, et, dans ce cas, la comparaison se fait par rapport à une image 22 réalisée lors d'une phase de calibration pendant laquelle la distorsion de l'image est maîtrisée.Advantageously, the tube 1 comprises means for analyzing the distribution of the plurality of points 21 received by the output screen 5. More precisely, the measurement of this distortion is carried out by analyzing the distribution of the points in the image 22 of the target 20. For the points of the image located between the points of the target 20, the determination of the distortion can be done by interpolation from the measured distortion for the points of the target 20 closest to the considered point of the image 22. The measurement can be absolute and the analysis consists in comparing the distribution of the points in the image 22 relative to to a theoretical distribution. The measurement can be relative, and in this case, the comparison is made with respect to an image 22 made during a calibration phase during which the distortion of the image is controlled.

Avantageusement, les moyens pour altérer localement le rayonnement secondaire modifie de façon linéaire la fonction de transfert entre le rayonnement primaire et le rayonnement secondaire. La fonction de transfert est déterminée de façon à ne pas masquer totalement le rayonnement primaire au niveau des points 21 pour pouvoir reconstituer l'information contenue dans le rayonnement primaire à l'aide d'un traitement adéquat. Plus précisément, on s'est rendu compte qu'en l'absence de mire 20, l'écran d'entrée 4 et plus précisément la conversion entre rayonnement primaire et secondaire présente des défauts de gain essentiellement multiplicatifs. Autrement dit, les défauts altèrent déjà de façon linéaire la fonction de transfert entre le rayonnement primaire et le rayonnement secondaire. On sait corriger de tels défauts par exemple en divisant une image dite utile, obtenue lorsque que rayonnement X traverse un objet 9, par une image de référence obtenue lorsque le même rayonnement X ne traverse aucun objet. II suffit donc d'appliquer ce type de correction pour retrouver une image utile nettoyée de la mire 20. II est bien entendu que cette phase de suppression de la mire 20 de l'image n'intervient qu'après la phase de correction géométrique de distorsion. Ces deux opérations de traitement de l'image sont par exemple réalisées après numérisation de l'image obtenue sur l'écran de sortie 5.Advantageously, the means for locally altering the secondary radiation linearly modifies the transfer function between the primary radiation and the secondary radiation. The transfer function is determined so as not to completely mask the primary radiation at the points 21 to be able to reconstruct the information contained in the primary radiation with the aid of a suitable treatment. More precisely, it has been realized that, in the absence of a pattern 20, the input screen 4 and more precisely the conversion between primary and secondary radiation has essentially multiplicative gain faults. In other words, the defects already linearly alter the transfer function between the primary radiation and the secondary radiation. It is known to correct such defects for example by dividing a so-called useful image, obtained when X radiation passes through an object 9, by a reference image obtained when the same X radiation passes through no object. It is therefore sufficient to apply this type of correction to find a useful image cleaned from the target 20. It is understood that this phase of suppression of the image 20 of the image occurs only after the phase of geometric correction of distortion. These two image processing operations are for example performed after scanning the image obtained on the output screen 5.

On choisit donc réaliser la mire 20 au moyen de points 21 semi-transparents au rayonnement secondaire.We thus choose to achieve the target 20 by means of semi-transparent points 21 secondary radiation.

Pour assurer une stabilité géométrique de la mire 20 sur l'écran d'entrée 4, l'ensemble des moyens pour réaliser la mire appartient à l'écran d'entré 4 et plus précisément, pour chaque point 21 de la mire 20, les moyens pour altérer localement le rayonnement secondaire comportent une couche déposée sur une surface de l'écran d'entrée 4. Cette couche peut être absorbante ou réfléchissante du rayonnement secondaire. Il est en effet possible d'augmenter le gain au niveau du point 21 au lieu de le réduire comme cela avait été expliqué à l'aide de l'encart de la figure 2.To ensure a geometric stability of the sight 20 on the input screen 4, the set of means for realizing the pattern belongs to the input screen 4 and more precisely, for each point 21 of the target 20, the means for locally altering the secondary radiation include a layer deposited on a surface of the input screen 4. This layer can be absorbent or reflective secondary radiation. It is indeed possible to increase the gain at point 21 instead of reducing it as explained in the box insert. figure 2 .

