X-ray tube electron sources

• US 20070053495A1
• Filed: 04/23/2004
• Published: 03/08/2007
• Est. Priority Date: 04/25/2003
• Status: Active Grant

• Current Assignee: Rapiscan Systems Incorporated (OSI Systems Incorporated)
• Original Assignee: Edward Morton, Russell Luggar
• Inventors: Luggar, Russell, Morton, Edward
• Granted Patent: US 7,512,215 B2
• Time in Patent Office: Days
• US Class Current: 378/136
• CPC Class Codes: H01J 2235/068 Multi-cathode assembly
• CPC Class Codes: H01J 35/04 Electrodes ; Mutual position thereof; Constructional adaptations therefor
• CPC Class Codes: H01J 35/066 Details of electron optical components, e.g. cathode cups
• CPC Class Codes: H01J 35/14 Arrangements for concentrating, focusing, or directing the cathode ray

Abstract

An X-ray tube includes an emitter wire (18) enclosed in a suppressor(14, 16). An extraction grid comprises a number of parallel wires (20) extending perpendicular to the emitter wire, and a focusing grid comprises a number of wires (22) parallel to the grid wires (20) and spaced apart at equal spacing to the grid wires (20). The grid wire are connected by means of switches to a positive extracting potential or a negative inhibiting potential, and the switches are controlled so that at any one time a pair of adjacent grid wires (22) are connected together to form an extracting pair, which produce an electron beam. The position of the beam is moved by switching different pairs of grid wires to the extracting potential.

Claims

1. An electron source for an X-ray scanner comprising:

electron emitting means defining a plurality of electron source regions;

an extraction grid defining a plurality of grid regions each associated with at least a respective one of the electron source regions; and

control means arranged to control the relative electrical potential between each of the grid regions and the respective source region so that the position from which electrons are extracted from the emitting means can be moved between said source regions.

2. An electron source according to claim 1 wherein the extraction grid comprises a plurality of grid elements spaced along the emitting means.

3. An electron source according to claim 2 wherein the emitting means comprises an elongate emitter member and the grid elements are spaced along the emitter member such that the source regions are each at a respective position along the emitter member.

4. An electron source according to claim 2 wherein the control means is arranged to connect each of the grid elements to either an extracting electrical potential which is positive with respect to the emitting means or an inhibiting electrical potential which is negative with respect to the emitting means.

5. An electron source according to claim 4 wherein the control means is arranged to connect the grid elements to the extracting potential successively in adjacent pairs so as to direct a beam of electrons between each pair of grid elements.

6. An electron source according to claim 5 wherein each of the grid elements is connected to the same electrical potential as either of the grid elements which are adjacent to it.

7. An electron source according to claim 5 wherein the control means connects the grid elements to either side of an adjacent pair to the inhibiting potential while each of said adjacent pairs is connected to the extracting potential.

8. An electron source according to claim 7 wherein the control means connects all remaining grid elements to the inhibiting potential adjacent pairs is connected to the extracting potential.

9. An electron source according to claim 3 wherein the grid elements comprise parallel elongate members.

10. An electron source according to claim 9 wherein the emitting member extends substantially perpendicularly to the grid elements.

11. An electron source according to claim 2 wherein the grid elements comprise wires.

12. An electron source according to claim 3 wherein the grid elements are planar and extend in a plane substantially perpendicular to the emitter member.

13. An electron source according to claim 2 wherein the grid elements are spaced from the emitting means by a distance approximately equal to the distance between adjacent grid elements.

14. An electron source according to claim 2 further comprising a plurality of focusing elements arranged to focus beams of electrons after they have passed the grid.

15. An electron source according to claim 14 wherein the focusing elements are elongate.

16. An electron source according to claim 14 wherein the focusing elements are parallel to the grid elements.

17. An electron source according to claim 16 wherein the focusing elements are aligned with the grid elements such that electrons passing between any pair of the grid elements will pass between a corresponding pair of focusing elements.

18. An electron source according to claim 17 wherein the focusing elements are spaced at equal intervals to the grid elements.

19. An electron source according to claim 14 wherein the focusing elements are arranged to be connected to an electric potential which is positive with respect to the emitter.

20. An electron source according to claim 19 wherein the focusing elements are arranged to be connected to an electric potential which is negative with respect to the grid elements.

21. An electron source according to claim 14 wherein the control means is arranged to control the potential applied to the focusing elements thereby to control focusing of the beams of electrons.

