EP1266391A2 - Radiation converter - Google Patents

Radiation converter

Info

Publication number
EP1266391A2
EP1266391A2 EP01935937A EP01935937A EP1266391A2 EP 1266391 A2 EP1266391 A2 EP 1266391A2 EP 01935937 A EP01935937 A EP 01935937A EP 01935937 A EP01935937 A EP 01935937A EP 1266391 A2 EP1266391 A2 EP 1266391A2
Authority
EP
European Patent Office
Prior art keywords
radiation
photocathode
converter according
radiation converter
electron
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP01935937A
Other languages
German (de)
French (fr)
Other versions
EP1266391B1 (en
Inventor
Manfred Fuchs
Erich Hell
Wolfgang KNÜPFER
Detlef Mattern
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Siemens AG
Original Assignee
Siemens AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Siemens AG filed Critical Siemens AG
Publication of EP1266391A2 publication Critical patent/EP1266391A2/en
Application granted granted Critical
Publication of EP1266391B1 publication Critical patent/EP1266391B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • 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
    • H01J31/49—Pick-up adapted for an input of electromagnetic radiation other than visible light and having an electric output, e.g. for an input of X-rays, for an input of infrared radiation
    • 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
    • H01J2231/50005—Imaging and conversion tubes characterised by form of illumination
    • H01J2231/5001—Photons
    • H01J2231/50031—High energy photons
    • H01J2231/50036—X-rays
    • 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
    • H01J2231/50068—Electrical
    • 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
    • H01J2231/501—Imaging and conversion tubes including multiplication stage

