WO2005119701A2 - Systeme pour la formation de rayons x et processus d'utilisation - Google Patents

Systeme pour la formation de rayons x et processus d'utilisation Download PDF

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Publication number
WO2005119701A2
WO2005119701A2 PCT/US2005/012807 US2005012807W WO2005119701A2 WO 2005119701 A2 WO2005119701 A2 WO 2005119701A2 US 2005012807 W US2005012807 W US 2005012807W WO 2005119701 A2 WO2005119701 A2 WO 2005119701A2
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WO
WIPO (PCT)
Prior art keywords
electron
target
subsystem
electron emission
spots
Prior art date
Application number
PCT/US2005/012807
Other languages
English (en)
Other versions
WO2005119701A3 (fr
Inventor
William Hullinger Huber
Colin Richard Wilson
John Scott Price
Peter Michael Edic
Mark Ernest Vermilyea
Forrest Frank Hopkins
Original Assignee
General Electric Company
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
Priority claimed from US11/048,159 external-priority patent/US7203269B2/en
Application filed by General Electric Company filed Critical General Electric Company
Priority to JP2007515079A priority Critical patent/JP2008501222A/ja
Priority to EP05762434A priority patent/EP1754242A2/fr
Publication of WO2005119701A2 publication Critical patent/WO2005119701A2/fr
Publication of WO2005119701A3 publication Critical patent/WO2005119701A3/fr

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J35/00—X-ray tubes
    • H01J35/02—Details
    • H01J35/14—Arrangements for concentrating, focusing, or directing the cathode ray
    • H01J35/153—Spot position control