22. An electron source according to claim 14 wherein the focusing elements comprise wires.

23. An electron source according to claim 14 wherein the focusing elements are planar and extend in a plane substantially parallel to the direction in which the source regions are arranged to emit electrons.

24. An electron source according to claim 4 wherein the grid elements are spaced from the emitter such that if a group of one or more adjacent grid elements are switched to the extracting potential, electrons will be extracted from a length of the emitter member which is longer than the width of said group of grid elements.

25. An electron source according to claim 24 wherein the grid elements are spaced from the emitter member by a distance which is at least substantially equal to the distance between adjacent grid elements.

26. An electron source according to claim 24 wherein the grid elements are spaced from the emitter member by a distance 5 mm.

28. An electron source according to claim 24 wherein the grid elements are arranged to at least partially focus the extracted electrons into a beam.

29. An electron source according to claim 1 wherein the source regions are formed on respective emitting members which are electrically insulated from each other and the control means is arranged to vary the electric potential of the emitting members to control said relative electric potentials.

30. An electron source according to claim 29 wherein the grid is held at a constant potential.

31. An electron source according to claim 30 further comprising focusing elements held at a constant potential.

32. An electron source according to claim 31 wherein the focusing elements are held at the same potential as the grid.

33. An electron source according to claim 31 wherein each focusing element is spaced at a distance between and in front of each adjacent pair of emitter members.

34. An electron source according to claim 1 wherein the control means activates each of the source regions in turn.

35. An electron source according to claim 1 wherein the control means controls the electric potentials of the source regions and the grid regions to extract electrons from a plurality of successive groupings of said source regions.

36. The electron source of claim 1 wherein said electron source and at least one anode comprise an X-ray tube.

37. The at least one anode according to claim 36 further comprising an elongate anode arranged such that beams of electrons produced by different grid elements will hit different parts of the anode.

54. An electron source according to claim 29 wherein the emitting members comprise emitter pads supported on an insulating emitter block.

55. An electron source according to claim 54 further comprising a layer of conductive material formed on the insulating block to provide electrical connection to the emitter pads.

56. An electron source according to claim 55 wherein the emitter pads are applied onto the layers of conductive material.

57. An electron source according to claim 54 further comprising a heating element adjacent to the emitter block.

58. An electron source according to claim 57 wherein the heating element comprises a block of insulating material with a layer of conductive material applied to it forming a heating element.

59. An electron source according to claim 54 further comprising a connecting element providing electrical connections for each of the emitter pads and flexible connecting elements providing electrical connections between the connecting element and the emitter block.

60. An electron source according to claim 59 wherein the connecting elements are arranged to accommodate relative movement of the connecting element and the emitter pad caused by thermal expansion.

27. (canceled)

38. (canceled)

39. (canceled)

40. (canceled)

41. (canceled)

43. An X-ray scanner according claim 41 wherein the source points are arranged in a linear array.

44. An X-ray scanner according to claim 43 wherein the detection means comprises a linear array of detectors extending in a direction substantially perpendicular to the linear array of source points.

45. An X-ray scanner according to claim 44 wherein the control means is arranged to record a reading from each of the detectors for each illumination.

46. An X-ray scanner according to claim 45 wherein the control means is arranged to use the readings from each of the detectors to reconstruct features of a respective layer of the object.

47. An X-ray scanner according to claim 46 wherein the control means is arranged to use the readings to build up a three dimensional reconstruction of the object.

42. An X-ray scanner comprising:

an X-ray source having a plurality of X-ray source points;

X-ray detection means; and

control means arranged to control the source to produce X-rays from a plurality of successive groupings of the source points and to record a reading of the detection means for each of the illuminations.

48. An X-ray scanner comprising:

an X-ray source comprising a linear array of source points; and

a detector array, comprising a linear arrangement of detectors, wherein the linear arrays are arranged substantially perpendicular to each other; and

control means, wherein control means is arranged to control either the source points or the detector array to operate in a plurality of successive groupings, each grouping comprising groups of different numbers of the source points or detectors, and to analyse readings from the detectors using a mathematical transform to produce a three-dimensional image of an object.

49. An X-ray scanner according to claim 48 wherein the control means is arranged to operate the source points in said plurality of groupings, and readings are taken simultaneously from each of the detectors for each of said groupings.

50. An X-ray scanner according to claim 48 wherein the control means is arranged to operate the detectors in said plurality of groupings and, for each grouping, to activate each of the source points in turn to produce respective readings.

51. (canceled)

52. (canceled)

53. (canceled)