La figure 3 illustre le fonctionnement des points 21 de la mire 20. Sur cette figure, on retrouve l'écran d'entrée 4 formé du scintillateur 10 et de la photocathode 11 ainsi que la fenêtre d'entrée 6. Le trajet du rayonnement primaire est matérialisé les flèches 8. Le rayonnement primaire traverse l'écran d'entrée 6 puis est converti en rayonnement secondaire dont le trajet est représenté par les flèches 30 qui aboutissent sur la photocathode 11 qui transforme le rayonnement secondaire en un faisceau d'électrons 31. Sur une couche intermédiaire 32, située entre le scintillateur 10 et la photocathode 11, les points 21 de la mire 20 sont déposés et absorbent une partie du rayonnement secondaire. Sur la figure 3, l'absorption est matérialisée par des flèches 30 en traits fins après traversée du point 21 par le rayonnement secondaire.The figure 3 illustrates the operation of the points 21 of the target 20. In this figure, there is the input screen 4 formed by the scintillator 10 and the photocathode 11 and the input window 6. The path of the primary radiation is materialized the arrows 8. The primary radiation passes through the input screen 6 and is converted into secondary radiation whose path is represented by the arrows 30 which end on the photocathode 11 which transforms the secondary radiation into a beam of electrons 31. On a intermediate layer 32, located between the scintillator 10 and the photocathode 11, the points 21 of the test pattern 20 are deposited and absorb a portion of the secondary radiation. On the figure 3 the absorption is indicated by arrows 30 in fine lines after passing through the point 21 by the secondary radiation.

Les figures 4a, 4b et 4c représente plusieurs exemples de disposition des points 21 de la mire 20 sur un écran d'entrée 4. Sur ces figures on a représenté le scintillateur 10, la couche intermédiaire 32 et la photocathode 11. Le scintillateur 10 comporte un substrat 35 et une substance scintillatrice 36 par exemple réalisée à base d'iodure de césium. Sur la figure 4a, la couche réalisant chaque point 21 est déposée sur le substrat 35 et plus précisément sur une face du substrat 35 portant la substance scintillatrice 36. L'émission du rayonnement secondaire dans la substance scintillatrice 36 se fait en partie vers l'arrière, c'est à dire dans une direction opposée à celle de la flèche 8. La couche formant chaque point 21 peut soit réfléchir la partie du rayonnement secondaire émise par l'arrière et dans ce cas, le gain dans la conversion entre rayonnement primaire et secondaire est augmenté, soit absorber cette partie du rayonnement secondaire et dans ce cas, réduire la réflexion du rayonnement secondaire sur le substrat 35 et donc réduire le gain de la conversion.The Figures 4a, 4b and 4c represents several examples of arrangement of the points 21 of the test pattern 20 on an input screen 4. In these figures there is shown the scintillator 10, the intermediate layer 32 and the photocathode 11. The scintillator 10 comprises a substrate 35 and a scintillator substance 36 for example made of cesium iodide. On the figure 4a the layer forming each point 21 is deposited on the substrate 35 and more precisely on one side of the substrate 35 carrying the scintillating substance 36. The emission of the secondary radiation in the scintillating substance 36 is partly towards the rear, that is to say in a direction opposite to that of the arrow 8. The layer forming each point 21 can either reflect the part of the secondary radiation emitted by the rear and in this case, the gain in the conversion between primary and secondary radiation is increased or absorb this part of the secondary radiation and in this case reduce the reflection of the secondary radiation on the substrate 35 and thus reduce the gain of the conversion.