Definitions

  • the invention relates generally to a system for forming x-rays, and more particularly to a system configured to direct electron beams at a plurality of discrete spots on a target to form x-rays.
  • X-ray scanning has been used in medical diagnostics, industrial imaging, and security related applications.
  • Commercially available x-ray sources typically utilize conventional thermionic emitters, which are helical coils made of tungsten wire and operated at high temperatures. Each thermionic emitter is configured to emit a beam of electrons to a single focal spot on a target.
  • thermionic emitters which are helical coils made of tungsten wire and operated at high temperatures.
  • Each thermionic emitter is configured to emit a beam of electrons to a single focal spot on a target.
  • helical coils formed of a metallic wire having a work function of 4.5 eV must be heated to about 2600 K. Due to its robust nature, tungsten wire has been the electron emitter of choice.
  • Such filament emitters lack a uniform emission profile necessary for proper beam steering and focusing. Further, a higher electron beam current will cause a reduction in the lifetime of such filament emitters. Additionally, such filament emitters require high quiescent power consumption, which leads to the need for larger, more complex cooling architectures, a larger system envelope, and greater cost.
  • An exemplary embodiment of the invention provides a system for forming x-rays that includes a target and at least one electron emission subsystem for generating a plurality of spots on the target.
  • the at least one electron emission subsystem includes a plurality of electron sources and each of the plurality of electron sources generates at least one of the plurality of spots on the target.
  • the system also includes a beam focusing subsystem for focusing electron beam emissions from the plurality of electron sources prior to the electron beam emissions striking the target.
  • Another exemplary embodiment of the invention provides a system for forming x- rays that includes a target, an electron emission subsystem for generating a plurality of spots on the target, and a transient beam protection subsystem for protecting the electron emission subsystem from transient beam currents, material emissions from the target, and electric field transients.
  • the electron emission subsystem includes a plurality of electron sources.
  • Another exemplary embodiment of the invention provides a system for forming x- rays that includes a target and an electron emission subsystem including a plurality of electron sources.
  • the electron emission subsystem is configured to generate a plurality of discrete spots on the target from which x-rays are emitted.
  • the target is enclosed within a first vacuum chamber and the electron emission subsystem is enclosed within a second vacuum chamber.
  • Another exemplary embodiment of the invention provides a method for x-ray scanning an object that includes emitting a beam of electrons from an electron source to strike a discrete or swept focal spot on a target for creating x-rays from the discrete or swept focal spot.
  • the method further includes focusing the beam of electrons from the electron source prior to the electron beam emissions striking the target and detecting the x-rays created from the discrete or swept focal spots.
  • FIG. 1 is a schematic view of an x-ray system constructed in accordance with an exemplary embodiment of the invention.
  • FIG. 2 is a schematic view of an exemplary embodiment of an x-ray generation subsystem for use in the x-ray system of FIG. 1.
  • FIG. 3 is a schematic view of an exemplary embodiment of an electron source array for use in the x-ray system of FIG. 1.
  • FIG. 4 is a side view of an electron source for use in the x-ray system of FIG. 1.
  • FIG. 5 is a schematic view of multiple steerable electron emission subsystems within the x-ray system of FIG. 1.
  • FIG. 6 is a schematic representation of the source and target vacuums of FIG. 5.
  • FIG. 7 is an expanded view of the beam dump mechanism within circle VII of FIG. 2.
  • FIG. 8a is a perspective view of an alternative source for use in the x-ray system of FIG. 1.
  • FIG. 8b is a cross-sectional view of the electron source of FIG. 8a taken along line Villa - Villa.
  • FIG. 9 is a perspective view of a target constructed in accordance with another exemplary embodiment of the invention.
  • FIG. 10 is a side view of a portion of the target of FIG. 9.
  • FIG. 1 1 illustrates process steps for obtaining x-rays of a subject in accordance with another exemplary embodiment of the invention.
  • the x-ray system 10 includes an x-ray generation subsystem 15 including a target 46 (FIG. 2), a detector 60, and an electronic computing subsystem 80.
  • a portion of the x-ray generation subsystem 15, which may include a steerable electron emission subsystem 20, may be encompassed in a first vacuum vessel 25, while the target 46 may be encompassed within a second vacuum vessel or target chamber 47 (FIG. 6).
  • the x- ray system 10 may be configured to accommodate a high throughput of articles, for example, screening of upwards of one thousand individual pieces of luggage within a one hour time period, with a high detection rate and a tolerable number of false positives.
  • the x-ray system 10 may be configured to accommodate the scanning of organic subjects, such as humans, for medical diagnostic purposes. Alternatively, the x-ray system 10 may be configured to perform industrial nondestructive testing.
