FIELD EMITTER BASED ELECTRON SOURCE FOR MULTIPLE SPOT X-RAY

• US 20090185660A1
• Filed: 01/21/2008
• Published: 07/23/2009
• Est. Priority Date: 01/21/2008
• Status: Active Grant

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Cao, Yang, Caiafa, Antonio, Vermilyea, Mark E., Zou, Yun, Inzinna, Louis Paul, Neculaes, Vasile Bogdan, Price, John Scott
• Granted Patent: US 7,809,114 B2
• Time in Patent Office: Days
• US Class Current: 378/122
• CPC Class Codes: H01J 1/3048 Distributed particle emitters
• CPC Class Codes: H01J 2235/062 Cold cathodes
• CPC Class Codes: H01J 2235/068 Multi-cathode assembly

Abstract

A multiple spot x-ray generator is provided that includes a plurality of electron generators. Each electron generator includes an emitter element to emit an electron beam, a meshed grid adjacent each emitter element to enhance an electric field at a surface of the emitter element, and a focusing element positioned to receive the electron beam from each of the emitter elements and focus the electron beam to form a focal spot on a shielded target anode, the shielded target anode structure producing an array of x-ray focal spots when impinged by electron beams generated by the plurality of electron generators. The plurality of electron generators are arranged to form an electron generator matrix that includes activation connections electrically connected to the plurality of electron generators, wherein each electron generator is connected to a pair of the activation connections to receive an electric potential therefrom.

Claims

1. A multiple spot x-ray generator comprising:

a plurality of electron generators arranged to form an electron generator matrix, the electron generator matrix including activation connections electrically connected to the plurality of electron generators and wherein each electron generator is connected to a pair of the activation connections to receive an electric potential therefrom;

a target anode configured to produce an array of x-ray focal spots providing tomographic imaging of an object when impinged by a plurality of electron beams generated by the plurality of electron generators;

an anode shield positioned about the target anode to capture backbombarding ions output from the target anode; and

wherein each electron generator further comprises;

an emitter element configured to emit an electron beam;

a meshed grid disposed adjacent each emitter element to enhance an electric field at a surface of the emitter element; and

a focusing element positioned to receive the electron beam from the emitter element and focus the electron beam to form a focal spot on the target anode.

2. The multiple spot x-ray generator of claim 1 wherein each electron generator further comprises:

a substrate layer having the emitter element arranged thereon; and

an insulating layer adjacent to the substrate layer, the insulating layer having a cavity therein to receive the emitter element and being configured to suppress flashover about the emitter element.

3. The multiple spot x-ray generator of claim 2 wherein the substrate layer further comprises a top surface having a silicon dioxide (SiO2) film thereon, the silicon dioxide film having a gap therein to allow for positioning of the emitter element on the top surface of the substrate.

4. The multiple spot x-ray generator of claim 2 wherein the insulating layer comprises a ceramic spacer having a stepped configuration.

5. The multiple spot x-ray generator of claim 2 wherein the emitter element comprises a carbon nano-tube (CNT) field emitter, the CNT field emitter including a plurality of CNT groups patterned to align with openings in the meshed grid.

6. The multiple spot x-ray generator of claim 5 wherein the substrate is curved to enhance convergence of the electron beam generated by the plurality of CNT groups.

7. The multiple spot x-ray generator of claim 1 wherein the target anode is positioned such that the electron beams strike the target with an angle of incidence between 10 to 90 degrees.

8. The multiple spot x-ray generator of claim 1 wherein the anode shield further comprises a tungsten coated inner surface.

9. The multiple spot x-ray generator of claim 1 wherein the target anode is operated at a biased voltage relative to the electron generators.

10. The multiple spot x-ray generator of claim 1 wherein the focusing element further comprises one of an angled focusing lens and an Einzel lens.

11. The multiple spot x-ray generator of claim 1 wherein the focusing element is comprised of a first piece having a first voltage, a second piece having a second voltage, a third piece having a third voltage and a fourth piece having a fourth voltage, and wherein the first piece, second piece, third piece and fourth piece form a dipole component configured to provide electron beam wobbling and wherein the first piece, second piece, third piece and fourth piece form a quadrupole component configured to provide beam shape correction during the electron beam wobbling.