Sur les figures 4b et 4c, la couche formant chaque point 21 est déposée sur la couche intermédiaire 32 séparant le scintillateur 10 et la photocathode 11 soit du coté du scintillateur 10, cas de la figure 4b, soit du coté de la photocathode 11, cas de la figure 4c. Autrement dit, on peut réaliser la mire entre le scintillateur 10 et la couche intermédiaire 32 ou entre la couche intermédiaire 32 et la photocathode 11.On the Figures 4b and 4c , the layer forming each point 21 is deposited on the intermediate layer 32 separating the scintillator 10 and the photocathode 11 is on the side of the scintillator 10, the case of the figure 4b , from side of the photocathode 11, case of the figure 4c . In other words, the pattern can be made between the scintillator 10 and the intermediate layer 32 or between the intermediate layer 32 and the photocathode 11.

La couche intermédiaire 32 peut comporter une couche conductrice alimentant la photocathode 11. La mire 20 peut être réalisée à l'intérieur de cette couche conductrice. Dans ce cas, il est avantageux de prévoir une ou plusieurs couches supplémentaires pour éviter une dégradation de la photocathode 11 et/ou de la couche conductrice par le matériau de la mire 20.The intermediate layer 32 may comprise a conductive layer supplying the photocathode 11. The pattern 20 may be made inside this conductive layer. In this case, it is advantageous to provide one or more additional layers to avoid degradation of the photocathode 11 and / or the conductive layer by the material of the pattern 20.

Sur la figure 4d, les points 21 sont réalisés à l'intérieur de la substance scintillatrice 36 afin de diminuer des interactions chimique notamment avec la photocathode 11.On the figure 4d the points 21 are made inside the scintillator substance 36 in order to reduce chemical interactions, in particular with the photocathode 11.

Lorsque le rayonnement secondaire est un rayonnement lumineux, la couche peut être réaliser par évaporation sous vide de particules d'aluminium tendant à réfléchir le second rayonnement, ou encore de particules de carbone tendant à absorber le second rayonnement. D'autres réalisations des points 21 de la mire 20 sont possibles tel qu'un changement local de propriété physique de la surface du scintillateur 10 en contact avec la couche intermédiaire 32. En effet, une substance scintillatrice 36 tel que l'iodure de césium est déposée sur son substrat 35 sous forme de croissance d'aiguilles. On peut par exemple lisser localement les pointes d'aiguilles pour altérer localement le rayonnement secondaire. Une autre réalisation consiste à opérer une modification physique ou chimique d'un des composants de l'écran d'entrée 4. A titre d'exemple, on peut s'écarter d'une composition stoechiométrique ou modifier des propriétés cristallines.When the secondary radiation is a light radiation, the layer may be made by vacuum evaporation of aluminum particles tending to reflect the second radiation, or carbon particles tending to absorb the second radiation. Other embodiments of the points 21 of the test pattern 20 are possible such as a local change of physical property of the surface of the scintillator 10 in contact with the intermediate layer 32. In fact, a scintillating substance 36 such as cesium iodide is deposited on its substrate 35 in the form of needle growth. For example, the needle tips may be locally smoothed to locally alter the secondary radiation. Another embodiment consists in making a physical or chemical modification of one of the components of the input screen 4. By way of example, it is possible to deviate from a stoichiometric composition or to modify crystalline properties.

Dans le cas de la figure 4c, où les points 21 de la mire 20 sont réalisés entre la couche intermédiaire 32 et la photocathode 11, les points peuvent altérer le rayonnement secondaire. Une variante de réalisation consiste pour les points 21 à n'altérer que le faisceau d'électrons émis par la photocathode 11 sans altérer le rayonnement secondaire. Les points 21 modifient alors le gain de la photocathode 11 dans la transformation de l'énergie véhiculée par le rayonnement secondaire en émission d'électrons. La photocathode 11 comporte par exemple un matériau semi-conducteur dont la composition est stoechiométrique. Pour réaliser les points 21, on peut par exemple s'écarter localement de la composition stoechiométrique.In the case of figure 4c where the points 21 of the pattern 20 are made between the intermediate layer 32 and the photocathode 11, the points can alter the secondary radiation. An alternative embodiment for the points 21 to alter only the electron beam emitted by the photocathode 11 without altering the secondary radiation. The points 21 then modify the gain of the photocathode 11 in the transformation of the energy carried by the secondary radiation into electron emission. The photocathode 11 comprises for example a semiconductor material whose composition is stoichiometric. To achieve the points 21, one can for example deviate locally from the stoichiometric composition.