  • the electron emission subsystem 20 and the target 46 may be stationary relative to the detector 60, which may be stationary or rotating, or the electron emission subsystem 20 and the target 46 may rotate relative to the detector 60, which may be stationary or rotating.
  • the electron emission subsystem 20 includes an electron source 26. Each electron beam generated within the electron emission subsystem 20 is steerable.
  • the electron source 26 is positioned within the electron emission subsystem 20 such that the electron emission subsystem 20 serves as a transient beam protection subsystem protecting the electron source 26 from transient voltages and/or currents.
  • the electron emission subsystem 20 protects the electron source 26 from sputter damage gasses in the target chamber 47 (FIG. 6).
  • a channel 33 extends between the target 46 and the electron source 26 to alleviate the deleterious effects of transient beam currents and material emissions striking at or near the electron source 26.
  • the transient beam protection subsystem functions more efficiently if the differential between the voltage potential of the target 46 is significantly higher than the voltage potential of the electron source 26 and its surrounding environs.
  • Such a transient beam protection subsystem serves to sink current from one or more electron sources if the potential of the anode or target 46 drops and to provide protection for one or more electron sources during transient beam emissions.
  • an x-ray generation subsystem 1 15 may be used, which includes an electron emission subsystem 120 having an emitter array 122.
  • the emitter array 122 includes a plurality of electron sources 26, each positioned within an alcove 29 and each being configured to emit a beam 44 of electrons to a discrete focal spot 48 on the target 46.
  • the transient beam protection subsystem for the FIG. 3 embodiment may include the combination of the channel 33, and the alcoves 29.
  • the transient beam protection subsystem may also include guard electrodes (not shown) as a further protection mechanism. Furthermore, such a transient beam protection subsystem serves to (a) sink current from one or more electron sources if the potential of the target 46 drops and (b) provide protection for one or more electron sources during transient beam emissions.
  • electron sources may be utilized.
  • suitable electron emitters include tungsten filament, tungsten plate, field emitter, thermal field emitter, dispenser cathode, thermionic cathode, photo-emitter, and ferroelectric cathode, provided the electron emitters are configured to emit an electron beam at multiple discrete focal spots on a target.
  • the x-ray generation subsystem 15 includes a beam focusing subsystem 40, a beam deflection subsystem 42, and a pinching electrode for selectively inhibiting or permitting electron beams from the electron source 26 to be emitted toward the target 46.
  • a pinch-off plate or beam grid which is configured to pinch off electron beams 44 when activated.
  • Another such mechanism is a conducting gate 32 (FIG. 4), which is configured to facilitate electron beam 44 generation when activated.
  • Yet another mechanism is a beam dump 105 (FIGS. 2, 7). The beam dump 105, when activated, diverts the electron beams 44 away from an undeflected path 27 toward the target 46 (FIGS. 2, 6, 7) to a deflected path 27c into the container.
  • the beam focusing subsystem 40 serves to form and focus a beam 44 of electrons into a pathway 27 (FIG. 5) toward the target 46.
  • the beam focusing subsystem 40 may include an electrostatic focusing component, such as, for example, a plurality of focusing plates each biased at a different potential, or a magnetic focusing component, such as, for example, a suitable combination of focusing solenoids, deflecting dipoles and beam-shaping quadrupole electromagnets. Electromagnets that produce higher order moments (6-pole, 8-pole, etc.) can be used to improve beam quality or to counter effects of edge-focusing that may occur due to a particular choice or design of elements in subsystem 40.
  • the beam deflection subsystem 42 serves to steer or deflect the electrons from the pathway 27 onto deflected pathways 27a, 27b (FIG. 5) toward numerous discrete focal spots 48 on the target 46 (FIG. 10).
  • the ability to steer electron beams to more than one focal spot 48 on the target 46 is significant in that it facilitates the use of a reduced number of electron emitters relative to the required number of x-ray focal spots.
  • the electron source 26 may be a low current-density electron source.
  • Optics, such as the beam focusing subsystem 40 is used to form high current-density beams 44 at the target 46 from a low current-density electron source. Each discrete electron beam 44 strikes the focal spots 48 on the target 46, creating x-ray beams 50 (FIG.
  • a beam deflection subsystem 42 may be unnecessary for an arrangement of electron sources such as the x-ray generation subsystem 1 15 having an emitter array 122 illustrated in FIG. 3, although a beam focusing subsystem 40 may still be employed. Since a plurality of electron sources 26 would be located adjacent to one another, steering the electron beams 44 from each electron source 26 likely would not be needed to produce electron beam strikes at a plurality of focal spots 48 on the target 46.
  • the beam deflection subsystem 42 may be electrostatically-based, magnetically- based, or a combination of the two.