Definitions

  • a radiation converter designed as an image intensifier is known.
  • Such image intensifiers have an input window with a radiation absorber for generating light photons as a function of the radiation incident on the radiation intensity.
  • a photocathode is arranged downstream of the radiation absorber and generates electrons depending on the light photons emitted by the radiation absorber. These electrons are accelerated to an electron receiver by an electrode system.
  • this electron receiver is designed as an output screen, which generates light photons due to the incident electrons.
  • an X-ray detector is known in which the photocathode is applied to a radiation absorber.
  • the photocathode is arranged at a distance opposite an amorphous selenium layer of an exit screen.
  • Another detector device is known from DE 44 29 925 Cl.
  • a shadow mask made of wires is provided on the radiation path side, which is connected downstream of a chevron plate.
  • a low-ohmic anode structure is provided on the rear side of the detector.
  • a photodetector is known from EP 0 053 530, in which an electron multiplier and a detector anode are connected downstream of a photocathode in the radiation direction.
  • the medical exposure of a patient is to keep the radiation exposure as small as is technically expedient in order to keep the radiation exposure of the patient as low as possible
  • the efficient use of the penetrating radiation that hits the radiation receiver has top priority.
  • the lower the radiation intensity striking the radiation receiver the lower the signals that can be derived from the radiation receiver.
  • the distance between the signal levels and the noise signals also becomes smaller, which goes hand in hand with a poorer ability to diagnose the visual representations that can be generated on the basis of these signals.
  • a compromise must therefore be made between a low radiation exposure of the patient and the radiation dose necessary for the good diagnosis of radiation images of the patient that can be generated.
  • the photographic film for example, is nothing more than a chemical enhancer that controls the ionization processes of the
  • Radiation in the microscopic range amplified by many orders of magnitude and made visible in the macroscopic range.
  • Storage phosphor panels latently store the radiation silhouette of an object.
  • light photons are generated on the basis of the latent image, which are converted into electrons by a readout with a photo ultiplier, which can be amplified up to a factor of 10 6 almost without noise and m electrical signals can be converted. These electrical signals are then available for visual representation.
  • the geometric jamming which results from a large input window and a smaller output window, is used to increase the luminance, for which the energy absorption of the electrons from the input luminescent screen to the output luminescent screen is used by an acceleration field in between.
  • a radiation m light-converting layer which has, for example, Csl, is brought into direct contact with a photodiode matrix made of amorphous silicon, so that the light photons generated by the layer due to incident radiation are converted into electrical signals via the photo diode matrix which can then be used for visualization.
  • the photons are not amplified by electrons, only relatively small signals can be derived from the photodiode matrix, which can only be amplified in a downstream device, for example an amplifier. Since the amounts of charge of these relatively small electrical signals also have to be conducted via complicated clock processes from the sometimes large-area flat panel detectors to the amplifiers via relatively long lines, the mean noise, measured by electrons, is almost twice as large as the signal that is generated from individual X-ray quanta. Particularly for fluoroscopy, in which only small X-ray doses are applied, the signals that can be derived from the flat panel detector are particularly low and are close to the noise range and therefore require complex artifact corrections. In fluoroscopy, for example, the signals of every second beam scan are used for correction purposes, so that the usual image repetition rates cannot be nearly achieved. The dynamic range of the signals that can be derived from the flat panel detector is also severely restricted.
  • a-S ⁇ : H readout plates are predominantly used as electron detectors.
  • fluoroscopy and radiography which differ by dose factors of 100-1000, requires a high computing effort.
  • radiography mode operated with a high dose
  • fluoroscopy mode operated with a low dose
  • residual images must be removed
  • a-S ⁇ : H readout plate can be removed by subtraction.
  • the object of the invention is to provide a radiation converter that can be used as universally as possible. Another goal is to improve the dynamics of the radiation converter.
  • a distance is provided between the radiation absorber and the photocathode. This can reduce the effect of UV photons, which adversely affects the measurement.
  • the dynamics of the proposed radiation converter are improved.
  • Another advantage is that the photocathode no longer has to be transparent due to the arrangement proposed here. This can save costs.
  • the distance is advantageously between 10 and 100 ⁇ m. A distance of approximately 50 ⁇ m has proven to be particularly advantageous.
  • the photocathode can expediently be opaque. Avalanche UV photons cannot reach the photocathode directly.
  • the photocathode is made from a metallic material that preferably contains gold, cesium, copper or antimony. It is also expedient that the photocathode is designed as a layer on the electron multiplier, wherein the electron multiplier can in turn be formed as a layer on the electron detector.
  • the electron multiplier has a perforated plastic film, preferably made of polyimide. The diameter of the holes is about 25 ⁇ m. It is advantageous if the radiation absorber, the electrode system, the electron multiplier and the electron detector are assigned a common, gas-tight housing, which results in a compact construction of the radiation converter.
  • a gas which absorbs UV photons is preferably accommodated in the housing. The gas can have at least one of the following components: argon, krypton, xenon, helium, neon, C0 2 , N 2 , hydrocarbon, dimethyl ether, methanol / ethanol vapor.
  • the radiation absorber advantageously converts radiation into light photons if it has a needle-like structure and consists of CsI: Na.
  • the electron detector is particularly advantageously designed as a 2D thin-layer panel and consists of a-Se, a-S ⁇ : H or poly-Si. Such an electron detector is simple in construction and inexpensive.
  • Fig. 1 is a schematic cross-sectional view of a radiation converter
  • Fig. 2 shows the modulation transfer function as a function of the spatial frequency.
  • the reference numeral 1 denotes a housing.
  • the housing has a radiation absorber 2, which converts radiation into light photons.
  • the radiation absorber 2 is either designed as a separate part or is arranged outside the housing 1 in the region of a first end face. It consists of a scintillator material, preferably of CsI.Na in a needle structure, the needles being directed towards a photocathode 3 are.
  • the photocathode 3 is arranged at a distance a of approximately 50 ⁇ m from the radiation absorber 2. It is designed as a layer, which is preferably made of copper, on a perforated polyimide film 4.
  • the polyimide film 4 acts as an electron multiplier. It is applied to an electron detector 5.
  • the electron detector 5 preferably has a pixel structure and converts the impinging electrons into electrical signals, which can be derived using suitable known measures, for example an electrical line, and on the basis of which it is possible to display them on a display device.
  • the electron detector 5 is preferably designed as a 2D thin-film panel and can preferably consist of a-Se, a-S ⁇ : H or poly-Si.
  • a gas, in particular quench gas, for example a mixture of argon and hydrocarbon, is accommodated within the housing 1, in particular between the radiation absorber 2 and the photocathode 3.
  • the function of the device is as follows:
  • X-rays are absorbed by the radiation absorber 2 and thereby converted into photons.
  • the photons release photoelectrons from the photocathode 3.
  • the photoelectrons reach the area of the perforated polyimide film 4.
  • a potential is applied between the photocathode 3 and the electron detector 5.
  • the applied electrical potential ensures that all photoelectrons are pulled from the surface of the photocathode by 3 m from the holes located next.
  • a charge carrier multiplication takes place through impact ionization.
  • the charge carrier multiplication or amplification can be set by the level of the applied potential. The signal / noise ratio can thus be improved.
  • the photoelectrons are accelerated by the potential applied to the electron detector.
  • the radiation absorber 2 can be provided with a UV photon-absorbing conductive layer.
  • the quench gas absorbs the UV photons generated by impact ionization so that they do not reach the photocathode 3, where they could inadvertently trigger photoelectrons.
  • the modulation transfer function is plotted against the spatial frequency.
  • the curves MTF 1 and MTF 2 show the modulation transfer function at a distance of the photocathode 3 from the radiation absorber 2 of 50 ⁇ m.
  • the curve MTF 2 shows the point spread function of an isotropic point source, the curve MTF 1 the aforementioned point spread function for a Lambert source.
  • the curve MTF 3 shows the modulation transfer function, here the radiation absorber 2 is in direct contact with the electron detector 5.
  • the curve MTF 3 thus represents the characteristic of conventional flat detectors.
  • the values MTF 4 indicate the modulation transfer function for a Lambert source, the radiation absorber 2 being arranged at a distance of 50 ⁇ m from the electron detector 5. It can be seen that the spaced arrangement does not bring about any significant change in the modulation transfer function.