La modification du gain de la photocathode 11 peut également être mise en oeuvre dans un intensificateur d'images lumineuses dont l'écran d'entrée est représentée de façon schématique sur la figure 4e qui ne fait pas partie de la présente invention. Cet écran d'entrée ne comporte pas de scintillateur et transforme directement le rayonnement primaire en électrons. En agissant sur le gain de la photocathode 11, sans altérer le rayonnement primaire, on est indépendant du spectre du rayonnement primaire.The modification of the gain of the photocathode 11 can also be implemented in a light image intensifier whose input screen is represented schematically on the figure 4e which is not part of the present invention. This input screen has no scintillator and directly transforms the primary radiation into electrons. By acting on the gain of the photocathode 11, without altering the primary radiation, it is independent of the spectrum of the primary radiation.

Claims (12)

  1. An electronic image intensifier tube comprising an input screen (4) designed to receive primary electromagnetic radiation and an output screen (5) emitting radiation as a function of the primary radiation, the input screen comprising:
    • a photocathode (11) emitting a beam of electrons in the tube towards the output screen (5), the emission of the beam of electrons being a function of the primary radiation,
    • a scintillator (10) placed in front of the photocathode in the direction of the path of the primary radiation and transforming the primary radiation into secondary electromagnetic radiation (30) to which the photocathode (11) is sensitive, the beam of electrons emitted by the photocathode being a function of the secondary radiation (30), characterised in that the input screen (4) further comprises a sight (20) placed in front of the photocathode in the direction of the path of the primary radiation and formed by a plurality of spots (21) distributed over the input screen (4), and in that the spots (21) locally alter the secondary radiation (30) without altering the primary radiation.
  2. The tube according to claim 1, characterised in that the sight (20) is permanently present on the input screen (4).
  3. The tube according to any one of the preceding claims, characterised in that the spots (21) linearly modify the transfer function between the primary radiation and the secondary radiation.
  4. The tube according to any one of the preceding claims, characterised in that the spots (21) are semi-transparent to the secondary radiation.
  5. The tube according to any one of the preceding claims, characterised in that each spot (21) of the sight (20) comprises a layer placed on a surface (32, 35) of the input screen (4).
  6. The tube according to claim 5, characterised in that the layer absorbs the secondary radiation.
  7. The tube according to claim 5, characterised in that the layer reflects the secondary radiation.
  8. The tube according to any one of claims 5 to 7, characterised in that the scintillator (10) comprises a substrate (10) and a scintillating substance (36) placed on the substrate (35), and in that the layer is disposed on the substrate (35).
  9. The tube according to any one of claims 5 to 7, characterised in that the layer is disposed between the scintillator (10) and the photocathode (11).
  10. The tube according to any one of the preceding claims, characterised in that it comprises means for analysing the distribution of the plurality of spots (21) on the sight (20) received by the output screen (5).
  11. The tube according to any one of the preceding claims, characterised in that it comprises means for producing a light offset from the photocathode (11).
  12. The tube according to any one of the preceding claims, characterised in that all of the means for producing the site (20) belong to the input screen (4).
EP07116775A 2006-09-26 2007-09-19 Correction of the distortion of an image intensifier electron tube Not-in-force EP1906432B1 (en)

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FR2803394A1 (en) * 1999-12-30 2001-07-06 Thomson Tubes Electroniques X-RAY IMAGE DETECTION SYSTEM FOR SCANNING X-RAY GENERATOR
FR2866714A1 (en) * 2004-02-19 2005-08-26 Jean Claude Robin Image capturing method for use in field of e.g. visible spectral band, involves selecting, according to parameter, signal emitted by one sensor, and utilizing selected signals as signal of captured image

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EP1906432A1 (en) 2008-04-02
US7728519B2 (en) 2010-06-01
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FR2906400A1 (en) 2008-03-28
US20080073492A1 (en) 2008-03-27
ATE507575T1 (en) 2011-05-15
FR2906400B1 (en) 2008-11-14

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