  • the beam deflection subsystem 42 may include an electrostatic steering mechanism that has one or more free standing electrically conducting plates that may be positioned within the channel 33. As beam currents 44 of electrons are emitted from the electron source 26, the plates can be charged to a fairly high negative potential with respect to ground.
  • the plates may be formed of an electrically conductive material, or be formed of an insulating material and coated with an electrically conductive coating.
  • the beam deflection subsystem 42 may include a magnetic steering mechanism with a magnetic core for correcting magnetic fields that have other higher-moment fields, such as, for example, hexapoles, so that the focal spot 48 (FIGS. 3, 10) shape is maintained over a wide set of deflection angles.
  • the magnetic steering mechanism may have no magnetic core.
  • suitable magnetic steering mechanisms include one or more coils, a coil-shaped electromagnet, and a fast switching magnetic-field- producing magnet, each of which being capable of producing magnetic fields with substantial quadrupole moments as well as dipole moments.
  • each electron emission subsystem 20 may be encompassed in a first vacuum vessel 25, while the target 46 may be encompassed within a second vacuum vessel 47 (FIGS. 5, 6).
  • Each of the first vacuum vessels 25 is separated from the second vacuum vessel 47 via a channel 33.
  • the differential pressures of each of the vacuum vessels 25, 47 are maintainable through the use of differential pumping through a narrow diameter pipe.
  • two gate valves 70, 72 connect each first vacuum vessel 25 with the second vacuum vessel 47 through the channels 33. Through this arrangement, if replacement of any single electron source 26 is required, the gate valve 70 may be kept in a closed state while the gate valve 72 is opened to allow removal of the electron source 26 from the vacuum vessel 25. Alternatively, a single gate valve may be used to separate the two vacuum vessels 25, 47.
  • the electron source 26 illustrated in FIG. 4 includes a base or substrate 28 and carbon nanotubes 36.
  • the carbon nanotubes 36 are positioned on a catalyst pad 34, which is itself located on a surface of the substrate 28.
  • the substrate 28 may be formed of silicon or another like material.
  • a dielectric spacer 30 is positioned over the substrate 28.
  • a well 35 is etched in the dielectric spacer 30, and the catalyst pad 34 is positioned therein.
  • a conducting gate 32 positioned over the spacer 30, serves to generate high electric fields in the vicinity of the tips of the carbon nanotubes 36, which promotes electron emissions within electron source 26.
  • the carbon nanotubes 36 may be grown selectively on the catalyst pad 34 through the use of chemical vapor deposition. The inherently high aspect ratio makes them particularly well suited for field emission.
  • a dispenser cathode 126 may be utilized as an electron source.
  • the dispenser cathode 126 may include a container 128 with a porous tungsten plug 129.
  • a coil 130 preferably formed of tungsten, is positioned within the container 128 and surrounded by an oxide-based solution, such as, for example, barium oxide, calcium oxide, or tin oxide.
  • a gridding mechanism 140 (FIG. 8b) may be placed between the dispenser cathode 126 and the target 46 (FIGS. 2, 5, 6) to permit or inhibit electron emissions from the dispenser cathode 126 from striking the target 46.
  • the oxide materials coat the tungsten plug 129, thereby lowering the work function for the dispenser cathode 126.
  • One advantage of using a dispenser cathode 126 is that the lowered work function requires that the tungsten coil 130 only needs to be heated up to 1300 °C, instead of the 2500 °C required for uncoated tungsten thermionic emitters.
  • a further advantage is the low cost of off-the-shelf dispenser cathodes 126. When the oxide materials have evaporated away, the dispenser cathode 126 can be discarded and replaced with another.
  • a plurality of electron emission subsystems 20 is arrayed around a target 46.
  • Each of the electron emission subsystems 20 is within a first vacuum vessel 25, while the target 46 is within a second vacuum vessel 47.
  • Each of the vacuum vessels 25, 47 are pumped so as to obtain a differential pressure between each of the first vacuum vessels 25 and the second vacuum vessel 47.
  • Each of the first vacuum vessels 25 is connectable with the second vacuum vessel 47 through a channel 33.
  • the differential pressure between the first vacuum vessels 25 and the second vacuum vessel 47 is maintained through the use of differential pumping. While six discrete electron emission subsystems 20 are illustrated each within a separate first vacuum vessel 25, it should be appreciated that any number of electron emission subsystems 20 may be utilized.
  • the beam deflection subsystem 42 steers the electron beams 44 (FIGS. 2, 3) from the pathway 27 to a deflected pathway 27a, 27b to strike the target 46 at an alternative discrete focal spot 48 (FIG. 3).
  • FIGS. 9, 10 next will be described an exemplary embodiment of the target 46.
  • the target 46 as illustrated in FIGS. 9 and 10 includes target planes 49, 49a, and 49b.
  • Target planes 49a and 49b are at an angle to target plane 49.
  • An undeflected electron beam 44 is intended to follow pathway 27 to strike the target 46 at a focal spot 48 along target plane 49.
  • a deflected electron beam 44 is intended to follow the deflected pathway 27a or 27b to strike the target 46 at a focal spot 48 along target plane 49a or 49b.
  • the target planes 49, 49a, 49b may be curved surfaces or they may be fiat surfaces at an angle relative to one another.