Landscapes

  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Measurement Of Radiation (AREA)
  • Conversion Of X-Rays Into Visible Images (AREA)
  • Transforming Light Signals Into Electric Signals (AREA)
  • Image-Pickup Tubes, Image-Amplification Tubes, And Storage Tubes (AREA)
  • Common Detailed Techniques For Electron Tubes Or Discharge Tubes (AREA)
  • Photometry And Measurement Of Optical Pulse Characteristics (AREA)

Abstract

The invention relates to a radiation converter, comprising a radiation absorber (2), for the generation of photons as a function of the intensity of the incident x-ray radiation and a photocathode (3), arranged within the radiation absorber (2), at a distance (a) in the direction of radiation. Said photocathode (3) is for the generation of electrodes as a function of the photons emitted by the radiation absorber (2), with a device for accelerating the electrons emitted by the photocathode to an electron detector (5). Said detector generates an electrical signal as a function of the arriving electrons. An electron multiplier (4) is arranged between the photocathode (3) and the electron detector (5), whereby the electrons emitted y the photocathode (3) may be multiplied by the electron multiplier (4).

Description

Beschreibungdescription
Strahlungswandlerradiation converter
Aus der DE 33 32 648 AI ist ein als Bildverstärker ausgeführter Strahlungswandler bekannt. Solche Bildverstärker weisen ein Eingangsfenster mit einem Strahlenabsorber zum Erzeugen von Lichtphotonen m Abhängigkeit von der Strahlenmtensitat auftreffender Strahlung auf. Dem Strahlenabsorber ist eine Photokathode nachgeordnet, die m Abhängigkeit von den von dem Strahlenabsorber ausgehenden Lichtphotonen Elektronen erzeugt. Diese Elektronen werden durch ein Elektrodensystem auf einen Elektronenempfanger beschleunigt. Beim Bildverstärker ist dieser Elektronenempfanger als Ausgangsschirm ausgeführt, der aufgrund der auftreffenden Elektronen Lichtphotonen erzeugt .From DE 33 32 648 AI a radiation converter designed as an image intensifier is known. Such image intensifiers have an input window with a radiation absorber for generating light photons as a function of the radiation incident on the radiation intensity. A photocathode is arranged downstream of the radiation absorber and generates electrons depending on the light photons emitted by the radiation absorber. These electrons are accelerated to an electron receiver by an electrode system. In the image intensifier, this electron receiver is designed as an output screen, which generates light photons due to the incident electrons.
Aus der US 5,369,268 ist ein Rontgendetektor bekannt, bei dem auf einem Strahlenabsorber die Photokathode aufgebracht ist. Die Photokathode ist mit einem Abstand gegenüberliegend angeordnet einer amorphen Selenschicht eines Ausgangsschirms.From US 5,369,268 an X-ray detector is known in which the photocathode is applied to a radiation absorber. The photocathode is arranged at a distance opposite an amorphous selenium layer of an exit screen.
Eine weitere Detektoreinrichtung ist aus der DE 44 29 925 Cl bekannt. Dabei ist strahlenemgangsseitig eine aus Drahten hergestellte Schattenmaske vorgesehen, welcher einer Chevron- Platte nachgeschaltet ist. Zur Erzeugung eines Bildsignals ist außerhalb des Detektors auf dessen Ruckseite eine nieder- ohmige Anodenstruktur vorgesehen. Aus der EP 0 053 530 ist ein Photodetektor bekannt, bei dem in Strahlungsrichtung ei- ner Photokathode ein Elektronenvervielfacher und eine Detektoranode nachgeschaltet sind.Another detector device is known from DE 44 29 925 Cl. In this case, a shadow mask made of wires is provided on the radiation path side, which is connected downstream of a chevron plate. To generate an image signal, a low-ohmic anode structure is provided on the rear side of the detector. A photodetector is known from EP 0 053 530, in which an electron multiplier and a detector anode are connected downstream of a photocathode in the radiation direction.
Da bei der medizinischen Untersuchung eines Patienten, im Unterschied zur zerstörungsfreien Werkstoffprüfung, die Strah- lenbelastung so klein zu halten ist, wie dies technisch sinnvoll ist, um die Strahlenbelastung des Patienten möglichst gering zu halten, ist die effiziente Nutzung der den Patien- ten durchdringenden und auf den Strahlenempfanger auftreffenden Strahlung oberstes Gebot. Je geringer jedoch die auf den Strahlenempfanger auftreffende Strahlenmtensitat ist, um so geringer sind auch die vom Strahlenempfanger ableitbaren Sig- nale. Der Abstand der Signalpegel zu den Rauschsignalen wird ebenfalls geringer, was mit einer schlechteren Diagnostizier- barkeit der aufgrund dieser Signale erzeugbaren bildlichen Darstellungen einher geht. Es ist also ein Kompromiß zwischen einer geringen Strahlenbelastung des Patienten und der für eine gute Diagnostizierbarkeit von erzeugbaren