12. The multiple spot x-ray generator of claim 1 wherein the emitter element comprises a dispenser cathode.

13. The multiple spot x-ray generator of claim 1 wherein the activation connections are electrically connected to the plurality of electron generators to form a plurality of row and column intersections that define a respective address location for each electron generator in the electron generator matrix;

and

wherein the plurality of activation connections electrically connected to the plurality of electron generators are configured to address each address location to independently activate an electron generator or sequentially activate a plurality of electron generators so as to emit electron beams therefrom.

14. An x-ray tube comprising:

a housing enclosing a vacuum-sealed chamber therein;

a target generally located at a first end of the chamber and configured to produce an array of x-ray focal spots providing tomographic imaging of an object when impinged by a plurality of electron beams;

a target shield housing the target and configured to trap ions therein generated by the interaction of the plurality of electron beams and the target and to intercept backscattered electrons;

a field emitter array generally located at a second end of the chamber to generate the plurality of electron beams and transmit the plurality of electron beams toward the target, the field emitter array including a plurality of field emitter units connected therein; and

wherein each of the plurality of field emitter units further comprises;

a substrate;

an emitter element positioned on the substrate and configured to generate an electron beam;

an extracting electrode positioned adjacent to the emitter element to extract the electron beam out therefrom, the extracting electrode including an opening therethrough;

a metallic grid disposed in the opening of the extracting electrode to enhance intensity and uniformity of an electric field at a surface of the emitter element; and

a focusing electrode positioned between the emitter element and the target to focus the electron beam as it passes therethrough.

15. The x-ray tube of claim 14 further comprising a plurality of activation connections electrically connected to the plurality of field emitter units, and wherein a pair of the activation connections are connected to each field emitter unit to deliver an electric potential thereto.

16. The x-ray tube of claim 15 wherein the plurality of field emitter units in the field emitter array are arranged in a plurality of rows and a plurality of columns, each of the plurality of rows and columns corresponding to a respective activation connection in the plurality of activation connections.

17. The x-ray tube of claim 16 wherein the activation connections corresponding to the emitter rows deliver an electric potential to the emitter elements in the field emitter units and wherein the activation connections corresponding to the emitter columns deliver an electric potential to the extraction electrode in the field emitter units.

18. The x-ray tube of claim 14 wherein the emitter element further comprises a plurality of carbon nanotube groups, the plurality of carbon nanotube groups aligned with openings in the metallic grid.

19. The x-ray tube of claim 14 wherein each of the plurality of emitter elements is curved to enhance focusing of the electron beam.

20. The x-ray tube of claim 14 wherein the housing is configured to be mountable to and rotate on a CT gantry.

21. The x-ray tube of claim 14 wherein each of the plurality of field emitter units further comprises a ceramic spacer positioned between the substrate and the extracting electrode, the ceramic spacer configured to suppress flashover.

22. A distributed x-ray source for an imaging system comprising:

a plurality of field emitters configured to generate at least one electron beam;

a shielded anode positioned in a path of the at least one electron beam and configured to emit a beam of high-frequency electromagnetic energy conditioned for use in a CT imaging process when the electron beam impinges thereon; and

wherein each of the plurality of field emitters further comprises;

a carbon nanotube (CNT) emitter element;

a gate electrode to extract the electron beam from CNT emitter element, the gate electrode including a meshed grid positioned in the electron beam path;

means for suppressing surface flashover in proximity to the CNT emitter element; and

means for focusing the electron beam to form a focal spot on the shielded anode.

23. The distributed x-ray source of claim 22 wherein the plurality of field emitters are arranged in an addressable two-dimensional matrix having a plurality of row and column intersections defining a respective address location for each field emitter in the two-dimensional matrix;

and

further comprising a plurality of control channels coupled to the plurality of field emitters, the control channels configured to address each address location to deliver an emitter voltage and an extraction voltage to each of the plurality of field emitters.

24. The distributed x-ray source of claim 22 wherein the CNT emitter element comprises a plurality of CNT groups, each of the CNT groups aligned with an opening in the meshed grid.