  • the angle of incidence of target planes 49a and 49b is chosen such that the deflected electron beams 44 strike the focal spots 48 along the target planes 49a, 49b at the same angle as the undeflected electron beam 44 strikes the focal spot 48 along the target plane 49.
  • the beam deflection subsystem 42 (FIGS.
  • the detector 60 may include a detector ring positioned adjacent to the x-ray generation subsystem 15.
  • the detector ring may be offset from the x-ray generation subsystem 15. It should be appreciated, however, that "adjacent to" should be interpreted in this context to mean the detector ring is offset from, contiguous with, concentric with, coupled with, abutting, or otherwise in approximation with the x-ray generation subsystem 15.
  • the detector ring may include a plurality of discrete detector modules that may be in linear, multi-slice, or area detector arrangements.
  • detector module includes a detector cell having a pitch of, for example, two millimeters by two millimeters, providing an isotropic resolution on the order of one millimeter in each spatial dimension.
  • detector module includes a detector cell having a pitch of one millimeter by one millimeter.
  • the electronic computing subsystem 80 is linked to the detector 60. The electronic computing subsystem 80 functions to reconstruct the data received from the detector 60, segment the data, and perform automated detection and/or classification.
  • One embodiment of the electronic computing subsystem 80 is described in U.S. patent application serial number 10/743,195, filed December 22, 2003, which is incorporated in its entirety by reference herein.
  • the range of electron beams 44 (FIG. 2) from each electron source 26 is expanded with a minimal loss of resolution.
  • the expanded range of electron beams 44 may translate into some redundancy, wherein some of the electron beams 44 from one electron source 26 may overlap others of the electron beams 44 from adjacent electron sources 26. Further, the expanded range of electron beams 44 may translate into a longer working life of the x-ray system 10 between maintenance since the increased redundancy may allow the x-ray system 10 to be used with a larger number of inoperable electron emission subsystems 20.
  • the arrangement of the transient beam protection subsystem inhibits transient vacuum arcs, vacuum discharges, or spits from the target 46 striking at or near the electron sources 26.
  • the channel 33 provides a narrow pathway through which a spit will unlikely be able to traverse all the way back to the electron sources 26.
  • the alcoves 29 can minimize any sputter damage to the electron sources 26.
  • the transient beam protection subsystem can sink current from the electron source 26 if the electric field within the x-ray generation subsystem 15 collapses due to discharges.
  • the architecture of the x-ray system 10 reduces the concern about the power dissipation of the electron sources 26, since the amount of power that is used is considerably less than in a comparable x-ray system utilizing thermionic electron emitters.
  • the focal spot positions are positioned adjacent to one another, providing little space in which to place focusing mechanisms.
  • a dedicated emitter design (FIG. 3) of x-ray generation subsystem 15
  • an electron source is required for each x-ray spot 48.
  • the emitters are positioned so close to each other that incorporating beam optics to deflect the beam would be difficult to achieve.
  • one- thousand electron emitters would be necessary.
  • the overall power requirement is difficult to accommodate.
  • the use of the beam focusing subsystem 40 allows for lower-density electron sources to be used, and the use of a beam deflection subsystem 42 permits multiple x-ray spots from a single electron source, and the use of alternative electron emitters (dispenser cathodes, field emission devices, for example) reduces quiescent power consumption, all of which reduce the overall power consumption.
  • a method for x-ray scanning an object At Step 200, a plurality of electron emission subsystems is provided adjacent to a target.
  • a transient beam protection subsystem is positioned in the vicinity of each electron emission subsystem arranged about the target.
  • each electron emission subsystem 20, 120 may be segregated from the target 46 through the use of the transient beam protection subsystem, including one or more of channel 33, the alcove 29, or guard electrodes (not shown).
  • the transient beam protection subsystem is designed to provide protection to the electron sources 26 against transient beam currents/voltages, material emissions from the target 46, and collapse of the electric field.
  • a first electron beam current is emitted from an electron emission subsystem to a first focal spot 48 on the target 46.
  • a second electron beam current is emitted from an electron emission subsystem to a second focal spot 48 on the target.
  • a single electron source 26 transmits both of the electron beam currents and one of the electron beam currents is subjected to deflection.
  • electron emission subsystems 120 which each incorporate an array of electron sources 26, no deflection of the electron beam currents is necessary, since each electron source is offset from the others. It should be appreciated that there may be numerous times that a current is emitted to a focal spot 48 on the target 46, and that there may be a loop executed N number of times, depending on the number of focal spots 48 desired.
  • a detector such as the detector 60, is provided to measure the x- rays emitted from the focal spots on the target.