Durchstrah- lungsbildern des Patienten notwendigen Strahlendosis zu schließen .Since, in contrast to non-destructive material testing, the medical exposure of a patient is to keep the radiation exposure as small as is technically expedient in order to keep the radiation exposure of the patient as low as possible, the efficient use of the penetrating radiation that hits the radiation receiver has top priority. However, the lower the radiation intensity striking the radiation receiver, the lower the signals that can be derived from the radiation receiver. The distance between the signal levels and the noise signals also becomes smaller, which goes hand in hand with a poorer ability to diagnose the visual representations that can be generated on the basis of these signals. A compromise must therefore be made between a low radiation exposure of the patient and the radiation dose necessary for the good diagnosis of radiation images of the patient that can be generated.
Der fotografische Film ist beispielsweise nichts anderes als ein chemischer Verstarker, der die Ionisationsprozesse derThe photographic film, for example, is nothing more than a chemical enhancer that controls the ionization processes of the
Strahlung im mikroskopischen Bereich um viele Größenordnungen verstärkt und im makroskopischen Bereich sichtbar macht.Radiation in the microscopic range amplified by many orders of magnitude and made visible in the macroscopic range.
Speicherleuchtstoffplatten speichern das Strahlenschattenbild eines Objektes latent. Durch Abtastung der Speicherleuchtstoffplatte mittels eines Lichtstrahles werden aufgrund des latenten Bildes Lichtphotonen erzeugt, die von einer Auslese mit einem Photo ultiplier in Elektronen gewandelt werden, die nahezu rauschfrei bis zu einem Faktor von 106 verstärkt und m elektrische Signale gewandelt werden können. Diese elektrischen Signale stehen dann für die bildliche Darstellung zur Verfugung.Storage phosphor panels latently store the radiation silhouette of an object. By scanning the storage phosphor plate by means of a light beam, light photons are generated on the basis of the latent image, which are converted into electrons by a readout with a photo ultiplier, which can be amplified up to a factor of 10 6 almost without noise and m electrical signals can be converted. These electrical signals are then available for visual representation.
Bei Rontgenbildverstarkern wird die geometrische Verkleme- rung, die sich aufgrund eines großen Eingangsfensters und eines kleineren Ausgangsfensters ergibt, zur Verstärkung der Leuchtdichte herangezogen, wozu unterstutzend die Energieaufnahme der Elektronen vom Eingangsleuchtschirm zum Ausgangsleuchtschirm durch ein hier zwischenliegendes Beschleuni- gungsfeld dient. Bei den sogenannten Flachbilddetektoren wird eine Strahlung m Licht wandelnde Schicht, die beispielsweise Csl aufweist, in direkten Kontakt mit einer Photodiodenmatrix aus amorphem Silizium gebracht, so daß die von der Schicht aufgrund auf- treffender Strahlung erzeugten Lichtphotonen über die Photo- diodenmatπx in elektrische Signale gewandelt werden können, die dann für die bildliche Darstellung zur Verfugung stehen. Da keine Verstärkung der Lichtphotonen über Elektronen erfolgt, sind nur relativ kleine Signale von der Photodioden- matrix ableitbar, die erst in einer nachgeschalteten Einrichtung, z.B. einem Verstarker, verstärkt werden können. Da die Ladungsmengen dieser relativ geringen elektrischen Signale dann auch noch über komplizierte Taktverfahren aus den zum Teil großflächigen Flachbilddetektoren über relativ lange Leitungen bis zu den Verstarkern geleitet werden müssen, ist das mittlere Rauschen, m Elektronen gemessen, fast doppelt so groß wie das Signal, das von einzelnen Rontgenquanten erzeugt wird. Insbesondere für die Fluoroskopie, bei der nur kleine Rontgendosen appliziert werden, sind die von dem Flachbilddetektor ableitbaren Signale besonders gering und liegen nahe des Bereiches des Rauschens und erfordern somit aufwendige Artefaktkorrekturen. Bei der Fluoroskopie werden beispielsweise die Signale jeder zweiten Strahlenabtastung zu Korrekturzwecken herangezogen, so daß die üblichen Bildwie- derholraten nicht annähernd erreicht werden können. Der dynamische Bereich der von dem Flachbilddetektor ableitbaren Signale ist zudem stark eingeschränkt.In the case of X-ray image intensifiers, the geometric jamming, which results from a large input window and a smaller output window, is used to increase the luminance, for which the energy absorption of the electrons from the input luminescent screen to the output luminescent screen is used by an acceleration field in between. In the so-called flat-panel detectors, a radiation m light-converting layer, which has, for example, Csl, is brought into direct contact with a photodiode matrix made of amorphous silicon, so that the light photons generated by the layer due