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  • X-Ray Techniques (AREA)
  • Radiation-Therapy Devices (AREA)

Abstract

Système et procédé pour former des rayons X. Un tel système à titre d'exemple inclut un sous-système de cible et d'émission d'électrons avec une pluralité de sources d'électrons. Chacune des pluralités de sources d'électron est configurée pour produire une pluralité de points discrets sur la cible à partir desquels les rayons X sont émis. Un autre système à titre d'exemple inclut une cible, un sous-système d'émission d'électrons avec une pluralité de sources d'électrons, chacune d'entre elles produisant au moins une des pluralités des points sur la cible, et un sous-système de protection du rayon transitoire pour la protection du sous-système d'émission d'électron contre les courants de rayons transitoires, les émissions matérielles provenant de la cible et les champs électriques transitoires.
PCT/US2005/012807 2004-05-28 2005-04-14 Systeme pour la formation de rayons x et processus d'utilisation WO2005119701A2 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
JP2007515079A JP2008501222A (ja) 2004-05-28 2005-04-14 Ｘ線を形成するためのシステム及びその使用法
EP05762434A EP1754242A2 (fr) 2004-05-28 2005-04-14 Systeme pour la formation de rayons x et processus d'utilisation

Applications Claiming Priority (6)

Application Number Priority Date Filing Date Title
US57614704P 2004-05-28 2004-05-28
US60/576,147 2004-05-28
US11/048,159 US7203269B2 (en) 2004-05-28 2005-02-01 System for forming x-rays and method for using same
US11/048,159 2005-02-01
US11/048,158 US7218700B2 (en) 2004-05-28 2005-02-01 System for forming x-rays and method for using same
US11/048,158 2005-02-01

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WO2005119701A2 true WO2005119701A2 (fr) 2005-12-15
WO2005119701A3 WO2005119701A3 (fr) 2006-03-09

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Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4288297B1 (ja) 2008-01-09 2009-07-01 三菱重工業株式会社 圧力制御装置および圧力制御方法
JP4885235B2 (ja) * 2008-08-12 2012-02-29 三菱重工業株式会社 接合装置および接合装置メンテナンス方法
WO2010131209A1 (fr) * 2009-05-12 2010-11-18 Koninklijke Philips Electronics N.V. Source de rayons x dotee d'une pluralite d'emetteurs d'electrons
GB2565138A (en) * 2017-08-04 2019-02-06 Adaptix Ltd X-ray generator

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4182955A (en) * 1977-10-26 1980-01-08 E M I Limited X-ray generating tubes
EP0024325A1 (fr) * 1979-08-16 1981-03-04 General Electric Company Système de tomographie à rayons-X avec balayage électronique
EP0657915A1 (fr) * 1993-12-06 1995-06-14 Picker International, Inc. Tubes à rayons X
DE19621066A1 (de) * 1996-05-24 1997-11-27 Siemens Ag Röntgenstrahler mit einem Führungs- und einem Kickmagnetsystem für Elektronen
US6259765B1 (en) * 1997-06-13 2001-07-10 Commissariat A L'energie Atomique X-ray tube comprising an electron source with microtips and magnetic guiding means

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4182955A (en) * 1977-10-26 1980-01-08 E M I Limited X-ray generating tubes
EP0024325A1 (fr) * 1979-08-16 1981-03-04 General Electric Company Système de tomographie à rayons-X avec balayage électronique
EP0657915A1 (fr) * 1993-12-06 1995-06-14 Picker International, Inc. Tubes à rayons X
DE19621066A1 (de) * 1996-05-24 1997-11-27 Siemens Ag Röntgenstrahler mit einem Führungs- und einem Kickmagnetsystem für Elektronen
US6259765B1 (en) * 1997-06-13 2001-07-10 Commissariat A L'energie Atomique X-ray tube comprising an electron source with microtips and magnetic guiding means

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EP1754242A2 (fr) 2007-02-21
JP2008501222A (ja) 2008-01-17

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