to incident radiation are converted into electrical signals via the photo diode matrix which can then be used for visualization. Since the photons are not amplified by electrons, only relatively small signals can be derived from the photodiode matrix, which can only be amplified in a downstream device, for example an amplifier. Since the amounts of charge of these relatively small electrical signals also have to be conducted via complicated clock processes from the sometimes large-area flat panel detectors to the amplifiers via relatively long lines, the mean noise, measured by electrons, is almost twice as large as the signal that is generated from individual X-ray quanta. Particularly for fluoroscopy, in which only small X-ray doses are applied, the signals that can be derived from the flat panel detector are particularly low and are close to the noise range and therefore require complex artifact corrections. In fluoroscopy, for example, the signals of every second beam scan are used for correction purposes, so that the usual image repetition rates cannot be nearly achieved. The dynamic range of the signals that can be derived from the flat panel detector is also severely restricted.
Bei den heutigen Flachbilddetektoren werden als Elektronende- tektoren vorwiegend a-Sι:H Ausleseplatten benutzt. Ein Betrieb solcher Flachbilddetektoren in verschiedenen Betriebsarten, wie Fluoroskopie und Radiographie, die sich um Dosisfaktoren von 100 - 1000 unterscheiden, erfordert einen hohen Rechenaufwand. Beim Übergang der mit einer hohen Dosis be- tπebenen Betriebsart Radiographie zur mit niedriger Dosis betriebenen Betriebsart Fluoroskopie müssen Restbilder m der a-Sι:H Ausleseplatte durch Subtraktion rechnerisch entfernt werden .In today's flat-panel detectors, a-Sι: H readout plates are predominantly used as electron detectors. Operating such flat panel detectors in various operating modes, such as fluoroscopy and radiography, which differ by dose factors of 100-1000, requires a high computing effort. When the radiography mode, operated with a high dose, changes to the fluoroscopy mode operated with a low dose, residual images must be removed a-Sι: H readout plate can be removed by subtraction.
Aufgabe der Erfindung ist es, einen möglichst universell ver- wendbaren Strahlungswandler anzugeben. Weiteres Ziel ist es, die Dynamik des Strahlungswandlers zu verbessern.The object of the invention is to provide a radiation converter that can be used as universally as possible. Another goal is to improve the dynamics of the radiation converter.
Diese Aufgabe wird durch die Merkmale des Patentanspruchs 1 gelost. Zweckmäßige Ausgestaltungen der Erfindung ergeben sich aus den Merkmalen der Patentansprüche 2 - 13.This object is achieved by the features of patent claim 1. Expedient embodiments of the invention result from the features of claims 2-13.
Beim erfmdungsgemaßen Strahlungswandler ist zwischen dem Strahlenabsorber und der Photokathode ein Abstand vorgesehen. Dadurch kann die die Messung nachteilig beeinflussende Wir- kung von UV-Photonen reduziert werden. Die Dynamik des vorgeschlagenen Strahlungswandlers ist verbessert. Ein weiterer Vorteil besteht darin, daß die Photokathode m Folge der hier vorgeschlagenen Anordnung nicht mehr transparent ausgeführt sein muß. Es kann dadurch eine Kostenersparnis erzielt wer- den.In the radiation converter according to the invention, a distance is provided between the radiation absorber and the photocathode. This can reduce the effect of UV photons, which adversely affects the measurement. The dynamics of the proposed radiation converter are improved. Another advantage is that the photocathode no longer has to be transparent due to the arrangement proposed here. This can save costs.
Vorteilhafterweise betragt der Abstand zwischen 10 und lOOμm. Als besonders vorteilhaft hat sich ein Abstand von etwa 50μm erwiesen. Die Photokathode kann zweckmaßigerweise opak ausge- bildet sein. UV-Photonen aus dem Lawinen-Bereich können nicht auf direktem Wege auf die Photokathode gelangen.The distance is advantageously between 10 and 100 μm. A distance of approximately 50 μm has proven to be particularly advantageous. The photocathode can expediently be opaque. Avalanche UV photons cannot reach the photocathode directly.
Nach einem weiteren Ausgestaltungsmerkmal ist die Photokathode aus einem metallischen Material hergestellt, das vor- zugsweise Gold, Cäsium, Kupfer oder Antimon enthalt. Zweck- maßig ist es weiter, daß die Photokathode als Schicht auf den Elektronenvervielfacher ausgebildet ist, wobei der Elektronenvervielfacher wiederum als Schicht auf dem Elektronendetektor ausgebildet sein kann. Nach einer besonders vorteil- haften Ausfuhrung weist der Elektronenvervielfacher eine gelochte, vorzugsweise aus Polyimid hergestellte, Kunststoffolie auf. Der Durchmesser der Locher betragt etwa 25 μm. Vorteilhaft ist es, wenn dem Strahlenabsorber, dem Elektrodensystem, dem Elektronenvervielfacher und dem Elektronendetektor ein gemeinsames, gasdichtes Gehäuse zugeordnet ist, wodurch sich ein kompakter Aufbau des Strahlungswandlers ergibt. Vorzugsweise ist im Gehäuse ein UV-Photonen absorbierendes Gas aufgenommen. Das Gas kann mindestens einen der folgenden Bestandteile aufweisen: Argon, Krypton, Xenon, Helium, Neon, C02, N2, Kohlenwasserstoff, Di-Methyl-Ather, Me- thanol-/Ethanol-Dampf .According to a further design feature, the photocathode is made from a metallic material that preferably contains gold, cesium, copper or antimony. It is also expedient that the photocathode is designed as a layer on the electron multiplier, wherein the electron multiplier can in turn be formed as a layer on the electron detector. According to a particularly advantageous embodiment, the electron multiplier has a perforated plastic film, preferably made of polyimide. The diameter of the holes is about 25 μm. It is advantageous if the radiation absorber, the electrode system, the electron multiplier and the electron detector are assigned a common, gas-tight housing, which results in a compact construction of the radiation converter. A gas which absorbs UV photons is preferably accommodated in the housing. The gas can have at least one of the following components: argon, krypton, xenon, helium, neon, C0 2 , N 2 , hydrocarbon, dimethyl ether, methanol / ethanol vapor.
Der Strahlenabsorber wandelt Strahlung n Lichtphotonen insbesondere dann vorteilhaft, wenn er eine nadelformige Struktur aufweist und aus CsI:Na besteht.The radiation absorber advantageously converts radiation into light photons if it has a needle-like structure and consists of CsI: Na.
Besonders vorteilhaft ist der Elektronendetektor als 2D-Dunn- schichtpanel ausgeführt und besteht aus a-Se, a-Sι:H oder Poly-Si. Ein solcher Elektronendetektor ist einfach im Aufbau und kostengünstig.The electron detector is particularly advantageously designed as a 2D thin-layer panel and consists of a-Se, a-Sι: H or poly-Si. Such an electron detector is simple in construction and inexpensive.
Weitere Vorteile und Einzelheiten der Erfindung ergeben sich aus der nachfolgenden Beschreibung eines Ausfuhrungsbeispie- les anhand der Zeichnungen. Hierin zeigen:Further advantages and details of the invention result from the following description of an exemplary embodiment with reference to the drawings. Show here:
Fig. 1 eine schematische Querschnittsansicht eines Strahlungswandlers undFig. 1 is a schematic cross-sectional view of a radiation converter and
Fig. 2 die Modulationstransferfunktion als Funktion der Ortsfrequenz . Bei dem m der Fig. 1 gezeigten Strahlungswandler ist mit dem Bezugszeichen 1 eine Gehäuse bezeichnet. Das Gehäuse weist einen Strahlenabsorber 2 auf, der Strahlung in Lichtphotonen wandelt. Der Strahlenabsorber 2 ist entweder als separates Teil ausgeführt oder außerhalb des Gehäuses 1 im Bereich ei- ner ersten Stirnseite angeordnet. Er besteht aus einem Szm- tillatormateπal, vorzugsweise aus CsI.Na in Nadelstruktur, wobei die Nadeln in Richtung einer Photokathode 3 gerichtet sind. Die Photokathode 3 ist in einem Abstand a von etwa 50μm von Strahlenabsorber 2 entfernt angeordnet. Sie ist als Schicht, die vorzugsweise aus Kupfer hergestellt ist, auf einer gelochten Polyimid-Folie 4 ausgeführt. Die Polyimid-Folie 4 wirkt als Elektronenvervielfacher . Sie ist aufgebracht auf einen Elektronendetektor 5. Der Elektronendetektor 5 weist vorzugsweise eine Pixelstruktur auf und wandelt die auftreffenden Elektronen in elektrische Signale, die über geeignete bekannte Maßnahmen, beispielsweise eine elektrische Leitung, ableitbar sind und aufgrund deren eine bildliche Darstellung an einer Anzeigevorrichtung möglich ist. Der Elektronendetektor 5 ist hierzu vorzugsweise als 2D-Dunnschιchtpanel ausgeführt und kann vorzugsweise aus a-Se, a-Sι:H oder Poly-Si bestehen. Innerhalb des Gehäuses 1, insbesondere zwischen dem Strahlenabsorber 2 und der Photokathode 3, ist ein Gas, insbesondere Quenchgas, beispielsweise eine Mischung aus Argon und Kohlenwasserstoff, aufgenommen.Fig. 2 shows the modulation transfer function as a function of the spatial frequency. In the radiation converter shown in FIG. 1, the reference numeral 1 denotes a housing. The housing has a radiation absorber 2, which converts radiation into light photons. The radiation absorber 2 is either designed as a separate part or is arranged outside the housing 1 in the region of a first end face. It consists of a scintillator material, preferably of CsI.Na in a needle structure, the needles being directed towards a photocathode 3 are. The photocathode 3 is arranged at a distance a of approximately 50 μm from the radiation absorber 2. It is designed as a layer, which is preferably made of copper, on a perforated polyimide film 4. The polyimide film 4 acts as an electron multiplier. It is applied to an electron detector 5. The electron detector 5 preferably has a pixel structure and converts the impinging electrons into electrical signals, which can be derived using suitable known measures, for example an electrical line, and on the basis of which it is possible to display them on a display device. For this purpose, the electron detector 5 is preferably designed as a 2D thin-film panel and can preferably consist of a-Se, a-Sι: H or poly-Si. A gas, in particular quench gas, for example a mixture of argon and hydrocarbon, is accommodated within the housing 1, in particular between the radiation absorber 2 and the photocathode 3.
Die Funktion der Vorrichtung ist folgende:The function of the device is as follows:
Rontgenstrahlen werden vom Strahlenabsorber 2 absorbiert und dabei in Photonen umgewandelt. Die Photonen setzen Photoelektronen aus der Photokathode 3 frei. Die Photoelektronen gelangen in den Bereich der gelochten Polyimid-Folie 4. Zwi- sehen der Photokathode 3 und dem Elektronendetektor 5 ist ein Potential angelegt. Durch das angelegte elektrische Potential wird erreicht, daß alle Photoelektronen von der Oberflache der Photokathode 3 m die nachstliegenden Locher gezogen werden. In dem stark anwachsenden elektrischen Feld findet durch Stoßionisation e ne Ladungstragervervielfachung statt. Die Ladungstragervervielfachung bzw. Verstärkung ist durch die Hohe des angelegten Potentials einstellbar. Damit kann das Signal/Rauschverhaltnis verbessert werden. Die Photoelektronen werden durch das angelegte Potential auf den Elektronen- detektor beschleunigt. Die dort akkumulierten Ladungen werden mit einer vorgegebenen Taktsequenz ausgelesen. Zur Reduzierung von UV-Photonen kann der Strahlenabsorber 2 mit einer UV-photonenabsorbierenden Leitschicht versehen sein. Durch das Quenchgas werden die bei der durch Stoßionisation erzeugten UV-Photonen absorbiert, damit diese nicht zur Photokathode 3 gelangen, wo sie Photoelektronen ungewollt auslosen konnten.X-rays are absorbed by the radiation absorber 2 and thereby converted into photons. The photons release photoelectrons from the photocathode 3. The photoelectrons reach the area of the perforated polyimide film 4. A potential is applied between the photocathode 3 and the electron detector 5. The applied electrical potential ensures that all photoelectrons are pulled from the surface of the photocathode by 3 m from the holes located next. In the rapidly growing electric field, a charge carrier multiplication takes place through impact ionization. The charge carrier multiplication or amplification can be set by the level of the applied potential. The signal / noise ratio can thus be improved. The photoelectrons are accelerated by the potential applied to the electron detector. The charges accumulated there are read out with a predefined clock sequence. To reduce UV photons, the radiation absorber 2 can be provided with a UV photon-absorbing conductive layer. The quench gas absorbs the UV photons generated by impact ionization so that they do not reach the photocathode 3, where they could inadvertently trigger photoelectrons.
In Fig. 2 ist über der Ortsfrequenz die Modulationstransferfunktion aufgetragen. Die Kurven MTF 1 und MTF 2 zeigen die Modulationstransferfunktion bei einem Abstand der Photokathode 3 vom Strahlenabsorber 2 von 50μm. Die Kurve MTF 2 zeigt die Punktbildfunktion einer isotropen Punktquelle, die Kurve MTF 1 die vorgenannte Punktbildfunktion für eine Lambertquelle .In Fig. 2, the modulation transfer function is plotted against the spatial frequency. The curves MTF 1 and MTF 2 show the modulation transfer function at a distance of the photocathode 3 from the radiation absorber 2 of 50 μm. The curve MTF 2 shows the point spread function of an isotropic point source, the curve MTF 1 the aforementioned point spread function for a Lambert source.
Die Kurve MTF 3 zeigt die Modulationstransferfunktion, wobei hier der Strahlenabsorber 2 in direktem Kontakt mit dem Elektronendetektor 5 ist. Die Kurve MTF 3 repräsentiert damit die Charakteristik von herkömmlichen Flachdetektoren. Die Werte MTF 4 geben die Modulationstransferfunktion für eine Lambertquelle an, wobei der Strahlenabsorber 2 in einem Abstand von 50μm von dem Elektronendetektor 5 angeordnet ist. Es zeigt sich, daß die beabstandete Anordnung keine wesentliche Änderung der Modulationstransferfunktion mit sich bringt. The curve MTF 3 shows the modulation transfer function, here the radiation absorber 2 is in direct contact with the electron detector 5. The curve MTF 3 thus represents the characteristic of conventional flat detectors. The values MTF 4 indicate the modulation transfer function for a Lambert source, the radiation absorber 2 being arranged at a distance of 50 μm from the electron detector 5. It can be seen that the spaced arrangement does not bring about any significant change in the modulation transfer function.

Claims

Patentansprüche claims
1. Strahlungswandler mit einem Strahlenabsorber (2) zum Erzeugen von Photonen in Abhängigkeit von der Intensität auf- treffender Röntgenstrahlung, mit einer dem Strahlenabsorber (2) in Strahlungsrichtung mit einem Abstand (a) nachgeordneten Photokathode (3) zum Erzeugen von Elektronen m Abhängigkeit von den vom Strahlenabsorber (2) ausgehenden Photonen, mit einer Einrichtung zum Beschleunigen der von der Photokathode (3) ausgehenden Elektronen auf einen Elektronendetektor (5) zum Erzeugen elektrischer Signale in Abhängigkeit von den auftreffenden Elektronen und mit einem zwischen der Photokathode (3) und dem Elektronende- tektor (5) angeordneten Elektronenvervielfacher (4), wobei die von der Photokathode (3) ausgehenden Elektronen durch den Elektronenvervielfacher (4) vervielfachbar sind.1. Radiation converter with a radiation absorber (2) for generating photons as a function of the intensity of X-ray radiation incident, with a photocathode (3) downstream of the radiation absorber (2) in the radiation direction with a distance (a) for generating electrons as a function of the photons emanating from the radiation absorber (2), with a device for accelerating the electrons emanating from the photocathode (3) onto an electron detector (5) for generating electrical signals as a function of the incident electrons, and with one between the photocathode (3) and the Electron multiplier (4) arranged electron detector (5), wherein the electrons emanating from the photocathode (3) can be multiplied by the electron multiplier (4).
2. Strahlungswandler nach Anspruch 1, wobei der Abstand (a) zwischen 10 und 100 μm ist.2. Radiation converter according to claim 1, wherein the distance (a) is between 10 and 100 microns.
3. Strahlungswandler nach einem der vorhergehenden Ansprüche, wobei die Photokathode (3) opak ist.3. Radiation converter according to one of the preceding claims, wherein the photocathode (3) is opaque.
4. Strahlungswandler nach einem der vorhergehenden Ansprüche, wobei die Photokathode (3) aus einem metallischen Material hergestellt ist, das vorzugsweise Gold, Cäsium, Kupfer oder Antimon enthalt.4. Radiation converter according to one of the preceding claims, wherein the photocathode (3) is made of a metallic material which preferably contains gold, cesium, copper or antimony.
5. Strahlungswandler nach einem der vorhergehenden Ansprüche, wobei die Photokathode (3) als Schicht auf dem Elektronenvervielfacher (4) ausgebildet ist.5. Radiation converter according to one of the preceding claims, wherein the photocathode (3) is designed as a layer on the electron multiplier (4).
6. Strahlungswandler nach einem der vorhergehenden An- Spruche, wobei der Elektronenvervielfacher (4) als Schicht auf dem Elektronendetektor (5) ausgebildet ist. 6. Radiation converter according to one of the preceding claims, wherein the electron multiplier (4) is designed as a layer on the electron detector (5).
7. Strahlungswandler nach einem der vorhergehenden Ansprüche, wobei der Elektronenvervielfacher (4) eine gelochte, vorzugsweise aus Polyimid hergestellte, Kunststoffolie aufweist .7. Radiation converter according to one of the preceding claims, wherein the electron multiplier (4) has a perforated, preferably made of polyimide, plastic film.
8. Strahlungswandler nach einem der vorhergehenden Ansprüche, wobei der Strahlenabsorber (2), der Elektronenver- vielfacher (4) und der Elektronendetektor (5) in einem gemeinsamen gasdichten Gehäuse (1) aufgenommen sind.8. Radiation converter according to one of the preceding claims, wherein the radiation absorber (2), the electron multiplier (4) and the electron detector (5) are accommodated in a common gas-tight housing (1).
9. Strahlungswandler nach einem der vorhergehenden Ansprüche, wobei im Gehäuse (1) ein UV-Photonen absorbierendes Gas aufgenommen ist.9. Radiation converter according to one of the preceding claims, wherein a UV photon absorbing gas is accommodated in the housing (1).
10. Strahlungswandler nach einem der vorhergehenden Ansprüche, wobei das Gas mindestens einen der folgenden Bestandteile aufweist: Argon, Krypton, Xenon, Helium, Neon, C02, N2, Kohlenwasserstoff, Di-Methyl-Ather, Methanol- /Ethanol-Dampf .10. Radiation converter according to one of the preceding claims, wherein the gas has at least one of the following constituents: argon, krypton, xenon, helium, neon, C0 2 , N 2 , hydrocarbon, dimethyl ether, methanol / ethanol vapor.
11. Strahlungswandler nach einem der vorhergehenden Ansprüche, wobei der Strahlenabsorber (2) aus einem Szintilla- tormaterial hergestellt ist, das vorzugsweise eine nadelfor- mige Struktur aus CsI:Na aufweist.11. Radiation converter according to one of the preceding claims, wherein the radiation absorber (2) is made of a scintillator material which preferably has a needle-shaped structure made of CsI: Na.
12. Strahlungswandler nach einem der vorhergehenden Ansprüche, wobei der Elektronendetektor (5) als 2D-Dunnschicht- panel ausgeführt ist.12. Radiation converter according to one of the preceding claims, wherein the electron detector (5) is designed as a 2D thin-film panel.
13. Strahlungswandler nach einem der vorhergehenden Ansprüche, wobei das 2D-Dunnschichtpanel aus a-Se, a-Si:H oder Poly-Si gebildet ist. 13. Radiation converter according to one of the preceding claims, wherein the 2D thin-film panel is formed from a-Se, a-Si: H or poly-Si.
EP01935937A 2000-03-23 2001-03-22 Radiation converter comprising a scintillator, a photocathode and an electron multiplier Expired - Lifetime EP1266391B1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
DE10014311A DE10014311C2 (en) 2000-03-23 2000-03-23 radiation converter
DE10014311 2000-03-23
PCT/DE2001/001109 WO2001071381A2 (en) 2000-03-23 2001-03-22 Radiation converter with a scintillator a photocathode and an electron multiplier

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EP1266391A2 true EP1266391A2 (en) 2002-12-18
EP1266391B1 EP1266391B1 (en) 2008-07-16

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EP (1) EP1266391B1 (en)
JP (1) JP2003528427A (en)
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WO (1) WO2001071381A2 (en)

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US7022994B2 (en) 2006-04-04
DE10014311A1 (en) 2001-10-04
DE50114124D1 (en) 2008-08-28
US20030164682A1 (en) 2003-09-04
EP1266391B1 (en) 2008-07-16
DE10014311C2 (en) 2003-08-14
WO2001071381A3 (en) 2002-04-18
JP2003528427A (en) 2003-09-24
WO2001071381A2 (en) 2001-09-27

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